Lithium ion secondary battery

Abstract

The present application relates to the technical field of secondary batteries, and discloses a lithium ion secondary battery. The lithium ion secondary battery comprises a positive electrode sheet and a negative electrode sheet; a negative electrode active material in the negative electrode sheet comprises a silicon-carbon material and graphite, and the silicon content C is 1%-20% on the basis of the mass of a negative electrode active layer; a positive electrode active layer in the positive electrode sheet comprises lithium cobalt oxide and a solid-state electrolyte, the solid-state electrolyte comprises 2%-40% of Ti, and the maximum particle size D1 of the solid-state electrolyte is 500 nm-3 μm; lithium cobalt oxide comprises Ti and Al, and the particle size Dv10 of lithium cobalt oxide is greater than the average particle size D2 of the solid-state electrolyte; and on the basis of the mass of the positive electrode active layer, the Ti content is A ppm, and the Al content is B ppm, wherein 0.05<A / B≤0.3. The present application can solve the problems of poor low-temperature discharge performance and high-temperature safety of existing lithium ion secondary batteries.

Description

A lithium-ion secondary battery

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202510351256.5, filed on March 24, 2025, entitled “A Lithium-ion Secondary Battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application belongs to the field of secondary battery technology, specifically relating to a lithium-ion secondary battery. Background Technology

[0004] With the rapid development of electric vehicles, portable electronic devices, and energy storage systems, the performance requirements for secondary batteries (such as lithium-ion batteries) are increasing, especially the demands on energy density and driving range. Energy density is one of the key factors determining battery range, and improving energy density hinges on optimizing the positive and negative electrode materials. Currently, commercially available lithium-ion secondary battery negative electrode active materials mainly use graphite, with a theoretical specific capacity of 372 mAh / g. Although it exhibits good cycle stability and conductivity, its energy density is approaching its theoretical limit, making it difficult to meet the demands of future high-energy-density batteries.

[0005] Silicon boasts a theoretical specific capacity of up to 4200 mAh / g, far exceeding that of graphite, making it an ideal candidate for next-generation high-energy-density anode active materials. However, silicon undergoes significant volume changes during charge and discharge, particularly at high temperatures, which can easily damage the internal structure of the battery. This leads to problems such as battery expansion and leakage in lithium-ion secondary batteries using graphite-doped silicon anodes. Furthermore, compared to graphite, silicon-carbon materials have lower electrical conductivity, especially at low temperatures, where their electrochemical performance deteriorates further, affecting the battery's low-temperature discharge performance. Summary of the Invention

[0006] Therefore, the technical problem to be solved by this application is to overcome the defects of existing lithium-ion secondary batteries, namely poor low-temperature discharge performance and poor high-temperature safety.

[0007] Therefore, this application provides the following technical solution.

[0008] This application provides a lithium-ion secondary battery, including a positive electrode and a negative electrode. The negative electrode includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. The negative active layer includes a negative active material, which includes silicon-carbon material and graphite. Based on the mass of the negative active layer, the silicon content is C, and C is 1% to 20%.

[0009] The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive active layer includes a positive active material and a solid electrolyte. The maximum particle size D1 of the solid electrolyte is 500 nm to 3 μm.

[0010] The solid electrolyte includes Ti element, and the mass content of Ti element in the solid electrolyte is 2% to 40%;

[0011] The positive electrode active material includes lithium cobalt oxide, which includes Ti and Al elements; the particle size Dv10 of the lithium cobalt oxide is greater than the average particle size D2 of the solid electrolyte.

[0012] Based on the mass of the positive electrode active layer, the content of Ti element is Appm, and the content of Al element is B ppm, satisfying 0.05 < A / B ≤ 0.3.

[0013] In some implementations, 0.1 ≤ A / B ≤ 0.2 is satisfied.

[0014] In some embodiments, the maximum particle size D1 of the solid electrolyte is 0.5 μm to 2 μm.

[0015] In some embodiments, the silicon content (C) in the negative electrode active layer is 1% to 20%.

[0016] In some embodiments, the ratio of the Ti element content Appm (A) in the positive electrode active layer to the silicon element content C in the negative electrode active layer satisfies 1250 ≤ A / C ≤ 130000.

[0017] In some embodiments, the solid electrolyte includes at least one of lithium aluminum titanium phosphorus oxide and lithium lanthanum titanium oxide.

[0018] In some embodiments, the solid electrolyte has a mass content of 0.1% to 2% in the positive electrode active layer.

[0019] In some embodiments, the lithium cobalt oxide includes a first particle with a particle size D3 of 8 μm to 40 μm; and a plurality of solid electrolyte particles are distributed around the first particle, with a vertical distance of 0 to 6 μm between the solid electrolyte particles and the first particle.

[0020] In some embodiments, the content of Ti element Appm in the positive electrode active layer satisfies 500≤A≤2000.

[0021] In some embodiments, the content of Al element B ppm in the positive electrode active layer satisfies 5000≤B≤10000.

[0022] In some embodiments, the lithium cobalt oxide has a particle size Dv10 of 2 μm to 5 μm.

[0023] In some embodiments, the median particle size Dv50 of the lithium cobalt oxide is 10 μm to 20 μm.

[0024] In some embodiments, the positive electrode active layer further includes a first conductive agent, which comprises carbon nanotubes, and the content of the carbon nanotubes is 0.1% to 2% based on the mass of the positive electrode active layer.

[0025] In some embodiments, the diameter of the carbon nanotubes is 5 nm to 100 nm.

[0026] In some embodiments, the silicon content in the silicon-carbon material is 35% to 70% by mass.

[0027] In some embodiments, the graphite includes one or more of artificial graphite and natural graphite.

[0028] In some embodiments, the silicon-carbon material includes a carbon substrate and silicon particles dispersed within the pores of the carbon substrate.

[0029] In some embodiments, the negative electrode active layer further includes a second conductive agent, which includes single-walled carbon nanotubes with a diameter of 1-50 nm.

[0030] In some embodiments, the content of the single-walled carbon nanotubes is 0.01%-3% based on the mass of the negative electrode active layer.

[0031] In some embodiments, the lithium-ion secondary battery further includes an electrolyte comprising a solvent, the solvent comprising ethyl propionate, wherein the ethyl propionate content is 20% to 60% based on the mass of the electrolyte.

[0032] In some embodiments, the positive electrode further includes a positive tab electrically connected to the positive current collector, the positive tab extending from one side of the positive current collector in the width direction. The width direction refers to the direction along the shorter side of the positive current collector.

[0033] The lithium-ion secondary battery further includes a separator, and the positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound into a core; at least one surface of the core in the thickness direction is provided with an adhesive, and the projections of the adhesive and the positive electrode tab in the thickness direction of the core are staggered along the height direction of the core.

[0034] In some embodiments, the shortest distance between the projection of the positive electrode tab and the adhesive in the thickness direction of the core is S, which satisfies 100mm≥S>0.

[0035] In some embodiments, the adhesive has a first end protruding from the positive electrode tab along the core height direction, and the positive electrode current collector has a second end protruding from the positive electrode tab along the core height direction. The distance between the first end and the second end along the core height direction is K, satisfying 125mm ≥ K > 15mm. The width direction of the positive electrode current collector is consistent with the core height direction.

[0036] In some embodiments, the adhesive comprises a hot melt adhesive.

[0037] The technical solution of this application has the following advantages:

[0038] This application discloses a lithium-ion secondary battery comprising a positive electrode and a negative electrode. The negative electrode comprises a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. The negative active layer comprises a negative active material, which includes silicon-carbon material and graphite. Based on the mass of the negative active layer, the silicon content is C, and the C content is 1% to 20%. The positive electrode comprises a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive active layer comprises a positive active material and a solid electrolyte. The maximum particle size D1 of the solid electrolyte is 500 nm to 3 μm. The solid electrolyte comprises Ti, and the Ti content in the solid electrolyte is 2% to 40% by mass. The positive active material comprises lithium cobalt oxide, which comprises Ti and Al. The particle size Dv10 of the lithium cobalt oxide is greater than the average particle size D2 of the solid electrolyte. Based on the mass of the positive active layer, the Ti content is Appm, and the Al content is B. ppm, satisfying 0.05 < A / B ≤ 0.3.

[0039] This application research found that adding an appropriate amount of solid electrolyte with a specific particle size to the positive electrode active layer can compensate for the poor low-temperature discharge performance of the battery caused by the decrease in electrolyte conductivity. This application effectively improves the low-temperature discharge performance of the battery by reasonably controlling the maximum particle size D1 of the solid electrolyte particles within the range of 0.5μm-3μm. Combined with the ability of a graphite-doped silicon anode to increase the battery's energy density, the lithium-ion secondary battery provided by this application can improve low-temperature discharge performance while ensuring high energy density. Furthermore, the average particle size D2 of the solid electrolyte is smaller than the particle size Dv10 of lithium cobalt oxide, which reduces the possibility of agglomeration between the solid electrolyte and lithium cobalt oxide. The uniformly distributed solid electrolyte can still maintain good ion conductivity at low temperatures, thereby more effectively improving the conductivity of the positive electrode active layer at low temperatures and enhancing the low-temperature discharge performance of the battery. Simultaneously, by controlling the A / B value to be greater than 0.05 and less than or equal to 0.3, both low-temperature discharge performance and high-temperature safety of the battery can be balanced. The lithium-ion secondary battery provided by this application can improve both low-temperature discharge performance and high-temperature safety while ensuring high energy density.

[0040] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0042] Figure 1 is a SEM image of the positive electrode in Example 5;

[0043] Figure 2 is a magnified SEM image of the positive electrode in Example 5;

[0044] Figure 3. Top view of the core;

[0045] Figure 4 shows the front view of the core.

[0046] Reference numerals: 1-Adhesive; 2-Positive electrode tab; 3-Solid electrolyte particle; 4-Lithium cobalt oxide particle; S-Shortest distance between the projections of the positive electrode tab and the adhesive in the thickness direction of the core; K-Distance between the first end and the second end along the height direction of the core. Detailed Implementation

[0047] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0048] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0049] Related technologies incorporate solid electrolytes into the electrode sheets of lithium-ion secondary batteries, thereby constructing a solid electrolyte layer on the surface of the electrode material. This enhances the conductivity of lithium ions at the positive / negative electrode interface, optimizes the conductivity of the electrolyte system, and thus improves the battery's rate performance. Furthermore, by mixing solid electrolytes into the electrode sheets, the use of liquid electrolytes is reduced, enhancing the battery's high-temperature safety performance. However, these technologies do not address the battery's low-temperature discharge performance. As temperature decreases, the ionic conductivity of the electrolyte drops significantly, especially below 0°C where it drops drastically. Combined with the inherently poor conductivity of silicon-carbon materials, which hinders lithium-ion diffusion, this further deteriorates the battery's low-temperature discharge performance. In other words, lithium-ion secondary batteries using graphite-doped silicon-carbon anodes face the problem of failing to discharge normally in extreme low-temperature weather conditions (e.g., below -20°C).

[0050] To address the aforementioned problems, this application provides a lithium-ion secondary battery, comprising a positive electrode and a negative electrode. The negative electrode includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. The negative active layer comprises a negative active material, which includes silicon-carbon material and graphite. Based on the mass of the negative active layer, the silicon content is C, and C is 1% to 20%. For example, the silicon content C in the negative active layer can be 1%, 5%, 10%, 15%, 20%, etc., or a value within any two of the above values.

[0051] The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive active layer includes a positive active material and a solid electrolyte. The maximum particle size D1 of the solid electrolyte is 500 nm to 3 μm.

[0052] The solid electrolyte includes Ti element, and the mass content of Ti element in the solid electrolyte is 2% to 40%;

[0053] The positive electrode active material includes lithium cobalt oxide, which includes Ti and Al elements; the particle size Dv10 of the lithium cobalt oxide is greater than the average particle size D2 of the solid electrolyte.

[0054] Based on the mass of the positive electrode active layer, the content of Ti element is Appm, and the content of Al element is B ppm, satisfying 0.05 < A / B ≤ 0.3.

[0055] This study found that the ionic conductivity of solid electrolytes does not decrease significantly with decreasing temperature. By adding an appropriate amount of solid electrolyte with a specific particle size to the positive electrode active layer, lithium ions can be conducted along the solid electrolyte under extreme low temperature conditions, thereby replacing part of the electrolyte's conduction path and ensuring that the battery can discharge normally under low temperature conditions. This compensates for the defect of poor low-temperature discharge performance of the battery caused by the decrease in electrolyte conductivity.

[0056] The maximum particle size D1 of the solid electrolyte has a significant impact on improving the low-temperature discharge performance of the battery. If the particle size of the solid electrolyte is too large, its ability to conduct lithium ions decreases; conversely, if the particle size is too small, the particles are prone to agglomeration, neither of which can improve the low-temperature discharge performance of the battery. Therefore, this application can effectively improve the low-temperature discharge performance of the battery by reasonably controlling the maximum particle size D1 of the solid electrolyte within the range of 0.5μm-3μm. Combined with the ability of graphite-doped silicon anode to improve the energy density of the battery, the lithium-ion secondary battery provided by this application can improve the low-temperature discharge performance while ensuring a high energy density. For example, the maximum particle size D1 of the solid electrolyte can be 500nm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, or a value within any two of the above values.

[0057] Furthermore, the average particle size D2 of the solid electrolyte is smaller than that of lithium cobalt oxide Dv10, meaning that the solid electrolyte particles are smaller and the lithium cobalt oxide particles are larger. This particle size distribution reduces the contact area between particles, lowering the possibility of agglomeration between the solid electrolyte and lithium cobalt oxide. In addition, the smaller solid electrolyte particles are more easily and uniformly dispersed around the larger lithium cobalt oxide particles, thus better filling the gaps between the lithium cobalt oxide particles, forming a continuous ion conduction path, and improving ion transport efficiency. Since the uniformly distributed solid electrolyte can still maintain good ion conductivity at low temperatures, it can more effectively improve the conductivity of the positive electrode active layer at low temperatures, thereby improving the low-temperature discharge performance of the battery.

[0058] Meanwhile, this study found that the ratio of Ti to Al in the positive electrode active layer, A / B, affects the battery's low-temperature discharge performance and high-temperature safety. Ti can improve lithium-ion conductivity, especially at low temperatures. Introducing Ti can lower the lithium-ion migration barrier and enhance the ionic conductivity of the positive electrode active layer, thus enabling the battery to maintain a high discharge capacity at low temperatures. However, excessive Ti can affect the battery's discharge capacity at room temperature, thereby affecting energy density. Furthermore, solid electrolytes are prone to gas generation when stored under high temperature and high voltage conditions, affecting battery safety. Al can stabilize the layered structure of lithium cobalt oxide, suppressing phase transitions and oxygen release at high temperatures, thereby improving the battery's high-temperature safety. Appropriate amounts of Al have little impact on low-temperature performance, but excessive Al may increase lithium-ion migration resistance and reduce ionic conductivity at low temperatures. Therefore, by adjusting the A / B value to be greater than 0.05 and less than or equal to 0.3, both low-temperature discharge performance and high-temperature safety of the battery can be balanced.

[0059] If the A / B value is too small, meaning the Ti content is too low or the Al content is too high, the low-temperature discharge performance cannot be effectively improved. If the A / B value is too large, meaning the Ti content is too high or the Al content is too low, the battery's high-temperature safety may be compromised. For example, the A / B value can be 0.06, 0.10, 0.15, 0.20, 0.25, 0.30, or a value within any two of the above ranges.

[0060] By controlling the Ti content in the solid electrolyte to be between 2% and 40%, the amount of solid electrolyte added can be reduced while ensuring the Ti content in the positive electrode active layer. This increases the lithium cobalt oxide content in the positive electrode active layer, thereby improving the battery's specific capacity and energy density while enhancing its low-temperature discharge performance. If the Ti content in the solid electrolyte is too low, it will not significantly improve the electrolyte's ionic conductivity, making it difficult to improve the battery's low-temperature discharge performance. Furthermore, if the required solid electrolyte content is too high, it will reduce the proportion of positive electrode active material, ultimately leading to a decrease in the battery's energy density. Conversely, if the Ti content in the solid electrolyte is too high, it may form excessive insulating phase, causing a decrease in the electrolyte's ionic conductivity. This necessitates increasing the electrolyte amount to compensate for the performance loss, thus reducing the energy density. For example, the Ti content in the solid electrolyte can be 2wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, or values ​​within any two of these ranges.

[0061] In summary, the lithium-ion secondary battery provided in this application can improve low-temperature discharge performance and high-temperature safety while ensuring high energy density.

[0062] It should be noted that the maximum particle size D1 refers to the maximum diameter of solid electrolyte particles observed in the field of view using a scanning electron microscope (SEM). The testing method for D1 includes: discharging the lithium-ion secondary battery to 0% SOC, disassembling and removing the positive electrode sheet, soaking it in dimethyl carbonate (DMC) solvent for 12 hours, and then rinsing it with DMC to remove the lithium salts (lithium salts present in the electrolyte and attached to the positive electrode sheet) adhering to the electrode sheet, and then using an argon ion milling machine (CP laser) to cut the positive electrode sheet; using energy dispersive spectroscopy (EDS) to locate the Ti enrichment sites, and then performing a spot scan at 5K magnification. Particles with a total Ti content in the enrichment sites ranging from 2wt% to 40wt% are considered solid electrolyte particles. These particles are then observed under SEM at 5K magnification, and the maximum diameter of the solid electrolyte particles in the field of view is recorded as D1.

[0063] The average particle size D2 refers to the average particle size of 10 solid electrolyte particles within the field of view observed by SEM. The D2 testing method includes: discharging the lithium-ion secondary battery to 0% SOC, disassembling and removing the positive electrode sheet, soaking it in dimethyl carbonate (DMC) solvent for 12 hours, and then rinsing it with DMC to remove the lithium salt adhering to the electrode sheet. The positive electrode sheet is then cut using an argon-ion milling machine with a CP laser. EDS surface scanning is used to find the Ti enrichment sites, and spot scanning is performed at 5K magnification. Particles with a total Ti content in the enrichment sites ranging from 2wt% to 40wt% are considered solid electrolyte particles. Then, SEM is observed at 5K magnification. If there are more than 10 solid electrolyte particles in the field of view, 10 solid electrolyte particles are randomly selected and their average particle size is calculated and recorded as D2. If the number of solid electrolyte particles in the field of view is less than 10, the field of view is changed and the test is repeated.

[0064] The Ti content in the solid electrolyte was determined by EDS. The test method included: discharging the lithium-ion secondary battery to 0% SOC, disassembling and removing the positive electrode, soaking it in dimethyl carbonate (DMC) solvent for 12 hours, and then rinsing it with DMC to remove the lithium salts attached to the electrode (lithium salts present in the electrolyte and attached to the positive electrode), and cutting the positive electrode with an argon ion mill using a CP laser; and then using an energy dispersive spectroscopy (EDS) spectrometer at 5K rate to scan the solid electrolyte particles to determine the Ti content in the solid electrolyte.

[0065] The test method for Ti and Al content in the positive electrode active layer is as follows: After discharging the lithium-ion secondary battery to 0% SOC, the positive electrode sheet is disassembled and removed. It is then soaked in dimethyl carbonate (DMC) solvent for 12 hours and rinsed with DMC to remove the lithium salt adhering to the electrode sheet. After calcining in a muffle furnace at 400℃ for 3 hours, the residual material of the positive electrode active layer is gently scraped off from the surface of the positive electrode current collector. The residual material of the positive electrode active layer is prepared into a standard solution according to the method in GBT 30902-2014. The concentrations of Ti and Al in the standard solution are then measured according to the test method in GBT 30902-2014. These concentrations are the Ti and Al content in the positive electrode active layer. The Ti content is recorded as Appm and the Al content is recorded as B ppm.

[0066] Particle size Dv10 is the particle size corresponding to a cumulative volume distribution of lithium cobalt oxide particles reaching 10%, and particle size Dv50 is the particle size corresponding to a cumulative volume distribution of lithium cobalt oxide particles reaching 50%. The test method includes: discharging the lithium-ion secondary battery to 0% SOC, disassembling and removing the positive electrode sheet, soaking it in dimethyl carbonate (DMC) solvent for 12 hours, and then rinsing it with DMC to remove the lithium salt attached to the electrode sheet. After calcining it in a muffle furnace at 400℃ for 3 hours, the residual material of the positive electrode active layer is gently scraped off from the surface of the positive electrode current collector to obtain the composite material. The Malvern particle size analyzer is used for measurement. The test steps are as follows: the composite material is dispersed in deionized water containing a dispersant (such as nonylphenol polyoxyethylene ether, content 0.02~0.03wt%) to form a mixture. The mixture is sonicated for 2 minutes and then placed in the Malvern particle size analyzer for testing.

[0067] The method for testing the mass content (C) of silicon in the negative electrode active layer is as follows: Thermogravimetric analysis (TGA) is used. The specific method is as follows: After discharging the lithium-ion secondary battery to 0% SOC, the negative electrode is disassembled and removed. It is then soaked in dimethyl carbonate (DMC) solvent for 12 hours, followed by rinsing with DMC to remove the lithium salt adhering to the electrode. After drying, the electrode is subjected to high-temperature treatment at 400℃ in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active material layer can then be peeled off from the current collector, and the negative electrode active material is collected. In the silicon content test, a thermogravimetric analyzer (e.g., a TGA550 thermogravimetric analyzer) is used. The sample amount is 5–15 mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature to 900℃ at a rate of 10℃ / min, and held at 900℃ for 40 minutes. This allows the non-silicon components in the negative electrode active layer to volatilize while the silicon is fully oxidized to silicon dioxide. The weight percentage at the end of the entire test process is the ash content of the negative electrode active layer; the ash content is divided by the molar mass of silicon dioxide (60) and then multiplied by the molar mass of silicon (28) to obtain the percentage content of silicon in the negative electrode active layer.

[0068] In some embodiments, the Ti content (Appm) in the positive electrode active layer satisfies 500 ≤ A ≤ 2000. By controlling the Ti content in the positive electrode active layer within this range, lithium-ion conductivity and low-temperature discharge performance can be improved, while reducing the gas production of the solid electrolyte under high temperature and high pressure conditions, thus enhancing the battery's high-temperature safety. Too low a Ti content will not effectively improve low-temperature discharge performance; too high a Ti content may lead to poor high-temperature safety. By simultaneously controlling the Ti and Al content in the positive electrode active layer, both low-temperature discharge performance and high-temperature safety of the battery can be balanced. For example, the value of A can be 500, 800, 1000, 1500, 2000, or a value within any range of two of the above values.

[0069] In some embodiments, the Al content (Bppm) in the positive electrode active layer satisfies 5000 ≤ B ≤ 10000. By controlling the Al content in the positive electrode active layer within this range, the layered structure of lithium cobalt oxide can be stabilized, suppressing phase transitions and oxygen release at high temperatures, thereby improving the high-temperature safety of the battery while ensuring its low-temperature performance. If the Al content is too low, it will be difficult to improve the high-temperature safety of the battery; if the Al content is too high, it may increase the migration resistance of lithium ions, reduce the ion conductivity at low temperatures, and lead to a decrease in the low-temperature discharge performance of the battery. By simultaneously controlling the Ti and Al content in the positive electrode active layer, both the low-temperature discharge performance and high-temperature safety of the battery can be balanced. For example, the value of B can be 5000, 6000, 7000, 8000, 9000, 10000, or a value within any two of the above ranges.

[0070] In some embodiments, the silicon content C in the negative electrode active layer and the Ti content Appm in the positive electrode active layer satisfy the relationship 1250≤A / C≤130000; for example, the value of A / C can be 1250, 2000, 10000, 20000, 50000, 80000, 100000, 110000, 130000, etc., or a value within the range of any two of the above values.

[0071] Understandably, a higher silicon content in the negative electrode active layer ensures higher battery energy density, but also results in poorer low-temperature discharge performance. Consequently, more solid electrolyte needs to be added to the positive electrode active layer. This application achieves high energy density, good low-temperature discharge performance, and high-temperature safety simultaneously by adjusting the A / C value within the aforementioned range. If the A / C value is too high, it indicates a low silicon content in the negative electrode active layer, affecting battery energy density, or a large amount of solid electrolyte added to the positive electrode active layer, which can easily generate gas during high-temperature storage, affecting high-temperature safety. Conversely, if the A / C value is too low, it indicates a high silicon content in the negative electrode active layer, affecting low-temperature discharge performance, or a small amount of solid electrolyte added to the positive electrode active layer, limiting its improvement on low-temperature discharge performance and failing to achieve optimal performance.

[0072] In some embodiments, the particle size Dv10 of the lithium cobalt oxide is 2μm to 5μm. For example, Dv10 can be 2μm, 1.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, or a value within the range of any two of the above values.

[0073] When the particle size Dv10 of lithium cobalt oxide is too large, it indicates that the overall particle size of lithium cobalt oxide is too large, resulting in an excessively long lithium-ion transport path and a decrease in the conductivity of lithium cobalt oxide. Conversely, if Dv10 is too small, it indicates that the overall particle size of lithium cobalt oxide is too small, making it prone to particle agglomeration, which also affects its conductivity. Furthermore, small particles have a larger specific surface area, leading to poor high-temperature safety. Therefore, this application controls the particle size Dv10 of lithium cobalt oxide within the range of 2μm to 5μm. At this range, the proportion of large lithium cobalt oxide particles is relatively large, which helps improve high-temperature safety, but it affects conductivity. By adding a solid electrolyte, the adverse effects of large lithium cobalt oxide particles on conductivity can be compensated for, thereby enabling the battery to further balance low-temperature discharge performance and high-temperature safety.

[0074] In some embodiments, the median particle size Dv50 of the lithium cobalt oxide is 10–20 μm. This avoids excessive electrode thickness, which is beneficial for improving battery energy density. Furthermore, this particle size facilitates uniform lithium ion diffusion, reduces internal resistance at high temperatures, minimizes heat accumulation, and improves high-temperature performance. Simultaneously, it also benefits ion conduction at low temperatures, improving low-temperature performance. This application controls the Dv10 and Dv50 of the lithium cobalt oxide particles, ensuring that the lithium cobalt oxide particle size Dv10 is greater than the average particle size D2 of the solid electrolyte. This allows the solid electrolyte to be uniformly dispersed around the large lithium cobalt oxide particles, improving ion transport efficiency and low-temperature discharge performance while reducing internal resistance at high temperatures, thus enhancing the battery's high-temperature performance. For example, Dv50 can be 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, or a value within any two of these ranges.

[0075] In some embodiments, the solid electrolyte includes at least one of lithium aluminum titanium phosphorus oxide and lithium lanthanum titanium oxide, wherein the lithium aluminum titanium phosphorus oxide is a superionic conductor type lithium aluminum titanium phosphorus oxide, and its chemical formula may be Li. 1+u Al u Ti 2-u (PO4)3, 0 < u ≤ 0.5; Lithium lanthanum titanium oxide is a perovskite type lithium lanthanum titanium oxide, and its chemical formula can be Li 3v La 2 / 3-v TiO3, 0 < v ≤ 0.2.

[0076] The aforementioned solid electrolyte has strong ion conductivity and a high dielectric constant, and good affinity for electrolytes. When applied to the positive electrode, it can improve the ion transport capability of the positive electrode at low temperatures, enabling lithium-ion secondary batteries using graphite-doped silicon negative electrodes to have high energy density, as well as good low-temperature discharge performance and high-temperature safety.

[0077] In some embodiments, the solid electrolyte in the positive electrode active layer has a mass content of 0.1% to 2.0%, and for example, it may be 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, or a value within the range of any two of the above values.

[0078] If the content of solid electrolyte in the positive electrode active layer is too low, its effect on improving the battery's low-temperature discharge performance is not significant; however, if the content of solid electrolyte is too high, it will affect the battery's discharge capacity at room temperature, thereby affecting energy density. Furthermore, solid electrolyte is prone to gas generation when stored under high temperature and high voltage conditions, affecting the battery's safety performance. Therefore, controlling the content of solid electrolyte in the positive electrode active layer within the range of 0.1% to 2.0% can effectively improve the battery's low-temperature discharge performance without sacrificing energy density and high-temperature safety.

[0079] In some embodiments, the lithium cobalt oxide includes a first particle and a second particle, wherein the particle size D3 of the first particle is 8 μm to 40 μm, and the particle size of the second particle is less than 8 μm; a plurality of solid electrolyte particles are distributed around the first particle, and the vertical distance between the solid electrolyte particles and the first particle is 0 to 6 μm.

[0080] It should be noted that particle size D3 refers to the maximum distance between any two points on the contour of a lithium cobalt oxide particle. The D3 testing method includes: capturing particle images using SEM, analyzing the particle contour using image processing software (such as ImageJ), and measuring the maximum distance between any two points on the particle contour; this distance is the particle size D3. For example, D3 can be 8μm, 9μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, etc., or a value within any range of two of the above values.

[0081] Compared to the second particle (small lithium cobalt oxide particles), the first particle (large lithium cobalt oxide particles) has a longer internal transport path, resulting in lower ionic conductivity and thus affecting lithium-ion transport. To address this, this application, during the preparation of the cathode slurry, first mixes the solid electrolyte with lithium cobalt oxide, then adds conductive agents, binders, and other substances to ensure that the solid electrolyte is uniformly distributed around the large lithium cobalt oxide particles. This results in several solid electrolyte particles distributed around the large lithium cobalt oxide particles, with a vertical distance of 0–6 μm between the solid electrolyte particles and the large lithium cobalt oxide particles. This improves the lithium-ion transport network, further enhances the ionic conductivity of the cathode active layer, and improves the low-temperature discharge performance of the battery.

[0082] In some embodiments, the positive electrode active layer further includes a first conductive agent, which comprises carbon nanotubes with a diameter of 5 nm to 100 nm. Due to their unique structure, carbon nanotubes possess superior conductivity and lithium intercalation properties. Adding carbon nanotubes with a diameter of 5 nm to 100 nm to the positive electrode active layer can further improve the battery's low-temperature discharge performance and high-temperature safety. This application's research found that if the diameter of the carbon nanotubes is too small, they tend to aggregate, making it difficult to form a conductive network, which is detrimental to lithium-ion transport and also hinders the reduction of internal resistance, affecting the battery's low-temperature discharge performance and high-temperature safety. Conversely, if the diameter of the carbon nanotubes is too large, it affects their crystallinity, resulting in unsatisfactory conductivity, strength, and toughness, which in turn negatively impacts the battery's low-temperature discharge performance and high-temperature safety.

[0083] Furthermore, chemical reactions may occur when the solid electrolyte comes into contact with the electrolyte, leading to the formation of an interfacial layer, increasing interfacial impedance, and affecting ion conduction. Using carbon nanotubes with a diameter of 5nm to 100nm can restrict the distribution of the electrolyte in the positive electrode active layer, reducing the contact area between the electrolyte and the solid electrolyte, thereby lowering the probability of side reactions. Simultaneously, the electron and ion conduction pathways can be optimized by controlling the diameter of the carbon nanotubes and the amount of solid electrolyte added, thus suppressing side reactions while improving the overall performance of the battery. For example, the diameter of the carbon nanotubes can be 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or a value within any two of the above ranges.

[0084] In some embodiments, the carbon nanotube content is 0.1% to 2% based on the mass of the positive electrode active layer. For example, the carbon nanotube content may be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, or a value within any two of the above ranges.

[0085] In some embodiments, the graphite includes one or more of artificial graphite and natural graphite.

[0086] A higher silicon content in a graphite-doped silicon anode is more beneficial for improving the energy density of the battery, but it is detrimental to the diffusion of lithium ions in the anode at low temperatures. Therefore, in some embodiments, the mass content of silicon element in the silicon-carbon material is 35%-70%, for example, it can be 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc., or values ​​within any two of the above ranges.

[0087] To balance the contradiction between the energy density and low-temperature discharge performance of high-silicon anode batteries, a solid electrolyte is added to the positive electrode active layer. This allows lithium ions to be conducted along the solid electrolyte, replacing part of the electrolyte's conduction path and ensuring that the battery can discharge normally under low-temperature conditions. This improves the battery's low-temperature discharge performance while maintaining its high energy density.

[0088] In some embodiments, the silicon-carbon comprises a carbon substrate and silicon particles dispersed within the pores of the carbon substrate, the carbon substrate comprising porous carbon and a carbon layer coating at least a portion of the surface of the porous carbon, and the silicon particles comprising Si, SiO2, or SiO2. n One or more of the following, where 0 < n < 2.

[0089] In some embodiments, the negative electrode active layer further includes a second conductive agent, which comprises single-walled carbon nanotubes with a diameter of 1–50 nm. Due to their unique structure, single-walled carbon nanotubes possess superior conductivity and lithium intercalation properties. By adding single-walled carbon nanotubes with a diameter of 1–50 nm to the negative electrode active layer, a stable three-dimensional conductive network can be formed between silicon-carbon and graphite particles. This network not only adapts to changes in silicon volume but also maintains the continuity of the electron conduction path during charging and discharging, thereby forming an efficient electron conduction path between the negative electrode active materials. In other words, the mixing of single-walled carbon nanotubes and silicon-carbon particles can significantly improve the electronic conductivity of silicon-carbon and reduce internal resistance. If the diameter of single-walled carbon nanotubes is too small, they are prone to aggregation, making it difficult to form a conductive network. This hinders electron transport to the current collector and also impedes the reduction of internal resistance, affecting the battery's low-temperature discharge performance. Conversely, if the diameter is too large, it affects the crystallinity of the single-walled carbon nanotubes, resulting in unsatisfactory conductivity, strength, and toughness, which in turn negatively impacts the battery's low-temperature discharge performance and high-temperature safety. For example, the diameter of single-walled carbon nanotubes can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or a value within any two of these ranges.

[0090] In some embodiments, the mass content of the single-walled carbon nanotubes in the negative electrode active layer is 0.01% to 3%. For example, the mass content of single-walled carbon nanotubes in the negative electrode active layer can be 0.01%, 0.1%, 0.2%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, or a value within any two of the above ranges.

[0091] In some embodiments, the electrolyte includes ethyl propionate (EP), and the content of ethyl propionate is 20% to 60% based on the mass of the electrolyte. For example, the content of EP can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a value within any two of the above ranges.

[0092] EP is a carboxylic acid ester solvent. Its low boiling point and low viscosity give it good fluidity, which can reduce the viscosity of the electrolyte and facilitate electrolyte wetting of the electrodes. Excessive EP content leads to high-temperature decomposition and the generation of large amounts of gas, potentially causing battery bulging and other safety issues. Conversely, insufficient EP content results in high electrolyte viscosity, hindering wetting and increasing the risk of localized lithium plating. When the EP content is between 20% and 60%, the EP works synergistically with the solid electrolyte, further improving the battery's low-temperature performance on top of the improved low-temperature discharge performance from the doped solid electrolyte. Furthermore, the secondary battery's negative electrode is doped with silicon-carbon, resulting in a secondary battery with both high energy density and superior low-temperature discharge performance.

[0093] In some embodiments, a diaphragm and a positive electrode tab are also included. The positive electrode sheet is stacked and wound with the diaphragm and the negative electrode sheet to form a core. The positive electrode tab is electrically connected to the positive electrode sheet and extends from one side of the width direction of the positive electrode sheet.

[0094] An adhesive is provided on at least one surface of the core in the thickness direction, and the projections of the adhesive and the positive electrode tab in the thickness direction of the core are offset along the height direction of the core; the adhesive is used to bond the core to the shell.

[0095] In some implementations, 100mm ≥ S > 0, where S is the shortest distance between the projections of the positive electrode tab and the adhesive in the core thickness direction; for example, S can be 2mm, 5mm, 8mm, 10mm, 50mm, 80mm, 100mm, etc., or a value within any two of the above values. The core height direction is shown in Figure 3, and the core thickness direction is shown in Figure 4.

[0096] The thickest part of the battery core often appears at the tab. If the adhesive and the tab overlap, the thickness will increase, resulting in poor core flatness and greater compression at the thickest point after hot pressing. Since solid electrolytes are easily oxidized and decomposed to produce gas under high temperature and high voltage conditions, this obstructs the gas release path, causing the core to thicken easily at high temperatures. This application addresses this by misaligning the projections of the adhesive and the positive tab in the core thickness direction (i.e., not overlapping), thereby improving core flatness, ensuring unobstructed gas flow, and preventing localized gas blockage that could lead to interface separation, increased thermal-PPG thickness expansion rate, or even cell failure. The addition of solid electrolyte improves low-temperature discharge performance, while the misalignment of the adhesive and the positive tab prevents the solid electrolyte from affecting high-temperature safety due to high-temperature gas production. Therefore, the battery of this application possesses both good low-temperature discharge performance and high-temperature safety.

[0097] In some embodiments, the distance between the negative electrode tab and the adhesive projection in the core thickness direction is equal to S, and its function is as described above, so it will not be repeated here.

[0098] In some embodiments, the adhesive has a first end near the positive electrode tab along the height direction of the core, and the positive current collector has a second end near the positive electrode tab along the height direction of the core. The distance between the first end and the second end along the height direction of the core is K, satisfying 125mm ≥ K > 15mm. Since the lower edge of the positive electrode tab welded to the positive electrode sheet is not visible to the naked eye, the S value is difficult to determine. K is the distance from the upper edge of the adhesive to the upper edge of the current collector, which is more intuitive and easier to measure. Controlling K to > 15mm allows the projections of the adhesive and the positive electrode tab in the thickness direction of the core to be misaligned, avoiding the overlap of the adhesive and the electrode tab which would lead to an increase in thickness. This results in good core flatness, unobstructed gas conduction paths, and prevents an increase in the thermal-PPG thickness expansion rate. The addition of solid electrolyte improves low-temperature discharge performance, and controlling K to > 15mm allows for the misalignment of the adhesive and the positive electrode tab, thereby avoiding the impact of high-temperature safety on the solid electrolyte due to high-temperature gas generation. This allows the battery of this application to have both good low-temperature discharge performance and high-temperature safety. For example, K can be 16mm, 18mm, 20mm, 25mm, 50mm, 100mm, 125mm, etc., or a value within the range of any two of the above values.

[0099] In some embodiments, the adhesive includes a hot melt adhesive with good high-temperature resistance, maintaining good adhesion even at high temperatures to ensure the bonding effect between the core and the casing, enabling the lithium-ion secondary battery of this application to meet high-temperature storage requirements. For example, the hot melt adhesive may be at least one of polyamide, polyester, polyethylene, and polyesteramide.

[0100] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0101] The solid electrolyte Li used in Examples 1-19 1.3 Al 0.3 Ti 1.7 The preparation method of (PO4)3 (abbreviated as LATP) is as follows:

[0102] According to Li 1.3 Al 0.3 Ti 1.7 The stoichiometric ratio of Li, Al, Ti, and P in (PO4)3 was determined by weighing Li2CO3, AlOOH, TiO2, and NH4H2PO4, mixing them, and ball milling them with anhydrous ethanol as the solvent. The ball-milled raw material was dried for 5 hours and then placed in a corundum crucible. It was first calcined at 300°C for 2 hours and then calcined at 700°C for 4 hours. The solid material obtained after calcination was ball-milled again, dried, and sieved to obtain white LATP powder.

[0103] Example 1

[0104] This embodiment provides a method for preparing a secondary battery, including:

[0105] Step 1: Positive electrode preparation: Lithium cobalt oxide, solid electrolyte LATP, first conductive agent, and PVDF (polyvinylidene fluoride) are mixed in a mass ratio of 96.52:0.48:1:2, and NMP is added. The mixture is stirred evenly to prepare a positive electrode slurry. The positive electrode slurry is coated on both sides of an aluminum foil. After baking and rolling, a positive electrode sheet with a thickness of 100μm is obtained. A groove of a fixed size is provided at a certain position on the positive electrode sheet. A nickel tab (positive tab 2) is laser-welded into this groove.

[0106] In this embodiment, lithium cobalt oxide comprises Ti and Al elements, wherein the Ti content is 300 ppm and the Al content is 7000 ppm. LATP accounts for 0.5% of the weight of lithium cobalt oxide, and the first conductive agent comprises carbon nanotubes and carbon black in a 1:1 mass ratio; the diameter of the carbon nanotubes is 20 nm.

[0107] Step 2: Mix the negative electrode active material with the second conductive agent, CMC-Li (carboxymethyl cellulose lithium), and PAA (polyacrylic acid) in a mass ratio of 97:0.4:0.1:2.5, and add deionized water to prepare a negative electrode slurry; coat the negative electrode slurry onto both sides of the carbon-coated copper foil, and after baking and rolling, obtain a negative electrode sheet with a thickness of 110μm. The negative electrode sheet has a groove of a fixed size at a certain position, and the copper-plated nickel electrode tab is laser welded into this groove;

[0108] The negative electrode active material includes silicon carbon and graphite, with silicon carbon accounting for 8% of the weight of graphite and silicon element content in silicon carbon being 70% by mass; the second conductive agent includes single-walled carbon nanotubes and carbon black in a mass ratio of 1:1, with the single-walled carbon nanotubes having a diameter of 10 nm.

[0109] Step 3: After the positive and negative electrode sheets are slit and made into sheets, they are wound with the separator to obtain the core;

[0110] Step 4: Then, adhesive 1 (hot melt adhesive) is set on one side of the core thickness direction, and aluminum-plastic film is used for encapsulation. Then, the core is baked, injected with liquid, formed, resealed, sorted and OCV is performed to obtain lithium-ion secondary batteries.

[0111] The electrolyte is a self-made electrolyte, in which ethylene carbonate (EC), ethylene carbonate (PC), and diethyl carbonate (DEC) are mixed in a weight ratio of 1:3:6 as a base solvent. Then, ethyl propionate and lithium salt LiPF6 are dissolved in the above base solvent to obtain the electrolyte, wherein the mass content of ethyl propionate (EP) is 40%.

[0112] The parameters of the secondary batteries prepared in each embodiment and comparative example are shown in Table 1 and Table 2.

[0113] The content of Ti in the solid electrolyte was determined by EDS.

[0114] Table 1. Parameters for each embodiment and comparative example.

[0115] Table 2 Parameters for each embodiment and comparative example

[0116] The SEM image of the positive electrode sheet of Example 5 is shown in Figure 1, and the enlarged image is shown in Figure 2. As can be seen from Figure 2, there are lithium cobalt oxide particles 4 with a maximum diameter in the range of 8μm to 40μm in the vertical distance between the edges of the solid electrolyte particles 3 and the edges.

[0117] The difference between Example 20 and Example 1 is that the solid electrolyte is lithium lanthanum titanium oxide (LLTO, Li). 0.3 La 0.567 TiO3), the mass content of Ti element in the solid electrolyte is 26%, A = 7000, A / B = 14.29%.

[0118] The difference between Example 21 and Example 1 is that the solid electrolyte is Li. 1.5 Al 0.5 Ti 1.5 (PO4)3, the mass content of Ti in the solid electrolyte is 16%, A = 7150, A / B = 14.22%.

[0119] The difference between Example 22 and Example 1 is that the solid electrolyte is Li. 1.01 Al 0.01 Ti 1.99 (PO4)3, the mass content of Ti in the solid electrolyte is 24%, A = 7070, A / B = 14.38%.

[0120] The lithium-ion secondary battery of Comparative Example 1 is basically the same as that of Example 17, except that LATP is not doped in Comparative Example 1.

[0121] Lithium-ion secondary battery performance testing methods:

[0122] 1. The test method for low-temperature discharge performance at -20℃ is as follows: The secondary battery is subjected to constant current and constant voltage at room temperature at 0.2C to the upper limit voltage, and then stopped at 0.02C. After standing for 5 minutes, it is discharged at 0.2C to 3.0V, and the discharge capacity C1 is recorded. Then, it is subjected to constant current and constant voltage at room temperature at 0.2C to the upper limit voltage, and then stopped at 0.02C to fully charge. The fully charged battery is placed in a constant temperature room or constant temperature chamber at -20℃, and after standing for 2 hours, it is discharged at 0.2C to 3.0V, and the discharge capacity C2 is recorded. C2 / C1 is the low-temperature discharge capacity retention rate at -20℃ and 0.2C.

[0123] 2. Thermal-PPG thickness expansion rate: The secondary battery is subjected to constant current and constant voltage at 0.2C at room temperature until the upper limit voltage is reached and cut off at 0.02C. The thickness h1 is measured for the first time using 600ppg (representing the pressure of 600g). Then, it is placed under 60℃±2℃ for storage for 35 days. After that, the secondary battery is removed and the thickness h2 is measured immediately. h2 / h1 is the thermal-PPG thickness expansion rate.

[0124] 3. Volumetric Energy Density (ED) Test: Volumetric energy density ED = E / V, where E is the battery's discharge energy. The test method is as follows: Charge the lithium-ion secondary battery at a current of 0.2C to the upper limit voltage, then charge it at a constant voltage until the current drops to 0.02C, and then discharge it at a current of 0.2C until it reaches 3.0V. The energy discharged is E. V is the volume of the lithium-ion secondary battery. The volume is obtained by measuring the battery's thickness, width, and length and calculating their product. E / V is the measured volumetric energy density.

[0125] The test results are shown in Table 3.

[0126] Table 3 Performance of lithium-ion secondary batteries in each embodiment and comparative example

[0127] As shown in Table 3, comparing the embodiments with Comparative Examples 1-4, the thermal-PPG thickness expansion rate of the lithium-ion secondary battery of this application is below 15%, while the low-temperature discharge capacity retention rate is above 59%. The low-temperature discharge performance of the secondary battery of this application is significantly improved, and it exhibits both excellent low-temperature performance and good high-temperature performance. Comparative Example 1 did not add a solid electrolyte, resulting in poor low-temperature performance of the secondary battery. Comparative Examples 2 and 3 show that if the maximum particle size D1 of the solid electrolyte is too small, it is prone to agglomeration, resulting in uneven dispersion and poor local conductivity; if the maximum particle size D1 of the solid electrolyte is too large, the large solid electrolyte particles themselves have poor conductivity, leading to a poor overall improvement in the low-temperature discharge performance of the cell. Therefore, adding a solid electrolyte with a maximum particle size D1 ranging from 500 nm to 3 μm to the positive electrode active layer of the secondary battery can significantly improve the low-temperature performance of the battery. Comparing Example 3 with Comparative Example 5, it is shown that the particle size Dv10 of lithium cobalt oxide is greater than the average particle size D2 of the solid electrolyte, which can further improve the low-temperature discharge performance of the battery.

[0128] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A lithium-ion secondary battery, comprising a positive electrode and a negative electrode, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, which includes silicon-carbon material and graphite. Based on the mass of the negative electrode active layer, the silicon content is C, and C is 1% to 20%. The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive active layer includes a positive active material and a solid electrolyte. The maximum particle size D1 of the solid electrolyte is 500 nm to 3 μm. The solid electrolyte includes Ti element, and the mass content of Ti element in the solid electrolyte is 2% to 40%; The positive electrode active material includes lithium cobalt oxide, which includes Ti and Al elements; the particle size Dv10 of the lithium cobalt oxide is greater than the average particle size D2 of the solid electrolyte. Based on the mass of the positive electrode active layer, the content of Ti element is Appm, and the content of Al element is B ppm, satisfying 0.05 < A / B ≤ 0.

3.

2. The lithium-ion secondary battery according to claim 1, characterized in that, At least one of the following conditions must be met: (1) 0.1 ≤ A / B ≤ 0.2; (2) The maximum particle size D1 of the solid electrolyte is 0.5 μm to 2 μm; (3) The silicon content C in the negative electrode active layer is 1% to 20%; (4) The ratio of the content of Ti element Appm in the positive electrode active layer to the mass content of silicon element C in the negative electrode active layer satisfies 1250≤A / C≤130000.

3. The lithium-ion secondary battery according to claim 1 or 2, characterized in that, The solid electrolyte includes at least one of lithium aluminum titanium phosphorus oxide and lithium lanthanum titanium oxide. And / or, the solid electrolyte in the positive electrode active layer has a mass content of 0.1% to 2%.

4. The lithium-ion secondary battery according to claim 1 or 2, characterized in that, The lithium cobalt oxide includes a first particle with a particle size D3 of 8 μm to 40 μm; a plurality of solid electrolyte particles are distributed around the first particle, and the vertical distance between the solid electrolyte particles and the first particle is 0 to 6 μm.

5. The lithium-ion secondary battery according to claim 1 or 2, characterized in that, The content of Ti element Appm in the positive electrode active layer satisfies 500≤A≤2000; And / or, the content of Al element B ppm in the positive electrode active layer satisfies 5000≤B≤10000; And / or, the particle size Dv10 of the lithium cobalt oxide is 2 μm to 5 μm; And / or, the median particle size Dv50 of the lithium cobalt oxide is 10 μm to 20 μm.

6. The lithium-ion secondary battery according to claim 1, characterized in that, The positive electrode active layer further includes a first conductive agent, which includes carbon nanotubes with a diameter of 5 nm to 100 nm. Optionally, the content of carbon nanotubes is 0.1% to 2% based on the mass of the positive electrode active layer.

7. The lithium-ion secondary battery according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The silicon content of the silicon-carbon material is 35% to 70% by mass; (2) The graphite includes one or more of artificial graphite and natural graphite; (3) The silicon-carbon material includes a carbon substrate and silicon particles dispersed in the pores of the carbon substrate; (4) The negative electrode active layer further includes a second conductive agent, which includes a single-walled carbon nanotube with a diameter of 1 to 50 nm.

8. The lithium-ion secondary battery according to claim 1, characterized in that, The lithium-ion secondary battery further includes an electrolyte, which includes a solvent, and the solvent includes ethyl propionate. The content of ethyl propionate is 20% to 60% based on the mass of the electrolyte.

9. The lithium-ion secondary battery according to claim 1, characterized in that, The positive electrode plate also includes a positive electrode tab, which is electrically connected to the positive current collector and extends from one side of the positive current collector in the width direction. The lithium-ion secondary battery further includes a separator, and the positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound into a core; at least one surface of the core in the thickness direction is provided with an adhesive, and the projections of the adhesive and the positive electrode tab in the thickness direction of the core are staggered along the height direction of the core.

10. The lithium-ion secondary battery according to claim 9, characterized in that, The shortest distance between the projection of the positive electrode tab and the adhesive in the thickness direction of the core is S, which satisfies 100mm≥S>0; And / or, the adhesive has a first end close to the positive electrode tab along the height direction of the core, and the positive current collector has a second end close to the positive electrode tab along the height direction of the core, the distance between the first end and the second end along the height direction of the core being K, satisfying 125mm≥K>15mm.

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