Patent Application
20240313263
The present disclosure generally relates to a technical field of secondary batteries, and more particularly to a lithium-ion battery.
A lithium-ion battery has been widely used in life and production due to its excellent performance. In recent years, with the development of consumer electronics and new energy vehicles, people have put forward higher requirements for the performance of the lithium-ion battery, especially the cycling performance needs to be further improved under high-temperature conditions. In a cycling process of the lithium-ion battery, especially a high-nickel and high-voltage ternary battery system, when the nickel content and working voltage in the ternary positive electrode material are relatively high, the gas production of the lithium-ion battery during the cycling is more serious. The possible reasons are as follows: on the one hand, with the increase in the nickel content, the original content of alkaline compounds on the surface of the positive electrode material increases, especially the content of lithium carbonate. During the cycling of the battery, lithium carbonate will decompose to generate gas. On the other hand, the proportion of lithium ions that can be de-intercalated in the high-nickel ternary material is larger, and the structure of the positive electrode material is easily changed or even collapsed at this time, which will cause the rupture of the positive electrode protective film and cause a large amount of gas to be generated by the side reactions when the positive electrode material is directly exposed to an electrolyte. At the same time, the activity of nickel ions is high, and it is easier and faster for the electrolyte to oxidize and decompose on the surface of the positive electrode material with high nickel content, which further increases the gas production during the cycling and deteriorates the high-temperature cycling performance.
The present disclosure provides a lithium-ion battery, including a positive electrode, a negative electrode and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes LiNixCoyMnzL(1-x-y-z)O2, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe, 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5, 0≤x+y+z≤1, and an upper limit voltage of the lithium-ion battery is ≥4.2 V.
The non-aqueous electrolyte includes a solvent, an electrolyte salt and a compound represented by formula 1:
A-D-B-E-C Formula 1
where A, B, and C are each independently selected from a group containing a cyclic carbonate group, a cyclic sulfate group, a cyclic sulfite group, a cyclic sulfonate group, a cyclic sulfone group, a cyclic sulfoxide group, a cyclic carboxylate group or a cyclic anhydride group;
D and E are each independently selected from a single bond, or a group containing a hydrocarbylene group, an ether bond, a sulfur-oxygen double bond or a carbon-oxygen double bond.
Based on a total mass of the non-aqueous electrolyte as 100%, the compound represented by the formula 1 is added in an amount of 0.01 to 5.0%.
In some embodiments, A, B, and C each independently contain 1 to 5 of the cyclic carbonate group(s), the cyclic sulfate group(s), the cyclic sulfite group(s), the cyclic sulfonate group(s), the cyclic sulfone group(s), the cyclic sulfoxide group(s), the cyclic carboxylate group(s) or the cyclic anhydride group(s), and a total number of the cyclic carbonate group(s), the cyclic sulfate group(s), the cyclic sulfite group(s), the cyclic sulfonate group(s), the cyclic sulfone group(s), the cyclic sulfoxide group(s), the cyclic carboxylate group(s) or the cyclic anhydride group(s) of A, B, and C is less than or equal to 10.
In some embodiments, A and C are each independently selected from a group represented by formula 2:
where n is selected from an integer of 0 to 4, and R1 is selected from hydrogen, halogen or a C1 to C5 halohydrocarbonyl group; R2, R3, R4, R5, R6, and R7 are each independently selected from a C1 to C3 hydrocarbylene group, a C1 to C3 alkoxy group, an oxygen atom,
in which at least one of R2, R3, and R4 is selected from
and at least one of R2, R3, and R4 is selected from the oxygen atom, and at least one of R5, R6, and R7 is selected from
and at least one of R5, R6, and R7 is selected from the oxygen atom.
In some embodiments, B is selected from a group represented by formula 3:
where m is selected from an integer of 1 to 4, and R8, R9, and R10 are each independently selected from a C1 to C3 hydrocarbylene group, a C1 to C3 alkoxy group, an oxygen atom,
at least one of R8, R9, and R10 is selected from
and at least one of R8, R9, and R10 is selected from the oxygen atom.
In some embodiments, D and E are each independently selected from a group represented by formula 4:
where z is selected from an integer of 0 to 4, R11 and R13 are each independently selected from a single bond or a C1 to C5 hydrocarbylene group, and R12 is selected from a single bond,
In some embodiments, D and E are each independently selected from the single bond or the C1 to C5 hydrocarbylene group, and A, B, and C are each independently selected from the cyclic carbonate group, the cyclic sulfate group, the cyclic sulfite group, the cyclic sulfonate group, the cyclic sulfone group, the cyclic sulfoxide group, the cyclic carboxylate group or the cyclic anhydride group, which is substituted or unsubstituted.
In some embodiments, when A, B or C is substituted, a substituent is selected from halogen, a hydrocarbonyl group or a halohydrocarbonyl group.
In some embodiments, when A, B or C is substituted, the substituent is selected from halogen, an alkyl group or a haloalkyl group.
In some embodiments, A and C are same as each other, A and B are same as or different from each other, and D and E are same as each other.
In some embodiments, the compound represented by the formula 1 is selected from one or more of following compounds:
In some embodiments, the positive electrode active material is selected from one or more of LiNi0.5Co0.2Mn0.3O2, LiNi0.6Co0.2Mn0.2O2, LiNi0.7Co0.1Mn0.2O2, LiNi0.8Co0.15Al0.05O2, LiNi0.8Co0.1Mn0.1O2, LiNi0.6Mn0.4O2, and LiNi0.8Mn0.2O2.
In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive including at least one of an unsaturated cyclic carbonate compound, a fluorinated cyclic carbonate compound, an aromatic additive, a fluorine-containing anisole compound, a dicarboxylic acid anhydride, lithium difluorophosphate, and lithium bisfluorosulfonimide (LiFSI).
In order that the technical problems, technical solutions and advantageous effects to be solved by the present disclosure can be more clearly understood, the present disclosure will be described in further detail with reference to the accompanying drawings and the embodiments. It should be understood that the particular embodiments described herein are only used to explain the present disclosure, but are not intended to limit the present disclosure.
The embodiment of the present disclosure provides a lithium-ion battery, including a positive electrode, a negative electrode and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer. The positive electrode material layer includes a positive electrode active material. The positive electrode active material includes LiNixCoyMnzL(1-x-y-z)O2, where L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe, 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5, 0≤x+y+z≤1. An upper limit voltage of the lithium-ion battery is ≥4.2 V. The non-aqueous electrolyte includes a solvent, an electrolyte salt and a compound represented by formula 1:
Formula 1 A-D-B-E-C
where A, B, and C are each independently selected from a group containing a cyclic carbonate group, a cyclic sulfate group, a cyclic sulfite group, a cyclic sulfonate group, a cyclic sulfone group, a cyclic sulfoxide group, a cyclic carboxylate group or a cyclic anhydride group;
D and E are each independently selected from a single bond, or a group containing a hydrocarbylene group, an ether bond, a sulfur-oxygen double bond or a carbon-oxygen double bond.
Based on a total mass of the non-aqueous electrolyte as 100%, the compound represented by the formula 1 is added in an amount of 0.01 to 5.0%.
According to the lithium-ion battery provided in the present disclosure, the inventors found that when the compound represented by the formula 1 is used in combination with a high-nickel ternary material, a ternary high-nickel lithium-ion battery with an increased capacity retention rate during the high-temperature cycling and a lower gas generation during the cycling can be obtained. In the lithium-ion battery provided in the present disclosure, the compound represented by the formula 1 decomposes on the surface of the positive electrode to form a protective film, which uniformly covers the surface of the positive electrode material. On the one hand, it inhibits the decomposition of original alkaline oxides such as lithium carbonate on the surface of the positive electrode material to reduce a gas generation. On the other hand, it can well protect the structural stability of the positive electrode. It is speculated that the decomposition product of the formula 1 on the surface of the positive electrode forms a complex with nickel ions to form a relatively stable protective film, which limits its dissolution. At the same time, the formed film has certain elasticity. With the expansion and contraction of the positive electrode material, the corresponding expansion and contraction will occur, so as to realize the protection of the positive electrode, and the film is not easy to break during the charge and discharge cycling.
It should be noted that the performance of the battery is related to the content of nickel in the positive electrode active material and the content of the compound represented by the formula 1 in the non-aqueous electrolyte. When the nickel content in the positive electrode active material is too small, although adding the compound represented by the formula 1 can improve the high-temperature cycling performance of the battery to a certain extent, its improvement effect is relatively low. However, when the nickel content in the positive electrode active material is high (0.5≤x≤1), the compound represented by the formula 1 has an extremely excellent improvement effect on the high-temperature cycling performance of the battery, indicating that the presence of nickel in the positive electrode active material has a clear relationship with the compound represented by the formula 1. As the nickel content increases, the more the compound represented by the formula 1 can play its role in improving the battery. At the same time, when the addition amount of the compound represented by the formula 1 is too small, the film-forming protective effect cannot be achieved, and the improvement effect on the battery performance is not apparent. When the addition amount of the compound represented by the formula 1 is too large, not only will the film become too thick and the impedance increase, but also the viscosity of the electrolyte will significantly increase, which will affect the performance of the battery. Therefore, only by adding an appropriate amount of the compound represented by the formula 1, can it have a better matching effect with the high-nickel ternary material.
When the charging upper limit voltage of the lithium-ion battery is higher, its electrolyte is more likely to decompose, and the compound represented by the formula 1 can effectively inhibit the decomposition of the electrolyte under high-voltage conditions, so it is especially suitable for a high-voltage lithium-ion battery with an upper limit voltage ≥4.2 V.
In some embodiments, x is selected from 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.83, 0.85, 0.88, 0.90, or 0.95.
In some embodiments, the positive electrode active material is selected from one or more of LiNi0.5Co0.2Mn0.3O2, LiNi0.6Co0.2Mn0.2O2, LiNi0.7Co0.1Mn0.2O2, LiNi0.8Co0.15Al0.05O2, LiNi0.8Co0.1Mn0.1O2, LiNi0.6Mn0.4O2, and LiNi0.8Mn0.2O2.
In some embodiments, the positive electrode active material incorporates element L by means of doping, and L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe. The doped element L can provide stronger A-O chemical bonds than Ni, Co, Mn and other active transition metals, inhibit the precipitation of lattice oxygen under a high voltage, and improve the structural stability of the material.
In some embodiments, A, B, and C each independently contain 1 to 5 of the cyclic carbonate group(s), the cyclic sulfate group(s), the cyclic sulfite group(s), the cyclic sulfonate group(s), the cyclic sulfone group(s), the cyclic sulfoxide group(s), the cyclic carboxylate group(s) or the cyclic anhydride group(s), and a total number of the cyclic carbonate group(s), the cyclic sulfate group(s), the cyclic sulfite group(s), the cyclic sulfonate group(s), the cyclic sulfone group(s), the cyclic sulfoxide group(s), the cyclic carboxylate group(s) or the cyclic anhydride group(s) of A, B, and C is less than or equal to 10.
In some embodiments, A and C are each independently selected from a group represented by formula 2:
where n is selected from an integer of 0 to 4, and R1 is selected from hydrogen, halogen, or a C1 to C5 halohydrocarbonyl group; R2, R3, R4, R5, R6, and R7 are each independently selected from a C1 to C3 hydrocarbylene group, a C1 to C3 alkoxy group, an oxygen atom,
in which at least one of R2, R3, and R4 is selected from
and at least one of R2, R3, and R4 is selected from the oxygen atom, and at least one of R5, R6, and R7 is selected from
and at least one of R5, R6, and R7 is selected from the oxygen atom.
In preferred embodiments, a combined group of —R3—R2—R4— and a combined group of —R7—R5—R6— are each independently selected from
In some embodiments, B is selected from a group represented by formula 3:
where m is selected from an integer of 1 to 4, and R8, R9, and R10 are each independently selected from a C1 to C3 hydrocarbylene group, a C1 to C3 alkoxy group, an oxygen atom,
at least one of R8, R9, and R10 is selected from
and at least one of R8, R9, and R10 is selected from the oxygen atom.
In preferred embodiments, a combined group of —R9—R8—R10— are each independently selected from
In some embodiments, D and E are each independently selected from a group represented by formula 4:
where z is selected from an integer of 0 to 4, R11 and R13 are each independently selected from a single bond or a C1 to C5 hydrocarbylene group, and R12 is selected from a single bond,
In some embodiments, A and C are same as each other, A and B are same as or different from each other, and D and E are same as each other.
When A and C are same as each other, and D and E are same as each other, the compound represented by the formula 1 has a symmetrical structure. Compared with an asymmetrical structure, the compound represented by the formula 1 of the symmetrical structure is more convenient in synthesis, and the yield of the product is higher, which is conducive to reducing the production cost.
In some embodiments, D and E are each independently selected from the single bond or the C1 to C5 hydrocarbylene group, and A, B, and C are each independently selected from the cyclic carbonate group, the cyclic sulfate group, the cyclic sulfite group, the cyclic sulfonate group, the cyclic sulfone group, the cyclic sulfoxide group, the cyclic carboxylate group or the cyclic anhydride group, which is substituted or unsubstituted. Preferably, when A, B or C is substituted, a substituent is selected from halogen, a hydrocarbonyl group or a halohydrocarbonyl group. More preferably, when A, B or C is substituted, the substituent is selected from halogen, an alkyl group or a haloalkyl group.
As an example, the compound represented by the formula 1 can be selected from one or more of following compounds:
In some embodiments, D and E are each independently selected from a group represented by formula 4:
where z is selected from an integer of 1 to 4, R11 and R13 are each independently selected from a single bond or a C1 to C5 hydrocarbylene group, and R12 is selected from
A, B, and C are each independently selected from the cyclic carbonate group, the cyclic sulfate group, the cyclic sulfite group, the cyclic sulfonate group, the cyclic sulfone group, the cyclic sulfoxide group, the cyclic carboxylate group or the cyclic anhydride group, which is substituted or unsubstituted. Preferably, when A, B or C is substituted, a substituent is selected from halogen, a hydrocarbonyl group or a halohydrocarbonyl group. More preferably, when A, B or C is substituted, the substituent is selected from halogen, an alkyl group or a haloalkyl group.
As an example, the compound represented by the formula 1 can be selected from one or more of following compounds:
In some embodiments, the compound represented by the formula 1 can also be selected from one or more of the following compounds:
It should be noted that the above are some of the compounds claimed in the present disclosure, but are not limited thereto, and should not be construed as limiting the present disclosure.
Those skilled in the art can know the preparation method of the above-mentioned compound according to the general knowledge in the field of chemical synthesis if they know the formula of the compound of the formula 1. For example:
Compound 1 can be prepared by a method as follows:
Organic solvents such as sorbitol, dimethyl carbonate, methanol alkaline substance catalyst potassium hydroxide, and DMF are placed in a reaction vessel, and reacted for several hours under heating conditions. A certain amount of oxalic acid is added to adjust the pH to neutrality. After filtering and recrystallization, an intermediate product 1 can be obtained. Then, the intermediate product 1, carbonate, thionyl chloride, etc. are esterified under high-temperature conditions to obtain an intermediate product 2, and then the intermediate product 2 is oxidized using an oxidizing agent such as sodium periodate to obtain the compound 1.
Compound 2 can be prepared by a method as follows:
Diacetone-D-mannitol, dimethyl carbonate, methanol, potassium carbonate, dioxane, etc. are reacted under heating and stirring for several hours. Then, a certain amount of oxalic acid is added to adjust the pH of the solution to neutrality. After filtering and concentrating, an intermediate product 3 is obtained. An appropriate amount of pure water, carbonate, acid, etc. are added to the intermediate product 3 to perform a hydrolysis reaction to obtain an intermediate product 4. Then, the intermediate product 4, thionyl chloride and carbonate solvent are reacted under heating conditions to obtain an intermediate product 5. Finally, the intermediate product 5 is oxidized using an oxidizing agent such as sodium periodate to obtain the compound 2.
In some embodiments, the solvent includes one or more of ether solvents, nitrile solvents, carbonate solvents and carboxylate solvents.
Ether solvents include cyclic ethers or linear ethers.
Examples of cyclic ethers include one or more of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF).
Examples of linear ethers include one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and diglyme (TEGDME).
Examples of nitrile solvents include one or more of acetonitrile, glutaronitrile, and malononitrile.
Carbonate solvents include cyclic carbonates or linear carbonates.
Examples of cyclic carbonates include one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC).
Examples of linear carbonates include one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, and dipropyl carbonate (DPC).
Carboxylate solvents include cyclic carboxylates or linear carbonates.
Examples of cyclic carboxylates include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone.
Examples of linear carbonates include one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.
In some embodiments, the electrolyte salt is selected from a lithium salt. In preferred embodiments, the electrolyte salt is selected from one or more of LiPF6, LiBF4, LiBOB, LIDFOB, LIN(SO2CF3)2, LIN(SO2C2F5)2, LiC(SO2CF3)3, LIN(SO2F)2, LiClO4, LiAsF6, LiSbF6, LiCF3SO3, Li2B10Cl10, a lithium salt of a lower aliphatic acid, and LiAlCl4.
In some embodiments, the concentration of the electrolyte salt in the non-aqueous electrolyte is from 0.1 mol/L to 8 mol/L.
In preferred embodiments, the concentration of the electrolyte salt in the non-aqueous electrolyte is from 0.5 mol/L to 4 mol/L. Specifically, the concentration of the electrolyte salt may be 0.5 mol/L, 1 mol/L, 1.5 mol/L, 2 mol/L, 2.5 mol/L, 3 mol/L, 3.5 mol/L or 4 mol/L.
In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive including at least one of an unsaturated cyclic carbonate compound, a fluorinated cyclic carbonate compound, an aromatic additive, a fluorine-containing anisole compound, a dicarboxylic acid anhydride, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide (LiFSI).
In some embodiments, the unsaturated cyclic carbonate compound includes at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 4,5-dimethyl vinylene carbonate, phenyl vinylene carbonate and 4,5-divinyl ethylene carbonate.
When the non-aqueous electrolyte contains the unsaturated cyclic carbonate compound, based on the total mass of the non-aqueous electrolyte as 100%, the content of the unsaturated cyclic carbonate compound is from 0.1 to 5%.
In some embodiments, the fluorinated cyclic carbonate compound includes one or more of fluoroethylene carbonate (FEC), 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methyl ethylene carbonate, 4,5-difluoro-4-methyl ethylene carbonate, 4-fluoro-5-methyl ethylene carbonate, 4,4-difluoro-5-methyl ethylene carbonate, 4-(fluoromethyl) ethylene carbonate, 4-(difluoromethyl)ethylene carbonate, 4-(trifluoromethyl)ethylene carbonate, 4-(fluoromethyl)-4-fluoroethylene carbonate, 4-(fluoromethyl)-5-fluoroethylene carbonate, 4-fluoro-4,5-dimethyl ethylene carbonate, 4,5-difluoro-4,5-dimethyl ethylene carbonate and 4,4-difluoro-5,5-dimethyl ethylene carbonate.
When the non-aqueous electrolyte contains the fluorinated cyclic carbonate compound, based on the total mass of the non-aqueous electrolyte as 100%, the content of the fluorinated cyclic carbonate compound is from 0.1 to 30%.
In some embodiments, the aromatic additive includes one or more of biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether, dibenzofuran and other aromatic compounds; 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene.
When the non-aqueous electrolyte contains the aromatic additive, based on the total mass of the non-aqueous electrolyte as 100%, the mass percent content of the aromatic additive is from 0.1 to 5%.
In some embodiments, the fluorine-containing anisole compound includes one or more of 2,4-difluoroanisole, 2,5-difluoroanisole, and 2,6-difluoroanisole. When the non-aqueous electrolyte contains the fluorine-containing anisole compound, based on the total mass of the non-aqueous electrolyte as 100%, the mass percent content of the fluorine-containing anisole compound is from 0.1 to 5%.
In some embodiments, the dicarboxylic acid anhydride includes one or more of succinic acid, maleic acid, and phthalic acid. When the non-aqueous electrolytic solution contains the dicarboxylic acid anhydride, based on the total mass of the non-aqueous electrolyte as 100%, the mass percent content of the dicarboxylic acid anhydride is from 0.1 to 5%.
In some embodiments, when the non-aqueous electrolyte contains lithium difluorophosphate, based on the total mass of the non-aqueous electrolyte as 100%, the mass percent content of lithium difluorophosphate is from 0.1 to 2%.
In some embodiments, when the non-aqueous electrolyte contains lithium bis(fluorosulfonyl)imide (LiFSI), based on the total mass of the non-aqueous electrolyte as 100%, the mass percent content of lithium bis(fluorosulfonyl)imide (LiFSI) is from 0.1 to 5%.
In some embodiments, the auxiliary additive also includes nitrogen-containing compounds such as 1-methyl-2-pyrrolidone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methyl succinimide; hydrocarbon compounds such as heptane, octane and cycloheptane; and fluorine-containing aromatic compounds such as fluorobenzene, difluorobenzene and trifluorotoluene.
It should be noted that, unless otherwise specified, in general, the mass percent content range of any optional substance in the non-aqueous electrolyte in the auxiliary additive is 10% or less, preferably, the mass percent content is from 0.1 to 5%.
In preferred embodiments, the positive electrode active material is selected from one or more of LiNi0.5Co0.2Mn0.3O2, LiNi0.6Co0.2Mn0.2O2, LiNi0.7Co0.1Mn0.2O2, LiNi0.8Co0.1Mn0.1O2, LiNi0.6Mn0.4O2, and LiNi0.8Mn0.2O2.
In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer covers a surface of the positive electrode current collector. The positive electrode current collector is selected from metal materials that can conduct electrons. Preferably, the positive electrode current collector includes one or more of Al, Ni, and stainless steel. In more preferred embodiments, the positive current collector is selected from aluminum foil.
In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent. The positive electrode active material, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.
The positive electrode binder includes one or more of thermoplastic resins such as polyvinylidene fluoride, vinylidene fluoride copolymers, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, ethylene-tetrafluoroethylene copolymers, vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, vinylidene fluoride-trichloroethylene copolymers, vinylidene fluoride-fluoroethylene copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, thermoplastic polyimides, polyethylene, polypropylene and so on; acrylic resins; and styrene butadiene rubbers.
The positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.
In some embodiments, the negative electrode includes a negative electrode material layer including a negative electrode active material. The negative electrode active material includes one or more of a silicon-based negative electrode, a carbon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode. The silicon-based negative electrode includes one or more of silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials. The carbon-based negative electrode includes one or more of graphite, hard carbon, soft carbon, graphene, and intermediate phase carbon microspheres. The tin-based negative electrode includes one or more of tin, tin carbon, tin oxide, and tin metal compounds. The lithium negative electrode includes one or more of metal lithium or a lithium alloy. The lithium alloy may specifically be at least one of a lithium-silicon alloy, a lithium-sodium alloy, a lithium-potassium alloy, a lithium-aluminum alloy, a lithium-tin alloy and a lithium-indium alloy.
In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer covers a surface of the negative electrode current collector. The negative electrode current collector is selected from metal materials that can conduct electrons. Preferably, the negative electrode current collector includes one or more of Cu, Ni, and stainless steel. In more preferred embodiments, the negative current collector is selected from aluminum foil.
In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. The negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer.
The negative electrode binder includes one or more of thermoplastic resins such as polyvinylidene fluoride, vinylidene fluoride copolymers, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, ethylene-tetrafluoroethylene copolymers, vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, vinylidene fluoride-trichloroethylene copolymers, vinylidene fluoride-fluoroethylene copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, thermoplastic polyimides, polyethylene, polypropylene and so on; acrylic resins; and styrene butadiene rubbers.
The negative electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.
In some embodiments, the battery further includes a separator, and the separator is located between the positive electrode and the negative electrode.
The separator can be an existing conventional separator, which can be a ceramic separator, a polymer separator, a non-woven fabric, an inorganic-organic composite separator, etc., including but not limited to separators such as single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP/PE, double-layer PP/PP, and triple-layer PP/PE/PP separators, and the like.
The present disclosure is further illustrated by way of examples below.
Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed according to a mass ratio of EC:DEC:EMC=1:1:1. Then, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol/L, and then each additive was added according to the following tables. The amount of the additive was calculated as a percent of the total mass of the electrolyte.
A positive active material, conductive carbon black Super-P and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 93:4:3, and then they were dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode active material is shown in the following tables. The positive electrode slurry was evenly coated on both sides of aluminum foil. After drying, calendering and vacuum drying, an aluminum lead-out wire was welded with an ultrasonic welder to obtain a positive electrode sheet with a thickness of 120 to 150 μm.
Negative electrode active material graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed at a mass ratio of 94:1:2.5:2.5, and then they were dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry was coated on both sides of copper foil. After drying, calendering and vacuum drying, a nickel lead-out wire was welded with an ultrasonic welder to obtain a negative electrode sheet with a thickness of 120 to 150 μm.
A three-layer separator with a thickness of 20 μm was placed between the positive electrode sheet and the negative electrode sheet, and then a sandwich structure composed of the positive electrode sheet, the negative electrode sheet and the separator was wound. Then, the wound body was flattened and put into an aluminum foil packaging bag, and baked under vacuum at 75° C. for 48 hours to obtain a battery cell to be filled with a liquid.
In a glove box with a water content of 20 ppm or less and an oxygen content of 50 ppm or less, the above-prepared electrolyte was injected into the battery cell, packaged under vacuum, and left standing at 45° C. for 24 h.
Then, the conventional formation of the first charging was carried out according to the following steps: charging at a constant current of 0.05 C for 180 min, charging at a constant current of 0.1 C for 180 min, charging at a constant current of 0.2 C for 120 min, aging at 45° C. for 48 h, secondary sealing under vacuum, then further charging at a constant current of 0.2 C to 4.4 V (LiNi0.5Co0.2Mn0.3O2/AG) or 4.2 V (LiNi0.8Co0.15Al0.05O2/AG) or 4.2 V (LiNi0.8Co0.1Mn0.1O2/AG) or 4.25 V (LiNi0.7Co0.1Mn0.2O2/AG) or 4.35 V (LiNi0.6Co0.2Mn0.2O2/AG), and discharging at a constant current of 0.2 C to 3.0 V.
The lithium-ion batteries prepared in Examples 1 to 42 and Comparative Examples 1 to 9 were subjected to the following performance tests.
The prepared lithium-ion battery was placed in an oven with a constant temperature of 45° C., charged at a constant current of 1C to 4.4 V (LiNi0.5Co0.2Mn0.3O2/AG) or 4.2 V (LiNi0.8Co0.15Al0.05O2/AG) or 4.2 V (LiNi0.8Co0.1Mn0.1O2/AG) or 4.25 V (LiNi0.7Co0.1Mn0.2O2/AG) or 4.35 V (LiNi0.6Co0.2Mn0.2O2/AG), then charged at a constant current and a constant voltage until the current drops to 0.05C, and then discharged at a constant current of 1C to 3.0 V, so as to circulate in this way. The first discharge capacity and the last discharge capacity were recorded, and the initial battery volume and the volume of the battery after 1000 cycles were measured.
The capacity retention rate during the high-temperature cycling was calculated according to the following formula:
Capacity retention ratio=last discharge capacity/first discharge capacity×100%.
The volume expansion rate during the high-temperature cycling is calculated according to the following formula:
Volume expansion rate (%)=(battery volume after cycle-initial battery volume)/initial battery volume×100%.
The batteries used in the following data tests are the same except for the differences listed in the tables.
1. The test results obtained in Examples 1 to 10 and Comparative Examples 1 to 4 are shown in Table 1.
As can be seen from the test results in Table 1, when the positive electrode active material is LiNi0.5Co0.2Mn0.3O2, by comparing Examples 1 to 10 and Comparative Example 1, adding the compound represented by the formula 1 can significantly inhibit gas production during the high-temperature cycling. When the content of the compound represented by the formula 1 is from 1% to 2%, the volume expansion rate of the battery during the high-temperature cycling is at least 7.2% to 8.2%, and at this time has the best capacity retention rate during the high-temperature cycling of 75.2% to 77.2%. Comparison of Examples 1 to 10 and Comparative Examples 2 and 3 show that when the content of the compound represented by the formula 1 is below 0.01% or above 5%, the gas production of the battery during the cycling increases significantly, and the high-temperature cycling performance also decreases significantly. This indicates that in the high-nickel ternary lithium-ion battery, the reasonable addition amount of the compound represented by the formula 1 is from 0.01% to 5%, too large or too small amount is not conducive to the improvement of the battery performance.
2. The test results obtained in Examples 7, 11 to 14 and Comparative Examples 1, 4 to 9 are shown in Table 2.
As can be found by comparing Examples 7, 11 to 14 and Comparative Examples 1, 4 to 9, when the nickel content of the positive electrode active material is relatively low, the cycle volume expansion rate in Comparative Example 5 is still 48.4%. The magnitude of improvement between Comparative Example 5 and Comparative Example 4 is much smaller than that between Example 7 and Comparative Example 1, and is also significantly smaller than that between Examples 11 to 14 and Comparative Examples 6 to 9. The cycling performance of the low-nickel battery system in Comparative Example 5 has not been significantly improved, that is, the improvement effect of the compound represented by the formula 1 on the battery performance is significantly related to the nickel content in the positive electrode active material. When the nickel content in the positive electrode active material is higher than a certain value, the compound represented by the formula 1 can play better cooperating role.
3. The test results obtained in Examples 15 to 24 and Comparative Example 6 are shown in Table 3.
As can be seen from the test data in Table 3, when the positive electrode active material is LiNi0.6Co0.2Mn0.2O2, by comparing Examples 15 to 24 and Comparative Example 6, adding the compound represent by the formula 1 can significantly reduce the gas production of the battery during the cycling and improve the high-temperature cycling performance of the battery. At the same time, the high-temperature cycling performance of the battery is improved to varying degrees by using different compounds represented by the formula 1.
4. The test results obtained in Examples 25 to 31 and Comparative Example 7 are shown in Table 4.
As can be seen from the test data in Table 4, when the positive electrode active material is LiNi0.7Co0.1Mn0.2O2, by comparing Examples 25 to 30 and Comparative Example 7, adding the compound represented by the formula 1 can significantly reduce the gas production of the battery during the cycling and improve the high-temperature cycling performance of the battery. At the same time, the high-temperature cycling performance of the battery is improved to varying degrees by using different compounds represented by the formula 1.
5. The test results obtained in Examples 32 to 35 and Comparative Example 8 are shown in Table 5.
As can be seen from the test data in Table 5, when the positive electrode active material is LiNi0.8Co0.15Al0.05O2, by comparing Examples 32 to 35 and Comparative Example 8, adding the compound represented by the formula 1 can significantly reduce the gas production of the battery during the cycling and significantly improve the capacity retention rate of the battery during the high-temperature cycling.
6. The test results obtained in Examples 36 to 42 and Comparative Example 9 are shown in Table 6.
As can be seen from the test data in Table 6, when the positive electrode active material is LiNi0.8Co0.1Al0.1O2, by comparing Examples 36 to 42 and Comparative Example 9, adding the compound represented by the formula 1 can significantly reduce the gas production of the battery during the cycling and significantly improve the capacity retention rate of the battery during the high-temperature cycling.
7. The lithium-ion batteries obtained in Example 7 and Comparative Example 1 were placed in an oven with a constant temperature of 45° C., charged at a constant current of 1C to 4.4 V (LiNi0.5Co0.2Mn0.3O2/AG), then charged at a constant current and a constant voltage until the current drops to 0.05C, and then discharged to 3.0 V at a constant current of 1C, so as to circulate in this way for 1000 cycles. The lithium-ion batteries were disassembled, and the positive electrodes were taken out for transmission electron microscope observation. The TEM image of the positive electrode in Example 7 is shown in
By comparing the transmission electron microscope images of
The above descriptions are only preferred embodiments of the present disclosure, and are not intended to limit the present disclosure. Any modifications, equivalent replacements and improvements made within the range of spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202011606717.2 | Dec 2020 | CN | national |
| 202110392954.1 | Apr 2021 | CN | national |
The present application is a national phase entry under 35 USC § 371 of International Application PCT/CN2021/138677, filed Dec. 16, 2021, which claims the benefit of and priority to Chinese Patent Application No. 202011606717.2, filed Dec. 28, 2020 and Chinese Patent Application No. 202110392954.1, filed Apr. 13, 2021, the entire disclosures of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2021/138677 | 12/16/2021 | WO |
