Secondary battery and electric device

Abstract

Provided are a secondary battery and an electric device. By reasonably designing the composition of an electrolyte and a positive electrode material of a secondary battery, the secondary battery satisfies formula I, wherein N is the molar ratio of lithium salts LiPO2F2 and LiPF6 in the electrolyte, and N = 0.01-11; W1 is the weight ratio of cyclic carbonate to chain carbonate; W2 is the weight percentage of element A in a positive electrode active material; and C is the weight percentage of a sulfur-containing additive in the electrolyte. Keeping formula II within a suitable range can ensure excellent kinetic performance and low impedance in a lithium-ion battery, so that the migration of lithium ions in the battery maintains a good state, and the secondary battery can maintain good cycle performance at a high voltage.

Description

A secondary battery and a power consuming device

[0001] The present application claims priority to the Chinese patent application No. 202411238261.7, filed on September 5, 2024, and entitled "A secondary battery and a power consuming device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a secondary battery and a power consuming device. BACKGROUND

[0003] With the entry of electric vehicles into millions of households, higher requirements are placed on power batteries. In order to meet the demand for the cruising range of electric vehicles, in addition to using high specific energy positive electrode materials, increasing the cut-off voltage of the battery is also an effective way to improve the energy density of the battery; however, the increase of the charging cut-off voltage is limited by the low oxidation stability of traditional carbonate electrolytes and their weak passivation ability on the positive electrode, in addition, the solid electrolyte interface layer (SEI layer) formed in the carbonate electrolyte with low ionic conductivity is not conducive to the cycle stability of the battery. SUMMARY

[0004] The purpose of the present application is to overcome the defects that the energy density and cycle stability of the existing secondary battery still need to be further improved, to reasonably design the composition of the electrolyte and the positive electrode material of the secondary battery, and to prepare a secondary battery with excellent comprehensive performance.

[0005] To achieve the above-mentioned purpose, the first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, the positive electrode active material in the positive electrode sheet comprises an A element, the A element comprises at least one of Al, Ti, Sr and W, the electrolyte comprises a cyclic carbonate, a chain carbonate, a lithium salt and a sulfur-containing additive; the lithium salt comprises LiPO2F2 and LiPF6;

[0006] The chain carbonate comprises ethyl methyl carbonate (EMC);

[0007] The mass percentage content of the ethyl methyl carbonate is greater than 50% based on the total weight of the electrolyte;

[0008] The secondary battery satisfies the following relationship:

[0009] Wherein, N is the mass ratio of the lithium salts LiPO2F2 and LiPF6 in the electrolyte, N = 0.01-11;

[0010] W1 is the weight ratio of the cyclic carbonate to the chain carbonate;

[0011] W2 is the weight percentage of the element A in the positive active material;

[0012] C is the weight percentage of the sulfur-containing additive in the electrolyte.

[0013] As an embodiment of the present application, the secondary battery satisfies:

[0014] As an embodiment of the present application, the secondary battery satisfies:

[0015] As an embodiment of the present application, the sulfur-containing additive includes at least one of 1,3-propane sultone (PS), vinyl sulfate (DTD), methane disulfonic acid methylene ester (MMDS), ethylene sulfite (ES), 1,4-butane sultone (1-4BS), and 1,3-propene sultone (PST).

[0016] As an embodiment of the present application, the sulfur-containing additive includes at least one of 1,3-propane sultone (PS), vinyl sulfate (DTD), and 1,3-propene sultone (PST).

[0017] As an embodiment of the present application, the sulfur-containing additive includes 1,3-propane sultone (PS) and 1,3-propene sultone (PST).

[0018] As an embodiment of the present application, the cyclic carbonate includes ethylene carbonate, and the mass fraction of the ethylene carbonate is 15% to 40% based on the total weight of the electrolyte.

[0019] As an embodiment of the present application, the secondary battery satisfies: W1 is 0.25 to 0.85.

[0020] As an embodiment of the present application, the secondary battery satisfies: W2 is 0.25% to 0.75%.

[0021] As an embodiment of the present application, the secondary battery satisfies: C is 0.1% to 5%.

[0022] As an embodiment of the present application, the electrolyte satisfies: the weight percentage of the lithium salt is 8% to 20% based on the total weight of the electrolyte.

[0023] As an embodiment of the present application, the lithium salt further includes at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorophosphate bis(oxalate), lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0024] As an embodiment of the present application, the cyclic carbonate further includes at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate.

[0025] As an embodiment of the present application, the chain carbonate further includes at least one of dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate.

[0026] In a second aspect of the present application, a power utilization device is provided, which includes the secondary battery of the first aspect of the present application.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] By reasonably designing the composition of the electrolyte and the positive electrode material of the secondary battery, the present application can maintain a suitable range, which can ensure excellent kinetic performance and low impedance in the lithium ion battery, so that the migration of lithium ions in the battery is maintained in a good state, and the secondary battery can maintain good cycle performance at high voltage. DETAILED DESCRIPTION

[0029] For better illustration of the purpose, technical solution and advantages of the present application, the present application will be further illustrated by specific examples below, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field. Unless otherwise specified, the reagents and materials used in the present application are commercially available.

[0030] The embodiments of the present application provide a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, the positive electrode active material in the positive electrode sheet includes an A element, the A element includes at least one of Al, Ti, Sr and W, the electrolyte includes a cyclic carbonate, a chain carbonate, a lithium salt and a sulfur-containing additive, the lithium salt includes LiPO2F2 and LiPF6;

[0031] The chain carbonate includes methyl ethyl carbonate (EMC);

[0032] The mass percentage of the methyl ethyl carbonate is greater than 50% based on the total weight of the electrolyte;

[0033] The secondary battery satisfies the following relationship:

[0034] Wherein, N is the mass ratio of the lithium salts LiPO2F2 and LiPF6 in the electrolyte, N = 0.01-11;

[0035] W1 is the weight ratio of the cyclic carbonate to the chain carbonate;

[0036] W2 is the weight percentage of element A in the positive electrode active material;

[0037] C is the weight percentage of sulfur-containing additive in the electrolyte.

[0038] The inventors of the present application have found that the ratio of cyclic carbonate to chain carbonate, the content of sulfur-containing additive, the content of element A in the positive electrode material, and the molar ratio of LiPO2F2 / LiPF6 in the secondary battery have a significant correlation with the performance of the secondary battery. By reasonably setting the above parameters to meet a specific relationship, the interface stability can be effectively improved and the interface impedance can be reduced.

[0039] The present application adds a double lithium salt to the electrolyte. The double salt system is beneficial to improve the interface stability and reduce the interface impedance. LiPO2F2 has excellent film-forming stability, which can reduce the initial internal resistance of the battery and inhibit the increase of internal resistance during the cycle process, thereby improving the capacity retention rate of the battery at room temperature. However, the solubility in the electrolyte is poor, and adding too much LiPO2F2 can cause a decrease in conductivity and a significant increase in impedance. The inventors of the present application have further found that when the ratio of cyclic carbonate to chain carbonate, the content of sulfur-containing additive, the content of element A in the positive electrode material, and the molar ratio of LiPO2F2 / LiPF6 in the secondary battery meet the above relationship, the secondary battery has good comprehensive performance, which meets the needs of new power batteries.

[0040] The addition of methyl ethyl carbonate in the electrolyte helps to improve the electrochemical performance of the battery at low temperature. However, if the addition amount is too high, it will cause the internal resistance to be too high, which will affect the development of the positive electrode capacity and further affect the cycle performance of the battery. Moreover, too much electrolyte may cause the battery to swell during the later cycle stage, which will affect the sealing and safety of the battery. However, by reasonably designing the parameters of the present application to meet the above specific relationship, the addition amount of methyl ethyl carbonate in the electrolyte can be further increased.

[0041] In some embodiments, the secondary battery satisfies:

[0042] When the relationship in the secondary battery falls within the above range, the cycle retention rate of the secondary battery is more excellent, and can reach more than 90% after 500 cycles.

[0043] In some embodiments, the secondary battery satisfies:

[0044] When the relationship in the secondary battery falls within the above range, the cycle retention rate and the direct current internal resistance (DCR) growth rate of the secondary battery are both maintained at an excellent level, and the growth rate of DCR is more slowly, and the DCR growth rate can be maintained within 20% after 500 cycles.

[0045] In some embodiments, the mass percentage of the ethyl methyl carbonate is greater than 55%, for example, can be any one of 56%, 58%, 60%, 62%, 64%, 65%, 67% or a range value between any two of them, based on the total weight of the electrolyte.

[0046] In some embodiments, the mass percentage of the ethyl methyl carbonate is less than 68%, based on the total weight of the electrolyte.

[0047] In some embodiments, the weight ratio W1 of the cyclic carbonate and the chain carbonate in the secondary battery satisfies: W1 is 0.25-0.85, and the W1 can be any one of 0.25, 0.43, 0.50, 0.65, 0.85 or a range value between any two of them. The cyclic carbonate solvent has high dielectric constant and large viscosity, the chain carbonate solvent has low dielectric constant and low viscosity, and controlling the ratio of the cyclic carbonate solvent and the chain carbonate solvent in a suitable range helps to improve the kinetic performance of the secondary battery.

[0048] In some embodiments, the weight percentage W2 of the A element in the positive electrode active material is 0.25%-0.75%, and the W2 can be any one of 0.25%, 0.4%, 0.5%, 0.6%, 0.75% or a range value between any two of them. The A element in the positive electrode active material can effectively improve the capacity retention rate of the battery under normal temperature cycling and reduce the DCR growth of the battery; this is because the introduction of A suppresses the lattice distortion caused by irreversible phase change, reduces the side reaction, and improves the migration kinetics of Li + .

[0049] In some embodiments, the mass concentration C of the sulfur-containing additive in the electrolyte is 0.1%-5%, and further preferably 0.1%-3%. The C can be any one of 0.1%, 1%, 2%, 3%, 4%, 5% or a range value between any two of them. The sulfur-containing additive can reduce the initial internal resistance of the battery and inhibit the internal resistance growth of the battery during storage, thereby improving the capacity retention rate under normal temperature cycling and high temperature storage. The main reason is that it can form a dense CEI interface film containing sulfur substances (Li2SO b ) at the positive electrode, improve the interface stability and reduce the interface impedance. The appropriate addition amount of the sulfur-containing additive can ensure that the electrolyte has a suitable viscosity, so that the migration of lithium ions in the battery is maintained in a good state, and the lithium ion secondary battery can maintain good cycle performance at high voltage.

[0050] In some embodiments, the sulfur-containing additive includes at least one of 1,3- propanesultone (PS), vinyl sulfates (DTD), methane disulfonic acid methylene ester (MMDS), ethylene sulfite (ES), 1,4 butanesultone (1-4BS), 1,3-propene sultone (PST).

[0051] In some embodiments, the sulfur-containing additive includes 1,3-propanesultone (PS), and at least one of vinyl sulfates (DTD), 1,3-propene sultone (PST).

[0052] In some embodiments, the sulfur-containing additive includes 1,3-propanesultone (PS) and 1,3-propene sultone (PST).

[0053] In some embodiments, the weight ratio of 1,3-propanesultone and 1,3-propene sultone is 0.1-20, specifically can be any one value or a range value between any two values of 0.1, 0.5, 2.5, 5, 7.5, 10, 15, 20. Limiting the weight ratio of the above-mentioned sulfur-containing additive within the range, the sulfur-containing additive can be decomposed to generate Li2S e O f , promote the formation of more uniform and dense SEI film, thereby further improving the cycle stability of the secondary battery and reducing the DCR.

[0054] In some embodiments, the electrolyte satisfies: the weight percentage of the lithium salt is 8%-20% based on the total weight of the electrolyte, specifically can be any one value or a range value between any two values of 8%, 12.6%, 14.96, 18.2%, 20%. The appropriate lithium salt concentration can ensure that the conductivity and viscosity are within the appropriate range, thereby ensuring the migration rate of active ions. Selecting a double lithium salt system can also improve the stability of the electrolyte and the cycle stability of the secondary battery.

[0055] In some embodiments, the lithium salt further includes at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide.

[0056] In some embodiments, the cyclic carbonate includes ethylene carbonate, and the mass percentage of ethylene carbonate is 15%-40% based on the total weight of the electrolyte, specifically can be any one value or a range value between any two values of 15%, 20%, 25%, 30%, 35%, 40%.

[0057] In some embodiments, the cyclic carbonate includes ethylene carbonate, and the sum of the mass percentages of the ethyl methyl carbonate and the ethylene carbonate based on the total weight of the electrolyte is greater than 75%.

[0058] In some embodiments, the cyclic carbonate includes ethylene carbonate, and the sum of the mass percentages of the ethyl methyl carbonate and the ethylene carbonate is greater than 80% based on the total weight of the electrolyte.

[0059] In some embodiments, the cyclic carbonate includes ethylene carbonate, and the sum of the content of the ethyl methyl carbonate and the ethylene carbonate is less than 90% based on the total weight of the electrolyte.

[0060] Ethylene carbonate has a high dielectric constant, and the graphite negative electrode has good compatibility, the SEI film formed on the graphite negative electrode has good passivation effect, which can effectively inhibit the further reduction of the anode to the electrolyte. The dielectric constant of ethylene carbonate solvent is high, and the viscosity is large, while the dielectric constant of ethyl methyl carbonate solvent is low, and the viscosity is low. Controlling the content of the two in a suitable range helps to improve the kinetic performance of the secondary battery.

[0061] In some embodiments, the cyclic carbonate further includes at least one of vinylene carbonate, vinyl ethylene carbonate, fluorinated ethylene carbonate, difluorinated ethylene carbonate.

[0062] In some embodiments, the chain carbonate further includes at least one of dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate. In some embodiments, the electrolyte further includes a silicon-containing additive, and the silicon-containing additive includes at least one of tris(trimethylsilyl)phosphite, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, trimethylfluorosilane, and heptamethyldisilazane.

[0063] In some embodiments, the positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and containing a positive electrode active material, and the positive electrode active material includes a compound with a chemical formula of Li a Ni x Co y Mn z A (1-x-y-z) O2, A includes at least one of Al, Ti, Sr, and W, 0.9≤a≤1.1, 0

[0064] In some embodiments, the positive electrode material can further include an M element, and the M element includes at least one of Zr, Zn, Cu, Cr, Mg, Fe, V, Y, Nb, In, La, Ce, Sb, and B.

[0065] The M element can be incorporated into the positive electrode active material by doping and / or surface coating, and the test method of the M element in the application is as follows: the positive electrode sheet is cut into small round sheets with a diameter of 12±2mm, 20 small round sheets are taken for ICP test, and the reference is EPA6010D-2018 inductively coupled plasma atomic emission spectrometry.

[0066] In some embodiments, the 0.5

[0067] In some embodiments, the 0.5

[0068] In some embodiments, the 0.5

[0069] In some embodiments, the 0.5

[0070] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and containing a negative electrode active material, the negative electrode active material includes a silicon-carbon composite material formed by a silicon-based material and a carbon-based material, the silicon-based material includes at least one of silicon element, silicon-oxygen material and silicon-carbon material; the carbon-based material includes graphite.

[0071] The second aspect of the application also provides a power utilization device, which includes the secondary battery of the first aspect of the application; the power utilization device includes but is not limited to electric vehicles and energy storage devices.

[0072] The following are specific embodiments of the application, and the technical solutions of the application are further described in combination with the embodiments, but the application is not limited to these embodiments. The reagents, methods and equipment used in the application are conventional reagents, methods and equipment in the technical field, unless otherwise specified.

[0073] Example 1

[0074] The present embodiment and comparative example provide a secondary battery, and the specific preparation process includes the following steps:

[0075] (1) Preparation of the positive electrode sheet:

[0076] The Al-containing compound Al(NO3)3·9H2O is dissolved in anhydrous ethanol to obtain an aluminum-containing solution. The mixture of the aluminum-containing solution, the positive electrode NCM (nickel-cobalt-manganese hydroxide) precursor and lithium hydroxide is further calcined at 300°C for 4h, and then calcined at 750°C in an O2 atmosphere for 6h to obtain the positive electrode active material Li(Ni 0.6 Mn0.28 Co 0.1 Al 0.02 )O2(NCM), the Al element accounts for 0.5% of the mass ratio of the positive active material; then the positive active material, the conductive agent acetylene black (Super P) and the binder polyvinylidene fluoride (PVDF) are uniformly mixed in a mass ratio of NCM:Super P:PVDF = 94:3:3, and uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. After the mixed black slurry is coated on both sides of the aluminum foil, it is baked, rolled, and cut into pieces to obtain a positive electrode sheet.

[0077] (2) Preparation of the negative electrode sheet:

[0078] The negative active material graphite, the conductive agent acetylene black (Super P) and the binder SBR are uniformly mixed in a mass ratio of graphite:Super P:SBR = 94:3:3, and uniformly dispersed in deionized water to form a uniform black slurry. After the mixed slurry is coated on both sides of the copper foil, it is baked, rolled, and cut into pieces to obtain a negative electrode sheet.

[0079] (3) Preparation of the electrolyte:

[0080] In a glove box filled with argon (H2O <1 ppm, O2 <1 ppm) at room temperature, ethylene carbonate (EC) and methyl ethyl carbonate (EMC) are uniformly mixed, dehydrated with 4A molecular sieves, and then mixed with lithium salt to obtain a mixed solvent. The electrolyte is obtained by continuously stirring and cooling with dry ice to ensure that the temperature of the electrolyte does not increase by more than 2°C. Then, a sulfur-containing additive is added, and the electrolyte is obtained after uniform mixing. The specific composition of the electrolyte is shown in Table 1.

[0081] Table 1

[0082] (4) Preparation of the lithium ion battery:

[0083] The prepared positive electrode sheet, separator (polyethylene), and negative electrode sheet are stacked in order with the separator between the positive and negative electrode sheets, and then wound, heat pressed, and shaped, and the tab is welded to obtain a bare cell. The bare cell is placed in an outer packaging aluminum plastic film and placed in an oven at 85±10°C for 24h. The electrolyte prepared above is injected into the dried battery, and then the lithium ion secondary battery is prepared after standing, formation, and capacity distribution.

[0084] Examples 2-24 and Comparative Examples 1-6

[0085] ​The preparation methods of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery are basically the same as those of Embodiment 1, and the changed parameters are the composition parameters of the electrolyte and the positive active material. For details, see Table 2. It should be noted that in the examples listed in Table 2, unless otherwise specified, the variables are single-factor variables. For example, in Examples 1-3, the variable is the mass ratio of lithium salts LiPO2F2 and LiPF6, but the total amount of lithium salts in the electrolyte remains unchanged.

[0086] Table 2

[0087] Example 25

[0088] The embodiment provides a secondary battery, wherein the preparation methods of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery are basically the same as those of Embodiment 1, and the difference from Embodiment 1 is that in the electrolyte, the total amount of sulfur-containing additives is kept unchanged, and the sulfur-containing additives further include 1,3-propylene sulfite, wherein the weight ratio of 1,3-propane sulfite and 1,3-propylene sulfite is 25.

[0089] Example 26

[0090] The embodiment provides a secondary battery, wherein the preparation methods of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery are basically the same as those of Embodiment 1, and the difference from Embodiment 1 is that in the electrolyte, the total amount of sulfur-containing additives is kept unchanged, and the sulfur-containing additives further include 1,3-propylene sulfite, wherein the weight ratio of 1,3-propane sulfite and 1,3-propylene sulfite is 10.

[0091] Example 27

[0092] The embodiment provides a secondary battery, wherein the preparation methods of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery are basically the same as those of Embodiment 1, and the difference from Embodiment 1 is that in the electrolyte, the total amount of sulfur-containing additives is kept unchanged, and the sulfur-containing additives further include 1,3-propylene sulfite, wherein the weight ratio of 1,3-propane sulfite and 1,3-propylene sulfite is 20.

[0093] Example 28

[0094] The embodiment provides a secondary battery, wherein the preparation methods of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery are basically the same as those of Embodiment 1, and the difference from Embodiment 1 is that in the electrolyte, the total amount of sulfur-containing additives is kept unchanged, and the sulfur-containing additives further include 1,3-propylene sulfite, wherein the weight ratio of 1,3-propane sulfite and 1,3-propylene sulfite is 0.1.

[0095] Example 29

[0096] This embodiment provides a secondary battery, wherein the preparation method of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery is basically the same as that of Embodiment 1, and the difference from Embodiment 1 is that in the electrolyte, the sulfur-containing additive is replaced by an equal amount of methylene methane disulfonate.

[0097] Embodiment 30

[0098] This embodiment provides a secondary battery, wherein the preparation method of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery is basically the same as that of Embodiment 1, and the difference from Embodiment 1 is that in the electrolyte, the sulfur-containing additive is replaced by an equal amount of 1,4 butane sultone.

[0099] Embodiment 31

[0100] This embodiment provides a secondary battery, wherein the preparation method of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery is basically the same as that of Embodiment 1, and the difference from Embodiment 1 is that in the electrolyte, the total weight of the chain carbonate is kept unchanged, and the ethyl methyl carbonate is replaced by an equal amount of mixed chain carbonate, and the mixed chain carbonate is composed of components in the following weight ratio: ethyl methyl carbonate: dimethyl carbonate = 20: 1.

[0101] Embodiment 32

[0102] This embodiment provides a secondary battery, wherein the preparation method of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery is basically the same as that of Embodiment 1, and the difference from Embodiment 1 is that in the electrolyte, the total weight of the chain carbonate is kept unchanged, and the ethyl methyl carbonate is replaced by an equal amount of mixed chain carbonate, and the mixed chain carbonate is composed of components in the following weight ratio: ethyl methyl carbonate: dimethyl carbonate: diethyl carbonate: methyl propyl carbonate: ethyl propyl carbonate = 60: 1: 1: 0.5: 0.5.

[0103] Embodiment 33

[0104] This embodiment provides a secondary battery, wherein the preparation method of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery is basically the same as that of Embodiment 1, and the difference from Embodiment 1 is that in the electrolyte, the total weight of the cyclic carbonate is kept unchanged, and the cyclic carbonate is composed of components in the following weight ratio: vinyl carbonate: difluoro vinyl carbonate = 2: 1.

[0105] Embodiment 34

[0106] The embodiment provides a secondary battery, wherein the preparation mode of the positive electrode sheet, the negative electrode sheet, the diaphragm and the lithium ion battery is basically consistent with that of the embodiment 1, and the difference from the embodiment 1 is that in the electrolyte, the total weight of lithium salt is kept unchanged, and the composition of the lithium salt comprises components in the following weight ratio: LiPO2F2: LiPF6: lithium difluoro (oxalato) borate: lithium bis (trifluoromethylsulfonyl) imide = 1: 1: 0.5: 0.5.

[0107] Embodiment 35

[0108] The embodiment provides a secondary battery, wherein the preparation mode of the positive electrode sheet, the negative electrode sheet, the diaphragm and the lithium ion battery is basically consistent with that of the embodiment 1, and the difference from the embodiment 1 is that in the electrolyte, the total weight of lithium salt is kept unchanged, and the composition of the lithium salt comprises components in the following weight ratio: LiPO2F2: LiPF6: lithium difluoro (oxalato) borate: lithium bis (trifluoromethylsulfonyl) imide = 1: 1: 0.5: 0.5.

[0109] Embodiment 36

[0110] The embodiment provides a secondary battery, wherein the preparation mode of the positive electrode sheet, the negative electrode sheet, the diaphragm and the lithium ion battery is basically consistent with that of the embodiment 1, and the difference from the embodiment 1 is that in the electrolyte, the mass ratio of LiPO2F2 and LiPF6 in the lithium salt is kept unchanged, the addition amount of the lithium salt is changed to 14.96%, and each component in the chain carbonate and the cyclic carbonate is reduced in proportion to keep the total amount of the electrolyte as 100%.

[0111] Embodiment 37

[0112] The embodiment provides a secondary battery, wherein the preparation mode of the positive electrode sheet, the negative electrode sheet, the diaphragm and the lithium ion battery is basically consistent with that of the embodiment 1, and the difference from the embodiment 1 is that in the electrolyte, the mass ratio of LiPO2F2 and LiPF6 in the lithium salt is kept unchanged, the addition amount of the lithium salt is changed to 18.2%, and each component in the chain carbonate and the cyclic carbonate is reduced in proportion to keep the total amount of the electrolyte as 100%.

[0113] Embodiment 38

[0114] The embodiment provides a secondary battery, wherein the preparation mode of the positive electrode sheet, the negative electrode sheet, the diaphragm and the lithium ion battery is basically consistent with that of the embodiment 1, and the difference from the embodiment 1 is that in the electrolyte, the mass ratio of LiPO2F2 and LiPF6 in the lithium salt is kept unchanged, the addition amount of the lithium salt is changed to 18.2%, and each component in the chain carbonate and the cyclic carbonate is reduced in proportion to keep the total amount of the electrolyte as 100%.

[0115] Embodiment 39

[0116] The embodiment provides a secondary battery, wherein the preparation mode of a positive electrode sheet, a negative electrode sheet, a diaphragm, an electrolyte and a lithium ion battery is basically consistent with that of the embodiment 1, and the difference from the embodiment 1 is that the preparation of a positive electrode active material: a W-containing compound WO3 is dissolved into ethanol to obtain a tungsten-containing solution, the tungsten-containing solution and an NCM precursor mixture are continuously calcined at 300 DEG C for 4h, and then calcined in an O2 atmosphere at 750 DEG C for 6h to obtain the positive electrode active material Li(Ni 0.6 Mn 0.2973 Co 0.1 W 0.0027 )O2, and the mass percentage of the W element in the positive electrode active material is 0.5%.

[0117] Embodiment 40

[0118] The embodiment provides a secondary battery, wherein the preparation mode of a positive electrode sheet, a negative electrode sheet, a diaphragm, an electrolyte and a lithium ion battery is basically consistent with that of the embodiment 1, and the difference from the embodiment 1 is that the preparation of a positive electrode active material: the titanium acid tetramethyl is dissolved into ethanol to obtain a titanium-containing solution, the mixture of the titanium-containing solution, an NCM precursor and lithium hydroxide is continuously calcined at 300 DEG C for 4h, and then calcined in an O2 atmosphere at 750 DEG C for 6h to obtain the positive electrode active material Li(Ni 0.6 Mn 0.3 Co 0.1 Ti 0.0087 )O2, and the mass percentage of the Ti element in the positive electrode active material is 1.5%.

[0119] Embodiment 41

[0120] The embodiment provides a secondary battery, wherein the preparation mode of a positive electrode sheet, a negative electrode sheet, a diaphragm, an electrolyte and a lithium ion battery is basically consistent with that of the embodiment 1, and the difference from the embodiment 1 is that the preparation of a positive electrode active material: the titanium acid tetramethyl and WO3 are dissolved into ethanol to obtain a titanium-containing and tungsten-containing solution, the mixture of the solution, an NCM precursor and lithium hydroxide is continuously calcined at 300 DEG C for 4h, and then calcined in an O2 atmosphere at 750 DEG C for 6h to obtain the positive electrode active material Li(Ni 0.6 Mn 0.3 Co 0.1 Ti 0.0044 W 0.0032 )O2, the mass percentage of the Ti element in the positive electrode active material is 0.75%, and the mass percentage of the W element in the positive electrode active material is 0.75%.

[0121] Comparative example 7

[0122] The comparative example provides a secondary battery, and the preparation mode of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery is basically consistent with that of example 1, and the difference from example 1 is that the black slurry for preparing the positive electrode sheet is not added with the aluminum-containing solution.

[0123] Comparative example 8

[0124] The comparative example provides a secondary battery, and the preparation mode of the positive electrode sheet, the negative electrode sheet, the separator and the lithium ion battery is basically consistent with that of example 1, and the difference from example 1 is that the black slurry for preparing the positive electrode sheet is not added with the aluminum-containing solution.

[0125] Performance test

[0126] The performance of the secondary batteries obtained in the above examples and comparative examples is tested, and the specific test items, test methods and results are as follows:

[0127] (1) Normal temperature DCR test: at 25±2℃, the soft package battery obtained in each example and comparative example is charged at 1C to 4.5V, and then discharged at 1C capacity for 30min, and then adjusted to 50% SOC, and then discharged at 10C constant current pulse for 10s, and then adjusted to 50% SOC according to the above SOC adjustment method, and then charged for 10s, and then calculated DCR=(voltage before pulse discharge-voltage after pulse discharge) / discharge current*100%. After 500 cycles, the DCR is tested again, and the DCR change rate=(500 cycles DCR-initial DCR) / initial DCR*100%.

[0128] (2) Normal temperature cycle performance test: at 25±2℃, the soft package battery obtained in each example and comparative example is charged and discharged at 1C / 2C in the range of 2.8-4.5V, and the discharge specific capacity of the battery after 500 cycles is recorded. The capacity retention rate of 500 cycles=500 cycles discharge specific capacity / first cycle discharge specific capacity*100%, and the data is recorded in table 3.

[0129] Table 3 Performance test results of the secondary batteries prepared in examples and comparative examples

[0130] From the above results, it can be seen that:

[0131] Through reasonable design of the composition of the electrolyte of the secondary battery and the positive electrode material, the present application can Keeping in a proper range, it can guarantee the excellent dynamic performance and low impedance in lithium ion battery, so that the migration of lithium ion in the battery is maintained in a good state, and the secondary battery can maintain good cycle performance at high voltage.

[0132] Specifically, the initial DCR of the obtained secondary battery is below 22 mΩ, and the lowest can be 14.7 mΩ; the cycle retention rate is above 86%, and the highest can be 94.5%; the internal resistance growth rate is below 25.5%, and the lowest can be 17.8%.

[0133] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not a limitation on the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode active material in the positive electrode comprises element A, and the element A includes at least one selected from Al, Ti, Sr, and W; the electrolyte comprises cyclic carbonate, chain carbonate, lithium salt, and sulfur-containing additive; and the lithium salt includes LiPO2F2 and LiPF6. The chain carbonates include ethyl methyl carbonate; Based on the total weight of the electrolyte, the mass percentage of methyl ethyl carbonate is greater than 50%; The secondary battery satisfies the following relationship: in, N is the mass ratio of lithium salts LiPO2F2 and LiPF6 in the electrolyte, N = 0.01-11; W1 is the weight ratio of cyclic carbonate to chain carbonate; W2 represents the weight percentage of element A in the positive electrode active material; C represents the weight percentage of sulfur-containing additives in the electrolyte.

2. The secondary battery according to claim 1, wherein, The secondary battery satisfies:

3. The secondary battery according to claim 1, wherein, The secondary battery satisfies:

4. The secondary battery according to any one of claims 1-3, wherein, The secondary battery satisfies at least one of the following characteristics: W1 is 0.25-0.85; W2 is 0.25%-0.75%; C is 0.1%-5%.

5. The secondary battery according to any one of claims 1-3, wherein, Based on the total weight of the electrolyte, the mass percentage of methyl ethyl carbonate is less than 68%.

6. The secondary battery according to any one of claims 1-3, wherein, The sulfur-containing additive includes at least one of 1,3-propanesulfonate lactone, vinyl sulfate, methylene disulfonate, vinyl sulfite, 1,4-butanesulfonate lactone, and 1,3-propenesulfonate lactone.

7. The secondary battery according to any one of claims 1-3, wherein, The sulfur-containing additive includes at least one of 1,3-propanesulfonate lactone, vinyl sulfate, and 1,3-propenesulfonate lactone.

8. The secondary battery according to any one of claims 1-3, wherein, The sulfur-containing additives include 1,3-propanesulfonate lactone and 1,3-propenesulfonate lactone.

9. The secondary battery according to claim 8, wherein, The weight ratio of 1,3-propanesulfonate lactone to 1,3-propenesulfonate lactone is 0.1-20.

10. The secondary battery according to any one of claims 1-3, wherein, The cyclic carbonate includes ethylene carbonate, and the mass fraction of the ethylene carbonate is 15%-40% based on the total weight of the electrolyte.

11. The secondary battery according to any one of claims 1-3, wherein, The cyclic carbonate includes ethylene carbonate, and the sum of the mass percentages of methyl ethyl carbonate and ethylene carbonate is greater than 75% based on the total weight of the electrolyte.

12. The secondary battery according to any one of claims 1-3, wherein, The electrolyte satisfies at least one of the following characteristics: Based on the total weight of the electrolyte, the lithium salt comprises 8%-20% by weight; The lithium salt also includes at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium difluorodi(oxalato)phosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide. The cyclic carbonates also include at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; The chain carbonate also includes at least one of dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

13. The secondary battery according to any one of claims 1-3, wherein, The electrolyte also includes a silicon-containing additive, which includes at least one of tris(trimethylsilane) phosphite, tris(trimethylsilane) phosphate, tris(trimethylsilyl) borate, trimethylfluorosilane, and heptamethyldisilazane.

14. The secondary battery according to any one of claims 1-3, wherein, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector and containing a positive active material. The positive active material includes materials with the chemical formula Li. a Ni x Co y Mn z A (1-x-y-z) Compounds of O2, where A includes at least one of Al, Ti, Sr, and W, 0.9 ≤ a ≤ 1.1, 0 < x < 1, 0 < y < 1, 0 <z<1,x+y+z<1。 15. The secondary battery according to claim 14, wherein, The positive electrode active material satisfies at least one of the following characteristics: 0.5 < x < 0.8, and 0.04 < y < 0.17; 0.5 < x < 0.8, and 0.04 < y < 0.14; 0.5 < x < 0.8, and 0.2 < z < 0.4; or 0.5<x<0.72, 0.25<z<0.4, 0.04<y<0.

15.

16. The secondary battery according to claim 14, wherein, The cathode material further includes element M, which includes at least one of Zr, Zn, Cu, Cr, Mg, Fe, V, Y, Nb, In, La, Ce, Sb, and B.

17. The secondary battery according to any one of claims 1-3, wherein, The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector and containing a negative active material, wherein the negative active material includes a silicon-carbon composite material formed by silicon-based materials and carbon-based materials.

18. The secondary battery according to claim 17, wherein, The silicon-based material includes at least one of elemental silicon, silicon-oxygen materials, and silicon-carbon materials.

19. The secondary battery according to claim 17, wherein, The carbon-based material includes graphite.

20. An electrical appliance, wherein, Includes the secondary battery as described in any one of claims 1-19.

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