Lithium ion secondary battery

Abstract

The invention relates to the technical field of batteries, in particular to a lithium ion secondary battery. Comprising a positive plate, a negative plate and electrolyte, the positive plate comprises a positive active material, and the positive active material comprises a ternary nickel-cobalt-manganese material and lithium cobalt oxide; in the positive electrode active material, the mass content w1 of the Ni element is 1%-20%; the negative plate comprises a silicon-based material; the electrolyte comprises a fluorosulfonamide compound and a first additive, and the first additive comprises fluorobenzene and / or acetic acid 2, 2-difluoroethyl ester; on the basis of the total mass of the electrolyte, the content c1 of the fluorosulfonamide compound is 1-20%; the content c2 of the first additive is 2.5%-20%; and c1 and c2 satisfy the following relation: 0.1 < = c1 / c2 < = 5.5. The lithium ion secondary battery provided by the invention has excellent cycle performance, high-temperature storage performance, low-temperature performance and safety performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium-ion secondary battery. Background Art

[0002] With the rapid development of lithium-ion battery technology, the demand for battery life is increasing. Pursuing higher energy density is a key development direction for the battery industry. The most common approach is to replace graphite with silicon-based materials with higher theoretical capacity. However, upon lithiation, silicon-based materials form lithium-silicon alloys, leading to electrolyte depletion and loss of active lithium, resulting in poor battery cycling performance and poor high-temperature storage performance.

[0003] Therefore, it is very important to invent a silicon-doped lithium-ion battery with excellent cycle performance and high-temperature storage performance. Summary of the Invention

[0004] The present invention aims to overcome the aforementioned problems existing in the prior art and provides a lithium-ion secondary battery. The lithium-ion secondary battery of the present invention (hereinafter referred to as the battery) has highly compatible positive and negative electrodes, and an electrolyte, ensuring good cycle performance and high-temperature storage performance while also exhibiting excellent low-temperature performance and safety.

[0005] In related technologies, lithium-silicon alloys are formed after lithiation of silicon-based materials, leading to electrolyte consumption and loss of active lithium, resulting in poor battery cycling performance and poor high-temperature storage performance. Fluorosulfonamide compounds can reduce the attack of the active lithium-silicon alloys generated by lithium-intercalated silicon-based materials on the electrolyte solvent, improving the battery's cycle life. They can also alleviate the problem of gassing at high temperatures.

[0006] However, in a ternary nickel-cobalt-manganese system, when the electrolyte contains a fluorosulfonamide compound, the low-temperature performance of the battery will be significantly reduced. The inventors have conducted a lot of research and found that the reason for the above problems may be that the fluorinated group in the fluorosulfonamide compound has low surface energy characteristics. Introducing it into the ternary nickel-cobalt-manganese system will change the surface hydrophilicity of the ternary nickel-cobalt-manganese material, making the surface of the material hydrophobic, resulting in the electrolyte's wettability to the ternary nickel-cobalt-manganese material becoming poor, thereby affecting the transmission efficiency of lithium ions on the surface of the ternary nickel-cobalt-manganese material. Especially under low temperature conditions, the viscosity of the electrolyte itself will increase, and the presence of the fluorosulfonamide compound further aggravates the resistance to lithium ion transmission, resulting in a significant decrease in the rate performance and low-temperature performance of the battery. Based on the above findings, the inventors of the present invention added a first additive to the electrolyte, whose fluorine atoms have high electronegativity, can enhance the stability and antioxidant properties of the molecule, effectively inhibit the oxidative decomposition of the electrolyte under high voltage, reduce solvent side reactions, and ensure the relative stability of the electrolyte system. At the same time, the intermolecular interactions of the first additive are relatively weak, reducing the intermolecular forces of the entire electrolyte system, thereby effectively reducing the viscosity of the electrolyte and improving the wettability of the electrolyte. However, if the first additive is added too much to the electrolyte, it will affect the solubility of the lithium salt, resulting in a decrease in lithium ion conductivity, which in turn affects the low-temperature discharge performance of the battery.

[0007] Therefore, if only the first additive is introduced, the cycle performance and low-temperature performance of the battery will not be significantly improved. The inventors of the present invention have conducted a lot of targeted research and found that by further regulating the content of the first additive and the fluorosulfonamide compound in the electrolyte, the safety performance, cycle performance, high-temperature storage performance and low-temperature performance of the battery can be significantly improved. If the content of the fluorosulfonamide compound is too high, the surface of the ternary nickel-cobalt-manganese material will become hydrophobic, and the wettability of the electrolyte to the ternary nickel-cobalt-manganese material will deteriorate, affecting the transmission efficiency of lithium ions, further exacerbating the resistance to lithium ion transmission, and thus causing the rate performance and low-temperature performance of the battery to decrease significantly. If the content of the first additive is too high, side reactions are likely to occur, generating gas byproducts, causing the battery to swell, and affecting the cycle stability and high-temperature storage performance of the battery. Therefore, when the content of the first additive and the fluorosulfonamide compound is regulated to reach an optimal balance, the resulting synergistic effect can enable the battery to have good safety performance, excellent cycle performance, high-temperature storage performance and low-temperature performance.

[0008] Based on this, the technical solution adopted in the present invention is as follows:

[0009] The present invention provides a lithium-ion secondary battery, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte; the positive electrode sheet comprises a positive electrode active layer, the positive electrode active layer comprises a positive electrode active material, the positive electrode active material comprises a ternary nickel-cobalt-manganese material and lithium cobalt oxide; the mass content w1 of the Ni element in the positive electrode active material is 1%-20%;

[0010] The negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material;

[0011] The electrolyte includes a fluorosulfonamide compound, and the fluorosulfonamide compound includes at least one of the substances represented by Formula I:

[0012]

[0013] wherein R1 and R2 each independently include at least one of the following groups which are substituted or unsubstituted with fluorine: a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, a C1-C6 cyano group, a phenyl group, a silane group, and a sulfone group;

[0014] The electrolyte further includes a first additive, wherein the first additive includes fluorobenzene and / or 2,2-difluoroethyl acetate;

[0015] Based on the total mass of the electrolyte, the content c1 of the fluorosulfonamide compound is 1%-20%; the content c2 of the first additive is 2.5%-20%; c1 and c2 satisfy: 0.1≤c1 / c2≤5.5.

[0016] Through the above technical solution, the present invention has at least the following advantages compared with the prior art: the battery of the present invention has good cycle performance, high temperature storage performance, low temperature performance and safety performance.

[0017] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. DETAILED DESCRIPTION

[0018] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0019] The present invention provides a lithium-ion secondary battery, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte; the positive electrode sheet comprises a positive electrode active layer, the positive electrode active layer comprises a positive electrode active material, and the positive electrode active material comprises a ternary nickel-cobalt-manganese material and lithium cobalt oxide; in the positive electrode active material, the mass content w1 of the Ni element is 1%-20%, for example, 1%, 3%, 5%, 7%, 9%, 11%, 13%, 15%, 18%, or 20%.

[0020] In one example, w1 is 10%-17%.

[0021] In the present invention, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material.

[0022] In the present invention, the electrolyte includes a fluorosulfonamide compound, and the fluorosulfonamide compound includes at least one of the substances represented by Formula I:

[0023]

[0024] wherein R1 and R2 each independently include at least one of the following fluorine-substituted or unsubstituted groups: C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C1-C6 cyano, phenyl, silyl, and sulfone, for example, C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C2 alkenyl, C3 alkenyl, C4 alkenyl, C5 alkenyl, C6 alkenyl, C2 alkynyl, C3 alkynyl, C4 alkynyl, C5 alkynyl, C6 alkynyl, C1 cyano, C2 cyano, C3 cyano, C4 cyano, C5 cyano, C6 cyano, phenyl, silyl, or sulfone.

[0025] In the present invention, the term "C1-C6 alkyl" refers to an alkyl group having 1 to 6 carbon atoms. "C2-C6 alkenyl" refers to an alkenyl group having 2 to 6 carbon atoms, and so on.

[0026] In one embodiment, the fluorosulfonamide compound includes

[0027]

[0028] At least one of .

[0029] In one embodiment, the fluorosulfonamide compound includes

[0030] In the present invention, the electrolyte further includes a first additive, which includes fluorobenzene and / or 2,2-difluoroethyl acetate; based on the total mass of the electrolyte, the content c1 of the fluorosulfonamide compound is 1%-20%, for example, 1%, 4%, 7%, 10%, 13%, 16% or 20%; the content c2 of the first additive is 2.5%-20%, for example, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%; c1 and c2 satisfy: 0.1≤c1 / c2≤5.5, for example, 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or 5.5.

[0031] In one example, c1 is 3%-15%.

[0032] In one example, c2 is 5%-14%.

[0033] In one example, 0.4≤c1 / c2≤2.5.

[0034] In one example, the first additive includes

[0035] At least one of .

[0036] In one example, the first additive includes At least one of .

[0037] In the present invention, the ternary nickel-cobalt-manganese material includes LiNi 0.6 Co 0.1 Mn 0.3 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.68 Co 0.09 Mn 0.23 O2、LiNi 0.7 Co 0.1 Mn 0.2 O2、LiNi 0.63 Co 0.09 Mn 0.28 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.55 Co 0.15 Mn 0.3 O2 and LiNi0.65 Co 0.15 Mn 0.2 At least one of O2.

[0038] Ternary nickel-cobalt-manganese materials have a high specific capacity and can increase the battery's energy density. However, when the nickel content in the ternary nickel-cobalt-manganese material is too high, its volume changes significantly during charge and discharge, which can easily lead to cracking of the electrode material and electrolyte penetration, accelerating battery capacity decay. The addition of lithium cobalt oxide, through its stable layered structure, can buffer the volume changes of the ternary nickel-cobalt-manganese material, reduce the risk of material cracking, and extend the battery's cycle life.

[0039] In the present invention, the mass content w1 of the Ni element in the positive electrode active material can be measured by conventional methods in the art, for example, by inductively coupled plasma (ICP) testing.

[0040] In the present invention, the content c1 of the fluorosulfonamide compound and the content c2 of the first additive can be obtained by conventional methods in the art, such as gas chromatography (GC), gas chromatography-mass spectrometry (GCMS) or liquid chromatography (LC).

[0041] In the present invention, the positive electrode active layer further comprises lithium titanium aluminum phosphate.

[0042] In one example, based on the total weight of the positive electrode active layer, the content of the lithium aluminum titanium phosphate is ≤5%, for example, 5%, 2%, 1.8%, 1.6%, 1.4%, 1.2%, 1%, 0.8%, 0.5% or 0.2%.

[0043] In one embodiment, based on the total weight of the positive electrode active layer, the content of the lithium aluminum titanium phosphate is 0.2%-3%.

[0044] In the present invention, based on the total weight of the positive electrode active layer, the content of the lithium titanium aluminum phosphate can be tested by conventional methods in the field, for example, discharging the battery to 0% SOC, disassembling and removing the positive electrode sheet, soaking and cleaning the residual electrolyte with DMC, scraping out the positive electrode powder, and testing using TGA thermal gravimetric method (nitrogen atmosphere). The peak of thermal gravimetric loss above 800°C is the weight loss peak of lithium titanium aluminum phosphate, and the weight loss ratio is about 5%. According to this weight loss ratio, the content of lithium titanium aluminum phosphate in the positive electrode active layer can be calculated.

[0045] In the present invention, the lithium-ion secondary battery further includes a separator, and the separator includes lithium titanium aluminum phosphate.

[0046] In one example, the average pore size D1 of the membrane is 20 nm-60 nm, for example, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm or 60 nm.

[0047] In one example, the average particle size D2 of the lithium aluminum titanium phosphate is 0.05 μm-4 μm, for example, 0.05 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm or 4 μm.

[0048] In one example, D2 is 0.1 μm-3 μm.

[0049] In one example, the diaphragm further includes a substrate, a ceramic layer, and a glue layer.

[0050] In one example, the substrate includes lithium aluminum titanium phosphate.

[0051] In one example, the ceramic layer includes lithium titanium aluminum phosphate.

[0052] In one embodiment, the glue layer includes lithium titanium aluminum phosphate.

[0053] In one example, the substrate and the ceramic layer include lithium titanium aluminum phosphate.

[0054] In one embodiment, the ceramic layer and the adhesive layer include lithium titanium aluminum phosphate.

[0055] In one example, based on the total weight of the separator, the content of the lithium aluminum titanium phosphate is 2%-30%, for example, 2%, 5%, 10%, 15%, 20%, 25% or 30%.

[0056] In one example, based on the total weight of the separator, the content of the lithium aluminum titanium phosphate is 10%-25%.

[0057] In the present invention, based on the total weight of the diaphragm, the content of the lithium titanium aluminum phosphate can be tested by conventional methods in the field, for example, by discharging the battery to 0% SOC, disassembling and removing the diaphragm, cleaning the diaphragm with DMC to remove the residual electrolyte, and testing the obtained diaphragm by TGA thermal gravimetric method (nitrogen atmosphere). The peak of thermal gravimetric loss above 800°C is the weight loss peak of lithium titanium aluminum phosphate, and the weight loss ratio is about 5%. The content of LATP in the diaphragm is calculated based on the weight loss ratio.

[0058] Lithium titanium aluminum phosphate has high ionic conductivity and can effectively conduct lithium ions. When lithium titanium aluminum phosphate is doped in the positive electrode active layer, an efficient ion transfer interface can be formed between the positive electrode active layer and the electrolyte, making it easier for lithium ions to escape from the positive electrode and enter the electrolyte, thereby improving the conductivity of lithium ions. Similarly, if lithium titanium aluminum phosphate is coated on the diaphragm, lithium titanium aluminum phosphate can interact with the porous structure of the diaphragm. Lithium titanium aluminum phosphate can fill part of the pores of the diaphragm to form a more continuous and stable ion conduction network. When lithium ions pass through the diaphragm, they can migrate more quickly to the negative electrode, thereby improving the ion transfer efficiency inside the battery. Moreover, the ion conduction characteristics of lithium titanium aluminum phosphate are relatively less affected by temperature. Therefore, whether it is doped in the positive electrode active layer or coated on the surface of the diaphragm, it can improve the lithium ion conduction rate and alleviate the limitation of low temperature on lithium ion conduction to a certain extent, thereby improving the low temperature performance of the battery.

[0059] In the present invention, the average pore size D1 of the diaphragm can be measured by conventional methods in the art, such as using a pore size tester to select at least 20 holes on the diaphragm, measuring the diameter of each hole, and taking the average value; the average particle size D2 of the lithium aluminum titanium phosphate can be measured by conventional methods in the art, such as direct observation by scanning electron microscopy (SEM), selecting at least 20 lithium aluminum titanium phosphate particles in the electron microscope image, measuring the diameter of each particle, and taking the average value. If the pores of the lithium aluminum titanium phosphate particles / diaphragm are regular circles, the diameter of the regular circles is the diameter of the pores of the lithium aluminum titanium phosphate particles / diaphragm; if the pores of the lithium aluminum titanium phosphate particles / diaphragm are non-"regular circles" (such as ellipses, irregular curved polygons, etc.), the diameter of the regular circles with the same area as the non-"regular circles" is the diameter of the pores of the lithium aluminum titanium phosphate particles / diaphragm.

[0060] In the present invention, the electrolyte further includes a nitrile compound, the nitrile compound includes a first nitrile compound and a second nitrile compound, the first nitrile compound includes at least one of the substances represented by Formula II and Formula III, and the second nitrile compound includes at least one of the substances represented by Formula IV:

[0061]

[0062] Wherein, R3, R4 and R5 each independently include substituted or unsubstituted C1-C6 alkyl groups, such as C1 alkyl groups, C2 alkyl groups, C3 alkyl groups, C4 alkyl groups, C5 alkyl groups or C6 alkyl groups; the substituted substituents include halogen.

[0063]

[0064] Wherein, R6, R7 and R8 each independently include substituted or unsubstituted C1-C6 alkyl groups, such as C1 alkyl groups, C2 alkyl groups, C3 alkyl groups, C4 alkyl groups, C5 alkyl groups or C6 alkyl groups; the substituted substituents include halogen.

[0065]

[0066] Wherein, m is selected from an integer of 2-4 (for example, 2, 3 or 4), and R9 includes At least one of R 10 and R 11 Each independently includes a C1-C3 alkyl group, for example, a C1 alkyl group, a C2 alkyl group or a C3 alkyl group.

[0067] In one example, the first nitrile compound includes At least one of .

[0068] In one example, the first nitrile compound includes and / or

[0069] In one example, the second nitrile compound includes At least one of .

[0070] In one example, the second nitrile compound includes and / or

[0071] In the present invention, based on the total mass of the electrolyte, the content c3 of the first nitrile compound is 0.01%-3%, for example, 0.01%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5% or 3%.

[0072] In one example, c3 is 0.1%-2.5%.

[0073] In the present invention, based on the total mass of the electrolyte, the content c4 of the second nitrile compound is 0.01%-3%, for example, 0.01%, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5% or 3%.

[0074] In one embodiment, c4 is 0.1%-2.5%.

[0075] In one example, c1, c3, and c4 satisfy: 0.1≤(c3+c4) / c1≤4, for example, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, or 4.

[0076] In one example, 0.2≤(c3+c4) / c1≤1.

[0077] When the contents of fluorosulfonamide compounds and nitrile compounds meet a specific relationship, the high-temperature cycle performance of the battery can be further improved while ensuring good low-temperature performance, and the high-temperature gassing of the battery can be suppressed. Among them, nitrile compounds contain cyano groups, which can provide more complexing sites and can form stable complexes with transition metal ions, effectively preventing the free migration and aggregation of transition metal ions in the electrolyte. At the same time, some nitrile compounds can also form a stable and uniform solid electrolyte interface film on the surface of the negative electrode, reducing the enrichment of transition metal ions at the negative end, avoiding the decomposition reaction of the electrolyte catalyzed by transition metal ions, thereby reducing the occurrence of side reactions in the electrolyte and improving the high-temperature cycle performance of the battery. The fluorosulfonamide compound has a high oxidation potential and can also form a stable interface film at the negative end, further preventing the occurrence of side reactions in the electrolyte, suppressing the problem of battery gassing at high temperatures, and improving the high-temperature cycle performance of the battery.

[0078] In the present invention, the content c3 of the first nitrile compound and the content c4 of the second nitrile compound can be obtained by conventional methods in the art, such as GC, GCMS or liquid chromatography (LC).

[0079] In the present invention, the average particle size of the silicon-based material is 2 μm-20 μm, for example, 2 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm or 20 μm.

[0080] In one example, the average particle size of the silicon-based material is 5 μm-15 μm.

[0081] In the present invention, the silicon-based material includes at least one of elemental silicon, silicon carbon, silicon oxygen and silicon alloy.

[0082] In one example, the silicon-based material includes silicon carbon.

[0083] In one example, the silicon carbon includes a porous carbon matrix and silicon particles located in pores of the porous carbon matrix.

[0084] Further research found that in the ternary nickel-cobalt-manganese system, when at high potential, Mn 3+ A disproportionation reaction will occur, and the generated Mn 2+Combining with the sulfur groups in fluorosulfonamide compounds will form byproducts, which in turn will destroy the conductivity of the solid electrolyte interface (CEI) film, hinder the migration of lithium ions, and affect the battery's rate performance and low-temperature performance. In addition, the formation of byproducts can cause battery inflation, increasing internal pressure and affecting the battery's structural integrity and safety.

[0085] The smaller average particle size of silicon-based materials can shorten the diffusion path of lithium ions in the material, accelerating the diffusion rate of lithium ions, thereby improving the battery's rate performance. Especially in low-temperature environments, the conductivity of the electrolyte decreases, slowing the migration of lithium ions in the electrolyte. Reducing the particle size of silicon-based materials can reduce the diffusion distance of lithium ions in the electrode material, making it easier for lithium ions to quickly embed and detach from the silicon-based material at low temperatures, further improving the battery's low-temperature performance.

[0086] In the present invention, the average particle size of the silicon-based material can be measured using conventional methods in the art. For example, the battery is discharged to 0% SOC, the negative electrode sheet is disassembled, and the cross-section of the negative electrode sheet is polished using an argon ion milling apparatus. At least 20 silicon-based material particles are selected from a SEM image, and the particle size of each particle is measured to obtain the average value. If the silicon-based material particles appear as regular circles in the image, the particle size is the diameter of the circle. If the silicon-based material particles appear as irregular circles in the image, the particle size is the diameter of an equivalent circle with the same area as the regular circle.

[0087] In the present invention, the electrolyte further includes a second additive, and the second additive includes at least one of ethylene sulfate and lithium difluorophosphate.

[0088] In one example, based on the total mass of the electrolyte, the content c5 of the second additive is 0.01%-2.5%, for example, 0.01%, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2% or 2.5%.

[0089] In one example, c5 is 0.5%-1%.

[0090] When the electrolyte contains a second additive, it can promote the optimization and improvement of the solid electrolyte interface film, allowing lithium ions to be evenly embedded and extracted on the electrode surface, avoiding problems such as electrode structure damage and material phase change caused by excessively high or low local lithium ion concentrations. The battery can maintain a high reversible capacity and good cycle performance, thereby effectively improving the battery's cycle stability and extending the battery's service life. Among them, ethylene sulfate can form a solid electrolyte interface film containing sulfur-containing polymeric organic matter and sulfur-containing inorganic matter on the surface of the negative electrode during the battery's charge and discharge process, reducing the contact between the negative electrode and the electrolyte, reducing the negative electrode impedance, and increasing the lithium ion transmission rate. Lithium difluorophosphate can participate in the formation process of the solid electrolyte interface film on the positive electrode surface and can protect the ternary nickel-cobalt-manganese material.

[0091] In the present invention, the ethylene sulfate can be obtained by testing by conventional methods in the art, such as by GC, GCMS or LC testing; the lithium difluorophosphate can be obtained by testing by conventional methods in the art, such as by ion chromatography (IC) testing.

[0092] In the present invention, the silicon content w2 in the negative electrode active layer is 1.5%-50%, for example, 1.5%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%.

[0093] In one example, w2 is 3%-30%.

[0094] In the present invention, the electrolyte also includes fluoroethylene carbonate. Based on the total mass of the electrolyte, the content c6 of the fluoroethylene carbonate is 5%-30%, for example, 5%, 8%, 11%, 14%, 17%, 20%, 23%, 26% or 30%.

[0095] In one example, c6 is 10%-25%.

[0096] When the silicon content in silicon-based materials is high, a large volume expansion will occur, causing internal stress accumulation, leading to structural cracking and peeling, and it will be impossible to form a stable SEI film on its surface, resulting in reduced battery charge and discharge efficiency. When the electrolyte contains fluoroethylene carbonate, a lithium fluoride-rich SEI film can be formed on the surface of the negative electrode, which can effectively reduce the occurrence of electrolyte side reactions on the negative electrode surface. During the charge and discharge process, the battery needs to undergo multiple charge and discharge cycles. As the number of cycles increases, the SEI film will continue to repair and adjust, and fluoroethylene carbonate will continue to react and consume on the electrode surface, especially in high temperature environments or high-rate charge and discharge conditions. The electrochemical reaction on the electrode surface will be more intense, and the consumption rate of fluoroethylene carbonate will be further accelerated. However, if it is in an electrolyte containing fluorosulfonamide compounds, since the fluorosulfonamide compounds contain -SO2N - The group can form a relatively stable and dense interface film rich in inorganic substances such as Li3N and Li2S on the surface of the positive and negative electrodes, effectively reducing the damage of the interface film on the surface of the positive and negative electrodes, thereby reducing the consumption of fluoroethylene carbonate and electrolyte solvents, and further reducing the generation of gassing during high-temperature cycling and storage of the battery, further improving the cycle stability of the battery.

[0097] In the present invention, the silicon content w2 in the negative electrode active layer can be measured by conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and removed, and then soaked in dimethyl carbonate (DMC) solvent for 12 hours, and then rinsed with DMC solvent to remove the lithium salt attached to the negative electrode sheet. After drying, the negative electrode sheet is high-temperature treated at 400°C in an inert atmosphere for 2 hours (for example, in a tube furnace under nitrogen or argon atmosphere). The negative electrode active layer can be peeled off from the negative electrode current collector and the negative electrode active layer is collected as a test sample. Using a thermogravimetric analyzer (for example, a TGA 550 thermogravimetric analyzer), the test sample amount is 5mg-15mg, and the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min in air or oxygen atmosphere, and kept at 900°C for 40 minutes, so that the non-silicon components in the negative electrode active layer are volatilized while the silicon is fully oxidized to silicon dioxide. The mass of the residual material is weighed, and the silicon content in the negative electrode active layer can be calculated using the following formula: silicon content in the negative electrode active layer = 7 × mass of the residual material / (15 × mass of the test sample).

[0098] In the present invention, the content c6 of the fluoroethylene carbonate can be obtained by testing using conventional methods in the art, such as GC, GCMS or LC testing.

[0099] In the present invention, the electrolyte further includes a sulfur-containing additive, and the sulfur-containing additive includes at least one of 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, methylene methanedisulfonate, and ethylene bissulfate.

[0100] In one example, the sulfur-containing additive includes 1,3-propane sultone.

[0101] In one example, based on the total mass of the electrolyte, the content c7 of the sulfur-containing additive is 0.5%-5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0102] Further research found that adding fluorosulfonamide compounds to the ternary nickel-cobalt-manganese system would cause the battery to become less stable after multiple charge and discharge cycles. However, when sulfur-containing additives were added to the electrolyte, a stable CEI film could be formed on the positive electrode surface, effectively preventing direct contact between the electrolyte and the positive electrode material, reducing the occurrence of side reactions, and maintaining the structural stability of the positive electrode material. This allowed the battery to maintain a high capacity and performance after multiple charge and discharge cycles, further improving the battery's cycle stability and extending its service life.

[0103] In the present invention, the content of the sulfur-containing additive can be measured by conventional methods in the art, such as GC, GCMS or LC.

[0104] In the present invention, the electrolyte further comprises a boron-containing lithium salt, and the boron-containing lithium salt comprises at least one of lithium difluorooxalatoborate, lithium bisoxalatoborate and lithium tetrafluoroborate.

[0105] In one example, the boron-containing lithium salt includes lithium difluorooxalatoborate.

[0106] In one example, based on the total mass of the electrolyte, the content c8 of the boron-containing lithium salt is 0.01%-2%, for example, 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%.

[0107] Lithium difluorooxalatoborate combines the advantages of lithium bis(oxalatoborate) and lithium tetrafluoroborate. When the electrolyte contains lithium difluorooxalatoborate, the lithium-ion secondary battery has excellent high-temperature cycle performance. In addition, lithium difluorooxalatoborate has good stability under low temperature conditions, and its electrolyte system has the characteristics of low viscosity and high ionic conductivity, which can further improve the rate performance and low-temperature performance of the battery. At the same time, the fluorine and boron elements in the lithium difluorooxalatoborate molecules easily participate in the film-forming reaction to form a dense inorganic-organic composite layer. For example: a solid electrolyte interface (SEI) film rich in LiF and organic boron polymer can be generated on the surface of the negative electrode through a reduction reaction, effectively isolating the electrolyte from direct contact with the negative electrode; a dense aluminum oxide-based passivation film can be induced to form on the surface of the positive electrode, inhibiting aluminum foil corrosion and interfacial side reactions, thereby improving the stability of the positive electrode.

[0108] In the present invention, the content c8 of the boron-containing lithium salt in the electrolyte can be obtained by testing using conventional methods in the art, such as IC testing.

[0109] In the present invention, the positive electrode active material includes a ternary nickel-cobalt-manganese material and lithium cobalt oxide. The positive electrode active material may also include active substances conventionally used in the art, such as lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate and a composite material of lithium iron manganese phosphate and carbon. The positive electrode active layer may also include a positive electrode conductor and a positive electrode binder. The positive electrode conductor, for example, includes at least one of superconducting carbon, acetylene black, conductive carbon black, carbon dots, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene and carbon nanofibers. The positive electrode binder may include a binder conventionally used in the art, such as at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber and aluminate coupling agent.

[0110] In the present invention, the negative electrode active material includes a silicon-based material. The negative electrode active material may also include a carbon-based material, and the carbon-based material may include, for example, at least one of artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon, and hard carbon. The negative electrode active layer may also include at least one of a lithium-aluminum alloy, a tin-based negative electrode material, and a lithium transition metal oxide. The negative electrode active layer may also include a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent may include a conductive agent conventionally used in the art, for example, including at least one of superconducting carbon, acetylene black, carbon black, carbon dots, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, and carbon nanofibers. The negative electrode binder may include a binder conventionally used in the art, for example, including at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, and an aluminate coupling agent.

[0111] In the present invention, the separator may include separators commonly used in the art, for example, at least one of polypropylene, polyethylene, and polyvinylidene fluoride.

[0112] In the present invention, the electrolyte also includes an organic solvent and an electrolyte salt, and the organic solvent includes a carbonate solvent and / or a carboxylate solvent. The carbonate solvent may include a cyclic carbonate solvent and a chain carbonate solvent. The cyclic carbonate solvent may include a cyclic carbonate conventionally used in the art, such as including at least one of ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC). The chain carbonate solvent may include a chain carbonate conventionally used in the art, such as including at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC). The carboxylate solvent may include a carboxylate conventionally used in the art, such as including at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) and ethyl butyrate (EB). The electrolyte salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyllithium or lithium bis(trifluoromethylsulfonyl)imide.

[0113] In the present invention, the electrolyte may further include other additives, such as at least one of vinylene carbonate, vinyl ethylene carbonate, vinyl sulfate, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, 1,3,6-hexanetrinitrile (HTCN), glycerol trinitrile and 1,2-bis(2-cyanoethoxy)ethane.

[0114] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0115] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. All other examples obtained by persons of ordinary skill in the art based on the examples of the present invention without creative work are within the scope of protection of the present invention.

[0116] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0117] The following examples illustrate the batteries of the present invention.

[0118] Example 1

[0119] Prepare the battery as follows:

[0120] (1) Preparation of positive electrode sheet

[0121] The ternary nickel-cobalt-manganese material (LiNi 0.6 Co 0.1 Mn 0.3 O2) and lithium cobalt oxide (LiCoO2) were uniformly mixed in a high-speed mixer at a mass ratio of 6:4 to obtain a positive electrode active material; wherein w1 was 14.47%.

[0122] The positive electrode active material, polyvinylidene fluoride, conductive carbon black and multi-walled carbon nanotubes were mixed uniformly in a mass ratio of 96.3:1.2:1.2:1.3, and N-methylpyrrolidone (NMP) was added to obtain a positive electrode slurry with a solid content of 65%. The positive electrode slurry was evenly coated on an aluminum foil with a thickness of 10 μm using a coating machine, and the positive electrode sheet was obtained after drying, rolling, die-cutting and sheeting.

[0123] (2) Preparation of negative electrode sheet

[0124] The negative electrode active material (a combination of artificial graphite and silicon-based material, wherein the average particle size of the silicon-based material is 10.5 μm and w2 is 5%), single-walled carbon nanotubes, multi-walled carbon nanotubes, styrene-butadiene rubber and sodium carboxymethyl cellulose are uniformly mixed in a mass ratio of 96.1:0.25:0.15:2.9:0.6, ethylene carbonate accounting for 1% of the total mass of the above materials is added, and then deionized water is added to obtain a negative electrode slurry with a solid content of 45%; the negative electrode slurry is evenly coated on a high-strength carbon-coated copper foil with a thickness of 6 μm, and the negative electrode sheet is obtained after drying, rolling, die-cutting and sheeting.

[0125] (3) Preparation of electrolyte

[0126] In a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), EC, PC and DEC were mixed in a mass ratio of 2:5:11 to obtain an organic solvent; (c1 is 8.5%), the first additive ( Add according to the mass ratio of 1:1, c2 is 6.4%) (c3 is 1.7%), (c4 is 1.7%), lithium difluorophosphate (c5 is 0.8%), fluoroethylene carbonate (c6 is 15%), 1,3-propane sultone (c7 is 3.5%), lithium difluorooxalatoborate (c8 is 0.5%), and 1% HTCN are stirred evenly, and 15% lithium hexafluorophosphate (LiPF6) is added. After passing the moisture and free acid tests, the electrolyte is obtained. Among them, c1 / c2 is 1.33; (c3+c4) / c1 is 0.4.

[0127] (4) Preparation of batteries

[0128] The positive electrode sheet prepared in step (1), the negative electrode sheet prepared in step (2), and a separator (comprising a polyethylene film, a boehmite ceramic layer located on both sides of the polyethylene film, and a polyvinylidene fluoride adhesive layer located on the outer surface of the boehmite ceramic layer; wherein the separator has a porous structure with an average pore size D1 of 40 nm; the ceramic layer comprises lithium titanium aluminum phosphate with an average particle size D2 of 1.5 μm and a content of lithium titanium aluminum phosphate of 21.5% based on the total weight of the separator). The positive electrode sheet, the separator, and the negative electrode sheet are stacked in this order and then wound to obtain a battery; the battery is placed in an outer packaging aluminum foil, the electrolyte prepared in step (3) is injected into the outer packaging, and the battery is obtained through vacuum packaging, standing, forming, shaping, and sorting.

[0129] Example 2

[0130] Prepare the battery as follows:

[0131] (1) Preparation of positive electrode sheet

[0132] The ternary nickel-cobalt-manganese material (LiNi 0.6 Co 0.1 Mn 0.3 O2) and lithium cobalt oxide (LiCoO2) were uniformly mixed in a high-speed mixer at a mass ratio of 6:4 to obtain a positive electrode active material; wherein w1 was 14.47%.

[0133] The positive electrode active material, polyvinylidene fluoride, conductive carbon black and multi-walled carbon nanotubes were mixed uniformly in a mass ratio of 96.3:1.2:1.2:1.3, and N-methylpyrrolidone (NMP) was added to obtain a positive electrode slurry with a solid content of 65%. The positive electrode slurry was evenly coated on an aluminum foil with a thickness of 10 μm using a coating machine, and the positive electrode sheet was obtained after drying, rolling, die-cutting and sheeting.

[0134] (2) Preparation of negative electrode sheet

[0135] The negative electrode active material (a combination of artificial graphite and silicon-based material, wherein the average particle size of the silicon-based material is 5.1 μm and w1 is 5%), single-walled carbon nanotubes, multi-walled carbon nanotubes, styrene-butadiene rubber and sodium carboxymethyl cellulose are uniformly mixed in a mass ratio of 96.1:0.25:0.15:2.9:0.6, ethylene carbonate accounting for 1% by mass of the above total materials is added, and then deionized water is added to obtain a negative electrode slurry with a cobalt content of 45%; the negative electrode slurry is evenly coated on a high-strength carbon-coated copper foil with a thickness of 6 μm, and the negative electrode sheet is obtained after drying, rolling, die-cutting and sheeting.

[0136] (3) Preparation of electrolyte

[0137] In a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), EC, PC and DEC were mixed in a mass ratio of 2:5:11 to obtain an organic solvent; (c1 is 3%), the first additive ( Add according to the mass ratio of 1:1, c2 is 6.2%) (c3 is 0.5%), (c4 is 2.5%), lithium difluorophosphate (c5 is 0.5%), fluoroethylene carbonate (c6 is 10%), 1,3-propane sultone (c7 is 3.5%), lithium difluorooxalatoborate (c8 is 0.5%), and 1% HTCN are stirred evenly, and 15% lithium hexafluorophosphate (LiPF6) is added. After passing the moisture and free acid tests, the electrolyte is obtained. Among them, c1 / c2 is 0.48; (c3+c4) / c1 is 1.

[0138] (4) Preparation of batteries

[0139] The positive electrode sheet prepared in step (1), the negative electrode sheet prepared in step (2), and a separator (comprising a polyethylene film, a boehmite ceramic layer located on both sides of the polyethylene film, and a polyvinylidene fluoride adhesive layer located on the outer surface of the boehmite ceramic layer; wherein the separator has a porous structure, the average pore size D1 of the pores is 20 nm; the adhesive layer comprises lithium titanium aluminum phosphate, the average particle size D2 of the lithium titanium aluminum phosphate is 0.1 μm, and the content of lithium titanium aluminum phosphate is 20% based on the total weight of the separator). The positive electrode sheet, the separator, and the negative electrode sheet are stacked in this order, and then wound to obtain a battery; the battery is placed in an outer packaging aluminum foil, the electrolyte prepared in step (3) is injected into the outer packaging, and the battery is obtained through vacuum packaging, standing, forming, shaping, sorting, and other processes.

[0140] Example 3

[0141] Prepare the battery as follows:

[0142] (1) Preparation of positive electrode sheet

[0143] The ternary nickel-cobalt-manganese material (LiNi 0.6 Co 0.1 Mn 0.3 O2) and lithium cobalt oxide (LiCoO2) were uniformly mixed in a high-speed mixer at a mass ratio of 7:3 to obtain a positive electrode active material; wherein w1 was 10.84%.

[0144] The positive electrode active material, polyvinylidene fluoride, conductive carbon black and multi-walled carbon nanotubes were mixed uniformly in a mass ratio of 96.3:1.2:1.2:1.3, and N-methylpyrrolidone (NMP) was added to obtain a positive electrode slurry with a solid content of 65%. The positive electrode slurry was evenly coated on an aluminum foil with a thickness of 10 μm using a coating machine, and the positive electrode sheet was obtained after drying, rolling, die-cutting and sheeting.

[0145] (2) Preparation of negative electrode sheet

[0146] The negative electrode active layer (a combination of artificial graphite and silicon-based materials, wherein the average particle size of the silicon-based material is 15 μm and w1 is 5%), single-walled carbon nanotubes, multi-walled carbon nanotubes, styrene-butadiene rubber and sodium carboxymethyl cellulose are uniformly mixed in a mass ratio of 96.1:0.25:0.15:2.9:0.6, ethylene carbonate accounting for 1% of the total mass of the above materials is added, and then deionized water is added to obtain a negative electrode slurry with a cobalt content of 45%; the negative electrode slurry is evenly coated on a high-strength carbon-coated copper foil with a thickness of 6 μm, and the negative electrode sheet is obtained after drying, rolling, die-cutting and sheeting.

[0147] (3) Preparation of electrolyte

[0148] In a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), EC, PC and DEC were mixed uniformly in a mass ratio of 2:5:11 to obtain an organic solvent; (c1 is 15%), the first additive ( c2 is 7%) (c3 is 2.5%), (c4 is 0.8%), lithium difluorophosphate (c5 is 1%), fluoroethylene carbonate (c6 is 20%), 1,3-propane sultone (c7 is 3.5%), lithium difluorooxalatoborate (c8 is 0.5%), and 1% HTCN are stirred evenly, and 15% lithium hexafluorophosphate (LiPF6) is added. After passing the moisture and free acid tests, the electrolyte is obtained. Among them, c1 / c2 is 2.14; (c3+c4) / c1 is 0.22.

[0149] (4) Preparation of batteries

[0150] The positive electrode sheet prepared in step (1), the negative electrode sheet prepared in step (2) and a separator (comprising a polyethylene film and a boehmite ceramic layer respectively located on both sides of the polyethylene film and a polyvinylidene fluoride adhesive layer located on the outer surface of the boehmite ceramic layer; wherein the separator has a porous structure with an average pore size D1 of 60 nm; the ceramic layer and the adhesive layer comprise lithium titanium aluminum phosphate with an average particle size D2 of 3 μm and a content of lithium titanium aluminum phosphate of 25% based on the total weight of the separator). The positive electrode sheet, the separator and the negative electrode sheet are stacked in this order and then wound to obtain a battery; the battery is placed in an outer packaging aluminum foil, the electrolyte prepared in step (3) is injected into the outer packaging, and the battery is obtained through vacuum packaging, standing, forming, shaping, sorting and other processes.

[0151] Example 4 Group

[0152] This group of examples is used to verify the impact of changes in the "ternary nickel-cobalt-manganese material".

[0153] This group of examples is carried out with reference to Example 1, except that the ternary nickel-cobalt-manganese material is changed, specifically as follows:

[0154] Example 4a, LiNi 0.6 Co 0.1 Mn 0.3 O2 is replaced by the same mass of LiNi 0.5 Co 0.2 Mn 0.3 O2; w1 is 12.06%;

[0155] Example 4b, LiNi 0.6 Co 0.1 Mn 0.3 O2 is replaced by the same mass of LiNi 0.68 Co 0.09 Mn 0.23 O2;w1 is 16.38%.

[0156] Example 5 Group

[0157] This set of embodiments is used to verify the impact of the change of w1.

[0158] This group of examples were carried out with reference to Example 1, except that w1 was controlled by changing the mass ratio of lithium cobalt oxide and the ternary nickel-cobalt-manganese material, as follows:

[0159] Example 5a is carried out in accordance with Example 1, except that LiNi 0.6 Co 0.1 Mn 0.3 O2 and LiCoO2 were mixed uniformly in a high-speed mixer at a mass ratio of 5:5 to obtain a positive electrode active material; w1 was 18.11%;

[0160] Example 5b is carried out in accordance with Example 1, except that LiNi 0.6 Co 0.1 Mn 0.3 O2 and LiCoO2 were uniformly mixed in a high-speed mixer at a mass ratio of 9:1 to obtain a positive electrode active material; w1 was 3.6%.

[0161] Example 6

[0162] This set of examples is used to verify the impact of changes in the "content c1 of the fluorosulfonamide compound".

[0163] This group of examples was carried out with reference to Example 1, except that the content of the fluorosulfonamide compound was changed, as follows:

[0164] In Example 6a, c1 is 1%; c1 / c2 is 0.16; (c3+c4) / c1 is 3.4;

[0165] In Example 6b, c1 is 20%; c1 / c2 is 3.13; and (c3+c4) / c1 is 0.17.

[0166] Example 7 Group

[0167] This set of examples is used to verify the impact of changing the “content c2 of the first additive”.

[0168] This group of examples is carried out with reference to Example 1, except that the content of the first additive is changed, specifically as follows:

[0169] Example 7a, c2 is 2.5%; c1 / c2 is 3.4;

[0170] Example 7b, c2 is 14%; c1 / c2 is 0.61;

[0171] In Example 7c, c2 is 20%; c1 / c2 is 0.43.

[0172] Example 8 Group

[0173] This set of embodiments is used to verify the impact of the change of "c1 / c2".

[0174] This group of examples is carried out with reference to Example 1, except that the content of the fluorosulfonamide compound and the first additive in the electrolyte is changed to achieve control, as follows:

[0175] In Example 8a, c1 is 3%, c2 is 14%, c1 / c2 is 0.21, and (c3+c4) / c1 is 1.13.

[0176] In Example 8b, c1 is 15%, c2 is 5%, c1 / c2 is 3; and (c3+c4) / c1 is 0.23.

[0177] Example 9 Group

[0178] This group of examples is used to verify the impact of changes in the "content of lithium aluminum titanium phosphate in the positive electrode active layer."

[0179] This group of examples was carried out with reference to Example 1, except that the separator did not include lithium aluminum titanium phosphate, and the content of lithium aluminum titanium phosphate in the positive electrode active layer was changed as follows:

[0180] Example 9a, the content of lithium aluminum titanium phosphate is 0%;

[0181] In Example 9b, the content of lithium aluminum titanium phosphate is 2%.

[0182] Example 10 Group

[0183] This group of examples is used to verify the impact of changes in the "content of lithium aluminum titanium phosphate in the diaphragm".

[0184] This group of examples was carried out with reference to Example 1, except that the content of lithium aluminum titanium phosphate in the separator was changed to achieve control, as follows:

[0185] Example 10a, the content of lithium aluminum titanium phosphate is 2.1%;

[0186] In Example 10b, the content of lithium aluminum titanium phosphate is 29.8%.

[0187] Example 11

[0188] Used to verify the impact of changing the "content c5 of the second additive".

[0189] The process is carried out in accordance with Example 1, except that the content of the second additive is changed to adjust the reaction conditions, as follows:

[0190] Example 11a, c5 is 0%;

[0191] Example 11b, c5 is 2.5%.

[0192] Example 12

[0193] Used to verify the impact of changes in the "content c6 of fluoroethylene carbonate".

[0194] The process was carried out with reference to Example 1, except that the content of fluoroethylene carbonate was changed to regulate the reaction, as follows:

[0195] In Example 12, c6 is 30%.

[0196] Example 13

[0197] Used to verify the impact of changes in the "content of sulfur-containing additives c7".

[0198] The process was carried out in accordance with Example 1, except that the content of the sulfur-containing additive was changed to control the reaction, as follows:

[0199] Example 13a, c7 is 0%;

[0200] Example 13b, c7 is 5%.

[0201] Example 14

[0202] Used to verify the impact of changes in the "content c8 of boron-containing lithium salt".

[0203] The process was carried out with reference to Example 1, except that the content of the boron-containing lithium salt was changed to control the reaction, as follows:

[0204] Example 14a, c8 is 0%;

[0205] Example 14b, c8 is 2%.

[0206] Comparative Example 1

[0207] Used to verify the impact of "the electrolyte does not include a fluorosulfonamide compound or a first additive".

[0208] The process was carried out in accordance with Example 1, except that the contents of the fluorosulfonamide compound and the first additive were changed to adjust the reaction conditions, as follows:

[0209] Comparative Example 1a, the electrolyte does not include the fluorosulfonamide compound, c1 is 0%, and c2 is 6.4%;

[0210] In Comparative Example 1b, the electrolyte does not include the first additive, c1 is 20%, and c2 is 0%.

[0211] Comparative Example 2

[0212] This group of comparison ratios is used to verify the impact of changes in "c1 / c2".

[0213] This comparative example was carried out with reference to Example 1, except that the contents of the fluorosulfonamide compound and the first additive were varied to achieve control, as follows:

[0214] In comparative example 2a, c1 is 1%, c2 is 20%, and c1 / c2 is 0.05;

[0215] In Comparative Example 2b, c1 is 20%, c2 is 2.5%, and c1 / c2 is 8.

[0216] Test Case

[0217] (1) High temperature cycle test

[0218] The batteries prepared in the examples and comparative examples were subjected to high temperature cycle tests. The specific test methods are as follows:

[0219] After measuring the open circuit voltage (OCV), the battery with 50% SOC is placed in a constant temperature environment at 45°C, charged to 4.48V at a constant current and constant voltage of 0.7C, left to stand for 30 minutes, and then discharged to 3.0V at a constant current of 0.5C, and the discharge capacity C0 is recorded; when the cycle reaches n times, the last discharge capacity C is recorded. n , then the calculation formula for the capacity retention rate of the nth cycle is: Capacity retention rate (%) = C n / C0×100%, record the results and see Table 1.

[0220] (2) High temperature float charge test

[0221] The batteries prepared in the examples and comparative examples were subjected to a high-temperature float charge test. The specific test method is as follows:

[0222] Under a constant temperature environment of 25°C, the battery charge was adjusted to 50% SOC, and the initial thickness T1 of the battery was tested. The battery was placed in a constant temperature environment of 45°C and charged to 4.48V at a constant current and constant voltage of 0.5C. The constant voltage charging was performed for 5 days as a cycle, and the thermal thickness expansion change of the battery was monitored. The final thermal thickness T2 of the battery after 45°C float charge was tested with the limiting conditions of obvious bulging of the battery or thickness expansion greater than 15%. The battery's 45°C float charge thickness expansion rate = (T2-T1) / T1×100%. The recorded results are shown in Table 1.

[0223] (3) Low temperature discharge test

[0224] The batteries prepared in the examples and comparative examples were subjected to low-temperature discharge tests. The specific test methods are as follows:

[0225] The corresponding battery was placed in a constant temperature environment at 25°C, discharged at 0.2C to 3.0V, and then charged at 0.7C constant current and constant voltage to 4.48V, with a cut-off current of 0.05C. After the battery was fully charged, it was allowed to stand for 5 minutes, and then discharged at 0.5C constant current to a cut-off voltage of 3.0V, and the initial capacity of the battery was recorded as Q1; then the battery was fully charged at 0.7C constant current and constant voltage to 4.48V, with a cut-off current of 0.05C, and then the fully charged battery was placed in a -30°C environment and allowed to stand for 4h. When the battery surface temperature reached the ambient temperature, it was discharged at 0.5C to 3.0V, and the battery discharge capacity was recorded as Q2. The low-temperature discharge capacity retention rate = Q2 / Q1×100%. The recorded results are shown in Table 1.

[0226] (4) 130℃ hot box test

[0227] The batteries prepared in the examples and comparative examples were subjected to a 130°C hot box test. The specific test method is as follows:

[0228] The resulting batteries were charged at a constant current and constant voltage of 0.5C until fully charged. They were then placed in a thermostat and heated starting at 20°C ± 5°C. The temperature was then raised at a rate of (5°C ± 2°C) / min to 130°C ± 2°C. The test was then held at this temperature for 30 minutes before the test was terminated. The battery passed the test if it did not catch fire or explode within 30 minutes. Five tests were performed for each group, and the results are recorded in Table 1.

[0229] Table 1

[0230]

[0231]

[0232] As can be seen from Table 1, the battery of the present invention has significantly improved cycle performance, high-temperature storage performance, low-temperature performance and safety performance compared with the comparative example.

[0233] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A lithium-ion secondary battery, characterized in that: Including positive electrode sheet, negative electrode sheet and electrolyte; The positive electrode sheet includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, the positive electrode active material includes a ternary nickel-cobalt-manganese material and lithium cobalt oxide; the mass content w1 of the Ni element in the positive electrode active material is 1%-20%; The negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; The electrolyte includes a fluorosulfonamide compound, and the fluorosulfonamide compound includes at least one of the substances represented by Formula I: wherein R1 and R2 each independently include at least one of the following groups which are substituted or unsubstituted with fluorine: a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, a C1-C6 cyano group, a phenyl group, a silane group, and a sulfone group; The electrolyte further includes a first additive, wherein the first additive includes fluorobenzene and / or 2,2-difluoroethyl acetate; Based on the total mass of the electrolyte, the content c1 of the fluorosulfonamide compound is 1%-20%; the content c2 of the first additive is 2.5%-20%; c1 and c2 satisfy: 0.1≤c1 / c2≤5.

5.

2. The lithium ion secondary battery according to claim 1, wherein w1 is 10%-17%; and / or, c1 is 3%-15%; and / or, c2 is 5%-14%; and / or, 0.4≤c1 / c2≤2.

5.

3. The lithium ion secondary battery according to claim 1 or 2, wherein The fluorosulfonamide compound includes At least one of; preferably including And / or, the first additive includes At least one of; preferably including At least one of .

4. The lithium ion secondary battery according to claim 1 or 2, wherein The positive electrode active layer also includes lithium aluminum titanium phosphate; And / or, the lithium-ion secondary battery further comprises a diaphragm, the diaphragm comprises lithium aluminum titanium phosphate; preferably, the average pore size D1 of the diaphragm is 20 nm-60 nm; Preferably, the average particle size D2 of the lithium aluminum titanium phosphate is 0.05 μm-4 μm, more preferably 0.1 μm-3 μm.

5. The lithium ion secondary battery according to claim 1 or 2, wherein The electrolyte further includes a nitrile compound, the nitrile compound including a first nitrile compound and a second nitrile compound, the first nitrile compound including at least one of the substances represented by Formula II and Formula III, and the second nitrile compound including at least one of the substances represented by Formula IV: wherein R3, R4 and R5 each independently include a substituted or unsubstituted C1-C6 alkyl group, and the substituted substituent includes halogen; wherein R6, R7 and R8 each independently include substituted or unsubstituted C1-C6 alkyl, and the substituted substituent includes halogen; Wherein, m is selected from an integer of 2-4, and R9 includes At least one of R 10 and R 11 Each independently includes a C1-C3 alkyl group.

6. The lithium ion secondary battery according to claim 5, wherein Based on the total mass of the electrolyte, the content c3 of the first nitrile compound is 0.01%-3%; preferably 0.1%-2.5%; And / or, the content c4 of the second nitrile compound is 0.01%-3%; preferably 0.1%-2.5%; and / or, c1, c3 and c4 satisfy: 0.1≤(c3+c4) / c1≤4; preferably, 0.2≤(c3+c4) / c1≤1; And / or, the first nitrile compound comprises At least one of; preferably including and / or And / or, the second nitrile compound comprises At least one of; preferably including and / or 7. The lithium ion secondary battery according to claim 1 or 2, wherein The average particle size of the silicon-based material is 2 μm-20 μm, preferably 5 μm-15 μm; And / or, the silicon-based material includes at least one of elemental silicon, silicon carbon, silicon oxygen and silicon alloy; preferably, the silicon-based material includes the silicon carbon; more preferably, the silicon carbon includes a porous carbon matrix and silicon particles located in the internal pores of the porous carbon matrix.

8. The lithium ion secondary battery according to claim 1 or 2, wherein The electrolyte further includes a second additive, wherein the second additive includes at least one of ethylene sulfate and lithium difluorophosphate; Preferably, based on the total mass of the electrolyte, the content c5 of the second additive is 0.01%-2.5%.

9. The lithium ion secondary battery according to claim 1 or 2, wherein The silicon content w2 in the negative electrode active layer is 1.5%-50%, preferably 3%-30%; And / or, the electrolyte further comprises fluoroethylene carbonate, and based on the total mass of the electrolyte, the content c6 of the fluoroethylene carbonate is 5%-30%, preferably 10%-25%.

10. The lithium ion secondary battery according to claim 1 or 2, wherein The electrolyte further includes a sulfur-containing additive, wherein the sulfur-containing additive includes at least one of 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, methylene methanedisulfonate, and ethylene bissulfate; preferably includes 1,3-propane sultone; more preferably, the content c7 of the sulfur-containing additive is 0.5%-5% based on the total mass of the electrolyte; And / or, the electrolyte further includes a boron-containing lithium salt, the boron-containing lithium salt including at least one of lithium difluorooxalatoborate, lithium bis(oxalatoborate) and lithium tetrafluoroborate; preferably including lithium difluorooxalatoborate; more preferably, based on the total mass of the electrolyte, the content c8 of the boron-containing lithium salt is 0.01%-2%.

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