A battery

Abstract

The embodiment of the present application provides a battery. The negative electrode sheet in the battery comprises a negative electrode current collector, the negative electrode current collector comprises a copper foil and a protective layer; the copper foil comprises a first surface and a second surface arranged oppositely in the thickness direction of the copper foil, and the protective layer is located on the first surface and the second surface; the copper foil comprises grains, the average particle size of the grains on the first surface is D1, the average particle size of the grains on the second surface is D2, and D1>D2; the number percentage of the grains with a particle size greater than 1.5 microns in the grains on the first surface is S1%; the protective layer comprises a metal element, the metal element comprises at least one of chromium and nickel, the mass content of the metal element in the negative electrode current collector is B1; the electrolyte comprises a trinitrile compound, and the mass percentage of the trinitrile compound in the electrolyte is A1%; wherein 1.5<=S1 / A1<=23, 70ppm<=B1<=650ppm. The negative electrode current collector in the battery is not easy to break, and the battery has excellent cycle performance.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and more particularly to a battery. Background Technology

[0002] With the increasing demand for high-energy-density lithium-ion batteries from new energy vehicles and portable electronic devices, silicon-based materials have become the most promising next-generation anode active materials due to their extremely high theoretical specific capacity; in order to improve the energy density of lithium batteries, lithium cobalt oxide cathodes are also developing towards high voltage.

[0003] However, due to the high hardness of silicon-based materials, the negative electrode current collector is easily scratched during the rolling process of the negative electrode sheet; and the electrolyte additives that are compatible with the high-voltage positive electrode are also prone to corroding the negative electrode current collector, which is detrimental to the cycle performance of the battery. Summary of the Invention

[0004] This application provides a battery in which the negative electrode current collector is not easily damaged and the battery has excellent cycle performance.

[0005] This application provides a battery, which includes a negative electrode and an electrolyte;

[0006] The negative electrode sheet includes a negative electrode current collector, which includes a copper foil and a protective layer; the copper foil includes a first surface and a second surface disposed opposite to each other along its thickness direction, and the protective layer is located on the first surface and the second surface;

[0007] The copper foil comprises grains, the average grain size of the grains on the first surface is D1, the average grain size of the grains on the second surface is D2, and D1 > D2; the percentage of grains with a grain size greater than 1.5 μm in the first surface is S1%;

[0008] The protective layer includes a metal element, which includes at least one of chromium and nickel, and the mass content of the metal element in the negative electrode current collector is B1.

[0009] The electrolyte comprises a trinitrile compound, and the mass percentage of the trinitrile compound in the electrolyte is A1%.

[0010] Among them, 1.5≤S1 / A1≤23, 70ppm≤B1≤650ppm.

[0011] In the battery described above, 3% ≤ S1% ≤ 45%; preferably, 5% ≤ S1% ≤ 30%;

[0012] And / or, 0.5% ≤ A1% ≤ 4.5%;

[0013] And / or, 200ppm≤B1≤500ppm;

[0014] And / or, the trinitrile compound includes a long-chain trinitrile compound, the long-chain trinitrile compound having 5 or more carbon atoms, the long-chain trinitrile compound having a branched molecular structure or an asymmetric molecular structure, and the long-chain trinitrile compound having a mass percentage content of less than 3% in the electrolyte.

[0015] In the battery described above, 0.05μm≤D1-D2≤0.8μm; preferably, 0.1μm≤D1-D2≤0.6μm;

[0016] And / or, D1 is 0.3-1.5 μm;

[0017] And / or, D2 is 0.3-1.5μm.

[0018] In the battery described above, the electrolyte further includes a dinitrile compound, and the mass percentage of the dinitrile compound in the electrolyte is A2%; A2 and B1 satisfy:

[0019] 20≤B1 / A2≤900;

[0020] Preferably, 1% ≤ A2% ≤ 5%;

[0021] Preferably, A2 / A1 > 1.

[0022] In the battery described above, the dinitrile compound includes at least one selected from succinic anion, glutaronitrile, adiponitrile, tetramethylsuccinic anion, 1,4-dicyano-2-butene, 1,4-di(cyanoethoxy)butane, 1,3-di(2-cyanoethoxy)propane, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, and 1,4-dicyano-2,3-diethyl-2-butene;

[0023] And / or, the trinitrile compound includes at least one selected from 1,3,6-hexanetrionitrile, 1,2,6-hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,1,1-tris(cyanoethoxymethylene)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,2,6-tris(cyanoethoxy)hexane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, tris(2-cyanoethyl) phosphate, 1,2,4-butanetrionitrile, 1,3,5-cyclohexanetrionitrile, 1,3,5-phenyltricyanide, and 1,2,3-propanetrionitrile.

[0024] In the battery described above, the electrolyte further includes fluoroethylene carbonate, wherein the mass percentage of the fluoroethylene carbonate in the electrolyte is less than 13%.

[0025] In the battery described above, the negative electrode sheet further includes a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising silicon-based particles;

[0026] The silicon-based particles include bulk silicon-based particles, wherein the average number of facets of the bulk silicon-based particles is less than or equal to 8;

[0027] And / or, the average particle size of the bulk silicon-based particles is 5 μm-12 μm;

[0028] Preferably, in the negative electrode active material, the mass percentage of the silicon-based particles is greater than or equal to 10%.

[0029] In the battery described above, the silicon-based particles further include spherical silicon-based particles, wherein the Dv50 of the spherical silicon-based particles is 6μm-15μm;

[0030] Preferably, the percentage of spherical silicon-based particles in the silicon-based particles is 30%-90%.

[0031] In the battery described above, the negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer stacked together, with the first negative electrode active layer close to the negative electrode current collector;

[0032] The first negative electrode active layer includes a first negative electrode active material, and the second negative electrode active layer includes a second negative electrode active material. The content of silicon-based particles in the first negative electrode active material is less than the content of silicon-based particles in the second negative electrode active material.

[0033] Preferably, in the first negative electrode active material, the mass percentage of the silicon-based particles is less than or equal to 40%;

[0034] Preferably, in the second negative electrode active material, the mass percentage of the silicon-based particles is greater than 40%.

[0035] The battery as described above, wherein the battery has a wound structure, and the first surface is close to the center of the battery; and / or,

[0036] The battery further includes a positive electrode sheet, 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 positive electrode substrate and a coating layer located on at least a portion of the surface of the positive electrode substrate;

[0037] The positive electrode substrate includes LiCoO2;

[0038] The coating layer includes Li7La 3-a Zr 2-b M a+b O 12 M includes at least one of Fe, Ti, Cu and Mn, where 0.01≤a≤0.5 and 0.05≤b≤0.3.

[0039] This application optimizes the bending resistance and corrosion resistance of copper foil by differentiating the grain size of the first and second surfaces. Simultaneously, matching the grain size of the first surface with the trinitrile compound content in the electrolyte balances the corrosion resistance of the copper foil with the high-temperature performance of the battery. Furthermore, selecting the content of metal elements in the protective layers of the first and second surfaces of the copper foil further reduces electrolyte corrosion. This application constructs a dual "mechanical-chemical" protection mechanism for the negative electrode current collector, thereby achieving comprehensive suppression of copper foil corrosion in high-energy-density battery systems while maintaining the bending resistance of the copper foil. Detailed Implementation

[0040] The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0041] The high hardness of silicon-based materials inevitably damages the negative electrode current collector during coating and rolling, destroying the protective layer in the negative electrode current collector and increasing the surface energy of the copper foil. At the same time, in order to adapt to high-voltage positive electrode sheets and improve the stability of positive electrode sheets, electrolytes containing trinitrile compounds are usually used. However, the strong polarity and high activity of trinitrile compounds themselves can cause the copper foil to dissolve and corrode.

[0042] While current methods such as pre-charging mechanisms, room-temperature aging, and shortening aging time can alleviate copper foil corrosion to some extent, they cannot fundamentally solve the problem of decreased battery K-value and subsequent cycle capacity degradation caused by copper foil corrosion. This application addresses this issue by controlling the grain size of the first and second surfaces of the copper foil, matching the grain size of the first surface with the amount of trinitrile compound added to the electrolyte, and selectively controlling the content of metal elements in the protective layer. This allows for the construction of a dual "mechanical-chemical" protection mechanism for the negative electrode current collector, thereby achieving comprehensive suppression of copper foil corrosion in high-energy-density battery systems and improving the battery's K-value and cycle performance.

[0043] In view of this, the first aspect of this application provides a battery, including a negative electrode and an electrolyte;

[0044] The negative electrode sheet includes a negative current collector, which includes a copper foil and a protective layer; the copper foil includes a first surface and a second surface disposed opposite to each other along its thickness direction, and the protective layer is located on the first surface and the second surface;

[0045] The copper foil comprises grains, with the average grain size of the grains on the first surface being D1 and the average grain size of the grains on the second surface being D2, where D1 > D2; the percentage of grains with a grain size greater than 1.5 μm in the first surface is S1%.

[0046] The protective layer includes a metal element, which includes at least one of chromium and nickel, and the content of the metal element in the negative electrode current collector is B1;

[0047] The electrolyte contains trinitrile compounds, and the mass percentage of trinitrile compounds in the electrolyte is A1%.

[0048] Among them, 1.5≤S1 / A1≤23, 70ppm≤B1≤650ppm.

[0049] In this application, a protective layer is located on a first surface and a second surface. The negative electrode current collector sequentially comprises a protective layer, a copper foil, and another protective layer in the thickness direction. The protective layer includes a metallic element, including at least one of chromium and nickel. In this application, the metallic element in the protective layer can exist in elemental form or in the form of a metal oxide. In this application, the first surface can be understood as the surface subjected to less winding tension in the battery; that is, in the battery, the first surface experiences less winding tension than the second surface.

[0050] The electrolyte in this application includes trinitrile compounds. Trinitrile compounds have a higher electrochemical window and are more suitable for high-voltage cathode systems (e.g., cathode sheets including lithium cobalt oxide), which can better improve the high-temperature stability of cathode active materials. However, due to the complexation of nitrile groups with copper, trinitrile compounds form an adsorption layer on the copper foil surface. Since commonly used trinitrile compounds have branched molecular structures or asymmetric structures with multiple strongly polar functional groups, multiple cyano groups are difficult to form ideal coordination bonds with the flat copper foil surface simultaneously. The middle cyano group will generate huge steric hindrance, causing the molecules to be unable to lie flat to form a dense monolayer. The resulting adsorption layer becomes loose, disordered, and contains a large number of voids. The copper foil surface at the adsorption layer defects is directly exposed to the electrolyte. More importantly, those cyano groups that fail to participate in coordination and are suspended outside the adsorption layer (especially highly active middle cyano groups) may have partially positively charged carbon atoms, which may attract corrosive anions (such as Cl-). - HF or water molecules gather around it, forming highly active localized corrosion micro-regions at the defects in the adsorption layer, initiating and accelerating pitting corrosion of the copper foil.

[0051] The protective layer protects the copper foil and reduces the probability of electrolyte corrosion. On one hand, the protective layer protects the surface of the copper foil, reducing direct contact corrosion between the electrolyte and the copper foil. On the other hand, the metal elements in the protective layer can form a dense oxide film (e.g., CuCr2O4), which alters the electrochemical potential of the copper foil (weakening electron donation and increasing potential). This reduces the potential difference of the galvanic cell between the copper foil and the negative electrode active layer, weakening the thermodynamic driving force of corrosion and further reducing the possibility of copper foil corrosion. By ensuring the metal element content B1 in the negative electrode current collector is between 70ppm and 650ppm, the density, thickness, and interfacial bonding strength of the protective layer can be effectively controlled. This significantly improves the chemical stability and corrosion resistance of the copper foil in the electrolyte environment, ensures good electronic conductivity of the protective layer, reduces the interfacial impedance between the negative electrode and the electrolyte, and avoids interfacial embrittlement caused by excessive metal elements, comprehensively improving the cycle stability and reliability of the battery.

[0052] While larger grains in copper foil are more susceptible to corrosion and precipitation, they also enhance the foil's resistance to bending. During battery cycling, the foil is less prone to breakage due to expansion and stress. Because the first surface faces inwards from the core, its grain boundaries experience less tensile stress and are less susceptible to corrosion. Conversely, the second surface faces outwards from the core, resulting in greater tensile stress and easier corrosion. This leads to a larger average grain size on the first surface, improving the copper foil's resistance to bending and reducing breakage during battery cycling. Conversely, a smaller average grain size on the second surface enhances the copper foil's corrosion resistance.

[0053] However, during battery cycling, the protective layer at the crease is more easily damaged, and an excessive number of large grains increases the likelihood of corrosion of the copper foil at the crease. When the percentage of grains larger than 1.5 μm (large grains) on the first surface (S1) and the mass percentage of trinitrile compounds in the electrolyte (A1) satisfy the condition 1.5 ≤ S1 / A1 ≤ 23, the trinitrile compounds in the electrolyte can more effectively protect the positive electrode, ensuring the battery's high-temperature and high-pressure stability. Furthermore, the copper foil, while possessing good bending resistance, also exhibits excellent resistance to electrolyte corrosion, thus enabling the battery to possess both excellent high-temperature performance and cycle performance. Specifically, when S1 / A1 < 1.5, the content of trinitrile compounds in the electrolyte is high. At this time, the trinitrile compounds cannot form a dense adsorption layer on the copper foil surface, increasing the corrosion and dissolution of the copper foil; or the number of large grains on the first surface is too small, resulting in insufficient bending resistance of the copper foil and poor cycle performance of the battery; when S1 / A1 > 23, the proportion of copper in large grains is high, which is not conducive to alleviating the corrosion and dissolution of the copper foil and is not conducive to the cycle performance of the battery; or the content of trinitrile compounds in the electrolyte is too low, which is not conducive to the high-temperature performance of the battery.

[0054] Therefore, by limiting the content of metal elements in the protective layer on the surface of the copper foil and matching the mass percentage of trinitrile compounds in the electrolyte with the content of large grains on the first surface of the copper foil, this application can achieve comprehensive suppression of copper foil corrosion under high temperature and high pressure, while also improving the bending resistance of the current collector, thereby improving the high temperature performance and cycle performance of the battery.

[0055] For example, B1 can be a range of any one or any two of 70ppm, 80ppm, 100ppm, 200ppm, 400ppm, 500ppm, and 650ppm.

[0056] S1 / A1 can be any one of 1.5, 1.6, 2, 5, 8, 10, 16, 20, 23, or a range consisting of any two of them.

[0057] In some embodiments, the mass percentage B1 of the metal element in the protective layer can be measured by the following method: disassembling the negative electrode sheet of the battery, removing the negative electrode active layer on the surface of the negative electrode current collector to obtain the negative electrode current collector, or using the prepared negative electrode current collector without a negative electrode active layer, adding the negative electrode current collector to hydrochloric acid for digestion, and then taking a portion of the solution for analysis using an ICP spectrometer to obtain the mass percentage of the metal element.

[0058] In some implementations, a field emission SEM (such as ZEISS Gemini or Tescan) can be used in conjunction with an EBSD system to test the average grain size D1 of the first surface and the average grain size D2 of the grains on the second surface, as well as the percentage of grains S1 with a grain size greater than 1.5 μm on the first surface.

[0059] In some implementations, gas chromatography-mass spectrometry (GC-MS) or high performance liquid chromatography-mass spectrometry (HPLC-MS) can be used to determine the mass percentage of trinitrile compounds in the electrolyte.

[0060] In some implementations, the protective layer may also be located on other surfaces of the copper foil to provide all-around protection for the copper foil and improve the cycle performance of the battery.

[0061] In some embodiments, the battery of this application is a wound battery. When the battery is a wound battery, the first surface is close to the center of the battery (i.e., the winding center), meaning that during the winding process, the first surface faces inward and the second surface faces outward. The solution of this application can minimize the possibility of damage to the negative electrode current collector during the winding process and improve the cycle performance of the battery.

[0062] Furthermore, by limiting the content of metal elements (chromium and / or nickel) in the negative electrode current collector to 200ppm≤B1≤500ppm, a precise balance can be achieved between corrosion resistance, interfacial stability, and electrochemical compatibility. Appropriate amounts of metal elements significantly improve the oxidation resistance and electrolyte corrosion resistance of the negative electrode current collector, reducing the risk of stress cracking during charge-discharge cycles. Therefore, it can effectively improve the interfacial compatibility of the negative electrode, reduce interfacial impedance, extend cycle life, and balance high-rate charge-discharge performance with battery safety and reliability.

[0063] Furthermore, when the content of trinitrile compound is 0.5%≤A1%≤4.5%, an appropriate amount of trinitrile compound can form a dense, uniform and stable interface film on the surface of the positive electrode active material. Its cyano group can complex transition metal ions, reduce the side reactions and capacity decay caused by the precipitation of transition metals in the positive electrode active material, and improve the battery cycle life and high temperature storage performance. Controlling the content of trinitrile compound can avoid the corrosion of copper foil caused by excessive trinitrile compound, and improve the high temperature safety and cycle stability of the battery.

[0064] For example, A1% can be a range of any one of 0.5%, 1%, 1.5%, 2%, 2.9%, 4%, 4.5%, or any two of them.

[0065] In some embodiments of this application, 3% ≤ S1% ≤ 45%.

[0066] Generally, reducing the percentage of large grains in copper foil can effectively improve the surface smoothness and grain refinement of the copper foil, reduce the risk of corrosion during battery cycling, and improve the battery's cycle performance. However, if the percentage of large grains in the copper foil is too low, the copper foil is prone to bending, and the processing technology of the copper foil becomes relatively more complex and costly. Therefore, by reasonably controlling the percentage of large grains on the first surface, it is possible to obtain copper foil with both excellent corrosion resistance and bending resistance while saving costs, thereby improving the overall reliability and safety of the battery.

[0067] For example, S1% can be a range of any one of 3%, 5%, 10%, 15%, 20%, 30%, 45%, or any combination thereof. Further, 5% ≤ S1% ≤ 30%.

[0068] This application does not specifically limit the trinitrile compound; it can be any compound containing three cyano groups commonly used in the art. For example, the trinitrile compound may include at least one of 1,3,6-hexanetrionitrile, 1,2,6-hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,1,1-tris(cyanoethoxymethylene)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,2,6-tris(cyanoethoxy)hexane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, tris(2-cyanoethyl) phosphate, 1,2,4-butanetrionitrile, 1,3,5-cyclohexanetrionitrile, 1,3,5-benzenetricyanate, and 1,2,3-propanetrionitrile.

[0069] In some embodiments of this application, the trinitrile compound includes a long-chain trinitrile compound, the long-chain trinitrile compound having 5 or more carbon atoms, the long-chain trinitrile compound having a branched molecular structure or an asymmetric molecular structure, and the long-chain trinitrile compound having a mass percentage content of less than 3% in the electrolyte.

[0070] Long-chain trinitrile compounds exhibit better reduction and thermal stability, which can further improve the high-temperature stability of cathode active materials. However, it is difficult for long-chain trinitrile compounds to simultaneously form ideal coordination bonds with the flat copper foil surface. The cyano groups in the middle create significant steric hindrance, resulting in a loose, disordered, and porous adsorption layer on the copper foil surface. This exposes the copper foil surface at defective areas directly to the electrolyte. Furthermore, the cyano groups that fail to participate in effective coordination and remain suspended outside the adsorption layer may have partially positively charged carbon atoms, which could attract corrosive anions (such as Cl-). - Water molecules may accumulate around the adsorption layer, forming highly active localized corrosion micro-regions at defects in the adsorption layer, initiating and accelerating pitting corrosion. Furthermore, by limiting the content of long-chain trinitrile compounds to 1.5 ≤ S1 / A1 ≤ 23 and 70 ppm ≤ B1 ≤ 650 ppm, this application can minimize the potential damage to the negative electrode current collector caused by long-chain trinitrile compounds. Further selection of the content of long-chain trinitrile compounds in the electrolyte can further reduce the negative impact of long-chain trinitrile compounds on the negative electrode current collector, while also ensuring the high-temperature cycle performance of the battery.

[0071] For example, the mass percentage of the long-chain trinitrile compound in the electrolyte can be any of 2.9%, 2%, 1%, 0.1%, or any combination thereof.

[0072] In some embodiments of this application, 0.05 μm ≤ D1 - D2 ≤ 0.8 μm. Further limiting the difference in average grain size between the first and second surfaces can significantly improve the stress distribution uniformity and interface stability of the negative electrode current collector. Reducing the grain size difference on both sides of the negative electrode current collector can effectively reduce the unevenness of the mechanical properties (strength, elongation, springback) of the inner and outer surfaces of the copper foil, reducing wrinkles, warping, and localized stress concentration caused by deformation differences during the negative electrode fabrication process (e.g., winding process); simultaneously, it can make the electrochemical activity and interface impedance of the inner and outer surfaces more consistent, avoiding localized current distortion, lithium plating, and exacerbated side reactions, thus improving charge-discharge uniformity and long-term cycle life. Reasonably controlling the size difference between the first and second surfaces can also balance the overall processability and structural stability of the copper foil, improving battery reliability and safety.

[0073] For example, D1-D2 can be a range of any one of 0.05μm, 0.1μm, 0.3μm, 0.5μm, 0.8μm, or any two of them. Further, 0.1μm ≤ D1-D2 ≤ 0.6μm.

[0074] Furthermore, D1 is 0.3-1.5 μm. By further limiting the average grain size of the first surface of the copper foil, a precise match can be achieved between processability, structural stability, and interfacial electrochemical performance. A suitable and uniform grain size can effectively improve the plasticity and elongation of the copper foil, reducing the risk of stress concentration, wrinkling, and cracking during the preparation of the negative electrode sheet; it can also optimize the flatness of the first surface and interfacial contact characteristics, reduce local impedance fluctuations, suppress lithium plating and side reactions during charging and discharging, and improve the interfacial stability and cycle life of the negative electrode sheet; it can also avoid the disadvantage of excessively small grains affecting the bending resistance of the copper foil, thus balancing the mechanical reliability and electrochemical consistency of the copper foil, and improving the overall performance and safety stability of the battery cell.

[0075] For example, D1 can be a range of any one of 0.3μm, 0.5μm, 0.8μm, 1μm, 1.3μm, 1.5μm, or any two of them.

[0076] Furthermore, D2 is 0.3μm-1.5μm. Further limiting the grain size of the second surface of the copper foil effectively balances mechanical strength, surface smoothness, and interfacial electrochemical stability. A suitable and uniform grain size enhances the tensile strength and deformation resistance of the copper foil, reducing the risk of stretching, warping, and breakage during cell assembly and cycling, ensuring the structural integrity of the negative electrode current collector. Simultaneously, optimizing the surface microstructure reduces interfacial contact impedance unevenness and localized current concentration, lowering the possibility of copper foil corrosion. Strict control of the grain size on the second surface avoids corrosion due to excessively large grains or adverse bending performance due to excessively small grains, thus balancing the mechanical reliability and electrochemical performance of the second surface of the copper foil, improving the overall safety and lifespan of the battery.

[0077] For example, D2 can be a range of any one of 0.3μm, 0.5μm, 0.8μm, 1μm, 1.3μm, 1.5μm, or any two of them.

[0078] In some embodiments of this application, the electrolyte further includes a dinitrile compound, wherein the mass percentage of the dinitrile compound in the electrolyte is A2%; A2 and B1 satisfy:

[0079] 20≤B1 / A2≤900.

[0080] In this application, the dinitrile compound can be a compound commonly used in the art that contains two cyano groups (-CN) in its molecular structure.

[0081] When the electrolyte includes a dinitrile compound, the nitrogen atom in the cyano group (-CN) of the dinitrile compound contains a lone pair of electrons, which can act as an electron donor to interact with empty d orbitals or partially positively charged regions on the surface of copper foil (Cu) (such as Cu on a cuprous oxide Cu2O film). + The dinitrile compound forms coordination bonds and is firmly adsorbed onto the copper foil surface. Furthermore, the dinitrile compound molecules can be arranged side-by-side and orderly on the copper foil surface, with the cyano groups at both ends anchored to adjacent copper active sites. This arrangement efficiently covers the copper foil surface, forming a hydrophobic and dense adsorption layer. This adsorption layer acts as a physical barrier film, reducing the corrosion of the copper foil by HF in the electrolyte and minimizing the entry of sulfur from sulfur-containing additives in the electrolyte into the grain boundaries of the copper foil, thus lowering the risk of foil breakage. Additionally, the dinitrile compound can participate in the formation of the CEI film, improving the stability of the positive electrode active material at high temperatures. This compensates for the impact of sulfur-containing additives in the electrolyte on the high-temperature performance of the battery, ensuring both high-temperature safety and performance.

[0082] The inventors discovered in their research that when B1 / A2 > 900, the excessively high content of metal elements in the negative electrode current collector leads to an increase in the interfacial resistance between the negative electrode current collector and the active layer, affecting the battery's rate performance; when B1 / A2 < 20, the content of metal elements in the negative electrode current collector is too low, and even the presence of dinitrile compounds cannot sufficiently suppress the possibility of copper foil dissolution, posing a risk of copper foil corrosion; when 20 ≤ B1 / B2 ≤ 900, the battery can simultaneously possess both low internal resistance and excellent ability to suppress copper foil corrosion.

[0083] For example, B1 / A2 can be a range of any one or any two of 20, 30, 50, 90, 100, 200, 400, 500, 700, 900.

[0084] In some embodiments of this application, when 1%≤A2%≤5%, by precisely controlling the appropriate content of dinitrile compounds in the electrolyte, sufficient dinitrile compounds are formed on the surface of the positive electrode active particles to form a CEI film. This effectively suppresses the dissolution of transition metals and side reactions in the positive electrode active material under high voltage. Furthermore, the cyano groups (-CN) in the dinitrile compounds can preferentially adsorb and moderately reduce on the surface of the negative electrode current collector (such as copper foil), forming a dense, stable, and low-impedance SEI film. This film can isolate corrosive components in the electrolyte (such as free HF and solvent decomposition products) from direct contact with the negative electrode current collector, while suppressing the oxidation and dissolution of metals and side reactions in the negative electrode current collector, avoiding localized corrosion and pitting corrosion. This effectively slows down or even prevents the electrolyte from corroding the negative electrode current collector. It can also prevent excessive dinitrile compounds from increasing the impedance of the CEI film and reducing the stability of the SEI film, resulting in a battery with both excellent cycle performance and rate performance.

[0085] For example, A2% can be a range of any one of 1%, 2%, 3%, 4%, 5%, or any two of them.

[0086] In some implementations, high-performance liquid chromatography-mass spectrometry (HPLC-MS) can be used to determine the mass percentage of dinitrile compounds in the electrolyte.

[0087] In some embodiments of this application, A2 / A1 > 1. On the one hand, sufficient trinitrile compounds can be retained to protect the positive electrode active material, maintaining the structural stability and electrochemical performance of the positive electrode active material at high temperatures; on the other hand, dinitrile compounds are used to regulate the complexation behavior of trinitrile compounds on copper foil, reducing the complexation of trinitrile compounds on copper foil, and dinitrile compounds can fill the pores in the adsorption layer formed by trinitrile compounds. The two work together to form a dense adsorption layer at the defects of copper foil, and after the dinitrile compounds form the adsorption layer, there will be no excess cyano groups attracting corrosive anions (such as Cl). -Water molecules gather around it, reducing or even avoiding the formation of highly active local corrosion micro-regions at the defects of the adsorption layer, further inhibiting the continuous dissolution of copper ions and the precipitation of copper metal on the surface of the negative electrode. This reduces the risk of copper dissolution while taking into account high-temperature performance, and further improves the high-temperature safety and cycle performance of the battery.

[0088] This application does not specifically limit the dinitrile compound, and it can be any compound containing two cyano groups commonly used in the art. Exemplarily, the dinitrile compound may include at least one selected from succinic anion, glutaronitrile, adiponitrile, tetramethylsuccinic anion, 1,4-dicyano-2-butene, 1,4-di(cyanoethoxy)butane, 1,3-di(2-cyanoethoxy)propane, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, and 1,4-dicyano-2,3-diethyl-2-butene.

[0089] In some embodiments, the dinitrile compound is a linearly symmetrical compound, for example, a dinitrile compound with a cyano group at each end. When the dinitrile compound has a linearly symmetrical structure, it can be arranged more closely on the copper foil surface, forming a hydrophobic and dense adsorption layer, further reducing the corrosion of the copper foil by HF in the electrolyte.

[0090] In some embodiments of this application, the electrolyte further includes fluoroethylene carbonate (FEC), wherein the mass percentage of fluoroethylene carbonate in the electrolyte is less than 13%.

[0091] Fluorinated ethylene carbonate (FEC) readily undergoes a ring-opening reaction with lithium pentafluorophosphate, a decomposition product of lithium salts (such as lithium hexafluorophosphate), leading to an increase in HF in the electrolyte and increasing the risk of HF corrosion of copper foil. Controlling the mass percentage of FEC to less than 13% can reduce the risk of HF corrosion of copper foil caused by excessive FEC.

[0092] Furthermore, when the electrolyte also includes a specific amount of FEC, precise synergy can be achieved in negative electrode film formation, interface stability, ion conduction, and safety performance: an appropriate amount of FEC can preferentially reduce and form a high-strength, high-density, and low-resistance SEI film on the surface of the negative electrode, significantly inhibiting the continuous decomposition and side reactions of the electrolyte, and improving the battery cycle life and high-temperature storage stability; its fluorine atoms can enhance the film's resistance to oxidation, solvent swelling, and lithium plating, while also taking into account the electrolyte's ionic conductivity and low-temperature charge-discharge performance; strictly controlling the specific content can avoid excessive FEC leading to increased viscosity, decreased rate capability, and increased gas production, and also prevent insufficient content from causing weak film formation and lifespan degradation, thereby maximizing the overall reliability, safety, and electrochemical performance of the battery.

[0093] For example, the mass percentage of fluoroethylene carbonate in the electrolyte can be any one of 12.9%, 12.8%, 12.5%, 10%, 8%, 7%, 6%, or any combination thereof.

[0094] In some implementations, high performance liquid chromatography-mass spectrometry (HPLC-MS) can be used to separately determine the mass percentage of FEC in the electrolyte.

[0095] In some embodiments of this application, the negative electrode sheet further includes a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising silicon-based particles.

[0096] In some embodiments of this application, the silicon-based particles include bulk silicon-based particles, wherein the average number of facets of the bulk silicon-based particles is less than or equal to 8.

[0097] In this application, the negative electrode active layer can be located on one side surface of the negative electrode current collector to form a negative electrode sheet, and the negative electrode active layer can also be located on both sides surface of the negative electrode current collector to form a negative electrode sheet.

[0098] During the coating and rolling process of the negative electrode sheet, due to the high hardness of silicon-based particles, the negative electrode current collector is squeezed by the bulk silicon-based particles during rolling. The sharp edges of the bulk silicon-based particles can easily scratch the negative electrode current collector, damage the protective layer, and cause the copper foil to deform and stretch. On the one hand, the stretching prevents the original protective layer from covering the newly exposed copper foil, resulting in the protective layer not providing adequate protection for the copper foil. On the other hand, the squeezing of the copper foil by the silicon-based particles causes the copper foil surface to become uneven, which increases the surface energy of the copper foil, making it more susceptible to corrosion by fluoride ions in the solution. The solution of this application is particularly suitable for mitigating the damage of bulk silicon-based particles to the negative electrode current collector and improving the cycle performance of the battery. Furthermore, the average number of sharp edges of the bulk silicon-based particles is less than or equal to 8, which can further reduce the damage of bulk silicon-based particles to the copper foil, slow down the damage to the protective layer, and slow down the corrosion of the copper foil.

[0099] In some embodiments of this application, the average particle size of the bulk silicon-based particles is 5μm-12μm. At this size, the particle size of the bulk silicon-based particles is suitable, which can not only reduce the compression of the negative electrode current collector by the bulk silicon-based particles, but also absorb some of the pressure due to the large gaps between the bulk silicon-based particles, further reducing the compression of the negative electrode current collector and extending the service life of the negative electrode current collector.

[0100] The average particle size of the bulk silicon-based particles refers to the average distance between any two points on the outer contour of the largest cross-section of the bulk silicon-based particles, with the line connecting the two points passing through the body center of the largest cross-section.

[0101] In some implementations, a cross-sectional SEM image of the negative electrode active layer can be obtained, and the average particle size of the bulk silicon-based particles can be obtained from the cross-sectional SEM image.

[0102] For example, the average particle size of the bulk silicon-based particles is a range of any one of 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, or any two of them.

[0103] In some embodiments of this application, when the mass percentage of silicon-based particles in the negative electrode active material is greater than 10%, the battery capacity can be improved. Furthermore, combined with 1.5≤S1 / A1≤23 and 70ppm≤B1≤650ppm, the cycle performance of the battery can be guaranteed, thereby obtaining a battery with both excellent capacity and cycle performance.

[0104] This application does not specifically limit the silicon-based particles; any silicon-based particle commonly used in the art can be used. For example, silicon-based particles may include elemental silicon, silicon oxide compounds (such as SiO2), etc. x One or more of the following: silicon-carbon composites (e.g., silicon carbide), silicon-nitrogen composites, and silicon alloys.

[0105] In some embodiments of this application, the silicon-based particles also include spherical silicon-based particles with a Dv50 of 6μm-15μm.

[0106] Compared to bulk silicon particles, spherical silicon particles do not have sharp edges, which can reduce the scratches on the protective layer during rolling. Furthermore, compared to bulk silicon particles, spherical silicon particles are subjected to more uniform force. Under the same force, the absence of sharp edges results in less deformation of the copper foil, reducing the exposure of fresh copper foil and thus reducing corrosion of the copper foil in the electrolyte.

[0107] When the Dv50 of spherical silicon-based particles is 6μm-15μm, an optimal balance can be achieved between structural stability, ion transport, rate performance, and cycle life. This effectively alleviates the huge volume effect of silicon during lithium insertion / extraction, reduces the risk of pulverization of spherical silicon-based particles, cracking of the anode active layer, and repeated rupture and reconstruction of the SEI film, and improves the structural integrity and long-term cycle stability of the anode active layer. At the same time, it shortens the lithium-ion diffusion path, reduces the transmission impedance, and improves fast charging and high-rate discharge performance. Strict control of particle size can avoid stress concentration and aggravated pulverization due to excessive size, or excessive specific surface area, increased side reactions, and reduced initial coulombic efficiency due to excessively small size. Thus, it balances the capacity utilization, processability, and electrochemical reliability of silicon-based anodes, and improves the overall performance and safety stability of the battery.

[0108] For example, the Dv50 of the spherical silicon-based particles can be any of 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or any combination thereof.

[0109] In some embodiments of this application, the percentage of spherical silicon particles in the silicon-based particles is 30%-90%, which can achieve a precise balance between structural stability, processability, and electrochemical performance. An appropriate proportion of spherical silicon particles can reduce the cost of the battery while making the negative electrode sheet more uniformly stressed during the rolling process. Under the same force, the deformation of the copper foil will be smaller, reducing the exposure of fresh copper foil and thus reducing the corrosion of the copper foil in the electrolyte. Moreover, spherical silicon particles can effectively alleviate the anisotropic stress during the lithium insertion and extraction process, reduce cracks and pulverization, and maintain structural integrity. At the same time, it can also optimize the conductive network and ion transport channels between silicon particles, reduce interface impedance, and improve rate performance. Strictly controlling the proportion can avoid stress concentration and cycle decay caused by too many blocky silicon particles, or surface area imbalance and increased side reactions caused by too many spherical silicon particles, thus taking into account the processability, structural stability, and long cycle life of the negative electrode sheet including silicon particles.

[0110] For example, the percentage of spherical silicon-based particles in the silicon-based particles can be any one of 30%, 40%, 50%, 70%, 80%, 90%, or any combination thereof.

[0111] In some implementations, a cross-sectional SEM image of the negative electrode active layer can be obtained, and the particle size of the spherical silicon particles, the particle size and number of edges of the blocky silicon particles, and the percentage of spherical silicon particles can be obtained from the cross-sectional SEM image of the negative electrode active layer.

[0112] In some implementations, the Dv50 of the spherical silicon-based particles is measured using a laser particle size analyzer before the negative electrode active layer is prepared.

[0113] In some embodiments of this application, the negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer stacked together, with the first negative electrode active layer close to the negative electrode current collector.

[0114] The first negative electrode active layer includes a first negative electrode active material, and the second negative electrode active layer includes a second negative electrode active material. The content of silicon-based particles in the first negative electrode active material is less than the content of silicon-based particles in the second negative electrode active material.

[0115] The negative electrode sheet comprises, in the thickness direction, a negative electrode current collector, a first negative electrode active layer, and a second negative electrode active layer. In this application, the first negative electrode active layer and the second negative electrode active layer may have a clear boundary line, or they may be an integral structure.

[0116] In some embodiments, silicon content in the cross-section of the negative electrode active layer can be measured using a scanning electron microscope and an energy dispersive X-ray spectrometer, respectively, in the region of the negative electrode active layer near the negative electrode current collector and the region of the negative electrode active layer far from the negative electrode current collector. The silicon content can then be used to calculate the silicon-based particle content in the first negative electrode active material and the silicon-based particle content in the second negative electrode active material.

[0117] By including a first negative electrode active layer and a second negative electrode active layer with different compositions in the negative electrode active layer, the first negative electrode active material in the first negative electrode active layer closer to the negative electrode current collector has a lower content of silicon-based particles; the second negative electrode active material in the second negative electrode active layer farther away from the negative electrode current collector has a higher content of silicon-based particles. When the content of silicon-based particles in the first negative electrode active layer is low, the compression of the negative electrode current collector can be reduced, and the rolling damage of the negative electrode current collector by silicon-based particles can be reduced. Furthermore, due to the stress relief of the first negative electrode active layer, the elongation of the copper foil can be reduced, thereby reducing the corrosion of the negative electrode current collector. The higher content of silicon-based particles in the second negative electrode active layer can increase the battery capacity.

[0118] In some embodiments of this application, the mass percentage of silicon-based particles in the first negative electrode active material is less than or equal to 40%, which can give the battery both excellent cycle performance and capacity.

[0119] Preferably, the first negative electrode active material is a carbon-based material. In this case, the first negative electrode active material does not contain silicon-based materials. The carbon-based material has lower hardness, which can reduce the damage to the negative electrode current collector caused by the negative electrode active material to a greater extent. This application does not particularly limit the carbon-based material, and it can be any carbon-based material commonly used in the art. For example, the carbon-based material may include at least one of graphite, hard carbon, soft carbon, intermediate carbon microspheres, and composite carbon materials.

[0120] In some embodiments of this application, when the mass percentage of silicon-based particles in the second negative electrode active material is greater than 40%, the battery can have both excellent cycle performance and capacity.

[0121] In some embodiments of this application, the negative electrode active layer (including a first negative electrode active layer and a second negative electrode active layer) further includes a negative electrode conductive agent and a negative electrode binder.

[0122] In some embodiments of this application, the negative electrode conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, graphene, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0123] In some embodiments of this application, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyurethane, polyacrylonitrile, acrylate adhesives, polytetrafluoroethylene (PTFE), lithium polyacrylate (PAALi), polyacrylic acid (PAA), sodium polymethyl cellulose (CMC-Na), and lithium polymethyl cellulose (CMC-Li).

[0124] In some embodiments, the mass percentage of the negative electrode conductive agent in the negative electrode active layer can be 0.5%-8% (e.g., 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%), and the mass percentage of the negative electrode binder can be 0.5%-18% (e.g., 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, or 18%).

[0125] It is understood that the battery also includes a separator and a positive electrode, with the positive electrode, separator, and negative electrode stacked together. This application does not limit the specific structure of the positive electrode, which can be a positive electrode commonly used in the art. For example, the positive electrode may include a positive current collector and a positive active layer located on at least one side surface of the positive current collector.

[0126] The positive electrode active layer may include a positive electrode active material, a conductive agent, and a binder. The positive electrode active material may include one or more of lithium nickel oxide, lithium titanate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide; the conductive agent may be selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite, and graphene; and the binder may be selected from one or more of polyvinylidene fluoride (PVDF), acrylic-modified PVDF, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene, polyacrylonitrile, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0127] In some embodiments of this application, the positive electrode active material includes a positive electrode substrate and a coating layer located on at least a portion of the surface of the positive electrode substrate; the positive electrode substrate includes LiCoO2; the coating layer includes Li7La. 3-a Zr 2-b M a+b O 12 M includes at least one of Fe, Ti, Cu and Mn, where 0.01≤a≤0.5 and 0.05≤b≤0.3.

[0128] The positive electrode active material in the positive electrode active layer includes the positive electrode substrate and the coating layer from the inside out. The coating layer can be located on the entire surface of the positive electrode substrate or on a portion of the surface of the positive electrode substrate.

[0129] The cathode substrate includes LiCoO2, which offers a combination of advantages: high discharge platform, high compaction density, excellent rate performance, and good cycle stability. Its regular layered structure and unobstructed lithium-ion diffusion channels enable high voltage and high specific capacity output, improving battery energy density. Its high compaction density further enhances volumetric energy density. Its excellent electronic conductivity meets the requirements for fast charging and high-rate discharging. Its strong structural stability allows for controllable phase transitions during charging and discharging, effectively suppressing lattice distortion and transition metal dissolution. When combined with a stable electrolyte system, it can significantly extend cycle life, improve high-temperature storage and safety performance, making it particularly suitable for lithium-ion battery systems with stringent requirements for energy density, voltage platform, and cycle consistency.

[0130] The coating layer includes Li7La 3-a Zr 2-b M a+b O 12 Li7La 3-a Zr 2-b M a+b O 12 It exhibits excellent chemical stability, which can significantly suppress the side reactions of LiCoO2 under high pressure and reduce the deposition of electrolyte decomposition products on the positive electrode surface, thereby improving the high-temperature cycle performance of the battery and extending its cycle life.

[0131] In some embodiments, the battery of this application still exhibits excellent electrochemical performance at a voltage of 4.53V.

[0132] This application also provides an electronic device including the aforementioned battery. This battery exhibits excellent rate performance and cycle performance under high voltage, making it suitable for various electronic devices (e.g., new energy vehicles and energy storage devices).

[0133] The present invention will be further described below with reference to specific embodiments.

[0134] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; and the reagents and materials are commercially available unless otherwise specified.

[0135] Example 1

[0136] The battery in this embodiment is prepared by a method including the following steps:

[0137] 1) Preparation of positive electrode sheet

[0138] The positive electrode active material LiCoO2, the binder polyvinylidene fluoride (PVDF 500), and the conductive material (Super P: carbon nanotubes = 2:1) were mixed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 98:2:2 and continuously stirred under the action of a stirrer to form a homogeneous and fluid positive electrode slurry. Subsequently, the positive electrode slurry was coated on both surfaces of an aluminum foil with a thickness of 10 μm and dried in a vacuum oven at 120 °C for 6 hours. Then, it was rolled and slit to obtain the positive electrode sheet.

[0139] 2) Preparation of negative electrode sheet

[0140] Graphite, conductive material (carbon black: carbon nanotubes = 1:4), sodium carboxymethyl cellulose, and binder (styrene-butadiene rubber: polyurethane = 1:2) were mixed in an aqueous solvent at a mass ratio of 98:1:0.5:0.5 and continuously stirred under the action of a stirrer to form a uniform and flowing first negative electrode slurry.

[0141] Silicon carbon particles (including spherical and blocky silicon carbon particles), graphite, conductive material (carbon black: carbon nanotubes = 1:4), sodium carboxymethyl cellulose, and binder (styrene-butadiene rubber: polyurethane = 1:2) are mixed in an aqueous solvent at a mass ratio of 88:10:1:0.5:0.5 and continuously stirred under the action of a stirrer to form a uniform and flowing second negative electrode slurry.

[0142] Subsequently, using a double-layer coating technology, the first negative electrode slurry and the second negative electrode slurry are coated on the two surfaces of the negative electrode current collector with a thickness of 8μm. The first negative electrode slurry is located on the surface of the negative electrode current collector. The sample is placed in a vacuum oven at 120℃ and dried for 6 hours. Then, after rolling and slitting, a negative electrode sheet including the first negative electrode active layer and the second negative electrode active layer is obtained.

[0143] The negative electrode current collector includes a copper foil and a protective layer on both surfaces of the copper foil. The protective layer includes Cr element, and the chromium content in the protective layer is 220 ppm.

[0144] 3) Electrolyte preparation

[0145] In an argon-filled glove box (moisture <1 ppm, oxygen <1 ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), and ethyl propionate (EP) were mixed in a volume ratio of 1:1:1:1 to form a homogeneous solvent. Then, 16% LiPF6, 2.9% adiponitrile, 1.8% 1,3,6-hexanetrionitrile, and 12.6% fluoroethylene carbonate (by mass percentage) were slowly added. After thorough stirring, the electrolyte was obtained.

[0146] 4) Preparation of the diaphragm

[0147] Alumina and polyacrylic acid are mixed at a mass ratio of 96:4 and dispersed in solvent water. After thorough stirring, a first mixed slurry with a solid content of 25% is obtained. The first mixed slurry is coated onto one side of a polyethylene substrate using a gravure roller. After drying in a multi-section oven at 60°C, a heat-resistant coating is formed with a thickness of 1μm.

[0148] Alumina and polyvinylidene fluoride were mixed and dispersed in N,N-dimethylacetamide at a mass ratio of 30:70. After stirring evenly, a second mixed slurry with a solid content of 10% was obtained. The second mixed slurry was continuously coated onto the heat-resistant coating on the side of the polyethylene substrate away from the polyethylene substrate and the other side of the polyethylene substrate using a gravure roller. Then, it was dried and shaped in a multi-section oven at a temperature of 60°C to obtain a diaphragm.

[0149] 5) Preparation of lithium-ion batteries

[0150] A bare cell is prepared by winding a positive electrode, a separator, and a negative electrode, with the first surface of the copper foil close to the center of the battery. The bare cell is then placed in an aluminum-plastic film, and electrolyte is injected into the dried bare cell. After vacuum sealing, room temperature standing, and high temperature formation, a lithium-ion battery is obtained.

[0151] The specific parameters of the battery are shown in Table 1 and Table 2.

[0152] Example 2

[0153] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0154] 2) Preparation of negative electrode sheet

[0155] The second negative electrode slurry is directly coated onto the two surfaces of the negative electrode current collector to obtain a negative electrode sheet including a negative electrode active layer.

[0156] Example 3

[0157] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0158] 2) Preparation of negative electrode sheet

[0159] The first negative electrode slurry also includes spherical silicon-carbon particles, which replace part of the graphite. The mass ratio of spherical silicon-based particles to graphite is 10:88.

[0160] The preparation methods of the batteries in Examples 4-19 and Comparative Examples 1-5 are basically the same as those in Example 1, with the differences shown in Tables 1 and 2. When the content of one or more electrolyte components in Table 1 is changed, the other components in the electrolyte are increased or decreased proportionally to make the sum of all electrolyte components 100%. The difference between Comparative Example 3 and Example 1 is that the second surface of the copper foil is closer to the center of the battery.

[0161] Performance testing

[0162] The following performance tests were performed on the batteries of the examples and the comparative examples, and the results are shown in Table 2.

[0163] 1) Cycle retention rate test

[0164] At 45°C, the lithium-ion battery was charged and discharged at a rate of 1.5C charging / 0.5C discharging. The discharge capacity Q2 of the 1000th charge and discharge cycle and the discharge capacity Q1 of the 1st charge and discharge cycle were recorded. The capacity retention rate was calculated as Q2 / Q1×100%.

[0165] 2) Fracture of the negative electrode current collector

[0166] The battery was disassembled after 200 cycles to obtain the negative electrode sheet. The fracture status of the negative electrode current collector was observed against the light. If the negative electrode current collector was intact, without any visible cracks, and did not transmit light, the fracture level was 0. If the negative electrode current collector had a minor crack that did not penetrate the current collector and showed point-like light transmission, the fracture level was 1. If the negative electrode current collector had a crack that penetrated the current collector, and the length of the transmitted light was less than 10% of the width of the current collector, the fracture level was 2. If the negative electrode current collector had a crack that penetrated the current collector, and the length of the transmitted light was greater than or equal to 10% but less than 50% of the width of the current collector, the fracture level was 3. If the negative electrode current collector had a crack that penetrated the current collector, and the length of the transmitted light was greater than or equal to 50% of the width of the current collector, or if the current collector was completely broken, the fracture level was 4.

[0167] 3) Pitting on the surface of the negative electrode

[0168] Fully charge a fresh battery, disassemble the battery, and observe the negative electrode in a fully charged state using a 2.5D magnification of 200x. Any obvious black or gray spots are called pits. Observe the pit locations under SEM and use EDS to confirm that the pit locations are Cu elements, which are pits caused by copper foil corrosion. Calculate the proportion of the pit area in the surface area of ​​the negative electrode in the SEM image.

[0169] 4) Ratio performance

[0170] At 25℃, charge and discharge the battery at 0.1C and record the discharge capacity C1 at 0.1C; charge and discharge the cell at 2C and record the discharge capacity C2 at 2C. The ratio of C2 / C1 measures the rate performance.

[0171] 5) Furnace temperature test pass rate

[0172] Place 30 batteries under a certain high temperature (130℃) for 30 minutes and observe whether the batteries catch fire or explode. Batteries that do not catch fire or explode are considered to have passed. Calculate the pass rate.

[0173] Table 1

[0174]

[0175]

[0176] Table 2

[0177]

[0178]

[0179] As can be seen from Tables 1 and 2, the negative electrode current collector in the battery of this application embodiment is not prone to corrosion and breakage, and the obtained battery has excellent cycle performance, rate performance and furnace temperature performance. This proves that by matching the content of trinitrile compound in the electrolyte with the number of large grains on the first surface of the copper foil near the winding center of the negative electrode current collector, the average grain size of the grains on the first surface of the copper foil is larger than the average grain size on the second surface. This further optimizes the content of metal elements in the protective layer on the surface of the copper foil, which can reduce the possibility of corrosion of the negative electrode current collector, improve the bending resistance of the negative electrode current collector, and improve the cycle performance, rate performance and high temperature performance of the battery.

[0180] As can be seen from Examples 1 and 2-5, 10-19, optimizing the composition of the negative electrode and electrolyte in the battery can further improve the overall performance of the battery. In particular, as can be seen from Examples 5 and 1, when the silicon-based particles include both spherical and blocky silicon-based particles, the negative electrode current collector can still have excellent corrosion resistance and bending resistance while reducing costs, and the resulting battery still has excellent cycle performance, rate performance, and furnace temperature performance. As can be seen from Examples 10 and 1, by optimizing the number of large grains on the first surface of the negative electrode current collector, the processing cost of the negative electrode current collector can be reduced, and the negative electrode current collector can still have excellent corrosion resistance and bending resistance, resulting in a battery with excellent cycle performance, rate performance, and furnace temperature performance.

[0181] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A battery, characterized in that, Including the negative electrode and the electrolyte; The negative electrode sheet includes a negative electrode current collector, which includes a copper foil and a protective layer; the copper foil includes a first surface and a second surface disposed opposite to each other along its thickness direction, and the protective layer is located on the first surface and the second surface; The copper foil comprises grains, the average grain size of the grains on the first surface is D1, the average grain size of the grains on the second surface is D2, and D1 > D2; the percentage of grains with a grain size greater than 1.5 μm in the first surface is S1%; The protective layer includes a metal element, which includes at least one of chromium and nickel, and the mass content of the metal element in the negative electrode current collector is B1. The electrolyte comprises a trinitrile compound, and the mass percentage of the trinitrile compound in the electrolyte is A1%. Among them, 1.5≤S1 / A1≤23, 70ppm≤B1≤650ppm.

2. The battery according to claim 1, characterized in that, 3%≤S1%≤45%; preferably, 5%≤S1%≤30%; And / or, 0.5% ≤ A1% ≤ 4.5%; And / or, 200ppm≤B1≤500ppm; And / or, the trinitrile compound includes a long-chain trinitrile compound, the long-chain trinitrile compound having 5 or more carbon atoms, the long-chain trinitrile compound having a branched molecular structure or an asymmetric molecular structure, and the long-chain trinitrile compound having a mass percentage content of less than 3% in the electrolyte.

3. The battery according to claim 1 or 2, characterized in that, 0.05μm≤D1-D2≤0.8μm; preferably, 0.1μm≤D1-D2≤0.6μm; And / or, D1 is 0.3-1.5 μm; And / or, D2 is 0.3-1.5μm.

4. The battery according to any one of claims 1-3, characterized in that, The electrolyte further includes a dinitrile compound, and the mass percentage of the dinitrile compound in the electrolyte is A2%; A2 and B1 satisfy: 20≤B1 / A2≤900; Preferably, 1% ≤ A2% ≤ 5%; Preferably, A2 / A1 > 1.

5. The battery according to claim 4, characterized in that, The dinitrile compound includes at least one selected from succinic anion, glutaronitrile, adiponitrile, tetramethylsuccinic anion, 1,4-dicyano-2-butene, 1,4-di(cyanoethoxy)butane, 1,3-di(2-cyanoethoxy)propane, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, and 1,4-dicyano-2,3-diethyl-2-butene. And / or, the trinitrile compound includes at least one selected from 1,3,6-hexanetrionitrile, 1,2,6-hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,1,1-tris(cyanoethoxymethylene)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,2,6-tris(cyanoethoxy)hexane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, tris(2-cyanoethyl) phosphate, 1,2,4-butanetrionitrile, 1,3,5-cyclohexanetrionitrile, 1,3,5-phenyltricyanide, and 1,2,3-propanetrionitrile.

6. The battery according to any one of claims 1-5, characterized in that, The electrolyte also includes fluoroethylene carbonate, wherein the mass percentage of fluoroethylene carbonate in the electrolyte is less than 13%.

7. The battery according to any one of claims 1-6, characterized in that, The negative electrode sheet further includes a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising silicon-based particles; The silicon-based particles include bulk silicon-based particles, wherein the average number of facets of the bulk silicon-based particles is less than or equal to 8; And / or, the average particle size of the bulk silicon-based particles is 5 μm-12 μm; Preferably, in the negative electrode active material, the mass percentage of the silicon-based particles is greater than or equal to 10%.

8. The battery according to claim 7, characterized in that, The silicon-based particles also include spherical silicon-based particles, wherein the Dv50 of the spherical silicon-based particles is 6μm-15μm; Preferably, the percentage of spherical silicon-based particles in the silicon-based particles is 30%-90%.

9. The battery according to claim 7 or 8, characterized in that, The negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer stacked together, with the first negative electrode active layer close to the negative electrode current collector; The first negative electrode active layer includes a first negative electrode active material, and the second negative electrode active layer includes a second negative electrode active material. The content of silicon-based particles in the first negative electrode active material is less than the content of silicon-based particles in the second negative electrode active material. Preferably, in the first negative electrode active material, the mass percentage of the silicon-based particles is less than or equal to 40%; Preferably, in the second negative electrode active material, the mass percentage of the silicon-based particles is greater than 40%.

10. The battery according to any one of claims 1-9, characterized in that, The battery has a wound structure, with the first surface close to the center of the battery; and / or, The battery further includes a positive electrode sheet, 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 positive electrode substrate and a coating layer located on at least a portion of the surface of the positive electrode substrate; The positive electrode substrate includes LiCoO2; The coating layer includes Li7La 3-a Zr 2-b M a+b O 12 M includes at least one of Fe, Ti, Cu and Mn, where 0.01≤a≤0.5 and 0.05≤b≤0.3.

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