Cathode Active Material and Lithium Ion Battery Comprising Said Cathode Active Material

Abstract

A cathode active material for a lithium ion battery includes particles having a core-shell structure, where each of the particles has a core including a core material and a shell including a shell material. The core material is selected from the group consisting of: layered oxides, including overlithiated layered oxides, compounds having an olivine structure, compounds having a spinel structure, and combinations thereof. The shell material includes a spinel compound. The shell material and/or the core material is at least partially delithiated.

Claims

1-10. (canceled)

11. A cathode active material for a lithium-ion battery, the cathode active material comprising: particles having a core-shell structure, each of the particles having a core comprising a core material and a shell comprising a shell material, wherein the core material is selected from the group consisting of: layered oxides, including overlithiated layered oxides, compounds having an olivine structure, compounds having a spinel structure and combinations thereof, the shell material comprises a spinel compound, and shell material and/or the core material is at least partially delithiated.

12. The cathode active material according to claim 11, wherein the shell material comprises a manganese spinel.

13. The cathode active material according to claim 12, wherein the shell material comprises λ-Mn.sub.2O.sub.4 or Li.sub.xMn.sub.2O.sub.4 having a degree of lithiation of x ≤ 1.

14. The cathode active material according to claim 11, wherein the shell material has a degree of lithiation of x ≤ 0.9.

15. The cathode active material according to claim 11, wherein the particles have a diameter from 0.1 .Math.m to 40 .Math.m inclusive.

16. The cathode active material according to claim 15, wherein the particles have a diameter from 1 .Math.m to 20 .Math.m inclusive.

17. The cathode active material according to claim 11, wherein the shell has a thickness from 0.01 .Math.m to 5 .Math.m inclusive.

18. The cathode active material according to claim 17, wherein the shell has a thickness from 0.05 .Math.m to 1 .Math.m inclusive.

19. The cathode active material according to claim 11, wherein the core is fully lithiated.

20. A lithium-ion battery comprising: a cathode comprising a cathode active material according to claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a schematic diagram of the construction of a lithium-ion battery according to one exemplary embodiment, and

[0028] FIG. 2 is a schematic diagram of a particle of the cathode active material in the exemplary embodiment.

[0029] The constituents shown and the size ratios of the constituents relative to one another are not to scale.

DETAILED DESCRIPTION OF THE DRAWINGS

[0030] The lithium-ion battery 10 shown in purely schematic form in FIG. 1 has a cathode 2 and an anode 5. The cathode 2 and the anode 5 each have a current collector 1, 6, wherein the current collectors may be in the form of metal foils. The current collector 1 of the cathode 2 may comprise aluminum, for example, and the current collector 6 of the anode 5 may comprise copper, for example.

[0031] The cathode 2 and the anode 5 are separated from one another via a separator 4 which is permeable to lithium ions but impermeable to electrons. Separators that may be employed include polymers, in particular a polymer selected from the group consisting of polyesters, in particular polyethylene terephthalate, polyolefins, in particular polyethylene and/or polypropylene, polyacrylonitriles, polyvinylidene fluoride, polyvinylidene-hexafluoropropylene, polyether imide, polyimide, aramid, polyether, polyether ketone, synthetic spider silk or mixtures thereof. A separator may optionally also be coated with ceramic material and a binder, for example, based on Al.sub.2O.sub.3.

[0032] In addition, the lithium-ion battery comprises an electrolyte 3 which is conductive for lithium ions and which may be a solid electrolyte or a liquid comprising a solvent and at least one lithium conductive salt dissolved therein, for example, lithium hexafluorophosphate (LiPF.sub.6). The solvent is preferably inert. Suitable solvents are for example organic solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate (FEC), sulfolanes, 2-methyltetrahydrofuran, acetonitrile and 1,3-dioxolane. Employable solvents also including ionic liquids. Such ionic liquids contain exclusively ions. Preferable cations, which may especially be alkylated, are imidazolium, pyridinium, pyrrolidinium, guanidinium, uronium, thiuronium, piperidinium, morpholinium, sulfonium, ammonium and phosphonium cations. Examples of employable anions include halide, tetrafluoroborate, trifluoroacetate, triflate, hexafluorophosphate, phosphinate and tosylate anions. Examples of ionic liquids include: N-methyl-N-propylpiperidinium bis(trifluormethylsulfonyl)imide, N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide, N-butyl-N-trimethylammonium bis(trifluormethylsulfonyl)imide, triethylsulfonium bis(trifluormethylsulfonyl)imide and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluormethylsulfonyl)imide. In one variant, two or more of the abovementioned liquids may be used. Preferred conductive salts are lithium salts which comprise inert anions and which are preferably non-toxic. Suitable lithium salt are in particular lithium hexafluorophosphate (LiPF.sub.6), lithium tetrafluoroborate (LiBF.sub.4) and mixtures of these salts. The separator 4 may be impregnated/wetted with the lithium salt electrolyte if the salt is liquid.

[0033] The anode 5 comprises an anode active material. The anode active material may be selected from the group consisting of carbon-containing materials, silicon, silicon suboxide, silicon alloys, aluminum alloys, indium, indium alloys, tin, tin alloys, cobalt alloys and mixtures thereof. The anode active material is preferably selected from the group consisting of synthetic graphite, natural graphite, graphene, mesocarbon, doped carbon, hard carbon, soft carbon, fullerene, silicon-carbon composite, silicon, surface-coated silicon, silicon suboxide, silicon alloys, lithium, aluminum alloys, indium, tin alloys, cobalt alloys, and mixtures thereof. Also suitable, in principle, are further anode active materials known per se from the prior art, for example niobium pentoxide, titanium dioxide, titanates such as lithium titanate (L.sub.i4Ti.sub.5O.sub.12), tin dioxide, lithium, lithium alloys and/or mixtures thereof.

[0034] In the lithium-ion battery 10, the cathode 2 comprises a cathode active material having a core-shell structure. The cathode active material comprises a multiplicity of particles 11. A schematic diagram of a particle 11 is shown in schematic form in FIG. 2. The particles 11 each comprise a core 12 and a shell 13. The diameter D of the particles 11 of the cathode active material is on average from 0.1 .Math.m to 40 .Math.m inclusive, preferably from 1 .Math.m to 20 .Math.m inclusive. The shell 13 of the particles 11 on average has a thickness d in the range from 0.01 .Math.m to 5 .Math.m inclusive, preferably from 0.05 .Math.m to 1 .Math.m inclusive.

[0035] The material of the core 12 may comprise a layered oxide such as, for example, NMC, NCA or LCO. The layered oxide may in particular be an overlithiated layered oxide (OLO). Alternatively, the material of the core 12 may be a compound having a spinel structure, for example LMO or LMNO, or a compound having an olivine structure, for example LFP or LMFP. The material of the shell 13 is a spinel compound, preferably comprising an exclusively manganese-containing spinel (for example λ-Mn.sub.2O.sub.4, Li.sub.xMn.sub.2O.sub.4 where x ≤ 1). The material of the core 12 and/or the material of the shell 13 are at least partially delithiated.

[0036] Production of a lithium-ion battery 10 comprising the core-shell cathode active material and an anode active material is hereinafter elucidated using a reference example, which does not have all of the features of the invention, and using an inventive exemplary embodiment.

[0037] Table 1 summarizes the substances and materials used in the examples.

TABLE-US-00001 Employed substances and materials. Description NMC811 LiNi.sub.0.8Mn.sub.0.1Co.sub.0.1O.sub.2 λ-Mn.sub.2O.sub.4 Manganese spinel, shell material of the cathode active material PVdF Polyvinylidene fluoride, binder NMP (electronic grade) N-methyl-2-pyrrolidone carrier solvent Aluminum carrier foil Carrier foil for cathode Natural graphite Anode active material SBR Styrene-butadiene rubber, binder CMC Carboxymethylcellulose, binder Super C65 (conductivity carbon black) Conductivity additive Copper carrier foil Carrier foil for anode Celgard Separator 2500 Separator (25 .Math.m) made of polypropylene (PP) Liquid electrolyte, comprising a solution of LiPF.sub.6 in organic carbonates (e.g. ethylene carbonate (EC), diethylene carbonate (DEC)) Liquid electrolyte comprising lithium conductivity salt Aluminum laminated film Packaging film for the cell

Example 1 (Reference Example)

[0038] A mixture of 94% by weight of NMC811, 3% by weight of PVdF and 3% by weight of conductivity carbon black is suspended in NMP with a high-shear dissolver-mixer at 20° C. This affords a homogeneous coating composition which is doctor-blade-coated onto a 15 .Math.m rolled aluminum carrier foil. Removing the NMP affords a composite cathode film having a basis weight of 21.3 mg/cm.sup.2.

[0039] In analogous fashion, an anode coating composition having a composition of 94% by weight of natural graphite, 2% by weight of SBR, 2% by weight of CMC and 2% by weight of Super C65 was produced and applied to a 10 .Math.m rolled copper carrier foil. The resulting anode film has a basis weight of 12.7 mg/cm.sup.2.

[0040] The cathode 2 comprising the cathode film is assembled with an anode 5 comprising the anode film, a separator 4 (25 .Math.m) made of polypropylene (PP) and a liquid electrolyte 3 comprising a 1 M solution of LiPF.sub.6 in EC/DMC (3:7 w/w) to afford a lithium-ion battery 10 having a 25 cm.sup.2 active electrode area, which is packaged in high-specification aluminum laminated film (thickness: 0.12 mm) and sealed. This affords a pouch cell having external dimensions of about 0.5 mm x 6.4 mm x 4.3 mm.

[0041] The lithium-ion battery 10 is subjected to a first charging to 4.2 V (C/10) and subsequently discharged to 2.8 V at C/10. The capacity of the first charging is 111 mAh and the capacity of the first discharging is 100 mAh. This results in a formation loss of about 10% for the complete lithium-ion battery 10. This corresponds to the expected formation loss of about 10% when using graphite as the anode active material.

Example 2 (Lithium-Ion Battery According to One Exemplary Embodiment of The Invention)

[0042] A mixture of 94% by weight of the disclosed cathode active material (consisting of ~ 5.5% by weight of a λ-Mn.sub.2O.sub.4 shell and ∼ 94.5% by weight of an NMC811 core), 3% by weight of PVdF and 3% by weight of conductivity carbon black is suspended in NMP with a high-shear mixing apparatus at 20° C. The diameter of the core 12 of the particles 11 is about 5 .Math.m and the thickness of the shell is about 0.06 .Math.m. This affords a homogeneous coating composition which is doctor-blade-coated onto a 15 .Math.m rolled aluminum collector-carrier foil. Removing the NMP affords a cathode film having a basis weight of 22.6 mg/cm.sup.2.

[0043] In analogous fashion, an anode coating composition having a composition of 94% by weight of natural graphite, 2% by weight of SBR, 2% by weight of CMC and 2% by weight of Super C65 was produced and applied to a 10 .Math.m rolled copper carrier foil. The resulting anode film has a basis weight of 12.7 mg/cm.sup.2.

[0044] The cathode 2 comprising the cathode film is assembled with an anode 5 comprising the anode film, a separator 4 (25 .Math.m) and an electrolyte 3 comprising a 1 M solution of LiPF.sub.6 in EC/DMC (3:7 w/w) to afford a lithium-ion battery 10 having a 25 cm.sup.2 electrode area which is packaged in aluminum laminated film (thickness: 0.12 mm) and sealed. This affords a pouch cell having external dimensions of about 0.5 mm x 6.4 mm x 4.3 mm.

[0045] The lithium-ion battery 10 is subjected to a first charging to 4.2 V (C/10) and subsequently discharged to 2.8 V at C/10. A charging of 111 mAh is observed for the first charging at C/10 while for the first C/10 discharging 104.5 mAh is observed.

Comparison of the Examples

[0046] The use of the core-shell cathode active material (example 2) in the cathode 2 results in a higher nominal capacity of the lithium-ion battery 10 relative to the reference example. This corresponds to a reduced formation loss which results from the fact that the spinel can absorb further cyclable lithium from the lithiated anode during the discharging. The increase in the basis weight of the cathode film in example 2 compared to the reference example (22.6 mg/cm.sup.2 instead of 21.3 mg/cm.sup.2) is a result of the λ-Mn.sub.2O.sub.4 particle shell 13 – the proportion of cobalt and nickel is the same in the two examples. It may alternatively or also be possible, to keep the nominal capacity constant for the inventive lithium-ion battery 10, and instead reduce the proportion of cobalt and nickel.

[0047] The lithium-ion battery 10 is not limited to graphite as the anode active material; it is advantageously also possible to utilize silicon-based anode active materials or other anode active materials.

[0048] Although the invention has been illustrated and described in detail using exemplary embodiments the invention is not limited by the exemplary embodiments. On the contrary, other variations of the invention may be derived therefrom without departing from the scope of protection of the invention defined by the claims.

TABLE-US-00002 List of reference numerals 1 Current collector 2 Cathode 3 Electrolyte 4 Separator 5 Anode 6 Current collector 10 Lithium-ion battery 11 Particle 12 Core 13 Shell