Secondary battery

Abstract

The invention discloses a secondary battery, and belongs to the technical field of batteries, and the secondary battery is characterized in that fluoroethylene carbonate and tris (dimethyl vinyl silicon) phosphate are added into an electrolyte to serve as compound components, meanwhile, a lanthanum element is introduced into a positive electrode active material, and the content relation between the lanthanum element and the two electrolyte components is dynamically regulated and controlled; therefore, the secondary battery not only has ideal energy density and cycle performance, but also is high in stability and low in gas production rate.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a secondary battery. Background Art

[0002] A high-nickel silicon-based lithium-ion battery refers to a new type of combined battery that uses high-nickel binary or ternary materials for the positive electrode material and silicon-based materials for the negative electrode material. This type of battery has a high theoretical energy density. However, in actual applications, due to the volume effect problem of silicon-based materials, the cycle performance of the battery is actually not ideal. At the same time, due to insufficient stability at the electrode interface of the battery, the gas generation problem is relatively serious.

[0003] In order to improve the cycle performance of high-nickel silicon-based lithium-ion batteries, fluoroethylene carbonate (FEC) is added to the battery electrolyte. However, this approach will increase the impedance of the electrode and reduce the overall ion / electron conduction efficiency of the battery, ultimately further deteriorating the cycle stability performance of the battery and making the gas generation problem more serious. Summary of the Invention

[0004] The purpose of this application is to overcome the deficiencies of the prior art and provide a secondary battery. By adding fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate (DMVSP) as compounding components to the electrolyte, and introducing lanthanum element into the positive electrode active material and dynamically regulating the content relationship between the lanthanum element and the two electrolyte components, the secondary battery not only has an ideal energy density and cycle performance, but also has high stability and low gas generation.

[0005] To achieve the above purpose, in the first aspect of this application, this application provides a secondary battery, including a positive electrode sheet, a negative electrode sheet, and an electrolyte; The electrolyte includes fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate; The positive electrode sheet includes a positive electrode active material, and the positive electrode active material contains lanthanum element; The secondary battery satisfies: (W1*W2) / D = 0.0005~0.02; Where W1% is the mass percentage of fluoroethylene carbonate in the electrolyte, W2% is the mass percentage of tris(dimethylvinylsilyl) phosphate in the electrolyte, and D ppm is the content of lanthanum element in the positive electrode active material.

[0006] The beneficial effects of this application are as follows: The present application provides a secondary battery. By adding fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate as compounding components to the electrolyte, and introducing lanthanum element into the positive electrode active material and dynamically regulating the content relationship between the lanthanum element and the two electrolyte components, the secondary battery not only has ideal energy density and cycling performance, but also has high stability and less gas generation. Detailed Embodiments

[0007] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0008] In the present application, among the technically characterized described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0009] In the present application, regarding the numerical range, unless otherwise specified, the above numerical range is considered continuous, and includes the minimum value and the maximum value of the range, as well as each value between such minimum value and maximum value. Further, when the range refers to an integer, it includes each integer between the minimum value and the maximum value of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0010] The present application will be further elaborated below with specific embodiments: A secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte; The electrolyte includes fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate; The positive electrode sheet includes a positive electrode active material, and the positive electrode active material contains lanthanum element; The secondary battery satisfies: (W1*W2) / D = 0.0005~0.02; Where W1% is the mass percentage content of fluoroethylene carbonate in the electrolyte, W2% is the mass percentage content of tris(dimethylvinylsilyl) phosphate in the electrolyte, and D ppm is the content of lanthanum element in the positive electrode active material.

[0011] In the technical solution of this application, in order to ensure the ion / electron transport efficiency of the secondary battery, taking into account the energy density, cycle performance and safety stability of the secondary battery, fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate are added as functional components to the electrolyte. Among them, fluoroethylene carbonate can improve the stability of ion / electron transport between the electrodes in the secondary battery. However, the addition of fluoroethylene carbonate will increase the impedance of the secondary battery electrodes. Introducing lanthanum element into the positive electrode active material of the secondary battery has the function of directly and effectively reducing the electrode resistance. However, since the addition of lanthanum element will affect the energy density of the battery, therefore, in combination with tris(dimethylvinylsilyl) phosphate, on the one hand, in the presence of tris(dimethylvinylsilyl) phosphate, it can coordinate with lanthanum element to jointly reduce the internal resistance, while maintaining a high capacity level of the secondary battery and maintaining a high energy density of the secondary battery. In addition, tris(dimethylvinylsilyl) phosphate can also form an oxide film on the surface of the positive electrode material, reducing the probability of side reactions between the electrolyte and the positive electrode material, and thus affecting the gas generation probability and gas generation amount of the secondary battery. Through the combined action of the three under a specific introduction amount relationship, the secondary battery has ideal cycle performance, energy density and safety and stability performance.

[0012] In some embodiments, (W1*W2) / D is one of 0.0005, 0.0008, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.008, 0.009, 0.01, 0.012, 0.014, 0.016, 0.018, 0.02 or the range value of any two of them.

[0013] Further preferably, (W1*W2) / D = 0.002 to 0.009.

[0014] The addition content of fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate in the electrolyte and the change of the introduction amount of lanthanum element in the positive electrode active material will affect the energy density, ion / electron transport efficiency, cycle stability and safety stability of the secondary battery. After constructing the relationship among the three, it is found that when the range of (W1*W2) / D is preferably within the above range, the secondary battery can take into account better cycle performance, energy density and stability, and the comprehensive performance is better.

[0015] In some embodiments, W1 = 1 to 10%.

[0016] Further preferably, W1 is one of 1%, 2%, 3%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or the range value of any two of them.

[0017] Further preferably, W1 = 7-10%.

[0018] The introduction of fluoroethylene carbonate has an impact on the electrode impedance and cycling performance of the secondary battery, and also affects the gas generation probability of the secondary battery. When this component is added to the electrolyte with a mass content within the above range, the optimization effect of the cycling performance of the secondary battery is better, and the electrode impedance in the secondary battery can be maintained at a low level.

[0019] In some embodiments, W2 = 0.1-1%.

[0020] Further preferably, W2 is one or any range value of two of 0.1%, 0.2%, 0.3%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%.

[0021] Further preferably, W2 = 0.5-0.8%.

[0022] After tris(dimethylvinylsilyl) phosphate is introduced into the electrolyte in combination with fluoroethylene carbonate, the electrolyte will have a synergistic effect with the lanthanum element in the positive electrode active material, control the stability of the positive electrode material of the secondary battery, and keep the gas generation amount of the secondary battery at a low level. When the mass content of this component is preferably within the above range, the energy density of the secondary battery is higher.

[0023] In some embodiments, D = 300-5200 ppm.

[0024] Further preferably, D is one or any range value of two of 300 ppm, 500 ppm, 800 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 4800 ppm, 5000 ppm, 5200 ppm.

[0025] Further preferably, D = 800-3000 ppm.

[0026] In existing secondary batteries, it is not uncommon to add lanthanum elements to the positive electrode active material to improve the electrode conductivity. In the secondary battery described in this application, based on the use of an electrolyte with two specific components, the introduction amount of lanthanum elements in the positive electrode active material needs to establish a content relationship with the electrolyte to ensure that the secondary battery can balance ideal electrochemical performance and safety performance during use. When the introduction amount of lanthanum elements is preferably within the above range, the secondary battery can achieve higher energy density and ion / electron transfer efficiency, and the electrochemical performance is better.

[0027] In some embodiments, W1 / D = 0.0002 to 0.033.

[0028] More preferably, W1 / D is one of 0.0002, 0.0005, 0.0008, 0.001, 0.0015, 0.002, 0.003, 0.004, 0.005, 0.008, 0.01, 0.015, 0.017, 0.02, 0.022, 0.025, 0.028, 0.03, 0.033 or a range value of any two of them.

[0029] More preferably, W1 / D = 0.003 to 0.01.

[0030] On the premise that synergistic effects occur among lanthanum element in tris(dimethylvinylsilyl) phosphate, fluoroethylene carbonate and the cathode active material, in the secondary battery, there is also a certain interaction between lanthanum element and fluoroethylene carbonate. By adjusting the proportional relationship between the two, the secondary battery can maintain the electrode impedance at a relatively low level. When W1 / D is preferably within the above range, the electrode impedance of the secondary battery is smaller and the electrochemical performance is better.

[0031] In some embodiments, W2 / D = 0.00002 to 0.0033.

[0032] More preferably, W2 / D is one of 0.00002, 0.00005, 0.00008, 0.0001, 0.00015, 0.0002, 0.00025, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.001, 0.0015, 0.017, 0.02, 0.0022, 0.0025, 0.0028, 0.003, 0.0033 or a range value of any two of them.

[0033] More preferably, W2 / D = 0.0002 to 0.0007.

[0034] The introduction of lanthanum element will affect the capacity performance of the active material to a certain extent, and thus affect the energy density. Therefore, in the secondary battery, through the compounding of tris(dimethylvinylsilyl) phosphate, the influence of lanthanum element on the electrode impedance and energy density of the secondary battery after introduction can be effectively balanced. When the addition amounts of the two are preferably within the above relationship range, the secondary battery can achieve a higher ion / electron conduction rate and conduction efficiency, and the energy density is maintained at a better level.

[0035] It should be noted that the mass percentage content of tris(dimethylvinylsilyl) phosphate and fluoroethylene carbonate in the electrolyte is confirmed by GC-MS method. The specific method is as follows: (1) Use the secondary battery charge and discharge equipment to discharge the battery until it is completely discharged. The discharge conditions are: current 0.3C, cut-off voltage 2.5V; (2) After recording the battery number / barcode, disassemble the secondary battery in a glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm) to collect the electrolyte. After removing the battery cover plate: ① If there is free electrolyte, use a pipette to collect the electrolyte into a 5 mL sample tube and seal it with sealing tape to prevent electrolyte leakage; ② If there is no free electrolyte, a hydraulic press (FY-30 hydraulic press of Beijing Heng'ao De Technology Co., Ltd.) can be used to continuously apply pressure until free electrolyte appears, and then collect the electrolyte into the sample tube and seal it.

[0036] ③ Add an appropriate amount of dichloromethane extractant to the secondary battery and record the content of dichloromethane. After adding dichloromethane, put the battery into an aluminum-plastic bag, seal it with a heat sealer, and transfer it to an ultrasonic oscillator for oscillation for 12 h to fully mix the electrolyte in the electrode plate with dichloromethane. Then, use a pipette to suck the mixture of dichloromethane and electrolyte into a 5 mL sample tube and seal the sample tube with sealing tape; (3) Inject the collected electrolyte sample into an Agilent Intuvo 9000 gas chromatography-mass spectrometry instrument for testing to obtain a GC-MS spectrum; dissolve fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate in EMC solvent to prepare solutions with different concentrations, and inject them into the Agilent Intuvo 9000 gas chromatography-mass spectrometry instrument respectively to obtain standard GC-MS spectra. Compare the GC-MS spectrum of the electrolyte to be tested with the standard GC-MS spectrum, and then determine the content of each component according to the peak area of each component in the electrolyte to be tested.

[0037] It should be noted that the content of lanthanum element in the positive electrode active material of this application is confirmed by alkali dissolution-ICP method. The specific method is as follows: Disassemble the positive electrode plate of the secondary battery in the empty battery state, dry it at 80 °C for 4 h, then place it in a muffle furnace and sinter it at 400 °C for 4 h. Subsequently, use a scraper to scrape off the positive electrode active material powder on the electrode plate; Accurately weigh 0.5 g of the positive electrode active material powder and disperse it in 20 mL of water. Then add 10 mL of 60% concentrated nitric acid and heat the mixture to 80 °C. After the powder is dissolved, add water to make the volume up to 100 mL to obtain the solution to be tested; Perform ICP testing on the solution to be tested (ICP emission spectrometer, model: ICAP PRO), select the spectral wavelengths for element detection, and set the experimental conditions: According to the characteristics of the sample and perform ICP testing on the solution to be tested, select the spectral wavelengths for element detection, and set the experimental conditions: gas flow rate 0.5 L / min, power 1150 W; Locate the wavelengths of various transition metal elements: lanthanum, nickel, cobalt, and manganese elements; Determine the La content of the elements in the positive electrode active material obtained by ICP testing, and then use the same method to test the contents of other transition metal elements. Based on the ratios of the various transition metal elements, confirm the chemical composition of the positive electrode active material, and then calculate the mass content of lanthanum in the positive electrode active material. In some embodiments, the electrolyte further includes a third additive, and the third additive includes at least one of 1,3 - propane sultone (PS) and lithium difluorophosphate (LiPO2F2).

[0038] In some embodiments, the electrolyte further includes a solvent and a lithium salt.

[0039] In some embodiments, the solvent includes at least one of carbonate solvents, carboxylate solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate solvents.

[0040] Exemplarily, the carbonate solvents include but are not limited to at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); the carboxylate solvents include but are not limited to at least one of ethyl acetate, methyl formate, and 1,4 - butyrolactone; the ether solvents include but are not limited to at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2 - dimethoxyethane; the sulfone solvents include but are not limited to at least one of methyl sulfone and dimethyl sulfoxide; the nitrile solvents include but are not limited to at least one of propionitrile, butyronitrile, 1-(2 - cyanoethyl)pyrrole, and 1,3,6 - hexanetricarbonitrile; the phosphate solvents include but are not limited to at least one of trimethyl phosphate and triethyl phosphate.

[0041] Further preferably, the solvent may further include but is not limited to at least one of fluorinated derivatives of carbonate solvents, fluorinated derivatives of carboxylate solvents, fluorinated derivatives of ether solvents, fluorinated derivatives of sulfone solvents, fluorinated derivatives of nitrile solvents, and fluorinated derivatives of phosphate solvents.

[0042] Further preferably, the electrolyte contains dimethyl carbonate (DMC).

[0043] Further preferably, the electrolyte contains the following parts by mass of the solvent: 70 - 75 parts of dimethyl carbonate, 8 - 12 parts of propylene carbonate, and 8 - 12 parts of ethylene carbonate.

[0044] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium trifluoromethanesulfonate, lithium bis(fluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, etc.

[0045] Further preferably, the concentration of the lithium salt in the electrolyte is 0.8 - 2.5 mol / L.

[0046] Further preferably, the concentration of the lithium salt in the electrolyte is one of 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, 2.5 mol / L or the range value of any two of them.

[0047] According to actual needs, for the secondary battery of the present application, after selecting tris(dimethylvinylsilyl)phosphate and fluoroethylene carbonate as electrolyte components, other suitable solvents, lithium salts and additives can be simultaneously selected, and the solvents and lithium salts with the addition amounts within the above - mentioned preferred ranges are selected for compounding, which is not limited by the above - mentioned scheme.

[0048] In some embodiments, the positive electrode active material further contains nickel element, and the mass content of the nickel element in the positive electrode active material is ≥90%. Further preferably, it is 90 - 95%.

[0049] In some embodiments, the negative electrode sheet includes a negative electrode active material; In some embodiments, the negative electrode active material contains silicon element.

[0050] Based on the synergistic effect of the electrolyte and the lanthanum - containing positive electrode active material, the secondary battery of the present application can effectively solve the dilemma that the high - nickel silicon - based secondary battery cannot have both high energy density, good cycle performance and high safety and stability. By constructing the relationship between the contents of tris(dimethylvinylsilyl)phosphate and fluoroethylene carbonate in the electrolyte and the content of lanthanum element in the positive electrode active material, the secondary battery can significantly improve the cycle performance and safety and stability on the premise of retaining the advantage of high energy density of the high - nickel silicon system.

[0051] In some embodiments, the positive electrode active material includes at least one of lanthanum - doped lithium nickel cobalt manganate and lanthanum - doped lithium nickel manganate.

[0052] In some embodiments, the negative electrode active material contains at least one of silicon - carbon composite material and silicon monoxide material.

[0053] Exemplarily, the silicon-carbon composite material can be prepared by CVD (chemical vapor deposition) method. Specifically, it can be: permeating silane into the carbon material by CVD method, and then obtaining the silicon-carbon composite material through heat sintering.

[0054] Those skilled in the art can also adopt other methods to prepare the silicon-carbon composite material according to the actual situation, or directly purchase commercially available products, which are not limited to the silicon-carbon composite material and its preparation methods mentioned above; similarly, the silicon monoxide material can also be prepared by oneself, for example, by reducing with silane sol-gel method, or by oxidizing-reducing method with materials containing silicon dioxide, or by purchasing semi-finished raw materials and then preparing them in a semi-synthetic manner, or by directly purchasing them, which are not limited to the obtaining methods exemplified in this application.

[0055] In some embodiments, the positive electrode plate further includes a current collector, and at least one side of the current collector is provided with a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material.

[0056] Further preferably, the positive electrode material layer further includes at least one of a conductive agent and a binder.

[0057] In some embodiments, the negative electrode plate further includes a current collector, and at least one side of the current collector is provided with a negative electrode material layer, and the negative electrode material layer includes a negative electrode active material; Further preferably, the negative electrode material layer includes a negative electrode material, a binder, a thickening agent and a conductive agent.

[0058] In some embodiments, the mass percentage content of nickel element in the positive electrode active material is 40-60%.

[0059] It should be noted that the test method for the mass percentage content of nickel element in the positive electrode active material in the battery of this application is the same as that for lanthanum element, and will not be elaborated here.

[0060] Further preferably, the positive electrode material includes LiNi a Mn b Co c N d O2, where 0.9≤a≤0.95, 0.025≤b≤0.05, 0.025≤c≤0.05, 0≤d<0.1, a + b + c + d = 1, and N contains La.

[0061] Further preferably, the N further includes at least one of Al, Na, Ti, Nb, Zr, W, Fe, and Cr.

[0062] Further preferably, the mass percentage content of silicon element in the negative electrode material layer is 0.5-12.5%.

[0063] Further preferably, the mass percentage content of silicon element in the negative electrode material layer is one of 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5%, 8%, 10%, 12%, 12.5% or the range value of any two of them.

[0064] It should be noted that the mass percentage content of silicon element in the negative electrode material layer of the secondary battery described in this application is tested by the alkali dissolution-ICP method.

[0065] The specific steps are as follows: After disassembling the negative electrode plate of the secondary battery in the empty battery state, it is washed with solvent DMC (dimethyl carbonate), soaked for 48 h, dried at 60 °C, and then the powder of the negative electrode active material layer is scraped off; Weigh the powder sample, place it in a nickel crucible pre-filled with potassium hydroxide, add a little potassium hydroxide to cover the surface of the sample, drop two drops of ethanol, heat it on an electric furnace until the potassium hydroxide melts and dehydrates, then transfer it to a muffle furnace at 1100 °C, keep it molten and insulated for 8 h, take out the nickel crucible and let it cool slightly. Put it into a 300 mL plastic beaker, add hot water for extraction, and wash out the crucible after the reaction. Add 6 mol HCl to acidify the extraction solution, oxidize it with 30% hydrogen peroxide, wait for it to cool, wash it out with water, transfer it to a 100 mL volumetric flask, make up the volume, and shake well. After standing, take out a portion of the solution and transfer it to another 100 mL volumetric flask, make up the volume, shake well, stand and clarify to obtain the solution to be tested. At the same time, prepare 1 blank solution as a control, that is, prepare 1 solution sample that does not add the sample to be tested but is prepared according to the above steps.

[0066] Perform ICP test on the solution to be tested (ICP emission spectrometer, model: ICAP PRO), select the spectral wavelength for element detection, and set the experimental conditions: According to the characteristics of the sample and perform ICP test on the solution to be tested, select the spectral wavelength for element detection, and set the experimental conditions: gas flow rate 0.5 L / min, power 1150 W; the determination wavelength of Si element is 288.158 nm; Measure the Si content of the element in it by ICP test, and then calculate and confirm the mass content of silicon element in the final negative electrode material layer through the mass of the originally scraped powder.

[0067] The following further elaborates the present invention with specific embodiments, and these embodiments should not be construed as limiting the scope of protection required by the present invention: Example 1 A secondary battery, and the preparation method includes the following steps: (1) Preparation of the positive electrode sheet: The positive electrode active material, the conductive agent acetylene black, and the binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone according to a mass ratio of 92:4:4, and a slurry is prepared by vacuum stirring. Subsequently, it is coated on both sides of the current collector aluminum foil, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained; the positive electrode active material is LiNi 0.9 Mn 0.05 Co 0.0465 La 0.0035 O2, and the mass percentage content of nickel element is 52.8%.

[0068] (2) Preparation of the negative electrode sheet: The negative electrode active material, the conductive agent acetylene black, the thickening agent sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are dispersed in water according to a mass ratio of 96.4:1:1.2:1.4, and a slurry is prepared by vacuum stirring. Subsequently, it is coated on both sides of the current collector copper foil, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained. The negative electrode material includes a silicon-carbon composite material, and the mass percentage content of silicon element in the negative electrode material layer is 10%; The silicon-carbon composite material is a commercially available silicon-carbon material; (3) Preparation of the separator: A PP separator with an average pore size of 2 μm and an air permeability of 300 s / 100 mL is used as the substrate, and then an alumina coating is applied on one side and dried to obtain a separator containing the coating; (4) The positive electrode sheet, the separator (the coated side is adjacent to the positive electrode sheet), and the negative electrode sheet are stacked and wound in sequence to assemble an electric core. The electric core is placed in an outer packaging shell, dried, and then electrolyte is injected. After vacuum packaging, standing, forming, and constant volume, the battery is obtained.

[0069] The parameters of each electrolyte are shown in Tables 1 and 2.

[0070] Examples 2 to 26, 29 to 30 A battery, which is only different from Example 1 in that the component composition of the electrolyte and the content of lanthanum element in the positive electrode active material are different, and the molar ratio of nickel element, cobalt element, and manganese element in the positive electrode active material remains unchanged. The results are shown in Tables 1 and 2.

[0071] Example 27 A battery, which is only different from Example 5 in that the positive electrode active material is LiNi 0.91 Mn 0.05 Co 0.039 La 0.0006Al0.0004 O2, and the mass percentage content of nickel element is 53.4%.

[0072] Example 28 A battery, which is only different from Example 5 in that the positive electrode active material is LiNi 0.9Mn 0.05 Co 0.049 La 0.001 O2, and the mass percentage content of nickel element is 52.8%.

[0073] Comparative Examples 1 to 4 A battery, which is only different from Example 1 in that the component composition of the electrolyte and the content of lanthanum element in the positive electrode active material are different, and the results are shown in Tables 1 and 2.

[0074] Comparative Example 5 A battery, which is only different from Example 5 in that tris(dimethylvinylsilyl) phosphate is not added to the electrolyte.

[0075] Comparative Example 6 A battery, which is only different from Example 5 in that the positive electrode active material is LiNi 0.9 Mn 0.05 Co 0.05 O2, and the mass percentage content of nickel element is 53.9%, that is, the positive electrode active material does not contain lanthanum element.

[0076] Among them, in Tables 1 and 2, the meanings of W1, W2 and D are as described above and will not be elaborated here. Each electrolyte includes additives, lithium salts and solvents. The solvents include dimethyl carbonate (DMC), propylene carbonate (PC), ethylene carbonate (EC). The M 锂 (mol / L) represents the concentration of lithium salt in the electrolyte. The third additive is PS and LiPO2F2. PS (wt%) and LiPO2F2 (wt%) represent the mass percentage contents of the third additives PS and LiPO2F2 in the electrolyte respectively. For Comparative Examples 5 and 6, due to the lack of some parameters, the results of some parameters are not counted and are represented by " / ".

[0077] Table 1 Table 2 Effect Example The following tests were carried out on the sodium ion secondary batteries obtained in each example and comparative example: (1) Gas generation test: The lithium ion secondary batteries were discharged until empty. The discharge conditions were: current 0.33C, cut-off voltage 2.5V, and then charged at constant volume to full charge according to the following conditions; (1.1) Constant current charge at 0.33C to the upper limit voltage of 4.25V, constant voltage charge until the current is less than or equal to 0.05C, and then discharge at 0.33C to the lower limit voltage of 2.75V; This is taken as one cycle, and the charge and discharge are carried out 3 times, and the discharge capacity of the third cycle is taken as the capacity of the battery; (1.2) Charge at a constant current of 0.33C until the upper limit voltage of 4.25V, and then charge at a constant voltage until the current is less than or equal to 0.05C; (1.3) Use the water displacement method to test the volume of the secondary battery, denoted as V0. Place the battery in an oven at 60°C for 60 minutes and then take it out. After the battery temperature drops to room temperature, use the water displacement method to test the volume of the battery again and denote it as V1. Then the gas generation amount of the battery during this storage period is the difference between V1 and V0. This value divided by the fixed volume capacity of the battery is the gas generation amount per ampere-hour of the secondary battery.

[0078] The specific steps are as follows: (i) Add an appropriate amount of pure water to the container and measure its density with a hydrometer and record it; (ii) Adjust the balance to be horizontal and tare (tare before each secondary battery test); (iii) Immerse the secondary battery body together with the tab in the solution, ensuring that the secondary battery does not contact the container wall. After stabilization, read and record the data as T; (iv) Close the balance, seal the container to prevent reagent volatilization.

[0079] The volume calculation formula of the secondary battery is T / ρliquid; Among them, before and after storage, tests are carried out respectively to obtain T0 and T1; Then the difference between V1 and V0: V1 - V0 = T1 / ρliquid - T0 / ρliquid Gas generation amount at 60°C storage = (V1 - V0) / secondary battery capacity; (2) Energy density test: Weigh the weight of the secondary battery to be tested, denoted as m; Place the secondary battery in a fixture, apply a force of 3000N, charge the single battery at a constant current of 0.33C to 4.3V, set aside for 30 minutes, discharge at a constant current of 0.33C to 2.5V, set aside for 30 minutes, charge and discharge continuously 3 times, calculate the third discharge capacity (in Ah) and energy E (take the average of three battery cores), and the discharge energy density: E / m (in Wh / kg); (3) Cycle performance test: Use the LAND system to perform cycle performance tests on the secondary batteries obtained in each example and comparative example on lithium-ion batteries at 25°C, so that the lithium-ion batteries are cycled with a charge and discharge rate of 0.5C / 1C, a cut-off current of 0.05C, and a voltage range of 2.5 - 4.25V for 1000 cycles. After the cycle ends, process the cycle data to obtain the capacity retention rate (the first cycle discharge capacity Q1 and the 1000th cycle discharge capacity Q2, and the capacity retention rate = 100%×Q2 / Q1), and obtain the capacity retention rate (%) of the battery after 1000 cycles.

[0080] The test results are shown in Table 3.

[0081] Table 3 It can be seen from Table 3 that: (1) Since fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate are simultaneously introduced as compounding components in the electrolyte of the secondary battery of the present application, and lanthanum element is introduced into the positive electrode active material, by dynamically adjusting the introduction amounts of these three key components, not only does it have ideal energy density and cycling performance, the energy density can reach more than 280 Wh / kg, at the same time the capacity retention rate after 1000 cycles can reach more than 85%, and the gas generation amount is small, not exceeding 6.5 mL / Ah at most, and the comprehensive performance is excellent; in contrast, products that do not introduce the three key components, or products that do not understand the regulation of the introduction amounts of the three, as shown in the comparative example products, cannot achieve the same above effects.

[0082] (2) It can be seen from Examples 1 to 26 that the changes in the addition contents of fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate in the electrolyte and the introduction amount of lanthanum element in the positive electrode active material will affect the energy density, ion / electron transport efficiency, cycling stability and safety stability of the secondary battery. After constructing the relationship among the three, it is found that when the range of (W1*W2) / D is preferably in the range of 0.002 to 0.009, the comprehensive performance of the secondary battery is better. At the same time, the introduction amounts of fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate in the electrolyte will affect the electrode impedance and the synergistic effect of the electrolyte and lanthanum element. When W1 is preferably in the range of 7 to 10%, and W2 is preferably in the range of 0.5 to 0.8%, the corresponding matching concentration of lanthanum element is 800 to 3000 ppm, which can further improve the energy density of the secondary battery to more than 300 Wh / kg, at the same time the cycle retention rate is further increased to more than 90%, and the gas generation amount can be within 6 mL / Ah.

[0083] (3) It can be seen from the comparison between Examples 18 to 26 and other examples that when (W1*W2) / D is regulated, in addition to the compounding of lanthanum element and tris(dimethylvinylsilyl) phosphate, which can effectively balance the influence of lanthanum element on the electrode impedance and energy density of the secondary battery after introduction, there is also a synergistic effect between lanthanum element and fluoroethylene carbonate itself. When the proportional relationship between W2 / D and W1 / D is further optimized, the comprehensive electrochemical performance of the secondary battery is better, especially in terms of cycling stability. After 1000 cycles, the capacity of the secondary battery can be maintained at a maximum of 96%.

Claims

1. A secondary battery, characterized in that: Including positive electrode sheet, negative electrode sheet and electrolyte; The electrolyte includes fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate; The positive electrode sheet includes a positive electrode active material, and the positive electrode active material contains lanthanum; The secondary battery satisfies: (W1*W2) / D=0.0005~0.02; Wherein W1% is the mass percentage of fluoroethylene carbonate in the electrolyte, W2% is the mass percentage of tris(dimethylvinylsilyl)phosphate in the electrolyte, and D ppm is the content of lanthanum in the positive electrode active material.

2. The secondary battery according to claim 1, characterized in that: The (W1*W2) / D=0.002~0.

009.

3. The secondary battery according to claim 1, characterized in that: The W1=1%~10%.

4. The secondary battery according to claim 1, characterized in that: The W2=0.1%~1%.

5. The secondary battery according to claim 1, characterized in that: The D=300~5200ppm.

6. The secondary battery according to claim 1, characterized in that: The W1 / D=0.0002~0.

033.

7. The secondary battery according to claim 1, characterized in that: The W2 / D=0.00002~0.0033.

8. The secondary battery according to claim 1, characterized in that: The positive electrode active material also contains nickel element, and the mass percentage of the nickel element in the positive electrode active material is ≥90%.

9. The secondary battery according to claim 1, characterized in that: The negative electrode plate includes a negative electrode material layer; the negative electrode material contains silicon.

10. An electrical device, characterized in that: It comprises the secondary battery as described in any one of claims 1 to 9, and the secondary battery is used as the power supply of the electrical device.

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