Additive for lithium ion rechargeable battery cells
A lithium ion rechargeable battery cell includes an anode having electroactive material-containing particles wherein the electroactive material is selective from one or more of silicon, germanium, and tin. A cathode includes an active material adapted to incorporate lithium and also to liberate lithium electrochemically. The anode is adapted to incorporate lithium during lithiation. Also provided is an electrolyte, wherein the electrolyte includes both a cyclic carbonate having a vinyl group and a fluorinated cyclic carbonate. The total amount of the cyclic carbonate including a vinyl group and the fluorinated cyclic carbonate together is in the range of 3.5 wt % to 70 wt % based on the total weight of the electrolyte solution.
1. A lithium ion rechargeable battery cell comprising:
an anode comprising electroactive material-containing particles wherein the electroactive material is selected from one or more of silicon, germanium and tin;
a cathode comprising an active material adapted to incorporate lithium and also to liberate lithium electrochemically, wherein the anode is adapted to incorporate lithium during lithiation; and
an electrolyte;
wherein the electrolyte comprises both a cyclic carbonate including a vinyl group and a fluorinated cyclic carbonate, wherein the total amount of the cyclic carbonate including a vinyl group and the fluorinated cyclic carbonate together is in the range 3.5 wt % to 70 wt % based on the total weight of the electrolyte solution.
2. A lithium ion rechargeable battery cell as claimed in claim 1 wherein the electroactive material-containing particles comprise fibres with a diameter of 10-500 nm and length of 1-150 μm, such fibres optionally being provided in the form of a scaffold or felt comprising such fibres.
3. A lithium ion rechargeable battery cell as claimed in claim 1 , wherein the electroactive material-containing particles comprise tubes with a wall thickness of ≧10 nm and length of ≧1 μm.
4. A lithium ion rechargeable battery cell as claimed in claim 1 , wherein the electroactive material-containing particles comprise ribbons with a thickness of 50-200 nm, a width of 500 nm to 1 μm and a length of ≧1 μm or felts comprising such ribbons.
5. A lithium ion rechargeable battery cell as claimed in claim 1 , wherein the electroactive material-containing particles comprise flakes with a thickness of 50-200 nm and the two other dimensions in the range of 1-20 μm.
6. A lithium ion rechargeable battery cell as claimed in claim 1 , wherein the electroactive material-containing particles comprise particles having a particle core and a plurality of silicon-containing structural elements attached thereto, wherein the structural elements comprise pillars, rods or nanowires having a diameter of no more than 1000 nm.
7. A lithium ion rechargeable battery cell as claimed in claim 1 , wherein the electroactive material-containing particles comprise silicon-containing porous particles, each particle having a network of voids or pores extending therethrough.
8. A lithium ion rechargeable battery cell as claimed in claim 7 wherein at least some of the walls between adjacent pores have a thickness of ≧10 nm and extend over a length of ≧100 nm, and wherein the diameter of the porous particles is 1-30 μm.
9. A lithium ion rechargeable battery cell as claimed in claim 1 , wherein at least some of the electroactive material-containing particles are carbon coated.
10. A lithium ion rechargeable battery cell as claimed in claim 1 , wherein the electroactive material-containing particles comprise silicon with a purity of 90-99.990% by weight.
11. A lithium ion rechargeable battery cell as claimed in claim 1 , wherein substantially all the electroactive material-containing particles in the anode comprise silicon.
12. A lithium ion rechargeable battery cell according to claim 1 , wherein the electrolyte comprises from about 2% to about 50% by weight of a cyclic carbonate including a vinyl group.
13. A lithium ion rechargeable battery cell according to claim 1 , wherein the cyclic carbonate including a vinyl group comprises vinylene carbonate.
14. A lithium ion rechargeable battery cell according to claim 1 , wherein the fluorinated cyclic carbonate comprises fluoroethylene carbonate, difluoroethylene carbonate or a mixture thereof.
15. A lithium ion rechargeable battery cell as claimed in claim 1 , wherein the electrolyte initially includes 0.05 to 0.25 wt % dissolved CO 2 .
16. A lithium ion rechargeable battery cell according to claim 1 wherein the cyclic carbonate including a vinyl group comprises vinylene carbonate and the fluorinated cyclic carbonate comprises fluoroethylene carbonate, difluoroethylene carbonate or a mixture thereof.
17. A lithium ion rechargeable battery cell according to claim 1 , wherein the electrolyte solution further comprises a C 1-8 chain carbonate, selected from one or more of dimethylcarbonate, diethyl carbonate, and ethyl methyl carbonate, wherein the ratio of the cyclic carbonate (including a cyclic carbonate including a vinyl group and/or a fluorinated cyclic carbonate) to the C 1-8 chain carbonate is in the range 30:70 to 50:50.
18. A lithium ion rechargeable battery cell according to claim 1 , wherein the electrolyte solution further comprises a cyclic carbonate other than a cyclic carbonate including a vinyl group or a fluorinated cyclic carbonate, wherein the cyclic carbonate is selected from one or more of the group comprising ethylene carbonate, propylene carbonate, and butylene carbonate.
19. A lithium ion rechargeable battery cell according to claim 1 wherein the electroactive material-containing particles comprise silicon and wherein the electrolyte comprises 1 to 8 wt % of a cyclic carbonate containing a vinyl group and, at least 3 wt % of a fluorinated cyclic carbonate.
20. A lithium ion rechargeable battery cell according to claim 1 , wherein the electrolyte further comprises an electrolyte salt, wherein the electrolyte salt is dissolved in the electrolyte solution to a concentration of between 0.7 to 2M, wherein the electrolyte comprises one or a mixture of lithium containing electrolyte salts selected from the group comprising LiPF 6 , LiBOB, LiCIO 4 or a mixture thereof.
21. A lithium ion rechargeable battery cell as claimed in claim 1 , wherein the anode comprises a porous composite comprising the electroactive material-containing particles and at least one other component selected from: another active material that can reversibly react electrochemically with lithium, a binder, a conductive material, a viscosity adjuster, a filler or a coupling agent.
22. A lithium ion rechargeable battery cell according to claim 1 wherein the structured electroactive material-containing particles have a smallest dimension of at least 10 nm and a largest diameter that is less than 60 μm.