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

[0001] This application is a divisional application of CN120184341A (application date May 19, 2025, application number 202510638427.2, invention title: A Secondary Battery). Technical Field

[0002] This application relates to the field of battery technology, specifically to a secondary battery. Background Technology

[0003] High-nickel silicon-based lithium-ion batteries refer to a new type of combined battery that uses high-nickel binary or ternary materials as the positive electrode material and silicon-based materials as the negative electrode material. These batteries have high theoretical energy density, but in practical applications, due to the volume effect of silicon-based materials, their cycle performance is not ideal. Furthermore, the batteries suffer from significant gas generation problems due to insufficient electrode interface stability.

[0004] To improve the cycle performance of high-nickel silicon-based lithium-ion batteries, fluoroethylene carbonate (FEC) is added to the battery electrolyte. However, this increases the electrode impedance and reduces the overall ion / electron conduction efficiency of the battery, ultimately further degrading the cycle stability of the battery and making the gas generation problem more serious. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the existing technology and provide a secondary battery. By adding fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate (DMVSP) as compound components to the electrolyte, and introducing lanthanum into the positive electrode active material and dynamically controlling the content relationship between lanthanum and the two electrolyte components, the secondary battery not only has ideal energy density and cycle performance, but also high stability and low gas production.

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

[0007] The electrolyte comprises fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate;

[0008] The positive electrode sheet includes a positive electrode active material, and the positive electrode active material contains lanthanum.

[0009] The secondary battery satisfies: (W1*W2) / D = 0.0005~0.02, unit ppm -1 ;

[0010] 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; wherein Dppm = 300ppm to 5200ppm;

[0011] The negative electrode sheet includes a negative electrode material layer, wherein the mass percentage of silicon in the negative electrode material layer is 0.5% to 12.5%.

[0012] The beneficial effects of this application are as follows:

[0013] This application provides a secondary battery that incorporates fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate as compound components in the electrolyte. Simultaneously, lanthanum is introduced into the positive electrode active material, and the content relationship between lanthanum and the two electrolyte components is dynamically controlled. This results in a secondary battery that not only possesses ideal energy density and cycle performance but also exhibits high stability and low gas production. The amount of lanthanum introduced into the positive electrode active material needs to be in relation to the electrolyte composition to ensure that the secondary battery achieves both ideal electrochemical and safety performance during use. When the amount of lanthanum introduced is within a specified range, the silicon-based secondary battery can achieve higher energy density and ion / electron transport efficiency, resulting in superior electrochemical performance. Detailed Implementation

[0014] 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.

[0015] 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.

[0016] 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.

[0017] The present application is further illustrated below with specific embodiments:

[0018] A secondary battery includes a positive electrode, a negative electrode, and an electrolyte;

[0019] The electrolyte comprises fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate;

[0020] The positive electrode sheet includes a positive electrode active material, and the positive electrode active material contains lanthanum.

[0021] The secondary battery satisfies: (W1*W2) / D = 0.0005~0.02, unit ppm -1 ;

[0022] 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; wherein Dppm = 300ppm to 5200ppm;

[0023] The negative electrode sheet includes a negative electrode material layer, wherein the mass percentage of silicon in the negative electrode material layer is 0.5% to 12.5%.

[0024] In this application's technical solution, to ensure the ion / electron transport efficiency of the secondary battery while considering its energy density, cycle performance, and safety stability, fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate are added to the electrolyte as functional components. Fluoroethylene carbonate can improve the stability of ion / electron transport between electrodes in the secondary battery; however, its addition increases the impedance of the electrodes. Introducing lanthanum into the positive electrode active material of the secondary battery directly and effectively reduces electrode resistance. However, since the addition of lanthanum affects the battery's energy density, the presence of tris(dimethylvinylsilyl)phosphate helps to coordinate with lanthanum to reduce internal resistance while maintaining a high capacity and energy density of the secondary battery. Furthermore, tris(dimethylvinylsilyl)phosphate can 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, thereby affecting the probability and amount of gas generation in the secondary battery. Through the combined effect of these three factors in establishing a specific introduction quantity relationship, the secondary battery achieves ideal cycle performance, energy density, and safety and stability.

[0025] In existing secondary batteries, it is not uncommon to add lanthanum to the positive electrode active material to improve the electrode conductivity. However, in the secondary battery described in this application, based on the use of two specific electrolyte components, the amount of lanthanum introduced into the positive electrode active material needs to be related to the electrolyte composition to ensure that the secondary battery can achieve both ideal electrochemical performance and safety performance during use. When the amount of lanthanum introduced is within the above range, the silicon-based secondary battery can achieve higher energy density and ion / electron transport efficiency, and has better electrochemical performance.

[0026] In some implementations, (W1*W2) / D = one or any two of the following values: 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, and 0.02.

[0027] More preferably, (W1*W2) / D = 0.002~0.009, in ppm. -1 .

[0028] The addition content of fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate in the electrolyte, as well as the introduction of lanthanum in the positive electrode active material, 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 was found that when the range of (W1*W2) / D is preferably within the above range, the secondary battery can achieve better cycle performance, energy density, and stability, resulting in better overall performance.

[0029] In some implementations, W1% = 1% to 10%.

[0030] More preferably, W1% is a range of one or any two of the following: 1%, 2%, 3%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, and 10%.

[0031] More preferably, W1% = 2% to 8%.

[0032] More preferably, W1% = 2% to 5%.

[0033] More preferably, W1% = 7% to 10%.

[0034] The introduction of fluoroethylene carbonate affects the electrode impedance and cycle performance of the secondary battery, and also affects the probability of gas generation in the secondary battery. When this component is added to the electrolyte at the mass content within the above range, the cycle performance of the secondary battery is better optimized, and the electrode impedance in the secondary battery can be maintained at a low level.

[0035] In some implementations, W2% = 0.1% to 1%.

[0036] More preferably, W2% is a range of one or any two of the following: 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%, and 1%.

[0037] More preferably, W2% = 0.2% to 0.8%.

[0038] More preferably, the W2% is 0.3% to 0.5%.

[0039] More preferably, the W2% is 0.5% to 0.8%.

[0040] When 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, controlling the stability of the positive electrode material of the secondary battery, so that the gas production of the secondary battery is maintained 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.

[0041] More preferably, D ppm is a range of one or any two of the following: 300ppm, 500ppm, 800ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 4800ppm, 5000ppm, and 5200ppm.

[0042] More preferably, the D ppm is 300ppm to 1500ppm.

[0043] More preferably, the D ppm is 800ppm to 3000ppm.

[0044] In existing secondary batteries, it is not uncommon to add lanthanum to the positive electrode active material to improve the conductivity of the electrode. However, in the secondary battery described in this application, based on the use of two specific electrolyte components, the amount of lanthanum introduced into the positive electrode active material needs to be related to the electrolyte composition to ensure that the secondary battery can achieve both ideal electrochemical performance and safety performance during use. When the amount of lanthanum introduced is preferably within the above range, the secondary battery can achieve higher energy density and ion / electron transport efficiency, and has better electrochemical performance.

[0045] In some embodiments, W1 / D = 0.0002 to 0.033, in ppm. -1 .

[0046] More preferably, W1 / D is a range of one or any two of the following: 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, and 0.033.

[0047] More preferably, the W1 / D = 0.003 to 0.01, in ppm. -1 .

[0048] Under the premise that lanthanum plays a synergistic role in tris(dimethylvinylsilyl)phosphate, fluoroethylene carbonate, and positive electrode active material, there is also a certain interaction between lanthanum and fluoroethylene carbonate in the secondary battery. By adjusting the ratio of the two, the electrode impedance of the secondary battery can be maintained at a low level. When W1 / D is preferably within the above range, the electrode impedance of the secondary battery is even lower and the electrochemical performance is better.

[0049] In some embodiments, W2 / D = 0.00002 to 0.0033, in ppm. -1 .

[0050] More preferably, W2 / D is a range of one or any two of the following: 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, and 0.0033.

[0051] More preferably, the W2 / D = 0.0002 to 0.0007, in ppm.-1 .

[0052] The introduction of lanthanum can affect the capacity of the active material to a certain extent, thus affecting the energy density. Therefore, in the secondary battery, the effects of lanthanum on the electrode impedance and energy density of the secondary battery after its introduction can be effectively balanced by the compounding of tris(dimethylvinylsilyl)phosphate. When the addition amounts of both are preferably within the above-mentioned range, the secondary battery can achieve higher ion / electron conduction rates and conduction efficiency, and maintain the energy density at a better level.

[0053] It should be noted that the mass percentage of tris(dimethylvinylsilyl)phosphate and fluoroethylene carbonate in the electrolyte described in this application was confirmed by GC-MS testing. The specific method is as follows:

[0054] (1) Discharge the battery using a secondary battery charging and discharging device. Discharge conditions: current 0.3C, cutoff voltage 2.5V;

[0055] (2) After recording the battery number / barcode, disassemble the secondary battery in a glove box (H2O≤0.1ppm, O2≤0.1ppm) to collect the electrolyte. After opening the battery cover:

[0056] ① If there is free electrolyte, collect the electrolyte into a 5mL sample tube with a pipette and seal it with sealing tape to prevent electrolyte leakage;

[0057] ② If there is no free electrolyte, a hydraulic press (Beijing Heng'ao Technology Co., Ltd.'s FY-30 hydraulic press) can be used to continuously pressurize until free electrolyte appears. Collect the electrolyte into the sample tube and seal it.

[0058] ③ Add an appropriate amount of dichloromethane extractant to the secondary battery and record the dichloromethane content. After adding dichloromethane, put the battery into an aluminum-plastic bag and seal it with a heat sealer. Transfer it to an ultrasonic oscillator and oscillate for 12 hours to allow the electrolyte in the electrode to mix thoroughly with the dichloromethane. Then, use a pipette to draw the mixture of dichloromethane and electrolyte into a 5mL sample tube and seal the sample tube with sealing glue.

[0059] (3) The collected electrolyte samples were injected into an Agilent Intuvo 9000 gas chromatograph-mass spectrometer using a microsyringe for testing, and GC-MS chromatograms were obtained. Fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate were dissolved in EMC solvent to prepare solutions of different concentrations, and these solutions were injected into the Agilent Intuvo 9000 gas chromatograph-mass spectrometer to obtain standard GC-MS chromatograms. The GC-MS chromatograms of the electrolyte to be tested were compared with the standard GC-MS chromatograms, and the content of each component was determined based on the peak area of ​​each component in the electrolyte to be tested.

[0060] It should be noted that the content of lanthanum in the positive electrode active material described in this application was confirmed by alkaline dissolution-ICP method, the specific method being as follows:

[0061] The positive electrode sheet of the empty secondary battery is disassembled, dried at 80°C for 4 hours, and then sintered in a muffle furnace at 400°C for 4 hours. Then, the positive active material powder on the electrode sheet is scraped off with a scraper.

[0062] Accurately weigh 0.5g of positive electrode active material powder and disperse it in 20mL of water. Then add 10mL of 60% nitric acid, mix and heat to 80℃. After the powder dissolves, add water to make up to 100mL to obtain the test solution.

[0063] ICP testing (ICP emission spectrometer, model: ICAP PRO) was performed on the test solution. The elemental detection wavelengths were selected, and the experimental conditions were set as follows: gas flow rate 0.5 L / min, power 1150 W. The wavelengths of each transition metal element—lanthanum, nickel, cobalt, and manganese—were determined. The La content in the positive electrode active material was obtained through ICP testing. Subsequently, the contents of other transition metal elements were tested using the same method. Based on the proportions of each transition metal element, the chemical composition of the positive electrode active material was confirmed, and the mass content of lanthanum in the positive electrode active material could be calculated.

[0064] In some embodiments, the electrolyte further includes a third additive, which includes at least one of 1,3-propanesulfonyl lactone (PS) and lithium difluorophosphate (LiPO2F2).

[0065] In some embodiments, the electrolyte further includes a solvent and a lithium salt.

[0066] In some embodiments, the solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

[0067] Exemplary examples 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); carboxylic acid ester solvents include, but are not limited to, at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; ether solvents include, at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; sulfone solvents include, at least one of methyl sulfone and dimethyl sulfoxide; nitrile solvents include, at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrionitrile; and phosphate ester solvents include, at least one of trimethyl triphosphate and triethyl phosphate.

[0068] More preferably, the solvent may also include, but is not limited to, at least one of carbonate solvent fluorinated derivatives, carboxylic acid ester solvent fluorinated derivatives, ether solvent fluorinated derivatives, sulfone solvent fluorinated derivatives, nitrile solvent fluorinated derivatives, and phosphate ester solvent fluorinated derivatives.

[0069] More preferably, the electrolyte contains dimethyl carbonate (DMC).

[0070] More preferably, the electrolyte contains the following solvents in parts by weight: 70-75 parts dimethyl carbonate, 8-12 parts propylene carbonate, and 8-12 parts ethylene carbonate.

[0071] 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.

[0072] More preferably, the concentration of lithium salt in the electrolyte is 0.8 mol / L to 2.5 mol / L.

[0073] 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.

[0074] The secondary battery described in this application can be formulated by selecting tris(dimethylvinylsilyl)phosphate and fluoroethylene carbonate as electrolyte components, and then simultaneously combining them with other suitable solvents, lithium salts and additives. The selection of solvents and lithium salts within the above-mentioned preferred range for compounding is not limited to the above-described scheme.

[0075] In some embodiments, the positive electrode active material further contains nickel, and the mass content of nickel in the positive electrode active material is ≥90%. More preferably, it is 90-95%.

[0076] In some embodiments, the negative electrode sheet includes a negative electrode active material;

[0077] The secondary battery described in this application, based on the synergistic effect of the electrolyte and the lanthanum-containing positive electrode active material, can effectively solve the dilemma of high-nickel silicon secondary batteries where energy density, cycle performance, and safety and stability cannot be simultaneously achieved. By constructing a relationship between the content of tris(dimethylvinylsilyl)phosphate and fluoroethylene carbonate in the electrolyte and the content of lanthanum in the positive electrode active material, the secondary battery can significantly improve cycle performance and safety and stability while retaining the high energy density advantage of the high-nickel silicon system.

[0078] In some embodiments, the positive electrode active material comprises at least one of lanthanum-doped lithium nickel cobalt manganese oxide and lanthanum-doped lithium nickel manganese oxide.

[0079] In some embodiments, the negative electrode active material contains at least one of silicon-carbon composite material and silicon suboxide material.

[0080] For example, the silicon-carbon composite material can be prepared by CVD (chemical vapor deposition), specifically by infiltrating silane into carbon material by CVD, followed by heating and sintering to obtain the silicon-carbon composite material.

[0081] Those skilled in the art may also use other methods to prepare silicon-carbon composite materials, or directly purchase commercially available products, depending on the actual situation. They are not limited to the silicon-carbon composite materials and their preparation methods mentioned above. Similarly, the silicon suboxide material can also be prepared in-house, for example by reduction using the silane sol-gel method, or by oxidation-reduction using silicon dioxide-containing materials, or by purchasing semi-finished raw materials and then preparing them in a semi-synthetic manner, or by purchasing them directly. They are not limited to the methods of acquisition exemplified in this application.

[0082] In some embodiments, the positive electrode sheet further includes a current collector, and at least one side of the current collector is provided with a positive electrode material layer, the positive electrode material layer including a positive electrode active material.

[0083] More preferably, the positive electrode material layer further includes at least one of a conductive agent and a binder.

[0084] In some embodiments, the negative electrode sheet further includes a current collector, and at least one side of the current collector is provided with a negative electrode material layer, the negative electrode material layer including a negative electrode active material;

[0085] More preferably, the negative electrode material layer includes a negative electrode material, a binder, a thickener, and a conductive agent.

[0086] In some embodiments, the nickel content in the positive electrode active material is 40-60% by mass.

[0087] It should be noted that the test method for the mass percentage of nickel in the positive electrode active material of the battery described in this application is the same as the test method for lanthanum, and will not be repeated here.

[0088] More preferably, the cathode 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.

[0089] More preferably, the N further comprises at least one of Al, Na, Ti, Nb, Zr, W, Fe, and Cr.

[0090] More preferably, the mass percentage of silicon in the negative electrode material layer is one or any two of the following values: 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5%, 8%, 10%, 12%, and 12.5%.

[0091] It should be noted that the mass percentage of silicon in the negative electrode material layer of the secondary battery described in this application was tested using the alkaline dissolution-ICP method.

[0092] The specific steps are as follows: After disassembling the negative electrode of the empty-charge secondary battery, clean it with the solvent DMC (dimethyl carbonate), soak it for 48 hours, dry it at 60℃, and scrape off the powder of the negative electrode active material layer. Weigh the powder sample, place it in a nickel crucible pre-filled with potassium hydroxide, add a small amount of potassium hydroxide to cover the sample surface, add two drops of ethanol, and heat it on an electric furnace until the potassium hydroxide melts and dehydrates. Then transfer it to a muffle furnace at 1100℃ and maintain the melting temperature for 8 hours. Remove the nickel crucible and allow it to cool slightly. Place it in a 300mL plastic beaker, add hot water for extraction, and wash out the crucible after the reaction. Add 6mol HCl to the extract for acidification, oxidize with 30% hydrogen peroxide, and after cooling, wash out with water. Transfer the extract to a 100mL volumetric flask, dilute to volume, and shake well. After standing, transfer the solution to another 100mL volumetric flask, dilute to volume, shake well, and allow it to stand until clear to obtain the test solution. At the same time, a blank solution is prepared as a control, that is, a solution sample prepared according to the above steps but without the test sample added.

[0093] ICP testing (ICP emission spectrometer, model: ICAP PRO) was performed on the test solution. The element detection wavelength was selected, and the experimental conditions were set as follows: gas flow rate 0.5 L / min, power 1150 W; Si element measurement wavelength 288.158 nm; the Si content of the elements was determined by ICP testing, and then the mass content of silicon in the final negative electrode material layer was confirmed by calculating the mass of the original scraped powder.

[0094] The present invention is further illustrated below with specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention:

[0095] Example 1

[0096] A secondary battery, the preparation method comprising the following steps:

[0097] (1) Preparation of the positive electrode sheet: The positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 92:4:4. 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 electrode active material is LiNi. 0.9 Mn 0.05 Co 0.0465 La 0.0035 O2, with a nickel content of 52.8% by mass.

[0098] (2) Preparation of 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, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after drying, cold pressing and cutting, the negative electrode sheet is obtained. The negative electrode material includes silicon-carbon composite material, and the mass percentage of silicon element in the negative electrode material layer is 10%.

[0099] The silicon-carbon composite material is a commercially available silicon-carbon material;

[0100] (3) Preparation of the diaphragm: PP diaphragm with an average pore size of 2μm and an air permeability of 300s / 100mL was used as the substrate, and then an alumina coating was applied to one side and dried to obtain a diaphragm with a coating.

[0101] (4) The positive electrode, separator (coated side against the positive electrode), and negative electrode are stacked, wound and assembled into a battery cell in sequence. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing, formation and volume adjustment, the battery is obtained.

[0102] The parameters of each electrolyte are shown in Tables 1 and 2.

[0103] Examples 2-26, 29-30

[0104] A battery differs from Example 1 only in the composition of the electrolyte and the content of lanthanum in the positive electrode active material, while the molar ratio of nickel, cobalt and manganese in the positive electrode active material remains unchanged. The results are shown in Tables 1 and 2.

[0105] Example 27

[0106] A battery differs from Example 5 only in that the positive electrode active material is LiNi. 0.91 Mn 0.05 Co 0.039 La 0.0006 Al 0.0004 O2, with a nickel content of 53.4% ​​by mass.

[0107] Example 28

[0108] A battery differs from Example 5 only in that the positive electrode active material is LiNi. 0.9 Mn 0.05 Co 0.049 La 0.001 O2, with a nickel content of 52.8% by mass.

[0109] Comparative Examples 1-4

[0110] A battery differs from Example 1 only in the composition of the electrolyte and the content of lanthanum in the positive electrode active material, as shown in Tables 1 and 2.

[0111] Comparative Example 5

[0112] A battery that differs from Example 5 only in that tris(dimethylvinylsilyl)phosphate is not added to the electrolyte.

[0113] Comparative Example 6

[0114] A battery, differing from Example 5 only in that the positive electrode active material is LiNi. 0.9 Mn 0.05 Co 0.05 The O2 has a nickel content of 53.9% by mass, meaning that the positive electrode active material does not contain lanthanum.

[0115] In Tables 1 and 2, the meanings of W1, W2, and D are as described above and will not be repeated here. Each electrolyte includes additives, lithium salts, and solvents. The solvents include dimethyl carbonate (DMC), propylene carbonate (PC), and ethylene carbonate (EC). 锂 (mol / L) represents the concentration of lithium salt in the electrolyte. The third additive is PS and LiPO2F2, where PS (wt%) and LiPO2F2 (wt%) represent the mass percentages of the third additives PS and LiPO2F2 in the electrolyte, respectively. For Comparative Examples 5 and 6, some parameters are missing, so the results for some parameters are not statistically analyzed and are represented by " / ".

[0116] Table 1

[0117] parameter <![CDATA[W1]]> <![CDATA[W2]]> D(ppm) <![CDATA[(W1*W2) / D]]> <![CDATA[W1 / D]]> <![CDATA[W2 / D]]> Example 1 10 1 5116 0.0020 0.0020 0.00020 Example 2 5 0.5 300 0.0083 0.017 0.0017 Example 3 10 0.8 3000 0.0027 0.0033 0.00027 Example 4 7 0.5 800 0.0044 0.0088 0.00063 Example 5 8 0.8 2000 0.0032 0.004 0.0004 Example 6 10 1 500 0.02 0.02 0.002 Example 7 5.5 1 5000 0.0011 0.0011 0.0002 Example 8 7 0.8 3000 0.0019 0.0023 0.00027 Example 9 10 1 1000 0.01 0.01 0.001 Example 10 10 0.8 500 0.016 0.02 0.0016 Example 11 8 0.6 1500 0.0032 0.0053 0.0004 Example 12 8 0.7 2500 0.0022 0.0032 0.00028 Example 13 6 0.8 800 0.006 0.0075 0.001 Example 14 8 1 1200 0.0067 0.0067 0.0008 Example 15 8 0.5 3500 0.0011 0.0023 0.00014 Example 16 10 0.7 3500 0.002 0.0029 0.0002 Example 17 7 0.5 500 0.007 0.014 0.001 Example 18 7 0.8 2800 0.002 0.0025 0.00029 Example 19 9 0.5 800 0.0056 0.011 0.00063 Example 20 8.5 0.8 3000 0.0023 0.0028 0.00027 Example 21 10 0.6 900 0.0067 0.011 0.00067 Example 22 9.5 0.8 1000 0.0076 0.0095 0.0008 Example 23 7 0.75 1100 0.0048 0.006 0.00068 Example 24 8.5 0.6 600 0.0085 0.014 0.001 Example 25 9 0.7 800 0.0079 0.011 0.00088 Example 26 9.5 0.75 900 0.0079 0.011 0.00083 Example 27 8 0.8 854 0.0075 0.0093 0.00094 Example 28 8 0.8 1424 0.0045 0.0056 0.00056 Example 29 1 0.5 500 0.001 0.002 0.001 Example 30 8 0.1 1000 0.0008 0.008 0.0001 Comparative Example 1 9 1 300 0.03 0.03 0.0033 Comparative Example 2 4 0.5 5000 0.0004 0.0008 0.0001 Comparative Example 3 3 0.2 4500 0.0001 0.00067 0.00004 Comparative Example 4 10 0.9 300 0.033 0.033 0.003 Comparative Example 5 8 / 2000 / 0.004 / Comparative Example 6 8 0.8 / / / /

[0118] Table 2

[0119]

[0120] Example of effect

[0121] The sodium-ion secondary batteries obtained in each embodiment and comparative example were tested as follows:

[0122] (1) Gas generation test: Each lithium-ion secondary battery was discharged under the following conditions: current 0.33C, cutoff voltage 2.5V, and then fully charged under the following conditions;

[0123] (1.1) Charge the battery at a constant current of 0.33C to the upper limit voltage of 4.25V, charge it at a constant voltage until the current is less than or equal to 0.05C, and then discharge it at 0.33C to the lower limit voltage of 2.75V; this is one cycle, charge and discharge for 3 cycles, and use the discharge capacity of the third cycle as the battery capacity;

[0124] (1.2) Charge at a constant current of 0.33C to the upper limit voltage of 4.25V, and charge at a constant voltage until the current is less than or equal to 0.05C;

[0125] (1.3) The volume of the secondary battery is tested using the water displacement method and recorded as V0. After the battery is placed in an oven at 60°C for 60 minutes, it is taken out and the battery temperature is lowered to room temperature. The volume of the battery is tested again using the water displacement method and recorded as V1. The amount of gas produced by the battery during this storage period is the difference between V1 and V0. This value divided by the battery's rated capacity is the amount of gas produced per ampere-hour of the secondary battery.

[0126] The specific steps are as follows:

[0127] (i) Add an appropriate amount of pure water to the container and test its density with a hydrometer and record it;

[0128] (ii) Adjust the balance to a level and tare the metal (tare the metal before testing each secondary battery);

[0129] (iii) Submerge the secondary battery body along with the tabs into the solution, ensuring that the secondary battery does not contact the container wall. After stabilization, take a reading and record the data as T.

[0130] (iv) Turn off the balance and seal the container to prevent the reagent from evaporating.

[0131] The formula for calculating the volume of a secondary battery is T / ρ_liquid;

[0132] Among them, tests were conducted before and after storage to obtain T0 and T1 respectively;

[0133] The difference between V1 and V0 is: V1 - V0 = T1 / ρliquid - T0 / ρliquid

[0134] Gas production at 60℃ = (V1-V0) / secondary battery capacity;

[0135] (2) Energy density test: Weigh the secondary battery to be tested and record it as m; place the secondary battery in the fixture and apply a force of 3000N. Charge the single battery to 4.3V with a constant current of 0.33C, let it rest for 30min, discharge it to 2.5V with a constant current of 0.33C, let it rest for 30min, and repeat the charge and discharge cycle 3 times. Calculate the third discharge capacity (in Ah) and energy E (take the average value of the three cells). Discharge energy density: E / m (in Wh / kg);

[0136] (3) Cyclic performance test: The secondary batteries obtained from each embodiment and comparative example were subjected to a cycle performance test of lithium-ion batteries at 25°C using a LAND system. The lithium-ion batteries were cycled for 1000 cycles under the conditions of a charge / discharge rate of 0.5C / 1C, a current cutoff of 0.05C, and a voltage range of 2.5 to 4.25V. After the cycle, the cycle data was processed to obtain the capacity retention rate (the discharge capacity Q1 of the first cycle and the discharge capacity Q2 of the 1000th cycle are calculated according to the capacity retention rate = 100% × Q2 / Q1). The capacity retention rate (%) of the battery after 1000 cycles was obtained.

[0137] The test results are shown in Table 3.

[0138] Table 3

[0139]

[0140]

[0141] As can be seen from Table 3:

[0142] (1) The secondary battery described in this application introduces fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate as compound components in the electrolyte and introduces lanthanum into the positive electrode active material. By dynamically adjusting the introduction amount of these three key components, it not only has ideal energy density and cycle performance, with an energy density of more than 280Wh / kg, but also a capacity retention rate of more than 85% after 1000 cycles, and low gas production, with a maximum of no more than 6.5mL / Ah, but also has excellent overall performance. In contrast, products that do not introduce the three key components, or products that do not understand how to control the introduction amount of the three components, as shown in the comparative product, cannot achieve the same effect.

[0143] (2) As can be seen from Examples 1 to 26, the addition content of fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate in the electrolyte and the introduction amount of lanthanum 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 was found that when the range of (W1*W2) / D is preferably in the range of 0.002 to 0.009, the overall performance of the secondary battery is better. At the same time, the introduction amount of fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate in the electrolyte will affect the electrode impedance and the synergistic effect of electrolyte and lanthanum. 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 lanthanum matching concentration is 800ppm to 3000ppm, which can further improve the energy density of the secondary battery to more than 300Wh / kg, while the cycle retention rate is further improved to more than 90%, and the gas production can be achieved within 6mL / Ah.

[0144] (3) According to the comparison of Examples 18-26 with other examples, when (W1*W2) / D is adjusted, in addition to the combination of lanthanum and tris(dimethylvinylsilyl)phosphate, the influence of lanthanum on the electrode impedance and energy density of the secondary battery after its introduction can be effectively balanced. In addition, there is also a synergistic effect between lanthanum and fluoroethylene carbonate. When the ratio of W2 / D and W1 / D is further optimized, the overall electrochemical performance of the secondary battery is better, especially in terms of cycle 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, Includes positive electrode, negative electrode, and electrolyte; The electrolyte comprises 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, unit ppm -1 ; Wherein W1% is the mass percentage of fluoroethylene carbonate in the electrolyte, where W1% = 1% to 10%; W2% is the mass percentage of tris(dimethylvinylsilyl)phosphate in the electrolyte, where W2% = 0.1% to 1%; and Dppm is the content of lanthanum in the positive electrode active material, where Dppm = 300ppm to 5200ppm. The negative electrode sheet includes a negative electrode material layer, wherein the mass percentage of silicon in the negative electrode material layer is 0.5% to 12.5%.

2. The secondary battery as described in claim 1, characterized in that, The (W1*W2) / D = 0.002~0.009, unit ppm -1 .

3. The secondary battery as described in claim 1, characterized in that, The W1% is between 2% and 8%.

4. The secondary battery as described in claim 3, characterized in that, The W1% is 2% to 5%.

5. The secondary battery as described in claim 1, characterized in that, The W1% is between 7% and 10%.

6. The secondary battery as described in claim 1, characterized in that, The W2% is between 0.2% and 0.8%.

7. The secondary battery as described in claim 6, characterized in that, The W2% is between 0.2% and 0.8%.

8. The secondary battery as described in claim 1, characterized in that, The W2% is between 0.5% and 0.8%.

9. The secondary battery as described in claim 1, characterized in that, The Dppm is between 300ppm and 1500ppm.

10. The secondary battery as described in claim 1, characterized in that, The Dppm is between 800ppm and 3000ppm.

11. The secondary battery as described in claim 1, characterized in that, The W1 / D ratio is 0.0002–0.033, in ppm. -1 .

12. The secondary battery as described in claim 1, characterized in that, The W1 / D ratio is 0.003 to 0.01, in ppm. -1 .

13. The secondary battery as described in claim 1, characterized in that, The W2 / D ratio is 0.00002 to 0.0033, in ppm. -1 .

14. The secondary battery as described in claim 1, characterized in that, The W2 / D ratio is 0.0002 to 0.0007, in ppm. -1 .

15. The secondary battery as described in claim 1, characterized in that, The electrolyte also includes a third additive, which includes at least one of 1,3-propanesulfonyl lactone and lithium difluorophosphate.

16. The secondary battery as described in claim 1, characterized in that, The electrolyte also includes a solvent and a lithium salt.

17. The secondary battery as described in claim 16, characterized in that, The solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

18. The secondary battery as described in claim 17, characterized in that, The carbonate solvents include at least one of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the carboxylic acid ester solvents include at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; the ether solvents include at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; the sulfone solvents include at least one of methyl sulfone and dimethyl sulfoxide; the nitrile solvents include at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrionitrile; and the phosphate ester solvents include at least one of trimethyl triphosphate and triethyl phosphate.

19. The secondary battery as described in claim 16 or 17, characterized in that, The solvent includes at least one of the following: carbonate solvent fluorinated derivatives, carboxylic acid ester solvent fluorinated derivatives, ether solvent fluorinated derivatives, sulfone solvent fluorinated derivatives, nitrile solvent fluorinated derivatives, and phosphate ester solvent fluorinated derivatives.

20. The secondary battery as described in claim 16, characterized in that, The electrolyte contains dimethyl carbonate.

21. The secondary battery as described in claim 20, characterized in that, The electrolyte contains the following solvents in parts by weight: 70-75 parts dimethyl carbonate, 8-12 parts propylene carbonate, and 8-12 parts ethylene carbonate.

22. The secondary battery as described in claim 16, characterized in that, 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.

23. The secondary battery as described in claim 16 or 22, characterized in that, The concentration of lithium salt in the electrolyte is 0.8 mol / L to 2.5 mol / L.

24. The secondary battery as described in claim 1, characterized in that, The negative electrode sheet includes a negative electrode active material.

25. The secondary battery as described in claim 24, characterized in that, The negative electrode active material contains silicon.

26. The secondary battery as described in claim 1, characterized in that, The positive electrode active material includes at least one of lanthanum-doped lithium nickel cobalt manganese oxide and lanthanum-doped lithium nickel manganese oxide.

27. The secondary battery as described in claim 25, characterized in that, The negative electrode active material contains at least one of silicon-carbon composite material and silicon suboxide material.

28. The secondary battery as described in claim 1, characterized in that, The positive electrode sheet also includes a current collector, and at least one side of the current collector is provided with a positive electrode material layer, the positive electrode material layer including a positive electrode active material.

29. The secondary battery as described in claim 28, characterized in that, The positive electrode material layer also includes at least one of a conductive agent and a binder.

30. The secondary battery as described in claim 1, characterized in that, The negative electrode sheet also includes a current collector, and at least one side of the current collector is provided with a negative electrode material layer, the negative electrode material layer including a negative electrode active material.

31. The secondary battery as described in claim 30, characterized in that, The negative electrode material layer includes a negative electrode material, a binder, a thickener, and a conductive agent.

32. The secondary battery as described in claim 1, 28, or 29, characterized in that, The positive electrode active material also contains nickel, and the mass content of nickel in the positive electrode active material is ≥90%.

33. The secondary battery as described in claim 32, characterized in that, The cathode 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.

34. The secondary battery as described in claim 33, characterized in that, The N also includes at least one of Al, Na, Ti, Nb, Zr, W, Fe, and Cr.

35. The secondary battery as described in claim 1, characterized in that, The silicon content in the negative electrode material layer is 5% to 10% by mass.

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