Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery. The battery comprises a positive plate and electrolyte, the positive plate comprises a positive current collector, a bottom coating and a positive active layer, and the bottom coating is located between the positive active layer and the positive current collector; the positive electrode active layer comprises a cobalt-containing positive electrode material; the bottom coating comprises a lithium supplementing agent and silicon dioxide, the lithium supplementing agent comprises lithium-rich lithium nickelate and / or lithium-rich lithium ferrite, the lithium-rich lithium nickelate comprises a substance with the chemical formula of Lia1Nib1M1c1O2, and M1 comprises at least one of elements Mn, Co, Al and Mg; the lithium-rich lithium ferrite comprises a substance with a chemical formula of Lia2Feb2M2c2O2, and M2 comprises at least one of elements of Mn, Co, Al and Mg; the average particle size of the silicon dioxide is 5-50nm; the electrolyte comprises a nitrile additive. According to the battery, the high-temperature storage and mechanical safety performance can be improved while the initial coulombic efficiency is improved.

Description

TECHNICAL FIELD

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

[0002] Lithium ion batteries are widely used in the fields of portable electronic devices and power batteries. With the continuous improvement of living quality, the market demand for high energy density lithium ion batteries is increasing, which promotes the development and application of high capacity silicon-based negative electrode materials. However, the silicon-based negative electrode, while improving the energy density of the battery, also brings two problems: on the one hand, its first coulomb efficiency is low, causing irreversible loss of active lithium, thereby reducing the specific capacity utilization rate of the positive electrode material; on the other hand, the silicon-based material itself has poor thermal stability, which affects the overall safety performance of the battery. Therefore, in view of the problems of low utilization rate of positive active material and insufficient safety of silicon-based negative electrode lithium ion battery, it is of important research value and application significance to explore effective solutions to improve the first coulomb efficiency and thermal safety performance of the battery. SUMMARY

[0003] The purpose of the present application is to overcome the problems of low first coulomb efficiency of silicon-based negative electrode system lithium ion battery and poor safety performance caused by insufficient thermal stability of silicon-based negative electrode in the prior art. A battery is proposed, which introduces a lithium supplement agent and small particle silicon dioxide into the positive electrode bottom coating to improve the positive electrode capacity and enhance the first coulomb efficiency, mechanical safety performance and high temperature storage performance of the battery.

[0004] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0005] A battery, comprising a positive electrode sheet and an electrolyte, the positive electrode sheet comprising a positive electrode current collector, a bottom coating and a positive electrode active layer, the positive electrode active layer being located on at least one side of the outer surface of the positive electrode current collector, and the bottom coating being located between the positive electrode active layer and the positive electrode current collector; the positive electrode active layer comprises a positive electrode active material, and the positive electrode active material comprises a cobalt-containing positive electrode material; the bottom coating comprises a lithium supplement agent and silicon dioxide;

[0006] The lithium supplement agent comprises lithium-rich lithium nickelate and / or lithium-rich lithium ironate, the lithium-rich lithium nickelate comprising a substance with a chemical formula of Li a1 Ni b1 M 1 c1 O2, 1 1 Comprising at least one of elements Mn, Co, Al and Mg;

[0007] The lithium-rich lithium ironate comprises a substance with a chemical formula of Li a2 Fe b2 M2 c2 For O2, 1 < a² ≤ 2, 0 < b² < 1, 0 < c² ≤ 0.3, M 2 Includes at least one of the elements Mn, Co, Al, and Mg;

[0008] The average particle size of the silica is 5nm-50nm;

[0009] The electrolyte includes nitrile additives.

[0010] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0011] (1) In the battery of the present invention, a cobalt-containing cathode material is used. This material has a two-dimensional layered structure, high tap density, good lithium-ion migration channels, excellent electrochemical reversibility and structural stability. Combined with nitrile additives in the electrolyte, it can play a dual role: on the one hand, it can utilize the high temperature stability and oxidation stability of nitrile additives to improve the high temperature storage performance of the battery; on the other hand, it can complex the transition metal ions dissolved from the cathode to improve the structural stability of the cathode and improve the cycle performance of the battery.

[0012] (2) By setting a base layer containing lithium replenishing agent between the positive electrode current collector and the positive electrode active layer, the excessive contact between the lithium replenishing agent and the electrolyte is avoided, which aggravates the side reaction and leads to the reduction of battery gas production and electrochemical performance. In particular, the contact between the lithium replenishing agent and the nitrile additives in the electrolyte is reduced, and the nitrile additives are avoided from being oxidized. While improving the battery's first efficiency, mechanical safety performance, electrochemical stability and high temperature storage performance are also improved.

[0013] (3) By introducing silicon dioxide into the base coating, the average particle size of silicon dioxide is controlled to be between 5nm and 50nm, so that it is evenly distributed on the surface of the lithium replenishing agent, further reducing the direct contact between the electrolyte and the lithium replenishing agent. At the same time, the coating of the positive electrode current collector prevents the base coating from falling off and causing the battery to short circuit, thereby improving the mechanical abuse performance, electrochemical stability and high temperature storage performance of the battery.

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0015] Figure 1 The image shown is a scanning electron microscope image of the surface of the base coating in one embodiment of the present invention.

[0016] Figure 2 The image shown is an EDS spectrum of silicon on the surface of the bottom coating in one embodiment of the present invention.

[0017] Figure 3 The image shown is a partial scanning electron microscope image of the undercoat surface in one embodiment of the present invention.

[0018] Figure 4 The diagram shown is a schematic diagram of the diaphragm along its thickness direction in one embodiment of the present invention.

[0019] Figure labels: 1 is the base film, 2 is the nitrogen-containing coating, and 3 is the adhesive layer. Detailed Implementation

[0020] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0021] This invention provides a battery comprising a positive electrode and an electrolyte. The positive electrode comprises a positive current collector, a base coating, and a positive active layer. The positive active layer is located on at least one outer surface of the positive current collector, and the base coating is located between the positive active layer and the positive current collector. The positive active layer comprises a positive active material, which includes a cobalt-containing positive electrode material. The base coating comprises a lithium supplement and silicon dioxide. The lithium supplement comprises lithium-rich nickel oxide and / or lithium-rich lithium iron ore, wherein the lithium-rich nickel oxide comprises a material with the chemical formula Li. a1 Ni b1 M 1 c1 For O2, 1 < a1 ≤ 2, 0 < b1 < 1, 0 < c1 ≤ 0.3, M 1 It includes at least one of the elements Mn, Co, Al, and Mg; the lithium-rich lithium iron ferrite includes the chemical formula Li a2 Fe b2 M 2 c2 For O2, 1 < a² ≤ 2, 0 < b² < 1, 0 < c² ≤ 0.3, M 2 It includes at least one of the elements Mn, Co, Al and Mg; the average particle size of the silica is 5nm-50nm; the electrolyte includes nitrile additives.

[0022] While using silicon-based anodes can improve energy density in lithium-ion batteries, it also leads to low initial coulombic efficiency and accelerated loss of active lithium in the cathode. To compensate for irreversible lithium loss, current technologies often involve directly adding lithium replenishing agents to the active layer of the cathode. These agents release lithium ions during the first charge, thereby improving the specific capacity utilization of the cathode material. However, lithium replenishing agents are typically highly chemically reactive and prone to side reactions with the electrolyte, resulting in problems such as battery gas generation and decreased cycle performance.

[0023] In this invention, to suppress side reactions while achieving effective lithium replenishment, a base coating containing a lithium replenishing agent is proposed between the positive electrode active layer and the current collector. This structure reduces direct contact between the lithium replenishing agent and the electrolyte, thereby reducing the degree of side reactions and improving the battery's initial coulombic efficiency, electrochemical stability, and high-temperature storage performance. To maximize the isolation between the electrolyte and the lithium replenishing agent, nano-sized silica is introduced into the base coating. Due to its small particle size and good dispersibility, silica can uniformly coat the surface of the lithium replenishing agent particles, forming a more effective physical barrier, further inhibiting the electrolyte's erosion of the lithium replenishing agent and reducing the intensity of side reactions.

[0024] Furthermore, regarding cathode materials, cobalt-containing cathodes such as lithium cobalt oxide with a layered structure are selected due to their high tap density, good lithium-ion migration channels, and excellent electrochemical reversibility and structural stability. Combined with nitrile additives in the electrolyte, they can play a dual role: firstly, they complex the transition metal ions dissolved from the cathode, inhibiting their catalytic oxidation of the electrolyte; secondly, their high oxidation and thermal stability improve the battery's performance under high-temperature conditions. However, lithium additives may dissolve high-valence metal ions (such as Ni) under high pressure or high temperature environments. 4+ or Fe 3+ These ions possess strong oxidizing properties and can attack nitrile additives, weakening their function. Therefore, this invention places the lithium replenishing agent within the undercoat and introduces nano-sized silica to prevent direct contact between the lithium replenishing agent and nitrile additives in the electrolyte, thus avoiding oxidative degradation of the latter and maintaining its high-temperature protection effect. Furthermore, nano-silica can enhance the adhesion strength between the undercoat and the current collector, improve the mechanical stability of the coating, and reduce the risk of undercoat detachment during battery stress or cycling, thereby improving the battery's safety performance and long-term cycle reliability under mechanical abuse conditions.

[0025] In this invention, the base coating comprises a lithium replenishing agent and silicon dioxide, wherein the average particle size of the silicon dioxide is 5nm-50nm, for example, 5nm, 6nm, 7nm, 8nm, 10nm, 12nm, 14nm, 16nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, or within any two of the above values.

[0026] In one embodiment, the average particle size of the silicon dioxide is 20nm-40nm.

[0027] In this invention, the silicon dioxide can be prepared by conventional methods in the art, such as chemical vapor deposition.

[0028] When the average particle size of silica is limited to a suitable range, on the one hand, silica can be distributed on the outer surface of the lithium replenisher, reducing the contact between the lithium replenisher and the electrolyte and mitigating side reactions; on the other hand, silica has a large specific surface area, which can coat the positive electrode current collector, reducing the risk of battery short circuit and improving the battery's mechanical abuse performance. When the average particle size of silica is too small (e.g., less than 5 nm), the high specific surface area and surface energy cause silica particles to agglomerate, resulting in uneven local distribution and loss of nano-effect. When subjected to external force, cracks around the locally agglomerated silica expand, leading to a decrease in the strength of the undercoating layer, which is not conducive to improving mechanical performance. The high specific surface area also increases the contact area with the electrolyte, leading to an aggravation of side reactions and an increase in the probability of battery gas generation. When the average particle size of silica is too large (e.g., greater than 50 nm), the large particle size cannot coat the positive electrode current collector well, and a small amount of silica falling off will expose the current collector, thereby increasing the risk of short circuit.

[0029] In this invention, based on the total mass of the base coating, the mass content of the silica is 5%-20%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or within any two of the above values. If the silica content is too low (<5%), a complete and dense coating layer cannot be formed on the surface of the lithium supplement particles, making it difficult to effectively prevent direct contact between them and nitrile additives in the electrolyte. This not only leads to the lithium replenishment agent undergoing side reactions and being consumed before the first charge, reducing lithium replenishment efficiency, but also causes nitrile additives to be oxidized and degraded by high-valence metal ions dissolved from the lithium replenishment agent, weakening their protective effect. Conversely, if the silica content is too high (>20%), since silica itself is an insulator, it will severely hinder the transport of electrons between the current collector and the positive electrode active layer, leading to increased internal resistance and intensified polarization. In addition, excessive silica will also increase the brittleness of the undercoating layer, making it prone to cracking under stress, thus providing channels for electrolyte penetration. Therefore, controlling the silica content within the above range can ensure that the undercoating layer performs optimally in terms of achieving efficient lithium replenishment, protecting functional additives, and maintaining interface stability.

[0030] In one embodiment, the silica content is 8%-15% by mass, based on the total mass of the base coating.

[0031] In this invention, the silicon dioxide covers at least a portion of the outer surface of the lithium replenishing agent.

[0032] It is understood that "at least partially" means that the silica can cover the entire outer surface of the lithium replenishing agent or a portion of the outer surface of the lithium replenishing agent, that is, the percentage of the projected area of ​​the silica on the outer surface of the lithium replenishing agent can be equal to 100% or less than 100%.

[0033] like Figure 1 The image shown is a scanning electron microscope image of the surface of the base coating in one embodiment of the present invention. Figure 2 The image shown is an EDS spectrum of silicon on the surface of the bottom coating in one embodiment of the present invention. Figure 3 The image shown is a partial scanning electron microscope image of the undercoat surface in one embodiment of the present invention, wherein... Figure 3 yes Figure 1 In a localized area, the area within the solid white line represents the lithium replenishment agent. Figure 2 It can be seen that silicon is distributed on the surface of the lithium supplement and titanium dioxide. Figure 3 The relatively larger particles are titanium dioxide, and the smaller particles are silicon dioxide.

[0034] In this invention, the electrolyte includes nitrile additives.

[0035] In this invention, the nitrile additives include at least one of adiponitrile (ADN), 1,3,6-hexanetrionitrile (HTCN), butadionitrile (SN), 1,4-dicyano-2-butene, pentaetheronitrile, trietheronitrile, ethylene glycol bis(propionitrile) ether, and glycerol trinitrile.

[0036] In this invention, based on the total weight of the electrolyte, the weight content of the nitrile additive is 0.1%-10%, for example, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or within any two of the above values.

[0037] In one embodiment, the nitrile additive has a weight content of 0.3%-8% based on the total weight of the electrolyte.

[0038] In another embodiment, the weight content of the nitrile additive is 0.5%-3% based on the total weight of the electrolyte.

[0039] In cobalt-containing cathode systems (such as lithium cobalt oxide), nitrile additives can effectively complex transition metal ions dissolved from the cathode, reducing the oxidation of the electrolyte by these transition metal ions and improving the structural stability of the cathode active material. However, when lithium replenishment agents are added to the cathode system to compensate for lithium loss during the initial charge and discharge cycle, high-valence metal ions (such as Ni) will dissolve under high temperature or high pressure. 4+ or Fe 3+These ions have strong oxidizing properties and can attack nitrile additives, weakening their function. To optimize the role of nitrile additives, their content needs to be adjusted within a suitable range. When the content of nitrile additives in the electrolyte is too low (e.g., less than 0.1%), the complexing ability of nitrile additives for transition metal ions at the positive electrode is insufficient, failing to effectively alleviate cobalt dissolution at the negative electrode, resulting in poor structural stability of the positive electrode. When the content of nitrile additives in the electrolyte is too high (e.g., >10%), the excessive amount of nitrile additives in the electrolyte leads to increased internal resistance and polarization in the battery, and also exacerbates the oxidation of nitrile additives by high-valence metal ions in the lithium supplement, resulting in decreased battery kinetics and stability.

[0040] Lithium-rich lithium iron ore and lithium-rich lithium nickel ore, acting as lithium replenishers, decompose and release active lithium during the first charge of the battery to compensate for lithium loss during the formation of the SEI film on the negative electrode, reducing irreversible capacity loss and thus improving the battery's energy density and initial coulombic efficiency. By setting an undercoat layer between the positive electrode active layer and the positive electrode current collector and adding a lithium replenisher to the undercoat layer, not only can the utilization rate of lithium ions in the positive electrode active material of silicon-based negative electrode lithium-ion batteries be improved, solving the problem of low initial coulombic efficiency, but it can also reduce the contact area between the electrolyte and the lithium replenisher to a certain extent, mitigating side reactions between the lithium replenisher and the electrolyte, avoiding battery gas generation and electrochemical performance deterioration; it can also play a protective role for the positive electrode sheet, improving battery safety performance and reducing the risk of battery short circuits caused by problems such as electrode breakage after being subjected to external impact.

[0041] For lithium-ion batteries with lithium cobalt oxide cathode systems, the high operating voltage of lithium cobalt oxide makes the electrolyte prone to oxidation and decomposition at high voltages, producing byproducts such as CO2 and H2, leading to increased internal resistance. Furthermore, lithium cobalt oxide is susceptible to lattice distortion during charge and discharge, causing cobalt dissolution. The dissolved cobalt ions migrate to the negative electrode surface, damaging the SEI film. To compensate for these drawbacks, adding appropriate amounts of nitrile additives to the electrolyte is necessary. Nitrile additives coordinate with transition metals in cobalt-containing cathode materials, inhibiting cobalt ion dissolution, improving cathode structural stability, and enhancing the interfacial stability of lithium cobalt oxide at high voltages, thereby improving the overall thermal stability and high-temperature storage performance of the battery. However, in cathode systems containing lithium replenishers, when the lithium replenisher comes into contact with nitrile additives in the electrolyte, the high-valence metal ions (such as Ni) in the lithium replenisher... 4+ Ni 3+ and Fe 3+ (etc.) and surface residual alkali will oxidize nitrile additives in the electrolyte to form lithium carbonate, Ni 2+ Fe 2+Nitrogen-containing organic compounds, such as lithium carbonate, increase interfacial impedance and may clog electrode pores, leading to poor battery kinetics. It can be seen that placing the lithium replenishing agent in the undercoat layer rather than adding it directly to the active layer can also provide a barrier effect, mitigating excessive contact between the electrolyte, especially nitrile additives in the electrolyte, and the lithium replenishing agent. In addition, small-diameter silica particles were added to the bottom coating to control the average particle size between 5nm and 50nm, thereby further reducing the contact between the lithium replenishing agent and the nitrile additives in the electrolyte, avoiding the increase of side reactions that would lead to the deterioration of the battery's dynamic performance, and also improving the battery's safety performance. The reasons are: (1) Small-diameter silica can be distributed on the surface of the lithium replenishing agent, reducing the contact area between the lithium replenishing agent and the electrolyte, and alleviating the battery's gas production; (2) Small-diameter silica has electronic insulation, a large specific surface area, and small gaps between particles. When used in the bottom coating, it can better wrap the positive electrode current collector. When the thickness of the bottom coating is constant, there are more small-diameter silica particles. When the positive electrode current collector is subjected to external force and breaks or cracks, a small amount of particle slippage at the fracture will not cause a large area of ​​aluminum foil to be exposed, reducing the most dangerous short circuit mode under mechanical abuse, namely the contact between the positive electrode current collector and the negative electrode active material, and improving the battery's mechanical abuse performance, such as needle penetration, heavy object impact, and unilateral extrusion.

[0042] In this invention, the average particle size of the silica can be obtained by conventional testing methods in the art, for example, by the following method: after discharging the battery to 0% SOC, the positive electrode sheet is disassembled and removed. After soaking in dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC to remove the lithium salt attached to the positive electrode sheet. The positive electrode sheet is then kept at 450°C for 180 minutes. The cooled positive electrode sheet is brushed off with a brush to obtain a positive current collector with a bottom coating on the surface. The cross-section is obtained by ion beam cutting. The obtained cross-section is observed in SEM using backscatter imaging mode. After magnification to a certain degree, EDS analysis is performed on the selected area to confirm the silica particles through elemental distribution. Ten silica particles are found and the distance between the two longest points of the edge contour of each silica particle is measured. The average value is taken as the average particle size of the silica.

[0043] In this invention, a1, b1, c1, a2, b2, c2, and M 1 and M 2 The types and contents of elements can be obtained through conventional testing methods in this field, such as the following method: Take about 0.1g of lithium supplement (lithium-rich nickel oxide or lithium-rich ferrite) sample, add 10mL of hydrochloric acid, and digest on a 350℃ hot plate for 10min. After cooling, make up to 100ml, then dilute 10 times, and take a portion of the solution for analysis using an ICP spectrometer. After obtaining the corresponding test parameters, a1, b1, c1, and M can be obtained by formula conversion. 1The types and amounts of elements (or a2, b2, c2 and M) 2 (The types and amounts of elements).

[0044] In this invention, the content of the nitrile additives in the electrolyte can be obtained by conventional testing methods in the art, such as by chromatography or chromatography-mass spectrometry.

[0045] In this invention, the base coating has a protrusion that is embedded in the positive electrode active layer;

[0046] In this invention, the height of the protrusion is 0.1μm-9μm, for example, 0.1μm, 0.2μm, 0.4μm, 0.6μm, 0.8μm, 1μm, 1.5μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, or within any two of the above values.

[0047] In one embodiment, the height of the protrusion is 1μm-5μm.

[0048] The undercoat has protrusions that are dispersed on the surface of the undercoat and embedded in the positive electrode active layer, forming an interlocking structure. This increases the surface roughness of the undercoat, thereby enhancing the adhesion between the undercoat and the positive electrode active layer. This prevents the positive electrode active layer from detaching when the battery is subjected to mechanical forces or its own volume expansion, thus improving battery cycle performance and safety. Furthermore, the protrusions in the undercoat contact the positive electrode active layer, shortening the lithium-ion migration path and improving lithium-ion transport efficiency. However, if the height of the protrusions is too large (e.g., greater than 9 μm), too much of the protrusion is embedded in the positive electrode active layer, increasing the contact area between the electrolyte and the lithium replenishing agent after the electrolyte penetrates the active layer, thus increasing side reactions between the lithium replenishing agent and the electrolyte. Conversely, if the height of the protrusions is too small (e.g., less than 0.1 μm), the surface roughness of the undercoat decreases, reducing the adhesion between the undercoat and the positive electrode active layer, which is detrimental to battery cycle performance.

[0049] It is understood that the height of the protrusion refers to the maximum distance from the highest point of the protrusion to the surface of the base coating. In the base coating, the silicon dioxide and titanium dioxide have high sphericity, resulting in better sliding properties during electrode rolling. Under rolling stress, they can accumulate on the surface of the positive electrode current collector. However, the lithium supplement has a larger particle size and lower sphericity, making it difficult to roll and causing it to protrude from the surface of the base coating.

[0050] In this invention, the height of the protrusion can be obtained by conventional testing methods in the art, such as by scanning electron microscopy, as follows: After discharging the lithium-ion secondary battery to 0% SOC, the positive electrode sheet is disassembled and removed. After soaking in dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC to remove the lithium salt attached to the positive electrode sheet. The positive electrode sheet is then kept at 450°C for 180 minutes. The cooled positive electrode sheet is brushed off with a brush to obtain a positive current collector with a base coating on the surface. The cross-section is obtained by ion beam cutting. The thickness of the base coating is obtained by scanning electron microscopy imaging of the obtained cross-section. Five different protrusions are selected in the obtained image, and their heights are measured using image analysis software. The average value is taken as the height of the protrusion.

[0051] In this invention, the base coating further includes conductive particles, the conductive particles being titanium dioxide, and the titanium dioxide including dopant elements Sn and / or Sb.

[0052] In this invention, the surface of the titanium dioxide is coated with an oxide of element Sn and / or an oxide of element Sb.

[0053] In one embodiment, the titanium dioxide includes the dopant elements Sn and Sb.

[0054] In one embodiment, the surface of the titanium dioxide is coated with an oxide of element Sn.

[0055] In another embodiment, the surface of the titanium dioxide is coated with an oxide of element Sb.

[0056] In this invention, the average particle size of the conductive particles is 50nm-500nm, for example, 50nm, 52nm, 54nm, 56nm, 58nm, 60nm, 65nm, 70nm, 80nm, 90nm, 100nm, 120nm, 140nm, 160nm, 180nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, or within any two of the above values.

[0057] In one embodiment, the average particle size of the conductive particles is 100nm-400nm.

[0058] In this invention, the conductivity of the conductive particles is 0.05 S / cm to 1 S / cm, for example, 0.05 S / cm, 0.06 S / cm, 0.07 S / cm, 0.08 S / cm, 0.1 S / cm, 0.2 S / cm, 0.3 S / cm, 0.4 S / cm, 0.5 S / cm, 0.6 S / cm, 0.7 S / cm, 0.8 S / cm, 0.9 S / cm, 1 S / cm, or within any two of the above values.

[0059] In this invention, based on the total mass of the base coating, the mass content of the conductive particles is 25%-75%, for example, 25%, 26%, 28%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or within any two of the above values.

[0060] In one embodiment, the mass content of the conductive particles is 40%-65% based on the total mass of the base coating.

[0061] Because silicon dioxide has electronic insulating properties, when it is distributed on the surface of the lithium supplement in the undercoat and its content in the undercoat reaches a certain level, it can lead to a decrease in the conductivity of the undercoat and even localized electronic insulation, affecting the overall conductivity of the positive electrode and hindering battery kinetics improvement. Adding conductive particles such as titanium dioxide can improve the conductivity of the undercoat. Controlling the content and average particle size of conductive particles helps improve the uniformity of their distribution in the undercoat, increasing electronic pathways and improving battery kinetics. However, when the content of conductive particles is too high (e.g., greater than 75%), the particles are difficult to disperse uniformly and may agglomerate locally in the undercoat, leading to excessive local current. Furthermore, excessive conductive particles significantly increase the conductivity of the undercoat. When the battery is subjected to mechanical damage and short circuit, the impedance between the undercoat and the negative electrode active material is low, increasing the short-circuit current and heat generation. The following factors can affect battery safety performance: When the content of conductive particles is too low (e.g., less than 25%), the insufficient content of conductive particles cannot form electronic pathways in the base coating, resulting in insufficient improvement in conductivity; when the average particle size of conductive particles is too small (e.g., less than 50 nm), the specific surface area of ​​conductive particles is large, and there is more contact between particles, which easily causes agglomeration and uneven distribution of conductive particles in the base coating; when the average particle size of conductive particles is too large (e.g., greater than 500 nm), the conductive particles cannot fill the gaps between the components in the base coating, making it difficult to form a "bridging" effect and failing to improve electronic conductivity.

[0062] In this invention, the average particle size of the conductive particles can be obtained by conventional testing methods in the art, for example, by the following method: after discharging the battery to 0% SOC, the positive electrode sheet is disassembled and removed. After soaking in dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC to remove the lithium salt attached to the positive electrode sheet. The positive electrode sheet is then kept at 450°C for 180 minutes. The cooled positive electrode sheet is brushed off with a brush to obtain a positive current collector with a base coating on the surface. The cross-section is obtained by ion beam cutting. The obtained cross-section is observed in SEM using backscatter imaging mode. After magnification to a certain degree, EDS analysis is performed on the selected area to identify conductive particles through elemental distribution. Ten conductive particles are found and the distance between the two longest points of the edge contour of each conductive particle is measured. The average value is taken as the average particle size of the conductive particles.

[0063] In this invention, the conductivity of the conductive particles can be obtained by conventional testing methods in the art, such as by a powder resistivity tester.

[0064] In this invention, the element Sn or element Sb in the titanium dioxide can be obtained by conventional testing methods in the art, for example by the following method: after discharging the battery to 0% SOC, the positive electrode sheet is disassembled and removed. After soaking in dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC to remove the lithium salt attached to the positive electrode sheet. The positive electrode sheet is then kept at 450°C for 180 minutes. The cooled positive electrode sheet is brushed off with a brush to obtain a positive electrode current collector with a bottom coating on the surface. The cross-section is obtained by ion beam cutting. The obtained cross-section is observed in SEM using backscatter imaging mode. After magnification to a certain degree, EDS analysis is performed on the selected area to find titanium dioxide particles through elemental distribution. Further EDS analysis is used to confirm the element Sn or element Sb.

[0065] In this invention, the average particle size of the lithium replenishing agent is 1μm-10μm, for example, 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or within any two of the above values.

[0066] In one embodiment, the lithium supplement has an average particle size of 3 μm-8 μm.

[0067] Adjusting the average particle size of the lithium replenishing agent within a suitable range can improve the lithium replenishment effect and enhance the battery's electrochemical performance. When the average particle size of the lithium replenishing agent is too large (e.g., greater than 10 μm), the specific surface area is too small, making incomplete reactions during the lithium replenishment process easy, resulting in low lithium replenishment efficiency and poor lithium replenishment effect. When the average particle size of the lithium replenishing agent is too small (e.g., less than 1 μm), the specific surface area of ​​the lithium replenishing agent is too large, increasing the contact area with the electrolyte. This intensifies the side reactions between the lithium replenishing agent and the electrolyte, leading to an increased risk of battery gas generation.

[0068] In this invention, the conductivity of the lithium supplement is 10. -8 S / cm - 10S / cm, for example, 10 -8 S / cm, 10 -7 S / cm, 10 -6 S / cm, 10 -5 S / cm, 10 -4 S / cm, 10 -3 S / cm, 10 -2 S / cm, 0.1S / cm, 0.15S / cm, 0.2S / cm, 0.25S / cm, 0.3S / cm, 0.4S / cm, 0.5S / cm, 1S / cm, 2S / cm, 3S / cm, 4S / cm, 5S / cm, 6S / cm, 8S / cm, 10S / cm, or within any two of the above values.

[0069] In one embodiment, the lithium supplement comprises lithium-rich nickel oxide with a conductivity of 10. -8 S / cm-10 -6 S / cm.

[0070] In one embodiment, the lithium supplement comprises lithium iron ferrite rich in lithium, the lithium iron ferrite having a conductivity of 10. -2 S / cm - 10S / cm.

[0071] In this invention, based on the total mass of the base coating, the mass content of the lithium replenishing agent is 10%-65%, for example, 10%, 12%, 14%, 16%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or within any two of the above values.

[0072] In one embodiment, the mass content of the lithium replenishing agent is 15%-40% based on the total mass of the base coating.

[0073] Adjusting the content of the lithium replenisher in the undercoat layer within a suitable range can ensure the battery's initial coulombic efficiency while preventing side reactions between the lithium replenisher and the electrolyte that could lead to battery gas production. When the lithium replenisher content is too low (e.g., less than 10%), the lithium ions provided by the lithium replenisher cannot compensate for the active lithium ions lost during the first charge, resulting in poor improvement in the battery's initial coulombic efficiency. When the lithium replenisher content is too high (e.g., greater than 65%), the amount of metal residue in the battery system increases, exacerbating the side reactions between the lithium replenisher and the electrolyte, leading to battery gas production.

[0074] In this invention, the average particle size of the lithium replenishing agent can be obtained by conventional testing methods in the art, for example, by the following method: after discharging the battery to 0% SOC, disassemble and remove the positive electrode sheet, soak it in dimethyl carbonate (DMC) solvent for 12 hours, then rinse it with DMC to remove the lithium salt attached to the positive electrode sheet, then keep the positive electrode sheet at 450°C for 180 minutes, brush off the positive electrode active material with a brush to obtain a positive electrode current collector with a bottom coating on the surface, cut it with an ion beam to obtain a cross section, observe the obtained cross section in SEM using backscatter imaging mode, perform EDS analysis on the selected area after magnification to a certain degree, confirm the lithium replenishing agent through elemental distribution, find 10 lithium replenishing agent particles and measure the distance between the two longest points of the edge contour of each lithium replenishing agent particle, and take the average value as the average particle size of the lithium replenishing agent.

[0075] In this invention, the base coating layer further includes an adhesive, which includes at least one of polyvinylidene fluoride (PVDF), oil-based polyacrylic acid, polyacrylonitrile, and polytetrafluoroethylene.

[0076] In this invention, based on the total mass of the base coating, the mass content of the adhesive is 3%-10%, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or within any two of the above values.

[0077] In this invention, the thickness of the base coating is 1μm-5μm, for example, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm or within any two of the above values.

[0078] In this invention, the lithium cobalt oxide includes at least one of the doping elements Al, Mg, Ti, Zr, La and Y.

[0079] In this invention, the median particle size Dv50 of the lithium cobalt oxide is 10μm-20μm, for example, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 20μm, or within any two of the above values; the particle size Dv99 is 30μm-47μm, for example, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 40μm, 41μm, 42μm, 43μm, 44μm, 45μm, 46μm, 47μm, or within any two of the above values.

[0080] In one embodiment, the median particle size Dv50 of the lithium cobalt oxide is 13 μm-18 μm.

[0081] In this invention, the tap density of the lithium cobalt oxide is 2.4 g / cm³. 3 -3.2g / cm 3 For example, 2.4 g / cm³ 3 2.5g / cm 3 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 2.9g / cm 3 3g / cm 3 3.2g / cm 3 Or within the range of any two of the above values.

[0082] Controlling the median particle size Dv50 of lithium cobalt oxide within a certain range can improve the kinetic performance, interfacial stability, and safety performance of the lithium cobalt oxide cathode. When the median particle size Dv50 of lithium cobalt oxide is too small (e.g., <10μm), the specific surface area of ​​lithium cobalt oxide is large, allowing for sufficient contact with the electrolyte. Although this can improve ion diffusion efficiency, the excessively large specific surface area will exacerbate side reactions with the electrolyte, leading to increased interfacial film thickness, accelerated dissolution of cathode transition metals, battery cycle degradation, and reduced high-temperature safety. When the median particle size of lithium cobalt oxide is too large (e.g., >20μm), the diffusion path of lithium ions within the lithium cobalt oxide becomes longer, resulting in decreased overall kinetic performance and hindering rate performance improvement. Further limiting the particle size Dv99 of lithium cobalt oxide can adjust the porosity and packing pattern of lithium cobalt oxide particles during stacking.

[0083] Adjusting the tap density of lithium cobalt oxide within a certain range is beneficial for improving the cycle performance and energy density of the battery. When lithium cobalt oxide has a higher tap density, more lithium cobalt oxide can be accommodated per unit volume under the same coating thickness and compaction density, which is beneficial for improving the positive electrode energy density. However, if the tap density of lithium cobalt oxide is too high (e.g., greater than 3.2 g / cm³), it will negatively impact the battery's performance. 3At this point, the particle size of lithium cobalt oxide increases relatively, the diffusion distance of lithium ions in lithium cobalt oxide increases, and the rate performance of the battery decreases; when the tap density of lithium cobalt oxide is too low (e.g., less than 2.4 g / cm³), the rate performance of the battery also decreases. 3 At this point, with the same capacity design, increasing the thickness of the positive electrode active layer actually reduces the overall volumetric energy density of the battery.

[0084] In this invention, the particle size Dv50 and particle size Dv99 of the lithium cobalt oxide can be obtained by conventional testing methods in the art, such as by laser particle size analyzer testing, specifically as follows: After discharging the battery to 0% SOC, the positive electrode sheet is disassembled and removed. After soaking in dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC to remove the lithium salt attached to the positive electrode sheet. The positive electrode sheet is then kept at 450°C for 180 minutes. The cooled positive electrode sheet is brushed off with a brush to obtain positive electrode active material powder. The collected positive electrode active material powder is taken as a sample, and the volume distribution curve is measured using a laser diffraction particle size analyzer. The median particle size Dv50 and particle size Dv99 of the lithium cobalt oxide are determined according to the equipment test values.

[0085] It should be noted that the residual positive electrode conductive agent in the positive electrode active material has a negligible effect on the test results of the particle size Dv50 and particle size Dv99 of the lithium cobalt oxide.

[0086] In this invention, the tap density of the lithium cobalt oxide can be measured using conventional testing methods in the art, for example, by the following method: After discharging the battery to 0% SOC, disassemble and remove the positive electrode sheet, soak it in dimethyl carbonate (DMC) solvent for 12 hours, then rinse it with DMC to remove the lithium salt adhering to the positive electrode sheet, then keep the positive electrode sheet at 450°C for 180 minutes, and brush off the positive electrode active material to obtain positive electrode active material powder; accurately weigh a certain mass of lithium cobalt oxide powder sample, put the powder into a cylindrical container of known volume, install the container on a tap density meter, and vibrate or tap it according to standard methods (such as ASTM B212 standard), and record the volume of the powder after vibration. The tap density calculation formula is: powder mass / volume after vibration.

[0087] In this invention, the battery further includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active layer located on at least one side surface of the negative current collector, the negative active layer including a negative active material, the negative active material including a silicon-based material, the silicon-based material including a first silicon-based material and / or a second silicon-based material.

[0088] In this invention, the sphericity of the first silicon-based material is α1, 0.6≤α1≤0.85, for example, 0.6, 0.62, 0.64, 0.66, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78, 0.8, 0.82, 0.84, 0.85, or within any two of the above values.

[0089] In this invention, the sphericity of the second silicon-based material is α2, where α2 > 0.85, and for example, 0.81, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, and 0.98 are within the range of any two of the above values.

[0090] In this invention, the silicon-based material includes at least one of silicon-carbon, silicon-oxygen, silicon alloy, and elemental silicon.

[0091] In one embodiment, the silicon-based material includes silicon-carbon.

[0092] In yet another embodiment, the first silicon-based material comprises first silicon-carbon.

[0093] In yet another embodiment, the second silicon-based material comprises a second silicon-carbon.

[0094] In this invention, based on the total mass of the negative electrode active layer, the silicon content is 4%-15%, for example, 4%, 4.7%, 4.8%, 4.9%, 5%, 5.5%, 6%, 6.5%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or within any two of the above values.

[0095] When silicon-based anode materials are used in batteries, the high specific capacity of silicon can improve the energy density of the battery. However, silicon-based materials undergo volume expansion during battery cycling, causing repeated rupture and growth of the SEI film on the surface of the silicon-based material, consuming active lithium and reducing the battery's initial efficiency. In addition, silicon-based anode materials also suffer from insufficient thermal stability, leading to low battery thermal safety. Therefore, controlling the content of elemental Si in the active layer of the anode helps to balance the battery's energy density and cycle expansion. Furthermore, combining it with a base coating containing lithium replenishing agents can ensure battery safety and electrical performance while maintaining the energy density of lithium-ion batteries.

[0096] In this invention, the sphericity α1 of the first silicon-based material and the sphericity α2 of the second silicon-based material can be obtained by conventional testing methods in the art, for example, by the following method: discharging the battery to 0% SOC, disassembling and removing the negative electrode, or directly removing the negative electrode, polishing its cross-section with an argon ion mill, and then imaging the obtained cross-section using backscatter imaging mode on a scanning electron microscope (SEM); and using image processing software such as ImagePro. Plus) The images of each silicon-based material particle in the SEM image (backscattered mode) of the negative electrode active layer at a certain magnification (e.g., 2500x) are analyzed to obtain the perimeter and area of ​​each particle. The equivalent radius of perimeter r1 and the equivalent radius of area r2 of each silicon-based material particle are calculated respectively. Then the sphericity of each particle is S = r2 / r1. The sphericity of each particle is then weighted and averaged to obtain the average sphericity of the silicon-based material. Silicon-based material particles with a sphericity less than or equal to 0.85 are counted as the first silicon-based material, and silicon-based material particles with a sphericity greater than 0.85 are counted as the second silicon-based material.

[0097] In this invention, the mass content of silicon in the negative electrode active layer can be tested using conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and soaked in dimethyl carbonate (DMC) solvent for 12 hours, then rinsed with DMC solvent to remove lithium salts adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active layer can then be peeled off from the negative electrode current collector, and the negative electrode active layer is collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the test sample amount is 5mg-15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 minutes, so that the non-silicon components in the negative electrode active layer volatilize while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash of the negative electrode active layer. The mass content of silicon in the negative electrode active layer can be calculated based on the mass of the ash. The calculation formula is as follows: Si content in the negative electrode active layer = 7 × mass of ash / (15 × mass of test sample).

[0098] In this invention, given that the lithium replenishment agent releases oxygen upon hydrolysis at high temperatures or under hygroscopic conditions, catalyzing the thermal runaway process of the lithium-ion battery, the battery further includes a separator comprising a base film and a nitrogen-containing coating located on at least one side surface of the base film opposite each other along the thickness direction, the nitrogen-containing coating comprising a nitrogen-containing heterocyclic material.

[0099] In this invention, the median particle size Dv50 of the nitrogen-containing heterocyclic material is 0.2 μm-1 μm, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or within any two of the above values.

[0100] Adjusting the median particle size Dv50 of nitrogen-containing heterocyclic materials within a suitable range is beneficial for controlling the density, uniformity, and porosity of nitrogen-containing coatings. When the median particle size Dv50 of nitrogen-containing heterocyclic materials is too large (e.g., greater than 1 μm), the nitrogen-containing coating has low flatness, a rough surface, and large gaps between particles. Under external force, large-sized nitrogen-containing heterocyclic materials are prone to detachment, which may cause micro-short circuits inside the battery and is detrimental to improving battery stability. When the median particle size Dv50 of nitrogen-containing heterocyclic materials is too small (e.g., less than 0.2 μm), the nitrogen-containing heterocyclic materials are too densely packed, the overall porosity of the separator decreases, the electrolyte wetting becomes more difficult, and the agglomeration tendency of nitrogen-containing heterocyclic materials cannot be avoided even when the particle size is too small, resulting in poor uniformity of the nitrogen-containing coating.

[0101] In this invention, the nitrogen-containing heterocyclic material includes at least one of melamine, melamine polyphosphate, melamine thiocyanate, melamine cyanurate, formaldehyde polymelamine hydrochloride, melamine polyphosphate, melamine polyphosphate, and piperazine pyrophosphate.

[0102] In this invention, the base film comprises a polyolefin.

[0103] In this invention, the polyolefin includes polypropylene (PP) and / or polyethylene (PE).

[0104] In this invention, the thickness of the nitrogen-containing coating is 0.3μm-5μm, for example, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.8μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, or within any two of the above values.

[0105] In this invention, since the positive electrode generates more heat during cycling, the nitrogen-containing coating is positioned directly opposite the positive electrode sheet, which can further increase the furnace temperature of the lithium-ion battery.

[0106] In this invention, the diaphragm further includes an adhesive layer located on the outermost side of the diaphragm.

[0107] In one embodiment, one side surface of the base film includes the nitrogen-containing coating and the adhesive layer disposed sequentially along the thickness direction, the nitrogen-containing coating being located between the base film and the adhesive layer, and the other side surface of the base film includes the adhesive layer.

[0108] In one embodiment, the base film includes a nitrogen-containing coating and an adhesive layer disposed sequentially along the thickness direction on both sides of the base film, with the nitrogen-containing coating located between the base film and the adhesive layer.

[0109] like Figure 4 The diagram shown is a schematic diagram of the diaphragm along the thickness direction in one embodiment of the present invention, wherein 1 is the base membrane, 2 is the nitrogen-containing coating, and 3 is the adhesive layer.

[0110] Lithium supplements release oxygen under high temperatures or water absorption conditions, catalyzing the thermal runaway process of the battery and thus affecting the stability of batteries containing lithium supplements. On the one hand, nitrogen-containing separators are heat-resistant and can improve the thermal safety performance of the battery. On the other hand, nitrogen-containing heterocyclic materials in nitrogen-containing separators can release inert gases such as nitrogen or ammonia at high temperatures, thereby diluting flammable gases and improving the thermal safety performance of the battery. Therefore, selecting separators with highly stable nitrogen-containing heterocyclic materials helps to improve the high-temperature safety of lithium-ion batteries. Their lithiophilic surfaces can preferentially adsorb lithium ions in the electrolyte, reducing the desolvation energy barrier of lithium ions and alleviating interfacial kinetic hysteresis. Nitrogen-containing heterocycles combine with free PF6, HF, and other substances in the electrolyte, reducing chemical corrosion of the positive electrode active material, alleviating interfacial degradation, improving the positive electrode interface, and thus improving high-temperature resistance. Placing the nitrogen-containing coating directly opposite the positive electrode sheet is beneficial for capturing HF and H2O residues in the electrolyte, reducing corrosion of the positive electrode active material, and improving the structural stability of the positive electrode.

[0111] In this invention, the thickness of the nitrogen-containing coating can be obtained by conventional testing methods in the art, for example by the following method: after discharging the battery to 0% SOC, disassemble and remove the separator, soak it in dimethyl carbonate (DMC) solvent for 12 hours, and then rinse it with DMC solvent to remove the lithium salt attached to the separator. Select the area of ​​the separator in the battery that extends beyond the negative electrode, polish the separator cross section with an argon ion polishing device, observe and measure the thickness of the separator using SEM. The boundary between the base film, nitrogen-containing coating and adhesive layer can be seen in the SEM image. Measure the thickness of the nitrogen-containing coating according to the interface, and take the average value after measuring 10 different test points.

[0112] In this invention, the median particle size Dv50 of the nitrogen-containing heterocyclic material can be obtained by conventional testing methods in the art. After discharging the lithium-ion secondary battery to 0% SOC, the separator is disassembled and removed. After soaking in dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC to remove the lithium salt attached to the separator. The cross-section is obtained by ion beam cutting. The obtained cross-section is observed by backscatter imaging in SEM. Twenty nitrogen-containing heterocyclic material particles are found and the distance between the two longest points of the edge contour of each particle is measured. The average value is the median particle size Dv50 of the nitrogen-containing heterocyclic material.

[0113] In this invention, the term "0% SOC" refers to the battery being discharged to 3.0V at 0.1C.

[0114] In this invention, the positive electrode sheet further includes a positive electrode conductive agent and a positive electrode binder, both of which are conventional choices for those skilled in the art. The positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), polyacrylate, polyimide, and styrene-butadiene rubber. The positive electrode conductive agent includes at least one of acetylene black, conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

[0115] In this invention, the negative electrode sheet further includes a negative electrode binder, a negative electrode conductive agent, and a negative electrode dispersant, all of which are conventional choices for those skilled in the art. The negative electrode binder includes at least one of polyacrylic acid (PAA), sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose, polyimide, styrene-butadiene rubber (SBR), and polyvinylidene fluoride. The negative electrode conductive agent includes at least one of acetylene black, conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene. The negative electrode dispersant includes carboxymethyl cellulose.

[0116] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0117] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0118] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0119] The following examples illustrate the lithium-ion secondary battery of the present invention.

[0120] Example 1:

[0121] Lithium-ion secondary batteries are prepared according to the following method:

[0122] (1) Preparation of the base coating:

[0123] 50 wt% titanium dioxide and 30 wt% lithium-rich nickel oxide (chemical formula Li) 1.23 Ni 0.75 Al 0.02O2 and 12 wt% silica are added to 8 wt% polyvinylidene fluoride (PVDF) adhesive solution and stirred evenly to obtain a primer slurry. The primer slurry is then applied to the surface of aluminum foil using a skip coating method to obtain a primer-coated aluminum foil.

[0124] The titanium dioxide contains elements Sb and Sn, has an average particle size of 265 nm, and an electrical conductivity of 0.33 S / cm; the lithium-rich nickel oxide has an average particle size of 5.5 μm and an electrical conductivity of 10. -7 S / cm; The average particle size of silica is 33nm, the height of the protrusions in the base coating is 2.4μm, and the thickness of the base coating is 3μm.

[0125] (2) Preparation of the positive electrode:

[0126] Lithium cobalt oxide, PVDF, and conductive carbon black were mixed in a mass ratio of 98.2:0.8:1 and then added to N-methylpyrrolidone (NMP) solvent. The mixture was stirred under vacuum for 5 hours to ensure the uniformity of the slurry, thus obtaining the positive electrode slurry. The positive electrode slurry was coated onto the surface of the base coating aluminum foil obtained in (1), dried in a vacuum drying oven at 120°C for 8 hours, and then rolled and slit to obtain the positive electrode sheet.

[0127] The lithium cobalt oxide also includes the dopant element Al. The median particle size Dv50 of the lithium cobalt oxide is 15.3 μm, the particle size Dv99 is 42.5 μm, and the tap density is 2.8 g / cm³. 3 .

[0128] (3) Preparation of negative electrode:

[0129] The negative electrode active material, carboxymethyl cellulose, negative electrode conductive agent, and SBR were mixed in a mass ratio of 96.6:0.25:0.25:2.9 and then added to deionized water. After stirring evenly, a negative electrode slurry was obtained. The negative electrode active material consisted of artificial graphite and second silicon carbide in a mass ratio of 80:20. The negative electrode slurry was uniformly coated onto both sides of a copper foil containing a carbon coating layer using a coating machine. After drying at 89°C for 12 hours, the negative electrode sheet was obtained by rolling and slitting.

[0130] The sphericity α2 of the second silicon-carbon is 0.9, and the mass content of elemental Si in the negative electrode active layer is 9.7%.

[0131] (4) Preparation of electrolyte:

[0132] A basic electrolyte was prepared by mixing ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), propyl propionate (PP), and diethyl carbonate (DEC) in a weight ratio of 1:2:1:3:3. Then, FEC, a nitrile additive (composed of SN:ADN:HTCN = 1:2:2), and LiPF6 were added to the basic electrolyte to obtain the final electrolyte. Based on the total weight of the electrolyte, the weight content of LiPF6 was 12%, the weight content of the nitrile additive was 1.8%, and the weight content of FEC was 10%.

[0133] (5) Battery fabrication:

[0134] Positive electrode sheet, separator and negative electrode sheet are rolled, slit, sheet made and wound to obtain core, core is packaged, baked, liquid injected, formed, second sealed, sorted and OCV to obtain battery.

[0135] The separator includes a base membrane and a nitrogen-containing coating on one side of the base membrane. The outer surfaces of both sides of the separator also include an adhesive layer, which is made of polyacrylic acid. The base membrane is made of polypropylene (PP). The nitrogen-containing coating includes melamine, with an average particle size of 0.56 μm. The positive electrode and the side of the separator with the nitrogen-containing coating are positioned opposite each other, and the thickness of the nitrogen-containing coating is 3.5 μm.

[0136] Example 2:

[0137] The difference from Example 1 is that:

[0138] The components in the base coating are: 73 wt% titanium dioxide and 15 wt% lithium-rich nickel oxide (chemical formula Li). 1.23 Ni 0.75 Al 0.02 In a solution containing O2, 5.0 wt% silica, and 7 wt% PVDF, the average particle size of titanium dioxide is 52 nm, and its electrical conductivity is 0.45 S / cm; the average particle size of lithium-rich nickel oxide is 3.1 μm, and its electrical conductivity is 10. -7 S / cm; the average particle size of silica is 21 nm, the height of the protrusions in the base coating is 1.2 μm, and the thickness of the base coating is 1 μm.

[0139] The median particle size (Dv50) of lithium cobalt oxide is 13.2 μm, the particle size (Dv99) is 30.4 μm, and the tap density is 2.4 g / cm³. 3 The sphericity α2 of the second silicon-carbon is 0.83.

[0140] Based on the total weight of the electrolyte, the weight content of nitrile additives is 0.52%.

[0141] The nitrogen-containing coating has a thickness of 0.4 μm and includes melamine trithiocyanate with an average particle size of 0.22 μm.

[0142] Example 3:

[0143] The difference from Example 1 is that:

[0144] The composition of the base coating is as follows: 32 wt% titanium dioxide, 40 wt% lithium-rich nickel oxide (chemical formula Li). 1.23 Ni 0.75 Al 0.02 In a solution containing O2, 18 wt% silica, and 10 wt% PVDF, the average particle size of titanium dioxide is 497 nm, and its electrical conductivity is 0.82 S / cm; the average particle size of lithium-rich nickel oxide is 8 μm, and its electrical conductivity is 10. -7 S / cm; the average particle size of silica is 40nm, the height of the protrusions in the base coating is 4.9μm, and the thickness of the base coating is 4.7μm.

[0145] The median particle size (Dv50) of lithium cobalt oxide is 17.9 μm, the particle size (Dv99) is 46.7 μm, and the tap density is 3.2 g / cm³. 3 The sphericity α2 of the second silicon-carbon is 0.97.

[0146] Based on the total weight of the electrolyte, the weight content of nitrile additives is 2.8%.

[0147] The nitrogen-containing coating has a thickness of 4.7 μm and includes piperazine pyrophosphate, with an average particle size of 0.95 μm.

[0148] Examples 4a-9b are based on the settings of Example 1, with differences shown in Tables 1-2;

[0149] Comparative Examples 1-7 are based on the setup of Example 1, with differences shown below and in Tables 1-2;

[0150] Comparative Example 1:

[0151] Based on Example 1, the difference is that the base coating does not contain lithium replenishing agent.

[0152] Comparative Example 2:

[0153] Based on Example 1, the difference is that the base coating does not contain silicon dioxide.

[0154] Comparative Example 3:

[0155] This comparative group is used to verify the effect of changes in the "average particle size of silica".

[0156] Comparative Example 4:

[0157] This set of examples is used to verify the effect of changes in "nitrile additives", wherein comparative example 4a does not contain nitrile additives.

[0158] Comparative Example 5:

[0159] Based on Example 1, the difference is that no base coating is provided; instead, a lithium replenishment layer is used. The lithium replenishment layer is provided by the following method: a lithium replenishing agent (chemical formula Li) is applied... 1.23 Ni 0.75 Al 0.02 O2), conductive carbon black and PVDF are mixed in a mass ratio of 92:3:5, NMP is added and stirred evenly to obtain a lithium replenishment layer slurry. The lithium replenishment layer slurry is coated onto the surface of aluminum foil to obtain a lithium replenishment layer with a thickness of 6 μm. The remaining steps are the same as in Example 1.

[0160] Comparative Example 6:

[0161] Based on Example 1, the difference is that the undercoating layer does not contain a lithium supplement, and the titanium dioxide content in the undercoating layer is adjusted to 80%; the positive electrode slurry consists of lithium cobalt oxide and a lithium supplement (chemical formula Li). 1.23 Ni 0.75 Al 0.02 O2), PVDF and conductive carbon black are composed of O2, PVDF and conductive carbon black in a ratio of 97.7:0.5:0.8:1.

[0162] Comparative Example 7:

[0163] Based on Example 1, the difference is that no base coating is provided, and no lithium replenishing agent is added to the positive electrode active layer.

[0164] The specific implementation examples and comparative examples are shown in Tables 1 and 2:

[0165] Table 1:

[0166]

[0167]

[0168] Table 2 (Continued from Table 1):

[0169]

[0170]

[0171] In this context, "*" indicates that the data in this section is based on Example 1, and " / " indicates that the corresponding data does not exist.

[0172] In the above examples and comparative examples: titanium dioxide contains elements Sb and Sn; lithium cobalt oxide contains element Al; the base membrane in the separator is PP, and the adhesive layer of the separator is polyacrylic acid containing boehmite.

[0173] Test example:

[0174] (1) Needle prick test:

[0175] The batteries prepared in the embodiments of the present invention and the batteries prepared in the comparative examples were discharged at 1C to 3.0V at room temperature, and then charged at a constant current of 1.5C to 4.5V with a cutoff current of 0.02C. This cycle was repeated 5 times. Within 48 hours after the cycle was completed, a steel needle with a diameter of 4mm was used to vertically penetrate the left, middle, and right positions of the lithium-ion battery at a speed of 30mm / s. The battery was considered to have passed the test if it did not catch fire or explode within 5 minutes. Each group of 15 batteries was tested, denoted by N. The number of batteries that passed the needle penetration test was recorded as n. "n / N" indicates that n out of the 15 batteries tested passed the needle penetration test. The test results are recorded in Table 3.

[0176] (2) Store at 85℃:

[0177] The batteries prepared in the embodiments of the present invention and the batteries prepared in the comparative examples were tested at 25℃±5℃ according to the following method: a) standing at 25℃±2℃ for 10 min; b) discharging at 0.2C to the lower limit voltage of 3.0V and standing for 10 min; c) charging at 1.5C to the upper limit voltage of 4.5V, stopping at 0.02C and standing for 10 min; d) discharging at 0.2C to the lower limit voltage of 3.0V to obtain the initial capacity; e) standing for 10 min; f) charging at 1.5C to the upper limit voltage of 4.5V, stopping at 0.02C; g) resting for 2 h; h) storing at 85℃±2℃ for 6 h. After storage, the samples were removed and the appearance of the batteries was observed for bulging. The degree of bulging was categorized as no bulging, slight bulging, bulging, and severe bulging. No bulging meant no change in appearance; slight bulging meant minimal change in appearance, with small dents that could recover after being pressed; bulging meant small bulging with minimal thickness change; and severe bulging meant significant deformation, large thickness change, and a large bulge. The order was: severe bulging > bulging > slight bulging > no bulging. The test results are recorded in Table 3.

[0178] (3) Initial Coulomb efficiency:

[0179] The batteries prepared in the embodiments of the present invention and the batteries prepared in the comparative examples were placed at 25℃±5℃ for 10 min; then charged at 3mA for 10 min, and placed at 10 min; then charged at a constant current of 0.1C to the upper limit cutoff voltage of 4.5V (cutoff current 0.02C), and the battery charging capacity was recorded; after placing at 10 min, the batteries were discharged at a constant current of 0.1C to the lower limit voltage of 3.0V, and the battery discharge capacity was recorded. The initial coulombic efficiency = (discharge capacity / charge capacity) × 100%. The test results are recorded in Table 3.

[0180] (4) Volumetric energy density:

[0181] The batteries prepared in the embodiments of the present invention and the batteries prepared in the comparative examples were charged at room temperature with a current of 0.5C to the upper limit voltage of 4.5V, and the cutoff current was 0.02C. After standing for 10 minutes, they were discharged at 0.2C to the lower limit voltage of 3.0V, and the discharge capacity of the batteries was recorded. Energy density = (battery discharge capacity × discharge voltage plateau) / (battery thickness × battery width × battery height). The test results are recorded in Table 3.

[0182] Table 3:

[0183]

[0184] As can be seen from Table 3, the battery prepared by the present invention improves the initial efficiency, high-temperature storage performance and mechanical safety performance compared with the comparative example.

[0185] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes a positive electrode sheet and an electrolyte. The positive electrode sheet includes a positive current collector, a base coating, and a positive active layer. The positive active layer is located on at least one outer surface of the positive current collector, and the base coating is located between the positive active layer and the positive current collector. The positive active layer includes a positive active material, which includes a cobalt-containing positive electrode material. The base coating includes a lithium supplement and silicon dioxide. The lithium supplement includes lithium-rich nickel oxide and / or lithium-rich ferrite, wherein the lithium-rich nickel oxide comprises lithium with the chemical formula Li a1 Ni b1 M 1 c1 For O2, 1 < a1 ≤ 2, 0 < b1 < 1, 0 < c1 ≤ 0.3, M 1 Includes at least one of the elements Mn, Co, Al, and Mg; The lithium-rich lithium iron phosphate includes lithium with the chemical formula Li. a2 Fe b2 M 2 c2 For O2, 1 < a² ≤ 2, 0 < b² < 1, 0 < c² ≤ 0.3, M 2 Includes at least one of the elements Mn, Co, Al, and Mg; The average particle size of the silica is 5nm-50nm; The electrolyte includes nitrile additives.

2. The battery according to claim 1, wherein, The base coating also includes conductive particles, which include titanium dioxide, and the titanium dioxide includes doping elements Sn and / or Sb. And / or, the surface of the titanium dioxide is coated with an oxide of element Sn and / or an oxide of element Sb; And / or, based on the total mass of the base coating, the mass content of the conductive particles is 25%-75%; And / or, the average particle size of the conductive particles is 50nm-500nm; And / or, the conductivity of the conductive particles is 0.05 S / cm - 1 S / cm; Preferably, the average particle size of the conductive particles is 100nm-400nm.

3. The battery according to claim 1, wherein, The average particle size of the lithium supplement is 1μm-10μm; And / or, the conductivity of the lithium supplement is 10. -8 S / cm-10S / cm; Preferably, the average particle size of the lithium replenishing agent is 3μm-8μm; And / or, based on the total mass of the base coating, the mass content of the lithium replenishing agent is 10%-65%; Preferably, the base coating has a protrusion that is embedded in the positive electrode active layer; More preferably, the height of the protrusion is 0.1μm-9μm.

4. The battery according to claim 1, wherein, The average particle size of the silica is 20nm-40nm; And / or, based on the total mass of the base coating, the silica content is 5%-20% by mass; And / or, the thickness of the base coating is 1μm-5μm.

5. The battery according to claim 1, wherein, The nitrile additives include at least one of adiponitrile, 1,3,6-hexanetrionitrile, butadionitrile, 1,4-dicyano-2-butene, pentaetheronitrile, trietheronitrile, ethylene glycol bis(propionitrile) ether, and glycerol trionitrile; And / or, based on the total weight of the electrolyte, the mass content of the nitrile additive is 0.1%-10%; Preferably, the mass content of the nitrile additive is 0.5%-3% based on the total weight of the electrolyte.

6. The battery according to claim 1, wherein, The cobalt-containing cathode material includes lithium cobalt oxide, which includes at least one of the doping elements Al, Mg, Ti, Zr, La and Y; And / or, the median particle size Dv50 of the lithium cobalt oxide is 10μm-20μm, and the particle size Dv99 is 30μm-47μm; And / or, the tap density of the lithium cobalt oxide is 2.4 g / cm³. 3 -3.2g / cm 3 .

7. The battery according to claim 1, wherein, The battery further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, which includes a silicon-based material. And / or, based on the total mass of the negative electrode active layer, the silicon content is 4%-15% by mass.

8. The battery according to claim 1, wherein, The battery further includes a separator, the separator comprising a base film and a nitrogen-containing coating located on at least one side surface of the base film opposite each other along the thickness direction, the nitrogen-containing coating comprising a nitrogen-containing heterocyclic material, the median particle size Dv50 of the nitrogen-containing heterocyclic material being 0.2 μm-1 μm; And / or, the nitrogen-containing heterocyclic material includes at least one of melamine, melamine polyphosphate, melamine thiocyanate, melamine cyanurate, formaldehyde polymelamine hydrochloride, melamine polyphosphate, and piperazine pyrophosphate.

9. The battery according to claim 8, wherein, The thickness of the nitrogen-containing coating is 0.3μm-5μm; Preferably, the nitrogen-containing coating is disposed opposite to the positive electrode sheet.

10. The battery according to claim 1, wherein, The silica covers at least a portion of the outer surface of the lithium replenishing agent.

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