Secondary battery

Abstract

A secondary battery, wherein tris(dimethylvinylsilyl)phosphate and 1,3-propane sultone are introduced into an electrolyte as functional additives, and contents of the two additives in the electrolyte and an adhesion force of a separator are simultaneously regulated to satisfy a predetermined relationship, so as to effectively suppress side reactions between active materials of electrode sheets and the electrolyte in the secondary battery, thereby reducing a probability of gas generation, and ultimately achieving desirable ion / electron transport efficiency and cycling performance.

Description

A type of secondary battery

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese patent application filed on January 23, 2025, with application number 202510110499.X and entitled "A Secondary Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, specifically to a secondary battery. Background Technology

[0004] Medium-high nickel lithium-ion rechargeable batteries refer to a type of rechargeable battery that uses binary or ternary materials containing medium or high nickel content as the positive electrode material. While these batteries possess high theoretical energy density, in practical applications, especially during long-cycle periods, the degree of side reactions between the electrode material and the electrolyte increases, leading to gas generation. This not only affects the cycle performance of the rechargeable battery but can also cause safety issues. Furthermore, medium-high nickel lithium-ion rechargeable batteries have stringent requirements for the selection of negative electrode materials. If silicon-containing active materials are chosen, not only are additional electrolyte additives required, but the silicon volume effect further increases the likelihood of gas generation, resulting in poor practical performance. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the existing technology and provide a secondary battery. The secondary battery of this application introduces tris(dimethylvinylsilyl)phosphate (DMVSP) and 1,3-propanesulfonate lactone as functional additives into the electrolyte, and at the same time controls the content of the two in the electrolyte and the adhesion of the separator, which can effectively suppress the side reactions between the electrode active material and the electrolyte in the secondary battery, reduce the probability of gas generation, and ultimately achieve ideal ion / electron transport efficiency and cycle performance.

[0006] To achieve the above objectives, in a first aspect of this application, a secondary battery is provided, the secondary battery comprising a positive electrode, a separator, and an electrolyte;

[0007] The electrolyte includes a first additive and a second additive;

[0008] The secondary battery satisfies: (b*c) / a=1~10;

[0009] Where a% is the mass percentage of the first additive in the electrolyte, b% is the mass percentage of the second additive in the electrolyte, and c N / m is the adhesion force of the diaphragm.

[0010] The first additive is tris(dimethylvinylsilyl)phosphate, and the second additive is 1,3-propanesulfonate lactone.

[0011] The beneficial effects of this application are as follows:

[0012] This application provides a secondary battery. The secondary battery of this application introduces tris(dimethylvinylsilyl)phosphate and 1,3-propanesulfonate lactone as functional additives into the electrolyte, and simultaneously regulates the content of the two in the electrolyte and the adhesion of the separator. This can effectively suppress the side reactions between the electrode active material and the electrolyte in the secondary battery, reduce the probability of gas generation, and ultimately achieve ideal ion / electron transport efficiency and cycle performance. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0014] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0015] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0016] The present application is further illustrated below with specific embodiments:

[0017] A secondary battery, the secondary battery comprising a positive electrode, a separator and an electrolyte;

[0018] The electrolyte includes a first additive and a second additive;

[0019] The secondary battery satisfies: (b*c) / a=1~10;

[0020] Where a% is the mass percentage of the first additive in the electrolyte, b% is the mass percentage of the second additive in the electrolyte, and c N / m is the adhesion force of the diaphragm.

[0021] The first additive is tris(dimethylvinylsilyl)phosphate, and the second additive is 1,3-propanesulfonate lactone.

[0022] In secondary batteries, the electrodes, especially the positive electrode, are prone to side reactions with the electrolyte during cycling, which produce gas. As the cycling process continues, the gas gradually accumulates between the separator and the electrode, causing some of the ion / electron transport channels connecting the separator and the electrode to fail, greatly reducing the conductivity, significantly weakening the cycle performance of the secondary battery, and even causing safety problems. Therefore, in this application, the secondary battery incorporates specific tris(dimethylvinylsilyl)phosphate and 1,3-propanesulfonate lactone as additives in the electrolyte. The former effectively enhances the electrolyte's protection of the positive electrode interface and reduces the impedance of CEI film formation, while the latter works synergistically with the former to improve the overall system's cycle stability by suppressing gas generation. By adjusting the ratio of the two additives, a balance between cycle performance and conductivity can be maintained in the secondary battery. Furthermore, the adhesion of the separator is also controlled. Under appropriate adhesion, the secondary battery ensures stable ion transport efficiency without excessive adhesion leading to over-adhesion between the separator and the electrode, thus preventing an increase in the probability of side reactions and ultimately achieving excellent electrochemical performance.

[0023] In some implementations, (b*c) / a is a range of one or any two of the following values: 1, 1.37, 2, 2.5, 2.6, 2.67, 2.7, 3, 3.13, 3.14, 3.2, 3.29, 3.43, 3.5, 4, 4.47, 4.57, 4.8, 5, 5.33, 5.63, 6, 6.06, 6.4, 6.43, 6.5, 6.86, 7, 7.50, 7.71, 8, 8.21, 8.56, 8.75, 9, 9.6, 9.69, 10.

[0024] It should be noted that the mass percentage content of the first and second additives in the electrolyte of this application was confirmed by GC-MS testing. The specific method is as follows:

[0025] The secondary battery was discharged at a rate of 0.3C and a cutoff voltage of 2V. The battery was then disassembled. If free electrolyte was present, it was collected directly into a 5mL sample tube using a pipette and sealed with adhesive tape. If no free electrolyte was present, the disassembled battery was pressurized using a hydraulic press (FY-30) until free electrolyte appeared. This was then collected into a 5mL sample tube using a pipette and sealed with adhesive tape. The electrolyte sample was then injected into an Agilent Intuvo 9000 gas chromatograph to analyze its composition. The concentrations of each component in the electrolyte were determined by comparison with a standard database.

[0026] The adhesion of the separator was confirmed by the following method: The secondary battery was disassembled, and the negative electrode was separated, leaving the positive electrode connected to the separator. Preliminary compositional analysis was performed on the separator to confirm whether its surface contained a fiber coating. If a fiber coating was present, a 200-300 mm long strip was taken from the separator in the longitudinal direction, then folded in half laterally. The folded strip was placed between two layers of lint-free paper, and then cut together with the lint-free paper into test strips 250 mm long and 15 mm wide. The lint-free paper was then separated, and 3M-18mm was selected. Using Scotch 300C double-sided tape, a 15mm wide separator and the electrode surface of the positive electrode sample are pasted onto a steel plate. After being rolled back and forth three times by a pressure roller, the adhesion is tested. If there is no fiber coating, a 25mm wide and 250mm long separator and positive electrode sample are cut along the length direction (M) of the separator using a bidirectional cutter. A 160mm long GA808 double-sided tape is pasted onto one end of the steel plate, and the 25mm wide separator and the electrode surface of the positive / negative electrode sample are pasted onto the steel plate. After being rolled back and forth three times by a pressure roller, the adhesion is tested.

[0027] The testing steps are as follows: Use a universal testing machine to replace the manual fixture (one end of the flat steel plate without double-sided adhesive is fixed with the fixture, and the free end of the test strip is fixed with the fixture), select the 500N sensor device for connection, select the adhesion test step, confirm the width of the test strip (15mm for test strips with fiber layer, 25mm for test strips without fiber layer), set the peel start point to 20mm, the end point to 90mm, the peel speed to 100mm / min, and the peel direction to 180°.

[0028] In some implementations, c = 3 to 15 N / m.

[0029] More preferably, c is a value within the range of one or any two of the following: 3N / m, 4N / m, 5N / m, 6N / m, 7N / m, 8N / m, 9N / m, 10N / m, 11N / m, 12N / m, 13N / m, and 15N / m.

[0030] In some implementations, (b*c) / a = 3 to 7.

[0031] As mentioned above, the addition of the first and second additives in the electrolyte actually needs to consider several factors: the degree of interface protection for the positive electrode, the passivation effect of electrolyte side reactions, ion / electron conduction efficiency, and the thickness and impedance of the SEI / CEI film during cycling. The content of both additives is not necessarily better the more there is. At the same time, the adhesion of the separator also needs to be considered, as well as the impact of the side reactions between the electrolyte and the electrode and the lithium ion transport efficiency through the separator. When the parameters of the above three key factors are controlled within the above range, the secondary battery can achieve a better system balance and further improve the electrochemical performance.

[0032] In some embodiments, the first additive has a mass percentage content of 0.3% to 1% in the electrolyte.

[0033] More preferably, the mass percentage of the first additive in the electrolyte is one or any two of the following: 0.3%, 0.32%, 0.33%, 0.35%, 0.4%, 0.45%, 0.5%, 0.51%, 0.6%, 0.7%, 0.74%, 0.78%, 0.8%, 0.85%, 0.9%, and 1%.

[0034] In some embodiments, the first additive has a mass percentage content of 0.5% to 0.7% in the electrolyte.

[0035] When the content of the first additive is preferably within the above range, the electrolyte can further balance its relationship with the stability improvement of the electrode interface and the thickness and impedance control of the interface CEI film, and the secondary battery has lower internal impedance and better cycle stability.

[0036] In some embodiments, the second additive has a mass percentage content of 0.1% to 0.8% in the electrolyte.

[0037] More preferably, the mass percentage of the second additive in the electrolyte is one or any two of the following: 0.1%, 0.12%, 0.15%, 0.2%, 0.3%, 0.38%, 0.4%, 0.5%, 0.6%, 0.7%, and 0.8%.

[0038] In some embodiments, the second additive has a mass percentage content of 0.2% to 0.4% in the electrolyte.

[0039] As another key additive component for synergistic effect, when the second additive is preferably within the above range, it can maintain high ion / electron conduction performance while reducing the probability and amount of gas generation during the cycle of the secondary battery, thereby further improving the cycle life and cycle efficiency of the secondary battery.

[0040] In some embodiments, the secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative electrode active material layer, and the secondary battery satisfies: a / d = 0.3~1.5, where d is the degree of graphitization of the negative electrode active material layer.

[0041] As the negative electrode corresponding to the positive electrode, the graphitization degree of its material is related to the overall kinetic performance and ion / electron transport efficiency of the secondary battery. The higher the graphitization degree, the better the kinetic performance of the secondary battery, the higher the ion / electron conduction efficiency, and the higher the conductivity. However, the interaction frequency between the negative electrode interface and the electrolyte increases, the probability of side reactions increases, the probability of generating high-impedance by-products increases, and the cycle stability performance decreases. In the secondary battery described in this application, since the first additive itself has the function of passivating interfacial side reactions, further optimizing the relationship between the amount of the first additive and the graphitization degree of the negative electrode based on the control of key parameters can further improve the electrochemical performance of the secondary battery.

[0042] More preferably, the a / d value is a range of one or any two of the following: 0.3, 0.32, 0.34, 0.35, 0.38, 0.4, 0.47, 0.51, 0.54, 0.55, 0.56, 0.6, 0.61, 0.65, 0.67, 0.73, 0.74, 0.75, 0.78, 0.8, 0.82, 0.84, 0.86, 0.87, 0.91, 1, 1.01, 1.08, 1.2, and 1.5.

[0043] In some implementations, a / d = 0.5 to 0.8.

[0044] In some implementations, d = 0.85 to 0.99.

[0045] More preferably, d is a range of one or any two of the following: 0.85, 0.88, 0.9, 0.91, 0.92, 0.95, 0.98, and 0.99.

[0046] In some implementations, d = 0.9 to 0.95.

[0047] It should be noted that the degree of graphitization of the negative electrode active material layer was confirmed by the following method:

[0048] After the secondary battery was disassembled in the glove box, the negative electrode sheet was scraped to remove powder. Then, the XRD characteristic peak spectrum of the powder was obtained by XRD diffraction. The graphite interplanar spacing d(002) of the powder was determined based on the spectrum. Finally, the degree of graphitization was calculated based on (0.3440-d(002)) / (0.3440-0.3354).

[0049] In some embodiments, the electrolyte further includes a solvent, which includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

[0050] In some embodiments, the secondary battery satisfies: c / w = 0.03 to 0.17, where w% is the mass percentage of solvent in the electrolyte.

[0051] The test method for the mass percentage content of the solvent is the same as that for the test methods for the mass percentage content of the first additive and the second additive, and will not be repeated here.

[0052] As mentioned above, the adhesion of the separator affects the ion transport efficiency between the separator and the electrode. Since the electrolyte is the main ion transport carrier, the composition of the electrolyte itself is also related, which in turn affects the cycle performance and conductivity of the secondary battery. In addition to additives, the solvent content in the electrolyte affects the fluidity of the electrolyte and its wettability to the separator and electrode. When the electrolyte and separator are matched within the above parameter range, the interaction efficiency of the devices in the secondary battery can be effectively improved, and ultimately, better electrochemical performance can be achieved.

[0053] More preferably, the c / w value is a range of one or any two of the following: 0.03, 0.035, 0.04, 0.047, 0.05, 0.059, 0.071, 0.08, 0.082, 0.091, 0.094, 0.10, 0.105, 0.106, 0.117, 0.118, 0.12, 0.129, 0.133, 0.14, 0.141, 0.15, 0.16, and 0.17.

[0054] In some implementations, the c / w ratio is 0.06 to 0.12.

[0055] In some embodiments, the solvent includes at least one of carbonate solvents and carboxylic acid ester solvents.

[0056] In some embodiments, the carbonate solvent includes at least one of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; the carboxylic acid ester solvent includes at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone.

[0057] In some implementations, w = 80-95%.

[0058] More preferably, w is a range of one or any two of 80%, 82%, 85%, 88%, 90%, 92%, 93%, and 95%.

[0059] In some implementations, w = 85-92%.

[0060] It should be noted that the method for confirming the solvent content in the electrolyte is the same as the method for confirming the first additive and the second additive.

[0061] In some embodiments, the electrolyte further includes a lithium salt.

[0062] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium difluoromethanesulfonylimide, lithium ditrifluoromethanesulfonylimide, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0063] More preferably, the concentration of lithium salt in the electrolyte is 0.8–2.5 mol / L.

[0064] More preferably, the concentration of lithium salt in the electrolyte is one or any two of the following: 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, and 2.5 mol / L.

[0065] In some embodiments, the positive electrode includes a current collector and a positive active material layer disposed on the surface of the current collector. The positive active material layer includes a positive active material, which includes at least one of lithium nickel cobalt manganese oxide and doped lithium nickel cobalt manganese oxide.

[0066] In some embodiments, the nickel content in the positive electrode active material is ≥50% by mass.

[0067] In some embodiments, the nickel content in the positive electrode active material is 50-70% by mass.

[0068] While positive electrode active materials with medium to high nickel content have high energy density, their operating voltage is generally high and their cycle performance is poor. Especially at higher temperatures, the probability and amount of gas generation increase, further shortening the cycle life. However, in the present application, based on the control of electrolyte composition and membrane adhesion, the secondary battery, after constructing the positive electrode sheet with a positive electrode active material with medium to high nickel content, can maintain good high-temperature cycle performance, low internal resistance, and long cycle life.

[0069] More preferably, the positive electrode active material includes Li x Ni a Mn b Co c N dO2, where 1≤x≤1.1, a>0, b>0, c>0, 0≤d<0.1, a+b+c+d=1 and N is at least one of Al, Na, Ti, Nb, Zr, W, Fe, Cr.

[0070] More preferably, the active material layer further includes a binder and a conductive agent.

[0071] In some embodiments, the negative electrode sheet includes a current collector and a negative electrode active material layer;

[0072] More preferably, the negative electrode active material layer includes a negative electrode active material, a binder, a thickener, and a conductive agent.

[0073] In some embodiments, the negative electrode active material comprises at least one of carbon-based materials, silicon-based materials, and silicon-carbon composite materials.

[0074] The present application is further illustrated below with specific embodiments, which should not be construed as limiting the scope of protection claimed in this application:

[0075] Example 1

[0076] A secondary battery, the preparation method comprising the following steps:

[0077] (1) Preparation of the positive electrode sheet: The positive active material, conductive agent acetylene black, and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 96:2:2. The mixture is then vacuum stirred to prepare a slurry, which is subsequently coated on both sides of the current collector aluminum foil. After drying, cold pressing, and slitting, the positive electrode sheet is obtained. The positive active material is Li. 1.04 Ni 0.63 Co 0.09 Mn 0.28 O2;

[0078] (2) Preparation of the negative electrode sheet: The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4. A slurry is prepared by vacuum stirring, and then coated onto both sides of the current collector copper foil. After drying, cold pressing, and slitting, the negative electrode sheet is obtained. The negative electrode active material comprises graphite prepared at a graphitization temperature of 3000℃ and a silicon-carbon composite material with a silicon content of 3%, with a mass ratio of 97:3. The particle size D of the negative electrode active material is... v50 It is 8.5μm;

[0079] (3) Preparation of the membrane: A PE membrane with an average pore size of 45 nm and a porosity of 45% was used as the substrate, and then coated with a 1.5 μm alumina coating on one side and dried to obtain a membrane containing the coating.

[0080] The preparation process of the alumina coating slurry is as follows: nano-sized alumina powder, thickener sodium carboxymethyl cellulose, dispersant sodium polyethylene glycol alkyl aryl ether sulfonate, wetting agent ethanol, binder polyvinyl alcohol (molecular weight 5000) and water are mixed at a ratio of 10:0.5:0.1:0.5:2:100, stirred and ground at a rate of 500 rpm for 60 minutes to obtain the slurry;

[0081] (4) Electrolyte preparation: Mix the first and second additives, solvent and lithium salt lithium hexafluorophosphate to obtain the electrolyte; the first additive is tris(dimethylvinylsilyl) phosphate and the second additive is 1,3-propanesulfonate lactone.

[0082] (5) The positive electrode, separator (coated side against the positive electrode), and negative electrode are stacked, wound and assembled into a cell in sequence. The cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing, formation and volume adjustment, the secondary battery is obtained.

[0083] The parameters of each electrolyte, the degree of graphitization of the negative electrode active material layer, and the adhesion of the separator are shown in Tables 1 and 2.

[0084] Examples 2-32

[0085] A secondary battery differs from Example 1 only in that the electrolyte composition is different and / or the membrane preparation process is different and / or the negative electrode active material is different, as shown in Tables 1 and 2.

[0086] The adhesion of the diaphragm is adjusted by changing the proportion of binder in the slurry during coating preparation; the higher the proportion of binder, the higher the adhesion of the diaphragm.

[0087] The degree of graphitization of the negative electrode active material layer is adjusted by changing the graphitization temperature during the preparation of graphite in the negative electrode active material; the higher the temperature, the higher the degree of graphitization.

[0088] Example 33

[0089] A secondary battery, differing from Example 1 only in that the positive electrode active material is Li. 1.05 Ni 0.7 Co 0.2 Mn 0.1 The results are shown in Tables 1 and 2, and the composition of the electrolyte and / or the preparation process of the membrane and / or the selection of the negative electrode active material are different.

[0090] Example 34

[0091] A secondary battery, differing from Example 1 only in that the positive electrode active material is Li. 1.06 Ni 0.8 Co0.1 Mn 0.1 The results are shown in Tables 1 and 2, and the composition of the electrolyte and / or the preparation process of the membrane and / or the selection of the negative electrode active material are different.

[0092] Comparative Examples 1-6

[0093] A battery differs from Example 1 only in that the electrolyte composition is different and / or the membrane preparation process is different and / or the negative electrode active material is different, as shown in Tables 1 and 2.

[0094] Comparative Examples 7-8

[0095] One battery differs from Example 33 only in that the composition of the electrolyte is different and / or the preparation process of the separator is different and / or the selection of the negative electrode active material is different, as shown in Tables 1 and 2.

[0096] Comparative Examples 9-10

[0097] One battery differs from Example 34 only in that the electrolyte composition is different and / or the membrane preparation process is different and / or the negative electrode active material is different, as shown in Tables 1 and 2.

[0098] Comparative Example 11

[0099] A battery differs from Example 3 only in that the first additive is replaced with an equal percentage by mass of lithium difluorooxalate borate.

[0100] Comparative Example 12

[0101] A battery differs from Example 3 only in that the second additive is replaced with an equal percentage by mass of butanesulfonate lactone.

[0102] Comparative Example 13

[0103] A battery differs from Example 3 only in that the first additive is replaced with a second additive in an equal mass percentage, that is, the electrolyte contains only the second additive.

[0104] Comparative Example 14

[0105] A battery differs from Example 3 only in that the second additive is replaced with an equal mass percentage of the first additive, that is, the electrolyte contains only the first additive.

[0106] Each electrolyte comprises a first additive, a second additive, a lithium salt, and a solvent, where a (wt%) and b (wt%) represent the mass percentage of the first and second additives in the electrolyte, respectively. The lithium salt is lithium hexafluorophosphate, w (wt%) represents the mass percentage of the solvent in the electrolyte, d represents the degree of graphitization of the negative electrode active material layer, and c (N / m) represents the adhesion force of the separator.

[0107] Table 1

[0108] Table 2

[0109] Example of effect

[0110] The secondary batteries obtained in each embodiment and comparative example were tested as follows:

[0111] (1) Cyclic performance test: The secondary battery was tested at 45°C using a LAND charge and discharge system. The charge and discharge cycle test was performed 1000 times at a charge and discharge rate of 0.05C / 1C, a cutoff current of 0.05C, and a working voltage of 2.5 to 4.25V. The initial discharge capacity was A0, and the discharge capacity after 1000 cycles was A1. The cycle capacity retention rate (%) after 1000 cycles was calculated as 100% * A1 / A0.

[0112] (2) DCR test:

[0113] The secondary battery was charged at 25°C with a constant current and constant voltage of 0.33C to 3.65V, with a cutoff current of 0.05C. After resting for 10 minutes, it was discharged at a constant current of 0.33C to 2.5V. This cycle was repeated twice. After resting for 10 minutes, it was charged at a constant current and constant voltage of 0.33C to 3.65V. After discharging to 50% of the discharge capacity of the second cycle, it was rested for 2 hours. (Discharge capacity of the second cycle) It was discharged at 1C for 18 seconds. The starting discharge voltage was recorded as V3, the voltage after the 18-second discharge was recorded as V4, and the 18-second discharge current was recorded as I1. The discharge current RDCR (I1, 18s) = |V3-V4| / I1.

[0114] The test results are shown in Table 3.

[0115] Table 3

[0116] As can be seen from Table 3:

[0117] (1) The secondary battery described in this application introduces specific tris(dimethylvinylsilyl) phosphate and 1,3-propanesulfonate lactone as additive components into the electrolyte, while adjusting the addition ratio of the two additives and regulating the adhesion of the secondary battery separator, ensuring that the secondary battery can achieve stable ion transport efficiency, low impedance of the electrode interface film layer, and low probability of side reactions, ultimately achieving excellent electrochemical performance. During high-temperature long-cycle testing, the cycle capacity retention rate can reach more than 75%, and the DCR is low, which can be maintained within 45mΩ.

[0118] (2) In contrast, in Comparative Examples 1 to 6, due to improper introduction of additive ratio or improper setting of membrane adhesion force, the parameter relationship (b*c) / a of the secondary battery construction does not meet the limited range of 1 to 10. The high temperature cycle stability and DCR performance of the product cannot be taken into account. The low high temperature cycle capacity retention rate is only about 67%, while the DCR reaches more than 50mΩ.

[0119] (3) As can be seen from the comparison between Comparative Examples 11-14 and the various embodiments, the introduction of the first additive and the second additive in the electrolyte is very important. The former can effectively improve the protection effect of the electrolyte on the positive electrode interface and reduce the impedance of CEI film formation, while the latter can work with the former to improve the overall system cycle stability by suppressing the gas generation effect. If the two are missing or replaced with other conventional additives, the same technical effect as the embodiments cannot be achieved.

[0120] (4) As can be seen from Examples 1-28, when the variable regulation of the secondary battery is performed, the electrochemical performance can be further optimized when (b*c) / a is further optimized to the range of 3-7. At the same time, the amount of the first additive and the second additive will have a certain impact on its performance. As the negative electrode corresponding to the positive electrode, the graphitization degree of its material is related to the overall kinetic performance and ion / electron transport efficiency of the secondary battery. The higher the graphitization degree, the better the kinetic performance and the higher the conductivity of the secondary battery. However, the interaction frequency between the negative electrode interface and the electrolyte increases, and the probability of side reactions also increases. The effect will increase because the first additive itself has the function of passivating interfacial side reactions. Therefore, further optimizing the relationship between the amount of the first additive and the graphitization degree of the negative electrode can also improve the electrochemical performance of the secondary battery. In addition, the adhesion of the separator will affect the ion transport efficiency between the separator and the electrode. The main ion transport carrier is the electrolyte. In addition to the additive, the solvent content in the electrolyte will also affect the fluidity of the electrolyte and its wettability to the separator and electrode. When the amount of solvent in the electrolyte and the adhesion of the separator are synergistically optimized, the interaction efficiency of the devices in the secondary battery can be effectively improved.

[0121] Therefore, when a = 0.5–7% and / or b = 0.2–0.4%, and / or a / d = 0.5–0.8, c / w = 0.06–0.12, the secondary battery has better performance, achieving a high-temperature cycle capacity retention rate of over 85% and a DCR reduction to below 38mΩ.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a separator, and an electrolyte; The electrolyte includes a first additive and a second additive; The secondary battery satisfies: (b*c) / a=1~10; Where a% is the mass percentage of the first additive in the electrolyte, b% is the mass percentage of the second additive in the electrolyte, and c N / m is the adhesion force of the diaphragm. The first additive is tris(dimethylvinylsilyl)phosphate, and the second additive is 1,3-propanesulfonate lactone.

2. The secondary battery as described in claim 1, characterized in that, The (b*c) / a = 3 to 7.

3. The secondary battery as described in claim 1, characterized in that, The first additive has a mass percentage content of 0.3% to 1% in the electrolyte, and / or the second additive has a mass percentage content of 0.1% to 0.8% in the electrolyte.

4. The secondary battery as described in claim 1, characterized in that, The first additive has a mass percentage content of 0.5% to 0.7% in the electrolyte, and / or the second additive has a mass percentage content of 0.2% to 0.4% in the electrolyte.

5. The secondary battery as described in claim 1, characterized in that, c = 3 ~ 15 N / m.

6. The secondary battery as described in claim 1, characterized in that, The secondary battery further includes a negative electrode sheet, which includes a negative electrode active material layer. The secondary battery satisfies the following condition: a / d = 0.3 to 1.5, where d is the degree of graphitization of the negative electrode active material layer.

7. The secondary battery as described in claim 6, characterized in that, a / d = 0.5 to 0.8, and / or d = 0.85 to 0.

99.

8. The secondary battery as described in claim 1, characterized in that, The electrolyte also includes a solvent, which includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

9. The secondary battery as described in claim 8, characterized in that, The secondary battery satisfies the following condition: c / w = 0.03 to 0.17, where w% is the mass percentage of solvent in the electrolyte.

10. The secondary battery as described in claim 8, characterized in that, c / w = 0.06 to 0.12, and / or w = 80% to 95%.

11. The secondary battery as described in claim 1, characterized in that, The positive electrode sheet includes a current collector and a positive electrode active material layer disposed on the surface of the current collector. The positive electrode active material layer includes a positive electrode active material, which includes at least one of lithium nickel cobalt manganese oxide and doped lithium nickel cobalt manganese oxide.

12. The secondary battery as described in claim 11, characterized in that, The positive electrode active material contains ≥50% nickel by mass.

13. The secondary battery as described in claim 12, characterized in that, The nickel content in the positive electrode active material is 50-70% by mass.

14. The secondary battery as described in claim 1, characterized in that, The electrolyte also includes lithium salt, and the concentration of lithium salt in the electrolyte is 0.8 to 2.5 mol / L.

15. An electrical appliance, characterized in that, Includes the secondary battery according to any one of claims 1 to 14, wherein the secondary battery is used as a power supply in an electrical device.

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