A lithium-ion battery

Abstract

In order to overcome the problem of increasing demand for high energy density and fast charging capability of lithium-ion batteries in the prior art, the present invention provides a lithium-ion battery, wherein the positive electrode plate comprises a positive electrode active material layer, the positive electrode active material of the positive electrode active material layer comprises lithium cobalt oxide and / or ternary nickel cobalt manganese oxide, the mass proportion of the lithium cobalt oxide in the positive electrode active material is a%, 0≤a≤100, the mass proportion of the ternary nickel cobalt manganese oxide in the positive electrode active material is b%, 0≤b≤100, a%+b%=100%, the compacted density of the positive electrode plate is ρg / cm3, 4.1*a%+3.3*b%≤ρ≤4.4*a%+3.8*b%; the negative electrode plate comprises a negative electrode active material layer, the negative electrode active material layer comprises a first active coating layer close to the negative electrode current collector and a second active coating layer away from the negative electrode current collector, the negative electrode active material of one of the first active coating layer and the second active coating layer is a capacity-type material, and the negative electrode active material of the other is a rate-type material.

Description

Technical Field

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

[0002] With the continuous development of consumer electronics, users are placing higher demands on device functionality and convenience. Modern electronic products not only pursue powerful hardware and software performance, but also require devices to be lightweight and easy to carry. In this context, batteries, as core components of electronic products, face increasingly stringent performance requirements. Especially with limited battery compartment space and increasingly airtight equipment, balancing battery size and performance becomes a key design issue.

[0003] Currently, most lithium-ion batteries on the market face the following challenges:

[0004] High energy density requirements: As devices become increasingly powerful, especially high-performance electronic products such as smartphones and laptops, the demand for battery energy density is increasing. Batteries need to store more energy in a limited space to meet the needs of long-term device use.

[0005] Fast-charging Capability: With the advancement of fast-charging technology, user demands for faster charging speeds continue to increase. However, traditional lithium-ion batteries tend to generate significant heat at high charging rates, leading to anxiety and discomfort during charging. Improving charging capacity while maintaining battery safety and efficiency during fast charging presents a major challenge for lithium-ion battery technology. Summary of the Invention

[0006] In response to the problem in the prior art that lithium-ion batteries have an increasing demand for high energy density and fast charging capabilities, the present invention provides a lithium-ion battery.

[0007] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0008] The present invention provides a lithium-ion battery, comprising a positive electrode plate, a negative electrode plate and a separator, wherein the positive electrode plate comprises a positive electrode active material layer, wherein the positive electrode active material of the positive electrode active material layer comprises lithium cobalt oxide and / or ternary nickel cobalt manganese oxide, wherein the mass proportion of the lithium cobalt oxide in the positive electrode active material is a%, 0≤a≤100, and the mass proportion of the ternary nickel cobalt manganese oxide in the positive electrode active material is b%, 0≤b≤100, a%+b%=100%, and the compacted density of the positive electrode plate is ρg / cm 3 ,4.1*a%+3.3*b%≤ρ≤4.4*a%+3.8*b%;

[0009] The negative electrode plate includes a negative electrode active material layer, which includes a first active coating layer close to the negative electrode current collector and a second active coating layer away from the negative electrode current collector. The negative electrode active material of one of the first active coating layer and the second active coating layer is a capacity-type material, and the negative electrode active material of the other active coating layer is a rate-type material.

[0010] Furthermore, the lithium cobalt oxide includes large-particle lithium cobalt oxide and small-particle lithium cobalt oxide, the Dn50 particle size of the large-particle lithium cobalt oxide is 12~20μm, the Dn99 particle size of the large-particle lithium cobalt oxide is ≤60μm, the Dn50 particle size of the small-particle lithium cobalt oxide is 2~6μm, the Dn99 particle size of the small-particle lithium cobalt oxide is ≤12μm, and the mass ratio of the large-particle lithium cobalt oxide to the small-particle lithium cobalt oxide is 8:2~7:3.

[0011] Furthermore, the lithium cobalt oxide is doped with Al, Mg and Ti elements, and the Al content in the lithium cobalt oxide is ≥100 ppm, the Mg content is ≥50 ppm, and the Ti content is ≥50 pmm.

[0012] Furthermore, the content of Ti element in the lithium cobalt oxide is 200-1500 ppm, the content of Mg element is 500-2000 ppm, and the mass ratio of Ti / Mg is 1:1-1:3.

[0013] Furthermore, the chemical formula of the ternary nickel-cobalt-manganese oxide is: LiNi x Co y Mn z O2, where: x+y+z=1, x≥y.

[0014] Furthermore, the ternary nickel-cobalt-manganese oxide is doped with Zr, Y, and W elements, and the content of Zr in the ternary nickel-cobalt-manganese oxide is ≥500ppm, the content of Y is ≥500ppm, and the content of W is ≥300ppm.

[0015] Furthermore, the content of Zr in the ternary nickel-cobalt-manganese oxide is 1000-4000 ppm, the content of Y in the ternary nickel-cobalt-manganese oxide is 1000-2500 ppm, and the content of W in the ternary nickel-cobalt-manganese oxide is 2000-4500 ppm.

[0016] Furthermore, the median particle size Dn50 of the ternary nickel-cobalt-manganese oxide is 2-15 μm.

[0017] Furthermore, the thickness of the positive electrode sheet is 50-200 μm.

[0018] Furthermore, the surface density of the positive electrode sheet is 130-300 g / m 2 .

[0019] Furthermore, the capacity-type material includes one or more of capacity-type graphite and capacity-type graphite-silicon-carbon composite materials, and the rate-type material includes one or more of rate-type graphite and rate-type graphite-silicon-carbon composite materials.

[0020] Furthermore, the negative electrode active material of the first active coating is capacity-type graphite, and the median particle size Dn50 of the capacity-type graphite is 10~18μm; the negative electrode active material of the second active coating is rate-type graphite, and the median particle size Dn50 of the rate-type graphite is 4~12μm.

[0021] Furthermore, when the negative electrode active material of the first active coating layer is capacity-type graphite and the negative electrode active material of the second active coating layer is rate-type graphite, the surface density ratio of the first active coating layer to the second active coating layer is 9:1 to 5:5.

[0022] Furthermore, the negative electrode active material of the first active coating is a capacity-type graphite-silicon-carbon composite material, the negative electrode active material of the second active coating is a rate-type graphite, and the mass proportion of the silicon-carbon material in the capacity-type graphite-silicon-carbon composite material is 1% to 30%.

[0023] Furthermore, when the negative electrode active material of the first active coating is a capacity-type graphite-silicon-carbon composite material and the negative electrode active material of the second active coating is a rate-type graphite, the surface density ratio of the first active coating and the second active coating is 8:2~7:3.

[0024] Furthermore, when the negative electrode active material of the first active coating layer is a capacity-type graphite-silicon-carbon composite material and the negative electrode active material of the second active coating layer is a rate-type graphite, the thickness of the base film of the separator is ≤4 μm.

[0025] Furthermore, the negative electrode active material of the first active coating is capacity-type graphite, and the negative electrode active material of the second active coating is rate-type graphite-silicon-carbon composite material.

[0026] Furthermore, when the negative electrode active material of the first active coating layer is capacity-type graphite and the negative electrode active material of the second active coating layer is rate-type graphite-silicon-carbon composite material, the thickness of the base film of the separator is ≥5 μm.

[0027] Furthermore, the negative electrode active material of the first active coating is a rate-type graphite-silicon-carbon composite material, and the negative electrode active material of the second active coating is a capacity-type graphite-silicon-carbon composite material; or,

[0028] The negative electrode active material of the first active coating is a capacity-type graphite-silicon-carbon composite material, and the negative electrode active material of the second active coating is a rate-type graphite-silicon-carbon composite material.

[0029] Furthermore, the surface density of the negative electrode sheet is 50-120 g / m 2 .

[0030] Furthermore, the cold pressed density of the negative electrode plate is 1.5-2.0 g / cm 3 .

[0031] The beneficial effects of the present invention are:

[0032] In the present invention, the lithium cobalt oxide used in the positive electrode active material has a high energy density and compaction density, but the overall particles of lithium cobalt oxide are larger, resulting in a longer charging time. In contrast, the particle size of ternary nickel cobalt manganese oxide is smaller, the energy density is lower than that of lithium cobalt oxide, and the compaction density is also lower. At the same charging rate, the charging time is shorter. The blending of lithium cobalt oxide and ternary nickel cobalt manganese oxide in a certain proportion can shorten the charging time while ensuring the energy density of the positive electrode active material. In practical applications, the blending ratio of lithium cobalt oxide and ternary nickel cobalt manganese oxide can be flexibly selected according to the requirements of the product's energy density, charging time and lithium-ion battery cost. When 4.1*a%+3.3*b%≤ρ≤4.4*a%+3.8*b% is met, the energy density and fast charging performance of the lithium-ion battery are relatively more balanced. When ρ<4.1*a%+3.3*b%, the energy density of the lithium-ion battery decreases and the fast charging performance increases. When ρ>4.4*a%+3.8*b%, the energy density of the lithium-ion battery increases and the fast charging performance decreases.

[0033] Secondly, the present invention improves the performance of lithium-ion batteries in terms of fast charging and energy density by coating the negative electrode current collector with a double layer of active material (the negative electrode active materials of the double layer of active material are capacity-type materials and rate-type materials, respectively). Capacity-type materials provide a higher specific capacity and can provide more energy over a longer period of time; while rate-type materials have faster electronic and ionic conductivity and are suitable for providing higher power output. By placing the capacity-type and rate-type materials in different active coatings, the energy density of the lithium-ion battery can be improved while ensuring that it can still maintain good power output during high-rate charge and discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of a negative electrode active material layer on a negative electrode sheet provided by one embodiment of the present invention.

[0035] The reference numerals in the drawings of the specification are as follows:

[0036] 100. Negative electrode current collector; 101. First active coating layer; 102. Second active coating layer. DETAILED DESCRIPTION

[0037] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0038] One embodiment of the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive electrode active material layer, wherein the positive electrode active material of the positive electrode active material layer comprises lithium cobalt oxide and / or ternary nickel cobalt manganese oxide, wherein the mass proportion of the lithium cobalt oxide in the positive electrode active material is a%, 0≤a≤100, and the mass proportion of the ternary nickel cobalt manganese oxide in the positive electrode active material is b%, 0≤b≤100, a%+b%=100%, and the compacted density of the positive electrode sheet is ρg / cm 3 , 4.1*a%+3.3*b%≤ρ≤4.4*a%+3.8*b%;

[0039] like Figure 1 As shown, the negative electrode plate includes a negative electrode active material layer, and the negative electrode active material layer includes a first active coating 101 close to the negative electrode current collector 100 and a second active coating 102 away from the negative electrode current collector 100. The negative electrode active material of one of the first active coating 101 and the second active coating 102 is a capacity type material, and the negative electrode active material of the other is a rate type material.

[0040] In the present invention, the lithium cobalt oxide used in the positive electrode active material has a high energy density and compaction density, but the overall particles of lithium cobalt oxide are larger, resulting in a longer charging time. In contrast, the particle size of ternary nickel cobalt manganese oxide is smaller, the energy density is lower than that of lithium cobalt oxide, and the compaction density is also lower. At the same charging rate, the charging time is shorter. The blending of lithium cobalt oxide and ternary nickel cobalt manganese oxide in a certain proportion can shorten the charging time while ensuring the energy density of the positive electrode active material. In practical applications, the blending ratio of lithium cobalt oxide and ternary nickel cobalt manganese oxide can be flexibly selected according to the requirements of the product's energy density, charging time and lithium-ion battery cost. When 4.1*a%+3.3*b%≤ρ≤4.4*a%+3.8*b% is met, the energy density and fast charging performance of the lithium-ion battery are relatively more balanced. When ρ<4.1*a%+3.3*b%, the energy density of the lithium-ion battery decreases and the fast charging performance increases. When ρ>4.4*a%+3.8*b%, the energy density of the lithium-ion battery increases and the fast charging performance decreases.

[0041] Secondly, in the present invention, by coating the negative electrode current collector 100 with a double layer of active material, the negative electrode active materials of the double layer of active material are respectively capacity-type materials and rate-type materials, thereby improving the performance of the lithium-ion battery in terms of fast charging and energy density. Among them, the capacity-type material provides a higher specific capacity and can provide more energy for a longer period of time; while the rate-type material has good electronic and ionic conductivity and is suitable for providing higher power output. By placing the capacity-type and rate-type materials in different active coatings, it is possible to improve the energy density of the lithium-ion battery while ensuring that it can still maintain good power output during high-rate charge and discharge.

[0042] In some embodiments, the lithium cobalt oxide includes large-particle lithium cobalt oxide and small-particle lithium cobalt oxide, the Dn50 particle size of the large-particle lithium cobalt oxide is 12~20μm, the Dn99 particle size of the large-particle lithium cobalt oxide is ≤60μm, the Dn50 particle size of the small-particle lithium cobalt oxide is 2~6μm, the Dn99 particle size of the small-particle lithium cobalt oxide is ≤12μm, and the mass ratio of the large-particle lithium cobalt oxide to the small-particle lithium cobalt oxide is 8:2~7:3.

[0043] When the Dn50 particle size of large-particle lithium cobalt oxide is 12-20μm and the Dn99 particle size of large-particle lithium cobalt oxide is ≤60μm, the large-particle lithium cobalt oxide has a lower specific surface area and better particle size uniformity, resulting in smaller volume changes during charge and discharge, a more stable lattice structure, and a longer service life. When the Dn50 particle size of small-particle lithium cobalt oxide is 2-6μm and the Dn99 particle size of small-particle lithium cobalt oxide is ≤12μm, the small-particle lithium cobalt oxide has a larger specific surface area and better particle size uniformity, providing more reaction sites, accelerating lithium ion migration, reducing the battery's internal resistance, and thus improving the battery's power density. The mass ratio of large-particle lithium cobalt oxide to small-particle lithium cobalt oxide is 8:2-7:3. The combined use of large-particle lithium cobalt oxide and small-particle lithium cobalt oxide ensures high energy density and stability during long-term use while providing high power output.

[0044] In some embodiments, the lithium cobalt oxide is doped with Al, Mg, and Ti. In the present invention, the performance of the positive electrode active material can be significantly improved by doping the lithium cobalt oxide with aluminum, magnesium, and titanium.

[0045] For aluminum element: Al 3+ Due to their chemical inertness, ions do not participate in electrochemical reactions and can enhance the structural rigidity of the lithium cobalt oxide lattice, inhibit lattice distortion, and thus reduce the volume change of lithium cobalt oxide during the charge and discharge cycle; Al 3+ The radius and Co 3+ The radius of aluminum is relatively close, so after aluminum doping, it can smoothly enter the lithium cobalt oxide lattice without significantly affecting the transmission path of lithium ions.

[0046] For magnesium: Mg 2+ Has a strong oxygen affinity (high oxygen binding energy), making Mg 2+ It can stabilize the bond with oxygen. When lithium cobalt oxide is doped with magnesium, Mg 2+ The oxygen affinity can enhance the binding ability of oxygen atoms in lithium cobalt oxide, preventing lithium cobalt oxide from releasing oxygen at high voltage, thereby improving the thermal stability of the positive electrode active material.

[0047] For titanium: Ti 4+ It can effectively improve the lattice structure of lithium cobalt oxide and enhance the structural stability of lithium cobalt oxide during the charge and discharge cycle. The positive tetravalent (+4) titanium ion can provide additional electrons, enhance the electronic conductivity of lithium cobalt oxide materials, and improve the conductivity of lithium-ion batteries. In addition, Ti 4+ Entering the lithium cobalt oxide lattice, replacing part of the Co 3+ 。 Ti 4+ The high valence state and low oxidation activity can enhance the thermal stability of the lithium cobalt oxide lattice, reduce the risk of lithium cobalt oxide releasing oxygen, and effectively prevent thermal runaway of lithium-ion batteries in high temperature environments.

[0048] In summary, the lithium cobalt oxide, the positive electrode active material of the lithium ion battery provided in the present application, is doped with aluminum, magnesium and titanium elements, which helps to improve the structural stability, conductivity and thermal stability of the positive electrode active material.

[0049] In some embodiments, the lithium cobalt oxide has an Al content of ≥100 ppm, a Mg content of ≥50 ppm, and a Ti content of ≥50 ppm. Preferably, the Al content is ≥1000 ppm, and most preferably, the Al content is between 5000 and 13000 ppm.

[0050] Al doping contributes to the structural stability of lithium cobalt oxide. The higher the Al doping level, the better the stability of the lithium cobalt oxide. However, excessive Al doping reduces the specific capacity of lithium cobalt oxide, thereby reducing the energy density. Taking all factors into consideration, the Al doping level is controlled between 5000 and 13000 ppm to achieve a balance between energy density and thermal stability.

[0051] In some embodiments, the content of Ti element in the lithium cobalt oxide is 200-1500 ppm, the content of Mg element is 500-2000 ppm, and the mass ratio of Ti / Mg is 1:1-1:3.

[0052] When the Ti content is too high, it is easy to accumulate on the surface of the lithium cobalt oxide material, causing performance deterioration. When the Ti content is too low, it cannot effectively improve the stability of the lithium cobalt oxide material. When the Mg content is too high, it is easy to cause uneven doping, thereby affecting the overall performance of the positive electrode active material. In the present invention, the Ti content in lithium cobalt oxide is controlled at 200~1500ppm, and the Mg content is controlled at 500~2000ppm to improve the thermal stability of the lithium ion battery.

[0053] In addition to Al doping, Mg and Ti are also doped to further enhance the performance of lithium cobalt oxide. When the Ti / Mg mass ratio is between 1:1 and 1:3, Al-Mg-Ti co-doping effectively suppresses the structural phase transition that occurs during high-voltage charge and discharge (this phase transition is one of the main causes of lithium cobalt oxide performance degradation). The incorporation of Mg and Al helps stabilize the lithium cobalt oxide lattice structure, while Ti accumulates on the surface of lithium cobalt oxide particles, improving the interfacial contact of the cathode active material and enhancing the rate performance of lithium-ion batteries. Furthermore, Ti doping effectively suppresses the oxidative activity of oxygen ions at high voltages and slows down side reactions between lithium cobalt oxide and the organic electrolyte, thereby improving the surface stability of the cathode active material.

[0054] In some embodiments, the chemical formula of the ternary nickel-cobalt-manganese oxide is: LiNi x Co y Mn z O2, where: x + y + z = 1, x ≥ y. The ternary nickel-cobalt-manganese oxide uses lithium nickel-cobalt-manganese oxide, with the proportion of nickel being no less than that of cobalt. Nickel has a higher specific energy density than cobalt, allowing it to store more energy per unit mass. Increasing the proportion of nickel can increase the energy density of lithium-ion batteries, thereby improving their energy storage capacity.

[0055] In some embodiments, the ternary nickel-cobalt-manganese oxide is doped with zirconium (Zr), yttrium (Y), and tungsten (W). The Zr content in the ternary nickel-cobalt-manganese oxide is ≥500 ppm, the Y content is ≥500 ppm, and the W content is ≥300 ppm. Preferably, the Zr content in the ternary nickel-cobalt-manganese oxide is 1000-4000 ppm, the Y content is 1000-2500 ppm, and the W content is 2000-4500 ppm. In the present invention, zirconium (Zr), yttrium (Y), and tungsten (W) are doped into the ternary nickel-cobalt-manganese oxide to improve the performance of the positive electrode active material.

[0056] For zirconium: zirconium ion (Zr 4+) has a large ionic radius, allowing it to partially replace lithium ions in the ternary nickel-cobalt-manganese oxide lattice. Zirconium ions interact with oxygen ions, strengthening the lattice. The introduction of zirconium ions enhances the stability of the ternary nickel-cobalt-manganese oxide solid solution, suppressing its decomposition under high temperature and pressure, thereby improving the material's thermal stability at high temperatures.

[0057] For yttrium element: yttrium ion (Y 3+ ) can replace lithium ions or transition metal ions, forming a stable ternary nickel-cobalt-manganese oxide solution structure, effectively reducing lattice distortion and volume expansion, and improving the structural stability of the material. Furthermore, yttrium ion doping can enhance the electronic and ionic conductivity of the ternary nickel-cobalt-manganese oxide, improving the battery's rate performance and charge-discharge rate. Furthermore, yttrium ions can inhibit the phase transitions that occur in the ternary nickel-cobalt-manganese oxide during the charge-discharge process, reducing irreversible capacity loss.

[0058] For tungsten element: tungsten ion (W 6+ The higher oxidation state of tungsten enhances the electron conduction path, thereby improving the conductivity of the ternary nickel-cobalt-manganese oxide. Furthermore, the introduction of tungsten ions optimizes ionic conductivity, helping to reduce the battery's internal resistance during high-rate discharge and enhance rate performance. Tungsten's high melting point and heat resistance enhance its thermal stability when incorporated into the ternary nickel-cobalt-manganese oxide. Tungsten doping reduces the decomposition of the ternary nickel-cobalt-manganese oxide at high temperatures, thereby extending the lifespan of lithium-ion batteries.

[0059] When the Zr content in the ternary nickel-cobalt-manganese oxide is 1000-4000ppm, the Y content is 1000-2500ppm, and the W content is 2000-4500ppm, the energy density, high-temperature performance, and fast-charging performance of the lithium-ion battery are more balanced. When the Zr, Y, and W content is too high, the high-temperature performance of the lithium-ion battery is improved, but the energy density is reduced. When the Zr, Y, and W content is too low, there is no significant effect on the energy density, high-temperature performance, and fast-charging performance of the lithium-ion battery.

[0060] In some embodiments, the median particle size Dn50 of the ternary nickel-cobalt-manganese oxide is 2-15 μm.

[0061] Compared to lithium cobalt oxide materials, ternary nickel cobalt manganese oxide has lower conductivity. In the present invention, the median particle size Dn50 of the ternary nickel cobalt manganese oxide is controlled within the range of 2 to 15 μm to balance its kinetic properties (such as conductivity) during the charge and discharge process. When the median particle size Dn50 of the ternary nickel cobalt manganese oxide is too large, it affects the capacity and charging time. In addition, the mixing of small particles of ternary nickel cobalt manganese oxide and large particles of lithium cobalt oxide helps to improve the compaction density of the positive electrode active material and the compactness of the positive electrode sheet after rolling.

[0062] In some embodiments, the thickness of the positive electrode sheet is 50-200 μm, and the surface density of the positive electrode sheet is 130-300 g / m 2 .

[0063] If the surface density of the positive electrode sheet is too high, the thickness of the positive electrode sheet will increase, causing lithium ions to migrate along a longer path during the charge and discharge process, which will reduce the charging speed and kinetic performance of the lithium-ion battery. In addition, if the surface density of the positive electrode sheet is too low, the content of active materials on the positive electrode sheet will be reduced, resulting in a decrease in the energy density of the lithium-ion battery. In the present invention, by controlling the thickness of the positive electrode sheet to between 50 and 200 μm and the surface density to between 130 and 300 g / m 2 Avoid the negative impact of too high or too low surface density to balance the charge and discharge performance and energy density of lithium-ion batteries.

[0064] In some embodiments, the capacity-type material includes one or more of capacity-type graphite and capacity-type graphite-silicon-carbon composite materials, and the rate-type material includes one or more of rate-type graphite and rate-type graphite-silicon-carbon composite materials.

[0065] Capacitive graphite, as described above, refers to graphite materials that offer high capacity (energy density). Its characteristic is its ability to release a large amount of electricity over a long period of time. Capacitive graphite generally has a relatively stable structure, making it suitable for long-term energy storage.

[0066] The above-mentioned rate-type graphite refers to a graphite material with good conductivity and low internal resistance. Its characteristics support fast charging and discharging processes and are suitable for situations requiring high power output.

[0067] In some embodiments, the negative electrode active material of the first active coating 101 is capacity-type graphite, and the median particle size Dn50 of the capacity-type graphite is 10-18 μm; the negative electrode active material of the second active coating 102 is rate-type graphite, and the median particle size Dn50 of the rate-type graphite is 4-12 μm.

[0068] The median particle size Dn50 of the aforementioned capacity-type graphite is 10-18 μm. Larger particle sizes of capacity-type graphite provide a higher specific capacity, meaning a higher lithium ion storage capacity per unit weight, thereby increasing the overall energy density of the lithium-ion battery. The median particle size Dn50 of the aforementioned rate-type graphite is 4-12 μm. Smaller particle sizes of rate-type graphite provide a larger specific surface area, reducing the electrochemical impedance within the lithium-ion battery and enabling faster lithium ion migration within the negative electrode active material layer, thereby increasing the charge and discharge rates of the lithium-ion battery.

[0069] When the negative electrode active material of the first active coating 101 is capacity-type graphite and the negative electrode active material of the second active coating 102 is rate-type graphite, the surface density ratio of the first active coating 101 to the second active coating 102 is 9:1 to 5:5.

[0070] The first active coating 101 uses capacity-type graphite, which is closer to the negative electrode current collector 100, shortening the electron transmission path. The second active coating 102 uses rate-type graphite, which is closer to the surface of the negative electrode plate, facilitating the rapid charging and discharging of the lithium-ion battery. This well-defined design balances energy density and power density, thereby optimizing the overall performance of the lithium-ion battery. By rationally designing the negative electrode plate structure, it is possible to achieve both high energy and rapid charging and discharging. When the areal density ratio of the first active coating 101 to the second active coating 102 is between 9:1 and 5:5, the energy density and fast-charging performance of the lithium-ion battery are more balanced. When the areal density ratio of the first active coating 101 to the second active coating 102 is too large, the energy density of the lithium-ion battery increases, while the fast-charging performance decreases. When the areal density ratio of the first active coating 101 to the second active coating 102 is too small, the fast-charging performance increases, while the energy density decreases.

[0071] In some embodiments, the negative electrode active material of the first active coating 101 is a capacity-type graphite-silicon-carbon composite material, and the negative electrode active material of the second active coating 102 is a rate-type graphite. The mass ratio of the silicon-carbon material to the capacity-type graphite-silicon-carbon composite material is 1% to 30%. Preferably, the mass ratio of the silicon-carbon material to the graphite-silicon-carbon composite material is 5% to 20%.

[0072] Silicon-carbon materials have high volume expansion properties and high energy density. If their content is too low (less than 1%), their effect on improving the product's energy density is limited. If their content exceeds 30%, the expansion of the negative electrode sheet becomes difficult to control, affecting the stability of the lithium-ion battery. In this invention, the mass ratio of silicon-carbon material to graphite-silicon-carbon composite material is controlled between 5% and 20%, effectively controlling the volume expansion of the negative electrode sheet while improving energy density.

[0073] When the negative electrode active material of the first active coating 101 is a capacity-type graphite-silicon carbon composite material and the negative electrode active material of the second active coating 102 is a rate-type graphite, the surface density ratio of the first active coating 101 to the second active coating 102 is 8:2-7:3.

[0074] By optimizing the distribution of silicon carbon and graphite and the coating process, such as the surface density ratio of the first active coating 101 and the second active coating 102 is between 8:2-7:3, it can not only take into account the improvement of the window of the charge and discharge dynamics of the entire negative electrode sheet and the protection of the diaphragm by the rate-type graphite content of the second active coating 102, but also effectively reduce the internal impedance of the lithium-ion battery and further enhance the charge and discharge performance of the lithium-ion battery.

[0075] Furthermore, the thickness of the base film of the separator is ≤4 μm.

[0076] The second active coating 102 of the negative electrode sheet first contacts the diaphragm. The angularity, hardness, and surface roughness of the particles in this active layer all affect the contact performance between the negative electrode sheet and the diaphragm. Because silicon carbon particles are harder than graphite, a double-layer coating method, placing the harder silicon carbon particles in the lower layer of the negative electrode sheet and the softer graphite in the upper layer of the negative electrode sheet, can reduce mechanical damage to the diaphragm. In this case, the base film of the diaphragm can be thinner (e.g., thickness ≤ 4μm) without worrying about the use of harder silicon particles in the negative electrode sheet puncturing the diaphragm and causing excessive self-discharge, thereby reducing the overall thickness of the lithium-ion battery and further improving the specific energy.

[0077] In some embodiments, the negative electrode active material of the first active coating 101 is capacity-type graphite, and the negative electrode active material of the second active coating 102 is a rate-type graphite-silicon-carbon composite material. The capacity-type graphite, as the negative electrode active material of the first active coating 101, is in direct contact with the negative electrode current collector 100, helping to improve the electronic conductivity of the negative electrode sheet. The rate-type graphite-silicon-carbon composite material, as the negative electrode active material of the second active coating 102, can effectively shorten the lithium ion transmission path and improve ionic conductivity.

[0078] When the negative electrode active material of the first active coating 101 is capacity-type graphite, and the negative electrode active material of the second active coating 102 is a rate-type graphite-silicon-carbon composite material, the thickness of the base film of the separator is ≥ 5 μm. Because the harder silicon-carbon particles in the second active coating 102 increase the risk of puncturing the separator, the thickness of the base film of the separator needs to be increased, for example, the thickness of the base film of the separator needs to be ≥ 5 μm to reduce the risk of silicon-carbon particles puncturing the separator.

[0079] In some embodiments, the negative electrode active material of the first active coating 101 is a rate-type graphite-silicon-carbon composite material, and the negative electrode active material of the second active coating 102 is a capacity-type graphite-silicon-carbon composite material; or, the negative electrode active material of the first active coating 101 is a capacity-type graphite-silicon-carbon composite material, and the negative electrode active material of the second active coating 102 is a rate-type graphite-silicon-carbon composite material.

[0080] By applying rate-type graphite-silicon-carbon composite materials and capacity-type graphite-silicon-carbon composite materials to different active coatings, the comprehensive performance of lithium-ion batteries can be optimized. Rate-type graphite-silicon-carbon composite materials have good electronic and ionic conductivity, can reduce internal resistance during high-rate charging, significantly improve the charging rate, and shorten the charging time. Capacity-type graphite-silicon-carbon composite materials have a higher specific capacity, can provide higher energy density, and provide longer-term stable output during discharge. In summary, the conductivity of rate-type graphite-silicon-carbon composite materials, combined with the high capacity characteristics of rate-type graphite-silicon-carbon composite materials, can effectively optimize rate performance and ensure the stability of the battery during high-rate discharge.

[0081] In some embodiments, the surface density of the negative electrode sheet is 50-120 g / m 2 Preferably, the surface density of the negative electrode sheet is 70~90g / m 2 .

[0082] If the surface density of the negative electrode sheet is too high, the thickness of the negative electrode sheet will be increased, resulting in the lithium ions needing to migrate along a longer path during the charge and discharge process, which will reduce the charging speed and kinetic performance of the lithium-ion battery. In addition, if the surface density of the negative electrode sheet is too low, the content of the negative electrode active material on the negative electrode sheet will be reduced, thereby reducing the energy density of the lithium-ion battery. In the present invention, by controlling the surface density of the negative electrode sheet to 70~90g / m 2 Avoid the negative impact of too high or too low surface density to optimize the balance between the charge and discharge performance and energy density of lithium-ion batteries.

[0083] In some embodiments, the cold pressed density of the negative electrode is 1.5-2.0 g / cm 3 Preferably, the cold pressed density of the negative electrode is 1.65~1.8g / cm 3 ; 30% charge compaction density is preferably 1.2~1.8g / cm 3 .

[0084] In the present invention, the negative electrode sheet is prepared by cold pressing, which can effectively reduce the gaps between the negative electrode active materials, increase the compaction density of the negative electrode sheet, and improve the efficiency of electron and ion conduction during the charge and discharge process of the lithium-ion battery.

[0085] Air transport standards generally require that lithium-ion batteries be shipped at a 30% SOC state of charge. In the present invention, the 30% SOC compaction density is controlled at 1.2-1.8 g / cm 3 It is beneficial to improve the volume energy density in the shipping state.

[0086] The present invention is further described below with reference to the following examples.

[0087] Example 1

[0088] This embodiment is used to illustrate the lithium-ion battery disclosed in the present invention, and includes the following operating steps:

[0089] 1) Preparation of positive electrode sheet:

[0090] S11. Material preparation:

[0091] Mixing lithium cobalt oxide doped with Al, Mg and Ti elements and lithium nickel cobalt manganese oxide doped with Zr, Y and W elements in a mass ratio of a:b;

[0092] A mixture of lithium cobalt oxide and lithium nickel cobalt manganese oxide, conductive carbon black, conductive carbon nanotubes, and PVDF binder were weighed respectively in a mass ratio of 97.5:1.0:0.5:1.0.

[0093] S12. Prepare slurry: Add binder (PVDF), conductive carbon black and conductive carbon nanotubes to NMP solvent and stir thoroughly until they are completely dissolved to obtain slurry; add lithium cobalt oxide and lithium nickel cobalt manganese oxide mixture to the above slurry, and stir with a mechanical stirrer until the mixed system forms a positive electrode slurry with uniform fluidity.

[0094] S13. Pole sheet coating: The above-mentioned positive electrode slurry is evenly coated on the aluminum foil, and the positive electrode sheet is obtained after baking, drying, cold pressing and shearing.

[0095] 2) Preparation of negative electrode sheet:

[0096] S21. Material preparation:

[0097] Capacitive graphite, conductive carbon nanotubes, CMC thickener, and SBR binder were weighed in a mass ratio of 96.0:1.0:1.5:1.5 respectively;

[0098] The rate-type graphite, conductive carbon nanotubes, CMC thickener and SBR binder were weighed respectively in a mass ratio of 96.0:1.0:1.5:1.5.

[0099] S22. Prepare slurry:

[0100] Conductive carbon nanotubes, CMC thickener, and SBR binder are added to deionized water and stirred thoroughly until completely dissolved to obtain a slurry. Capacitive graphite is added to the above slurry and stirred thoroughly in a vacuum environment until the mixed system forms a slurry of the first active coating 101 with uniform fluidity.

[0101] Conductive carbon nanotubes, CMC thickener, and SBR binder are added to deionized water and stirred thoroughly until completely dissolved to obtain a slurry. The rate-type graphite is added to the above slurry and stirred thoroughly in a vacuum environment until the mixed system forms a slurry of the second active coating 102 with uniform fluidity.

[0102] S23. Pole sheet coating: The slurry of the first active coating layer 101 and the slurry of the second active coating layer 102 are uniformly coated on the copper foil in sequence, and the negative electrode sheet is obtained after baking, drying, cold pressing and shearing.

[0103] 3) Preparation of lithium-ion batteries:

[0104] The positive electrode sheet, separator and negative electrode sheet are stacked in order, with the separator placed in the middle of the positive and negative electrode sheets to play an isolating role. Then they are wound to obtain a core structure. The core structure is then placed in an aluminum-plastic film outer packaging or a steel shell mold, baked to remove moisture in the battery, and then the electrolyte is injected. After vacuum packaging, standing, formation, shaping, sorting and other processes, the required lithium-ion battery is obtained.

[0105] Examples 2 to 18

[0106] Examples 2 to 18 are used for comparative illustration of the lithium-ion batteries disclosed herein. They include most of the steps in Example 1, except that the formulations in Tables 1 and 2 are used. Table 1 shows the formulations of the positive electrode active materials of Examples 1 to 18, and Table 2 shows the formulations of the negative electrode active materials of Examples 1 to 18.

[0107] Examples 19-30

[0108] Examples 19 to 30 are used for comparative illustration of the lithium-ion batteries disclosed herein. They include most of the steps in Example 1, except that the formulations in Tables 3 and 4 are used. Table 3 shows the formulations of the positive electrode active materials of Examples 19 to 30, and Table 4 shows the formulations of the negative electrode active materials of Examples 19 to 30.

[0109] Comparative Examples 1 to 4

[0110] Comparative Examples 1 to 4 are used to compare and illustrate the lithium-ion batteries disclosed herein. They include most of the operating steps of Example 1, except that the formulations in Tables 5 to 7 are used. Table 5 shows the formulations of the positive electrode active materials for Comparative Examples 1 to 4, Table 6 shows the formulations of the negative electrode active materials for Comparative Examples 1 and 2, and Table 7 shows the formulations of the negative electrode active materials for Comparative Examples 3 and 4.

[0111] Table 1

[0112]

[0113] Note: In Table 1, the positive electrode active material M in Examples 1 to 18 is lithium cobalt oxide, and the positive electrode active material N is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0114] Table 2

[0115]

[0116] Table 3

[0117]

[0118] Note: In Table 3, the positive electrode active material M in Examples 19 to 30 is lithium cobalt oxide, and the positive electrode active material N is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0119] Table 4

[0120]

[0121] Table 5

[0122]

[0123] Note: In Table 5, the positive electrode active material M in Comparative Examples 1 to 4 is lithium cobalt oxide, and the positive electrode active material N is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0124] Table 6

[0125]

[0126] Table 7

[0127]

[0128] Note: In Table 7, the negative electrode sheets in Comparative Examples 3 and 4 have only one negative electrode active material layer, which uses a mixture of capacity-type graphite and rate-type graphite. The mass ratio refers to the mass ratio of the capacity-type graphite to the rate-type graphite.

[0129] Performance Testing

[0130] The lithium-ion batteries prepared in the above examples and comparative examples were subjected to the following performance tests:

[0131] ① Volume energy density test: The lithium-ion battery prepared above was tested under standard test conditions (charging current 0.7C, charge cut-off voltage 4.45V, charge cut-off current 0.05C, 0.2C discharge rate to 3.0V). The discharge capacity C1 and platform voltage V1 at 0.2C rate were recorded. The thickness of the lithium-ion battery was then measured using a 600g flat plate thickness gauge at 30% SOC. The volume energy density of the battery was calculated according to the following formula:

[0132] Volume energy density (Wh / L) = (C1*V1) / (battery thickness*width*length).

[0133] ② High-temperature cycle test: After standing for 2 hours at 45±2°C, perform standard charge and discharge cycles with a voltage window of 4.45V to 3V, a charge current of 0.7C, a charge cutoff current of 0.05C, a cyclic discharge current of 0.5C, and a charge-discharge interval of 10 minutes. Calculate the capacity retention rate of the lithium-ion battery after the cycle. The calculation formula is as follows: Capacity retention rate (%) after the nth cycle = (discharge capacity after the nth cycle) / (discharge capacity after the first cycle) * 100%.

[0134] ③Charging performance test: Charge the above lithium-ion battery at different rates such as 0.5C and 1C. When the battery reaches the rated voltage, record the charging time.

[0135] The test results are shown in Table 8.

[0136] Table 8

[0137]

[0138] As can be seen from Examples 1 to 4, the performance of lithium-ion batteries shows obvious regular changes as the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide changes. When the lithium cobalt oxide ratio is higher, the energy density is higher (such as 770.0Wh / L in Example 1), but its rate performance is poor and the charging time is longer (1C charging requires 100.3 minutes). This is because although lithium cobalt oxide has a high energy density, its conductivity and lithium ion diffusion capacity are limited, resulting in a decrease in fast charging performance. Conversely, as the mass ratio of lithium nickel cobalt manganese oxide increases, the energy density gradually decreases (such as the energy density of 695.0Wh / L in Example 4), but the fast charging performance is significantly improved (1C charging time is reduced to 75.5 minutes), which is because lithium nickel cobalt manganese oxide has higher electronic conductivity and ion diffusion rate. In addition, the structure of lithium nickel cobalt manganese oxide is more stable, which can effectively inhibit the decomposition of the positive electrode active material under high voltage cycling and improve the cycling performance (such as the capacity retention rate of 94.30% in Example 4). By adjusting the mass ratio of lithium cobalt oxide and lithium nickel cobalt manganese oxide (such as the mass ratio of lithium cobalt oxide and lithium nickel cobalt manganese oxide in Example 2 is 60:40; at the same time, the compaction density of the positive electrode sheet is ρ 3.95g / cm3 , satisfying 4.1*a%+3.3*b%≤ρ≤4.4*a%+3.8*b%), which can improve the balance of lithium-ion battery energy density, high temperature performance and fast charging performance.

[0139] As shown in Examples 2 and 5-8, increasing the particle size of lithium cobalt oxide and lithium nickel cobalt manganese oxide reduces the capacity retention and fast-charging performance of lithium-ion batteries. This is because as the particle size of lithium cobalt oxide and lithium nickel cobalt manganese oxide increases, the specific surface area decreases, the active sites decrease, the lithium ion insertion / deinsertion paths become longer, the diffusion resistance increases, and the fast-charging performance decreases. At the same time, the contact area between particles decreases, the conductive path is restricted, and the internal resistance increases. During cycling, the particles are prone to cracking or falling off due to stress concentration, resulting in active material failure and ultimately reduced capacity retention and fast-charging efficiency. Comparing Examples 2 and 5-8, it can be seen that when the median particle sizes of large-particle lithium cobalt oxide, small-particle lithium cobalt oxide, and lithium nickel cobalt manganese oxide are 15.5μm, 4.5μm, and 3.8μm, respectively (Example 2), the energy density, high-temperature performance, and fast-charging performance of the lithium-ion battery are more balanced.

[0140] It can be seen from Examples 2, 9 to 12 that by increasing the doping amount of Al, Mg, and Ti elements in lithium cobalt oxide, and / or increasing the doping amount of Zr, Y, and W elements in lithium nickel cobalt manganese oxide, the energy density and fast charging performance of the lithium ion battery show a downward trend, while the capacity retention rate shows an upward trend. The increase in the doping amount of Al, Mg, and Ti and / or the increase in the doping amount of Zr, Y, and W improves the structural stability of the positive electrode active material, reduces high-temperature phase transitions and side reactions, inhibits capacity decay, and significantly improves the capacity retention rate. However, the doping elements reduce the active site density of the positive electrode active material, resulting in a decrease in energy density and fast charging performance. Comparing Examples 2, 9 to 12, it can be seen that when the doping amounts of Al, Mg, and Ti in lithium cobalt oxide are 8000ppm, 700ppm, and 1400ppm, respectively, and the doping amounts of Zr, Y, and W in lithium nickel cobalt manganese oxide are 2500ppm, 1500ppm, and 3000ppm, respectively, the energy density, high-temperature performance, and fast charging performance of the lithium ion battery are more balanced.

[0141] As shown in Examples 11, 13, and 16, reducing the particle size of the capacity-type graphite in the first active coating 101 and / or the rate-type graphite in the second active coating 102 on the negative electrode sheet (e.g., the median particle size of the capacity-type graphite in Example 13 was 12.3 μm, and the median particle size of the rate-type graphite was 5.6 μm) further improved the fast-charging performance of lithium-ion batteries. Furthermore, increasing the ratio of the rate-type graphite in the second active coating 102 to the capacity-type graphite in the first active coating 101 (e.g., the areal density ratio of the capacity-type graphite to the rate-type graphite in Example 16 was 7.0:3.0) further enhanced the fast-charging performance of lithium-ion batteries. This is because reducing the particle size of the graphite (capacity-type or rate-type) increases the particle specific surface area, providing more active sites; increasing the ratio of the rate-type graphite optimizes the electrode layer structure and enhances the efficiency of the fast-charging reaction.

[0142] As shown in Examples 15, 17, and 18, increasing the cold-pressed compaction density of the negative electrode sheet significantly increases the energy density of the lithium-ion battery, but the capacity retention rate and fast-charging performance show a downward trend. This is because increasing the cold-pressed compaction density can reduce porosity and increase the stacking efficiency of the negative electrode active material, thereby improving the energy density of the lithium-ion battery. However, excessively high compaction density can introduce mechanical stress, leading to particle breakage or structural damage, thereby affecting capacity retention and fast-charging performance.

[0143] In Examples 19-30, the first active coating layer 101 and the second active coating layer 102 of the negative electrode sheet utilize a capacity-specific material (e.g., capacity-specific graphite, capacity-specific graphite-silicon-carbon composite material) and a rate-specific material (e.g., rate-specific graphite, rate-specific graphite-silicon-carbon composite material) as the negative electrode active materials, respectively. In other words, silicon-carbon materials are added to the negative electrode active materials of the first active coating layer 101 (or / or the second active coating layer 102). An overall comparison of Examples 19-30 with Comparative Examples 3 and 4 shows that the addition of silicon-carbon materials to the negative electrode active materials improves the energy density and fast-charging performance of the lithium-ion battery, while decreasing its high-temperature cycling performance (capacity retention). This is because the theoretical specific capacity of silicon is approximately ten times that of graphite (graphite is approximately 372 mAh / g, while silicon is approximately 4200 mAh / g). Combining silicon with graphite significantly increases the overall specific capacity of the negative electrode, thereby improving the battery's energy density. Since the gram capacity of the negative electrode active material is improved after silicon doping, under the same positive electrode sheet surface density conditions, the negative electrode only needs to be coated with a smaller mass of negative electrode active material to meet the design requirements of the NP ratio. The lower coating amount leads to a thinner negative electrode sheet thickness, thereby reducing the lithium ion diffusion path and improving the fast charging capability of the lithium-ion battery. However, silicon will undergo large volume expansion and contraction during the charging and discharging process, especially during the lithium ion insertion and deinsertion process. The volume expansion of silicon can reach about 300%, which will cause damage to the electrode structure, forming cracks or falling off, thereby affecting the high-temperature cycle performance of the lithium-ion battery.

[0144] In Comparative Example 1, the compaction density of the positive electrode sheet is 3.60 g / cm 3 , does not satisfy 4.1*a%+3.3*b%≤ρ≤4.4*a%+3.8*b%. (In Comparative Example 1, the mass proportion of lithium cobalt oxide in the positive electrode active material is 40%, and the mass proportion of lithium nickel cobalt manganese oxide in the positive electrode active material is 60%, then 3.62g / cm 3 ≤ρ≤4.04g / cm 3 At this time, the upper limit of the compaction density of the positive electrode is 4.04g / cm 3 , the lower limit is 3.62g / cm 3 As shown in Table 1, the test results of Examples 2, 5 to 18 and Comparative Example 1 show that when the compaction density of the positive electrode sheet is less than the lower limit of the compaction density of the positive electrode sheet of 3.62 g / cm 3 The energy density of lithium-ion batteries decreases significantly.

[0145] In Comparative Example 2, the compaction density of the positive electrode sheet is 4.25 g / cm 3, does not satisfy 4.1*a%+3.3*b%≤ρ≤4.4*a%+3.8*b%. (In Comparative Example 2, the mass proportion of lithium cobalt oxide in the positive electrode active material is 40%, and the mass proportion of lithium nickel cobalt manganese oxide in the positive electrode active material is 60%, then 3.62g / cm 3 ≤ρ≤4.04g / cm 3 At this time, the upper limit of the compaction density of the positive electrode is 4.04g / cm 3 , the lower limit is 3.62g / cm 3 As shown in Table 1, by comparing the test results of Examples 2, 5 to 18 and Comparative Example 2, it can be seen that when the compaction density of the positive electrode sheet is greater than the upper limit of the compaction density of the positive electrode sheet of 4.04 g / cm 3 When the temperature is too high, the high temperature cycle performance (capacity retention) of lithium-ion batteries is significantly reduced.

[0146] In Comparative Examples 3 and 4, the negative electrode plate has only one negative electrode active material layer, and the material used in the negative electrode active material layer is a mixture of capacity-type graphite and rate-type graphite.

[0147] In Comparative Example 3, the mass ratio of capacity-type graphite to rate-type graphite is 70%:30%. The test results shown in Table 1 indicate that while the energy density of the lithium-ion battery in Comparative Example 3 is higher, the high-temperature cycling performance (capacity retention) of the lithium-ion battery in Comparative Example 3 is significantly lower than that of Examples 2 and 5-18. This indicates that the negative electrode active material used in the negative electrode sheet in Comparative Example 3 fails to achieve a balance between the energy density and high-temperature cycling performance of the lithium-ion battery.

[0148] In Comparative Example 4, the mass ratio of capacity-type graphite to rate-type graphite is 30%:70%. The test results shown in Table 1 indicate that compared with Examples 2 and 5-18, the lithium-ion battery in Comparative Example 4 has a lower energy density, while its capacity retention and fast-charging performance show no significant differences. This indicates that the negative electrode active material used in the negative electrode sheet of Comparative Example 4 also struggles to achieve a balance between energy density and high-temperature cycling performance in lithium-ion batteries.

[0149] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, and a separator, characterized in that: The positive electrode plate includes a positive electrode active material layer, wherein the positive electrode active material of the positive electrode active material layer includes lithium cobalt oxide and ternary nickel cobalt manganese oxide, wherein the mass proportion of the lithium cobalt oxide in the positive electrode active material is a%, 0<a<100, and the mass proportion of the ternary nickel cobalt manganese oxide in the positive electrode active material is b%, 0<b<100, a%+b%=100%, and the compaction density of the positive electrode plate is ρg / cm 3 , 4.1*a%+3.3*b%≤ρ≤4.4*a%+3.8*b%; The negative electrode plate includes a negative electrode active material layer, the negative electrode active material layer includes a first active coating layer close to the negative electrode current collector and a second active coating layer away from the negative electrode current collector, the negative electrode active material of one of the first active coating layer and the second active coating layer is a capacity type material, and the negative electrode active material of the other active coating layer is a rate type material; The lithium cobalt oxide includes large-particle lithium cobalt oxide and small-particle lithium cobalt oxide, the large-particle lithium cobalt oxide has a Dn50 particle size of 12 to 20 μm, the large-particle lithium cobalt oxide has a Dn99 particle size of ≤60 μm, the small-particle lithium cobalt oxide has a Dn50 particle size of 2 to 6 μm, the small-particle lithium cobalt oxide has a Dn99 particle size of ≤12 μm, and the mass ratio of the large-particle lithium cobalt oxide to the small-particle lithium cobalt oxide is 8:2 to 7:3; The lithium cobalt oxide is doped with Al, Mg, and Ti elements, wherein the content of Al in the lithium cobalt oxide is 5000-13000 ppm, the content of Ti is 200-1500 ppm, the content of Mg is 500-2000 ppm, and the mass ratio of Ti / Mg is 1:1-1:3; The ternary nickel-cobalt-manganese oxide is doped with Zr, Y, and W elements. The Zr content in the ternary nickel-cobalt-manganese oxide is 1000-4000 ppm, the Y content in the ternary nickel-cobalt-manganese oxide is 1000-2500 ppm, and the W content in the ternary nickel-cobalt-manganese oxide is 2000-4500 ppm.

2. The lithium-ion battery according to claim 1, wherein The chemical formula of the ternary nickel-cobalt-manganese oxide is: LiNi x Co y Mn z O2, where: x+y+z=1, x≥y.

3. The lithium-ion battery according to claim 1, wherein The median particle size Dn50 of the ternary nickel-cobalt-manganese oxide is 2-15 μm.

4. The lithium-ion battery according to claim 1, wherein The thickness of the positive electrode sheet is 50-200 μm, and the surface density of the positive electrode sheet is 130-300 g / m 2 .

5. The lithium-ion battery according to claim 1, wherein The capacity type material includes one or more of capacity type graphite and capacity type graphite-silicon carbon composite material; the rate type material includes one or more of rate type graphite and rate type graphite-silicon carbon composite material.

6. The lithium-ion battery according to claim 1, wherein The negative electrode active material of the first active coating is capacity-type graphite, and the median particle size Dn50 of the capacity-type graphite is 10-18 μm; the negative electrode active material of the second active coating is rate-type graphite, and the median particle size Dn50 of the rate-type graphite is 4-12 μm.

7. The lithium-ion battery according to claim 6, characterized in that The surface density ratio of the first active coating layer to the second active coating layer is 9:1 to 5:

5.

8. The lithium-ion battery according to claim 1, wherein The negative electrode active material of the first active coating is a capacity-type graphite-silicon-carbon composite material, and the negative electrode active material of the second active coating is a rate-type graphite. The mass proportion of the silicon-carbon material in the capacity-type graphite-silicon-carbon composite material is 1% to 30%.

9. The lithium-ion battery according to claim 1, wherein The surface density ratio of the first active coating layer to the second active coating layer is 8:2 to 7:

3.

10. The lithium-ion battery according to claim 1, wherein The thickness of the base film of the separator is ≤4 μm.

11. The lithium-ion battery according to claim 1, wherein The negative electrode active material of the first active coating is capacity-type graphite, and the negative electrode active material of the second active coating is rate-type graphite-silicon-carbon composite material.

12. The lithium-ion battery according to claim 1, wherein The thickness of the base film of the separator is ≥5 μm.

13. The lithium-ion battery according to claim 1, wherein The negative electrode active material of the first active coating is a rate-type graphite-silicon-carbon composite material, and the negative electrode active material of the second active coating is a capacity-type graphite-silicon-carbon composite material; or The negative electrode active material of the first active coating is a capacity-type graphite-silicon-carbon composite material, and the negative electrode active material of the second active coating is a rate-type graphite-silicon-carbon composite material.

14. The lithium-ion battery according to any one of claims 1 to 13, characterized in that The surface density of the negative electrode sheet is 50-120 g / m 2 .

15. The lithium-ion battery according to any one of claims 1 to 13, characterized in that: The cold pressed density of the negative electrode plate is 1.5-2.0 g / cm 3 .

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