Lithium ion secondary battery

Abstract

The invention relates to the technical field of lithium batteries, and provides a lithium ion secondary battery, which comprises a pole piece and an electrolyte, the pole piece comprises a current collector and a tab, the tab is electrically connected with the current collector, and the tab protrudes from one side of the current collector in the width direction; the sectional area of the tab is marked as A mm < 2 >; the electrolyte comprises a carboxylic ester solvent; based on the total mass of the electrolyte, the mass ratio of the carboxylic ester solvent is marked as B%; a and B satisfy A * B > = 1. According to the lithium ion secondary battery provided by the invention, the temperature rise of the battery can be reduced, the safety performance of the battery is improved, the battery fire caused by too high temperature in the charging process of the battery is prevented, and the high-temperature storage performance and cycle performance of the battery are improved.

Description

Technical Field

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

[0002] With the continuous advancement of science and technology and the booming electric vehicle market, the performance requirements of lithium-ion batteries, as the core components of electric vehicles, are also increasing. Among them, fast charging technology is one of the important development directions in the field of electric vehicles, because it can significantly shorten the charging time and improve the user experience. However, fast charging technology shortens the charging time by increasing the charging current or voltage, but it may also cause the internal temperature of the battery to rise rapidly, thus causing a series of safety issues. For example, high temperature may cause gas to be generated inside the battery, causing the battery to swell or even explode; high temperature may also accelerate the chemical reaction of the internal materials of the battery, causing the battery performance to deteriorate or even fail. In addition, the current and voltage fluctuations during the fast charging process may also damage the structure and performance of the battery. Therefore, it is particularly important to develop a fast-charging and safe lithium-ion battery technology. Summary of the invention

[0003] The object of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a lithium-ion secondary battery. By adjusting the cross-sectional area A of the tab and the mass proportion B of the carboxylic acid ester solvent to satisfy A*B≥1, the resistance of thermal diffusion of the battery can be reduced (the internal resistance can be reduced), the temperature rise of the battery can be reduced, the safety performance of the battery can be improved, and the high-temperature storage performance and cycle performance of the battery can be improved.

[0004] In order to achieve the above object, the present invention provides a lithium ion secondary battery, the battery comprising a pole piece and an electrolyte;

[0005] The pole piece includes a current collector and a pole ear, the pole ear is electrically connected to the current collector, and the pole ear protrudes from one side in the width direction of the current collector; the cross-sectional area of ​​the pole ear is recorded as A mm 2 ;

[0006] The electrolyte includes a carboxylate solvent; based on the total mass of the electrolyte, the mass proportion of the carboxylate solvent is recorded as B%; A and B satisfy: A*B≥1.

[0007] By adjusting the cross-sectional area A of the pole ear and the mass proportion B of the carboxylic acid ester solvent to satisfy A*B≥1, the combined effect of the two can greatly reduce the resistance of thermal diffusion of the battery (reduce the internal resistance), and when local rapid temperature rise occurs inside the battery, the heat can be quickly exchanged out to reduce the temperature rise of the battery, improve the safety performance of the battery, and prevent the battery from catching fire due to excessive temperature during charging.

[0008] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0009] The lithium-ion secondary battery provided by the present invention can reduce the internal resistance of the battery, reduce the temperature rise of the battery, improve the high-temperature storage performance and cycle performance of the battery, improve the safety performance of the battery, and prevent the battery from catching fire due to excessively high temperature during the battery charging process.

[0010] The endpoints and any values ​​of the range disclosed in this article are not limited to the precise range or value, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Herein, in the absence of special instructions, data ranges include endpoints. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Shown is a schematic structural diagram of a lithium-ion secondary battery in an example of the present invention.

[0012] Figure 2 Shown is a schematic structural diagram of a positive electrode sheet and a negative electrode sheet in an example of the present invention.

[0013] Figure numerals: 1 - battery cell; 2 - pole ear; 21 - positive pole ear; 22 - negative pole ear; 3 - positive electrode collector; 4 - negative electrode collector. DETAILED DESCRIPTION

[0014] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0015] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0016] In the present invention, the terms "lithium battery", "lithium-ion battery" and "lithium-ion secondary battery" all have the same meaning and refer to batteries, which generally include an electrode assembly (such as a positive electrode sheet, a negative electrode sheet and a separator), a container (shell) for accommodating the electrode assembly, and an electrolyte.

[0017] In the present invention, the term "Dv50" refers to the particle size corresponding to when the cumulative volume particle size distribution percentage of a sample reaches 50%. Dv50 can be tested using a laser particle size analyzer.

[0018] The present invention provides a lithium ion secondary battery, the battery comprising a pole piece and an electrolyte; the pole piece comprises a current collector and a pole ear, the pole ear is electrically connected to the current collector, and the pole ear protrudes from one side in the width direction of the current collector; the cross-sectional area of ​​the pole ear is recorded as A mm2 ; The electrolyte includes a carboxylate solvent; based on the total mass of the electrolyte, the mass proportion of the carboxylate solvent is recorded as B%; A and B satisfy: A*B≥1.

[0019] The tab is a connecting component between the positive and negative electrodes inside the battery and the external circuit. It can reduce the internal resistance of the battery, making the current transmission between the internal battery and the external circuit smoother. In addition, the tab can effectively transfer the heat inside the battery to the external environment, reducing the temperature rise of the battery during fast charging. The larger the cross-sectional area A of the tab, the better the effect of reducing internal resistance and temperature rise. However, the tab can usually only reduce the temperature of a local area of ​​the battery (the tab negative electrode area), and if the cross-sectional area of ​​the tab is too large, it will affect the energy density of the battery. Therefore, only adjusting the cross-sectional area of ​​the tab to reduce internal resistance and temperature rise has limited improvement effect.

[0020] The present invention further adds a carboxylate solvent to the electrolyte, and the viscosity of the carboxylate solvent is reduced, which can improve the dynamics of the electrolyte and reduce the internal resistance of the battery; and the heat exchange rate between the carboxylate solvent and the tab is high; the higher the content of the carboxylate solvent, the better the effect of reducing the internal resistance and reducing the temperature rise. When the cross-sectional area A of the tab and the mass proportion B of the carboxylate solvent are adjusted to meet A*B≥1, the combined effect of the two can greatly reduce the resistance of thermal diffusion of the battery (reduce the internal resistance), and when local rapid temperature rise occurs inside the battery, the heat can be quickly exchanged out, the battery temperature rise can be reduced, the safety performance of the battery can be improved, and the battery fire caused by the high temperature during the battery charging process can be prevented, and the high temperature storage performance and cycle performance of the battery can be improved.

[0021] In some embodiments, Figure 1 The figure shows a schematic diagram of the structure of a battery, wherein a is a top view of the battery, b is a side view of the battery, and c is a schematic diagram of a cross-section of the battery. The battery includes a battery cell 1 and a tab 2 connected to the battery cell. The cross-sectional area A of the tab = tab width * tab thickness. The tab width refers to the distance of the tab in the width direction of the battery cell, and the tab thickness refers to the distance of the tab in the thickness direction of the battery cell.

[0022] Furthermore, the electrode sheet includes a positive electrode sheet and a negative electrode sheet. The battery includes a positive electrode sheet, a separator and a negative electrode sheet which are stacked.

[0023] In some embodiments, Figure 2 As shown, the positive electrode sheet includes a positive electrode collector 3 and a positive electrode ear 21, the positive electrode ear 21 is electrically connected to the positive electrode collector 3, and the positive electrode ear 21 protrudes from one side of the positive electrode collector 3 in the width direction. In some embodiments, as Figure 2As shown, the negative electrode sheet includes a negative electrode collector 4 and a negative electrode ear 22 . The negative electrode ear 22 is electrically connected to the negative electrode collector 4 , and the negative electrode ear 22 protrudes from one side of the negative electrode collector 4 in the width direction.

[0024] In some embodiments, the cross-sectional area of ​​the positive electrode ear may be the same as or different from the cross-sectional area of ​​the negative electrode ear, preferably the same or similar. When the cross-sectional area of ​​the positive electrode ear is the same as or similar to the cross-sectional area of ​​the negative electrode ear, it is helpful to evenly distribute the current inside the battery, reduce the problem of local overheating or performance degradation caused by uneven current distribution, help reduce the risk of thermal runaway caused by overheating of the battery, and improve the safety of the battery.

[0025] In some embodiments, the positive electrode ear includes aluminum metal; and / or, the negative electrode ear includes nickel metal. For example, the positive electrode ear is made of aluminum metal, and the negative electrode ear is made of nickel metal. When A and B satisfy A*B≥1, the adjustment electrode ear is made of metal aluminum and metal nickel with good thermal conductivity, and the carboxylate solvent has a very high heat exchange with nickel and aluminum, which can further improve the heat dissipation of the battery, reduce the temperature rise of the battery during fast charging, and improve the safety performance of the battery during fast charging.

[0026] In some embodiments, the value of A*B may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 53, 60 or a greater value. Preferably, A and B satisfy: 5≤A*B≤30. The value of A*B may be adjusted according to the size of the battery (different types of batteries may have different values ​​of the cross-sectional area A of the tab). The greater the value of A*B, the better the effect of reducing the internal resistance and reducing the temperature rise.

[0027] In some embodiments, the cross-sectional area A of the tab satisfies: 0.1≤A≤1. For example, the cross-sectional area of ​​the tab may be 0.1 mm 2 , 0.2mm 2 , 0.3mm 2 , 0.4mm 2 , 0.5mm 2 , 0.6mm 2 , 0.7mm 2 , 0.8mm 2 , 0.9mm 2 , 1mm 2 Or any point value in the range consisting of the above two point values.

[0028] In some embodiments, the mass proportion B of the carboxylate solvent satisfies: 13.3≤B≤53.3. For example, the mass proportion of the carboxylate solvent in the electrolyte can be 13.3%, 14%, 15%, 18%, 20%, 25%, 30%, 33%, 35%, 40%, 43%, 45%, 48%, 50%, 52%, 53.3% or any point value in the range consisting of any two of the above point values.

[0029] When A and B satisfy A*B≥1, adjusting the values ​​of A and B within the above range can further reduce the internal resistance of the battery and reduce the temperature rise of the battery, and avoid the tab cross-sectional area A being too large to affect the energy density of the battery; it can also avoid B being too large, and the carboxylate solvent content being too high, which increases the probability of side reactions at the positive and negative electrodes to produce gas, increasing the risk of gas production and explosion of the battery, and thus adjusting the values ​​of A and B can further improve the safety performance of the battery.

[0030] In some embodiments, the carboxylate solvent includes a C1-C6 linear carboxylate solvent; preferably, the C1-C6 linear carboxylate solvent includes at least one of ethyl butyrate, ethyl acetate, methyl propionate, propyl formate, methyl acetate, ethyl formate, and methyl formate, more preferably ethyl butyrate. The C1-C6 linear carboxylate solvent has a relatively low viscosity, can improve the kinetics of the electrolyte, and reduce the internal resistance of the battery.

[0031] In some embodiments, the carboxylate solvent is ethyl butyrate (EB). Ethyl butyrate has a higher melting point and lower viscosity, which helps to reduce the resistance of lithium ions to migrate in the electrolyte, thereby improving the conductivity of the electrolyte and being able to reduce the internal resistance of the battery. In addition, ethyl butyrate is particularly stable and will not react with the positive and negative electrodes, especially with lithium during fast charging, which greatly improves the safety performance of the battery.

[0032] In some embodiments, the carboxylate solvent is ethyl butyrate, the positive electrode ear is made of aluminum metal, and the negative electrode ear is made of nickel metal. The present invention has found that ethyl butyrate has the best heat exchange with aluminum and nickel among all carboxylate solvents. It is further preferred that ethyl butyrate is used in combination with aluminum and nickel ear tabs, which can more significantly improve the safety performance and fast charging performance of the battery.

[0033] In some embodiments, the cross-sectional area of ​​the battery cell is recorded as C mm 2 , the nominal capacity of the battery is recorded as Q mAh; C, Q and A satisfy: C / A*7≥Q.

[0034] In some embodiments, Figure 1 The schematic diagram of the battery structure is shown in FIG. Figure 1 As shown in c, the cross-sectional area of ​​the battery cell C = battery cell width * battery cell thickness.

[0035] The cross-sectional area of ​​the cell can also be called the cross-sectional area of ​​the battery. The larger the cross-sectional area C of the cell, the more positive and negative electrode materials can be accommodated, and the larger the battery capacity. The size of the cross-sectional area of ​​a lithium-ion battery is a key factor affecting the heat accumulation of a lithium-ion battery. If the cross-sectional area C is too large, the heat inside the battery is not easy to diffuse, which can easily cause the battery temperature to rise. The tabs are connected to the inside of the battery and can conduct the heat out in time. By adjusting C, Q and A to meet C / A*7≥Q, when C increases, A can be adjusted to increase at the same time, so that the tabs can transfer more heat and reduce the problem of poor battery heat dissipation caused by the increase in C; at the same time, the battery capacity Q can be reduced and the cross-sectional area A of the tabs can be increased, which can reduce the current during the battery operation process. The smaller the current, the lower the temperature rise of the battery.

[0036] Furthermore, when A and B satisfy A*B≥1, and C, Q and A are adjusted to satisfy C / A*7≥Q, the temperature rise of the battery during the fast charging process can be reduced by adjusting the battery cross-sectional area and battery capacity, which greatly reduces the temperature rise of the battery during the fast charging process, prevents the battery from catching fire due to excessively high temperature during charging, and further improves the battery safety performance.

[0037] In some embodiments, C satisfies: 0.16 mm 2 ≤C≤120mm 2 , for example, the cross-sectional area C of the battery cell can be 0.16mm 2 , 1mm 2 , 10mm 2 , 20mm 2 , 30mm 2 , 40mm 2 , 50mm 2 、60mm 2 , 70mm 2 、80mm 2 、90mm 2 , 100mm 2 、110mm 2 , 120mm 2 Or any point value in the range formed by the above two points. Q satisfies: 60mAh≤Q≤250mAh. For example, the nominal capacity of the battery is recorded as Q, which can be 60mAh, 80mAh, 100mAh, 120mAh, 150mAh, 180mAh, 200mAh, 220mAh, 250mAh, or any point value in the range formed by the above two points, or any point value in the range formed by the above two points.

[0038] In some embodiments, the capacity of the battery discharged using a current of 1 times the nominal capacity Q is recorded as C1, and the capacity of the battery discharged using a current of 2 times the nominal capacity Q is recorded as C2, and C2 / C1≥70%. C2 is the discharge capacity of the battery under high rate conditions, and the discharge capacity C2 does not show a significant decrease, indicating that the polarization of the battery is small. The ratio of the current discharge of 1 times and 2 times the nominal capacity of the battery can be, for example, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 99% or any point value in the range composed of the above two point values. When A and B satisfy A*B≥1, adjusting C2 / C1≥70% can reduce the charging polarization during the lithium-ion battery process, prevent the voltage from changing too fast, reduce the thermal effect of the battery, and further reduce the temperature rise of the battery.

[0039] In some embodiments, the electrolyte includes a first additive and a second additive; the first additive includes reduced yellow G; the second additive includes drometrizole trisiloxane. The first additive and the second additive are further added to the electrolyte. The two additives can form a solid electrolyte interface on the surface of the positive and negative electrodes, especially a SEI film on the surface of the negative electrode, thereby inhibiting the formation of lithium dendrites during fast charging, reducing the risk of lithium dendrites piercing the diaphragm to cause a battery short circuit, reducing the probability of battery fire during fast charging, and improving the safety performance of the battery.

[0040] In some embodiments, the first additive includes Vat Yellow G, whose chemical formula is

[0041] The second additive includes drometrizole trisiloxane, whose chemical formula is

[0042]

[0043] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.1%-1%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any point value in the range of any two of the above points. Based on the total mass of the electrolyte, the mass proportion of the second additive is 0.1%-1%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any point value in the range of any two of the above points.

[0044] Further optimizing the types and addition amounts of the first additive and the second additive can form a more stable and denser SEI film on the surface of the negative electrode, effectively inhibit the growth of lithium dendrites, and further improve the safety performance of the battery.

[0045] In some embodiments, the mass ratio of the first additive to the second additive is 1:(0.8-1.2), for example, the mass ratio may be 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1, 1:1.05, 1:1.1, 1:1.15, 1:1.2. When the first additive and the second additive are used in combination and the mass ratio of the two is adjusted to meet the above range, the effect of the combination of the two additives can be better exerted, the growth of lithium dendrites can be more effectively reduced, and the probability of battery fire during fast charging can be further reduced.

[0046] In some embodiments, the electrolyte further includes an electrolyte lithium salt, for example, the electrolyte lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bistrifluoromethylsulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyl lithium or lithium bis(trifluoromethylsulfonyl)imide. The above-mentioned lithium salt additive is added to the electrolyte, and the lithium salt additive can improve the ionic conductivity of the electrolyte, make the migration rate of lithium ions in the electrolyte faster, thereby improving the fast charging performance of the battery.

[0047] In some embodiments, the positive electrode sheet includes a positive electrode active material, the positive electrode active material includes a ternary material, and the chemical formula of the ternary material is Li a Ni x Co y Mn z A k O2, wherein 0.9≤a≤1.1, 0.3≤x≤0.98, 0<y≤0.2, 0<z≤0.3, 0≤k≤0.05, and A includes at least one of Al, Mg, Ti, Y, B, P, Zr, W, and Nb. The ternary material has a layered structure, which provides a shorter ion diffusion path, is conducive to the rapid diffusion and insertion / deinsertion process of lithium ions in the positive electrode active material, thereby improving the charge and discharge rate and performance of the battery.

[0048] In some embodiments, the Dv50 of the ternary material is 2 μm to 10 μm (for example, it can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any point value in the range of any two of the above points), and / or the specific surface area of ​​the ternary material is 0.5-10 m 2 / g (for example, 0.5m 2 / g, 1m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g or any point value in the range formed by the above two point values). When the Dv50 and specific surface area of ​​the ternary material are in the above range, the contact area between the ternary material and the electrolyte is larger, and the diffusion path of lithium ions is shorter, which is conducive to the insertion and extraction of lithium ions in the material under high current density and improves the fast charging performance of the battery.

[0049] In some embodiments, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes at least one of artificial graphite, natural graphite, mesophase carbon microbeads, hard carbon, soft carbon, nano-silicon, silicon oxygen, silicon carbon, and silicon alloy.

[0050] In some embodiments, the electrolyte includes a third additive; the mass proportion of the third additive is 0.1%-3% based on the total mass of the electrolyte; preferably, the third additive includes at least one of vinyl sulfate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, methylene disulfonate, and 1,3-propane sultone. The addition of the third additive to the electrolyte can improve the dynamic performance of the battery and the cycle performance of the battery.

[0051] In some embodiments, the electrolyte further includes a carbonate solvent; preferably, based on the total mass of the electrolyte, the mass proportion of the carbonate solvent is 40%-90%, for example, it can be 40%, 45%, 50%, 60%, 70%, 80%, 90% or any point value in the range of the above two point values. When A and B satisfy A*B≥1, adjusting the electrolyte to further add a carbonate solvent can make the interface generated by the electrolyte at the negative electrode more stable, improve the cycle performance of the battery, and improve the safety performance of the battery.

[0052] In some embodiments, the carbonate solvent includes, but is not limited to, at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorinated derivatives thereof.

[0053] The lithium-ion secondary battery of the present invention can be applied to the field of electric vehicles. First, the lithium-ion secondary battery of the present invention can ensure the safety of the battery during fast charging and reduce the risk of safety accidents caused by battery failure, which is crucial to protecting the personal safety and property safety of users. Secondly, the lithium-ion secondary battery of the present invention can improve the charging efficiency and shorten the charging time, thereby improving the convenience of electric vehicles, which is of great significance for promoting the popularization and development of electric vehicles.

[0054] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0056] The present invention is described in detail below in conjunction with specific embodiments, which are used to understand but not to limit the present invention.

[0057] The batteries of the examples and comparative examples of the present invention were prepared according to the following preparation method, and the differences from Example 1-1 are shown below.

[0058] Example 1-1

[0059] (1) Preparation of positive electrode film: LiNi cobalt manganese oxide LiNi 0.33 Co 0.33 Mn 0.33 O2 (Dv50 is 3.0μm, specific surface area is 1.5m 2 / g), conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) are dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent in a ratio of 96:2:2, and are fully stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and the positive electrode film is obtained after drying, rolling and slitting.

[0060] (2) Preparation of negative electrode membrane: Disperse the negative electrode active material graphite, the conductive agent acetylene black, the binder sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in an appropriate amount of deionized water at a ratio of 95:2:2:1, and stir and mix thoroughly to form a uniform negative electrode slurry; evenly coat the negative electrode slurry on the negative electrode current collector copper foil, and obtain the negative electrode sheet after drying, rolling and slitting.

[0061] (3) Preparation of electrolyte: Ethylene carbonate, ethyl methyl carbonate, and ethyl butyrate (EB) are mixed evenly, and lithium difluorophosphate, vinyl sulfate, lithium difluorobisoxalate phosphate, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, reduced yellow G, and drometrizole trisiloxane are added thereto for stirring and dissolution. The mass proportion of ethyl butyrate EB in the electrolyte is 15% (the mass ratio of ethylene carbonate to ethyl methyl carbonate is 1:2.4, and the mass proportion of the two in the total electrolyte can be calculated). The mass of lithium difluorophosphate added is 0.5% of the total mass of the electrolyte, the mass of vinyl sulfate added is 0.5% of the total mass of the electrolyte, the mass of lithium difluorobisoxalate phosphate added is 0.5% of the total mass of the electrolyte, the mass of lithium bisfluorosulfonyl imide added is 4% of the total mass of the electrolyte, the mass of lithium hexafluorophosphate added is 13% of the total mass of the electrolyte, the mass of the first additive reduced yellow G added is 0.5% of the total mass of the electrolyte, and the mass of the second additive drometrizole trisiloxane added is 0.5% of the total mass of the electrolyte. After passing the physical property test, the electrolyte is obtained.

[0062] (4) Assemble the battery: Wind the positive electrode film, isolation film (PE diaphragm) and negative electrode film in order, so that the isolation film is between the positive and negative electrodes to play an isolating role, and then stack the sheets to obtain a bare cell, and place the bare cell in an outer packaging shell, dry it, and inject the electrolyte. After vacuum packaging, standing, forming, shaping and other processes, the preparation of the lithium-ion battery is completed. The cross-sectional area A of the positive and negative ears is the same, the width of the ear is 6mm, the thickness of the ear is 0.08mm, and the cross-sectional area A of the positive and negative ears = 6mm*0.08mm = 0.48mm 2 The battery width is 98mm, the cell thickness is 3.7mm, and the cell cross-sectional area is C = 98mm*3.7mm = 362.6mm 2 The nominal capacity of the battery is Q=5500 mAh. The positive electrode ear and the negative electrode ear are connected to the positive electrode collector and the negative electrode collector respectively by ultrasonic welding.

[0063] The performance of the tested battery is as follows:

[0064] (1) High temperature storage performance

[0065] The battery of the embodiment and the comparative example was cycled at 25°C for 2 weeks, and the capacity of the battery was recorded as Q1. Then the battery was fully charged, and the thickness was tested at L1. The battery was placed at 60°C for 35 days. After 35 days, the battery was discharged to 3.0V, and its discharge capacity Q2 was recorded. Then the battery was fully charged, and the thickness was tested at L2. The residual capacity rate of the battery = (Q1 / Q2) × 100%,

[0066] Battery thickness expansion = (L2-L1) / L1

[0067] (2) Cycle performance

[0068] The batteries of the comparative example and the embodiment were charged and discharged for 100 cycles at 25° C. at a rate of 1C; at the same time, the capacity of the 100th week was divided by the capacity of the 1st week to obtain the cycle capacity retention rate.

[0069] During the cycle, a temperature probe is attached to the surface of the battery cell to record the battery cell problems in real time.

[0070] (3) 130℃ furnace temperature test

[0071] The batteries of the comparative example and the example at 4.45V are placed in an oven, and the temperature is raised from room temperature to 130°C at a rate of 5°C / min, and left to stand at 130°C for 1 hour to observe whether they catch fire or explode. Ten batteries of each example and comparative example are prepared for furnace temperature test. If the battery does not catch fire or explode, it is judged that the furnace temperature test has passed and is recorded as PASS. The furnace temperature test results are recorded separately for each battery, and the furnace temperature test results of 10 batteries are counted and recorded.

[0072] The method is carried out with reference to Example 1-1, except that: the mass proportion B of ethyl butyrate EB in the electrolyte is adjusted in Example 1 and Comparative Example 1; the cross-sectional area A of the tab is adjusted in Example 2 and Comparative Example 2; the type of carboxylic acid ester is changed in Example 3; and EB is not added in Comparative Example 3. The method is carried out with reference to Example 2-1, except that: an equal amount of ethyl acetate replaces EB in Example 3-1, and an equal amount of methyl acetate replaces EB in Example 3-2. The specific differences are shown in Table 1.

[0073] Table 1

[0074]

[0075]

[0076] The performance test data of Example 1-3 and Comparative Examples 1-3 are recorded in Table 2.

[0077] Table 2

[0078]

[0079]

[0080] It can be seen from Table 2 that the present invention can reduce the temperature rise of the battery, improve the safety performance of the battery, and enhance the high temperature storage performance and cycle performance of the battery by adjusting the cross-sectional area A of the tab and the mass proportion B of the carboxylic acid ester solvent to satisfy A*B≥1, especially when 5≤A*B≤30.

[0081] The method is carried out with reference to Example 1-1, except that: in Example 4, the cross-sectional area A of the tab is changed; in Example 5, the thickness of the battery cell is changed so that the cross-sectional area C of the battery cell is changed. The specific differences are shown in Table 3.

[0082] Table 3

[0083]

[0084] The performance test data of Example 4 and Example 5 are recorded in Table 4.

[0085] Table 4

[0086]

[0087]

[0088] It can be seen from Table 4 that by adjusting C / A*7≥Q, the temperature rise can be further reduced, the battery deterioration is reduced, and the battery safety and battery performance are further improved.

[0089] The method was carried out with reference to Example 1-1, except that the addition amount of the first additive and the second additive was changed in Example 6, and one of the first additive and the second additive was added or neither of them was added in Example 7. The specific differences and performance tests are shown in Table 5.

[0090] Table 5

[0091]

[0092] It can be seen from Table 5 that when the first additive and the second additive are used in combination and the mass ratio of the two is adjusted to meet the characteristic range of the present invention, the probability of battery fire during the fast charging process can be more effectively reduced.

[0093] It should be noted that, in this article, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium ion secondary battery, characterized in that: The battery comprises a pole piece and an electrolyte; The pole piece includes a current collector and a pole ear, the pole ear is electrically connected to the current collector, and the pole ear protrudes from one side in the width direction of the current collector; the cross-sectional area of ​​the pole ear is recorded as A mm 2 ; The electrolyte includes a carboxylate solvent; based on the total mass of the electrolyte, the mass proportion of the carboxylate solvent is recorded as B%; A and B satisfy: A*B≥1.

2. The lithium ion secondary battery according to claim 1, characterized in that: A and B satisfy: 5≤A*B≤30; Preferably, A satisfies: 0.1≤A≤1; Preferably, B satisfies: 13.3≤B≤53.

3.

3. The lithium ion secondary battery according to claim 1, characterized in that: The carboxylate solvent includes a C1-C6 linear carboxylate solvent; Preferably, the C1-C6 linear carboxylic acid ester solvent includes at least one of ethyl butyrate, ethyl acetate, methyl propionate, propyl formate, methyl acetate, ethyl formate, and methyl formate, more preferably ethyl butyrate.

4. The lithium-ion secondary battery according to claim 1, characterized in that: The cross-sectional area of ​​the battery cell is recorded as Cmm 2 , the nominal capacity of the battery is recorded as Q mAh; C, Q and A satisfy: C / A*7≥Q; Preferably, C satisfies: 0.16 mm 2 ≤C≤120mm 2 ; and / or, Q satisfies: 60mAh≤Q≤250mAh.

5. The lithium ion secondary battery according to claim 1, characterized in that: The capacity of the battery discharged using a current 1 times the nominal capacity Q is recorded as C1, the capacity of the battery discharged using a current 2 times the nominal capacity Q is recorded as C2, and C2 / C1≥70%.

6. The lithium ion secondary battery according to any one of claims 1 to 5, characterized in that: The electrolyte includes a first additive and a second additive; The first additive includes vat yellow G; The second additive includes drometrizole trisiloxane.

7. The lithium ion secondary battery according to claim 6, characterized in that: Based on the total mass of the electrolyte, the mass proportion of the first additive is 0.1%-1%; And / or, based on the total mass of the electrolyte, the mass proportion of the second additive is 0.1%-1%.

8. The lithium ion secondary battery according to claim 6, characterized in that: The mass ratio of the first additive to the second additive is 1:(0.8-1.2).

9. The lithium ion secondary battery according to claim 1, characterized in that: The pole pieces include a positive pole piece and a negative pole piece; Preferably, the positive electrode sheet comprises a positive electrode collector and a positive electrode ear, the positive electrode ear is electrically connected to the positive electrode collector, and the positive electrode ear protrudes from one side in the width direction of the positive electrode collector; Preferably, the negative electrode sheet comprises a negative electrode current collector and a negative electrode ear, wherein the negative electrode ear is electrically connected to the negative electrode current collector and the negative electrode ear protrudes from one side in the width direction of the negative electrode current collector; Preferably, the positive electrode tab comprises aluminum metal; and / or the negative electrode tab comprises nickel metal.

10. The lithium ion secondary battery according to claim 9, characterized in that: The positive electrode sheet includes a positive electrode active material, the positive electrode active material includes a ternary material, and the chemical formula of the ternary material is Li a Ni x Co y Mn z A k O2, wherein 0.9≤a≤1.1, 0.3≤x≤0.98, 0<y≤0.2, 0<z≤0.3, 0≤k≤0.05, and A includes at least one of Al, Mg, Ti, Y, B, P, Zr, W, and Nb; Preferably, the Dv50 of the ternary material is 2 μm to 10 μm, and / or the specific surface area of ​​the ternary material is 0.5 m 2 / g-10m 2 / g.

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