A secondary battery

Abstract

The application discloses a secondary battery, and belongs to the technical field of batteries. The secondary battery is characterized in that tri(dimethylvinylsilyl) phosphate and 1,3-propane sulfone lactone are introduced into an electrolyte as functional additives, the content of the two in the electrolyte and the adhesion force of a diaphragm are simultaneously regulated, the side reaction between an active material of an electrode sheet and the electrolyte in the secondary battery can be effectively inhibited, the gas generation probability is reduced, and finally, ideal ion / electron transmission efficiency and cycle performance are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery. BACKGROUND

[0002] The medium-high nickel lithium ion secondary battery refers to a secondary battery using a binary or ternary material containing medium or high content of nickel as a positive electrode material. Such a battery has high theoretical energy density, but in actual application, especially in long cycle process, the degree of side reaction between the pole piece material and the electrolyte increases, and gas generation is caused, which not only affects the cycle performance of the secondary battery, but also causes safety problems; in addition, the medium-high nickel lithium ion secondary battery has high selection strictness for the negative electrode material, if the active material containing silicon is selected, not only additional electrolyte additives need to be compounded, but also the possibility of gas generation is further increased due to the silicon volume effect problem, and the actual application effect is not good. SUMMARY

[0003] The purpose of the present application is to overcome the deficiencies in the prior art and provide a secondary battery. The secondary battery described in the present application can effectively inhibit the side reaction between the pole piece active material and the electrolyte in the secondary battery, reduce the probability of gas generation, and ultimately realize the ideal ion / electron transmission efficiency and cycle performance by introducing tris(dimethylvinylsilyl) phosphate (DMVSP) and 1,3-propane sulfone lactone as functional additives in the electrolyte, and simultaneously regulating the content of the two in the electrolyte and the adhesion force size relationship of the separator.

[0004] To achieve the above-mentioned purpose, in the first aspect of the present application, the present application provides a secondary battery, the secondary battery comprising a positive electrode pole piece, a separator and an electrolyte;

[0005] The electrolyte comprises a first additive and a second additive;

[0006] The secondary battery satisfies (b*c) / a = 1-10;

[0007] Wherein a% is the mass percentage content of the first additive in the electrolyte, b% is the mass percentage content of the second additive in the electrolyte, and c N / m is the adhesion force of the separator;

[0008] The first additive is tris(dimethylvinylsilyl) phosphate, and the second additive is 1,3-propane sulfone lactone.

[0009] The present application has the following beneficial effects:

[0010] The application provides a secondary battery, the secondary battery described in the application, the battery can effectively inhibit the side reaction between the active material of the pole piece and the electrolyte in the secondary battery, reduce the gas generation probability, and finally realize the ideal ion / electron transmission efficiency and cycle performance by introducing tri(dimethylvinylsilyl) phosphate and 1,3-propane sulfone lactone as functional additives in the electrolyte, simultaneously regulating the content of the two in the electrolyte and the adhesion force size relationship of the diaphragm. DETAILED DESCRIPTION

[0011] To make the objectives, technical solutions, and advantages of the embodiments of the application clearer, the technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are some but not all of the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0012] In the application, the technical features described in an open way include a closed technical solution composed of listed features, and also include an open technical solution containing listed features.

[0013] In the application, if no special description is provided, the numerical range is regarded as continuous and includes the minimum value and the maximum value of the range and each value between the minimum value and the maximum value. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all the ranges disclosed in the application should be understood as including any and all sub-ranges.

[0014] The application will be further described below with specific embodiments:

[0015] A secondary battery, the secondary battery comprising a positive pole piece, a diaphragm, and an electrolyte;

[0016] The electrolyte comprises a first additive and a second additive;

[0017] The secondary battery satisfies (b*c) / a = 1-10;

[0018] wherein a% is the mass percentage content of the first additive in the electrolyte, b% is the mass percentage content of the second additive in the electrolyte, and c N / m is the adhesion force of the diaphragm;

[0019] The first additive is tri(dimethylvinylsilyl) phosphate, and the second additive is 1,3-propane sulfone lactone.

[0020] The pole piece, especially the positive pole piece, in the secondary battery is prone to side reaction with the electrolyte during the cycle process, thereby generating gas. With the continuous cycle process, the generated gas gradually accumulates between the diaphragm and the pole piece, causing the ion / electron transmission channel between part of the diaphragm and the pole piece to fail, greatly reducing the conductivity efficiency, greatly weakening the cycle performance of the secondary battery, and even causing safety problems. Therefore, in the scheme of the present application, specific tris(dimethylvinylsilyl) phosphate and 1,3-propane sulfone lactone are introduced into the electrolyte of the secondary battery as additive components, wherein the former can effectively improve the protection effect of the electrolyte on the positive pole piece interface and reduce the impedance of the CEI film, and the latter can cooperate with the former to improve the cycle stability of the overall system by inhibiting the gas generation effect; the addition content ratio of the two additives can be adjusted to maintain the balance of the cycle performance and the conductivity efficiency of the secondary battery, and the secondary battery also regulates the adhesion of the diaphragm. Under the appropriate adhesion, the secondary battery can ensure stable ion transmission efficiency and will not cause the diaphragm and the pole piece to be excessively attached due to excessive adhesion, thereby increasing the probability of side reaction, and finally achieving excellent electrochemical performance.

[0021] In some embodiments, the (b*c) / a = one or a range value of any two of 1, 2, 2.5, 2.6, 3, 3.2, 3.5, 4, 5, 6, 6.5, 7, 8, 10.

[0022] It should be noted that the mass percentage content of the first additive and the second additive in the electrolyte is tested and confirmed by GC-MS method, and the specific method is as follows:

[0023] The secondary battery is subjected to emptying and discharging under the condition of 0.3C rate and cut-off voltage 2V, and then the secondary battery is disassembled. If there is free electrolyte, it is directly collected into a 5mL sample tube with a straw, and sealed with sealing glue. If there is no free electrolyte, the disassembled secondary battery is pressurized to appear free electrolyte by using a hydraulic machine FY-30, and then collected into a 5mL sample tube with a straw, and sealed with sealing glue. Then, the electrolyte sample is injected into an Agilent Intuvo 9000 gas chromatograph to test the electrolyte composition, and the concentration of each component in the electrolyte is given by comparing with the standard database.

[0024] The adhesion of the separator is confirmed by disassembling the secondary battery, then separating the negative electrode sheet, leaving the positive electrode sheet connected to the separator, confirming whether the separator surface contains a fiber coating by preliminary component analysis of the separator, if it contains a fiber coating, taking a 200-300 mm length sample of the separator in the longitudinal direction, then folding it in half along the transverse direction, placing the folded sample between two layers of dust-free paper, then cutting the test sample into a 250 mm length, 15 mm width together with the dust-free paper, separating the dust-free paper, selecting 3M-18 mm Scotch 300C double-sided tape to paste the cut 15 mm wide separator to the positive electrode sheet sample on the steel plate, rolling back and forth with the pressure roller three times, and then testing the adhesion; if it does not contain a fiber coating, use a bidirectional cutting knife to cut a 25 mm wide, 250 mm long separator along the length of the separator (M), paste the cut 25 mm wide separator to the positive electrode sheet / negative electrode sheet sample on the steel plate with a 160 mm long GA808 double-sided tape on one end of the steel plate, and roll back and forth with the pressure roller three times to test the adhesion.

[0025] The test procedure is as follows: replace the manual clamp (fix one end of the flat steel plate without double-sided tape with a clamp, and fix the free end of the test sample with a clamp) with a universal testing machine, select a 500N sensor device online, select the adhesion test step, confirm the width of the test sample (15mm for the fiber layer test sample, and 25mm for the test sample without the fiber layer), set the peeling starting point to 20mm and the ending point to 90mm, the peeling speed to 100mm / min, and the peeling direction to 180°.

[0026] In some embodiments, c = 3-15 N / m.

[0027] Further preferably, c = one of 3 N / m, 4 N / m, 5 N / m, 6 N / m, 8 N / m, 10 N / m, 12 N / m, 13 N / m, 15 N / m, or a range value of any two thereof.

[0028] In some embodiments, (b*c) / a = 3-7.

[0029] As described above, in practice, the addition amount of the first additive and the second additive in the electrolyte needs to consider several factors: the degree of interface protection of the positive electrode sheet, the passivation of electrolyte side reactions, ion / electron conduction efficiency, and the thickness, impedance, etc. of the SEI / CEI film layer during the cycle process, and the content of both additives is not the more the better, while also considering the influence of the adhesion of the separator on the side reactions between the electrolyte and the electrode sheet and the transmission efficiency of lithium ions through the separator. When the three key factors are within the above-mentioned range, the secondary battery can achieve a better system balance, and the electrochemical performance is further improved.

[0030] In some embodiments, the first additive has a mass percentage content in the electrolyte of 0.3-1%.

[0031] Further preferably, the first additive has a mass percentage content in the electrolyte of one of 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range value of any two thereof.

[0032] In some embodiments, the first additive has a mass percentage content in the electrolyte of 0.5-0.7%.

[0033] When the content of the first additive is preferably within the above range, the electrolyte can further balance the relationship between the improvement of the stability of the electrode interface and the thickness and impedance control of the interface CEI film layer, and the secondary battery has lower internal impedance and better cycle stability.

[0034] In some embodiments, the second additive has a mass percentage content in the electrolyte of 0.1-0.8%.

[0035] Further preferably, the second additive has a mass percentage content in the electrolyte of one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or a range value of any two thereof.

[0036] In some embodiments, the second additive has a mass percentage content in the electrolyte of 0.2-0.4%.

[0037] As another key auxiliary component of synergistic effect, the second additive, when preferably within the above range, can maintain high ion / electron conduction performance while reducing the gas generation probability and amount of the secondary battery during the cycle process, further improving the cycle life and cycle efficiency of the secondary battery.

[0038] In some embodiments, the secondary battery further comprises a negative electrode sheet comprising a negative electrode active material layer, and the secondary battery satisfies a / d = 0.3-1.5, where d is the graphitization degree of the negative electrode active material layer.

[0039] As the negative electrode corresponding to the positive electrode, the graphitization degree of its material is related to the overall kinetic performance and ion / electron transport efficiency of the secondary battery. The higher the graphitization degree, the better the kinetic performance of the secondary battery, the higher the ion / electron conduction efficiency, and the higher the conductivity. However, the interaction frequency between the negative electrode interface and the electrolyte increases, the probability of side reactions increases, the probability of generating high-impedance by-products increases, and the cycle stability performance decreases. In the secondary battery described in this application, since the first additive itself has the function of passivating interfacial side reactions, further optimizing the relationship between the amount of the first additive and the graphitization degree of the negative electrode based on the control of key parameters can further improve the electrochemical performance of the secondary battery.

[0040] More preferably, the a / d value is a range of one or any two of the following: 0.3, 0.4, 0.6, 0.8, 1, 1.2, 1.5.

[0041] In some implementations, a / d = 0.5 to 0.8.

[0042] In some implementations, d = 0.85 to 0.99.

[0043] More preferably, d is a range of one or any two of the following: 0.85, 0.88, 0.9, 0.91, 0.92, 0.95, 0.98, and 0.99.

[0044] In some implementations, d = 0.9 to 0.95.

[0045] It should be noted that the degree of graphitization of the negative electrode active material layer was confirmed by the following method:

[0046] After the secondary battery was disassembled in the glove box, the negative electrode sheet was scraped to remove powder. Then, the XRD characteristic peak spectrum of the powder was obtained by XRD diffraction. The graphite interplanar spacing d(002) of the powder was determined based on the spectrum. Finally, the degree of graphitization was calculated based on (0.3440-d(002)) / (0.3440-0.3354).

[0047] In some embodiments, the electrolyte further includes a solvent, which includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

[0048] In some embodiments, the secondary battery satisfies: c / w = 0.03 to 0.16, where w% is the mass percentage of solvent in the electrolyte.

[0049] The test method for the mass percentage content of the solvent is the same as that for the test methods for the mass percentage content of the first additive and the second additive, and will not be repeated here.

[0050] As described above, the adhesion of the separator will affect the ion transmission efficiency between the separator and the electrode sheet, and the main transmission carrier of the ion is the electrolyte, so the composition of the electrolyte itself is also related, thereby affecting the cycle performance and conductivity of the secondary battery. In addition to the additive, the solvent content in the electrolyte will affect the flowability of the electrolyte and the wettability of the separator and the electrode sheet. When the electrolyte in the above parameter range is matched with the separator, the interaction efficiency of the device in the secondary battery can be effectively improved, and ultimately the electrochemical performance is more optimal.

[0051] Further preferably, the c / w is one of 0.03, 0.04, 0.05, 0.08, 0.10, 0.12, 0.14, 0.15, 0.16 or a range value of any two thereof.

[0052] In some embodiments, the c / w is 0.06-0.12.

[0053] In some embodiments, the solvent includes at least one of a carbonate solvent and a carboxylic acid ester solvent.

[0054] In some embodiments, the carbonate solvent includes at least one of propylene carbonate, vinyl carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; and the carboxylic acid ester solvent includes at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone.

[0055] In some embodiments, the w is 80-95%.

[0056] Further preferably, the w is one of 80%, 82%, 85%, 88%, 90%, 92%, 93%, 95% or a range value of any two thereof.

[0057] In some embodiments, the w is 85-92%.

[0058] It should be noted that the method for confirming the content of the solvent in the electrolyte is the same as the method for confirming the first additive and the second additive.

[0059] In some embodiments, the electrolyte further includes a lithium salt.

[0060] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorobisoxalate borate, lithium triflate, lithium bisfluoromethanesulfonimide, lithium bis-trifluoromethanesulfonimide, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, etc.

[0061] Further preferably, the concentration of the lithium salt in the electrolyte is 0.8-2.5 mol / L.

[0062] 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 a range value of any two thereof.

[0063] In some embodiments, the positive electrode tab comprises a current collector and a positive active material layer disposed on the surface of the current collector, the positive active material layer comprising a positive active material, the positive active material comprising at least one of lithium nickel cobalt manganese oxide, doped lithium nickel cobalt manganese oxide.

[0064] In some embodiments, the mass percentage content of nickel element in the positive active material is ≥50%.

[0065] In some embodiments, the mass percentage content of nickel element in the positive active material is 50-70%.

[0066] Although the positive active material with medium-high nickel content has a high energy density, its working voltage is generally high and its cycle performance is poor, especially at high temperature, the gas production probability and amount increase, and the cycle life is further shortened. In the present application, based on the regulation of electrolyte composition and separator adhesion, the secondary battery can maintain good high-temperature cycle performance, low internal resistance value and long cycle life after the positive electrode tab is constructed with the positive active material with medium-high nickel content.

[0067] Further preferably, the positive active material comprises Li x Ni a Mn b Co c N d O2, wherein 1≤x≤1.1, a>0, b>0, c>0, 0≤d<0.1, a+b+c+d=1 and N is at least one of Al, Na, Ti, Nb, Zr, W, Fe, Cr.

[0068] Further preferably, the active material layer further comprises a binder and a conductive agent.

[0069] In some embodiments, the negative electrode tab comprises a current collector and a negative active material layer;

[0070] Further preferably, the negative active material layer comprises a negative active material, a binder, a thickening agent and a conductive agent.

[0071] In some embodiments, the negative active material comprises at least one of a carbon-based material, a silicon-based material, and a silicon-carbon composite material.

[0072] The present application is further illustrated in the following specific examples, which are not to be construed as limiting the scope of the application as claimed:

[0073] Example 1

[0074] A secondary battery, the preparation method comprising the following steps:

[0075] (1) Preparation of the positive electrode sheet: disperse the positive active material, conductive agent acetylene black, and binder polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of 96:2:2, prepare the slurry by vacuum stirring, then coat on both sides of the current collector aluminum foil, dry, cold-press, and cut to obtain the positive electrode sheet; the positive active material is Li 1.04 Ni 0.63 Co 0.09 Mn 0.28 O2;

[0076] (2) Preparation of the negative electrode sheet: disperse the negative active material, conductive agent acetylene black, thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber in water at a mass ratio of 96.4:1:1.2:1.4, prepare the slurry by vacuum stirring, then coat on both sides of the current collector copper foil, dry, cold-press, and cut to obtain the negative electrode sheet; the negative active material comprises graphite prepared at a graphitization temperature of 3000℃ and silicon-carbon composite material with a silicon content of 3%, the mass ratio of the two being 97:3, and the particle size D v50 of the negative active material is 8.5μm;

[0077] (3) Preparation of the separator: use PE separator with an average pore size of 45nm and a porosity of 45% as the substrate, then coat a single-sided 1.5μm aluminum oxide coating, dry to obtain the separator containing the coating;

[0078] The preparation process of the aluminum oxide coating slurry is as follows: mix nanoscale aluminum oxide powder, thickening agent sodium carboxymethyl cellulose, dispersing agent sodium polyethylene glycol alkyl aryl ether sulfonate, wetting agent ethanol, binder polyvinyl alcohol (molecular weight 5000), and water at a mass ratio of 10:0.5:0.1:0.5:2:100, stir at a speed of 500rpm, and grind for a total of 60min to obtain the slurry;

[0079] (4) Preparation of the electrolyte: mix the first and second additives, solvent, and lithium salt lithium hexafluorophosphate to obtain the electrolyte; the first additive is tris(dimethylvinylsilyl) phosphate, and the second additive is 1,3-propane sultone;

[0080] (5) The positive electrode sheet, the separator (the coating side is close to the positive electrode sheet), and the negative electrode sheet are sequentially stacked and roll-wound to assemble a battery cell, the battery cell is placed in an outer packaging shell, electrolyte is injected after drying, and the battery cell is vacuum packaged, left to stand, formed, and constant volume after standing, to obtain the secondary battery.

[0081] The electrolyte parameters, the graphitization degree of the negative electrode active material layer, and the adhesion of the separator are shown in Tables 1 and 2.

[0082] Examples 2-32

[0083] A secondary battery, which is different from Example 1 only in that the component composition of the electrolyte is different and / or the preparation process of the separator is different and / or the selection of the negative electrode active material is different, and the results are shown in Tables 1 and 2.

[0084] The adhesion of the separator is adjusted by adjusting the proportion of the binder in the slurry during preparation, the higher the proportion of the binder, the higher the adhesion of the separator.

[0085] The graphitization degree of the negative electrode active material layer is adjusted by adjusting the graphitization temperature during the preparation of graphite in the negative electrode active material, the higher the temperature, the higher the graphitization degree.

[0086] Example 33

[0087] A secondary battery, which is different from Example 1 only in that the positive electrode active material is Li 1.05 Ni 0.7 Co 0.2 Mn 0.1 O2, and the component composition of the electrolyte is different and / or the preparation process of the separator is different and / or the selection of the negative electrode active material is different, and the results are shown in Tables 1 and 2.

[0088] Example 34

[0089] A secondary battery, which is different from Example 1 only in that the positive electrode active material is Li 1.06 Ni 0.8 Co 0.1 Mn 0.1 O2, and the component composition of the electrolyte is different and / or the preparation process of the separator is different and / or the selection of the negative electrode active material is different, and the results are shown in Tables 1 and 2.

[0090] Comparative Examples 1-6

[0091] A battery, which is different from Example 1 only in that the component composition of the electrolyte is different and / or the preparation process of the separator is different and / or the selection of the negative electrode active material is different, and the results are shown in Tables 1 and 2.

[0092] Comparative Examples 7-8

[0093] A battery, which is different from Example 33 only in that the component composition of the electrolyte is different and / or the preparation process of the separator is different and / or the selection of the negative active material is different, and the results are shown in Tables 1 and 2.

[0094] Comparative Examples 9-10

[0095] A battery, which is different from Example 34 only in that the component composition of the electrolyte is different and / or the preparation process of the separator is different and / or the selection of the negative active material is different, and the results are shown in Tables 1 and 2.

[0096] Comparative Example 11

[0097] A battery, which is different from Example 3 only in that the first additive is replaced by lithium difluoro(oxalato)borate with the same mass percentage.

[0098] Comparative Example 12

[0099] A battery, which is different from Example 3 only in that the second additive is replaced by butane sulfone lactone with the same mass percentage.

[0100] Comparative Example 13

[0101] A battery, which is different from Example 3 only in that the first additive is replaced by the second additive with the same mass percentage, i.e. the electrolyte only contains the second additive.

[0102] Comparative Example 14

[0103] A battery, which is different from Example 3 only in that the second additive is replaced by the first additive with the same mass percentage, i.e. the electrolyte only contains the first additive.

[0104] Each electrolyte includes a first additive, a second additive, a lithium salt, a solvent, wherein a (wt%) and b (wt%) represent the mass percentage of the first additive and the second additive in the electrolyte, respectively. The lithium salt is lithium hexafluorophosphate, w (wt%) represents the mass percentage of the solvent in the electrolyte; d represents the graphitization degree of the negative active material layer, and c (N / m) represents the adhesion of the separator.

[0105] Table 1

[0106]

[0107]

[0108] Table 2

[0109]

[0110]

[0111] Effect Example

[0112] The secondary batteries obtained in each example and comparative example were subjected to the following tests.

[0113] (1) Cycle performance test: the secondary battery was subjected to charge-discharge cycle test at 45°C using a LAND charge-discharge system at a charge-discharge rate of 0.05C / 1C, a 0.05C cutoff current, and a working voltage of 2.5-4.25V for 1000 times. The discharge capacity after 1000 cycles was A1, and the first discharge capacity was A0. The cycle capacity retention rate (%) after 1000 cycles was calculated as 100%*A1 / A0.

[0114] (2) DCR test:

[0115] The secondary battery was subjected to constant current-constant voltage charging at 25°C at a rate of 0.33C to 3.65V, and the cutoff current was 0.05C. After 10 min, it was subjected to constant current discharging at 0.33C to 2.5V, and this was repeated for 2 cycles. After 10 min, it was subjected to constant current-constant voltage charging at 0.33C to 3.65V, and after discharging to 50% SOC of the second cycle discharge capacity, it was left to stand for 2 h. After 1C discharging for 18 s, the voltage at the start of discharging was V3, the voltage after 18 s of discharging was V4, the discharging current was I1, and the RDCR discharge (I1, 18 s) was |V3-V4| / I1.

[0116] The test results are shown in Table 3.

[0117] Table 3

[0118]

[0119]

[0120] According to Table 3, it can be seen that:

[0121] (1) The secondary battery described in the present application can realize stable ion transmission efficiency, low impedance of the interface film layer of the pole piece, and small probability of side reactions, and ultimately achieve excellent electrochemical performance, because the specific tris(dimethylvinylsilyl) phosphate and 1,3-propane sultone are introduced as additive components in the electrolyte, the addition content ratio of the two additives is adjusted, and the adhesion of the separator of the secondary battery is controlled.

[0122] (2) In contrast, in Comparative Examples 1-6, due to improper introduction of the additive ratio or improper adhesion of the separator, the parameter relationship (b*c) / a of the secondary battery construction does not meet the defined range of 1-10, and the high-temperature cycle stability and DCR performance of the product cannot be balanced, with the high-temperature cycle capacity retention rate being only about 67%, and the DCR being as high as 50 mΩ or more.

[0123] (3) As can be seen from the comparison of Comparative Examples 11-14 and the respective examples, the introduction of the first additive and the second additive in the electrolyte is very critical, the former can effectively improve the protection effect of the electrolyte on the positive electrode plate interface and reduce the impedance of the CEI film, and the latter can improve the cycle stability of the overall system by inhibiting the gas production effect, if either of them is missing or replaced by other conventional additive types, the same technical effect as the examples cannot be achieved.

[0124] (4) As can be seen from Examples 1-28, when (b*c) / a is further preferably in the range of 3-7, the electrochemical performance can be optimized to a higher degree, and since the addition amount of the first additive and the second additive will affect their performance, and as the negative electrode corresponding to the positive electrode plate, the graphitization degree of the material is related to the kinetic performance and ion / electron transmission efficiency of the overall secondary battery, the higher the graphitization degree, the better the kinetic performance of the secondary battery, the higher the conductivity, but the interaction frequency between the negative electrode interface and the electrolyte increases, and the probability of side reactions also increases, since the first additive itself has the effect of passivating the interface side reactions, further optimizing the relationship between the addition amount of the first additive and the graphitization degree of the negative electrode can also improve the electrochemical performance of the secondary battery; in addition, the adhesion of the separator will affect the ion transmission efficiency between the separator and the plate, and the main transmission carrier of the ion is the electrolyte, in addition to the additive, the solvent content in the electrolyte also affects the flowability of the electrolyte and the wettability of the separator and the plate, when the solvent content in the electrolyte and the adhesion of the separator are optimized in coordination, the interaction efficiency of the devices in the secondary battery can be effectively improved.

[0125] Therefore, when a = 0.5-7% and / or b = 0.2-0.4%, and / or a / d = 0.5-0.8, and / or c / w = 0.06-0.12, the performance of the secondary battery is more optimal, with the highest high-temperature cycle capacity retention rate being above 85%, and the DCR being reduced to within 38 mΩ.

Claims

1. A secondary battery, characterized by 1. The secondary battery includes a positive electrode sheet, a separator, and an electrolyte; The electrolyte includes a first additive and a second additive; The secondary battery satisfies (b*c) / a = 1-10; Wherein a% is the mass percentage content of the first additive in the electrolyte, b% is the mass percentage content of the second additive in the electrolyte, and c N / m is the adhesion of the separator; The first additive is tris(dimethylvinylsilyl) phosphate, and the second additive is 1,3-propane sultone.

2. The secondary battery according to claim 1, wherein The (b*c) / a = 3-7.

3. The secondary battery according to claim 1, wherein The mass percentage content of the first additive in the electrolyte is 0.3-1%, and / or the mass percentage content of the second additive in the electrolyte is 0.1-0.8%.

4. The secondary battery according to claim 1, wherein c = 3-15 N / m.

5. The secondary battery according to claim 1, wherein The secondary battery further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material layer, and the secondary battery satisfies a / d = 0.3-1.5, wherein d is the graphitization degree of the negative electrode active material layer.

6. The secondary battery according to claim 1, wherein The electrolyte further includes a solvent, and the solvent includes at least one of a carbonate-based solvent, a carboxylate-based solvent, an ether-based solvent, a sulfone-based solvent, a nitrile-based solvent, and a phosphate-based solvent.

7. The secondary battery according to claim 6, wherein the negative electrode is a lithium metal electrode. The secondary battery satisfies c / w = 0.03-0.16, wherein w% is the mass percentage content of the solvent in the electrolyte.

8. The secondary battery of claim 1, wherein The positive electrode sheet includes a current collector and a positive electrode active material layer disposed on the surface of the current collector, and the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide and doped lithium nickel cobalt manganese oxide.

9. The secondary battery according to claim 8, wherein the negative electrode is a lithium metal electrode. The mass percentage content of nickel in the positive electrode active material is ≥50%.

10. An electrical device, characterized by The secondary battery includes the secondary battery according to any one of claims 1-9, and the secondary battery is used as a power supply in an electrical device.

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