A lithium-ion battery

Abstract

This invention relates to the technical field of lithium-ion batteries and provides a lithium-ion battery. The battery includes a positive electrode, a negative electrode, and an electrolyte; the negative electrode includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector, the negative active material layer including a negative active material, the negative active material including a silicon-based material; the oil absorption value of the silicon-based material is denoted as M mL / 100g; the electrolyte includes a first additive, the first additive including compound X, the mass percentage of compound X based on the total mass of the electrolyte is denoted as A%; A and M satisfy: 2.5 × 10⁻⁶. ‑3 A value of ≤A / M≤0.17 can improve the furnace temperature safety performance of the battery.

Description

Technical Field

[0001] This invention relates to the technical field of lithium-ion batteries, and specifically to a lithium-ion battery. Background Technology

[0002] Silicon-doped anodes are considered a crucial direction for future battery technology development due to their high energy density, potential low cost, and broad application prospects. However, challenges remain, such as the stability of electrode materials, the maturity of fabrication processes, and the need for large-scale commercialization, to achieve widespread market application and commercial success. Currently, the most significant challenge is the volume expansion issue caused by silicon-doped anodes. Silicon undergoes significant volume changes during battery charging and discharging, making silicon-doped anode materials more prone to structural damage and material delamination during cycling. These issues may limit battery lifespan and reliability, especially under high power output or frequent charge-discharge conditions. Furthermore, silicon expansion during charging and use may lead to thermal runaway or even explosions, affecting furnace temperature safety. Furnace temperature safety remains a critical issue that needs to be addressed in the research and commercialization of silicon-doped anode lithium-ion batteries. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide a lithium-ion battery that improves the furnace temperature safety performance of the battery by adding compound X to the electrolyte and adjusting the ratio of the oil absorption value of the negative electrode silicon-based material to the content of compound X.

[0004] To achieve the above objectives, the present invention provides a lithium-ion battery, the battery comprising a positive electrode, a negative electrode, and an electrolyte;

[0005] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. The oil absorption value of the silicon-based material is denoted as M mL / 100g.

[0006] The electrolyte includes a first additive, which includes compound X. The mass percentage of compound X based on the total mass of the electrolyte is denoted as A%. The chemical formula of compound X is shown in Formula I.

[0007] Formula I: Among them, R1, R2, R3, and R4 independently include hydrogen atoms, substituted or unsubstituted alkane groups, substituted or unsubstituted alkene groups, substituted or unsubstituted aromatic groups, halogen substituents, and cyano groups; if substituted, the substituent is a halogen or a cyano group; n satisfies: 1≤n≤20;

[0008] A and M satisfy: 2.5 × 10-3 ≤A / M≤0.17.

[0009] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0010] The lithium-ion battery provided by this invention can improve the furnace temperature safety of the battery by adjusting the ratio of the oil absorption value of the silicon-based material to the content of compound X, when a specific relationship is satisfied.

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to those ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In this document, unless otherwise specified, data ranges include endpoints. Detailed Implementation

[0012] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0013] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0014] In this invention, the terms "battery", "lithium battery", "lithium-ion battery" and "lithium-ion secondary battery" all have the same meaning, referring to lithium-ion secondary batteries, which typically include electrode components (e.g., positive electrode, negative electrode and separator), a container (shell) housing the electrode components, and an electrolyte.

[0015] In this invention, the term "alkane group" refers to a group formed by the loss of one or more hydrogen atoms from an alkane molecule, wherein all carbon atoms in the molecule are linked by carbon-carbon single bonds. For example, it can be methyl (CH3-), ethyl (C2H5-), etc.

[0016] In this invention, the alkane group can be replaced by a halogen or a cyano group. When a hydrogen atom in the alkane group is replaced by a halogen, a haloalkane group is formed. For example, when a hydrogen atom of methyl (CH3-) is replaced by chlorine, chloromethyl (CH2Cl-) is formed. When a hydrogen atom in the alkane group is replaced by a cyano group, a cyanoalkane group is formed. For example, when a hydrogen atom of ethyl (C2H5-) is replaced by a cyano group, cyanoethyl (NCC2H4-) is formed.

[0017] In this invention, the term "olefinic group" refers to a group formed by the loss of one or more hydrogen atoms from an olefin molecule, which contains a carbon-carbon double bond in its structure. For example, it can be vinyl (CH2=CH-), etc.

[0018] In this invention, the olefin group can be replaced by a halogen or a cyano group. When a hydrogen atom in the olefin group is replaced by a halogen, a haloolefin group is formed. For example, when a hydrogen atom in a vinyl group (CH2=CH-) is replaced by chlorine, a chlorovinyl group (such as CH2=CCl-) is formed. When a hydrogen atom in the olefin group is replaced by a cyano group, a cyanoolefin group is formed. For example, when a hydrogen atom in a vinyl group is replaced by a cyano group, a cyanovinyl group (CH2=CHCN) is formed.

[0019] In this invention, the term "aromatic group" refers to a group obtained by substituting some hydrogen atoms on a phenyl group or a phenyl group. It can also be understood as a group formed after an aromatic hydrocarbon loses hydrogen atoms from the benzene ring. Examples include phenyl (Ph-), p-methylphenyl (-Ph-CH3), etc.

[0020] In this invention, the aromatic group can be substituted with a halogen or a cyano group. When a hydrogen atom on the aromatic group is substituted with a halogen, a haloaromatic group is formed. For example, when a hydrogen atom of a phenyl group (Ph-) is substituted with chlorine, a chlorophenyl group (-Ph-Cl) is formed. If the substitution occurs at the para-position of the methyl group, when a hydrogen atom of a methylphenyl group (-Ph-CH3) is substituted with chlorine, a chloromethylphenyl group (-Ph-CH3) is formed (where one hydrogen atom of Ph is substituted with Cl). When a hydrogen atom on the aromatic group is substituted with a cyano group, a cyanoaromatic group is formed. For example, when a hydrogen atom of a phenyl group is substituted with a cyano group, a phenylcyano group (Ph-CN) is formed. Similarly, if a hydrogen atom of a methylphenyl group (a hydrogen atom on a non-methyl group) is substituted with a cyano group, the corresponding cyano-p-methylphenyl group is formed.

[0021] In this invention, the term "halogen substituent" refers to the case where halogen atoms F, Cl, or Br are used as substituent groups.

[0022] In this invention, the term "cyano" refers to a substituent group containing a cyano group (-CN).

[0023] This invention provides a lithium-ion battery, the battery comprising a positive electrode, a negative electrode, and an electrolyte;

[0024] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. The oil absorption value of the silicon-based material is denoted as M mL / 100g.

[0025] The electrolyte includes compound X, and the mass percentage of compound X based on the total mass of the electrolyte is denoted as A%. The chemical formula of compound X is shown in Formula I.

[0026] Formula I: Among them, R1, R2, R3, and R4 independently include hydrogen atoms, substituted or unsubstituted alkane groups, substituted or unsubstituted alkene groups, substituted or unsubstituted aromatic groups, halogen substituents, and cyano groups; if substituted, the substituent is a halogen or a cyano group; n satisfies: 1≤n≤20;

[0027] A and M satisfy: 2.5 × 10 -3 ≤A / M≤0.17.

[0028] For example, n in chemical formula I can be an integer, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20.

[0029] This invention improves electrolyte wettability and increases battery electrolyte retention by adjusting the oil absorption value of the silicon-based negative electrode material. Compound X can form a film on the negative electrode. A suitable oil absorption value allows the silicon-based negative electrode material to be fully wetted by the electrolyte, increasing the contact area of ​​compound X on the negative electrode. During the formation of the SEI film, this allows for a stronger bond between the SEI film and the negative electrode, improving the structural stability of the SEI film. The oil absorption value of the silicon-based negative electrode material is synergistic with the mass percentage of compound X in the electrolyte. A higher oil absorption value helps compound X form a more stable and dense SEI film on the negative electrode, suppressing the expansion of the silicon-containing negative electrode, reducing polarization heat generation, and improving the thermal stability of the battery, thereby jointly improving the furnace temperature safety of the battery.

[0030] In this invention, the mass percentage A of compound X in the electrolyte and the oil absorption value M of the silicon-based material satisfy the following condition: 2.5 × 10⁻⁶. -3 The ratio ≤A / M≤0.17, where A / M can be, for example, 0.0025, 0.004, 0.006, 0.008, 0.01, 0.03, 0.05, 0.07, 0.1, 0.13, 0.15, 0.17, or any value within the range of any two of these values. This improves electrolyte wettability, allowing compound X to form a more stable SEI film at the negative electrode, mitigating negative electrode expansion, reducing polarization heat generation, and improving battery furnace temperature safety. Simultaneously, satisfying the above relationship between A and M avoids A / M>0.17, where the low oil absorption value of the silicon-based material results in insufficient electrolyte wettability at high temperatures or a low mass percentage of compound X in the electrolyte, preventing the formation of a stable and robust SEI film and leading to poor battery furnace temperature safety; it also avoids A / M<2.5×10⁻⁶. -3If the oil absorption value of silicon-based materials is too high, it will cause uneven distribution of negative electrode materials, resulting in uneven distribution of electrolyte, which will lead to unstable battery performance and affect the battery's cycle performance.

[0031] In some embodiments, the mass percentage A of compound X in the electrolyte and the oil absorption value M of the silicon-based material satisfy 5 × 10⁻⁶. -3 ≤A / M≤0.1;

[0032] In some embodiments, the oil absorption value M of the silicon-based material satisfies: 10≤M≤100. The oil absorption value of the silicon-based material can be, for example, 10mL / 100g, 20mL / 100g, 30mL / 100g, 40mL / 100g, 50mL / 100g, 60mL / 100g, 70mL / 100g, 80mL / 100g, 90mL / 100g, 100mL / 100g, or any value within the range of the above two values.

[0033] For example, the test method for oil absorption value M may include the following steps: weigh the clean beaker and glass rod and record the mass as m1, add 5g of composite material and record the total mass as m2, add dioctyl phthalate (DOP) dropwise with a titration bottle and stir thoroughly. Stop adding DOP when a clump is formed, weigh the total weight of the beaker at this time and record it as m3. Oil absorption value M = (m3-m2) / (m2-m1)×100.

[0034] In some embodiments, the mass percentage A% of compound X in the electrolyte satisfies: 0.1≤A≤5, for example, it can be any point value in the range of 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or any point value in the range of the above pairs; in one example, A satisfies: 0.5≤A≤2.

[0035] When the above range is met, silicon-based materials can better synergize with compound X in the electrolyte, providing good wettability to the electrolyte while promoting the formation of a more stable and robust SEI film of compound X on the negative electrode, inhibiting the expansion of the negative electrode, reducing polarization heat generation, and improving the furnace temperature safety of the battery.

[0036] In some embodiments, compound X represented by formula I includes at least one of the following compounds:

[0037]

[0038] Preferably, compound X is shown in Formula I-1.

[0039] Further selection of compound X as shown above results in stronger chemical bonding at the negative electrode, making the SEI film more robust. The fluoride layer formed by compound X can also further improve the strength of the SEI film, improve the performance of the interfacial film, better suppress the expansion of the battery negative electrode during charge and discharge cycles, thereby improving the battery cycle stability and improving the battery furnace temperature safety.

[0040] In some embodiments, the Dv50 of the silicon-based material is denoted as Cμm; the electrolyte includes a second additive, which includes a sulfur-containing additive; the mass percentage of the sulfur-containing additive based on the total mass of the electrolyte is denoted as B%; the sulfur-containing additive includes at least one of 1,3-propanesulfonyl lactone (PS), vinyl sulfate (DTD), and vinyl sulfite (ES); A, B, and C satisfy: 0.01 ≤ (A+B) / C ≤ 2, and the value of (A+B) / C can be, for example, 0.01, 0.02, 0.05, 0.1, 0.3, 0.5, 0.7, 1, 1.3, 1.5, 1.7, 2, or any value within the range of the above pairs of values. In the electrolyte, the combined use of sulfur-containing additives and compound X can form a more robust composite SEI film at the negative electrode. This effectively suppresses the volume expansion of the negative electrode during cycling, further improving the battery's furnace temperature safety. Furthermore, since compound X significantly affects the SEI film impedance, the addition of sulfur-containing additives reduces this impact, increasing the lithium-ion insertion / extraction rate and improving the battery's low-temperature performance. When the mass ratio of compound X and sulfur-containing additives in the electrolyte further satisfies the above relationship with the Dv50 of the silicon-based material, the particle size of the silicon-carbon material can provide a suitable specific surface area, further increasing the electrolyte wetting contact area and the number of reactive sites. This is beneficial for the film formation of sulfur-containing additives and compound X at the negative electrode, further reducing the interfacial impedance during battery charge and discharge, thereby further improving the battery's low-temperature cycling stability.

[0041] In some embodiments, the sulfur-containing additive is vinyl sulfate. When the sulfur-containing additive is vinyl sulfate, its combination with compound X can form a smoother and more uniform composite SEI film, resulting in higher density and stability of the SEI film, improved high-temperature resistance, and effective enhancement of battery furnace temperature safety. Simultaneously, the use of vinyl sulfate reduces the impedance of the SEI film, further improving the battery's low-temperature cycling performance.

[0042] The possible mechanism described above is that compound X may copolymerize with the functional groups of ethylene sulfate through its unsaturated bonds, forming a stable network structure. This strengthens the connections between SEI film layers, further stabilizing the structure of the composite SEI film and resulting in a smoother and more uniform SEI film. Simultaneously, the smooth and uniform composite SEI film provides smoother ion transport channels. Furthermore, the formation of sulfides and other components in the inorganic layer of the SEI film reduces lithium-ion transport impedance, improves electrode / electrolyte interface contact and electron transport performance, reduces polarization, and thus enhances the furnace temperature safety and low-temperature cycling performance of the battery.

[0043] In some implementations, A, B, and C satisfy: 0.2 ≤ (A+B) / C ≤ 1.5, where the value of (A+B) / C can be, for example, 0.2, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, or any value within the range of the above values. When A, B, and C further satisfy the above range, the furnace temperature safety of the battery can be further improved, and the low-temperature cycle performance of the battery can be enhanced.

[0044] In some implementations, the mass percentage B% of the sulfur-containing additive satisfies the following condition: 0.05 ≤ B ≤ 10. For example, it can be any value within the range of 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any of the values ​​in pairs mentioned above. In one example, B satisfies the condition: 1 ≤ B ≤ 5. Further satisfying the above range with the mass percentage of the sulfur-containing additive avoids B < 0.05, which would result in an uneven SEI film formation due to insufficient sulfur-containing additive, negatively impacting battery cycle life and thermal stability. It also avoids B > 10, which would lead to an excessively thick SEI film, resulting in excessive impedance in the lithium-ion battery and a decrease in low-temperature cycle performance.

[0045] In some embodiments, the Dv50(C) of the silicon-based material satisfies: 5≤C≤15, for example, it can be any point value in the range of 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm or the range of the above two points. In one example, the Dv50(C) of the silicon-based material satisfies: 6≤C≤10. When the Dv50 of silicon-based materials further meets the above range, it can avoid the situation where, when C>15μm, the particle size of silicon-based materials is too large, causing more drastic volume changes in silicon-carbon materials during charge and discharge. The SEI film formed by compound X and sulfur-containing additives cannot suppress the volume expansion of silicon-carbon particles, leading to repeated rupture and growth of the SEI film, and the increased thickness of the SEI film deteriorates low-temperature performance. It also avoids the situation where, when C<5μm, the particle size of silicon-based materials is too small, causing the electrolyte to not wet the electrode well. The SEI film formed by compound X and sulfur-containing additives on the negative electrode is not stable and firm enough. Under high-temperature conditions, the SEI film is more susceptible to stress damage, which may lead to larger volume changes in the negative electrode, affecting the structural stability of the battery and thus affecting the furnace temperature safety of the battery.

[0046] In some embodiments, the pore volume of the silicon-based material is 0.0001 cm. 3 / g-0.1cm 3 / g, for example, can be 0.0001cm 3 / g, 0.0005cm 3 / g, 0.001cm 3 / g, 0.005cm 3 / g, 0.01cm 3 / g, 0.02cm 3 / g, 0.03cm 3 / g, 0.04cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 / g, 0.09cm 3 / g, 0.1cm 3 / g or any value within the range formed by the pairwise values ​​mentioned above. Preferably, the pore volume of the silicon-based material is 0.0005 cm³. 3 / g-0.05cm 3 / g. When the pore volume of the silicon-based material further meets the above-mentioned range, a larger pore volume is more conducive to the wetting of the negative electrode by the electrolyte, thereby enabling compound X and sulfur-containing additives to form a film on the negative electrode better; and a larger pore structure can provide a better heat dissipation path, thereby helping to reduce the risk of battery overheating. At the same time, it can avoid the pore volume being too large, which would affect the film formation of compound X and sulfur-containing additives; and avoid the pore volume being too small, which may lead to poor heat dissipation of the negative electrode material. Under high power or high load conditions, the battery may generate too much heat, which cannot be effectively dissipated, increasing the risk of overheating and safety, and affecting the safety of the battery furnace temperature.

[0047] For example, the open-pore volume of silicon-based materials can be measured using a Tri Star II surface area analyzer. Specifically, the process may include the following steps: pulverizing the silicon-based material into powder, adding approximately 1g of sample to a sample tube, and weighing the sample and sample tube. Then, placing the sample tube in a degassing station for degassing treatment, and after degassing, weighing the sample tube to obtain the mass of the degassed sample. Then, using the surface area analyzer, inputting the sample mass data, and starting the instrument to measure the sample, the analyzer will automatically perform isothermal adsorption and desorption analysis, calculating the specific surface area and open-pore volume by measuring the amount of nitrogen adsorbed on the sample surface.

[0048] In some embodiments, the silicon content in the negative electrode active material is 1%-20%, for example, it can be 1%, 3%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or any value within the range of any two of the above values. In one example, the silicon-based material includes at least one of silicon-carbon, silicon-oxygen, elemental silicon, and silicon alloys; preferably, the silicon-based material includes silicon-carbon.

[0049] When the silicon content further meets the above range, it can further improve the cycle stability and lifespan of the battery. It avoids the situation where the silicon content is too high, resulting in a large volume change in the negative electrode, which causes the SEI film to be damaged and reconstructed, leading to continuous consumption of lithium ions, electrolyte decomposition, and lithium deposition, thus deteriorating the cycle performance of the battery. It also avoids the situation where the silicon content is too low, which would fail to meet the battery's capacity requirements.

[0050] For example, the method for testing the silicon content in this invention can be performed using thermogravimetric analysis, such as a Shimadzu DTG-60 thermogravimetric analyzer. The test conditions are: sample volume 5 mg, air atmosphere, heating rate 10 °C / min from room temperature to 900 °C and holding at that temperature for 40 min. The relationship between the silicon content (x) and the final weight residual percentage (y) of the entire test is: x = 7y / 15.

[0051] In some embodiments, the negative electrode current collector includes a polymer layer and a conductive layer located on at least one side of the polymer layer.

[0052] In some embodiments, the polymer in the polymer layer is selected from at least one of polyethylene, polypropylene (PP), ethylene-propylene copolymer, polyethylene terephthalate (PET), polyethylene terephthalate, and poly(p-phenylene terephthalamide). These polymers possess good insulation and chemical stability, preventing internal short circuits in the battery and improving its mechanical strength to some extent.

[0053] In some embodiments, the thickness of the polymer is 2.5 μm-15 μm, for example, it can be any value within the range of 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4 μm, 8, 10, 12, 15, or any value within the range of any pair of values ​​mentioned above. The polymer thickness satisfying the above range avoids excessively thick polymers, which can hinder ion transport, reduce battery charge / discharge performance, and increase the overall battery thickness, thus reducing battery energy density; conversely, excessively thin polymers can reduce battery mechanical strength and chemical stability, decrease battery cycle performance, and may even cause a short circuit.

[0054] In some embodiments, the conductive layer comprises one or both of copper or copper alloys.

[0055] For example, the conductive layer can be obtained by vapor deposition or electroplating, and the thickness of the conductive layer can be adjusted by changing the deposition time or electroplating time.

[0056] In some embodiments, the electrolyte further includes a third additive, which includes at least one selected from nitrile compounds, acid anhydrides, and fluoroethylene carbonate. In one example, the mass percentage of the third additive, based on the total mass of the electrolyte, is 0.1%-15%, for example, it can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any value within the range of any two of the above values. Nitrile compounds can improve the thermal and chemical stability of the electrolyte, thereby reducing the risk of thermal runaway during battery overcharging; acid anhydrides, as film-forming additives, can improve the formation of the SEI film and increase the conductivity of the electrolyte; fluoroethylene carbonate can reduce the internal resistance of the battery, improve the charge-discharge performance of the battery, and enhance the stability and uniformity of the SEI film. Further addition of a third additive to the electrolyte can further enhance the stability of the SEI film, improve the battery furnace temperature safety, enhance the battery cycle stability, and improve battery performance.

[0057] In some embodiments, the electrolyte further comprises an organic solvent and an electrolyte lithium salt.

[0058] In some embodiments, the organic solvent comprises carbonates and / or carboxylic acid esters.

[0059] In some embodiments, the organic solvent comprises at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl butyrate (EB), and γ-butyrolactone (GBL).

[0060] In some embodiments, the electrolyte lithium salt includes at least one selected from lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalate) phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0061] In some embodiments, the mass content of the electrolyte lithium salt is 10%-15% based on the total mass of the electrolyte, for example, it can be 10%, 11%, 12%, 13%, 14% or 15%.

[0062] In some embodiments, the negative electrode active material further comprises a carbon-based material.

[0063] In some embodiments, the carbon-based material includes at least one of natural graphite, artificial graphite, mesophase carbon microspheres, soft carbon, hard carbon, and graphene.

[0064] In some embodiments, the negative electrode active material layer further comprises a negative electrode conductive agent and a negative electrode binder.

[0065] In some embodiments, the negative electrode active material layer comprises, by mass percentage, 80%-99.8% negative electrode active material, 0.1%-10% negative electrode conductive agent, and 0.1%-10% negative electrode binder.

[0066] In one embodiment, the negative electrode conductive agent comprises at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0067] In one embodiment, the negative electrode binder comprises at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0068] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer coated on one or both surfaces of the positive current collector, the positive active material layer including a positive active material.

[0069] In some embodiments, the positive electrode active material includes LiNi. x Co y Mn z M 1-x-y-z O2 or LiLPO4, wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, 0≤x+y+z≤1, M includes at least one of Mn and Al, M includes at least one of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Sc, Ti, Nb, Mo, Zr, Ta, W, B, F, Si, and L includes at least one of Mn, Fe, Co.

[0070] In some embodiments, the positive electrode active material layer further comprises a positive electrode conductive agent and a positive electrode binder.

[0071] In some embodiments, the positive electrode active material layer comprises, by mass percentage, 80%-99.8% positive electrode active material, 0.1%-10% positive electrode conductive agent, and 0.1%-10% positive electrode binder.

[0072] In some embodiments, the positive electrode conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and metal powder.

[0073] In some embodiments, the positive electrode binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0074] In some implementations, the positive current collector can be a positive current collector conventionally used in the art, such as aluminum foil or a composite current collector.

[0075] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0076] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0077] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0078] Example 1-1

[0079] 1) Preparation of positive electrode sheet

[0080] Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), super P (SP), and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of an aluminum foil. The coated aluminum foil was dried, and then rolled and slit to obtain the desired positive electrode sheet.

[0081] 2) Preparation of negative electrode sheet

[0082] The negative electrode active material, artificial graphite, was mixed with SiC, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) in a mass ratio of 94.5:2.5:1.5:1:0.5. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a negative electrode active slurry. The negative electrode active slurry was uniformly coated on both surfaces of a composite current collector (the polymer coating included ethylene propylene copolymer, and the conductive layers on both sides were copper foil). The coated composite current collector was dried at room temperature, then transferred to an 80°C oven for drying for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained.

[0083] 3) Preparation of electrolyte

[0084] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC, PC, DEC, and PP were mixed evenly in a mass ratio of 10:20:40:30. Then, fully dried lithium hexafluorophosphate (LiPF6) at a concentration of 1 mol / L was quickly added to dissolve it. After dissolving, compound X was added (the specific dosage is shown in Table 1). The mixture was stirred evenly, and after passing the tests for moisture and free acid, the desired electrolyte was obtained.

[0085] 4) The diaphragm was purchased from Asahi Kasei.

[0086] 5) Battery manufacturing

[0087] The positive electrode sheet from step 1), the negative electrode sheet from step 2), and the separator are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and the electrolyte from step 3) is injected into the outer packaging. After vacuum sealing, settling, formation, shaping, and sorting, a battery is obtained. The battery of this invention has a charge / discharge range of 3.0V-4.5V.

[0088] Performance testing:

[0089] i) 45℃ Cyclic Performance Test

[0090] The batteries obtained in the examples and comparative examples were subjected to charge-discharge cycles at 45°C at a rate of 1C within the charge-discharge cutoff voltage range. The discharge capacity of the first cycle was measured as x1 mAh, and the discharge capacity of the Nth cycle was measured as y1 mAh. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R1 = y1 / x1. The number of cycles when the cycle capacity retention rate R1 was 80% was recorded.

[0091] ii) Low-temperature discharge capacity retention test

[0092] The batteries obtained in the examples and comparative examples were subjected to 5 charge-discharge cycles at -20°C at a 1C rate, and then charged to 4.5V at a 1C rate. The 1C capacity Q0 was recorded. The fully charged batteries were then left at -20°C for 4 hours, and then discharged to 3V at a 0.2C rate. The discharge capacity Q1 was recorded. The low-temperature discharge capacity retention rate was calculated as follows: Low-temperature discharge capacity retention rate (%) = Q1 / Q0 × 100%

[0093] iii) Furnace temperature safety test

[0094] The examples and comparative examples were repeated 10 times. The fully charged batteries of each example and comparative example were placed at 130°C for 1 hour, and the number of batteries that did not catch fire or explode was observed.

[0095] Examples 1-2 and Comparative Examples 1-4 were performed in accordance with Example 1-1, with the main differences shown in Table 1. Specifically, in Example 1, the mass percentage (A) of compound X in the electrolyte was changed. In Example 2, the oil absorption value (M) of the silicon-based material was changed. In Comparative Example 1, compound X was not added to the electrolyte. In Comparative Example 2, the A / M ratio did not meet the required range. In Comparative Example 3, the mass percentage of compound X was too small. In Comparative Example 4, the mass percentage of compound X was too large.

[0096] Table 1

[0097]

[0098]

[0099] Note: In Table 1, " / " indicates that the corresponding data was not measured.

[0100] As shown in Table 1, the lithium-ion battery provided by the present invention can improve the furnace temperature safety of the battery by adjusting the ratio of the oil absorption value of the silicon-based material to the content of compound X, and the ratio of the content of compound X to the oil absorption value of the silicon-based material.

[0101] Example 3 was carried out in accordance with Examples 1-1, with the main differences shown in Table 2. In Example 3, the type of compound X was changed.

[0102] Table 2

[0103] Compound X type Furnace temperature pass rate Example 1-1 Formula I-1 10 / 10 Example 3-1 Formula I-3 8 / 10 Example 3-2 Formula I-4 8 / 10 Example 3-3 Equations I-1 and I-3; their ratio is 1:1 8 / 10

[0104] As shown in Table 2, changing the type of compound X in this invention can improve the safety of the battery furnace temperature. When compound X shown in Formula I-1 is used, the furnace temperature safety performance of the battery can be improved even better.

[0105] Example 4 was performed in accordance with Examples 1-1, with the main differences shown in Table 3. In Example 4, the pore volume of the silicon-based material was changed.

[0106] Table 3

[0107]

[0108]

[0109] As shown in Table 3, by controlling the opening volume of the silicon-based material within a suitable range, the present invention can help improve the heat dissipation and thermal conductivity of the silicon-based material and improve the safety of the battery furnace temperature.

[0110] Examples 5-8 were performed following Examples 1-1, with the addition of sulfur-containing additives to the electrolyte. The main differences are shown in Table 4. Specifically, Example 5 changed the mass percentage (B) of the sulfur-containing additive in the electrolyte. Example 6 changed the Dv50 (C) of the silicon-based material. In Example 7, the value of (A+B) / C was not within the protection range. In Example 8, conventional copper foil was used as the negative electrode current collector.

[0111] Table 4

[0112]

[0113] As shown in Table 4, by adding sulfur-containing additives to the electrolyte and controlling the ratio of the mass percentage of compound X and the mass percentage of sulfur-containing additives in the electrolyte to the silicon-based material Dv50, the present invention can improve the battery furnace temperature safety performance, enhance the high-temperature cycle performance of the battery, and also take into account the low-temperature performance of the battery.

[0114] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte; The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. The oil absorption value of the silicon-based material is denoted as M mL / 100g. The electrolyte includes a first additive, which includes compound X. The mass percentage of compound X based on the total mass of the electrolyte is denoted as A%. The chemical formula of compound X is shown in Formula I. Formula I: Among them, R1, R2, R3, and R4 independently include hydrogen atoms, substituted or unsubstituted alkane groups, substituted or unsubstituted alkene groups, substituted or unsubstituted aromatic groups, halogen substituents, and cyano groups; if substituted, the substituent is a halogen or a cyano group; n satisfies: 1≤n≤20; A and M satisfy: 2.5 × 10 -3 ≤A / M≤0.

17.

2. The lithium-ion battery according to claim 1, characterized in that, A and M satisfy: 5 × 10 -3 ≤A / M≤0.1; And / or, M satisfies: 10 ≤ M ≤ 100; And / or, A satisfies: 0.1≤A≤5.

3. The lithium-ion battery according to claim 1, characterized in that, A satisfies 0.5≤A≤2.

4. The lithium-ion battery according to claim 1, characterized in that, Compound X represented by Formula I includes at least one of the following compounds: (I-1)、 (I-2)、 (I-3)、 (I-4)、 (I-5)、 (I-6)、 (I-7) 。 5. The lithium-ion battery according to claim 1, characterized in that, The Dv50 of the silicon-based material is denoted as C μm; The electrolyte includes a second additive, which includes a sulfur-containing additive; the mass percentage of the sulfur-containing additive based on the total mass of the electrolyte is denoted as B%. A, B, and C satisfy: 0.01 ≤ (A+B) / C ≤ 2.

6. The lithium-ion battery according to claim 5, characterized in that, The sulfur-containing additive includes at least one of 1,3-propanesulfonyl lactone, vinyl sulfate, and vinyl sulfite.

7. The lithium-ion battery according to claim 5, characterized in that, A, B, and C satisfy: 0.2 ≤ (A+B) / C ≤ 1.5; And / or, B satisfies: 0.05 ≤ B ≤ 10; And / or, C satisfies: 5≤C≤15.

8. The lithium-ion battery according to claim 5, characterized in that, B satisfies: 1≤B≤5.

9. The lithium-ion battery according to claim 1, characterized in that, The pore volume of the silicon-based material is 0.0001 cm. 3 / g-0.1 cm 3 / g.

10. The lithium-ion battery according to claim 1, characterized in that, The pore volume of the silicon-based material is 0.0005 cm. 3 / g-0.05 cm 3 / g.

11. The lithium-ion battery according to claim 1, characterized in that, The negative electrode current collector includes a polymer layer and a conductive layer located on at least one side of the polymer layer.

12. The lithium-ion battery according to claim 11, characterized in that, The polymer in the polymer layer is selected from at least one of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, and poly(p-phenylene terephthalamide).

13. The lithium-ion battery according to claim 11, characterized in that, The thickness of the polymer layer is 2.5 μm-15 μm.

14. The lithium-ion battery according to claim 1, characterized in that, The mass percentage of silicon in the negative electrode active material is 1%-20%; And / or, the silicon-based material includes at least one of silicon-carbon, silicon-oxygen, elemental silicon, and silicon alloy.

15. The lithium-ion battery according to claim 13, characterized in that, The silicon-based material includes silicon-carbon.

16. The lithium-ion battery according to any one of claims 1-15, characterized in that, The electrolyte also includes a third additive, which includes at least one of nitrile compounds, acid anhydride compounds, and fluoroethylene carbonate.

17. The lithium-ion battery according to claim 1, characterized in that, The third additive accounts for 0.1%-15% of the total mass of the electrolyte.

Images