Electrolyte, battery, battery pack, and electrical equipment

Abstract

The present invention provides an electrolyte, a battery, a battery pack, and an electrical device; the electrolyte includes a first additive and a second additive, the first additive includes a compound as shown in Formula I: #imgabs0# Formula I, and the second additive includes a compound as shown in Formula II: #imgabs1# Formula II. The electrolyte provided by the present invention not only has a significant enhancement effect on the anti-overcharge protection performance of the battery by combining the specific first additive and the second additive, but also can inhibit the gas production of the battery, so that the high-temperature cycle performance of the battery is effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to an electrolyte, a battery, a battery pack, and an electrical device. Background Art

[0002] Currently, one of the biggest obstacles restricting the application of high-capacity power batteries is battery safety. Overcharging is the most common safety issue that occurs during battery use. When the battery is overcharged, it is very easy to cause dangers such as explosion and fire.

[0003] To address the problem of battery overcharging, a traditional method is to prevent battery overcharging by installing a gas pressure detection device, an explosion-proof safety valve in the battery safety cap or by adding a dedicated overcharging protection circuit. However, this method not only increases the cost and complexity of the battery, but also has unsatisfactory safety effects. Another method is to prevent overcharging by establishing an internal protection mechanism for the battery, which is mostly to add an overcharge protection agent to the electrolyte. This method is economical and easy to operate, and can effectively enhance the overcharge protection of the battery. However, existing overcharge protection agents mostly use biphenyl, cyclohexylbenzene, etc. Although they can play a certain role in the overcharge safety of the battery, they will also affect the normal cycle performance of the battery. Summary of the invention

[0004] The present invention provides an electrolyte which can improve the overcharge safety of a battery and at the same time enhance its cycle performance.

[0005] The present invention also provides a battery. Since the battery includes the above electrolyte, the battery has good overcharge resistance and cycle stability.

[0006] The present invention also provides a battery pack. Since the battery pack includes the above-mentioned battery, the battery pack has the advantages of long cycle life and good overcharge safety performance.

[0007] The present invention also provides an electric device. Since the electric device comprises the battery pack, the electric device has good safety and a long service life.

[0008] In a first aspect, the present invention provides an electrolyte, comprising a first additive and a second additive, wherein the first additive comprises a compound as shown in Formula I:

[0009] ,

[0010] In Formula I, R1, R3 and R4 are each independently -CN, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C1-C 30 and at least two of R1, R3 and R4 are -CN; R2 is a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C1-C30 One of the alkyl groups;

[0011] The second additive comprises a compound as shown in Formula II:

[0012] ,

[0013] In Formula II, R5, R6, and R7 are independently substituted or unsubstituted C1-C 30 Alkyl, substituted or unsubstituted C6-C 30 Aromatic base.

[0014] Furthermore, in the formula I, R1, R3 and R4 are each independently a fluorine atom, a chlorine atom, a bromine atom, a C1-C 20 Alkyl, C1-C 20 Fluorinated alkyl, C1-C 20 alkyl bromide, C1-C 20 One of the chloroalkyl groups; R2 is C1-C 20 Alkyl, C1-C 20 Fluorinated alkyl, C1-C 20 alkyl bromide, C1-C 20 One of the chloroalkyl groups;

[0015] And / or, in the formula II, R5, R6, and R7 are each independently one of C1-C5 chloroalkyl, C1-C5 bromoalkyl, C1-C5 fluoroalkyl, phenyl, benzyl, and phenethyl.

[0016] Furthermore, the first additive comprises a compound having a structure such as any one or more of Formula 1-1 to Formula 1-6:

[0017]

[0018]

[0019]

[0020] Furthermore, the second additive comprises a compound having a structure such as any one or more of Formula II-1 to Formula II-8:

[0021] ,

[0022] ,

[0023] ,

[0024] .

[0025] Furthermore, in the electrolyte, the mass percentage content of the first additive is not higher than 2wt%;

[0026] And / or, in the electrolyte, the mass percentage of the second additive is not higher than 7wt%.

[0027] Furthermore, in the electrolyte, the mass percentage content of the first additive is 1wt%-2wt%;

[0028] And / or, in the electrolyte, the mass percentage of the second additive is 5-7wt%.

[0029] Furthermore, a third additive is included, and the third additive includes at least one of vinylene carbonate or its derivatives, cyclic carbonates, and cyclic carbonates substituted by halogens.

[0030] Further, the third additive includes at least one of vinylene carbonate, vinyl ethylene carbonate, methylene vinyl carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate and bisfluoroethylene carbonate.

[0031] Furthermore, it also includes lithium salts and non-aqueous organic solvents; the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, tris(trifluoromethylsulfonyl)methyl lithium, lithium dioxalateborate, lithium dimalonateborate, lithium oxalatephosphate, and lithium tris(difluoromalonate)phosphate; the non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0032] Furthermore, in the electrolyte, the concentration of the lithium salt is 0.5 mol / L-2 mol / L.

[0033] In a second aspect, the present invention provides a battery comprising a positive electrode sheet, a negative electrode sheet and the electrolyte described in the first aspect.

[0034] In a third aspect, the present invention provides a battery pack, comprising the battery described in the second aspect.

[0035] In a fourth aspect, the present invention provides an electrical device, comprising the battery described in the second aspect or the battery pack described in the third aspect.

[0036] The electrolyte provided by the present invention not only has a significant enhancement effect on the anti-overcharge protection performance of the battery by combining a specific first additive and a second additive, but also can inhibit the gas production of the battery, so that the high-temperature cycle performance of the battery is effectively improved. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific implementation methods listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0038] In a first aspect, the present invention provides an electrolyte, comprising a first additive and a second additive, wherein the first additive comprises a compound as shown in Formula I:

[0039] ,

[0040] In Formula I, R1, R3 and R4 are each independently -CN, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C1-C 30 and at least two of R1, R3 and R4 are -CN; R2 is a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C1-C 30 One of the alkyl groups;

[0041] The second additive comprises a compound as shown in Formula II:

[0042] ,

[0043] In Formula II, R5, R6, and R7 are independently substituted or unsubstituted C1-C 30 Alkyl, substituted or unsubstituted C6-C 30 Aromatic base.

[0044] In the present invention, the electrolyte not only greatly improves the overcharge protection performance of the battery by combining the specific first additive and the second additive, but also can inhibit the gas production of the battery, so that the high-temperature cycle performance of the battery is improved; in detail, in addition to the polymerization reaction of the second additive in the electrolyte during overcharging, the first additive will also synergistically participate in the polymerization, so that a sufficient amount of polymer is generated inside the battery in a relatively short time to pierce the diaphragm, narrow the lithium ion migration channel, or even close the channel, and a micro-short circuit occurs inside the battery, preventing the battery voltage from continuing to rise, thereby preventing the battery temperature from continuing to rise, and reducing the safety hazard of battery overcharging; in addition, the first additive also has a strong coordination effect with transition metal ions, which can inhibit the dissolution of transition metal ions. At the same time, the first additive can preferentially capture H protons when the electrolyte undergoes an oxidative side reaction, inhibiting the decomposition of lithium salts (such as LiPF6), and the cyanide itself can also react with H2O to generate amino groups, which plays a role in removing water, thereby inhibiting the gas production of the battery, reducing the decomposition of the electrolyte, and improving the high-temperature cycle performance of the battery.

[0045] It should be noted that the first additive and the second additive of the present invention can be obtained through existing methods such as purchasing commercial products, synthesizing by conventional methods or custom synthesis.

[0046] In one embodiment, in Formula I, R1, R3 and R4 are each independently a fluorine atom, a chlorine atom, a bromine atom, a C1-C 20 Alkyl, C1-C 20 Fluorinated alkyl, C1-C 20 alkyl bromide, C1-C 20 One of the chloroalkyl groups; R2 is C1-C 20 Alkyl, C1-C 20 alkyl bromide, C1-C 20 Fluorinated alkyl, C1-C 20 One of the chloroalkyl groups;

[0047] And / or, in the formula II, R5, R6, and R7 are each independently one of C1-C5 chloroalkyl, C1-C5 bromoalkyl, C1-C5 fluoroalkyl, phenyl, benzyl, and phenethyl.

[0048] Exemplarily, R1, R3 and R4 are each independently C1-C 10 Alkyl, C1-C 10 Fluorinated alkyl, C1-C 10 alkyl bromide, C1-C 10 One of the chloroalkyl groups; R2 is C1-C 10 Alkyl, C1-C 10 Fluorinated alkyl, C1-C 10 alkyl bromide, C1-C 10 chloroalkyl; further, R1, R3 and R4 are each independently C1-C5 alkyl, C1-C5 fluoroalkyl, C1-C5 bromoalkyl, C1-C5 chloroalkyl; R2 is C1-C5 alkyl, C1-C5 fluoroalkyl, C1-C5 bromoalkyl, C1-C5 chloroalkyl. In addition, the alkyl involved in formula I and formula II can be a straight chain alkyl or a branched alkyl, and the present invention does not make any special restrictions on this.

[0049] In one embodiment, the first additive comprises a compound having a structure such as any one or more of Formula 1-1 to Formula 1-6:

[0050]

[0051]

[0052]

[0053] In one embodiment, the second additive comprises a compound having a structure such as any one or more of Formula II-1 to Formula II-8:

[0054] ,

[0055] ,

[0056] ,

[0057] .

[0058] In a specific embodiment, in the electrolyte, the mass percentage content of the first additive is not higher than 2wt%;

[0059] And / or, in the electrolyte, the mass percentage of the second additive is not higher than 7wt%.

[0060] Among them, the first additive can better balance the relationship between the battery's anti-overcharge performance and high-temperature cycle performance within the above range. If the mass percentage content of the first additive is higher than 2wt%, it will cause the viscosity of the electrolyte to increase, hinder the migration of lithium ions, and thus increase the battery impedance; on the other hand, the additive has an impact on the formation of the negative electrode SEI film. If the content is too much, the SEI film is too dense and thick, which will affect the transmission efficiency of lithium ions and increase the impedance, which is not conducive to the improvement of the high-temperature cycle performance of the battery; similarly, a certain amount of the second additive can also help balance the relationship between the battery's anti-overcharge performance and high-temperature cycle performance. If the mass percentage content of the second additive is higher than 7 wt%, it will dilute other effective ingredients in the electrolyte. At the same time, excessive addition of the additive will cause an increase in battery polarization, and the deviation of the positive and negative electrode potentials of the battery during charging and discharging will increase, which will weaken the battery's cycle performance and service life.

[0061] In a more preferred embodiment, in the electrolyte, the mass percentage of the first additive is 1wt%-2wt%;

[0062] And / or, in the electrolyte, the mass percentage of the second additive is 5-7 wt %.

[0063] Exemplarily, in the electrolyte, the mass percentage of the first additive is 1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, etc.; the mass percentage of the second additive is 5.1 wt%, 5.3 wt%, 5.5 wt%, 5.7 wt%, 5.9 wt%, 6.1 wt%, 6.3 wt%, 6.5 wt%, 6.7wt%, 6.9 wt%, etc.

[0064] In a specific embodiment, a third additive is further included, and the third additive includes at least one of vinylene carbonate or its derivatives, cyclic carbonate, and cyclic carbonate substituted by halogen. The third additive has good affinity to the surface of the electrode, and can build a stable SEI film on the surface of the electrode, thereby protecting the electrode structure from solvent molecules, HF, F in the electrolyte. - and other impurities, which helps to further improve the high temperature cycle performance of the battery.

[0065] The amount of the third additive is not particularly limited in the present invention. Generally speaking, the amount of the third additive does not exceed 10 wt % of the electrolyte.

[0066] In a specific embodiment, the third additive includes one or more of vinylene carbonate, vinyl ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate and bisfluoroethylene carbonate. In a more preferred embodiment, the third additive is vinylene carbonate, wherein the introduction of vinylene carbonate can reduce the initial capacity loss of lithium-ion batteries and has a significant improvement effect on the stability of SEI film under high temperature conditions.

[0067] In a specific embodiment, a lithium salt and a non-aqueous organic solvent are also included; the lithium salt can be an organic lithium salt and / or an inorganic lithium salt conventional in the art; the inorganic lithium salt includes but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium hexafluoroantimonate (LiSbF6), lithium hexafluorotantalate (LiTaF6), lithium tetrachloroaluminate (LiAlCl4), Li2B 10 Cl 10 、Li2B 10 F 10, at least one of trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, tri(trifluoromethylsulfonyl)methyl lithium, etc.; organic lithium salts include but are not limited to chelated orthoborates and chelated orthophosphates. Lithium salts, such as lithium bisoxalate borate [LiB(C2O4)2], lithium bismalonate borate [LiB(O2CCH2CO2)2], lithium bis(difluoromalonate)borate [LiB(O2CCF2CO2)2], lithium (malonate oxalate)borate [LiB(C2O4) (O2CCH2CO2)], lithium (difluoromalonate oxalate)borate [LiB(C2O4) (O2CCF2CO2)], lithium trioxalatephosphate [LiP(C2O4)3] and lithium tris(difluoromalonate)phosphate [LiP(O2CCF2CO2)3], and any combination of two or more of the above lithium salts.

[0068] In order to promote efficient ion transport and enable the first additive and the second additive to more fully play their roles when the battery is overcharged, preferably, the lithium salt includes at least one of LiPF6, LiBF4, LiAsF6, LiClO4, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, tri(trifluoromethylsulfonyl)methyl lithium, lithium bisoxalate borate, lithium bismalonate borate, lithium oxalate phosphate, and tri(difluoromalonate)phosphate; the non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0069] Furthermore, in the electrolyte, the concentration of the lithium salt is 0.5 mol / L-2 mol / L.

[0070] Among them, when the lithium salt is within the above range, the lithium salt can be dissolved in the organic solvent to form an electrolyte with high stability and good lithium conductivity, and at the same time, the viscosity of the electrolyte can be appropriate, so that lithium ions can migrate quickly in the electrolyte, so that the battery exhibits excellent rate and cycle performance. When the lithium salt concentration is as low as 0.5 mol / L or less, the conductivity of the electrolyte decreases, which will affect the rate and cycle performance of the entire battery system; when the lithium salt concentration is as high as 2 mol / L or more, the viscosity of the electrolyte is too large, which is also not conducive to the increase of the rate of the entire battery system; in a more preferred embodiment, the lithium salt concentration is 0.9 mol / L~1.3 mol / L.

[0071] Exemplarily, the mass percentage of the non-aqueous organic solvent is 60wt%-92wt%, preferably 65wt%-85wt%. When the organic solvent is within the above range, the lithium salt can be fully dissolved in the electrolyte, which helps to prepare an electrolyte with high conductivity and strong stability, so that the electrochemical performance of the battery is stable.

[0072] In a second aspect, the present invention provides a battery, comprising the electrolyte, positive electrode sheet and negative electrode sheet described in the first aspect.

[0073] It should be noted that the above-mentioned batteries may include but are not limited to single cells, battery modules, battery packs, etc., that is, the actual application form of the battery provided by the present invention can be but is not limited to the listed products, and can also be other application forms. When the battery is a single cell, it includes at least one of a cylindrical battery, a square battery, etc.

[0074] Generally speaking, the positive electrode sheet includes a positive electrode current collector and a positive electrode active slurry layer located on the positive electrode current collector, wherein the positive electrode active slurry layer includes a positive electrode active material, a positive electrode binder and a positive electrode conductive agent; the negative electrode sheet includes a negative electrode current collector and a negative electrode active slurry layer located on the negative electrode current collector, wherein the negative electrode active slurry layer includes a negative electrode active material, a negative electrode binder and a negative electrode conductive agent. The specific types of the positive electrode active material, the positive electrode binder, the positive electrode conductive agent, the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are not subject to specific restrictions and can be selected according to needs.

[0075] Exemplarily, the above-mentioned positive electrode active materials include but are not limited to: LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-b M b O2、LiCo 1-b M b O2、LiFe 1-b M b PO4、Li2Mn 1-b O4、LiNi x Co y Mn z At least one of O2, etc., M is selected from one or more of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, 0≤a<0.2, 0≤b<1, x+y+z=1.

[0076] Furthermore, the positive electrode active materials include but are not limited to LiCoO2, LiFeMnPO4, LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.

[0077] The above-mentioned negative electrode active materials include but are not limited to: graphite and / or silicon, such as natural graphite, artificial graphite, mesophase microcarbon beads (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy, etc.

[0078] The positive electrode binder and the negative electrode binder are independently selected from at least one of styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0079] As for the particle size distribution of the above-mentioned positive electrode active material and the negative electrode active material, the present invention does not make any specific limitation. For example, the D50 of the above-mentioned positive electrode active material or the negative electrode active material can be 5-16µm, specifically including but not limited to: 6µm, 7µm, 8µm, 9µm, 10µm, 11µm, 12µm, 13µm, 14µm, 15µm, etc.; D99 can be 14-30µm, specifically including but not limited to: 15µm, 16µm, 17µm, 18µm, 19µm, 20µm, 21µm, 22µm, 23µm, 24µm, 25µm, 26µm, 27µm, 28µm, 29µm, etc.; D10 can be 2-10µm, specifically including but not limited to: 3µm, 4µm, 5µm, 6µm, 7µm, 8µm, 9µm, etc.

[0080] The thickness and surface density of the positive electrode sheet and the negative electrode sheet are not specifically limited in the present invention. However, in order to balance the battery capacity, cycle life and energy density, in a specific embodiment, the thickness of the positive electrode sheet or the negative electrode sheet is 40-120µm, including but not limited to: 50µm, 60µm, 70µm, 80µm, 90µm, 100µm, 110µm, etc.; the surface density of the positive electrode sheet or the negative electrode sheet is 3-10mg / cm 2 , including but not limited to: 3.5mg / cm 2 , 4mg / cm 2 , 4.5mg / cm 2 , 5mg / cm 2 , 5.5mg / cm 2 , 6mg / cm 2 、6.5mg / cm 2 , 7mg / cm 2 、7.5mg / cm 2 , 8mg / cm 2 、8.5mg / cm2 , 9mg / cm 2 、9.5mg / cm 2 wait.

[0081] Exemplarily, the battery further includes a separator, such as polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, etc.

[0082] In a third aspect, the present invention provides a battery pack, comprising the battery described in the second aspect.

[0083] In a fourth aspect, the present invention provides an electrical device, comprising the battery described in the second aspect or the battery pack described in the third aspect.

[0084] It should be noted that the above-mentioned electronic equipment can be any conventional equipment that requires electricity, for example, including but not limited to computers, electric cars, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc.

[0085] The present invention is further described below in conjunction with specific embodiments:

[0086] The sources of the first additive and the second additive involved in the following experiments are shown in Table 1.

[0087] Table 1:

[0088]

[0089] Example 1

[0090] This example provides an electrolyte, including LiPF6 (1.1 mol / L), 1.0 wt% of a first additive, 1.5 wt% of a second additive, and the balance being a non-aqueous organic solvent, wherein the non-aqueous organic solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 3:6:1, the structure of the first additive is as shown in Formula Ι-1, and the structure of the second additive is as shown in Formula Ⅱ-1.

[0091] The preparation method of the above-mentioned electrolyte includes the following steps: mixing EC, EMC, and DEC in a mass ratio of 3:6:1 as a non-aqueous organic solvent, adding a first additive and a second additive to the non-aqueous organic solvent, mixing evenly, and then adding LiPF6 to obtain an electrolyte with a LiPF6 concentration of 1.1 mol / L.

[0092] Embodiment 2-7

[0093] The method is basically the same as Example 1, except that the amount of the first additive and / or the amount of the second additive is changed. For details, see Table 2.

[0094] Examples 8-12

[0095] It is basically the same as Example 2, except that the structure of the first additive is changed, see Table 2 for details.

[0096] Examples 13-19

[0097] It is basically the same as Example 2, except that the structure of the second additive is changed, see Table 2 for details.

[0098] Embodiment 20

[0099] It is basically the same as Example 1, except that the concentration of LiPF6 is 0.5 mol / L.

[0100] Embodiment 21

[0101] It is basically the same as Example 1, except that the concentration of LiPF6 is 2 mol / L.

[0102] Examples 22-23

[0103] The method is basically the same as Example 1, except that the electrolyte further includes a third additive, which is vinylene carbonate and fluoroethylene carbonate, respectively, and the amounts used are 3wt% and 5wt%, respectively.

[0104] Comparative Example 1

[0105] The method is basically the same as that of Example 1, except that the first additive and the second additive are not added.

[0106] Comparative Example 2

[0107] It is basically the same as Example 1, except that the first additive is not added and the content of the second additive is 8 wt %.

[0108] Comparative Example 3

[0109] It is basically the same as Example 1, except that the second additive is not added and the content of the first additive is 3 wt %.

[0110] Test Example 1

[0111] This example provides a series of lithium-ion batteries, each of which includes the electrolyte of the above-mentioned embodiment or comparative example.

[0112] 1. Preparation of positive electrode sheet: The positive electrode active material lithium nickel manganese cobalt, the conductive agent CNT (Carbon Nanotube), and the binder PVDF (polyvinylidene fluoride) are fully stirred and mixed in N-methylpyrrolidone solvent at a mass ratio of 100:2:1.6 to form a uniform positive electrode slurry. The slurry is coated on the positive electrode current collector Al foil, dried and rolled, and then cut and die-cut to obtain a compaction density of 3.5g / cm 3 The positive electrode.

[0113] 2. Preparation of negative electrode sheet: Mix the negative electrode active material graphite, conductive agent acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 100:1:3.4:1.6 in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry. Apply the slurry on the negative electrode current collector Cu foil, dry it, roll it, and then cut it into pieces with a compaction density of 1.55g / cm 3 The negative electrode.

[0114] 3. Preparation of lithium-ion batteries

[0115] The positive and negative electrodes and polypropylene separators are stacked in a Z-shaped stacking manner to form a lithium-ion battery movement in one direction, and then assembled into a soft-pack battery by hot pressing. Vacuum injection is performed according to the injection coefficient of 2.8g / Ah. After sealing, high-temperature aging, formation, aging, and capacity separation are performed to produce a square aluminum shell battery with a length of 180 mm, a height of 100 mm, and a width of 45 mm, and a capacity of 50Ah.

[0116] Performance Test:

[0117] The lithium ion battery prepared in Test Example 1 was subjected to the following test, and the test results are shown in Table 2:

[0118] 1. Battery cycle test at 45°C:

[0119] The test method is: in a 45±2℃ constant temperature box, charge the lithium-ion battery to 4.3V at 0.33C constant current and constant voltage, with a cut-off current of 0.05C, and then discharge it to 2.0V at 0.33C constant current after being set aside. Perform multiple charge and discharge cycles under the above conditions. Calculate the capacity retention rate of the battery after 500 cycles, with 6 batteries in each group.

[0120] Capacity retention rate (%) = discharge capacity after 500 cycles (mAh) / discharge capacity after the third cycle (mAh) · 100%; the capacity retention rate of each group of 6 batteries after 500 cycles is averaged and recorded in Table 2.

[0121] 2. Battery overcharge test:

[0122] Test method: Before the formal test begins, the battery cells need to be pre-conditioned to ensure that the performance of the test object is in an activated and stable state. The fresh battery is charged to 4.3V at 0.33C constant current and constant voltage at 25°C, cut off at 0.05C, and left for 30 minutes. It is discharged to 2.5V at 0.33C constant current and left for 30 minutes. The charge and discharge are repeated no more than 5 times. If the discharge capacity change of the battery cell for two consecutive times is not higher than 3% of the rated capacity, it is considered that the battery cell has completed the pre-conditioning and the cycle can be terminated.

[0123] Charge to 4.3V at 0.33C constant current and constant voltage, cut off at 0.05C, leave for 30 minutes, then charge to 10V at 1C constant current, test the temperature change of the battery during charging, and observe the battery status after the test. Observe for 1 hour, and observe for 7 days after the test; if the battery does not catch fire or explode, and the surface temperature rise is less than 150℃, it is considered to have passed.

[0124] Table 2:

[0125]

[0126] In the table: “ / ” means that there is no such component in the electrolyte.

[0127] It can be seen from the data in Table 2 that, compared with Comparative Example 1, when the second additive with a mass fraction of 8% was added to the electrolyte of Comparative Example 2 and when the first additive with a mass fraction of 3% was added to the electrolyte of Comparative Example 3, the overcharge prevention performance of the battery was improved to a certain extent, but the cycle performance of the battery was not significantly improved; when the first additive and the second additive were added to the electrolyte of the embodiment at the same time, the cycle performance and overcharge prevention performance of the battery were significantly enhanced.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that: Composed of a first additive, a second additive, a third additive, a lithium salt and a non-aqueous organic solvent; or composed of a first additive, a second additive, a lithium salt and a non-aqueous organic solvent, wherein the first additive is any one or more of the compounds represented by formula 1-1 to formula 1-3: The second additive is any one or more compounds of Formula II-1, Formula II-2, Formula II-6 to Formula II-8: ， ， ； In the electrolyte, the mass percentage content of the first additive is 1wt%; And, the mass percentage of the second additive is 6wt%.

2. The electrolyte according to claim 1, characterized in that The third additive includes at least one of a cyclic carbonate and a cyclic carbonate substituted by a halogen.

3. The electrolyte according to claim 2, characterized in that The third additive includes at least one of vinylene carbonate, vinyl ethylene carbonate, methylene vinyl carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, and bisfluoroethylene carbonate.

4. The electrolyte according to claim 1, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, trifluorosulfonyl lithium, lithium difluoro(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, tris(trifluoromethylsulfonyl)methyl lithium, lithium bisoxalateborate, lithium bismalonateborate, lithium oxalatephosphate, and lithium tris(difluoromalonate)phosphate; the non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

5. The electrolyte according to claim 4, characterized in that In the electrolyte, the concentration of the lithium salt is 0.5 mol / L-2 mol / L.

6. A battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and the electrolyte according to any one of claims 1 to 5.

7. A battery pack, characterized in that: Comprising the battery as claimed in claim 6.

8. An electrical device, characterized in that: Comprising the battery according to claim 6 or the battery pack according to claim 7.

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