Lithium ion secondary battery

Abstract

This invention relates to the field of battery technology, specifically to a lithium-ion secondary battery. It includes a battery cell, tab adhesive, and a casing. The battery cell includes tabs, one end of which is electrically connected to the battery cell, and the other end extends out of the casing. The tab adhesive partially covers the tabs. The tab adhesive includes a first adhesive layer with a melting point of 90°C to 120°C, a second adhesive layer with a melting point of 140°C to 170°C, and a third adhesive layer with a melting point of 90°C to 130°C, all stacked together. The first adhesive layer is in contact with the casing, the third adhesive layer is in contact with the tabs, and the second adhesive layer is located between the first and third adhesive layers. The battery cell also includes a positive electrode sheet, which includes a positive electrode active material, including Li. a Ni b Co c Mn d M e O2, 0.9≤a≤1.1, 0.8≤b≤0.975, 0.005≤c≤0.2, 0.005≤d≤0.14, 0≤e≤0.1, and M includes at least one of Al, Zr, B, Y, Sr, W, Ti, Mg, and Nb. The lithium-ion secondary battery of this invention, while possessing a high-nickel cathode material, effectively avoids thermal runaway, ensuring the safe use of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and specifically to a lithium-ion secondary battery. Background Technology

[0002] With the development of the electric vehicle and energy storage industries, the requirements for rechargeable batteries are becoming increasingly stringent, demanding performance characteristics such as low cost and high energy density. In lithium-ion batteries, high-nickel cathode materials are favored by the power tool market due to their low cost and high energy density. To further improve the energy density of high-nickel cathode materials, batteries containing these materials typically employ methods such as minimizing particle size to increase compaction density, or increasing the nickel content to 80% or higher. However, these methods exacerbate gas generation in the high-nickel materials, potentially leading to thermal runaway during fast charging and reducing safety performance. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and to provide a lithium-ion secondary battery (hereinafter referred to as the battery) that can prevent thermal runaway of batteries containing high-nickel cathode materials during fast charging and has high safety performance.

[0004] Related technologies contain high-nickel cathode materials (for example, when the chemical formula of the cathode material is Li). a Ni b Co c Mn d M e Batteries with a nickel content (b≥0.8, indicating high nickel content) are prone to thermal runaway under O2 conditions. The inventors of this invention, through extensive research, discovered that designing the tab sealant can effectively prevent thermal runaway. This is because lithium-ion batteries generally consist of a positive electrode assembly, a negative electrode assembly, a separator, a packaging film, and an electrolyte. The packaging film provides space for the positive electrode assembly, negative electrode assembly, separator, and electrolyte, and its seal is achieved through heat sealing with tab sealant. To create a sealed environment that isolates moisture and air, ensuring the battery's sealing performance, the tab sealant must have reliable sealing properties. However, when high-nickel batteries are fast-charged, the increased nickel content reduces the thermal stability of the positive electrode material, thus lowering the onset temperature of thermal runaway and increasing the heat released during runaway. This leads to a rapid increase in battery temperature. Because the tab sealant has good sealing properties, the high internal temperature cannot be transferred to the outside in a short time, causing the separator to shrink thermally, leading to a short circuit between the positive and negative electrodes, decomposition of the SEI film, and ultimately, battery fire and explosion. If the heat inside the battery can be released in time before the battery fires and explodes, thermal runaway can be effectively avoided, ensuring the battery's safety performance. Based on this, the inventors of this invention propose the following solution:

[0005] This invention provides a lithium-ion secondary battery, comprising a cell, tab adhesive, and a casing; the cell includes tabs, one end of which is electrically connected to the cell, and the other end of which extends out of the casing; the tab adhesive partially covers the tabs; the tab adhesive includes a first adhesive layer, a second adhesive layer, and a third adhesive layer stacked together, the first adhesive layer contacting the casing, the third adhesive layer contacting the tabs, and the second adhesive layer located between the first and third adhesive layers; the melting point of the first adhesive layer is 90℃~120℃, the melting point of the second adhesive layer is 140℃~170℃, and the melting point of the third adhesive layer is 90℃~130℃; the cell further includes a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising Li a Ni b Co c Mn d M e O2, 0.9≤a≤1.1, 0.8≤b≤0.975, 0.005≤c≤0.2, 0.005≤d≤0.14, 0≤e≤0.1, M includes at least one of Al, Zr, B, Y, Sr, W, Ti, Mg and Nb.

[0006] Research has shown that a higher Ni content in the cathode material reduces the thermal stability of the active material, leading to a lower thermal runaway initiation temperature and a greater release of heat during thermal runaway. Furthermore, when the internal battery temperature rises, the current density is highest and the temperature rises fastest at the tabs. Therefore, designing the tab adhesive to ensure battery safety is a reliable approach. This invention utilizes a three-layer tab adhesive with different melting points, where the melting points of the first and third layers are lower than that of the second layer. In the event of thermal runaway, partial melting of the tab adhesive provides a heat dissipation channel for the battery, while the remaining portion of the tab adhesive does not melt, maintaining this channel and thus improving battery safety.

[0007] Specifically, the melting point of the first adhesive layer is 90℃ to 120℃. A first adhesive layer with a melting point within this range can melt promptly when the internal temperature of the battery rises, providing a heat dissipation channel. The melting point of the third adhesive layer is 90℃ to 130℃. A third adhesive layer with a melting point within this range has strong metal-affinity properties. When the third adhesive layer melts during battery manufacturing, the bonding force between the third adhesive layer and the electrode tabs is stronger, thereby further improving the battery's room-temperature sealing performance and preventing electrolyte leakage. Furthermore, when the melting point of the third adhesive layer is within the above range, it can melt promptly when the internal temperature of the battery rises, providing a heat dissipation channel.

[0008] When both the first and third adhesive layers meet the above melting point range, when thermal runaway occurs in the battery, the fusion interface between the first adhesive layer and the casing, and between the third adhesive layer and the tabs, can melt first. This reduces the overall sealing tension of the casing and tabs, making the interface easier to open and providing a heat dissipation channel for the battery. This releases internal heat, improves safety, and prevents the tab adhesive from responding slowly and failing to form a heat dissipation channel in time when the battery temperature reaches 120°C and thermal runaway occurs, thus causing further heat accumulation and potentially leading to fires, explosions, or other accidents.

[0009] In addition, the melting point of the second adhesive layer needs to be controlled in a coordinated manner, so that the melting point of the second adhesive layer is 140℃~170℃. The second adhesive layer with a melting point within the above range can play a good role in skeleton support and barrier function, preventing over-melting and avoiding battery short circuit; and ensuring that there is no risk of interface segregation of the tab adhesive during heat sealing, avoiding battery leakage and gas swelling.

[0010] Through the above technical solution, the present invention has at least the following advantages compared with the prior art: the lithium-ion secondary battery of the present invention, while having a high nickel positive electrode material, can effectively avoid thermal runaway and ensure the safety performance of the battery.

[0011] 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

[0012] Figure 1 The diagram shows the relative positions of the tab and the tab adhesive in an example of the present invention.

[0013] Figure 2 The diagram shown is a schematic diagram of the tab adhesive in an example of the present invention.

[0014] Explanation of reference numerals in the attached figures

[0015] 1: Tab, A: Tab adhesive, A1: First adhesive layer; A2: Second adhesive layer; A3: Third adhesive layer. Detailed Implementation

[0016] 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.

[0017] This invention provides a lithium-ion secondary battery, comprising a battery cell, tab adhesive, and a casing. The battery cell includes tabs, one end of which is electrically connected to the battery cell, and the other end extending out of the casing; the tab adhesive partially covers the tabs.

[0018] The tab adhesive comprises a first adhesive layer, a second adhesive layer, and a third adhesive layer stacked together. The first adhesive layer is in contact with the housing, the third adhesive layer is in contact with the tab, and the second adhesive layer is located between the first adhesive layer and the third adhesive layer. The melting point of the first adhesive layer is 90℃~120℃ (e.g., 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, or 120℃), the melting point of the second adhesive layer is 140℃~170℃ (e.g., 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, or 170℃), and the melting point of the third adhesive layer is 90℃~130℃ (e.g., 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, or 130℃).

[0019] In one example, the melting point of the first adhesive layer is 95°C to 120°C. The melting point of the second adhesive layer is 145°C to 160°C. The melting point of the third adhesive layer is 95°C to 130°C.

[0020] The battery cell further includes a positive electrode sheet, which comprises a positive electrode active material, including Li. a Ni b Co c Mn d M eO2, 0.9≤a≤1.1 (e.g., 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.05, or 1.1), 0.8≤b≤0.975 (e.g., 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, or 0.975), 0.005≤c≤0.2 (e.g., 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, or 0.08). 0.005 ≤ d ≤ 0.14 (e.g., 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.18, 0.19 or 0.2), 0.005 ≤ d ≤ 0.14 (e.g., 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13 or 0.14), 0 ≤ e ≤ 0.1 (e.g., 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1), M includes at least one of Al, Zr, B, Y, Sr, W, Ti, Mg and Nb.

[0021] In some embodiments, 0.88 ≤ b ≤ 0.95. By further controlling the content of element Ni in the positive electrode active material, the structural stability and conductivity of the positive electrode active material can reach a better level, which is beneficial to improving the high-temperature cycle performance and rate performance of the battery.

[0022] In this invention, the difference T between the melting point of the second adhesive layer and the melting point of the first adhesive layer is... 12 The temperature range is 25℃ to 65℃, for example, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, or 65℃. When T... 12 Within this range, the battery exhibits high strength during the heat sealing process, making it less prone to leakage. Furthermore, when the battery temperature rises to a certain level, the first adhesive layer melts to form a heat dissipation channel, and the second adhesive layer maintains this channel, which helps improve the battery's safety performance.

[0023] In some embodiments, the difference T between the melting point of the second adhesive layer and the melting point of the first adhesive layer is... 12 The temperature ranges from 35℃ to 55℃.

[0024] In this invention, the difference T between the melting point of the third adhesive layer and the melting point of the first adhesive layer is... 13The temperature range is -35℃ to 25℃, for example, -35℃, -30℃, -25℃, -20℃, -15℃, -10℃, -5℃, 0℃, 5℃, 10℃, 15℃, 20℃, or 25℃. The temperature difference T between the third adhesive layer and the first adhesive layer. 13 Within this range, the thermal melting deformation of the two is basically synchronized. The fusion interface between the first adhesive layer and the shell, and between the third adhesive layer and the tab, can melt almost simultaneously, which makes the overall sealing interface tension of the shell and the cell decay faster, the interface is easier to open, provides heat dissipation channels, releases the internal heat of the battery, and improves safety.

[0025] In some embodiments, the difference T between the melting point of the third adhesive layer and the melting point of the first adhesive layer is... 13 The temperature range is -10℃ to 10℃.

[0026] In this invention, b and T 12 Satisfies: 0.012≤b / T 12 ≤0.04 (e.g., 0.012, 0.015, 0.02, 0.025, 0.03, 0.035, or 0.04). As mentioned earlier, the thermal stability of the positive electrode active material decreases with increasing nickel content, leading to a lower onset temperature for thermal runaway and an increase in the released heat. Therefore, when the nickel content increases, the difference between the melting points of the first and second adhesive layers needs to be appropriately increased. This ensures that the first adhesive layer can melt promptly to form a heat dissipation channel, while the second adhesive layer remains unmelted to maintain this channel. If the nickel content is high, but the difference between the melting points of the first and second adhesive layers is low, both layers may melt, making it impossible to maintain the opening of the heat dissipation channel and hindering heat dissipation. Therefore, when the nickel content and the difference between the melting point of the second adhesive layer and the melting point of the first adhesive layer, T... 12 Within this range, when the battery temperature rises to a certain level, the first adhesive layer can melt and open in time, and the second adhesive layer can maintain the opening, thereby releasing the excess gas and heat generated by the side reaction to improve the battery's safety performance.

[0027] In some embodiments, 0.016 ≤ b / T 12 ≤0.028.

[0028] In this invention, the battery cell further includes a negative electrode sheet, which comprises 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 comprises a silicon-based material. The mass content of element Si in the negative active layer is s, and s is the difference T between the melting point of the third adhesive layer and the melting point of the first adhesive layer. 13 Satisfy: -200≤T 13 / s≤600 (e.g., -200, -150, -100, -50, 0, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, or 600). When the negative electrode active layer contains silicon-based materials, although it has a high theoretical specific capacity and a working voltage plateau (approximately 0.2–0.3 V vs. Li / Li), it is still possible to achieve this. + While silicon-based materials are suitable and can improve battery energy density, the high-nickel cathode active material used in this invention has a higher specific capacity and greater lithium-ion extraction. On the other hand, silicon-based materials have lower kinetics than carbon-based materials, leading to a mismatch between the kinetics of the positive and negative electrodes. This results in a higher probability of lithium plating in silicon-containing systems, causing greater safety issues. Furthermore, when the negative electrode contains silicon, the battery experiences greater volume expansion during charging and discharging, requiring better sealing. Therefore, as the silicon content in the negative electrode increases, volume expansion and side reactions also increase, further lowering the thermal runaway initiation temperature and the amount of heat released in the high-nickel battery. Therefore, to further ensure battery safety, it is necessary to simultaneously increase the difference in melting points between the first and third adhesive layers. This ensures that when the thermal runaway initiation temperature decreases, at least one of the first or third adhesive layers can begin to melt, forming a heat dissipation channel to guarantee battery safety. Furthermore, when this relationship is satisfied, the layer structure with similar melting points on both sides of the tab adhesive can increase the heat-sealing strength at the tab under the same heat-sealing conditions, thus ensuring good battery sealing. If T 13 An excessively high / s value can lead to poor adhesion between the first adhesive layer and the casing, as well as between the third adhesive layer and the tabs, during the heat sealing process. This results in poor battery sealing, and under normal cycling conditions, moisture from the environment may seep in, potentially causing battery fires, explosions, or other failures.

[0029] In some embodiments, -45≤T 13 / s≤70.

[0030] In this invention, the melting points of the first adhesive layer, the second adhesive layer, and the third adhesive layer can be obtained by methods conventional in the art, such as differential scanning calorimetry (DSC testing).

[0031] In this invention, the mass content of element Si in the negative electrode active layer is 1.5% to 40%, for example, 1.5%, 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%.

[0032] In some embodiments, s is 15% to 30%. When the silicon content is too high (e.g., greater than 40%), the battery volume expands more during charging and discharging, requiring better battery sealing. When the silicon content is within this range, it can better match the tab adhesive design, thereby ensuring the battery's sealing and safety performance. In addition, if the silicon content is too low (e.g., less than 1.5%), the improvement in battery energy density is not significant; if it is too high (e.g., greater than 40%), it leads to large overall battery volume expansion, poor cycle stability, and decreased conductivity.

[0033] In this invention, the silicon-based material includes at least one of elemental silicon, silicon-oxygen, silicon-carbon, and silicon alloys.

[0034] In some embodiments, the silicon-carbon comprises silicon-carbon composite particles. The silicon-carbon composite particles comprise porous carbon material and silicon material distributed within the pores of the porous carbon material. When the silicon-based material has this structure of silicon-carbon composite particles, the silicon material, as the active component, exhibits a high lithium storage capacity, while the porous carbon material can significantly buffer the volume expansion of the silicon material, improve electronic conductivity, and stabilize the SEI film on the surface of the silicon-based material, thereby achieving a balance between high energy density and long cycle life.

[0035] In this invention, the silicon content in the silicon-based material is 20% to 100%, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%.

[0036] In this invention, the sphericity of the silicon-based material is 0.5 to 1, for example, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0037] In some embodiments, the sphericity of the silicon-based material is 0.7 to 0.98.

[0038] In some embodiments, the sphericity of the silicon-based material is 0.7 to 0.9.

[0039] During the lithiation / delithiation process of batteries, volume expansion / contraction causes significant stress, leading to cracking and fragmentation of silicon-based materials. This can also cause the previously intact SEI film to rupture. Fresh silicon re-contaminates the electrolyte to re-form the SEI film. With repeated cycling, the SEI film undergoes a cycle of formation, rupture, and formation, becoming increasingly thicker, thus affecting the active Li. +The loss of electrolyte and the increase in interfacial resistance shorten the battery cycle life; they also disrupt the originally regular distance between particles, causing pulverized particles to detach from the conductive network, resulting in loss of electrical contact between the silicon-based material and the current collector, leading to a decrease in battery capacity and eventual failure. When the sphericity of the silicon-based material is within an appropriate range, it can not only alleviate the cracking and pulverization of the silicon-based material and the repeated formation and rupture of the SEI, reducing side reactions of the electrolyte, but also enable the battery to have a suitable gas production rate, which can increase the internal pressure of the battery. When the internal temperature of the battery rises to a certain temperature, the first and third adhesive layers begin to melt. At this time, the appropriate internal pressure helps to facilitate the opening of the first adhesive layer in contact with the casing and the third adhesive layer in contact with the tabs, and together with the melting of the first and third adhesive layers, it helps to form heat dissipation channels. Sphericity can be determined by the following method: Analyze the images of each silicon-based material particle in a scanning electron microscope (SEM) image containing silicon-based material at a certain magnification (e.g., 2500x) using image processing software (e.g., Image Pro Plus) to obtain the perimeter and area of ​​each silicon-based material particle. Calculate the perimeter equivalent radius r1 and area equivalent radius r2 of each silicon-based material particle. Then, sphericity = r2 / r1, and take the average value.

[0040] In this invention, the negative electrode active layer undergoes a thermogravimetric analysis in an air or oxygen atmosphere, where it is kept at 900°C for 40 minutes. The residual amount is 3% to 90%, for example, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0041] The residual amount was tested using thermogravimetric analysis (TGA). The specific method is as follows: After discharging the battery to 0% SOC, the negative electrode sheet was disassembled and removed. It was then soaked in dimethyl carbonate (DMC) solvent for 12 hours, followed by rinsing with DMC to remove the lithium salt adhering to the negative electrode sheet. After drying, the negative electrode sheet was 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 could then be peeled off from the negative electrode current collector, and the negative electrode active layer was collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the test sample amount was 5 mg to 15 mg. Under an air or oxygen atmosphere, the temperature was increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 minutes. This allowed the non-silicon components in the negative electrode active layer to volatilize while the silicon was fully oxidized to silicon dioxide. The remaining amount of material is the residual amount. It can be understood that the residual amount after thermogravimetric analysis of the negative electrode active layer in an air or oxygen atmosphere, held at 900℃ for 40 minutes, is the ash content of the negative electrode active layer. The mass content s of element Si in the negative electrode active layer can be calculated based on the mass of the ash, using the following formula: s = 7 × mass of the ash / 15.

[0042] In this invention, the negative electrode active layer further includes a carbon-based material. The carbon-based material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, and hard carbon.

[0043] In this invention, the negative electrode active layer further includes a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent includes, for example, at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, and carbon nanotubes (including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes). The negative electrode binder may include binders conventionally used in the art, such as at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0044] In some embodiments, the negative electrode conductive agent includes at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. Carbon nanotubes can form a large number of conductive contact sites between the electrode active material particles of the battery. Due to the significant increase in active sites, the possible side reaction sites between the high-nickel material and the electrolyte increase significantly, leading to increased gas production. As mentioned above, an appropriate amount of gas inside the battery can promptly assist in opening the heat dissipation channels when the temperature rises, thereby promoting the release of heat from inside the battery, reducing further heat accumulation, and mitigating the occurrence of thermal runaway.

[0045] In this invention, based on the total mass of the negative electrode active layer, the content of the negative electrode active material, calculated based on the silicon-based material and the carbon-based material, is 80%-99.8% (e.g., 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, or 99.8%), the content of the negative electrode conductive agent is 0.1%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.1%), and the content of the negative electrode binder is 0.1%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.1%).

[0046] In this invention, the positive electrode active material includes a first particle and a second particle.

[0047] In some embodiments, the first particle comprises a single-crystal particle, and the second particle comprises a polycrystalline particle. Single-crystal particles exhibit excellent structural stability due to the uniformity of their internal crystal structure and consistent grain orientation; however, single-crystal particles can increase the Li... + The limited transmission distance is detrimental to the rate performance of the battery. Polycrystalline particles, composed of numerous primary particles, have grain boundaries that negatively impact the structural stability of the material. Furthermore, the primary particles in polycrystalline particles pose a greater risk of side reactions with the electrolyte, resulting in poor stability. However, the smaller particle size of the primary particles in polycrystalline particles significantly shortens the Li-C4 transmission distance. + The transmission distance is increased, which is beneficial to the rate performance of the battery. Blending polycrystalline and monocrystalline particles can improve cycle performance and rate performance to some extent.

[0048] In some embodiments, the first particle includes Li a1 Ni b1 Co c1 Mn d1 M 1 e1O2, 0.9≤a1≤1.1 (e.g., 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.05, or 1.1), 0.9≤b1≤0.99 (e.g., 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or 0.99), 0.01≤c1≤0.1 (e.g., ... For example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1), 0.01≤d1≤0.1 (e.g., 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1), 0≤e1≤0.05 (e.g., 0, 0.01, 0.02, 0.03, 0.04, or 0.05), M 1 It includes at least one of Al, Zr, B, Y, Sr, W, Ti, Mg and Nb.

[0049] In some embodiments, the second particle includes Li a2 Ni b2 Co c2 Mn d2 M 2 e2 O2, 0.9≤a²≤1.1 (e.g., 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.05, or 1.1), 0.8≤b²≤0.95 (e.g., 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, or 0.95), 0.01≤c²≤0.2 (e.g., 0.01, 0.02) 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2), 0.01≤d2≤0.1 (e.g., 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1), 0≤e2≤0.05 (e.g., 0, 0.01, 0.02, 0.03, 0.04, or 0.05), M 2 It includes at least one of Al, Zr, B, Y, Sr, W, Ti, Mg and Nb.

[0050] Further controlling the Ni content in monocrystalline and polycrystalline particles can improve the high-temperature cycle performance and rate performance of the battery. This is because monocrystalline particles have better structural stability than polycrystalline particles, while polycrystalline particles have better conductivity than monocrystalline particles. Therefore, they have different compatibility with different Ni contents. When the Ni content in both is within a specific range, the structural stability and conductivity of the positive electrode active material can reach a superior level.

[0051] In this invention, the elemental content in the positive electrode active material can be obtained by methods conventional in the art, such as inductively coupled plasma (ICP).

[0052] In this invention, the particle size Dv10 of the first particle is 0.5 μm to 2 μm, for example, 0.5 μm, 1 μm, 1.5 μm, or 2 μm. The particle size Dv50 of the first particle is 0.5 μm to 5 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm. The particle size Dv90 of the first particle is ≤10 μm, for example, 10 μm, 9 μm, 8 μm, 7 μm, 6 μm, or 5 μm.

[0053] In this invention, the particle size Dv10 of the second particle is 3μm to 12μm, for example, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, or 12μm. The particle size Dv50 of the second particle is 5μm to 20μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, or 20μm. The particle size Dv90 of the second particle is ≤25μm, for example, 25μm, 24μm, 23μm, 22μm, 21μm, 20μm, 19μm, 18μm, 17μm, 16μm, or 15μm.

[0054] The inventors of this invention discovered that when the particle sizes Dv10, Dv50, and Dv90 of the first particles and the second particles are within a specific range, the first and second particles can maintain a relatively stable bulk and surface structure during battery charge-discharge cycles, enabling the battery to have relatively good stability under certain nickel content conditions. Combined with the unique three-layer tab adhesive with different melting points of this invention, the cycle stability of the battery is further improved, and the risk of thermal runaway of the battery is reduced.

[0055] In this invention, the particle size (e.g., Dv10, Dv50, and Dv90) of the first and second particles, measured by volume, can be obtained by methods conventional in the art, such as a laser particle size analyzer.

[0056] In this invention, the second particle comprises a plurality of primary particles, wherein the average particle size of the primary particles is 100 nm to 600 nm, for example, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, or 600 nm. The term "a plurality of" refers to the number of primary particles constituting the second particle being greater than or equal to 2.

[0057] In some embodiments, the average particle size of the primary particles is 300nm-500nm.

[0058] In this invention, the average particle size of the primary particles can be obtained by conventional methods in the art, such as by SEM. Specifically, take a positive electrode sheet and test the particle size of the primary particles of all second particles within the field of view at 7.3 mm × 10 kX. Take the average value to obtain the average particle size of the primary particles.

[0059] In this invention, the BET specific surface area of ​​the second particle is 0.3 m². 2 / g~1m 2 / g, for example, 0.3m 2 / g, 0.35m 2 / g, 0.4m 2 / g, 0.45m 2 / g, 0.5m 2 / g, 0.55m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g or 1m 2 / g.

[0060] In one example, the BET specific surface area of ​​the second particle is 0.35 m². 2 / g~0.6m 2 / g.

[0061] In this invention, the ratio of the average particle size of the second particle to the average particle size of the first particle is 1 to 10, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0062] In some embodiments, the ratio of the average particle size of the second particle to the average particle size of the first particle is 3 to 4.5.

[0063] When the ratio of the average particle size of the second particle to the average particle size of the first particle is too small (e.g., less than 1), it affects the specific capacity of the positive electrode active material, thus impacting the battery's energy density. When the ratio is too large (e.g., greater than 10), it increases the risk of side reactions between the positive electrode active material and the electrolyte, affecting the battery's high-temperature cycle performance and exacerbating gas production. When the ratio of the average particle size of the second particle to the average particle size of the first particle is within a specific range, single-crystal and polycrystalline particles can bond more tightly. At this point, the tight bonding between single-crystal and polycrystalline particles is not limited to particle packing, but more importantly, it involves surface energy compatibility. This is beneficial not only for Li... + This improves the rate performance of the battery by increasing the transfer of energy between the positive electrode active material and the electrolyte; it also helps to increase the compaction density of the positive electrode active material, thereby improving the energy density of the battery; and it delays the occurrence of side reactions between the positive electrode active material and the electrolyte, thus improving the high-temperature cycle performance of the battery.

[0064] In this invention, based on the total mass of the positive electrode active material, the content of the first particle is 50% to 99.9%, for example, 50%, 60%, 70%, 80%, 90% or 99.9%.

[0065] In some embodiments, the content of the first particle is 70% to 90% based on the total mass of the positive electrode active material.

[0066] The inventors of this invention have discovered that a specific ratio of the first particle content to the specific average particle size enables the first and second particles to bind more tightly. This is beneficial for Li + The transmission of energy improves the rate performance of the battery; it is beneficial to increase the compaction density of the positive electrode active material, thereby increasing the energy density of the battery; and it can delay the occurrence of side reactions between the positive electrode active material and the electrolyte, thus improving the high-temperature cycle performance of the battery.

[0067] In this invention, the average particle size of the first particle is 1.5 μm to 5 μm, for example, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm.

[0068] In some embodiments, the average particle size of the first particle is 2 μm to 4 μm.

[0069] In this invention, the average particle size of the second particle is 5μm to 20μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0070] In some embodiments, the average particle size of the second particle is 9 μm to 13 μm.

[0071] In this invention, the average particle size of the first particle and the average particle size of the second particle can be obtained by conventional methods in the art, such as by SEM. Specifically: take a positive electrode sheet, test the particle size of all first particles within the field of view at 7.3 mm × 10 kX, and take the average value to obtain the average particle size of the first particle; test the particle size of all second particles within the field of view, and take the average value to obtain the average particle size of the second particle.

[0072] In this invention, the compaction density of the positive electrode sheet is 3.1 g / cm³. 3 ~3.7g / cm 3 For example, 3.1 g / cm³ 3 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 Or 3.7g / cm 3 .

[0073] In some embodiments, the positive electrode active material may further comprise lithium cobalt oxide.

[0074] In this invention, the positive electrode sheet further includes a positive electrode conductive agent, which includes at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. The positive electrode sheet also includes a positive electrode binder, which may include binders conventionally used in the art, such as at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0075] In this invention, the battery cell further includes a separator, the separator comprising a substrate layer and a ceramic layer located on at least one side surface of the substrate layer; the ceramic layer faces the negative electrode sheet.

[0076] Understandably, when the ceramic layer on the substrate surface faces the negative electrode, if the cell fails, lithium ions cannot be embedded on the surface of the negative electrode and are prone to lithium deposition, existing in the form of lithium dendrites. The continuous growth of lithium dendrites may pierce the separator, causing a short circuit between the positive and negative electrodes, resulting in serious safety issues such as fire and explosion. In this case, the ceramic layer of the separator can effectively prevent lithium dendrites from piercing the separator, improving the safety of the cell.

[0077] In some embodiments, the substrate layer may comprise conventional polymeric materials in the art, such as polyethylene and / or polypropylene. The ceramic layer comprises inorganic particles. The inorganic particles comprise at least one selected from boehmite (hydrated aluminum hydroxide), magnesium oxide, magnesium hydroxide, BaSO4, CaSiO3, CaSiO4, Al2O3, and TiO2.

[0078] In this invention, the thickness of the substrate layer is 3μm-10μm, for example, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm. The thickness of the ceramic layer is 0.5μm-5μm, for example, 0.5μm, 1μm, 2μm, 3μm, 4μm or 5μm.

[0079] In some embodiments, the diaphragm further includes an adhesive layer, which may include, for example, polyvinylidene fluoride and / or polymethyl methacrylate. The thickness of the adhesive layer is 0.5 μm to 5 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm.

[0080] In some embodiments, the diaphragm includes the substrate layer, the ceramic layers located on both sides of the substrate layer, and the adhesive layer located on the outer surface of one side of the ceramic layer.

[0081] In some embodiments, the diaphragm includes the substrate layer, the ceramic layer located on one side surface of the substrate layer, and the adhesive layer located on both outer surfaces of the diaphragm.

[0082] In some embodiments, the battery cell includes a multi-tab wound core structure. The multi-tab wound core structure refers to a cell where the number of tabs (the total number of positive and negative tabs) is greater than two. When the number of tabs is greater than two, the energy density and high-temperature cycle performance of the battery can be further improved. This is because a larger current-carrying area of ​​the tabs is beneficial for increasing heat dissipation and improving electron transport rate, effectively reducing the internal resistance of the positive / negative electrode. Furthermore, the multi-tab structure can reduce heat concentration at the tabs, lowering the risk of thermal runaway under abnormal conditions such as overcharging and over-discharging, and improving battery safety.

[0083] In some embodiments, the battery cell may have a centrally located tab structure. A centrally located tab structure means that the tab is located in the middle of the electrode sheet, i.e., the tab is not located at the beginning or end of the electrode sheet.

[0084] In some embodiments, the application voltage range of the lithium-ion secondary battery is 2.8V to 4.3V.

[0085] In this invention, unless otherwise specified, all contents refer to mass contents.

[0086] 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.

[0087] 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.

[0088] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0089] The following examples illustrate the lithium-ion secondary battery of the present invention.

[0090] Example 1

[0091] (1) Preparation of positive electrode

[0092] The positive electrode active material, polyvinylidene fluoride, single-walled carbon nanotubes and multi-walled carbon nanotubes were mixed evenly in a mass ratio of 97.4:1.2:0.4:1, and N-methylpyrrolidone (NMP) was added to obtain a positive electrode slurry with a solid content of 65%. The positive electrode slurry was evenly coated onto a 10μm aluminum foil using a coating machine, dried, and then rolled, die-cut and sheet-made to obtain the positive electrode sheet.

[0093] The compaction density of the positive electrode sheet is 3.35 g / cm³. 3 ;

[0094] The positive electrode active material comprises a first particle and a second particle with a mass ratio of 90:10. The first particle is a single crystal particle and is LiNi. 0.93 Co 0.05 Mn 0.01 B 0.01 O2, with an average particle size of 3μm; the second particle is a polycrystalline particle, and the second particle is LiNi. 0.9 Co 0.04 Mn 0.03 Al 0.03 O2, with an average particle size of 11 μm, the second particle includes several primary particles, the average particle size of the primary particles is 400 nm; the ratio of the average particle size of the second particle to the average particle size of the first particle is 3.67.

[0095] (2) Preparation of negative electrode

[0096] The negative electrode active material, single-walled carbon nanotubes, multi-walled carbon nanotubes, polyvinylidene fluoride, and sodium carboxymethyl cellulose were mixed evenly in a weight ratio of 96.1:0.25:0.15:2.9:0.6 to obtain a material. Ethylene carbonate (EC) accounting for 1% of the total weight of the material was added, and deionized water was added to obtain a negative electrode slurry (solid content of 45%). The negative electrode slurry was evenly coated on a high-strength carbon-coated copper foil with a thickness of 4μm, dried, and then rolled, die-cut, and sheeted to obtain a negative electrode sheet.

[0097] The compaction density of the negative electrode is 1.5 g / cm³. 3 ;

[0098] The negative electrode active material is a mixture of artificial graphite and silicon-based material (silicon-carbon composite particles (porous carbon material and silicon material distributed in the pores of the porous carbon material), with a sphericity of 0.8 and a silicon content of 53%) at a mass ratio of 55:45; the mass content of elemental Si in the negative electrode active layer is 23%.

[0099] (3) Preparation of electrolyte

[0100] In a glove box filled with inert gas (argon) (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate are mixed evenly in a mass ratio of 15:10:10:65. Then, 1.25 mol / L of fully dried lithium hexafluorophosphate is quickly added and stirred evenly. Finally, 0.5% of succinate based on the total mass of the electrolyte is added. After passing the tests for moisture and free acid, the electrolyte is obtained.

[0101] (4) Preparation of the diaphragm

[0102] A conventional commercial diaphragm is selected, consisting of a 5μm thick polyethylene substrate, a 1μm thick ceramic layer on one side of the substrate, and 1.5μm thick polyvinylidene fluoride adhesive layers on both sides of the outer surface of the diaphragm, with the ceramic layer facing the negative electrode.

[0103] (5) Preparation of lithium-ion batteries

[0104] The positive electrode, negative electrode and separator are wound by a winding machine to obtain a battery core in which the positive and negative electrode are separated by the separator. Then, the battery is obtained by welding tabs, attaching tab adhesive, placing it into the shell, encapsulating, injecting liquid, forming, cutting with air bag, and sorting. Its structure is multi-tab winding.

[0105] Among them, such as Figure 1 and Figure 2As shown, tab adhesive A is provided on the tab 1 located on the battery cell. The tab adhesive A includes a first adhesive layer A1, a second adhesive layer A2 and a third adhesive layer A3 stacked in sequence. The first adhesive layer A1 is in contact with the housing, the third adhesive layer A3 is in contact with the tab 1, and the second adhesive layer A2 is located between the first adhesive layer A1 and the third adhesive layer A3. Specific parameters are shown in Table 1.

[0106] Example 2

[0107] The procedure is carried out in accordance with Example 1, except that:

[0108] (1) Preparation of positive electrode

[0109] The positive electrode active material comprises a first particle and a second particle with a mass ratio of 80:20. The first particle is a single crystal particle and is LiNi. 0.95 Co 0.03 Mn 0.01 B 0.01 O2, with an average particle size of 2μm; the second particle is a polycrystalline particle, and the second particle is LiNi. 0.92 Co 0.02 Mn 0.02 Al 0.04 O2, with an average particle size of 9 μm, the second particle includes several primary particles, the average particle size of the primary particles is 300 nm; the ratio of the average particle size of the second particle to the average particle size of the first particle is 4.5.

[0110] (2) Preparation of negative electrode

[0111] The silicon-based material consists of silicon-carbon composite particles with a sphericity of 0.9 and a silicon content of 53%.

[0112] (5) Preparation of lithium-ion batteries

[0113] See Table 1 for specific parameters.

[0114] Example 3

[0115] The procedure is carried out in accordance with Example 1, except that:

[0116] (1) Preparation of positive electrode

[0117] The positive electrode active material comprises a first particle and a second particle with a mass ratio of 70:30. The first particle is a single crystal particle and is LiNi. 0.91 Co 0.04 Mn 0.02 B 0.03 O2, with an average particle size of 4 μm; the second particle is a polycrystalline particle, and the second particle is LiNi. 0.83 Co 0.1 Mn 0.05 Al0.02 O2, with an average particle size of 13 μm, the second particle includes several primary particles, the average particle size of the primary particles is 500 nm; the ratio of the average particle size of the second particle to the average particle size of the first particle is 3.25.

[0118] (2) Preparation of negative electrode

[0119] The silicon-based material is nano-silicon with a sphericity of 0.7 and a silicon content of 100%. The mass ratio of artificial graphite to silicon-based material is 76:24.

[0120] (5) Preparation of lithium-ion batteries

[0121] See Table 1 for specific parameters.

[0122] Example 4 group

[0123] This set of examples is used to verify the impact of the change in "b".

[0124] This set of embodiments refers to Embodiment 1 or Embodiment 3, and b is adjusted by changing the first particle and the second particle, as follows:

[0125] Example 4a is performed in accordance with Example 3, except that:

[0126] The first particle is LiN. i0.90 Co 0.07 Mn 0.015 B 0.015 O2, the second particle is LiNi 0.8 Co 0.07 Mn 0.08 Al 0.05 O2;

[0127] Example 4b is performed in accordance with Example 1, except that:

[0128] The first particle is LiNi 0.96 Co 0.02 Mn 0.01 B 0.01 O2, the second particle is LiNi 0.94 Co 0.02 Mn 0.02 Al 0.02 O2;

[0129] Example 4c is performed in accordance with Example 1, except that:

[0130] The positive electrode active material is LiNi 0.8 Co 0.07 Mn 0.08 Al 0.05O2, with an average particle size of 13 μm, includes several primary particles with an average particle size of 400 nm.

[0131] Example 5 group

[0132] This set of examples is used to verify "T" 12 The impact of the change.

[0133] Example 5a was performed in accordance with Example 1, and Example 5b was performed in accordance with Example 3, except that T was adjusted by changing the melting point of the first adhesive layer, the melting point of the second adhesive layer, and the melting point of the third adhesive layer. 12 See Table 1 for details.

[0134] Example 6 group

[0135] This set of examples is used to verify "T" 13 The impact of the change.

[0136] Example 6a was performed in accordance with Example 1, and Example 6b was performed in accordance with Example 2, except that T was adjusted by changing the melting point of the first adhesive layer, the melting point of the second adhesive layer, and the melting point of the third adhesive layer. 13 See Table 1 for details.

[0137] Example 7

[0138] Used to verify "b / T" 12 The impact of the change.

[0139] The procedure was carried out in accordance with Example 3, except that the b / T ratio was adjusted by changing the melting points of the first adhesive layer, the second adhesive layer, and the third adhesive layer. 12 See Table 1 for details.

[0140] Example 8 group

[0141] This set of examples is used to verify the impact of changes in the "mass content s of element Si in the negative electrode active layer".

[0142] This set of embodiments follows the same procedure as Embodiment 1, except that s is controlled by changing the mass ratio of artificial graphite to silicon-based material in the negative electrode active material, as detailed below:

[0143] Example 8a: Artificial graphite and silicon-based materials were mixed at a mass ratio of 71:29; the mass content of element Si in the negative electrode active layer was 15%.

[0144] Example 8b: Artificial graphite and silicon-based materials were mixed at a mass ratio of 41:59; the mass content of element Si in the negative electrode active layer was 30%.

[0145] Example 8c: Artificial graphite and silicon-based materials were mixed at a mass ratio of 96:4; the mass content of element Si in the negative electrode active layer was 2%.

[0146] In Example 8d, artificial graphite and silicon-based materials were mixed at a mass ratio of 21:79; the mass content of elemental Si in the negative electrode active layer was 40%.

[0147] Example 9 group

[0148] This set of examples is used to verify the impact of changes in the sphericity of silicon-based materials.

[0149] This set of embodiments follows the same procedure as Embodiment 1, except that the sphericity of the silicon-based material is changed, as follows:

[0150] Example 9a: The sphericity of the silicon-carbon composite particles is 0.99;

[0151] In Example 9b, the sphericity of the silicon-carbon composite particles was 0.5.

[0152] Example 10

[0153] The procedure was carried out in accordance with Example 1, except that the positive electrode active material was changed. Specifically, the positive electrode active material contained a first particle, a second particle, and lithium cobalt oxide in a mass ratio of 72:8:20.

[0154] Example 11

[0155] The process was carried out in accordance with Example 1, except that the negative electrode active material was changed. Specifically, the negative electrode active material was entirely silicon-based, wherein the silicon-based material was silicon-carbon composite particles (porous carbon material and silicon material distributed in the pores of the porous carbon material), with a sphericity of 0.8 and a silicon content of 24%.

[0156] Table 1

[0157]

[0158]

[0159] All of the above embodiments satisfy the following:

[0160] The particle size Dv10 of the first particle is 0.5μm to 2μm, the particle size Dv50 is 0.5μm to 5μm, and the particle size Dv90 is ≤10μm;

[0161] The particle size of the second particle is Dv10, which is 3μm to 12μm; the particle size is Dv50, which is 5μm to 20μm; and the particle size is Dv90, which is ≤25μm.

[0162] The BET specific surface area of ​​the second particle is 0.3 m². 2 / g~1m2 / g.

[0163] Comparative Example 1

[0164] The procedure was carried out in accordance with Example 1, except that the tab adhesive had a single-layer structure and a melting point of 105°C.

[0165] Comparative Example 2

[0166] The procedure was carried out in accordance with Example 1, except that the tab adhesive had a single-layer structure and a melting point of 160°C.

[0167] Comparative Example 3

[0168] The procedure was carried out in accordance with Example 1, except that the positive electrode active material was changed. Specifically:

[0169] The positive electrode active material comprises a first particle and a second particle with a mass ratio of 99:1, wherein the first particle is LiNi. 0.98 Co 0.01 Mn 0.005 B 0.005 O2, the second particle is LiNi 0.97 Co 0.01 Mn 0.01 Al 0.01 O2.

[0170] Test case

[0171] (1) Thermogravimetric test

[0172] The batteries prepared in the examples were subjected to thermogravimetric analysis of the negative electrode active layer, and the residual amount results were rounded and recorded in Table 2.

[0173] (2) Hot box test

[0174] The batteries prepared in the examples and comparative examples were subjected to thermal chamber tests, and the results are recorded in Table 2. This test was used to evaluate the thermal stability of the batteries. The higher the pass rate, the lower the risk of thermal runaway and the better the safety performance of the battery.

[0175] 130℃ Hot Chamber Test: Under an environment of 25℃±3℃, discharge at 0.2C to the cutoff voltage of 3.0V, and let stand for 10 minutes; charge at 0.5C constant current and constant voltage to the upper limit voltage of 4.2V, with a cutoff current of 0.02C. Test the voltage, internal resistance, and thickness of the fully charged state at 25℃±3℃. Place the fully charged battery in the test chamber, and heat the chamber at a rate of (5±2)℃ / min. When the temperature inside the chamber reaches 130℃±2℃, maintain this temperature for 60 minutes. After the test, observe whether the battery catches fire. If it catches fire, it fails; if it does not catch fire, it passes.

[0176] 135℃ Hot Chamber Test: Under an environment of 25℃±3℃, discharge at 0.2C to the cutoff voltage of 3.0V, and let stand for 10 minutes; charge at 0.5C constant current and constant voltage to the upper limit voltage of 4.2V, with a cutoff current of 0.02C. Test the voltage, internal resistance, and thickness of the fully charged state at 25℃±3℃. Place the fully charged battery in the test chamber, and heat the chamber at a rate of (5±2)℃ / min. When the temperature inside the chamber reaches 135℃±2℃, maintain this temperature for 60 minutes. After the test, observe whether the battery catches fire. If it catches fire, it fails; if it does not catch fire, it passes.

[0177] 140℃ Hot Chamber Test: Under an environment of 25℃±3℃, discharge at 0.2C to the cutoff voltage of 3.0V, and let stand for 10 minutes; charge at 0.5C constant current and constant voltage to the upper limit voltage of 4.2V, with a cutoff current of 0.02C. Test the voltage, internal resistance, and thickness of the fully charged state at 25℃±3℃. Place the fully charged battery in the test chamber, and heat the chamber at a rate of (5±2)℃ / min. When the temperature inside the chamber reaches 140℃±2℃, maintain the temperature for 60 minutes. After the test, observe whether the battery catches fire. If it catches fire, it fails; if it does not catch fire, it passes.

[0178] The result is expressed as "number of passes / 10". For example, "10 / 10" means that all 10 tests were passed, and "5 / 10" means that 5 out of 10 tests were passed.

[0179] (3) Drop test

[0180] The batteries prepared in the examples and comparative examples were subjected to drop tests, and the results are recorded in Table 2. This test was used to evaluate the safety performance of the batteries.

[0181] After installing the battery, it was discharged at 0.2C to the cutoff voltage of 3.0V in an environment of 25℃±3℃, and left to stand for 10 minutes. Then, it was charged at 0.5C constant current and constant voltage to 50% SOC. The battery was then dropped from a height of 1.5 meters above a granite rock, with the tabs facing down 20 times. If the battery opened, it was considered a failure; if it did not open, it was considered a pass. Ten batteries were tested for each example and comparative example. The results are expressed as "number of passes / 10", for example, "10 / 10" means all 10 tests passed, and "5 / 10" means 5 out of 10 tests passed.

[0182] (4) Sealing test

[0183] The batteries prepared in the examples and comparative examples were subjected to sealing tests, and the results are recorded in Table 2. This test was used to evaluate the safety performance of the batteries.

[0184] In an environment of 25℃±3℃, the battery was discharged at 0.2C to the lower limit voltage of 3.0V, allowed to stand for 10 minutes, and then placed in a 25℃ constant temperature chamber. It was then fully charged at a constant current of 0.7C (100% SOC), with a cutoff current of 0.02C. After full charging, the battery was stored in an environment with a temperature of 60℃ and a relative humidity of 95%. The battery thickness was tested every 3 days, and the pass rate on day 30 was recorded in Table 2. An expansion rate exceeding 10% was considered a failure; an expansion rate not exceeding 10% (less than or equal to 10%) was considered a pass. Ten batteries were tested for each example and comparative example, and the results were expressed as "number of passes / 10". For example, "10 / 10" meant all 10 tests passed, and "5 / 10" meant 5 out of 10 tests passed.

[0185] (5) Energy density test

[0186] The energy density of the batteries prepared in the examples and comparative examples was tested using the following specific methods:

[0187] Charge the battery at 0.7C to the upper limit voltage (4.3V), cut off the current at 0.025C, discharge at 0.5C to the lower limit voltage (2.5V), output the discharge capacity and operating voltage, measure the battery mass using a balance, and calculate the energy density using the formula: Energy density = Discharge capacity × Operating voltage / Mass. Record the results in Table 2.

[0188] Table 2

[0189]

[0190]

[0191] Note: " / " in Table 2 indicates that this test was not performed and there is no data.

[0192] As can be seen from Table 2, the lithium-ion secondary battery of the present invention has a higher energy density compared with the comparative example. At the same time, the pass rates of the hot box test, drop test and sealing test are all high, indicating that the lithium-ion secondary battery of the present invention can effectively prevent thermal runaway of batteries containing high nickel cathode materials during fast charging and has high safety performance.

[0193] 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 lithium-ion secondary battery, characterized in that, The lithium-ion secondary battery includes a cell, tab adhesive, and a casing; the cell includes a tab, one end of which is electrically connected to the cell, and the other end of which extends out of the casing; the tab adhesive partially covers the tab; the tab adhesive includes a first adhesive layer, a second adhesive layer, and a third adhesive layer stacked together, the first adhesive layer being in contact with the casing, the third adhesive layer being in contact with the tab, and the second adhesive layer being located between the first adhesive layer and the third adhesive layer; The melting point of the first adhesive layer is 90℃~120℃, the melting point of the second adhesive layer is 140℃~170℃, and the melting point of the third adhesive layer is 90℃~130℃; The battery cell further includes a positive electrode sheet, which comprises a positive electrode active material, including Li. a Ni b Co c Mn d M e O2, wherein 0.9≤a≤1.1, 0.8≤b≤0.975, 0.005≤c≤0.2, 0.005≤d≤0.14, 0≤e≤0.1, and M includes at least one of Al, Zr, B, Y, Sr, W, Ti, Mg and Nb.

2. The lithium-ion secondary battery according to claim 1, wherein, 0.88≤b≤0.95； And / or, the difference T between the melting point of the second adhesive layer and the melting point of the first adhesive layer 12 The temperature ranges from 25℃ to 65℃. And / or, the difference T between the melting point of the third adhesive layer and the melting point of the first adhesive layer. 13 The temperature ranges from -35℃ to 25℃.

3. The lithium-ion secondary battery according to claim 1 or 2, wherein, b and the difference T between the melting point of the second adhesive layer and the melting point of the first adhesive layer 12 Satisfies: 0.012≤b / T 12 ≤0.04; preferably 0.016≤b / T 12 ≤0.

028.

4. The lithium-ion secondary battery according to claim 1 or 2, wherein, The battery cell further includes a negative electrode sheet, which comprises a negative current collector and a negative active layer located on at least one side of the negative current collector. The negative active layer comprises a silicon-based material. The mass content of element Si in the negative active layer is s, and s is the difference T between the melting point of the third adhesive layer and the melting point of the first adhesive layer. 13 Satisfy: -200≤T 13 / s≤600; preferably, -45≤T 13 / s≤70.

5. The lithium-ion secondary battery according to claim 4, wherein, The concentration of s is 1.5% to 40%; preferably 15% to 30%. And / or, the silicon-based material includes at least one of elemental silicon, silicon oxide, silicon carbon, and silicon alloys; And / or, the sphericity of the silicon-based material is 0.5 to 1; preferably 0.7 to 0.98; And / or, the negative electrode active layer, after being subjected to thermogravimetric analysis in an air or oxygen atmosphere and kept at 900°C for 40 minutes, has a residual content of 3% to 90%.

6. The lithium-ion secondary battery according to claim 1 or 2, wherein, The positive electrode active material includes a first particle and a second particle; The first particle includes a single crystal particle, and the second particle includes a polycrystalline particle; The first particle includes Li a1 Ni b1 Co c1 Mn d1 M 1 e1 O2, 0.9≤a1≤1.1, 0.9≤b1≤0.99, 0.01≤c1≤0.1, 0.01≤d1≤0.1, 0≤e1≤0.05, M 1 Including at least one of Al, Zr, B, Y, Sr, W, Ti, Mg, and Nb; The second particle includes Li a2 Ni b2 Co c2 Mn d2 M 2 e2 O2, 0.9≤a2≤1.1, 0.8≤b2≤0.95, 0.01≤c2≤0.2, 0.01≤d2≤0.1, 0≤e2≤0.05, M 2 Including at least one of Al, Zr, B, Y, Sr, W, Ti, Mg, and Nb; Preferably, based on the total mass of the positive electrode active material, the content of the first particle is 50% to 99.9%; more preferably, it is 70% to 90%.

7. The lithium-ion secondary battery according to claim 6, wherein, The particle size Dv10 of the first particle is 0.5μm to 2μm, the particle size Dv50 is 0.5μm to 5μm, and the particle size Dv90 is ≤10μm; And / or, the particle size Dv10 of the second particle is 3μm to 12μm, the particle size Dv50 is 5μm to 20μm, and the particle size Dv90 is ≤25μm; And / or, the second particle includes a plurality of primary particles, the average particle size of which is 100 nm to 600 nm; And / or, the BET specific surface area of ​​the second particle is 0.3 m². 2 / g~1m 2 / g.

8. The lithium-ion secondary battery according to claim 6, wherein, The ratio of the average particle size of the second particle to the average particle size of the first particle is 1 to 10; preferably 3 to 4.

5. Preferably, the average particle size of the first particle is 1.5 μm to 5 μm; more preferably, it is 2 μm to 4 μm. Preferably, the average particle size of the second particle is 5 μm to 20 μm; more preferably, it is 9 μm to 13 μm.

9. The lithium-ion secondary battery according to claim 1 or 2, wherein, The compaction density of the positive electrode is 3.1 g / cm³. 3 ~3.7g / cm 3 .

10. The lithium-ion secondary battery according to claim 1 or 2, wherein, The positive electrode sheet also includes a positive electrode conductive agent, which includes at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. The battery cell further includes a negative electrode sheet, the negative electrode sheet including a negative electrode conductive agent, the negative electrode conductive agent including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

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