A secondary battery

Abstract

The present application discloses a secondary battery, belonging to the field of battery technology. The secondary battery is prepared by adding fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate as compound components to the electrolyte, introducing lanthanum into the positive electrode active material, and dynamically regulating the content relationship between the lanthanum and the two electrolyte components. This ensures that the secondary battery has not only ideal energy density and cycle performance, but also high stability and low gas production.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery. Background Art

[0002] High-nickel silicon-based lithium-ion batteries refer to a new type of battery that uses high-nickel binary or ternary materials for the positive electrode and silicon-based materials for the negative electrode. These batteries have high theoretical energy density, but in practice, the battery's cycling performance is less than ideal due to the volume effect of the silicon-based material. Furthermore, the battery suffers from severe gassing issues due to insufficient electrode interface stability.

[0003] In order to improve the cycle performance of high-nickel silicon-based lithium-ion batteries, people add fluoroethylene carbonate (FEC) to the battery electrolyte. However, this practice will increase the electrode impedance and reduce the overall ion / electron conduction efficiency of the battery, which will ultimately further deteriorate the battery's cycle stability performance and make the gas production problem more serious. Summary of the Invention

[0004] The purpose of the present 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, introducing lanthanum into the positive electrode active material and dynamically regulating the content relationship between lanthanum and the two electrolyte components, the secondary battery not only has ideal energy density and cycle performance, but also has high stability and low gas production.

[0005] To achieve the above-mentioned object, in a first aspect of the present application, the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte;

[0006] The electrolyte includes fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate;

[0007] The positive electrode plate includes a positive electrode active material, and the positive electrode active material contains lanthanum;

[0008] The secondary battery satisfies: (W1*W2) / D=0.0005~0.02;

[0009] 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.

[0010] The beneficial effects of this application are:

[0011] The present application provides a secondary battery, which adds fluoroethylene carbonate and tris(dimethylvinylsilyl) phosphate as compound components to the electrolyte, introduces lanthanum into the positive electrode active material, and dynamically regulates the content relationship between the lanthanum and the two electrolyte components, so that the secondary battery not only has ideal energy density and cycle performance, but also has high stability and low gas production. DETAILED DESCRIPTION

[0012] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0013] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0014] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0015] The present application is further described below with specific examples:

[0016] A secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte;

[0017] The electrolyte includes fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate;

[0018] The positive electrode plate includes a positive electrode active material, and the positive electrode active material contains lanthanum;

[0019] The secondary battery satisfies: (W1*W2) / D=0.0005~0.02;

[0020] 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.

[0021] In the technical solution of this application, to ensure the ion / electron transmission efficiency of the secondary battery while balancing the secondary battery's energy density, cycle performance, and safety and stability, fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate are added to the electrolyte as functional components. Fluorinated ethylene carbonate can enhance the stability of ion / electron transmission between the electrodes in the secondary battery, but the addition of fluoroethylene carbonate increases the impedance of the secondary battery electrodes. Introducing lanthanum into the secondary battery's positive electrode active material directly and effectively reduces the electrode resistance, but the addition of lanthanum affects the battery's energy density. Therefore, the presence of tris(dimethylvinylsilyl)phosphate can coordinate with lanthanum to reduce internal resistance while maintaining a high capacity level and energy density. 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 production in the secondary battery. Through the joint action of the three under the construction of a specific introduction amount relationship, the secondary battery has ideal cycle performance, energy density and safe and stable performance.

[0022] In some embodiments, the (W1*W2) / D=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 any two of the range values.

[0023] Further preferably, (W1*W2) / D=0.002~0.009.

[0024] The addition content of fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate in the electrolyte and the change in the introduction amount of lanthanum element in the positive electrode active material will affect the energy density, ion / electron transmission efficiency, cycle stability and safety stability of the secondary battery. After constructing the relationship between the three, it was 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 has better overall performance.

[0025] In some embodiments, W1=1~10%.

[0026] Further preferably, W1 is a range value of one or any two of 1%, 2%, 3%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, and 10%.

[0027] More preferably, W1=7~10%.

[0028] The introduction of fluoroethylene carbonate has an impact on the electrode impedance and cycle performance of the secondary battery, and also affects the gas production probability of the secondary battery. When this component is added to the electrolyte at a mass content within the above range, the cycle performance optimization effect of the secondary battery is better, and the electrode impedance in the secondary battery can be maintained at a low level.

[0029] In some embodiments, W2=0.1~1%.

[0030] Further preferably, W2 is in the range of one or any 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%, and 1%.

[0031] Further preferably, W2=0.5~0.8%.

[0032] After tris(dimethylvinylsilyl)phosphate is introduced into the electrolyte in combination with fluoroethylene carbonate, the electrolyte will synergistically act with the lanthanum element in the positive electrode active material to control 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.

[0033] In some embodiments, the D=300~5200 ppm.

[0034] Further preferably, D=one or any two of 300ppm, 500ppm, 800ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 4800ppm, 5000ppm, 5200ppm.

[0035] More preferably, the D=800~3000ppm.

[0036] It is not uncommon to add lanthanum to the positive electrode active material in existing secondary batteries to improve the conductivity of the electrode. In the secondary battery described in the present application, based on the use of an electrolyte with two specific components, the amount of lanthanum introduced in the positive electrode active material needs to establish a content relationship with the electrolyte to ensure that the secondary battery can have both ideal electrochemical performance and safety performance when in use. When the amount of lanthanum introduced is preferably within the above range, the secondary battery can achieve higher energy density and ion / electron transmission efficiency, and better electrochemical performance.

[0037] In some embodiments, W1 / D=0.0002~0.033.

[0038] Further preferably, the W1 / D=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 any two of the range values.

[0039] Further preferably, W1 / D=0.003~0.01.

[0040] Under the premise that tris(dimethylvinylsilyl)phosphate, fluoroethylene carbonate and lanthanum element in the positive electrode active material act synergistically, in the secondary battery, lanthanum element and fluoroethylene carbonate also have a certain interaction. By adjusting the ratio between the two, the secondary battery can maintain the electrode impedance at a lower 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.

[0041] In some embodiments, W2 / D=0.00002~0.0033.

[0042] Further preferably, the W2 / D=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 any two of the range values.

[0043] Further preferably, W2 / D=0.0002~0.0007.

[0044] The introduction of lanthanum will affect the capacity of the active material to a certain extent, and thus affect the energy density. Therefore, in the secondary battery, the compounding of tris(dimethylvinylsilyl)phosphate can effectively balance the effect of the introduction of lanthanum on the secondary battery electrode impedance and energy density. When the addition amounts of the two are preferably within the above-mentioned 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.

[0045] It should be noted that the mass percentage of tris(dimethylvinylsilyl)phosphate and fluoroethylene carbonate in the electrolyte described in this application is confirmed by GC-MS testing, and the specific method is:

[0046] (1) Use the secondary battery charging and discharging equipment to discharge the battery. The discharge conditions are: current 0.3C, cut-off voltage 2.5V;

[0047] (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 removing the battery cover:

[0048] ① If there is free electrolyte, use a pipette to collect the electrolyte into a 5 mL sample tube and seal it with sealing glue to prevent leakage;

[0049] ② If there is no free electrolyte, use a hydraulic press (FY-30 hydraulic press, Beijing Hengaode Technology Co., Ltd.) to continuously pressurize until free electrolyte appears, collect the electrolyte into a sample tube and seal it.

[0050] 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 it for 12 hours to allow the electrolyte in the electrode to fully mix 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;

[0051] (3) The collected electrolyte samples were injected into an Agilent Intuvo9000 gas chromatograph-mass spectrometer using a microinjector for testing to obtain GC-MS spectra. Fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate were dissolved in EMC solvent to prepare solutions of different concentrations, and injected into an Agilent Intuvo9000 gas chromatograph-mass spectrometer to obtain standard GC-MS spectra. The GC-MS spectra of the electrolyte to be tested were compared with the standard GC-MS spectra, and the content of each component in the electrolyte to be tested was determined based on the peak area of ​​each component.

[0052] It should be noted that the content of lanthanum in the positive electrode active material described in this application is confirmed by alkaline dissolution-ICP method, and the specific method is as follows:

[0053] The secondary battery in the empty state was disassembled to obtain the positive electrode sheet, which was dried at 80°C for 4 hours and then placed in a muffle furnace and sintered at 400°C for 4 hours. The positive electrode active material powder on the sheet was then scraped off with a scraper.

[0054] Accurately weigh 0.5g of positive electrode active material powder and disperse it in 20mL of water. Then add 10mL of 60% nitric acid and heat to 80℃. After the powder is dissolved, add water to make the volume 100mL to obtain the test solution.

[0055] Perform ICP testing on the test solution (ICP emission spectrometer, model: ICAP PRO), select the element detection spectrum wavelength, and set the experimental conditions: Based on the characteristics of the sample and the test solution, perform ICP testing on the element detection spectrum wavelength, and set the experimental conditions: gas flow rate 0.5L / min, power 1150W; locate the wavelength of each transition metal element: lanthanum, nickel, cobalt, and manganese; obtain the La content of the positive electrode active material through ICP testing, and then use the same method to test the content of other transition metal elements. Confirm the chemical composition of the positive electrode active material based on the ratio of each transition metal element, and then calculate the mass content of lanthanum in the positive electrode active material.

[0056] In some embodiments, the electrolyte further includes a third additive, wherein the third additive includes at least one of 1,3-propane sultone (PS) and lithium difluorophosphate (LiPO 2 F 2 ).

[0057] In some embodiments, the electrolyte further includes a solvent and a lithium salt.

[0058] In some embodiments, the solvent includes at least one of a carbonate solvent, a carboxylate solvent, an ether solvent, a sulfone solvent, a nitrile solvent, and a phosphate solvent.

[0059] Illustratively, the carbonate solvent includes but is 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 solvent includes but is not limited to at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; the ether solvent includes at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; the sulfone solvent includes at least one of methyl sulfone and dimethyl sulfoxide; the nitrile solvent includes at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrinitrile; and the phosphate solvent includes at least one of trimethyl triphosphate and triethyl phosphate.

[0060] Further preferably, the solvent may also 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.

[0061] More preferably, the electrolyte contains dimethyl carbonate (DMC).

[0062] More preferably, the electrolyte solution comprises the following solvents in parts by mass: 70-75 parts of dimethyl carbonate, 8-12 parts of propylene carbonate, and 8-12 parts of ethylene carbonate.

[0063] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium trifluoromethanesulfonate, lithium bisfluoromethanesulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, and the like.

[0064] Further preferably, the concentration of lithium salt in the electrolyte is 0.8-2.5 mol / L.

[0065] Further preferably, the concentration of the lithium salt in the electrolyte is in the range of one or any two 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, and 2.5 mol / L.

[0066] The secondary battery described in the present application can be prepared according to actual needs by selecting tris(dimethylvinylsilyl)phosphate and fluoroethylene carbonate as the electrolyte components, and then simultaneously combining other suitable solvents, lithium salts and additives. The solvents and lithium salts can be compounded in amounts within the above-mentioned preferred ranges and are not limited to the above-mentioned solution.

[0067] In some embodiments, the positive electrode active material further contains nickel, and the mass content of the nickel in the positive electrode active material is ≥ 90%, more preferably 90-95%.

[0068] In some embodiments, the negative electrode plate includes a negative electrode active material;

[0069] In some embodiments, the negative electrode active material contains silicon.

[0070] The secondary battery described in the present application is based on the synergistic effect of the electrolyte and the lanthanum-containing positive electrode active material, which can effectively solve the dilemma of high-nickel-silicon secondary batteries in that they cannot achieve both energy density, cycle performance, and safety and stability. By constructing the 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 the cycle performance and safety and stability while retaining the advantage of high energy density of the high-nickel-silicon system.

[0071] In some embodiments, the positive electrode active material includes at least one of lanthanum-doped lithium nickel manganese cobalt oxide and lanthanum-doped lithium nickel manganese oxide.

[0072] In some embodiments, the negative electrode active material contains at least one of a silicon-carbon composite material and a silicon monoxide material.

[0073] For example, the silicon-carbon composite material can be prepared by a CVD (chemical vapor deposition) method, specifically, silane is infiltrated into a carbon material by a CVD method, and then heated and sintered to obtain the silicon-carbon composite material.

[0074] Those skilled in the art may also adopt other methods to prepare silicon-carbon composite materials according to actual conditions, or directly purchase commercial products, and are not limited to the above-mentioned silicon-carbon composite materials and the preparation methods mentioned therein; similarly, the silicon dioxide material may also be prepared by oneself, for example, by reduction preparation using the silane sol-gel method, or by oxidation-reduction preparation using a silicon dioxide-containing material, or by purchasing semi-finished raw materials and then preparing them in a semi-synthetic manner, or by directly purchasing them, and are not limited to the acquisition methods exemplified in this application.

[0075] In some embodiments, the positive electrode sheet further includes a current collector, 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.

[0076] Further preferably, the positive electrode material layer further includes at least one of a conductive agent and a binder.

[0077] In some embodiments, the negative electrode sheet further includes a current collector, 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;

[0078] Further preferably, the negative electrode material layer includes a negative electrode material, a binder, a thickener and a conductive agent.

[0079] In some embodiments, the mass percentage of nickel element in the positive electrode active material is 40-60%.

[0080] It should be noted that the test method for the mass percentage of nickel element in the positive electrode active material of the battery described in this application is the same as the test method for lanthanum element, and the details are not repeated here.

[0081] Further preferably, the positive electrode material includes LiNi a Mn b Co c N dO2, wherein 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 includes La.

[0082] More preferably, the N further includes at least one of Al, Na, Ti, Nb, Zr, W, Fe, and Cr.

[0083] Further preferably, the mass percentage of silicon element in the negative electrode material layer is 0.5-12.5%.

[0084] Further preferably, the mass percentage of silicon element in the negative electrode material layer is within the range of one or any two of 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5%, 8%, 10%, 12%, and 12.5%.

[0085] It should be noted that the mass percentage of silicon element in the negative electrode material layer of the secondary battery described in the present application is tested using the alkaline dissolution-ICP method.

[0086] The specific steps are as follows: the negative electrode of an empty secondary battery is disassembled and cleaned with DMC (dimethyl carbonate) solvent, soaked for 48 hours, and dried at 60°C. The powder of the negative electrode active material layer is then scraped off. A sample of the powder is weighed and placed in a nickel crucible pre-filled with potassium hydroxide. A small amount of potassium hydroxide is added to cover the sample surface. Two drops of ethanol are then added. The sample is heated on an electric furnace until the potassium hydroxide melts and dehydrates. The sample is then transferred to a muffle furnace at 1100°C and held at this temperature for 8 hours. The nickel crucible is removed and allowed to cool slightly. The sample is then placed in a 300 mL plastic beaker and extracted with hot water. After the reaction, the crucible is washed out. The extract is acidified with 6 mol HCl and oxidized with 30% hydrogen peroxide. After cooling, the extract is washed out with water and transferred to a 100 mL volumetric flask, brought to volume, and shaken well. After standing, the solution is aliquoted into another 100 mL volumetric flask, brought to volume, shaken well, and allowed to settle to obtain the test solution. At the same time, a blank solution was prepared as a control, that is, a solution sample was prepared according to the above steps without adding the test sample.

[0087] The solution to be tested was subjected to ICP testing (ICP emission spectrometer, model: ICAP PRO), the element detection spectral wavelength was selected, and the experimental conditions were set: based on the characteristics of the sample and the solution to be tested, the element detection spectral wavelength was selected, and the experimental conditions were set: gas flow rate 0.5L / min, power 1150W; Si element determination wavelength 288.158nm; the Si content of the element was tested by ICP, and then the mass content of the silicon element in the final negative electrode material layer was confirmed by calculation with the mass of the original scraped powder.

[0088] The present invention is further described below with reference to specific examples, which are not to be construed as limiting the scope of the present invention.

[0089] Example 1

[0090] A secondary battery, the preparation method comprising the following steps:

[0091] (1) Preparation of positive electrode sheet: The positive electrode active material, conductive agent acetylene black and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone in a mass ratio of 92:4:4, and the slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector aluminum foil, dried, cold pressed and cut to obtain the positive electrode sheet; the positive electrode active material is LiNi 0.9 Mn 0.05 Co 0.0465 La 0.0035 O2, the mass percentage of nickel element is 52.8%.

[0092] (2) Preparation of negative electrode sheets: The negative electrode active material, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.4:1:1.2:1.4, and the slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and dried, cold pressed, and cut to obtain the negative electrode sheet. The negative electrode material includes a silicon-carbon composite material, and the mass percentage of silicon element in the negative electrode material layer is 10%;

[0093] The silicon-carbon composite material is a commercially available silicon-carbon material;

[0094] (3) Preparation of the diaphragm: A PP diaphragm with an average pore size of 2 μm and an air permeability of 300 s / 100 mL was used as the substrate, and then an aluminum oxide coating was applied to one side and dried to obtain a diaphragm containing the coating;

[0095] (4) The positive electrode sheet, the separator (the coating side is against the positive electrode sheet), and the negative electrode sheet are stacked and wound in order to form a battery cell, and the battery cell is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, and constant capacity, the battery is obtained.

[0096] The parameters of each electrolyte are shown in Tables 1 and 2.

[0097] Examples 2-26, 29-30

[0098] A battery, the difference from Example 1 only being that the components of the electrolyte and the content of lanthanum in the positive electrode active material are different, wherein the molar ratio of nickel, cobalt, and manganese in the positive electrode active material remains unchanged, and the results are shown in Tables 1 and 2.

[0099] Example 27

[0100] A battery, the difference from Example 5 is that the positive electrode active material of the positive electrode active material is LiNi 0.91 Mn 0.05 Co 0.039 La 0.0006Al0.0004 O2, the mass percentage of nickel element is 53.4%.

[0101] Example 28

[0102] A battery, the difference from Example 5 is that the positive electrode active material of the positive electrode active material is LiNi 0.9 Mn 0.05 Co 0.049 La 0.001 O2, the mass percentage of nickel element is 52.8%.

[0103] Comparative Examples 1-4

[0104] A battery having the same difference from Example 1 is that the components of the electrolyte and the content of lanthanum in the positive electrode active material are different. The results are shown in Tables 1 and 2.

[0105] Comparative Example 5

[0106] A battery, the only difference from Example 5 is that tris(dimethylvinylsilyl)phosphate is not added to the electrolyte.

[0107] Comparative Example 6

[0108] A battery, the difference from Example 5 is that the positive electrode active material is LiNi 0.9 Mn 0.05 Co 0.05 O2, the mass percentage of nickel element is 53.9%, that is, the positive electrode active material does not contain lanthanum element.

[0109] In Table 1 and Table 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 the lithium salt in the electrolyte. The third additives are PS and LiPO2F2. PS (wt%) and LiPO2F2 (wt%) represent the mass percentages of the third additives PS and LiPO2F2, respectively, in the electrolyte. For Comparative Examples 5 and 6, some parameters were missing, so the results are not included in the analysis and are represented by " / ".

[0110] Table 1

[0111]

[0112] Table 2

[0113]

[0114] Effect Examples

[0115] The sodium ion secondary batteries obtained in each embodiment and comparative example were tested as follows:

[0116] (1) Gas production test: Each lithium-ion secondary battery is discharged under the following discharge conditions: current 0.33C, cut-off voltage 2.5V, and then fully charged under the following conditions;

[0117] (1.1) Charge at a constant current of 0.33C to an upper voltage of 4.25V, charge at a constant voltage until the current is less than or equal to 0.05C, and then discharge at 0.33C to a lower voltage of 2.75V; this is a cycle, charge and discharge three times, and use the discharge capacity of the third cycle as the battery capacity;

[0118] (1.2) Charge at a constant current of 0.33C to an upper voltage of 4.25V, and then charge at a constant voltage until the current is less than or equal to 0.05C;

[0119] (1.3) The volume of a secondary battery is measured using the water displacement method, recorded as V0. The battery is placed in a 60°C oven for 60 minutes, then removed. After the battery cools to room temperature, the volume is measured again using the water displacement method, recorded as V1. The gas production of the battery during this storage period is the difference between V1 and V0. This value, divided by the battery's rated capacity, is the gas production per ampere-hour of the secondary battery.

[0120] The specific steps are:

[0121] (i) Add an appropriate amount of pure water to the container and measure its density using a densitometer and record it;

[0122] (ii) Adjust the balance to a level and tare the balance (tare the balance before each secondary battery test);

[0123] (iii) Immerse the secondary battery body and its tabs in the solution, ensuring that the secondary battery does not contact the container wall. After stabilization, read the reading and record the value as T;

[0124] (iv) Turn off the balance and seal the container tightly to prevent evaporation of the reagent.

[0125] The volume calculation formula of secondary batteries is T / ρ liquid;

[0126] Among them, before storage and after storage, tests are performed respectively to obtain T0 and T1;

[0127] The difference between V1 and V0 is: V1-V0=T1 / ρliquid-T0 / ρliquid

[0128] Gas production at 60°C storage = (V1-V0) / secondary battery capacity;

[0129] (2) Energy density test: Weigh the weight of the secondary battery to be tested, record it as m; place the secondary battery in a fixture, apply a force of 3000N, charge the single battery to 4.3V at a constant current of 0.33C, leave it for 30min, discharge it to 2.5V at a constant current of 0.33C, leave it for 30min, and charge and discharge it three times continuously. Calculate the third discharge capacity (in Ah) and energy E (take the average value of three cells), discharge energy density: E / m (in Wh / kg);

[0130] (3) Cycle performance test: The secondary batteries obtained in each embodiment and comparative example were subjected to a cycle performance test of lithium-ion batteries using a LAND system at 25°C. The lithium-ion batteries were cycled for 1000 cycles at a charge and discharge rate of 0.5C / 1C, a current cutoff of 0.05C, and a voltage range of 2.5-4.25V. After the cycle was completed, the cycle data was processed to obtain the capacity retention rate (the first cycle discharge capacity Q1 and the 1000th cycle discharge capacity Q2 were calculated based on the capacity retention rate = 100% × Q2 / Q1), and the capacity retention rate (%) of the battery after 1000 cycles was obtained.

[0131] The test results are shown in Table 3.

[0132] Table 3

[0133]

[0134] According to Table 3, we can see that:

[0135] (1) The secondary battery described in the present application simultaneously 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, the secondary battery not only has ideal energy density and cycle performance, the energy density can reach more than 280Wh / kg, and the capacity retention rate after 1000 cycles can reach more than 85%, and the gas production is small, with a maximum of no more than 6.5mL / Ah, and the overall performance is excellent. In contrast, products that do not introduce the three key components, or products that do not know how to regulate the introduction amount of the three components, as shown in the comparative products, cannot achieve the same effect as above.

[0136] (2) According to Examples 1 to 26, it can be seen that 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 transmission efficiency, cycle stability and safety stability of the secondary battery. After constructing the relationship between the three, it was found that when the range of (W1*W2) / D is preferably within the range of 0.002~0.009, the comprehensive 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 the electrolyte and lanthanum. When W1 is preferably within the range of 7~10% and W2 is preferably within the range of 0.5~0.8%, the corresponding lanthanum matching concentration is 800~3000ppm, which can further improve the energy density of the secondary battery to more than 300Wh / kg, and the cycle retention rate is further improved to more than 90%, and the gas production can be achieved within 6mL / Ah.

[0137] (3) According to the comparison between Examples 18 to 26 and other Examples, it can be seen that when (W1*W2) / D is regulated, in addition to the compounding of lanthanum and tris(dimethylvinylsilyl)phosphate, which can effectively balance the influence of lanthanum on the electrode impedance and energy density of the secondary battery after its introduction, there is also a synergistic effect between lanthanum and fluoroethylene carbonate. When the ratio of W2 / D and W1 / D is further optimized, the comprehensive 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: Including positive electrode sheet, negative electrode sheet and electrolyte; The electrolyte includes fluoroethylene carbonate and tris(dimethylvinylsilyl)phosphate; The positive electrode plate 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, wherein W1%=1%~10%, W2% is the mass percentage of tris(dimethylvinylsilyl)phosphate in the electrolyte, wherein W2%=0.1%~1%, and D ppm is the content of lanthanum in the positive electrode active material, wherein D ppm=300ppm~5200ppm.

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

009.

3. The secondary battery according to claim 1, wherein: The W1 / D=0.0002~0.

033.

4. The secondary battery according to claim 1, wherein: The W2 / D=0.00002~0.0033.

5. The secondary battery according to claim 1, wherein: 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%.

6. The secondary battery according to claim 1, wherein: The negative electrode plate includes a negative electrode material layer; the negative electrode material contains silicon element.

7. An electrical device, characterized in that: The secondary battery according to any one of claims 1 to 6 is used as a power supply for the electrical device.

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