U.S. patent application number 15/735423 was filed with the patent office on 2018-06-28 for method of activating two-dimensional materials for multivalent/polyatomic-ion intercalation battery electrodes.
This patent application is currently assigned to University of Houston System. The applicant listed for this patent is University of Houston System. Invention is credited to Yan Yao, Hyun Deog Yoo.
Application Number | 20180183038 15/735423 |
Document ID | / |
Family ID | 57609043 |
Filed Date | 2018-06-28 |
United States Patent
Application |
20180183038 |
Kind Code |
A1 |
Yao; Yan ; et al. |
June 28, 2018 |
METHOD OF ACTIVATING TWO-DIMENSIONAL MATERIALS FOR
MULTIVALENT/POLYATOMIC-ION INTERCALATION BATTERY ELECTRODES
Abstract
A method for activating two-dimensional host materials for a
multivalent/polyatomic ion battery may include adding a pillaring
salt in electrolyte. This process may be followed by in-situ
electrochemically intercalating the pillaring ions, solvent
molecules and multivalent ions into the van der Waals gap of host
materials. After the activation process, the host material is
transformed into an interlayer-expanded 2D material with
significantly enhanced specific capacity and rate performance for
multivalent ion intercalation.
Inventors: |
Yao; Yan; (Pearland, TX)
; Yoo; Hyun Deog; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Houston System |
Houston |
TX |
US |
|
|
Assignee: |
University of Houston
System
Houston
TX
|
Family ID: |
57609043 |
Appl. No.: |
15/735423 |
Filed: |
June 20, 2016 |
PCT Filed: |
June 20, 2016 |
PCT NO: |
PCT/US2016/038311 |
371 Date: |
December 11, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62181873 |
Jun 19, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 10/054 20130101; H01M 4/5815 20130101; H01M 4/1397 20130101;
H01M 4/139 20130101; H01M 4/13 20130101; H01M 4/136 20130101; H01M
4/0445 20130101 |
International
Class: |
H01M 4/04 20060101
H01M004/04; H01M 4/136 20060101 H01M004/136; H01M 4/1397 20060101
H01M004/1397; H01M 4/58 20060101 H01M004/58; H01M 10/054 20060101
H01M010/054 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with government support under Grant
No. N00014-13-1-0543 awarded by the Office of Naval Research. The
government has certain rights in the invention.
Claims
1. A method for forming an intercalation electrode for an ion
battery, the method comprising: adding a pillaring salt to an
electrolyte, wherein the pillaring salt is chemically stable and
soluble in the electrolyte and has a formula LX, where L is a
cation and X is an anion, and L or X has a size suitable to expand
layers of a host material to a desirable level; positioning the
host material in the pillaring salt and the electrolyte, wherein
the host material is a two-dimensional, layered material selected
from an elemental, metal, chalcogenide, metal oxide, oxy-halide,
hydroxide, titanate, metal phosphate, or phosphonate; and
intercalating a pillaring ions of the pillaring salt into a van der
Waals gap of the host material, wherein once expanded, an
interlayer distance of the host material does not change during a
charging stage and a discharging stage.
2. The method of claim 1, wherein the pillaring ions of the
pillaring salt is imidazolium, pyridinium, ferrocenium,
alkyl-ammonium, pyrrolidinium, or piperridinium, and the anion is
Cl.sup.-, TFSI.sup.-, BF.sub.4.sup.-, or
AlCI.sub.xR.sub.4-x.sup.-.
3. The method of claim 1, wherein the host material is the
elemental, and the elemental is selected from graphite or
black-phosphorous.
4. The method of claim 1, wherein the host material is the metal,
and the metal has a formula MX.sub.2, where M=Ti, Mo, V, W, Nb, Ta,
Zr, or Hf and X.dbd.S or Se.
5. The method of claim 1, wherein the host material is the
chalcogenide, and the chalcogenide has a formula
(MS).sub.1-x(TS.sub.2).sub.2, where 0.ltoreq.x.ltoreq.1, M=Sn, Pb,
and T=Ti, Nb, or Ta; MPX.sub.3, where M=Mg, V, Mn, Fe, Co, Ni, Zn,
Cd, or In and X.dbd.S or Se; or AMS.sub.2, where A=Li, Na, K, Rb,
Cs, or Fr and M=Ti, V, Cr, Mn, Fe, Co, or Ni.
6. The method of claim 1, wherein the host material is the metal
oxide, and the metal oxides the metal oxides has a formula
M.sub.xO.sub.y, where M=is a metal or a combination of metals that
includes an alkali metal, and x and y are values determined by an
oxidation state of M; or MOXO.sub.4, where M=Ti, V, Cr, or Fe and
X.dbd.P or As.
7. The method of claim 1, wherein the host material is the
oxy-halide, and the oxy-halide has a formula MOX, where M=Ti, V,
Cr, or Fe and X.dbd.Cl or Br.
8. The method of claim 1, wherein the host material is the
hydroxide or the titanate.
9. The method of claim 1, wherein the host material is the metal
phosphate, and the metal phosphate has a formula
M(HPO.sub.4).sub.2, where M=Ti, Zr, Ce, or Sn).
10. The method of claim 1, wherein the host material is the
phosphonate, and the phosphonate has the formula
Zr(O.sub.3PR.sub.2).sub.2, where R.dbd.H, Ph, or Me.
11. The method of claim 1, wherein the host material is expanded by
the pillaring ions and solvent molecules in a first stage.
12. The method of claim 11, wherein the host material is further
expanded by the pillaring ions, the solvent molecules, and
multivalent ions or polyatomic ions in a second stage.
13. The method of claim 12, wherein the multivalent ions or the
polyatomic ions are MgCl.sup.+, and the electrode is for a
rechargeable magnesium battery.
14. The method of claim 12, wherein the multivalent ions or the
polyatomic ions comprise a multivalent metal.
15. The method of claim 12, wherein the van der Waals gap of the
host material is filled to a maximum with the pillaring ions, the
solvent molecules, and multivalent ions or polyatomic ions in a
third stage.
16. The method of claim 15 further comprising deintercalating the
multivalent ions or polyatomic ions from the van der Waals gap
during a charging process, wherein the interlayer distance of the
host material does not change when deintercalating is complete.
17. The method of claim 1, wherein the host material is
electrochemically intercalated.
18. The method of claim 17, wherein the host material utilized as a
working electrode during electrochemical activation, a counter
electrode is place in the pillaring salt and the electrolyte during
the electrochemical activation, and a voltage differential is
applied to the working electrode and the counter electrode during
the electrochemical activation.
19. An electrode for an ion battery comprising: a host material,
wherein the host material is a two-dimensional, layered material
selected from an elemental, metal, chalcogenide, metal oxide,
oxy-halide, hydroxide, titanate, metal phosphate, or phosphonate;
and a pillaring ion, a solvent, and a multivalent ion or polyatomic
ion intercalated into a van der Waals gap of the host material,
wherein the pillaring ion is selected from a cation L or an anion
X, where L or X has a size suitable to expand layers of the host
material to a desirable level, and the multivalent ion or
polyatomic ion, wherein further an interlayer spacing of the host
material does not change during a charged stage and discharged
stage.
20. The electrode of claim 19, wherein the pillaring ion of the
pillaring salt is imidazolium, pyridinium, ferrocenium,
alkyl-ammonium, pyrrolidinium, or piperridinium, and the anion is
Cl.sup.-, TFSI.sup.-, BF.sub.4.sup.-, or
AlCI.sub.xR.sub.4-x.sup.-.
21. The electrode of claim 19, wherein the host material is the
elemental, and the elemental is selected from graphite or
black-phosphorous.
22. The electrode of claim 19, wherein the host material is the
metal, and the metal has a formula MX.sub.2, where M=Ti, Mo, V, W,
Nb, Ta, Zr, or Hf and X.dbd.S or Se.
23. The electrode of claim 19, wherein the host material is the
chalcogenide with a formula (MS).sub.1-x(TS.sub.2).sub.2, where
0.ltoreq.x.ltoreq.1, M=Sn, Pb, and T=Ti, Nb, Ta; MPX.sub.3, where
M=Mg, V, Mn, Fe, Co, Ni, Zn, Cd, or In and X.dbd.S or Se; or
AMS.sub.2, where A=Li, Na, K, Rb, Cs, or Fr and M=Ti, V, Cr, Mn,
Fe, Co, or Ni.
24. The method of claim 19, wherein the host material is the metal
oxide with a formula M.sub.xO.sub.y, where M=is a metal or a
combination of metals that includes an alkali metal, and x and y
are values determined by an oxidation state of M; or MOXO.sub.4,
where M=Ti, V, Cr, or Fe and X.dbd.P or As.
25. The electrode of claim 19, wherein the host material is the
oxy-halide with a formula MOX, where M=Ti, V, Cr, or Fe and
X.dbd.Cl or Br.
26. The electrode of claim 19, wherein the host material is the
hydroxide or the titanate.
27. The electrode of claim 19, wherein the host material is the
metal phosphate with a formula M(HPO.sub.4).sub.2, where M=Ti, Zr,
Ce, or Sn).
28. The electrode of claim 19, wherein the host material is the
phosphonate with a formula Zr(O.sub.3PR.sub.2).sub.2, where
R.dbd.H, Ph, or Me.
29. The electrode of claim 19, wherein the van der Waals gap of the
host material is filled to a maximum in the discharged stage, and
the multivalent ion or polyatomic ion are deintercalated from the
van der Waals gap in the charged stage.
30. The electrode of claim 19, wherein the interlayer spacing of
the host material relative to a pristine sample is 50% larger or
more.
31. The electrode of claim 19, wherein the electrode has a specific
capacity of 120 mAh/g or greater.
32. The electrode of claim 19, wherein the multivalent ion or the
polyatomic ion is MgCl.sup.+, and the electrode is for a
rechargeable magnesium battery.
33. The electrode of claim 19, wherein the multivalent ions or the
polyatomic ions comprise a multivalent metal.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 62/181,873 filed on Jun. 19, 2015, which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0003] This invention relates to multivalent/polyatomic-ion
batteries. More particularly, to a method for activating
two-dimensional materials as high-capacity and high-rate
intercalation electrodes in such batteries.
BACKGROUND OF INVENTION
[0004] The first rechargeable magnesium battery was proposed in as
early as 2000, which delivered an energy density only comparable to
Ni--Cd batteries. Surprisingly, this material still represents one
of the most successful cathode materials for rechargeable magnesium
batteries after more than ten years of R&D in this field. For
aluminum, only V.sub.2O.sub.5 and TiO.sub.2 have been attempted as
cathodes, neither of which exhibited practical energy density.
These results reflect the intrinsic difficulty of electrochemical
storage of multivalent cations in insertion compounds. Compared to
monovalent cations, multivalent metal cations are characterized by
small ion radii and high charge number. These characteristics
indicate the high polarization strength of multivalent cation, and
result in strong electronic interaction between the cations and the
negatively charged coordinating atoms in the insertion host, which
in turn leads to unfavorable insertion and diffusion. The
insertion/diffusion of these cations are sluggish in common
frameworks that work well for lithium.
[0005] During the past decade, a wide range of insertion compounds
have been screened for magnesium storage, including layered
transition metal chalcogenides, transition metal oxides, and
mesoporous polyanionic magnesium salts
(Mg.sub.1.03Mn.sub.0.97SiO.sub.4, MgCoSiO.sub.4 with discharge
voltage at 1.65 V). For oxides, no practical cycling stability has
been reported.
[0006] Only cheveral phases (CPs, Mg.sub.xMo.sub.6S.sub.8-ySe.sub.y
(y=0, 1, 2)) have exhibited practical magnesium insertion at a
1.1-1.3 V vs. Mg/Mg.sup.2+. To date, there is no cathode material
exhibiting practical energy density and cyclability suitable for
electrochemical storage of multivalent metal ions. In particular,
there has been no demonstration of an Mg ion full cell with higher
than 2V voltage, which includes an Mg insertion cathode, an Mg
anode and a compatible electrolyte.
[0007] Methods for activating two-dimensional materials as
high-capacity and high-rate intercalation electrodes in batteries
are discussed herein.
SUMMARY OF INVENTION
[0008] In one embodiment, a method for activating two-dimensional
host materials for a multivalent/polyatomic ion battery may include
adding a pillaring salt in electrolyte. This process may be
followed by in-situ electrochemically intercalating the pillaring
ions, solvent molecules and multivalent/polyatomic ions into the
van der Waals gap of host materials. After the activation process,
the host material is transformed into an interlayer-expanded 2D
material with significantly enhanced specific capacity and rate
performance for multivalent/polyatomic ion intercalation. Using
this method, the interlayer spacing of 2D material relative to a
pristine sample may be 50% larger or more. In comparison, pervious
methods only increase the spacing less than 10%.
[0009] In some embodiments, an electrode for a
multivalent/polyatomic ion battery may be formed from
two-dimensional host materials that have been activated. The van
der Waals gap of the host material may be intercalated with
pillaring ions and multivalent/polyatomic ions. In a discharged
stage, van der Waals gaps of the host material may be substantially
filled with the pillaring ions and multivalent/polyatomic ions. In
a charged stage, the multivalent/polyatomic ions are
de-intercalated from the host material, but the pillaring ions may
remain. Further, an interlayer spacing of the host material does
not change during a charged stage and discharged stage.
[0010] In one embodiment, polyatomic MgCl.sup.+ is identified as
the Mg storage carrier, which allows for a significantly reduced
diffusion barrier (in comparison to Mg.sup.2+) to realize high
specific capacity and charge-discharge rates.
[0011] The foregoing has outlined rather broadly various features
of the present disclosure in order that the detailed description
that follows may be better understood. Additional features and
advantages of the disclosure will be described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a more complete understanding of the present disclosure,
and the advantages thereof, reference is now made to the following
descriptions to be taken in conjunction with the accompanying
drawings describing specific embodiments of the disclosure,
wherein:
[0013] FIG. 1 shows an illustrative structure of a
multivalent/polyatomic-ion battery.
[0014] FIG. 2 shows the in-situ activation process of layered
materials at various state of charge.
[0015] FIG. 3 shows the cyclic voltammograms of APC electrolytes
with or without PY14Cl.
[0016] FIG. 4 shows in operando XRD characterization and
corresponding galvanostatic voltage profile.
[0017] FIG. 5 shows the galvanostatic voltage profile of an
expanded TiS.sub.2 electrode with a current density of 24 mA/g.
[0018] FIG. 6 shows another set of in operando XRD patterns to
check the structural irreversibility of each stage 1, 2, and 3.
[0019] FIG. 7 shows SEM images of expanded TiS.sub.2 at different
stages (0-5) on the discharge curve in FIG. 5.
[0020] FIG. 8 shows EDS spectra for stage 1 to 4 and XPS spectra of
MG2s, Cl2p and N1s for stage 0 to 5.
[0021] FIG. 9 shows XPS spectra of MG2s, Cl2p and N1s for stage 0
to 5.
[0022] FIG. 10 shows NMR spectra of samples after sonication and
heating in DMSO-d.sub.6 solutions.
[0023] FIGS. 11a-11b show impedance analysis of TiS.sub.2 electrode
at different stages of electrochemical activation, more
particularly (a) a capacitance vs frequency plot and (b) Nyquist
plot.
[0024] FIG. 12a-12f show electrochemical performances of
electrochemically activated TiS.sub.2. (a) Galvanostatic voltage
profiles of activated TiS.sub.2 electrode at various C-rate. The
number of MgCl.sup.+ intercalation per TiS.sub.2 is also shown in
the top axis. (b) A linear relationship between the peak current in
cyclic voltammogram and the square root of the scan rate that is
characteristic of diffusion limited mechanism. (c) Comparison of
diffusivity calculated from GITT of activated TiS.sub.2 with
pristine TiS.sub.2, pristine MoS.sub.2, and peo-MoS.sub.2 (ref.
44). (d) Specific capacity at different C-rate for the
electrochemically activated TiS.sub.2 compared to other Mg.sup.2+
ion storage materials in the full cells with Mg metal anode at
25.degree. C. (e) Cycling performance at 1C. The dip in capacity
curve indicates a decrease of room temperature due to the HVAC
malfunction. (f) Voltage profiles of activated TiS.sub.2 electrode
in pure APC electrolyte without PY14.sup.+ ions, compared with that
of the pristine TiS.sub.2 electrode.
[0025] FIG. 13 shows a cyclic voltammogram of expanded TiS.sub.2 at
varied scan rates from 0.1 to 10 mV s.sup.-1. The vertical axis
shows current normalized by scan rate.
[0026] FIGS. 14a-14b respectively show (a) cycling stability of
activated TiS.sub.2|Mg cell at 24 mA g.sup.-1 (1C-rate) in 0.25 M
APC electrolyte that contains 0.2 M PY14.sup.+ ion, and (b) voltage
profiles of the TiS.sub.2.
[0027] FIGS. 15a-15d respectively show voltage profiles of layered
TiS.sub.2 cathode (dotted) and Mg anode (solid) measured
simultaneously in a three-electrode cell vs a Mg/Mg.sup.2+
reference electrode at the 2.sup.nd, 13.sup.rd, 80.sup.th and
137.sup.th cycle.
[0028] FIG. 16 shows a voltage profile of electrochemical
activation of MoS.sub.2 in 0.2 M PY14Cl+APC electrolyte at 17 mA
g.sup.-1.
DETAILED DESCRIPTION
[0029] Refer now to the drawings wherein depicted elements are not
necessarily shown to scale and wherein like or similar elements are
designated by the same reference numeral through the several
views.
[0030] Referring to the drawings in general, it will be understood
that the illustrations are for the purpose of describing particular
implementations of the disclosure and are not intended to be
limiting thereto. While most of the terms used herein will be
recognizable to those of ordinary skill in the art, it should be
understood that when not explicitly defined, terms should be
interpreted as adopting a meaning presently accepted by those of
ordinary skill in the art.
[0031] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only, and are not restrictive of the invention, as
claimed. In this application, the use of the singular includes the
plural, the word "a" or "an" means "at least one", and the use of
"or" means "and/or", unless specifically stated otherwise.
Furthermore, the use of the term "including", as well as other
forms, such as "includes" and "included", is not limiting. Also,
terms such as "element" or "component" encompass both elements or
components comprising one unit and elements or components that
comprise more than one unit unless specifically stated
otherwise.
[0032] Developing high energy, high power, and safe batteries is of
great significance to address the society's energy needs, such as
distributed power sources, electric vehicles, and devices that
handle large amounts of power. Among existing battery technologies,
rechargeable lithium batteries theoretically possess the highest
gravimetric energy density because the small formula weight of
lithium and the unbeatable 3861 mAh g.sup.-1 specific capacity.
However, metallic lithium anode cannot be directly used because
they form dendritic and mossy metal deposits during repeated charge
and discharge cycles, leading to serious safety concerns.
Alternative insertion compounds (e.g. graphite and
Li.sub.4Ti.sub.5O.sub.12) result in a significant drop in energy
density--both gravimetrically and volumetrically (see Table 1).
Magnesium rechargeable batteries (MRBs) have recently emerged as an
attractive alternative candidate for future energy storage in terms
of safety, energy density, and scalability.
TABLE-US-00001 TABLE 1 Key parameters comparison of lithium,
magnesium, and aluminum. Lithium Magnesium Aluminum Gravimetric
3861 (Li metal) 2205 (Mg metal) 2980 (Al metal) Capacity (mAh
g.sup.-1) 372 (graphite) Volumetric 2066 (Li metal) 3833 (Mg metal)
8046 (Al metal) Capacity (mAh cm.sup.-3) 837 (graphite) Potential
-3.04 (Li metal) -2.37 (Mg metal) -1.66 (Al metal) (V vs NHE) -2.9
(graphite) -1.49 (Li.sub.4Ti.sub.5O.sub.12) Global Production
2.5*10.sup.7 (very low) 6.3*10.sup.9 (high) 4.0*10.sup.10 (high)
(kg yr.sup.-1) M.sup.n+ Radius (.ANG.) 0.68 0.65 0.50 Polarization
21.6 47.3 120 Strength (10.sup.5/pm.sup.-2)
[0033] Alternatively, electrodes based on light-weight multivalent
metals with densities of 1.7-2.7 g/cm.sup.3 such as magnesium and
aluminum offer up to seven times higher volumetric specific
capacity than lithium-ion battery anodes. In addition, their redox
potentials are 0.7-1.4 V higher than lithium, implying potentially
better safety; but not too high (e.g. the redox potential of
aluminum is lower than the popular anode Li.sub.4Ti.sub.5O.sub.12)
so that the theoretically achievable working potential is not
compromised. More interestingly, studies on the electrochemical
deposition of magnesium showed that magnesium can be plated in a
uniform dendrite-free manner and will serve as a safe anode
material. Rechargeable magnesium batteries are therefore regarded
as a potentially low-cost, ultra-high energy, and safe technology
for energy storage.
[0034] However, the development of practical MRBs remains hindered
largely due to the limited choices of Mg-intercalation cathodes.
The high dissociation energy to break the Mg--Cl bond of
electro-active species in an Mg electrolyte and the sluggish
solid-state Mg.sup.2+ diffusion are considered as key challenges.
The development of Mg-ion intercalating cathodes has proved
particularly challenging because of the relatively higher energy
barrier for Mg.sup.2+ migration in host materials, typically larger
than 0.7 eV. For this reason, most Mg-ion cathodes studied so far
show poor performance. For example, layered titanium disulphide
(TiS.sub.2), a classic Li-ion intercalation host with 220 mAh
g.sup.-1 of reversible capacity, demonstrates merely 20 mAh
g.sup.-1 capacity when used as a Mg-ion cathode. The difference in
terms of capacity can be understood when comparing the migration
energy barriers for two diffusion species, 1.2 eV for Mg.sup.2+
(ref. 24) vs. 0.38 eV for Li.sup.+ (ref. 25). Two general
approaches were developed in the past to reduce the barrier:
nanosizing cathode particles and introducing dipole molecules
(e.g., H.sub.2O) in cathode or electrolyte. Both approaches are
effective in boosting capacity to certain extent, but also come
with issues such as lower volumetric density and incompatibility
with Mg metal anode. Therefore, it is highly desirable to have an
alternative approach for the development of MRBs towards high
energy and power densities as well as good cycling stability.
[0035] The development of Mg-ion intercalating cathodes is also
hindered by the Mg desolvation and intercalation process at the
electrolyte-cathode interface. Among the popular Mg-depositing
electrolytes such as the dichloro complex (DCC), all-phenyl complex
(APC), and magnesium aluminium chloride complex (MACC), the
consensus is that the monovalent Mg.sub.xCl.sub.y.sup.+.nTHF specie
is the electro-active component. Although the dimer,
Mg.sub.2Cl.sub.3.sup.+, has long been considered as the dominated
specie supported from the recrystallization of electrolytes, the
grand-potential phase diagram for the Mg--Cl-THF system was
recently calculated and clarified MgCl.sup.+.3THF and
MgCl.sub.2.2THF as the most stable species and a complex dynamic
equilibria exist among MgCl.sup.+, AlCl.sub.4.sup.-, MgCl.sub.2 and
AlCl.sub.3 species. Mass spectrometry study also supports the
finding. Furthermore, in order to enable Mg.sup.2+ intercalation in
cathode, one has to break the Mg--Cl bond of the electro-active
species first. The dissociation energy of Mg--Cl bond in a
coordinated complex is calculated to exceed 3 eV using density
functional theory, which presents the second challenge for
Mg.sup.2+ intercalating cathode development.
[0036] To overcome the challenges outlined above for an efficient
Mg.sup.2+ intercalating cathode, research has been conducted on
potentially viable MRB designs that are also applicable to other
layered host materials. Systems and methods for activating
two-dimensional host materials to expand the van der Waals gap of
the host materials, such as with pillaring ions, are discussed
herein.
[0037] As a nonlimiting example, research discussed herein showed
an MRB that is based on a monovalent MgCl.sup.+ storage mechanism
that would enable very low migration energy barrier, no need to
break Mg--Cl bond at the cathode, and maintain the dendrite-free
Mg-metal deposition at the anode can be provided. The cathode
involves MgCl.sup.+ intercalation or coordination, the electrolyte
contains MgCl.sup.+ species, and the anode magnesium deposition and
stripping involves MgCl.sup.+. A MgCl.sup.+ based intercalation
cathode has never been reported previously because the size of
MgCl.sup.+ is so large that the conventional intercalation approach
is inefficient. In this work, two-dimensional TiS.sub.2 is expanded
to an unusually large value of 1.86 nm (327% as large as the
pristine form) to accommodate the intercalation of large
MgCl.sup.+. During discharge, MgCl.sup.+ ions are intercalated into
a cathode while being simultaneously regenerated at the Mg anode
enabled by the dynamic equilibrium among electroactive species in
Mg electrolyte. It was demonstrated that a MRB with a high
reversible capacity of 270 mAh g.sup.-1 and an excellent cycling
stability for 500 cycles with 80% capacity retention can be
produced. The new storage mechanism can be extended to a wide range
of multivalent/polyatomic ion batteries (e.g. Ca.sup.2+, Al.sup.3+)
and two-dimensional materials, highlighting the importance of an
unexploited new route of materials design in multivalent ion energy
storage. A combination of theoretical modelling, in-operando
spectroscopic, and electrochemical study confirms the MgCl.sup.+
intercalation mechanism. This research opens up new possibilities
for a variety of low-cost multivalent/polyatomic ion batteries.
[0038] FIG. 1 illustrates an arrangement for a
multivalent/polyatomic ion battery (MIB) 100. The MIB 100 may
provide positive 110 and negative 120 electrodes in an electrolyte
130. It shall be understood that the electrode(s) may be formed of
a layered electrode material that allows for intercalation. The
positive electrode 110 may be formed from any layered-structure
materials. In some embodiments, the layered-structure materials may
be selected from those listed in table 2. The negative electrode
120 may be Mg, Ca, or Al metal. The electrolyte 130 may be any
suitable nonaqueous electrolyte with the proposed pillaring salt
discussed herein. In some embodiments, suitable nonaqueous
electrolytes may include phenyl complex (APC),
MgCl.sub.2--AlCl.sub.3/diglyme, MgCl.sub.2--Mg(TFSI).sub.2/DME, or
Mg(CB.sub.11H.sub.12).sub.2/tetraglyme. In some embodiments, the
chemical formula for pillaring salt is LX. The pillaring salt may
be selected from chemically stable options and may also be soluble
in an electrolyte form pillaring ions, such as L.sup.+ or X.sup.-.
Whether L.sup.+ or X.sup.- is utilized as the pillaring ion will
depend on the host material to be intercalated. The pillaring ions
L.sup.+ or X.sup.- have a size suitable to expand layers of the
host material to a desirable level. Nonlimiting examples of the
pillaring ion L.sup.+ may include imidazolium, pyridinium,
ferrocenium, alkyl-ammonium, pyrrolidinium, and/or piperridinium.
Nonlimiting examples of X.sup.- could include Cl.sup.-,
bis(trifluoromethane)sulfonimide or TFSI.sup.-, BF.sub.4.sup.-,
and/or AlCl.sub.xR.sub.4-x.sup.- (R=organic ligand such as alkyl,
aryl, or alkoxide group).
[0039] In some embodiments, an active ion for charging/discharging
stages may be a multivalent ion or polyatomic ion. In some
embodiments, the multivalent ions or the polyatomic ions comprise a
multivalent metal. The multivalent metal may be a metal with a high
gravimetric/volumetric capacity, such as, but not limited to 120
mAh/g or greater. In some embodiments, the suitable multivalent ion
includes Mg.sup.2+, Ca.sup.2+, Zn.sup.2+, or Al.sup.3+. In some
embodiments, suitable polyatomic ions may be formed from the
multivalent ions, such as, but not limited to, MgCl.sup.+,
Mg.sub.2Cl.sub.3.sup.+, Mg.sub.2Cl.sub.2.sup.2+, and
AlCl.sub.4.sup.-. Nonlimiting examples of the host materials are
provided in table 2 below. In some embodiments, the host material
or layered material may be selected from elementals, metals,
chalcogenides, metal oxides, oxy-halides, hydroxides, titanates,
metal phosphates, phosphonates, or the like. Nonlimiting examples
of suitable elementals include graphite and black-phosphorous.
Nonlimiting examples of suitable metals may include any metal
satisfying the formula MX.sub.2 (where M=Ti, Mo, V, W, Nb, Ta, Zr,
or Hf; and X.dbd.S or Se). Nonlimiting examples of suitable
chalcogenides may include any chalcogenides satisfying the formula
(MS).sub.1+x(TS.sub.2).sub.2 (0.ltoreq.x.ltoreq.1)(where M=Sn or
Pb; and T=Ti, Nb or Ta). Further examples of suitable chalcogenides
may include any chalcogenides satisfying the formula MPX.sub.3
(where M=Mg, V, Mn, Fe, Co, Ni, Zn, Cd or In; and X.dbd.S or Se).
Additional examples of suitable chalcogenides may include any
chalcogenides satisfying the formula AMS.sub.2 (A=Li, Na, K, Rb,
Cs, or Fr; M=Ti, V, Cr, Mn, Fe, Co, or Ni). Nonlimiting examples of
suitable metal oxides may include any metal oxides satisfying the
formula M.sub.xO.sub.y (such as V.sub.2O.sub.5, MoO.sub.3,
Mo.sub.18O.sub.52, LiNbO.sub.2, Li.sub.xV.sub.3O.sub.8, where M=is
a metal or a metal and combination of metals that includes an
alkali metal, and x or y are values determined by oxidation states
of the element(s) of M). Further examples of suitable metal oxides
may include any metal oxides satisfying the formula MOXO.sub.4
(where M=Ti, V, Cr, or Fe; and X.dbd.P or As). Nonlimiting examples
of suitable oxy-halides may include any oxy-halides satisfying the
formula MOX (where M=Ti, V, Cr, or Fe; and X.dbd.Cl or Br).
Nonlimiting examples of suitable hydroxides may include
Ni(OH).sub.2 or Mn(OH).sub.2. Nonlimiting examples of suitable
titanates may include K.sub.2Ti.sub.4O.sub.9 or KTiNbO.sub.5.
Nonlimiting examples of suitable metal phosphates may include any
metal phosphates satisfying the formula M(HPO.sub.4).sub.2 (where
M=Ti, Zr, Ce, or Sn). Nonlimiting examples of suitable phosphonates
may include any phosphonates satisfying the formula
Zr(O.sub.3PR.sub.2).sub.2 (where R.dbd.H, Ph, or Me).
TABLE-US-00002 TABLE 2 Candidates for the layered materials Lattice
Type Illustrative Nonlimiting Examples Elemental Graphite,
Black-Phosphorous Metal MX.sub.2 (M = Ti, Mo, V, W, Nb, Ta, Zr, Hf;
X = S, Se) chalcogenides (MS).sub.1+x(TS.sub.2).sub.2 (0 < x
< 1)(M = Sn, Pb; T = Ti, Nb, Ta) MPX.sub.3 (M = Mg, V, Mn, Fe,
Co, Ni, Zn, Cd, In; X = S, Se) AMS.sub.2 (A = Group 1A Alkali
metal: M = Ti, V, Cr, Mn, Fe, Co, Ni) Metal Oxides M.sub.xO.sub.y
(M = a metal or combination of metals, e.g. V.sub.2O.sub.5,
MoO.sub.3, Mo.sub.18O.sub.52, LiNbO.sub.2, Li.sub.xV.sub.3O.sub.8)
MOXO.sub.4 (M = Ti, V, Cr, Fe; X = P, As) Oxy-Halides MOX (M = Ti,
V, Cr, Fe; X = Cl, Br) Hydroxide Ni(OH).sub.2, Mn(OH).sub.2
Titanates K.sub.2Ti.sub.4O.sub.9, KTiNbO.sub.5 Metal
M(HPO.sub.4).sub.2 (M = Ti, Zr, Ce, Sn) Phosphates and
Zr(O.sub.3PR.sub.2).sub.2 (R = H, Ph, Me) Phosphonates
[0040] The chemical formula for pillaring salt is LX. Nonlimiting
examples of L.sup.+ may include imidazolium, pyridinium,
ferrocenium, alkyl-ammonium, pyrrolidinium, and/or piperridinium.
Nonlimiting examples of X.sup.- could include Cl.sup.-, TFSI.sup.-,
BF.sub.4.sup.-, and/or AlCI.sub.xA.sub.4-x.sup.-.
[0041] Methods for activating two-dimensional host materials may
include adding a pillaring salt in electrolyte, which may be
selected from the various options discussed previously. In some
embodiments, this process may be followed by chemically or
electrochemically intercalating the pillaring ions, solvent
molecules and multivalent/polyatomic ions into the van der Waals
gap of host materials in-situ or ex-situ. The intercalating process
may include placing the host material in the pillaring salt and the
electrolyte mixture. Optional considerations for selecting
pillaring salts include, but are not limited to, the size of the
pillaring ion that can expand the layer to a desirable distance,
the degree of chemical stability, and the compatibility with the
host material and the electrolyte mixture. In some embodiments, the
intercalation may occur chemically, such as by exposing the host
material to a solution with the pillaring salts. In other
embodiments, the intercalation may occur electrochemically by
applying current to the host material in electrolyte mixtures or by
combinations of both chemical and electrochemical routes. The
intercalation process may progress through multiple stages as the
separation distance between layers grows. In a first stage,
pillaring ions and/or solvent molecules may expand the van der
Waals gap of the host materials. In some embodiments, reversible
intercalation of multivalent/polyatomic ions may occur in stage 1
to a certain level. In a second stage, as the pillaring ions and/or
solvent molecules continue to expand the gap or separation distance
between the layers, eventually the gap becomes large enough that
multivalent/polyatomic ions begin to fill the van der Waals gap of
the host materials as well. Reversible intercalation of
multivalent/polyatomic ions may occur or continue to occur in stage
2 to a certain level. In a third stage, the process continues until
activation is considered complete, such as when a maximum amount of
multivalent/polyatomic ions fill the gaps of the host material. In
some embodiments, these processes are followed by a significant
change in the structure (for example, but not limited to,
structural expansion or disordering) or the chemical composition
(e.g., but not limited to, ratio of solvent to pillaring molecules)
of host materials. These changes can be used as parameters to
determine the optimal condition for activating two-dimensional host
materials. The fourth stage represents a charging process where the
multivalent/polyatomic ions are deintercalated from the gap to
leave the pillaring ions and/or solvent molecules. Notably, once
expanded, the interlayer distance does not decrease during the
transition from the third stage to the fourth stage. During
charging and discharging, the host material cycles between stages
three and four.
[0042] In some embodiments, the pillaring ions, solvent molecules,
and/or multivalent/polyatomic ions may be formed chemically without
electrical stimulation from mixing the pillaring salt, electrolyte,
and/or metal material(s). In other embodiments involving
electrochemical intercalation, the host material is utilized as the
working electrode during electrochemical activation and a counter
and/or reference electrodes may also be place in the electrolyte
mixture. The counter and/or reference electrode(s) may be formed
from a metal constituent that is part of the multivalent ion that
intercalates the host material. The application of a voltage
differential to the working and counter electrodes may cause or
accelerate formation of the pillaring ions, solvent molecules,
and/or multivalent ions. Further, the application of the voltage
differential may also cause or aid acceleration of the pillaring
ions, solvent molecules, and/or multivalent ions into the host
materials. After the activation process with or without electric
stimulation, the host material is transformed into an
interlayer-expanded 2D material with significantly enhanced
specific capacity and rate performance for multivalent/polyatomic
ion intercalation. The host material retains the increase
separation distance between the layers, even when cycling between
charge/discharge states.
[0043] An electrode for a multivalent/polyatomic ion battery may be
formed from two-dimensional host materials that have been
activated, such as by the methods discussed. In particular, the van
der Waals gap of the host material may be intercalated with
pillaring ions, solvent molecules and polyatomic or multivalent
ions. In a discharged stage (e.g. third stage), van der Waals gaps
of the host material may be substantially filled with the pillaring
ions, solvent molecules and polyatomic or multivalent ions. In a
charged stage (e.g. fourth stage), the polyatomic or multivalent
ions are denintercalated from the host material, but the pillaring
ions and solvent molecules may remain. Further, an interlayer
spacing of the host material does not change during a charged stage
and discharged stage.
[0044] FIG. 2 shows an illustrative example of the in-situ
activation process of layered materials at various states of
activation. While TiS.sub.2 is used as a nonlimiting model compound
of the host material to illustrate the structural change during
activation due to its high electronic conductivity, it shall be
understood that similar structural changes may occur in the other
embodiments discussed previously. Stage 0 is the host material
(e.g. TiS.sub.2) in its pristine form. A pillaring salt (e.g.
PY14Cl) and electrolyte (e.g. APC) may be mixed. In stage 1 when
current is applied to the host material that is exposed to the
pillaring salt and electrolyte mixture, both pillaring ions (e.g.
PY14.sup.+) and/or solvents may be intercalated into the van der
Waals gap, expanding the interlayer spacing of the host. In some
embodiments, layered materials of stage 1 may be subjected to
activation at low current density for a predetermined amount of
time corresponding to the first stage change. As a nonlimiting
example, the current density may be 5 mA/g or less. In stage 2, in
addition to more pillaring ions being intercalated, the polyatomic
or multivalent ions in the electrolyte, e.g. MgCl.sup.+, may be
able to intercalated into the host due to the opening up of the van
der Waals gap, which results further increase in the interlayer
distance. In some embodiments, layered materials of stage 2 may be
subjected to activation at low current density for a predetermined
amount of time corresponding to the second stage change. As a
nonlimiting example, the current density may be 5 mA/g or less. In
stage 3, more pillaring ions and/or polyatomic or multivalent ions
in the electrolyte (e.g. MgCl.sup.+) are intercalated and may be
reduced to form a solid-electrolyte interphase (SEI) layer to fill
the van der Waals gap. In some embodiments, layered materials of
stage 3 may be subjected to activation at low current density for a
predetermined amount of time corresponding to the third stage
change. As a nonlimiting example, the current density may be 5 mA/g
or less. Once stage 3 is reached, the activation process may be
considered to be completed. The transition from stage 3 to stage 4
is the regular charging process, MgCl.sup.+ are deintercalated from
the gap leaving the pillaring ions remained in the gap. However,
the interlayer distance would not decrease. For the discharging
process, stage 4 goes back to stage 3. It is preferable to have the
step from stage 2 to stage 3, which enables a stable transformation
of the layered structure into high capacity electrode. Without this
step, the specific capacity of the electrode is less than 100
mAh/g.
[0045] In some embodiments, the electrodes may demonstrate a
specific capacity of 120 mAh/g or greater. In some embodiments, the
electrodes may demonstrate a specific capacity of 150 mAh/g or
greater. In some embodiments, the electrodes may demonstrate a
specific capacity of 200 mAh/g or greater. In some embodiments, the
electrodes may demonstrate a specific capacity of 250 mAh/g or
greater. In some embodiments, the interlayer spacing of 2D material
relative to a pristine sample may be 50% larger or more. In some
embodiments, the interlayer spacing of 2D material relative to a
pristine sample may be 100% larger or more. In some embodiments,
the interlayer spacing of 2D material relative to a pristine sample
may be 150% to 250% larger or more. In some embodiments, the
interlayer spacing of 2D material relative to a pristine sample may
be 200% larger or more. In comparison, pervious methods only
increase the interlayer spacing less than 10%. In one embodiment, a
TiS.sub.2 electrode was activated with 1-butyl-1methylpyrrolidinium
chloride (PY14Cl) added all phenyl complex (APC) electrolyte
electrochemically. After activation, the electrode demonstrated 270
mAh/g specific capacity with excellent rate performance. In the
other embodiment, a MoS.sub.2 electrode was activated in the same
procedure and demonstrated 280 mAh/g. In some embodiments,
MgCl.sup.+ is identified as the Mg storage carrier, which allows
for a significantly reduced diffusion barrier to realize high
specific capacity and charge-discharge rates.
Experimental Example
[0046] The following examples are included to demonstrate
particular aspects of the present disclosure. It should be
appreciated by those of ordinary skill in the art that the methods
described in the examples that follow merely represent illustrative
embodiments of the disclosure. Those of ordinary skill in the art
should, in light of the present disclosure, appreciate that many
changes can be made in the specific embodiments described and still
obtain a like or similar result without departing from the spirit
and scope of the present disclosure.
[0047] Electrochemical Activation of 1T-TiS.sub.2 for MgCl-Ion
Storage
[0048] It is known that intercalating organic molecules or bulky
ions can expand the layered materials by 10-60 .ANG..
1-butyl-1-methylpyrrolidinium ion (PY14.sup.+) was chosen as the
pillaring material to expand TiS.sub.2 because of the bulky size
and electrochemical stability of PY14.sup.+. 0.2 M PY14Cl is
dissolved into a standard all-phenyl complex (APC) electrolyte.
Cyclic voltammetry characterization of the mixed electrolyte
reveals a small increase in overpotential for Mg deposition and a
small drop in the Coulombic efficiency compared to the pure APC
electrolyte (Table 3). FIG. 3 show the cyclic voltammetry of APC
electrolytes with or without PY14Cl. A platinum wire and magnesium
foil were used as the working and counter electrodes, respectively.
Voltage was scanned with the speed of 25 mV s.sup.-1. The APC
electrolytes with or PY14Cl small increase in overpotential for Mg
deposition from 155 to 266 mV and a slight drop in Coulombic
efficiency from 100% to 95.2%.
TABLE-US-00003 TABLE 3 Electrochemical performance of Mg-ion
electrolyte with and without PY14Cl additive Voltage Overpotential
for Coulombic window Mg deposition efficiency (V) (V) (%) APC 2.6
0.155 100.0 APC + 0.2M PY14Cl 2.8 0.266 95.2
[0049] To enable MgCl.sup.+ intercalation in TiS.sub.2, an
electrochemical activation step is required to expand the
interlayer spacing of two-dimensional TiS.sub.2 assisted by
PY14.sup.+ ions. As shown from stage 0 to 3 in FIG. 4, the
activation process was completed in the first discharge at low
current density of 5 mA g.sup.-1 for .about.100 hours. When the
activation is completed, the MRB shows a reversible capacity as
high as 270 mAh g.sup.-1 at 24 mA g.sup.-1 (FIG. 4, stage 3 to 5),
which is 1350% as large as the capacity of pristine TiS.sub.2 (20
mAh g.sup.1)..sup.23 Note that this activation step is a
kinetically sluggish process. If conducted at a higher current
density (24 mA g.sup.-1), the long plateau between stages 2 to 3
would be absent and the incomplete activation leads to low
reversible capacity of merely .about.60 mAh g.sup.-1 (FIG. 5 shows
the galvanostatic voltage profile of an expanded TiS.sub.2
electrode without the activation process at 0 V. Incomplete
activation leads to low reversible capacity of 60 mAh
g.sup.-1).
[0050] To shed light on the structural evolution of TiS.sub.2
during the activation, we conducted in-operando X-ray diffraction
(XRD) measurement. The configuration of an in-operando cell is
shown in FIG. 4. An Mg metal anode was placed on the Be window to
avoid electrochemical dissolution of Be metal. Centre of Mg metal
was punched out to enhance the intensity of X-ray that reaches to
and returns from TiS.sub.2. X-ray diffraction patterns were scanned
by D/teX Ultra 250 detector from 2.theta.=3.degree. to 40.degree.
with step size of 0.04.degree. and scanning speed of 1.degree. or
2.degree. per minute under Bragg-Brentano focusing. Cu
K.sub..alpha. radiation was used and the voltage and current was 40
kV and 44 mA, respectively. Since beryllium metal undergoes
electrochemical reaction with TiS.sub.2 electrode in APC
electrolyte, we placed Mg foil anode on the Be window and TiS.sub.2
electrode under the Mg foil separated by a PP/PE/PP separator. In
this configuration, Mg acts as sacrificial anode and Be is kept as
Be.sup.0 because of ca. 0.53 V higher standard electrode potential.
This configuration has been used before to measure in operando XRD
of high voltage Li-ion cathode. XRD spectra (FIG. 4) shows a peak
at 15.56.degree. for as-fabricated cell (stage 0), corresponding to
the pristine TiS.sub.2 (001) plane with c=5.69 .ANG.. When
discharging to 1.0 V vs Mg/Mg.sup.2+ (stage 1), new peaks evolve at
8.13.degree. and 16.31.degree., corresponding to (001) and (002)
planes with c=10.87 .ANG.. Further discharging to 0.2 V vs Mg
(stage 2) results in four new peaks at 4.74.degree., 9.49.degree.,
14.26.degree., and 19.04.degree., corresponding (001) to (004)
planes with c=18.63 .ANG.. The structure transformation from stages
1 to 2 is irreversible. In other words, the structure does not
return to the previous stage even charging back to 2.0 V vs Mg.
FIG. 6 shows another set of in operando XRD patterns to check the
structural irreversibility of each stage 1, 2, and 3. The discharge
cut-off voltage was controlled to 1.0, 0.2, and 0.0 V followed by
charging back to 2.0 V to confirm the structural irreversibility of
each stage 1, 2, and 3. Note that complete 4.74.degree. peak was
detected in the diffraction pattern of stage 2 for this
measurement. From stage 2 to 3, we could not identify any peak
shift; instead, peak intensity is attenuated, suggesting structural
disorder developed during the long voltage plateau. Beginning from
stage 3, the TiS.sub.2 layers retain its interlayer distance upon
charge/discharge, and the electrodes remain compact without
exfoliating into single layers. The calculated interlayer spacing
for each stage is shown in Table 4.
TABLE-US-00004 TABLE 4 Interlayer spacing calculated from in
operando XRD patterns using Bragg's formula 2.theta. (.degree.)
Interlayer Stage Measured Corrected distance/.ANG. n in (00n) 0
15.64 15.56 5.69 1 1 8.21 8.13 10.87 1 16.39 16.31 10.86 2 2, 3, 4,
5 4.82 4.74 18.63 1 9.57 9.49 18.62 2 14.34 14.26 18.63 3 19.12
19.04 18.64 4
[0051] The nature of intercalating species is investigated further
by combining a variety of tools including energy dispersive
spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS),
near-edge X-ray absorption fine structure (NEXAFS), inductively
coupled plasma-optical emission spectroscopy (ICP-OES), electron
energy loss spectroscopy (EELS), and nuclear magnetic resonance
(.sup.1H-NMR). First, the EDS and XPS spectra (FIG. 8-9) reveal a
simultaneous increase in the peak intensity of Mg and Cl from stage
2 to 3 and then a simultaneous decrease from stage 3 to 4. The
atomic ratio of Mg to Cl calculated from the EDS results at each
stage is 1.0.+-.0.2.
[0052] FIG. 10 shows NMR spectra of samples after sonication and
heating in DMSO-d.sub.6 solutions. Chemical shifts at boxes A, B,
C, D, and E represent the proton of PY14.sup.+ ion, while those at
boxes F and G represent the proton of THF solvent. Chemical shift
at 2.5 ppm and 3.4 ppm correspond to DMSO-d.sub.6 and H.sub.2O,
respectively. Stage 0 shows negligible amount of PY14.sup.+ and
THF. Note that the sample at stage 0 was deliberately dipped in
PY14.sup.+ containing Mg-ion electrolyte and then rinsed with the
same washing condition as the samples at stages 1-4. That means the
PY14.sup.+ and THF signal at stages 1-4 does not come from the
trace amount of salt or solvents that can be possibly remained
after washing. Combining the .sup.1H-NMR and electrochemical
results, only a small amount of THF molecules (.about.0.5-0.6 per
one MgCl.sup.+ ion) in the activated TiS.sub.2 electrode were
found. Such small amount of THF is much lower than the three THF
molecules observed in tetra-coordinated solvation
(MgCl.sup.+.3THF), therefore excluding the solvation effect as the
dominant performance enhancement factor.
[0053] FIGS. 11a-11b show impedance analysis of TiS.sub.2 electrode
at different stages of electrochemical activation. Impedance was
measured by 3-electrode cell at fixed potential of 1.8 V vs
Mg/Mg.sup.2+ with 0.2 M PY14Cl in APC electrolyte. FIG. 11a shows a
capacitance vs frequency plot. The increase in capacitance as stage
3 corresponds to large interfacial area than stage 1 and 2. FIG.
11b shows a Nyquist plot. The impedance results show that the
charge transfer impedance greatly reduced during the
electrochemical activation step. Following the discharging step,
PY14.sup.+ will stay inside the van der Waals gap, while highly
mobile MgCl.sup.+ can intercalate reversibly during electrochemical
cycling.
[0054] Electrochemistry of MRBs with MgCl.sup.+ Intercalation
[0055] After investigating the activation step, the electrochemical
performance of the activated TiS.sub.2 MRBs is studied. FIG. 12a
shows excellent rate performance with high reversible capacity of
272 mAh g.sup.-1 at 0.1C (24 mA g.sup.-1), 194 mAh g.sup.-1 at 1C
(240 mA g.sup.-1), and 162 mAh g.sup.-1 at 2C (480 mA g.sup.-1),
which correspond to 1.14, 0.81 and 0.68 MgCl.sup.+ intercalation
per formula of TiS.sub.2, respectively. More than one MgCl.sup.+
intercalation per TiS.sub.2 formula unit is due to the creation of
additional accessible sites by expanding TiS.sub.2 gallery. The
typical discharging voltage profiles possess a sloping profile,
which is related to the one phase reaction of forming
MgCl.sub.x(TiS.sub.2). This sloping shape of the voltage profile
coincides with the theoretical calculation for Mg.sup.2+
intercalation into layered TiS.sub.2, but with lower voltage than
expected. The decreased voltage is related with the weaker
interaction between MgCl.sup.+ ion and expanded TiS.sub.2 that
leads to smaller formation energy.
[0056] To confirm the mechanism is indeed intercalation rather than
adsorption, cycling voltammetry (CV) was measured at scan rate (v)
from 0.1 to 10 mV s.sup.-1. FIG. 13 shows cyclic voltammogram of
expanded TiS.sub.2 at varied scan rates from 0.1 to 10 mV s.sup.-1.
The vertical axis shows current normalized by scan rate. FIG. 12b
shows the linear relationship between peak current versus
v.sup.1/2, indicating the diffusion-limited intercalation mechanism
rather than a capacitance effect. Galvanostatic intermittent
titration technique (GITT) was also used to determine ion
diffusivity as a function of depth-of-discharge and the
composition-dependent electrode kinetics. FIG. 12 shows
galvanostatic intermittent titration curve of an activated
TiS.sub.2 electrode. The CV and GITT studies were carried out with
a three-electrode coin cell. FIG. 13 shows a schematic of a
three-electrode coin cell. Ring-shaped Mg metal foil was used as a
reference electrode without blocking the working and counter
electrodes. The reference electrode was connected out of the coin
cell by polypropylene-coated stainless steel foil (50 .mu.m and 350
.mu.m thick before and after coating, respectively). Vacuum grease
was applied on the joint for hermetic sealing of the cell. The
three-electrode arrangement was used because a two-electrode
configuration could obscure the true cathode potential due to the
overpotential of Mg at the anode. FIG. 12c shows the average
diffusivity of 10.sup.-9 cm.sup.2 s.sup.-1 for the activated
TiS.sub.2. The Mg diffusivity is initially high at the level of
2.times.10.sup.-8 cm.sup.2 s.sup.-1 but decreases with increasing
Mg concentration, and then stays constant as 10.sup.-10 cm.sup.2
s.sup.-1 towards the end of process. In comparison, pristine
TiS.sub.2, pristine MoS.sub.2, and PEO-expanded MoS.sub.2 exhibit
average Mg diffusivity of 10.sup.-12 to 10.sup.-13 cm.sup.2
s.sup.-1, which is two to three orders of magnitude lower than the
Mg diffusivity in activated TiS.sub.2.
[0057] FIG. 12d shows outstanding specific capacity and rate
capability of activated TiS.sub.2 compared to other Mg-ion storage
materials in the full cells with Mg metal anode at 25.degree. C. In
terms of cycling stability in FIG. 12e, the activated TiS.sub.2
electrode exhibits 80% capacity retention after 500 cycles at
1C-rate (240 mA g.sup.1). The Coulombic efficiency is consistently
higher than 98%. At 0.1C-rate (24 mA g.sup.-1), the cell retains
89% of initial capacity after 50 cycles; and the reversible
capacity increases from 200 mAh g.sup.-1 to 270 mAh g.sup.-1 during
initial 10 cycles due to the activation progresses. FIGS. 14a-14b
show (a) cycling stability of activated TiS.sub.2|Mg cell at 24 mA
g.sup.-1 (1C-rate) in 0.25 M APC electrolyte that contains 0.2 M
PY14.sup.+ ion; and (b) voltage profiles of the TiS.sub.2|Mg cell
for initial 10 cycles. Future examination can clarify the capacity
decay mechanism and improve cycling stability using functional
binders (e.g., poly(acrylic acid) or carboxymethyl cellulose) that
are effective for electrodes with volume change during the
activation step. For practical concern, the electrodes reported
here have an areal capacity of 1.4 mAh cm.sup.-2, which could be
further increased by downsizing the TiS.sub.2 particles for faster
activation of the electrode. The activated material at stage 4
(i.e. completely de-intercalated) was transferred into a new cell
with a standard APC electrolyte solution without PY14.sup.+ (FIG.
12f). The performance is largely retained with the reversible
capacity of about 200 mAh g.sup.-1, which proves the genuine
MgCl.sup.+ intercalation in the activated TiS.sub.2 electrode. The
smaller capacity compared to the original cell is most likely due
to the inevitable material loss during washing and transferring the
electrode.
[0058] The proposed electrochemical reactions in the cell could be
summarized in following equations:
Cathode: TiS.sub.2+MgCl.sup.++e.sup.-(MgCl)TiS.sub.2 (1)
Anode: 1/2Mg+1/2MgCl.sub.2MgCl.sup.++e (2)
Overall: TiS.sub.2+1/2Mg+1/2MgCl.sub.2(MgCl)TiS.sub.2 (3)
Electrolyte:
2PhMgCl+AlCl.sub.3.fwdarw.Mg.sub.2Cl.sub.3.sup.++AlPh.sub.2Cl.sub.2.sup.--
MgCl.sup.++MgCl.sub.2+AlPh.sub.2Cl.sub.2.sup.- (4)
[0059] During the discharge, Equation 1 describes the intercalation
of MgCl.sup.+ into the activated TiS.sub.2 in the cathode. Equation
2 describes the simultaneous generation of MgCl.sup.+ at the Mg
anode by converting from MgCl.sub.2 species in APC electrolyte due
to the dynamic equilibrium among those species (Equation 4).
Therefore, MgCl.sub.2 are consumed form or replenished into the
electrolyte during the electrochemical cycling (Equation 3). Thus
the energy density of the present cell is limited by the solubility
of MgCl.sub.2 in THF. It has been previously demonstrated the
solubility of MgCl.sub.2 can increase dramatically if the Cr
acceptors are present in solution. Although we recognize the
chemical composition of the original APC electrolyte
(PhMgCl:AlCl.sub.3=2:1) will change to (Ph.sub.2Mg:AlCl.sub.3=1:1)
during the discharge when MgCl.sub.2 is consumed, it is argued such
compositional change will still allow reversible Mg-deposition and
stripping supported by our experimental data in FIG. 15a-15d
showing voltage profiles of layered TiS.sub.2 cathode (dotted) and
Mg anode (solid) measured simultaneously in a three-electrode cell
vs a Mg/Mg.sup.2+ reference electrode at the 2.sup.nd, 13.sup.rd,
80.sup.th and 137.sup.th cycle. The electrochemical voltage
profiles of the Mg anode at the 2.sup.nd, 13.sup.rd, 8.sup.th and
137.sup.th cycles reflect minimum change during the prolonged
electrochemical cycling.
[0060] The MgCl-ion storage mechanism can be generalized to other
two-dimensional materials. For example, molybdenum disulphide
(MoS.sub.2) also demonstrated .about.270 mAh g.sup.-1 after 10
cycles in the APC-PY14Cl mixed electrolyte. FIG. 16 shows voltage
profile of electrochemical activation of MoS.sub.2 in 0.2 M
PY14Cl+APC electrolyte at 17 mA g.sup.-1. The reversible capacity
increases with cycling and reaches the maximum value of 270 mAh
g.sup.-1 after 10 cycles.
[0061] In summary, a novel MRB enabled by a monovalent MgCl.sup.+
storage mechanism. A class of two-dimensional host materials that
are electrochemically activated to expand the interlayer spacing
significantly over its pristine value to accommodate the large
MgCl.sup.+. With the activated cathode, the reversible capacity and
rate performance of a multivalent/polyatomic-ion battery surpass
the state-of-the-art MRB. Most importantly, a new direction is
identified towards overcoming the challenge of high migration
energy barrier in multivalent/polyatomic-ion batteries. This work
has general implications for multivalent cathode design, as well as
the unique advantage of adapting two-dimensional materials for
advanced energy storage. These batteries are a promising technique
for the pursuit of ultra-high-density energy storage which will
deliver over four times higher volumetric energy densities than
those of state-of-the-art lithium-ion batteries. The intrinsic
safety of these batteries adds to the flexibility in packaging
battery system for electric vehicles. The system and method is a
departure from currently available technology and represents a
significant change in the performance of the current
state-of-the-art energy storage solutions for distributed power
source, grid, and EV applications.
[0062] Material Preparation.
[0063] Layered TiS.sub.2 (99.8%, Strem Chemical Inc.) was used as
purchased. TiS.sub.2 powders have an average particle size of 10
.mu.m. A slurry of active material (70 wt. %), Super-P carbon (20
wt. %), and polyvinylidene fluoride (10 wt. %) dispersed in
N-methyl-2-pyrrolidone was spread on a piece of stainless steel
mesh (400 mesh, 0.8 cm.sup.2) and dried as the working electrode
with active material mass loading of 0.5-1.0 mg cm.sup.-2. To
prepare samples for analysis, we prepared electrode by cold
pressing 7 mg of TiS.sub.2 powders onto stainless steel mesh at 10
MPa without using binder or conductive agent. Freshly polished
magnesium foil (50 .mu.m thick, 99.95%, GalliumSource, LLC) was
used as both the counter and reference electrodes in 2- or
3-electrode cell test. Standard all-phenyl complex (APC)
electrolyte, a solution of 0.25 M
[Mg.sub.2Cl.sub.3].sup.+[AlPh.sub.2Cl.sub.2].sup.- in
tetrahydrofuran (THF, Acros Co.), was prepared following D. Aurbach
et al. as the Mg-ion electrolyte. 0.2 M
1-butyl-1-methylpyrrolidinium chloride (PY14Cl, >98.0%, TCI
America Co.) was mixed in the APC electrolyte.
[0064] Electrochemical Testing.
[0065] 2-Electrode coin cells and 3-electrode tube cells were
fabricated in an Ar-filled glove box for electrochemical
characterizations. For the coin cell configuration, the sequence is
following: a magnesium foil anode, a glass fibre separator (210
.mu.m thick, grade 691, VWR Co.), a tri-layer
polypropylene/polyethylene/polypropylene (PP/PE/PP) separator (25
.mu.m thick, Celgard 2325, Celgard LLC.), and a cathode. For the
3-electrode configuration, a ring-shaped magnesium foil was used as
the reference electrode connected out of the coin cell by
polypropylene coated stainless steel foil. The electrochemical
characterizations were conducted using a potentiostat (VMP-3,
Bio-Logic Co.) and battery cyclers (CT2001A, Lanhe Co.) using the
mixture electrolyte conducted at room temperature.
[0066] Embodiments described herein are included to demonstrate
particular aspects of the present disclosure. It should be
appreciated by those of skill in the art that the embodiments
described herein merely represent exemplary embodiments of the
disclosure. Those of ordinary skill in the art should, in light of
the present disclosure, appreciate that many changes can be made in
the specific embodiments described and still obtain a like or
similar result without departing from the spirit and scope of the
present disclosure. From the foregoing description, one of ordinary
skill in the art can easily ascertain the essential characteristics
of this disclosure, and without departing from the spirit and scope
thereof, can make various changes and modifications to adapt the
disclosure to various usages and conditions. The embodiments
described hereinabove are meant to be illustrative only and should
not be taken as limiting of the scope of the disclosure.
* * * * *