VOPO
An electrode comprising a space group Pna2 1 VOPO 4 lattice, capable of electrochemical insertion and release of alkali metal ions, e.g., sodium ions. The VOPO 4 lattice may be formed by solid phase synthesis of KVOPO 4 , milled with carbon particles to increase conductivity. A method of forming an electrode is provided, comprising milling a mixture of ammonium metavanadate, ammonium phosphate monobasic, and potassium carbonate; heating the milled mixture to a reaction temperature, and holding the reaction temperature until a solid phase synthesis of KVOPO 4 occurs; milling the KVOPO 4 together with conductive particles to form a conductive mixture of fine particles; and adding binder material to form a conductive cathode. A sodium ion battery is provided having a conductive NaVOPO 4 cathode derived by replacement of potassium in KVOPO 4 , a sodium ion donor anode, and a sodium ion transport electrolyte. The VOPO 4 , preferably has a volume greater than 90 Å 3 per VOPO 4 .
1. A method of forming an electrode, comprising:
milling a mixture of ammonium metavanadate, ammonium phosphate monobasic, and potassium carbonate;
solid phase synthesizing KVOPO 4 by heating the milled mixture to a reaction temperature;
milling the KVOPO 4 together with conductive particles to form a conductive mixture of fine particles; and
replacing potassium ions with sodium ions to form NaVOPO 4 .
2. The method according to claim 1 , wherein said heating is at a temperature of between 600° C. and 800° C. for about 10 hours.
3. The method according to claim 1 , wherein the conductive particles comprise carbon particles.
4. The method according to claim 1 , further comprising adding a binder material selected from one or more of the group consisting of a poly (vinylidene fluoride), a polytetrafluoroethylene, a styrene butadiene rubber, and a polyimide.
5. The method according to claim 1 , wherein the NaVOPO 4 has a lattice having a crystalline structure having orthorhombic symmetry with space group Pna2 1 .
6. The method according to claim 1 , wherein further comprises an insoluble conductive additive.
7. The method according to claim 1 , wherein the conductive particles comprise conductive carbon.
8. The method according to claim 1 , further comprising:
providing a sodium donor anode and a sodium ion transport electrolyte to form a sodium ion battery; and
operating the sodium ion battery with a discharge voltage curve comprising a first voltage plateau region comprising 3.8 V, and a second voltage plateau region comprising 2 V, the electrode having a capacity of at least C=133 mAhg −1 .
9. The method according to claim 1 , wherein the conductive mixture, after replacement of the potassium ions with sodium ions comprises NaVOPO 4 particles having particle size of 200 nm and conductive particles having a particle size of 2 μm.
10. The method according to claim 1 , further comprising a poly(vinylidene fluoride) binder.
11. The method according to claim 1 , wherein the electrode has a capacity of at least C=133 mAhg −1 .
12. The method according to claim 1 , wherein the NaVOPO 4 comprises a lattice having a volume greater than 90 Å 3 per VOPO 4 .
13. A method of forming an NaVOPO 4 electrode, comprising a VOPO 4 lattice,
the VOPO 4 lattice having a volume greater than 90 Å 3 per VOPO 4 ; and
a portion of the VOPO 4 lattice having two sodium ions per VOPO 4 ,
the method comprising:
forming a mixture of ammonium metavanadate, ammonium phosphate monobasic, and potassium carbonate;
synthesizing KVOPO 4 in a solid phase by heating the mixture;
combining the KVOPO 4 with conductive particles to form a conductive mixture; and
replacing at least a portion of potassium ions with sodium ions to form a NaVOPO 4 .
14. The method according to claim 13 , wherein the NaVOPO 4 has orthorhombic symmetry has space group Pna2 1 .
15. The method according to claim 13 , wherein the KVOPO 4 is milled together with the conductive particles comprising carbon particles, before the replacement of at least a portion of potassium with sodium.
16. The method according to claim 13 , further comprising forming a sodium ion battery by providing a sodium battery anode and a sodium ion transport electrolyte in combination with the electrode, the sodium ion battery having a capacity of at least C=133 mAhg −1 , and a discharge voltage curve comprising a first voltage plateau region comprising 3.8 V, and a second voltage plateau region comprising 2 V.