Electrolyte, secondary battery and electrical equipment

Abstract

This application discloses an electrolyte, a secondary battery, and an electrical device, belonging to the field of secondary battery technology. The electrolyte includes a lithium salt, an organic solvent, and a first additive; the first additive includes at least one of the compounds represented by Formula I and Formula II. The electrolyte of the present application can form a dense, stable, and strong protective film on the surface of the positive electrode, protecting the integrity of the positive electrode particles during the cycle process, and inhibiting flatulence caused by oxidative decomposition of the electrolyte and transition metal dissolution caused by HF attack on the positive electrode material, thereby improving the cycle performance of the secondary battery and improving the battery's high-temperature storage gas production.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to electrolytes, secondary batteries and electrical equipment. Background Art

[0002] The vigorous development of global industrialization has led to the increasing depletion of traditional fossil energy and serious environmental pollution problems, forcing humanity to seek a transformation in the new energy structure. Among them, secondary batteries are widely used in portable electronic products and new energy vehicles due to their advantages such as high operating voltage, long cycle life, high energy density, low self-discharge, and no memory effect. With the development of new energy vehicles, people have put forward higher requirements for the energy density and cycle life of secondary batteries. In order to obtain higher energy density, the Ni content in NCM ternary positive electrode materials has been continuously increased. However, with the increase in Ni content, lattice oxygen is easily released from the positive electrode surface. At the same time, the strong catalytic property of tetravalent Ni ions makes it easy for the electrolyte to undergo oxidative decomposition on the positive electrode surface and produce a large amount of gas, which leads to rapid degradation of the electrochemical performance of secondary batteries. Summary of the Invention

[0003] The purpose of this application is to provide an electrolyte that can improve the technical problems of existing batteries.

[0004] An embodiment of the present application provides an electrolyte, wherein the electrolyte includes a lithium salt, an organic solvent, and a first additive; the first additive includes at least one of the compounds shown in Formula I and Formula II:

[0005]

[0006] wherein R1, R2, R3, R4, R5, and R6 are independently selected from the group consisting of fluorine-substituted or unsubstituted C1-C6 alkyl, fluorine-substituted or unsubstituted C2-C6 alkenyl, fluorine-substituted or unsubstituted C2-C6 alkynyl, fluorine-substituted or unsubstituted C2-C6 alkoxy, fluorine-substituted or unsubstituted C2-C6 amino, fluorine-substituted or unsubstituted C6-C 12 aryl, fluorine-substituted or unsubstituted C5~C 12 At least one of the heterocyclic groups.

[0007] Optionally, in some embodiments of the present application, the first additive includes at least one of the compounds shown in Formula (A1) to Formula (A4):

[0008]

[0009] Optionally, in some embodiments of the present application, the mass fraction of the first additive in the electrolyte is 0.1 wt%-5.0 wt%. Preferably, the mass fraction of the first additive in the electrolyte is 0.5 wt%-2.0 wt%. In the electrolyte of the present application, too little first additive may result in a passivation film that is too thin and easily ruptured at the interface, failing to effectively inhibit the continued oxidative decomposition of the electrolyte. Too much first additive may result in a passivation film that is too thick at the interface, increasing the impedance and polarization of the battery.

[0010] Optionally, in some embodiments of the present application, the mass fraction of the lithium salt in the electrolyte is 10wt%-15wt%. Preferably, the mass fraction of the lithium salt in the electrolyte is 12wt%-13wt%. In the electrolyte of the present application, too low a content of lithium salt affects the conductivity of the electrolyte, while too high a content increases the viscosity of the electrolyte.

[0011] Optionally, in some embodiments of the present application, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). Preferably, the lithium salt is lithium hexafluorophosphate (LiPF6).

[0012] Optionally, in some embodiments of the present application, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), diphenyl carbonate (DPhC), methyl formate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (γ-GBL), acetonitrile (AN) and cyclopentane sulfone (TMS).

[0013] Optionally, in some embodiments of the present application, the electrolyte further includes a second additive, the second additive including at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinyl sulfite (ES), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) phosphite (TMSPi), tripropargyl phosphate (TPP), 1,3-propane sultone (PS), and lithium difluorophosphate (LiPO2F2). The simultaneous use of the second additive and the first additive in the electrolyte can further improve the stability and density of the interface film, prevent the continuous decomposition of the electrolyte on the positive and negative electrode surfaces, and thus significantly improve the cycle performance and high-temperature storage gas production of the secondary battery.

[0014] Optionally, in some embodiments of the present application, the mass fraction of the second additive in the electrolyte is 0.01 wt% to 10 wt%.

[0015] In addition, an embodiment of the present application further provides a secondary battery, comprising: a positive electrode plate, a separator, a negative electrode plate and an electrolyte; the electrolyte adopts the electrolyte described above, or the electrolyte is prepared by the preparation method described above.

[0016] Optionally, in some embodiments of the present application, the positive electrode sheet includes a general formula of Li a Ni x Co y Mn z A b A ternary material of O2, wherein 0.9≤a≤1.1, 0.8≤x<1, x+y+z=1, 0≤b≤0.1, and A comprises at least one of Al, Mg, Ti, Zr, Zn, W, Nb, Mo, B, and F.

[0017] The secondary battery containing the above electrolyte of the present application has good cycle performance.

[0018] The present application also provides an electrical device comprising the aforementioned secondary battery. The electrical device may be, for example, a mobile phone, a computer, a wearable device, a mobile power supply, an electric vehicle, or an energy storage device.

[0019] The beneficial effects of this application are:

[0020] The electrolyte of this application improves the high-temperature storage gas generation and cycle performance of the battery by adding a new additive containing an isothiocyanate structure and a boron-based anion receptor. On the one hand, the additive containing the isothiocyanate structure can polymerize on the surface of the positive electrode to form a stable passivation film, which prevents the strong oxidizing Ni 4+It further oxidizes and decomposes with the electrolyte, preventing excessive side reaction products from being deposited on the positive electrode surface and causing an increase in interface impedance. At the same time, it inhibits the corrosion of NCM particles by HF, avoids the generation of cracks in NCM particles during the cycle, and inhibits the dissolution of positive transition metal ions at high temperatures. On the other hand, additives containing boron-based anion receptors can react with PF6 in the electrolyte. - 、F - The anions combine with each other, thereby increasing the dissociation degree of the lithium salt, reducing the content of LiF on the electrode surface, and effectively reducing the impedance of the interface film during the cycle. DETAILED DESCRIPTION

[0021] The following is a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only some of the embodiments of the present application, and not all of them. All other embodiments derived by persons skilled in the art based on the embodiments of the present application without inventive effort are within the scope of protection of the present application. Furthermore, in the description of the present application, the term "including" means "including but not limited to." The terms "first," "second," and "third," etc., are used merely as indicators and do not impose numerical requirements or establish an order. Various embodiments of the present invention may be presented in the form of a range. It should be understood that describing in a range format is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the present invention. Therefore, the range description should be considered to specifically disclose all possible subranges and individual numbers within the range. For example, a range description of 1 to 6 should be considered to specifically disclose subranges, such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., as well as individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range.

[0022] During research and practice, the inventors of this application discovered that as the Ni content in the ternary cathode material continues to increase, the oxidizability of the material in the delithiation state is significantly enhanced. The highly oxidizing tetravalent Ni ions will intensify the oxidative decomposition of the electrolyte, causing the oxidative decomposition products of the electrolyte to continuously deposit on the cathode surface, resulting in a continuous increase in the cathode internal resistance. In addition, LiPF6 in the electrolyte easily reacts with trace water to produce HF, which will corrode the cathode, leading to the dissolution of transition metals and thus destroying the cathode structure.

[0023] Therefore, the inventors of this application proposed a new electrolyte that can form a dense, stable and strong protective film on the surface of the positive electrode, protect the integrity of the positive electrode particles during the cycle, and inhibit the flatulence problem caused by the oxidative decomposition of the electrolyte and the dissolution of transition metals caused by HF attack on the positive electrode material.

[0024] The present invention provides an electrolyte, a secondary battery, and an electrical device. These are described in detail below. It should be noted that the order in which the following embodiments are described does not limit the preferred order of the embodiments.

[0025] An embodiment of the present application provides an electrolyte, including a lithium salt, an organic solvent, and a first additive, wherein the first additive includes at least one of the compounds shown in Formula I and Formula II:

[0026]

[0027] wherein R1, R2, R3, R4, R5, and R6 are independently selected from the group consisting of fluorine-substituted or unsubstituted C1-C6 alkyl, fluorine-substituted or unsubstituted C2-C6 alkenyl, fluorine-substituted or unsubstituted C2-C6 alkynyl, fluorine-substituted or unsubstituted C2-C6 alkoxy, fluorine-substituted or unsubstituted C2-C6 amino, fluorine-substituted or unsubstituted C6-C 12 aryl, fluorine-substituted or unsubstituted C5~C 12 At least one of the heterocyclic groups.

[0028] In some embodiments, the first additive includes at least one of the compounds shown in Formula (A1) to Formula (A4):

[0029]

[0030] In some embodiments, the mass fraction of the first additive in the electrolyte is 0.1wt%-5.0wt%. For example, the mass fraction of the first additive in the electrolyte can be 0.1wt%, 0.2wt%, 0.3wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2.0wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5.0wt%. In the electrolyte of the present application, too little first additive may form a passivation film at the interface that is too thin and easy to break, and cannot effectively inhibit the continuous oxidative decomposition of the electrolyte; too much first additive may form a passivation film at the interface that is too thick, increasing the impedance and polarization of the battery.

[0031] In some embodiments, the mass fraction of the lithium salt in the electrolyte is 10 wt%-15 wt%. For example, the mass fraction of the lithium salt in the electrolyte can be 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%. In the electrolyte of the present application, too low a content of the lithium salt affects the conductivity of the electrolyte, while too high a content increases the viscosity of the electrolyte.

[0032] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). Preferably, the lithium salt is lithium hexafluorophosphate (LiPF6).

[0033] In some embodiments, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methylpropyl carbonate (MPC), diphenyl carbonate (DPhC), methyl formate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (γ-GBL), acetonitrile (AN) and sulfolane (TMS).

[0034] In some embodiments, in addition to the first additive described above, the electrolyte of the present application may further include a second additive, wherein the second additive includes at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinyl sulfite (ES), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) phosphite (TMSPi), tripropargyl phosphate (TPP), 1,3-propane sultone (PS), and lithium difluorophosphate (LiPO2F2). The simultaneous use of the second additive and the first additive in the electrolyte can further improve the stability and density of the interfacial film, prevent the continuous decomposition of the electrolyte on the positive and negative electrode surfaces, and thus significantly improve the cycle performance and high-temperature storage gas production of the secondary battery.

[0035] Furthermore, the mass fraction of the second additive in the electrolyte is 0.01 to 10 wt %. That is, based on the total mass of the electrolyte, the mass percentage of the second additive is 0.01 to 10%. Specifically, the mass fraction of the second additive in the electrolyte can be 0.01 wt %, 0.05 wt %, 0.1 wt %, 0.2 wt %, 0.3 wt %, 0.5 wt %, 0.6 wt %, 0.8 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, or 10 wt %.

[0036] In some embodiments, the synthesis of the compound represented by formula (A1) uses 4-isothiocyanatophenol as a raw material, and the synthesis steps include:

[0037]

[0038] In some embodiments, the compound represented by formula (A2) is synthesized using the compound represented by formula (A1) as a raw material and fluorinated using a fluorination agent. The synthesis steps include:

[0039]

[0040] In some embodiments, the synthesis of the compound represented by formula (A3) can refer to the synthesis mechanism of the compound represented by formula (A1); similarly, the synthesis of the compound represented by formula (A4) can also refer to the synthesis mechanism of the compound represented by formula (A2), using the compound represented by formula (A3) as a raw material and fluorination using a fluorination reagent to obtain the compound.

[0041] The present invention also provides a method for preparing an electrolyte, comprising the following steps:

[0042] In an inert gas environment, lithium salt and an organic solvent are mixed to obtain a colorless and transparent mixed liquid;

[0043] The additive is mixed with the colorless and transparent mixed liquid to obtain an electrolyte.

[0044] In some embodiments, the temperature rise during the mixing process is controlled to be between 0-2°C. In the electrolyte of the present application, since the addition of lithium salt causes the electrolyte temperature to rise, causing the lithium salt to decompose to a certain extent due to heat, the electrolyte temperature is controlled when the lithium salt is added. When the electrolyte temperature rises by more than 2°C, the addition of lithium salt is stopped. When the electrolyte temperature is below 2°C, the addition of lithium salt can continue.

[0045] Furthermore, during the mixing process, the temperature increase can be controlled by a temperature control method commonly used in the art, for example, the temperature control method is selected from at least one of ice bath, dry ice circulation cooling, and liquid nitrogen cooling.

[0046] In some embodiments, the organic solvent needs to be dehydrated before being mixed with the organic solvent. Preferably, the dehydration is carried out by molecular sieve adsorption.

[0047] The present application also provides a secondary battery comprising: a positive electrode, a separator, a negative electrode, and an electrolyte; the electrolyte is the electrolyte described above, or the electrolyte is prepared by the preparation method described above. The secondary battery containing the electrolyte described above has good cycle performance.

[0048] In some embodiments, the positive electrode comprises a general formula of Li a Ni x Co y Mnz A b A ternary material of O2, wherein 0.9≤a≤1.1, 0.8≤x<1, x+y+z=1, 0≤b≤0.1, and A comprises at least one of Al, Mg, Ti, Zr, Zn, W, Nb, Mo, B, and F.

[0049] The present application also provides an electrical device including the aforementioned secondary battery. The electrical device may be, for example, a mobile phone, a computer, a wearable device, a mobile power supply, an electric vehicle, or an energy storage device.

[0050] The present application has been subjected to multiple tests, and part of the test results are cited as a reference to further describe the invention in detail, which will be described in detail in conjunction with specific embodiments.

[0051] Example 1

[0052] This embodiment provides an electrolyte, and the steps of preparing the electrolyte include:

[0053] At room temperature, in an argon-filled glove box (H2O<1ppm, O2<1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 3:7 to obtain a mixed solvent; LiPF6 was added gradually to the obtained mixed solvent, and stirring was continued while cooling with dry ice to ensure that the electrolyte temperature did not rise by more than 2°C. LiPF6 was then added to control the mass fraction of LiPF6 in the electrolyte to 12.5%, ultimately obtaining a colorless transparent liquid. An additive (compound A1) equivalent to 0.1% of the total mass of the electrolyte was added, and stirring was performed to obtain an electrolyte.

[0054] In this embodiment, the preparation method of the additive (Compound A1) is as follows:

[0055]

[0056] S1. At room temperature, slowly add compound a1 and tert-butyl lithium in a molar ratio of 1:1 to diethyl ether solvent, and stir for 12 h. After the reaction is completed, a solid precipitate is obtained, which is washed with diethyl ether solvent, filtered, and dried to obtain compound a2;

[0057] S2. Dissolve the dried solid precipitate a2 in ether solvent, slowly add trimethyl borate and stir for 12 hours to obtain a precipitate, wash, filter and dry the precipitate to obtain compound A1.

[0058] In this example, according to the above preparation method, the total yield of compound A1 is 82.9% and the purity is 99.8%. 1H-NMR: chemical shifts are 3.39 ppm (methoxy group -OCH3), 6.85 ppm and 7.21 ppm (aromatic protons), 13 C-NMR: chemical shifts are 29 ppm, 117.2 ppm, 124.1 ppm, 126.3 ppm, 136.9 ppm, 156.3 ppm respectively.

[0059] In this embodiment, the preparation of the positive electrode sheet includes:

[0060] The positive electrode active material Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 (NMC811), conductive agent acetylene black (Super P) and binder polyvinylidene fluoride (PVDF) are mixed evenly in the mass ratio of NMC811:Super P:PVDF=94:3:3, and evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. The mixed slurry is coated on both sides of aluminum foil, and then baked, rolled and slit to obtain the positive electrode sheet.

[0061] In this embodiment, the preparation of the negative electrode sheet includes:

[0062] The negative electrode active material graphite, the conductive agent acetylene black (Super P) and the binder SBR were mixed uniformly in a mass ratio of graphite:SuperP:SBR=94:3:3, and evenly dispersed in deionized water to form a uniform black slurry. The mixed slurry was coated on both sides of the copper foil, and then baked, rolled and slit to obtain the negative electrode sheet.

[0063] In this embodiment, the production of the soft pack battery includes:

[0064] A secondary battery, the production steps of which include: stacking the prepared positive electrode sheet, polyolefin separator, and negative electrode sheet in order, with the separator located between the positive and negative electrode sheets, winding, hot pressing and shaping, and welding the tabs to obtain a bare battery cell, placing the bare battery cell in an outer packaging aluminum-plastic film, and baking it in an oven at 85±10°C for 24 hours, injecting the prepared electrolyte into the dried battery, allowing it to stand, forming, and dividing the capacity, thereby completing the preparation of a lithium-ion soft-pack battery.

[0065] Examples 2 to 7

[0066] Examples 2 to 7 provide an electrolyte and a secondary battery. Examples 2 to 7 differ from Example 1 in that the content of the additive (Compound A1) in the electrolyte of Examples 2 to 7 is different from that in Example 1. Examples 2 to 7 are based on Example 1, with increasing amounts of Compound A1 added, as shown in Table 1. Other conditions are the same as in Example 1.

[0067] Example 8

[0068] This embodiment provides an electrolyte and a secondary battery. The difference from embodiment 3 is that the additive in the electrolyte of embodiment 8 is compound A2, while the additive in embodiment 3 is compound A1, as shown in Table 1. Other conditions are the same as those of embodiment 3.

[0069] In this embodiment, the preparation method of the additive (Compound A2) is as follows:

[0070]

[0071] Compound A1 is used as a raw material and fluorinated using a fluorination reagent to obtain compound A2.

[0072] Examples 9-10

[0073] Examples 9 and 10 provide an electrolyte and a secondary battery. Examples 9 and 10 differ from Example 8 in that the content of the additive (Compound A2) is different. Examples 9 and 10 are based on Example 8, with increasing amounts of Compound A2 added, as shown in Table 1. Other conditions are the same as in Example 8.

[0074] Example 11

[0075] This embodiment provides an electrolyte and a secondary battery. The difference between Example 11 and Example 3 is that the additives in the electrolyte of Example 11 include compound A1 and vinylene carbonate (VC), as shown in Table 1. Other conditions are the same as those in Example 3.

[0076] Examples 12-13

[0077] Examples 12-13 provide an electrolyte and a secondary battery. The difference between Examples 12-13 and Example 3 is that the amount of lithium salt (LiPF6) used in the electrolyte of Examples 12-13 is different from that in Example 3, as shown in Table 1. Other conditions are the same as those in Example 3.

[0078] Example 14

[0079] This embodiment provides an electrolyte and a secondary battery. The difference between embodiment 14 and embodiment 3 is that the type of positive electrode active material is different. Embodiment 14 uses Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Example 3 uses Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, see Table 1 for details. Other conditions are the same as those in Example 3.

[0080] Example 15

[0081] This embodiment provides an electrolyte and a secondary battery. The difference between Example 15 and Example 3 is that the type of positive electrode active material is different. Example 15 uses Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Example 3 uses Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, see Table 1 for details. Other conditions are the same as those in Example 3.

[0082] Example 16

[0083] This embodiment provides an electrolyte and a secondary battery. The difference from embodiment 3 is that the additive in the electrolyte of embodiment 8 is compound A3, while the additive in embodiment 3 is compound A1, as shown in Table 1. Other conditions are the same as those of embodiment 3.

[0084] In this embodiment, the structure of the additive (Compound A3) is as follows:

[0085]

[0086] Examples 17-18

[0087] Examples 17-18 provide an electrolyte and a secondary battery. Examples 17-18 differ from Example 16 in the content of the additive (Compound A3). Examples 17-18 are based on Example 16, with increasing amounts of Compound A3 added, as shown in Table 1. Other conditions are the same as in Example 16.

[0088] Example 19

[0089] This embodiment provides an electrolyte and a secondary battery. The difference from Example 3 is that the additive in the electrolyte of Example 8 is Compound A4, while the additive in Example 3 is Compound A1, as shown in Table 1. Other conditions are the same as those in Example 3.

[0090] In this embodiment, the structure of the additive (Compound A4) is as follows:

[0091]

[0092] Examples 20-21

[0093] Examples 20-21 provide an electrolyte and a secondary battery. Examples 20-21 differ from Example 19 in the content of the additive (Compound A4). Examples 20-21 are based on Example 19, with increasing amounts of Compound A4 added, as shown in Table 1. Other conditions are the same as in Example 19.

[0094] Comparative Example 1

[0095] Comparative Example 1 provides an electrolyte and a secondary battery. The difference between Comparative Example 1 and Example 3 is that Comparative Example 1 does not use any electrolyte additives, as shown in Table 1. Other conditions are the same as those in Example 3.

[0096] Comparative Example 2

[0097] Comparative Example 2 provides an electrolyte and a secondary battery. The difference between Comparative Example 2 and Example 3 is that Comparative Example 2 uses phenyl isothiocyanate instead of Compound A1 in Example 3 as the electrolyte additive, as shown in Table 1. Other conditions are the same as those in Example 3.

[0098] Comparative Example 3

[0099] Comparative Example 3 provides an electrolyte and a secondary battery. The difference between Comparative Example 3 and Example 3 is that Comparative Example 3 uses 4-ethylphenyl isothiocyanate instead of Compound A1 in Example 3 as the electrolyte additive, as shown in Table 1. Other conditions are the same as those in Example 3.

[0100] Comparative Examples 4-5

[0101] Comparative Examples 4 and 5 provide an electrolyte and a secondary battery, respectively. Comparative Examples 4 and 5 differ from Examples 14 and 15 in that no electrolyte additives are used in Comparative Examples 4 and 5, as shown in Table 1. Other conditions in Comparative Examples 4 and 5 are the same as in Examples 14 and 15, respectively.

[0102] Test performance

[0103] In this test example, battery performance tests were performed on the batteries obtained from Examples 1 to 15 and Comparative Examples 1 to 5.

[0104] 1. Room Temperature Cycling Performance Test: At 25±2°C, the soft-pack batteries obtained from each embodiment and comparative example were subjected to charge and discharge cycling tests at a charge and discharge rate of 1C / 1C within the range of 2.8-4.25V. The battery's first-cycle discharge capacity and the discharge capacity after 500 cycles were recorded. The 500-cycle capacity retention rate = 500-cycle discharge capacity / first-cycle discharge capacity * 100%. The recorded data are shown in Table 1.

[0105] 2. High-Temperature Storage Performance: The soft-pack batteries obtained from each example and comparative example were placed at 60±2°C and charged and discharged at a charge / discharge rate of 1C / 1C in the range of 2.8-4.25V. The first-week discharge capacity of the battery was recorded. The battery was then stored at 60±2°C for 7 days, and the charge and discharge test was repeated, with the discharge capacity recorded. High-Temperature Storage Capacity Retention = Discharge Capacity after 7 Days / Discharge Capacity in the First Week * 100%. The recorded data are shown in Table 1.

[0106] 3. High-Temperature Gas Generation Test: The soft-pack batteries obtained from Examples 1-15 and Comparative Examples 1-5 were each charged at 25±2°C at a constant current rate of 1C to 4.25V. They were then charged at a constant voltage rate of 4.25V until the current dropped below 0.05C, bringing them to a fully charged state at 4.25V. The volume of the fully charged battery before storage was measured and recorded as V0. The fully charged battery was then placed in a 70±2°C oven. After 5 days, the battery was removed and its post-storage volume was immediately measured and recorded as V1. Volume expansion ratio = (V1-V0) / V0*100%. The results are shown in Table 1.

[0107] Table 1

[0108]

[0109]

[0110] Analyze the experimental results in Table 1:

[0111] (1) By comparing the experimental results of Examples 1 to 7 and Comparative Example 1, it can be seen that the addition of the additive (Compound A1) can significantly improve the room temperature cycle performance and high temperature storage capacity retention rate of the secondary battery, and at the same time, it also has a significant inhibitory effect on the gas production of the battery. It can also be seen that in the electrolyte system of the solvent and lithium salt components, the electrochemical performance is optimal when 1.0wt% of the additive (Compound A1) is added. This is because when the amount of the additive added is too small, the interface film formed is not dense and stable enough; when the amount of the additive added exceeds the amount of the additive of the present invention, the passivation layer will be too thick, the interface impedance will increase, and the electrochemical performance of the secondary battery will deteriorate. In terms of comprehensive performance, the content of Compound A1 is preferably 0.5-2wt%, and the most preferred content can be determined according to specific needs.

[0112] (2) Comparison of the experimental results of Examples 8-10 and Comparative Example 1 shows that the addition of the additive (Compound A2) significantly improves the room-temperature cycling performance and high-temperature storage retention of the secondary battery, while also significantly inhibiting gas production. It can also be seen that, in this solvent and lithium salt electrolyte system, the addition of 1.5 wt% of the additive (Compound A2) results in superior electrochemical performance.

[0113] (3) It can be seen from the experimental results of Examples 3 and 11 that when Compound A1 is combined with vinylene carbonate, the cycle performance and high-temperature storage gas generation of the secondary battery are more significantly improved.

[0114] (4) By comparing the experimental results of Examples 3 with those of Examples 12 and 13, it can be seen that too high or too low a lithium salt content will result in poor performance. When the lithium salt content is too low, the electrolyte conductivity is low, and when the lithium salt content is too high, the electrolyte viscosity increases. In addition, changes in the lithium salt content will also cause differences in the solvation structure, affecting the solvation energy barrier and affecting the film formation during the desolvation process, thereby changing the interfacial film components. Therefore, it is necessary to optimize the lithium salt content.

[0115] (5) It can be seen from the experimental results of Example 3 and Comparative Examples 2 and 3 (the phenyl isothiocyanate additive of Comparative Example 2 and the 4-ethyl phenyl isothiocyanate additive of Comparative Example 3 contain isothiocyanate groups but no boron anion receptor) that the additives of the combination of isothiocyanate and boron anion receptor have better electrochemical performance than the additives containing a single isothiocyanate functional group; because the boron anion receptor contained in the additive structure can further stabilize LiPF6 in the electrolyte, thereby preventing the formation of HF and LiF, and at the same time, the isothiocyanate group forms a stable passivation film on the surface of the positive and negative electrodes by polymerization, which can play a better coordination role.

[0116] (6) It can be seen from the experimental results of Examples 3, 14, and 15 and Comparative Examples 1, 4, and 5 that the performance improvement of the additive in the high nickel system is more obvious than that in the low nickel and medium nickel systems. This is because the high nickel material has stronger oxidizing properties and more serious interfacial side reactions with the electrolyte. By adding the additive, the decomposition of the electrolyte can be significantly inhibited, thereby significantly improving the electrochemical performance of the battery.

[0117] In summary, Table 1 shows that the overall performance of the batteries of Examples 1 to 21 of the present application is significantly superior to that of the batteries of Comparative Examples 1 to 5. Furthermore, the aforementioned effects indicate that the use of the electrolyte containing the additives of the present application, which contain an isothiocyanate structure and a boron-based anion receptor, is beneficial for improving the cycle performance of secondary batteries and improving the gas generation during high-temperature storage of the battery cells. The specific use of the additive compounds used in the examples of the present application can be adjusted according to the application scenario.

[0118] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0119] The above is a detailed introduction to an electrolyte, a secondary battery and an electrical device provided in the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for technical personnel in this field, based on the ideas of the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. An electrolyte, characterized in that The electrolyte includes a lithium salt, an organic solvent, and a first additive; the first additive includes at least one of the compounds shown in Formula I and Formula II: wherein R1, R2, R3, R4, R5, and R6 are independently selected from the group consisting of fluorine-substituted or unsubstituted C1-C6 alkyl, fluorine-substituted or unsubstituted C2-C6 alkenyl, fluorine-substituted or unsubstituted C2-C6 alkynyl, fluorine-substituted or unsubstituted C2-C6 alkoxy, fluorine-substituted or unsubstituted C2-C6 amino, fluorine-substituted or unsubstituted C6-C 12 aryl, fluorine-substituted or unsubstituted C5~C 12 At least one of the heterocyclic groups; The mass fraction of the first additive in the electrolyte is 0.1wt%-5.0wt%; The mass fraction of the lithium salt in the electrolyte is 10 wt%-15 wt%.

2. The electrolyte according to claim 1, characterized in that The first additive includes at least one of the compounds shown in formula (A1) to formula (A4):

3. The electrolyte according to claim 1, characterized in that The mass fraction of the first additive in the electrolyte is 0.5 wt % to 2.0 wt %.

4. The electrolyte according to claim 1, characterized in that The mass fraction of the lithium salt in the electrolyte is 12 wt%-13 wt%.

5. The electrolyte according to claim 1, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

6. The electrolyte according to claim 1, characterized in that The organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, diphenyl carbonate, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, acetonitrile and sulfolane.

7. The electrolyte according to claim 1, characterized in that The electrolyte further includes a second additive, the second additive including at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, vinyl sulfite, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, tripropargyl phosphate, 1,3-propane sultone, and lithium difluorophosphate; The mass fraction of the second additive in the electrolyte is 0.01 wt % to 10 wt %.

8. A secondary battery, characterized in that include: Positive electrode sheet, separator, negative electrode sheet and electrolyte; The electrolyte is the electrolyte according to any one of claims 1 to 7.

9. The secondary battery according to claim 8, characterized in that The positive electrode plate includes a general formula of Li a Ni x Co y Mn z A b A ternary material of O2, wherein 0.9≤a≤1.1, 0.8≤x<1, x+y+z=1, 0≤b≤0.1, and A comprises at least one of Al, Mg, Ti, Zr, Zn, W, Nb, Mo, B, and F.

10. Electrical equipment, characterized in that: The secondary battery according to claim 9 is included.

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