Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery. The battery comprises a negative plate, the negative plate comprises a negative current collector, a negative active layer located on the surface of at least one side of the negative current collector and a lithium supplementing layer located on the side, away from the negative current collector, of the negative active layer, the lithium supplementing layer comprises a lithium supplementing material, and the lithium supplementing material is provided with an inner core, a middle area and a surface layer area in the direction from the center to the surface; the surface layer area at least partially covers the outer surface of the middle area, and the middle area is located between the inner core and the surface layer area; the inner core comprises lithium magnesium alloy, and the diameter of the inner core is 10-50 [mu] m; the middle area comprises lithium carbonate and / or lithium phosphate, and the thickness of the middle area is 100-500 nm; the surface layer area comprises lithium polyacrylate, and the thickness of the surface layer area is 20-100 nm. The battery provided by the invention has good first coulombic efficiency, rate capability and cycling stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery. BACKGROUND

[0002] Currently, commercial lithium ion batteries mainly use graphite as the negative electrode material, but its theoretical specific capacity is limited, which is difficult to meet the development needs of the market for high energy density and high cycle stability batteries. In contrast, silicon-carbon materials have higher specific capacity, and silicon-doped negative electrode systems help to improve the energy density of the battery. However, such systems generally have large volume expansion and low first coulomb efficiency during the cycle process, which easily leads to electrode material pulverization and battery structure deformation, thereby limiting the actual contribution of energy density and affecting the overall cycle performance of the lithium ion battery. SUMMARY

[0003] During the cycle process of the battery, the irreversible loss of active lithium is one of the key factors leading to the performance degradation of the battery. For high energy density silicon-doped negative electrode systems, additional active lithium is often pre-stored through lithium supplement technology to offset the irreversible loss during the cycle, thereby optimizing the electrode interface and structural stability, and improving the cycle life and first coulomb efficiency of the battery. However, the present inventors have found that if pure lithium powder is selected for lithium supplement, the lithium supplement material will react with the residual water in the negative active layer, and while replacing water with an oil-based solvent (such as NMP) can avoid severe side reactions, the compatibility is still poor. At the same time, pure lithium powder has very high chemical activity and is easy to react with water or oxygen, which not only introduces safety risks, but can even cause spontaneous combustion or explosion, significantly increasing the safety hazards of the lithium supplement process.

[0004] The purpose of the present application is to overcome the deficiencies in the prior art and provide a battery having a lithium supplement layer on the surface of the negative electrode sheet. The lithium supplement layer contains a lithium supplement material with a multi-level structure, which includes a core, an intermediate zone and a surface layer. The core includes a lithium-magnesium alloy, the surface layer includes lithium polyacrylate, and the intermediate zone includes a composite layer formed by lithium phosphate and / or lithium carbonate. By providing a lithium supplement layer on the surface of the negative electrode, the first capacity loss of the battery can be compensated for, the problem of low first coulomb efficiency of the silicon-carbon negative electrode can be improved, thereby improving the cycle stability of high energy density lithium ion batteries and helping to alleviate the volume expansion of the battery during the cycle process.

[0005] To solve the above problems, the present application provides the following technical solutions: This invention provides a battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active layer located on at least one side of the surface of the negative electrode current collector, and a lithium replenishment layer located on the side of the negative electrode active layer away from the negative electrode current collector. The lithium replenishment layer comprises a lithium replenishment material having a core, an intermediate region, and a surface region in a direction from the center to the surface. The surface region at least partially covers the outer surface of the intermediate region, and the intermediate region is located between the core and the surface region. The core comprises a lithium-magnesium alloy, and the diameter of the core is 10 μm-50 μm. The intermediate region comprises lithium carbonate and / or lithium phosphate, and the thickness of the intermediate region is 100 nm-500 nm. The surface region comprises lithium polyacrylate, and the thickness of the surface region is 20 nm-100 nm.

[0006] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: (1) In this invention, the core of the lithium replenishment material includes a lithium-magnesium alloy. During the pre-lithiation process, lithium is gradually released from the lithium-magnesium alloy, which avoids the accumulation of lithium ions that may occur when replenishing lithium powder, resulting in excessively high local lithium concentration or even lithium dendrite growth. Compared with pure lithium powder, the lithium-magnesium alloy also has good mechanical properties, which can improve the overall structural stability of the lithium replenishment material. When used in silicon-carbon anode, it can improve the ability to withstand the volume expansion stress of silicon-carbon material, and alleviate the structural failure and active lithium loss caused by the volume expansion of silicon-carbon anode while ensuring the lithium replenishment efficiency. (2) In this invention, the intermediate region of the lithium replenishment material includes a composite layer composed of lithium carbonate and / or lithium phosphate. Both lithium carbonate and lithium phosphate have good stability against oxygen and water in the battery system. Lithium carbonate also has a certain degree of hygroscopicity, which can absorb water molecules and thus prevent water in the environment from directly contacting the core. The intermediate region can isolate water and oxygen in the environment and prevent the lithium magnesium alloy in the core from contacting water or oxygen, which would lead to increased side reactions and safety risks. (3) The surface region of the lithium replenishment material is a coating layer composed of lithium polyacrylate. The lithium replenishment material with the coating layer has improved stability in air and can further improve the compatibility between the lithium replenishment material and the oil-based components, thereby further improving the safety performance of the battery, suppressing lithium dendrites, optimizing the lithium replenishment effect of the battery, and improving the battery cycle stability and first coulombic efficiency. (4) In this invention, the thickness of the core, intermediate region and surface region in the lithium replenishment material is further adjusted within a suitable range to ensure efficient transport of lithium ions inside the lithium replenishment material and between the lithium replenishment layer and the negative electrode active layer, thereby improving the battery dynamic performance and first coulombic efficiency.

[0007] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0008] Figure 1 The diagram shown is a schematic diagram of the lithium replenishment material in one embodiment of the present invention.

[0009] Figure 2 The diagram shown is a schematic diagram of the lithium replenishment layer in one embodiment of the present invention.

[0010] Figure labeling: 10 is the surface region, 20 is the intermediate region, 30 is the core, 1 is the lithium replenishment material, 4 is the first region, and 5 is the second region. Detailed Implementation

[0011] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0012] The present invention provides a battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active layer located on at least one side of the surface of the negative electrode current collector, and a lithium replenishment layer located on the side of the negative electrode active layer away from the negative electrode current collector, the lithium replenishment layer comprising a lithium replenishment material having a core, an intermediate region and a surface region in a direction from the center to the surface, the surface region at least partially covering the outer surface of the intermediate region, the intermediate region being located between the core and the surface region.

[0013] In this invention, the core comprises a lithium-magnesium alloy, and the diameter of the core is 10μm-50μm, for example, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, or within any two of the above values.

[0014] In this invention, the intermediate region comprises lithium carbonate and / or lithium phosphate, and the thickness of the intermediate region is 100nm-500nm, for example, 100nm, 120nm, 140nm, 160nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, or within any two of the above values.

[0015] In one embodiment, the intermediate region comprises lithium carbonate and lithium phosphate.

[0016] In this invention, the surface region comprises lithium polyacrylate, and the thickness of the surface region is 20nm-100nm, for example, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, 35nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or within any two of the above values.

[0017] A lithium replenishment layer with a multi-level structure is formed on the surface of the negative electrode. The core consists of a lithium-magnesium alloy, the middle region consists of lithium phosphate and / or lithium carbonate, and the surface region consists of lithium polyacrylate (PAA-Li). This lithium replenishment material is used to form a lithium replenishment layer on the negative electrode, enabling precise lithium replenishment and significantly improving the initial coulombic efficiency and cycle capacity retention of the silicon-doped negative electrode. The lithium-magnesium alloy preferentially delithilates during charging, and Li... + The lithium, slowly released from the alloy, reacts with the silicon-carbon material with the electrolyte to achieve lithium intercalation and participate in the formation of the SEI film. This avoids a significant decrease in the battery's initial coulombic efficiency due to the loss of active lithium, and also avoids the risk of excessively high local lithium concentration and lithium dendrite growth that may occur when adding lithium from pure lithium powder, which would increase the risk of membrane puncture and negatively impact battery safety. The intermediate layer, made of lithium carbonate and / or lithium phosphate, coats the surface of the lithium-magnesium alloy. This isolates the highly active lithium-magnesium alloy from the electrolyte, oxygen, and water in the air, forming a physical barrier that mitigates side reactions and inhibits the continuous decomposition of the electrolyte, thereby improving the battery's cycle stability. The surface layer uses PAA-Li to improve the compatibility between the lithium-magnesium alloy and the oil-based components, avoiding safety risks when the lithium-magnesium alloy encounters N-methylpyrrolidone (NMP), and further improving the safety performance of the negative electrode containing lithium replenishment material. The reason is that water is often used as a solvent in negative electrode slurry. However, if pure lithium powder is used as the lithium replenishment material, the lithium replenishment material has high activity and is prone to react with the water remaining in the negative electrode, increasing the safety risk. Using an oil-based solvent (such as NMP) can avoid the occurrence of violent side reactions between pure lithium powder and residual solvent to a certain extent, but there is still a problem of poor compatibility between it and the oil-based components, which can easily cause safety risks during battery cycling. Therefore, a surface layer is set on the outer layer of the lithium replenishment material to further improve the compatibility between the lithium replenishment material and the oil-based components, thereby improving the safety performance of the battery.

[0018] Adjusting the diameter of the core and the thickness of the intermediate and surface regions within appropriate ranges can optimize the lithium replenishment effect of the lithium replenishment material, improving the battery's kinetic and safety performance. When the core diameter is too small (e.g., <10μm), the core has a large specific surface area, and the surface coating enhances the lithium replenishment effect. However, the increased contact area with the electrolyte leads to intensified side reactions, and the lithium replenishment material also carries the risk of aggregation, resulting in increased local lithium concentration and potentially triggering lithium plating. When the core diameter is too large (e.g., >50μm), the path for lithium ions to escape from the lithium replenishment material lengthens, which is detrimental to improving lithium replenishment efficiency and battery rate performance. When the thickness of the intermediate region is too small (e.g., <100nm), the intermediate region cannot effectively isolate the electrolyte and water and oxygen in the air, further intensifying side reactions, reducing the stability of the lithium replenishment material, and degrading battery safety performance. When the thickness of the intermediate region is too large (e.g., >500nm), the path for lithium ions to escape from the lithium replenishment material lengthens, which is also detrimental to improving lithium replenishment efficiency and battery rate performance. When the thickness of the surface region is too low (e.g., <200nm), the surface region accounts for too little, which cannot effectively improve the compatibility between the lithium replenishment material and the oil-based components, leading to a deterioration in the battery's safety performance. When the thickness of the surface region is too high (e.g., >100nm), the path for lithium ions to escape from the lithium replenishment material increases, which is not conducive to improving the lithium replenishment efficiency and the battery's rate performance.

[0019] like Figure 1 The diagram shown is a structural schematic of a lithium replenishment material in one embodiment of the present invention, wherein 10 is the surface region, 20 is the middle region, 30 is the core, and 1 is the lithium replenishment material.

[0020] In this invention, the diameter of the core, the thickness of the intermediate region, and the thickness of the surface region can be measured by conventional testing methods in the art, such as the following method: a certain amount of lithium replenishment material is treated with argon ion polishing technology to obtain a cross-sectional sample of the lithium replenishment material. The obtained cross-section is then imaged by scanning electron microscopy (SEM) and magnified to a certain magnification (e.g., 10K). The entire SEM image is processed by image processing software (such as Image Pro Plus). The core, intermediate region, and surface region are distinguished by the interface. The maximum diameter of the core is measured, and the thickness is measured at three different sites in both the intermediate region and the surface region. A total of 30 different lithium replenishment materials are measured, and the core diameter, the thickness of the intermediate region, and the thickness of the surface region are measured and averaged.

[0021] In this invention, based on the total mass of the lithium-magnesium alloy, the mass content of Mg element is 0.5%-1.2%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, or within any two of the above values.

[0022] Maintaining the Mg content in lithium-magnesium alloys within a suitable range ensures the lithium replenishment efficiency of the material during battery cycling and reduces the risk of lithium dendrite growth. When the Mg content is too low (e.g., <0.5%), the lithium replenishment efficiency decreases, and lithium diffusion kinetics are affected. When the Mg content is too low (e.g., >1.2%), excessive lithium dendrite growth may lead to reduced lithium replenishment efficiency or localized lithium plating problems.

[0023] In this invention, along a first direction of the negative electrode sheet, the surface of the negative electrode sheet includes alternately distributed first and second regions. The first region includes the lithium replenishing material, wherein the lithium replenishing material has a unit area mass content of 0.2 mg / cm³ in the first region. 2 -10mg / cm 2 For example, 0.2 mg / cm³ 2 0.5 mg / cm 2 1mg / cm 2 2mg / cm 2 4mg / cm 2 6mg / cm 2 8mg / cm 2 10mg / cm 2 Or it falls within the range formed by any two of the above values.

[0024] In this invention, the first region and the second region may also be alternately distributed along a first direction perpendicular to the negative electrode sheet.

[0025] In this invention, the width ratio of the first region to the second region is (1-5):1, for example, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or within any two of the above values.

[0026] In this invention, the width of the first region is 1mm-5mm, for example, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm or 5mm.

[0027] In this invention, the width of the second region is 1mm-2mm, for example, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm or 2mm.

[0028] In this invention, the second region does not include the lithium replenishment material.

[0029] In this invention, the battery further includes tabs, and the first direction refers to the direction along which the tabs extend.

[0030] In this invention, the first region and the second region are formed by intermittently replenishing lithium by providing a lithium replenishment layer on the surface of the negative electrode active layer away from the negative electrode current collector. The first region is the lithium replenishment region and the second region is the non-lithium replenishment region.

[0031] In this invention, the width of the first region and the width of the second region have the conventional meaning in the art, referring to the average value of the size of a single first region and the size of a single second region along the first direction.

[0032] Adjusting the mass content per unit area of ​​the lithium replenishment material in the first region to a suitable range can mitigate the impact of lithium replenishment residue on battery performance while ensuring the lithium replenishment effect. When the mass content per unit area of ​​the lithium replenishment material in the first region is too low (e.g., <0.2 mg / cm³), it can negatively affect battery performance. 2 The amount of lithium replenishing material used is insufficient, and it cannot fully replenish the Li consumed in SEI film formation. + This leads to the deactivation of active sites due to the depletion of active lithium, and the SEI film also becomes structurally unstable due to insufficient active lithium, continuously consuming electrolyte, which is detrimental to the structural stability of the negative electrode and further improvement of the battery's initial coulombic efficiency and rate performance; when the mass content per unit area of ​​the lithium replenishment material in the first region is too high (e.g., >10 mg / cm³), 2 At this point, the negative electrode is over-lithiated, and the excess lithium additive releases a large amount of Li. + This catalyzes side reactions in the electrolyte, leading to battery bloating and excessive Li. + It can also deposit lithium dendrites on the surface of the negative electrode, which can easily increase the risk of the separator being punctured, thus hindering the improvement of battery safety performance.

[0033] Adjusting the width ratio of the first and second regions can indirectly control the amount of lithium replenishment material, significantly improving the initial coulombic efficiency of the battery with minimal impact on rate performance. This is because after lithium replenishment, the lithium residue formed by the replenishment material (such as lithium fluoride) adversely affects lithium-ion transport, making it difficult for lithium ions to intercalate into the negative electrode active material, thus deteriorating the kinetic performance of the negative electrode. By interspersing lithium replenishment material on the surface of the negative electrode and adjusting the width of the regions where the lithium replenishment material is placed, efficient lithium replenishment can be ensured while reducing the adverse effects of lithium residue on lithium-ion transport. The second region is a non-lithiation region, free from the obstruction of lithium residue, allowing lithium ions to pass through unimpeded, which is beneficial for balancing the kinetics of the negative electrode and improving the cycle life of the lithium replenishment system. In addition, conventional negative electrode sheets have uneven specific capacity distribution. Using interspersed lithium replenishment allows lithium ions to diffuse from the replenishment region to the non-lithiation region, improving the uniformity of the specific capacity distribution of the negative electrode and avoiding the problems of low lithium replenishment efficiency and interface lithium deposition caused by full-surface lithium replenishment. When the width ratio of the first region to the second region is too low (e.g., less than 1:1), the width of the first region is too low while the width of the second region is too high, resulting in a low proportion of the lithium replenishment area in the lithium replenishment layer, reducing the lithium replenishment efficiency and hindering the improvement of the battery's initial coulombic efficiency. When the width ratio of the first region to the second region is too high (e.g., greater than 5:1), the width of the first region is too high while the width of the second region is too low, the lithium replenishment residue in the negative electrode sheet hinders the migration efficiency of lithium ions, which is not conducive to improving the battery's rate performance.

[0034] like Figure 2 The diagram shown is a schematic diagram of the lithium replenishment layer in one embodiment of the present invention, wherein 4 is the first region and 5 is the second region.

[0035] In this invention, the ratio of the width of the first region to the width of the second region can be measured by conventional testing methods in the art, such as by scanning electron microscopy (SEM). Specifically, after imaging the lithium replenishment layer of the negative electrode sheet by SEM, the widths of the first and second regions at different locations on the image are measured by selecting the first region and the second region at different locations (points can be taken on the same first region or on different first regions), and the arithmetic mean is taken. The ratio is then calculated.

[0036] In this invention, whether or not lithium replenishment material is present can be determined by electrochemical testing. For example, if the constant current constant voltage charging (CCCV) curve in the first week shows a characteristic slope inflection point at the 3.0V platform, it indicates that lithium in the replenishment region is successfully inserted.

[0037] In this invention, the battery further includes a positive electrode plate, the projection area of ​​the positive electrode plate on the negative electrode plate is a fourth region, and the area of ​​the negative electrode plate extending beyond the positive electrode plate is a third region.

[0038] In this invention, the lithium replenishing material in the third region has a unit area mass content of w1, and the lithium replenishing material in the fourth region has a unit area mass content of w2, where w1 > w2.

[0039] In this invention, w1 is 0.2 mg / cm³. 2 -20mg / cm 2 For example, 0.2 mg / cm³ 2 0.5 mg / cm 2 1mg / cm 2 2mg / cm 2 4mg / cm 2 6mg / cm 2 8mg / cm 2 10mg / cm 2 15mg / cm 2 20mg / cm 2 Or it falls within the range formed by any two of the above values.

[0040] In this invention, w2 is 0.1 mg / cm³. 2 -10mg / cm 2 For example, 0.1 mg / cm³ 2 0.5 mg / cm 2 1mg / cm 2 2mg / cm 2 4mg / cm 2 6mg / cm 2 8mg / cm 2 10mg / cm 2 Or it falls within the range formed by any two of the above values.

[0041] To further improve the problem of edge lithium plating caused by uneven current distribution in the negative electrode (SOC difference > 25%), SOC regulation is achieved through regional gradient lithium replenishment in the negative electrode. The third region located at the edge of the negative electrode has high impedance and uses lithium replenishment material with high mass content per unit area, while the fourth region located in the center has reduced mass content per unit area of ​​the lithium replenishment material. This allows for precise control of the amount of lithium replenishment material within the critical safety window, eliminating lithium plating problems, reducing local SOC differences, and improving the battery's fast charging capability.

[0042] In this invention, the relationship between w1 and w2 can be obtained by conventional testing methods in the art, such as by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), specifically as follows: after imaging the lithium replenishment layer of the negative electrode sheet by SEM, the content of element P in the third region and the fourth region is determined by EDS, and the relationship between w1 and w2 is determined by the magnitude of the P content.

[0043] In this invention, the battery includes a separator with a thickness of 5μm-15μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or within any two of the above values.

[0044] In one embodiment, the thickness of the diaphragm is 7 μm-12 μm.

[0045] Adjusting the separator thickness within a suitable range can improve battery safety performance without affecting battery energy density. When the separator thickness is too high (e.g., >15μm), the migration resistance of lithium ions increases, leading to increased Li-ion release from the lithium replenishment layer. + Decreased transmission efficiency leads to decreased lithium replenishment efficiency. Meanwhile, since the separator is an inactive material, excessive thickness can reduce the battery's energy density. When the separator thickness is too low (e.g., <5μm), lithium dendrite growth can occur if the local lithium concentration is too high. The low separator thickness increases the risk of lithium dendrites piercing the separator, which is detrimental to improving the battery's safety performance.

[0046] In this invention, the thickness of the separator can be obtained by conventional testing methods in the art, for example, by the following method: the separator is removed from the cell, and the separator is selected from the head, tail or superanode area of ​​the cell, where the separator is not bonded to the electrode, so that a relatively complete separator can be obtained. The separator is cleaned with anhydrous ethanol to remove electrolyte and residual lithium salt, and then placed in a vacuum oven at 40°C to dry and remove solvent, so as to obtain a test sample. A high-magnification image of the cross section of the obtained sample is taken with SEM, magnified to a certain magnification (e.g., 2K-5K), and the thickness of the separator is measured at 10 different points, and the average value is taken.

[0047] In this invention, the negative electrode active layer includes a negative electrode active material, which includes silicon-based material and carbon-based material. The silicon-based material includes at least one of nano-silicon particles, silicon-oxygen particles and silicon-carbon materials. The carbon-based material includes graphite, which includes artificial graphite and / or natural graphite.

[0048] In this invention, the median particle size Dv50 of the nano-silicon particles is 10nm-100nm, for example, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 25nm, 30nm, 35nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or within any two of the above values.

[0049] In this invention, the median particle size Dv50 of the silicon-oxygen particles is 1μm-20μm, for example, 1μm, 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, or within any two of the above values.

[0050] In this invention, the median particle size Dv50 of the graphite is 10μm-20μm, for example, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm or within any two of the above values.

[0051] In this invention, the median particle size Dv50 of the silicon-carbon material is 5μm-20μm, for example, 5μm, 6μm, 7μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, or within any two of the above values.

[0052] In this invention, the silicon-carbon material comprises a porous carbon matrix and silicon particles located in the pores within the porous carbon matrix.

[0053] In this invention, based on the total mass of the negative electrode active layer, the mass content of silicon element is 0.5%-70%, for example, 0.5%, 0.6%, 1%, 1.5%, 2%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, or within any two of the above values.

[0054] Silicon-oxygen particles and silicon-carbon materials in the negative electrode active layer can improve the overall specific capacity of the negative electrode sheet, while nano-silicon particles can achieve rapid lithium intercalation. Adjusting the median particle size Dv50 of silicon-based materials (silicon-carbon materials and / or silicon-oxygen particles and / or nano-silicon particles) within a suitable range is beneficial to improving the overall electrochemical performance of the negative electrode active material. When the median particle size Dv50 of silicon-carbon materials and / or silicon-oxygen particles and / or nano-silicon particles is too small, the silicon-carbon materials, silicon-oxygen particles, and nano-silicon particles have a high specific surface area and a large contact area with the electrolyte, resulting in the consumption of more active lithium during the first charging cycle, thus causing a low initial coulombic efficiency of the negative electrode active material. When the median particle size Dv50 of silicon-carbon materials and / or silicon-oxygen particles and / or nano-silicon particles is too large, the diffusion path of lithium ions inside the silicon-carbon materials, silicon-oxygen particles, and nano-silicon particles is long, resulting in poor kinetic performance of the negative electrode active material, which is not conducive to further improvement of battery rate performance. Graphite can buffer the volume expansion of silicon-based materials in the negative electrode active layer during battery cycling. Adjusting the median particle size Dv50 of graphite can further improve the lithium-ion transport efficiency. When the median particle size Dv50 of graphite is too large (e.g., >20μm), the transport path of lithium ions in graphite increases, the efficiency decreases, and it is not conducive to improving the overall dynamics of the negative electrode. When the median particle size Dv50 of graphite is too low (e.g., <10μm), its contact area with the electrolyte increases, which can easily lead to an increase in the amount of SEI film formed and an increase in the first irreversible lithium loss, which is not conducive to further improving the first coulombic efficiency of the battery.

[0055] In this invention, the median particle size Dv50 of the nano-silicon particles, the silicon-oxygen particles, the silicon-carbon material, and the graphite can be obtained by conventional testing methods in the art, such as by a laser particle size analyzer.

[0056] In this invention, the mass content of silicon in the negative electrode active layer can be obtained by conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and soaked in dimethyl carbonate (DMC) solvent for 12 hours, then rinsed with DMC solvent to remove the lithium salt adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active layer can then 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 (e.g., a TGA 550 thermogravimetric analyzer), the test sample amount is 5mg-15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 minutes, so that the non-silicon components in the negative electrode active layer volatilize while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash of the negative electrode active layer. The mass content of silicon in the negative electrode active layer can be calculated based on the mass of ash. The calculation formula is as follows: Mass content of silicon in the negative electrode active layer = 7 × mass of ash / (15 × mass of test sample).

[0057] In this invention, the outer surface of the graphite has a coating layer, which includes hard carbon.

[0058] In this invention, the thickness of the coating layer is 20nm-600nm, for example, 20nm, 30nm, 40nm, 50nm, 60nm, 80nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 600nm, or within any two of the above values.

[0059] Applying a coating layer to the graphite surface can prevent direct contact between silicon particles and the electrolyte, reducing side reactions and improving the structural stability of graphite. Simultaneously, hard carbon on the graphite surface provides a rapid diffusion channel for lithium ions, shortening the path for lithium ions to embed into the graphite and alleviating lithium ion accumulation on the graphite surface. Furthermore, hard carbon itself has good electronic conductivity, and coating the graphite surface can optimize the conductive network of the negative electrode and reduce charge transfer resistance. When the coating layer thickness is too low (e.g., <20nm), the coating layer on the graphite surface not only fails to adequately optimize the lithium ion diffusion channel and the electronic conductivity of the electrode, but also fails to effectively isolate excessive contact between graphite and the electrolyte, which is detrimental to further improving the structural stability and cycle performance of the battery. When the coating layer thickness is too high (e.g., >600nm), the proportion of active material in the negative electrode active layer decreases, which is detrimental to further improving the battery energy density.

[0060] In this invention, the thickness of the coating layer can be obtained by conventional testing methods in the art, such as by SEM, specifically as follows: the battery is discharged to 0% SOC, the negative electrode is disassembled and removed, the cross-section of the negative electrode is polished with an argon ion mill, and the obtained cross-section is imaged using backscatter imaging mode on a scanning electron microscope (SEM) device. Twenty different graphite particles are randomly selected, and the coating layer is distinguished by the interface. Three different positions are selected in each graphite particle, and the coating layer thickness is measured using electron microscopy image analysis software such as ImageJ. The coating layer thickness of all selected particles is measured and the average value is taken, which is the thickness of the coating layer.

[0061] In this invention, the graphite comprises a first particle and a second particle, wherein the median particle size Dv50 of the first particle is 15μm-22μm, for example, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 20μm, 21μm, 22μm or within any two of the above values.

[0062] In this invention, the median particle size Dv50 of the second particle is 3μm-8μm, for example, 3μm, 3.2μm, 3.4μm, 3.6μm, 3.8μm, 4μm, 4.5μm, 5μm, 6μm, 7μm, 8μm, or within any two of the above values.

[0063] In this invention, the mass ratio of the first particle to the second particle is 1.5-2.1, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1 or within any two of the above values.

[0064] In this invention, the first particle is formed from a plurality of primary particles, wherein "a plurality of" means that the number of the primary particles constituting the first particle is ≥2.

[0065] In this invention, the specific surface area of ​​the first particle is 1.5 cm². 2 / g-3cm 2 / g, for example, 1.5cm 2 / g, 1.6cm 2 / g, 1.7cm 2 / g, 1.8cm 2 / g、2cm 2 / g, 2.2cm 2 / g, 2.4cm 2 / g, 2.6cm 2 / g, 2.8cm 2 / g, 3cm 2 / g or within the range of any two of the above values.

[0066] In this invention, the specific surface area of ​​the second particle is 2 cm². 2 / g-10cm 2 / g, for example, 2cm 2 / g, 2.2cm 2 / g, 2.4cm 2 / g, 2.6cm 2 / g, 3cm 2 / g, 3.5cm 2 / g、4cm 2 / g, 5cm 2 / g、6cm 2 / g、7cm 2 / g、8cm 2 / g、9cm 2 / g, 10cm 2 / g or within the range of any two of the above values.

[0067] The first particle has a larger particle size and lower specific surface area, enabling it to construct a framework structure in the negative electrode active layer. The second particle has a smaller particle size and a larger specific surface area, allowing it to fill the gaps between particles, thereby optimizing the packing density, improving the overall energy density of the negative electrode, and shortening the lithium-ion transport path, reducing charge transfer resistance. When the mass ratio of the first particle to the second particle is too low (e.g., <1.5), the compaction density of the negative electrode is low, which is not conducive to further improving the energy density of the battery. At the same time, the overall specific surface area of ​​graphite increases, and the increased effective contact area with the electrolyte leads to aggravated side reactions, which is not conducive to improving the cycle stability of the battery. When the mass ratio of the first particle to the second particle is too high (e.g., >2.1), the battery kinetics decrease, resulting in insufficient specific capacity, which is not conducive to further improving the energy density and rate performance of the battery.

[0068] In this invention, the median particle size Dv50 of the first particle and the second particle can be obtained by conventional testing methods in the art, such as measuring it using a Malvern particle size analyzer. The testing steps are as follows: dispersing graphite in deionized water containing a dispersant (such as ethanol, content 0.02wt%-0.03wt%) to form a mixture, sonicating the mixture for 2 minutes, and then placing it in a Malvern particle size analyzer for testing. The resulting particle size distribution curve has two peaks.

[0069] In this invention, the specific surface area of ​​the first particle and the second particle can be obtained by conventional testing methods in the art, such as the Brunauer-Emmett-Teller (BET) test method, or by measuring with a TriStar II specific surface area analyzer, with N2 being the adsorbed gas.

[0070] In this invention, the compaction density of the negative electrode sheet is 0.9 g / cm³. 3 -1.85g / cm 3 For example, 0.9 g / cm³ 3 1g / cm 3 1.2g / cm 3 1.4g / cm 3 1.6g / cm 3 1.8g / cm 3 1.85g / cm 3 Or it falls within the range formed by any two of the above values.

[0071] Adjusting the compaction density of the negative electrode sheet within the aforementioned range can reduce the gaps between the active material particles, increase the packing density, and improve the overall energy density of the negative electrode sheet. It can also optimize electron transport efficiency between particles and reduce the internal resistance of the negative electrode sheet. A suitable compaction density can also adjust the porosity of the negative electrode sheet, helping to improve the wetting performance of the electrolyte. When the compaction density of the negative electrode sheet is too low (e.g., <0.9 g / cm³), it will negatively impact the overall energy density. 3 This is detrimental to further improvement of the overall energy density and kinetics of the negative electrode; when the compaction density of the negative electrode is too high (e.g., >1.85 g / cm³), it hinders further improvement. 3 If the porosity of the negative electrode is too low, the electrolyte will not wet properly, and the resistance to ion transport will increase, which will not be conducive to further improving the rate performance of the battery.

[0072] In this invention, the compaction density of the negative electrode sheet can be obtained by conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and removed. After soaking in DMC solvent for 12 hours, it is rinsed with DMC solvent to remove the lithium salt adhering to the negative electrode sheet. Then, the surface residue of the negative electrode sheet is washed off with deionized water and dried. At least 20 sites are selected on the negative electrode sheet, and the thickness of the negative electrode sheet at each site is measured using a micrometer. The average value h (in μm) is taken. The negative electrode sheet is punched into a disc with a diameter of 44.3 mm using a punching die. Ten discs are taken, and the mass of each disc is weighed. The average value m (in mg) is taken. The areal density M1 is calculated as M1 = (m - m1) × 100 / 1540.55, where m1 is the mass of the negative electrode current collector in the disc (in mg), and the areal density is in mg / cm³. 2The compaction density is calculated using the areal density M1 and the average thickness h, as follows: Compaction density = M1 × 20 / (h - thickness of the negative electrode current collector), where the unit of the thickness of the negative electrode current collector is μm.

[0073] The present invention also provides a method for preparing a lithium-replenishing material. When the intermediate region is lithium phosphate, the preparation of the lithium-replenishing material includes at least the following steps: S1, Li powder and Mg powder are melted under argon protection and atomized under high pressure to obtain lithium-magnesium alloy powder, which is the first precursor; S2, a Li3PO4 layer was prepared on the surface of lithium-magnesium alloy powder by plasma deposition using PH3 and O2 to obtain the second precursor; S3, the second precursor is dispersed in an ethanol solution of acrylic acid, an initiator is added to form a PAA-Li coating layer, and the lithium supplement material is obtained.

[0074] In this invention, the melting temperature is 500℃-1000℃.

[0075] In this invention, the atomization pressure is 10MPa-13MPa and the atomization time is 280s-380s.

[0076] In this invention, the plasma deposition power is 1kW-5kW and the deposition rate is 5nm / min-20nm / min.

[0077] In this invention, the concentration of the acrylic acid ethanol solution is 1wt%-10wt%.

[0078] In this invention, the initiator includes K2S2O8.

[0079] In this invention, the initiator content is 0.5wt%-5wt% based on the total mass of the acrylic acid ethanol solution.

[0080] In this invention, the polymerization reaction temperature is 50℃-100℃, and the polymerization reaction time is 20min-60min.

[0081] In this invention, step S3 further includes washing and drying.

[0082] When the intermediate region is lithium carbonate, step S2 in the preparation of the lithium replenishment material is replaced by the following preparation method: The lithium-magnesium alloy obtained in step S1 is subjected to surface oxidation treatment in a dry air and carbon dioxide mixed atmosphere at room temperature to 200°C to form an initial lithium carbonate layer. It is then dispersed in a CO2-containing system, and the temperature and pressure are adjusted to allow the lithium carbonate layer to grow further. After the reaction is completed, it is aged, washed and dried to obtain a third precursor with a lithium carbonate coating layer.

[0083] In this invention, the CO2-containing system includes a supercritical CO2 system and at least one of alcohols, ethers, and esters containing dissolved CO2. The supercritical CO2 system has a pressure of 7.5 MPa-30 MPa and a temperature of 31°C-80°C.

[0084] In this invention, the growth temperature of the lithium carbonate layer is 0℃-60℃, and the growth time is 0.5h-24h.

[0085] When the intermediate region consists of lithium carbonate and lithium phosphate, the order in which the lithium phosphate layer and the lithium carbonate layer are prepared during the preparation of the lithium replenishment material is not limited. For example, the lithium phosphate layer can be prepared first, followed by the lithium carbonate layer.

[0086] In this invention, the battery further includes an electrolyte. The electrolyte is composed of a solvent, a lithium salt, and additives. The solvent may include at least one of cyclic carbonates, linear carbonates, and carboxylic acid esters. The cyclic carbonate may include ethylene carbonate (EC) and / or propylene carbonate (PC). The linear carbonate may include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The carboxylic acid esters include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (MP), ethyl propionate (EP), and propyl propionate (PP). The lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorosulfonylimide (LiDSI), lithium dioxolane borate (LiBOB), lithium difluorooxolane borate (LiDFOB), and lithium perchlorate (LiClO4). The additives include at least one of vinylene carbonate (VC), ethyl difluoroacetate (DFEA), fluoroethylene carbonate (FEC), vinyl sulfate (PS), trimethyl phosphate (TMP), and adiponitrile (AND).

[0087] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0088] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0089] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0090] The following preparation examples illustrate the lithium supplementation material of the present invention.

[0091] Preparation Example 1: S1, 99.14wt% Li powder and 0.86wt% Mg powder were melted at 650℃ under argon protection, and then gas-atomized under high pressure to obtain lithium-magnesium alloy powder. The atomization pressure was 12MPa and the atomization time was 300s, thus obtaining the first precursor. S2, a Li3PO4 layer was prepared on the surface of lithium magnesium alloy powder by plasma deposition using PH3 and O2. The deposition power was 2kW, the deposition rate was 10nm / min, and the deposition time was 35min, thus obtaining the second precursor. S3, the second precursor is dispersed in an ethanol solution of acrylic acid, 1 wt% of initiator K2S2O8 is added, and polymerization is carried out at 80°C for 40 min to form a PAA-Li coating layer, thus obtaining the lithium supplement material, denoted as A1.

[0092] At this point, in the lithium replenishment material A1, the diameter of the core is 35 μm, the thickness of the middle region is 334 nm, and the thickness of the surface region is 56 nm.

[0093] Preparation Example 2: S1, 99.47wt% Li powder and 0.53wt% Mg powder were melted at 650℃ under argon protection, and then gas-atomized under high pressure to obtain lithium-magnesium alloy powder. The atomization pressure was 11.5MPa and the atomization time was 280s, thus obtaining the first precursor. S2, a Li3PO4 layer was prepared on the surface of lithium magnesium alloy powder by plasma deposition using PH3 and O2. The deposition power was 2kW, the deposition rate was 10nm / min, and the deposition time was 10min, thus obtaining the second precursor. S3, the second precursor is dispersed in an ethanol solution of acrylic acid, 1 wt% of initiator K2S2O8 is added, and polymerization is carried out at 80°C for 20 min to form a PAA-Li coating layer, thus obtaining the lithium supplement material, denoted as A2.

[0094] At this point, in the lithium replenishment material A2, the core diameter is 10 μm, the thickness of the middle region is 103 nm, and the thickness of the surface region is 21 nm.

[0095] Preparation Example 3: S1, 98.9 wt% Li powder and 1.1 wt% Mg powder were melted at 650 °C under argon protection, and then gas-atomized under high pressure to obtain lithium-magnesium alloy powder. The atomization pressure was 12.5 MPa and the atomization time was 320 s, thus obtaining the first precursor. S2, a Li3PO4 layer was prepared on the surface of lithium magnesium alloy powder by plasma deposition using PH3 and O2. The deposition power was 2kW, the deposition rate was 10nm / min, and the deposition time was 50min, thus obtaining the second precursor. S3, the second precursor is dispersed in an ethanol solution of acrylic acid, 1 wt% of initiator K2S2O8 is added, and polymerization is carried out at 80°C for 60 min to form a PAA-Li coating layer, thus obtaining the lithium supplement material, denoted as A3.

[0096] At this point, in the lithium replenishment material A3, the core diameter is 49 μm, the thickness of the middle region is 497 nm, and the thickness of the surface region is 100 nm.

[0097] Preparation Example 4: The preparation examples in this group are used to verify the effect of changes in the "proportion of Mg in lithium-magnesium alloys", as detailed below: Preparation Example 4a was carried out with reference to Preparation Example 1, except that the Li powder content in step S1 was 99.55 wt% and the Mg powder content was 0.45 wt%, and the resulting lithium supplement material was denoted as A4a. Preparation Example 4b was carried out with reference to Preparation Example 1, except that the Li powder content in step S1 was 98.68 wt% and the Mg powder content was 1.32 wt%, and the resulting lithium supplement material was denoted as A4b.

[0098] Preparation Example 5: The examples in this group are used to verify the impact of changes in the "intermediate region," as detailed below: Preparation Example 5a was carried out in accordance with Example 1, except that step S2 was different. The lithium-magnesium alloy obtained in step S1 was subjected to surface oxidation treatment at 150°C in a mixed atmosphere of dry air and carbon dioxide to form an initial lithium carbonate layer. Then, it was dispersed in a supercritical CO2 system, and the temperature was adjusted to 60°C and the pressure to 15 MPa, so that the lithium carbonate layer could be further grown at 50°C for 4 hours. After the reaction was completed, it was aged, washed and dried to obtain the third precursor. The final lithium supplement material was designated as A5a, with a thickness of 328 nm.

[0099] Preparation Example 5b was carried out in accordance with Preparation Example 3, except that a lithium carbonate layer was prepared on the surface of the prepared second precursor. Specifically, the obtained second precursor was subjected to surface oxidation treatment at 150°C in a mixed atmosphere of dry air and carbon dioxide to form an initial lithium carbonate layer. Then, it was dispersed in a supercritical CO2 system, and the temperature was adjusted to 50°C and the pressure to 10 MPa, so that the lithium carbonate layer could be further grown at 50°C for 2 hours. After the reaction was completed, it was aged, washed and dried to obtain a second precursor with a lithium carbonate coating layer. The final lithium supplement material was denoted as A5b, and the thickness of the middle region was 330 nm.

[0100] Comparative preparation example 1: This set of preparation examples is used to verify the effects of changes in "core diameter, intermediate region thickness, and surface region thickness", as detailed below: Comparative preparation example 1a was carried out with reference to preparation example 1, except that the atomization time in step S1 was 270s, the deposition time in step S2 was 9min, and the polymerization time in step S3 was 15min. The resulting lithium-supplementing material was denoted as D1a. At this time, the diameter of the core was 8μm, the thickness of the middle region was 97nm, and the thickness of the surface region was 16nm. Comparative preparation example 1b was prepared with reference to preparation example 1, except that the atomization time in step S1 was 330s, the deposition time in step S2 was 52min, and the polymerization time in step S3 was 70min. The resulting lithium-supplemented material was denoted as D1b. At this time, the diameter of the core was 53μm, the thickness of the middle region was 505nm, and the thickness of the surface region was 103nm.

[0101] Comparative preparation group 2: The preparation examples in this group are used to verify the impact of changes in the structure of "lithium supplementation materials", as detailed below: Comparing preparation example 2a, the preparation was carried out with reference to preparation example 1, except that step S2 was not performed. The resulting lithium replenishment material is denoted as D2a. At this time, the lithium replenishment material does not contain the intermediate region. Comparing preparation example 2b, the preparation was carried out with reference to preparation example 1, except that step S3 was not performed. The resulting lithium replenishment material is denoted as D2b. At this time, the lithium replenishment material does not contain the surface layer region. Comparative preparation example 2c was carried out with reference to preparation example 1, except that steps S2 and S3 were not performed. The resulting lithium replenishment material is denoted as D2c. In this case, the lithium replenishment material does not contain the intermediate region and the surface region.

[0102] Comparative preparation example 3: The preparation was carried out in accordance with Example 1, except that the core was made of pure lithium powder and no high-pressure atomization step was required. The resulting lithium-added material was denoted as D3.

[0103] The following examples illustrate the battery of the present invention.

[0104] Example 1: (1) Preparation of the positive electrode: Lithium cobalt oxide, carbon black, and polyvinylidene fluoride (PVDF) are added to a vacuum mixer in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) is added and the mixture is thoroughly mixed under vacuum until a uniform and fluid positive electrode slurry is formed. The positive electrode slurry is then uniformly coated on both sides of an aluminum foil, dried, rolled, slit, and punched to obtain the positive electrode sheet.

[0105] (2) Preparation of negative electrode: The negative electrode active material, single-walled carbon nanotubes, polyacrylic acid (PAA), and styrene-butadiene rubber were added to a vacuum mixer in a mass ratio of 96.5:1.5:1:1. N-methylpyrrolidone (NMP) was added and the mixture was thoroughly mixed under vacuum until a uniform and fluid negative electrode slurry was formed. The negative electrode slurry was uniformly coated on both sides of the carbon-coated copper foil, dried, rolled, slit, and punched to obtain the negative electrode sheet. The lithium replenishing material A1 was uniformly attached to one side of the polyethylene terephthalate (PET) film, with the side containing the lithium replenishing material facing the negative electrode active layer. The lithium replenishing material was pressed onto one side of the negative electrode sheet by rolling to form a lithium replenishing layer. The preparation of the lithium replenishing layer on the other side of the negative electrode sheet was repeated.

[0106] The negative electrode active material is composed of silicon-carbon material and graphite with a hard carbon coating layer in a mass ratio of 15:85. The thickness of the graphite hard carbon coating layer is 110 nm. The graphite has a first particle and a second particle, with a mass ratio of 1.8 between the first particle and the second particle. The particle size Dv50 of the silicon-carbon material is 11.8 μm, the particle size Dv50 of the graphite is 15.2 μm, the particle size Dv50 of the first particle is 18.5 μm, the particle size Dv50 of the second particle is 5.8 μm, and the mass content of silicon in the negative electrode active layer is 7%.

[0107] (3) Battery fabrication: The positive electrode, separator (polyethylene, 9μm thick), and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The separator is then wound to form a core, which is placed in an aluminum-plastic film shell. After drying, electrolyte is injected. The battery is then obtained through processes such as encapsulation, aging, formation, secondary sealing, and sorting. The electrolyte is composed of EC, PC, PP, LiPF6, FEC, and PS in a mass ratio of 12:12:47:15:10:4.

[0108] Examples 2-4 and Examples 8-11, as well as the comparative example, were performed with reference to Example 1. In Example 10a, the mass ratio of silicon carbide to graphite was 1:99, and in Example 10b, the mass ratio of silicon carbide to graphite was 60:40. Specific settings are shown in Table 1. Table 1: Note:" "" indicates that the value is the same as that in Example 1, and " / " indicates that the relevant value does not exist.

[0109] Example 5 was performed in accordance with Example 1, except that the lithium replenishment layer had a first region and a second region. This was achieved by changing the preparation method of the lithium replenishment layer. Specifically, lithium replenishment material A1 was attached to one side surface of the PET film at intervals. In Examples 5a, 5b, 5c, 5d, and 5e, the mass content of lithium replenishment material per unit area in the first region was 5.3 mg / cm³, respectively. 2 0.5 mg / cm 2 9.8 mg / cm 2 0.15 mg / cm 2 and 10.2 mg / cm 2 ; Examples 6 and 7 are carried out with reference to Example 5a, except that the mass content of the lithium replenishing material per unit area is different in the third region and the fourth region. This is achieved by changing the preparation method of the lithium replenishing layer. Specifically, the lithium replenishing material A1 is attached to one side surface of the PET film at intervals, and the mass content of the lithium replenishing material per unit area is different in the regions corresponding to the third region and the fourth region in the negative electrode sheet. In Example 7, the entire lithium replenishing layer is provided, without the first region and the second region. The specific settings for Examples 5 through 7 are shown in Table 2: Table 2: Note:" "" indicates that the value is the same as or similar to that in Example 1, and " / " indicates that the relevant value does not exist.

[0110] Test example: (1) Cyclic capacity retention: The batteries obtained in the embodiments of the present invention and the batteries obtained in the preparation examples were tested at 25°C. They were charged at a constant current of 1C to 4.45V, charged at a constant voltage of 0.05C, left to stand for 10 minutes, discharged at 0.5C to 3V, left to stand for 10 minutes, and the first discharge capacity was recorded. Cyclic tests were performed using this charge and discharge procedure. The capacity retention rate after the 1000th discharge was obtained by dividing the capacity after the first discharge by the capacity after the 1000th discharge. The test results are recorded in Table 3.

[0111] (2) First Coulomb efficiency: The batteries obtained in the embodiments and preparation examples of this invention were charged at 25°C to 4.45V at 0.1C, with a cutoff current of 0.05C, and left to stand for 10 minutes. The initial charging capacity was recorded as Q. The batteries were then discharged at a constant current of 0.1C to 3.0V and left to stand for 10 minutes. The initial discharge capacity of the batteries was recorded as q. The initial coulombic efficiency of the batteries was then: η = q / Q × 100%. The test results are recorded in Table 3.

[0112] (3) Thickness expansion rate: The batteries obtained in the embodiments of the present invention and the batteries obtained in the preparation examples were tested at 25°C. They were charged at a constant current of 1C to 4.45V and charged at a constant voltage of 0.05C. The battery thickness was measured and recorded as the initial thickness h0. The battery thickness was tested once every 100T. This charge and discharge step was used to perform a 1000T cycle test. The thickness of the fully charged battery at the 1000T was recorded as h1. The thickness expansion rate is calculated as (h1-h0) / h0×100%. The test results are recorded in Table 3.

[0113] (4) 130℃ furnace temperature test: The batteries prepared in the embodiments of the present invention and the batteries prepared in the comparative examples were discharged to 3.0V at a discharge rate of 0.5C at room temperature, and then charged to the upper limit voltage at a discharge rate of 0.7C, with a cutoff current of 0.05C. The fully charged batteries were then placed in an oven and heated at a rate of 5±2℃. Once the temperature inside the oven reached 131±2℃, it was kept constant for 60 minutes. A battery that did not catch fire or explode was considered to have passed the test. Ten batteries were tested in each group, and the pass rate was recorded as N / 10, meaning N out of ten batteries passed the test. The test results are recorded in Table 3.

[0114] Table 3: As can be seen from Table 3, the battery prepared by the present invention improves the initial coulombic efficiency while also exhibiting good cycle performance, thickness expansion rate, and safety performance compared to the comparative example.

[0115] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active layer located on at least one side of the surface of the negative current collector, and a lithium replenishment layer located on the side of the negative active layer away from the negative current collector, the lithium replenishment layer includes a lithium replenishment material, the lithium replenishment material having a core, an intermediate region and a surface region in a direction from the center to the surface, the surface region at least partially covering the outer surface of the intermediate region, the intermediate region being located between the core and the surface region; The core comprises a lithium-magnesium alloy, and the diameter of the core is 10μm-50μm; The intermediate region includes lithium carbonate and / or lithium phosphate, and the thickness of the intermediate region is 100nm-500nm; The surface region comprises lithium polyacrylate, and the thickness of the surface region is 20nm-100nm.

2. The battery according to claim 1, wherein, Based on the total mass of the lithium-magnesium alloy, the mass content of Mg is 0.5%-1.2%; Along a first direction of the negative electrode, the surface of the negative electrode includes alternating first and second regions. The first region includes the lithium replenishing material, wherein the lithium replenishing material has a mass content of 0.2 mg / cm³ per unit area in the first region. 2 -10mg / cm 2 ; Preferably, the width ratio of the first region to the width of the second region is (1-5):

1.

3. The battery according to claim 2, wherein, The battery also includes a positive electrode plate, the projection area of ​​the positive electrode plate on the negative electrode plate is a fourth region, and the area of ​​the negative electrode plate that extends beyond the positive electrode plate is a third region; Preferably, the lithium replenishing material in the third region has a unit area mass content of w1, and the lithium replenishing material in the fourth region has a unit area mass content of w2, where w1 > w2.

4. The battery according to claim 3, wherein, w1 is 0.2 mg / cm 2 -20mg / cm 2 ; And / or, w2 is 0.1 mg / cm³ 2 -10mg / cm 2 .

5. The battery according to claim 1, wherein, The battery includes a separator with a thickness of 5μm-15μm; Preferably, the thickness of the diaphragm is 7μm-12μm.

6. The battery according to claim 1, wherein, The negative electrode active layer includes a negative electrode active material, which includes silicon-based material and carbon-based material. The silicon-based material includes at least one of nano-silicon particles, silicon-oxygen particles and silicon-carbon materials. The carbon-based material includes graphite, which includes artificial graphite and / or natural graphite. And / or, the median particle size Dv50 of the nano-silicon particles is 10nm-100nm; And / or, the median particle size Dv50 of the silicon-oxygen particles is 1μm-20μm; And / or, the median particle size Dv50 of the graphite is 10 μm-20 μm; And / or, the median particle size Dv50 of the silicon-carbon material is 5μm-20μm; Preferably, based on the total mass of the negative electrode active layer, the mass content of silicon element is 0.5%-70%; Preferably, the silicon-carbon material comprises a porous carbon matrix and silicon particles located in the pores within the porous carbon matrix.

7. The battery according to claim 6, wherein, The outer surface of the graphite has a coating layer, which includes hard carbon. And / or, the thickness of the coating layer is 20nm-600nm.

8. The battery according to claim 6, wherein, The graphite includes a first particle and a second particle, wherein the median particle size Dv50 of the first particle is 15μm-22μm; And / or, the median particle size Dv50 of the second particle is 3μm-8μm; Preferably, the mass ratio of the first particle to the second particle is 1.5-2.

1.

9. The battery according to claim 8, wherein, The specific surface area of ​​the first particle is 1.5 cm². 2 / g-3cm 2 / g; And / or, the specific surface area of ​​the second particle is 2 cm². 2 / g-10cm 2 / g.

10. The battery according to claim 1, wherein, The compaction density of the negative electrode sheet is 0.9 g / cm³. 3 -1.85g / cm 3 .

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