Lithium metal battery
In some aspects, the present disclosure provides a lithium metal battery having a negative electrode that comprises a substantially pure lithium metal and a positive electrode that comprises the epsilon polymorph of vanadyl phosphate (ε-VOPO 4 ). The lithium metal can have less than five ppm of non-metallic elements by mass. The ε-VOPO 4 can be made from solvothermally synthesized H 2 VOPO 4 , and be optimized to reversibly intercalate two Li-ions to reach full theoretical capacity with a coulombic efficiency of 98%. This material can adopt a stable 3D tunnel structure and can extract two Li-ions per vanadium ion, giving a theoretical capacity of 305 mAh/g, with an upper charge/discharge plateau at around 4.0 V, and one lower at around 2.5 V. The ε-VOPO 4 particles may be modified with niobium (Nb) to improve the cycling stability.
1 . An energy storage device comprising:
a negative electrode comprising a layer of lithium metal with an impurity level of less than about 100 parts-per-million (ppm) by mass; and
a positive electrode comprising a plurality of ε-VOPO 4 primary particles modified with a niobium coating,
wherein the niobium coating is localized on a surface of the plurality of ε-VOPO 4 primary particles,
wherein the niobium coating has a thickness of about 1 nm to about 100 nm, wherein the plurality of ε-VOPO 4 primary particles is delithiated when the energy storage device is in a charged state,
wherein the plurality of ε-VOPO 4 primary particles modified with the niobium coating exhibits reduced interparticle cracking, and
wherein the positive electrode has a specific capacity of at least 260 mAh/g.
2 . The energy storage device of claim 1 , wherein the impurity level is based at least in part on an amount of one or more non-metallic elements.
3 . The energy storage device of claim 2 , wherein the one or more non-metallic elements comprise nitrogen or oxygen.
4 . The energy storage device of claim 1 , wherein the impurity level is based at least in part on an amount of one or more metallic elements.
5 . The energy storage device of claim 4 , wherein the one or more metallic elements comprise magnesium or aluminum.
6 . The energy storage device of claim 5 , wherein the layer of lithium metal comprises less than 0.1 weight % (wt %) or atomic % (at %) of one or more non-conductive impurities.
7 . The energy storage device of claim 6 , wherein the layer of lithium metal comprises less than one (1) non-lithium crystalline subsurface structure per mm 3 .
8 . The energy storage device of claim 1 , wherein the positive electrode is configured to maintain the specific capacity for at least 100 charge/discharge cycles between 1.6 and 4.5 Volts at a charge/discharge rate of at least C/10.
9 . The energy storage device of claim 1 , wherein the niobium coating is coated on the plurality of ε-VOPO 4 primary particles to reduce electrolyte penetration into the positive electrode.
10 . The energy storage device of claim 1 , wherein the niobium coating is coated on the plurality of ε-VOPO 4 primary particles to reduce side reactions between an electrolyte and the positive electrode.
11 . The energy storage device of claim 1 , wherein the niobium coating is coated on the plurality of ε-VOPO 4 primary particles to reduce interparticle stress in the positive electrode.
12 . The energy storage device of claim 1 , wherein a concentration of niobium in the positive electrode is at least 1.0 mol %.
13 . The energy storage device of claim 1 , wherein the specific capacity of the positive electrode is at least 275 mAh/g at a discharge rate of C/10.
14 . The energy storage device of claim 1 , wherein the plurality of ε-VOPO 4 primary particles modified with the niobium coating is sintered.
15 . The energy storage device of claim 1 , wherein the positive electrode comprises at least graphene or a carbon nanotube.
16 . The energy storage device of claim 15 , wherein the positive electrode comprises the graphene and a binder material on a current collector substrate.
17 . The energy storage device of claim 1 , wherein the positive electrode has a current-voltage profile which displays peaks representing a dual-lithium ion exchange per transition metal ion of at least about 90%.
18 . The energy storage device of claim 1 , wherein the energy storage device is configured to maintain at least 90% of the specific capacity when cycled at least 100 times from 1.6 V to 4.5 V at a rate of at least C/5.