Electrolyte additive, electrolyte, and secondary battery, and electric device

Abstract

The application provides an electrolyte additive, an electrolyte and a secondary battery, and a power utilization device, and the structure of the electrolyte additive is shown in formula (I): wherein x, y and n are each independently a natural number, and n is greater than or equal to 1; R1, R2 and R3 are each independently at least one selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted unsaturated hydrocarbon group and a substituted or unsubstituted aryl group. The electrolyte additive is particularly suitable for an electrolyte used in high working voltage, and can improve the long cycle performance, high-temperature cycle performance and high-temperature storage performance of the battery under high working voltage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrolyte additive, an electrolyte, a secondary battery and an electric device. BACKGROUND

[0002] With the progress of science and technology, consumers have increasingly high requirements for the endurance of 3C electronic products and new energy vehicles, etc., which requires continuous improvement of the energy density of batteries. Although the energy density of batteries can be improved by developing high-voltage positive electrode materials, the existing electrolyte is prone to serious oxidation at high voltage, which leads to adverse consequences such as battery swelling. In addition, high voltage will exacerbate the dissolution of transition metal ions in the positive electrode material, which not only causes the collapse of the structure of the positive electrode material, but also causes the solid-state electrolyte membrane on the surface of the negative electrode to be damaged, thereby causing the capacity of the battery to rapidly decay. SUMMARY

[0003] In view of this, the present application provides an electrolyte additive, an electrolyte, a secondary battery and an electric device, which is particularly suitable for electrolyte used at high working voltage, and can improve the long cycle performance, high temperature cycle performance and high temperature storage performance of the battery at high working voltage.

[0004] The first aspect of the present application provides an electrolyte additive, the structure of which is shown in formula (I):

[0005]

[0006] wherein x, y and n are each independently a natural number, and n≥1; R1, R2, R3 are each independently selected from at least one of a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted unsaturated hydrocarbon group and a substituted or unsubstituted aryl group.

[0007] The above-mentioned electrolyte additive can be preferentially oxidized and decomposed during the charging and discharging process of the battery, and a cathode-electrolyte interface (CEI) film can be generated on the surface of the positive electrode plate, thereby stabilizing the interface between the positive electrode plate and the electrolyte, inhibiting the side reaction of the electrolyte, inhibiting the dissolution of transition metal elements in the positive electrode material at high voltage, greatly reducing the interface impedance, improving the room temperature and high temperature cycle performance of the battery, improving the high temperature storage performance of the battery, and significantly prolonging the service life of the battery.

[0008] Optionally, 1≤n≤3.

[0009] Optionally, 0≤x≤5; 0≤y≤5.

[0010] Optionally, the number of carbon atoms in the substituted or unsubstituted alkyl group is 1-5; the number of carbon atoms in the substituted or unsubstituted unsaturated hydrocarbon group is 2-5; and the number of carbon atoms in the substituted or unsubstituted aryl group is 6-10.

[0011] Optionally, each of the substituents in the substituted alkyl group, the substituted unsaturated hydrocarbon group is independently selected from at least one of a halogen atom, a cyano group, a carboxyl group and a sulfonic acid group; and the substituents in the substituted aryl group are selected from at least one of a halogen atom, a cyano group, a carboxyl group, a sulfonic acid group and an alkyl group.

[0012] Optionally, each of the substituents in the substituted alkyl group, the substituted unsaturated hydrocarbon group and the substituted aryl group is independently selected from a halogen atom.

[0013] The second aspect of the embodiments of the present application provides an electrolyte, which comprises an organic solvent, an electrolyte salt and at least one electrolyte additive as shown in formula (I):

[0014]

[0015] wherein x, y and n are each independently a natural number, and n≥1; and each of R1, R2 and R3 is independently selected from at least one of a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted unsaturated hydrocarbon group and a substituted or unsubstituted aryl group.

[0016] The electrolyte additive described above can be used to improve the high-voltage resistance of the electrolyte, thereby improving the long cycle performance, high-temperature cycle performance and high / low-temperature storage performance of the battery under high working voltage.

[0017] Optionally, the mass percentage of the electrolyte additive is 0.1%-20% based on the total weight of the electrolyte.

[0018] Optionally, the electrolyte further comprises a negative electrode film former; and the mass percentage of the negative electrode film former is 0.1%-15% based on the total weight of the electrolyte.

[0019] The third aspect of the present application provides a secondary battery, which comprises a positive electrode, a negative electrode and an electrolyte; wherein the electrolyte comprises the electrolyte additive provided by the first aspect of the present application.

[0020] Thanks to the adoption of the electrolyte additive provided by the embodiments of the present application, the battery can still have good long cycle performance, high-temperature cycle performance and high / low-temperature storage performance under a relatively high working voltage.

[0021] The fourth aspect of the present application provides a power consumption device, which comprises the secondary battery provided by the third aspect of the present application. DETAILED DESCRIPTION

[0022] Currently, in order to meet the demand of consumers for the endurance of electronic devices, the industry often improves the energy density of the battery by developing positive electrode materials with high working voltage. However, the existing electrolyte system cannot match the above-mentioned high-voltage battery system. Taking lithium batteries as an example, when the battery voltage is higher than 4.2V (vs Li / Li + ), the side reaction of electrolyte and positive electrode material will be intensified, the electrolyte is easy to oxidize and decompose and generate gas, resulting in rapid consumption of electrolyte, battery swelling, battery capacity attenuation and other adverse consequences, and even causing safety hazards.

[0023] To solve the above problems, the application provides an electrolyte additive, and the structure of the electrolyte additive is shown as formula (I):

[0024]

[0025] wherein x, y and n are each independently a natural number, and n≥1; R1, R2, R3 are each independently selected from at least one of a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted unsaturated hydrocarbon group, and a substituted or unsubstituted aryl group.

[0026] The above dicyanocyclic lactone electrolyte additive has both cyano and cyclic lactone structures, and the oxidation potential of the cyclic lactone structure is relatively low, which can make the electrolyte additive oxidize other components in the electrolyte during the charging and discharging process of the secondary battery, and generate a dense and uniform (cathode-electrolyte interface, CEI) film on the surface of the positive electrode sheet. The above-mentioned CEI film can effectively inhibit the side reaction of electrolyte and positive electrode material, thereby effectively inhibiting the oxidation of electrolyte, greatly reducing the risk of battery swelling, and improving the safety performance of the battery. At the same time, the synergistic effect of cyano and cyclic lactone structure can further modify the interface of the above-mentioned CEI film to further improve the interface stability of the positive electrode sheet / electrolyte, long-term inhibit the increase of positive electrode film layer impedance and electrochemical transmission impedance during the cycle process, and significantly improve the room temperature and high temperature cycle performance of the battery. In addition, the two cyano groups in the electrolyte additive can also complex transition metal ions in the positive electrode material (such as high-nickel ternary positive electrode material, etc.), forming a relatively stable ring structure, which can effectively inhibit the dissolution of transition metal ions in the positive electrode material under high voltage, thereby improving the problem of structure collapse of the positive electrode material, and significantly reducing the risk of transition metal ions migrating to the negative electrode surface to damage the solid electrolyte membrane, further improving the high-voltage resistance of the battery. At the same time, the above-mentioned substance with cyano group can adsorb H2O and HF and other fluorine-containing substances that may be generated during the cycle process of the battery, and form amide substances, reduce the high-temperature swelling caused by the catalysis of HF and other fluorine-containing substances on the decomposition of electrolyte solvent, and further improve the high-temperature cycle and high-temperature storage performance of the battery under high-voltage conditions.

[0027] In some embodiments of the present application, 1≤n≤3. Exemplarily, the value of n can be 1, 2, or 3. In this way, the steric hindrance of the electrolyte additive can be controlled within a more appropriate range, so that it can maintain a relatively high surface reactivity and can fully play its effect during the first charge-discharge and subsequent cycles of the battery. At the same time, it is also beneficial to control the viscosity of the final electrolyte within a more appropriate range, which is beneficial to the wetting of the electrolyte to the electrode and is also beneficial to ensuring that the ionic conductivity of the electrolyte is relatively high, thereby being beneficial to the rate performance of the battery.

[0028] In some embodiments of the present application, 0≤x≤5. Exemplarily, the value of x can be 0, 1, 2, 3, 4, or 5. In this way, it is beneficial to control the viscosity of the final electrolyte within an appropriate range, so as to control the ionic conductivity of the electrolyte to be relatively high and the wetting performance to be good; and also, the steric hindrance of the electrolyte additive can be relatively small, so that it can smoothly generate a CEI film on the surface of the positive electrode sheet and can effectively inhibit the dissolution of transition metal ions in the positive electrode.

[0029] In some embodiments of the present application, 0≤y≤5. Exemplarily, the value of y can be 0, 1, 2, 3, 4, or 5. Controlling the value of y within the above range can achieve the same principle and similar effect as controlling the value of x, which will not be described herein again.

[0030] In some specific embodiments, the above electrolyte additive simultaneously satisfies 1≤n≤3, 0≤x≤5, and 0≤y≤5.

[0031] In some embodiments of the present application, the number of carbon atoms in the substituted or unsubstituted alkyl group is 1-5; the number of carbon atoms in the substituted or unsubstituted unsaturated hydrocarbon group is 2-5; and the number of carbon atoms in the substituted or unsubstituted aryl group is 6-10. That is, R1, R2, and R3 in the electrolyte additive are each independently selected from at least one of a hydrogen atom, a halogen atom, a substituted or unsubstituted C 1～5 alkyl group, a substituted or unsubstituted C 2～5 unsaturated hydrocarbon group, and a substituted or unsubstituted C 6～10 aryl group. Limiting the number of carbon atoms in the above hydrocarbon group or aryl group within a certain range is beneficial to maintaining the viscosity of the electrolyte additive within an appropriate range, so as to ensure the wetting performance and ionic conductivity performance of the electrolyte. Exemplarily, the number of carbon atoms in the substituted or unsubstituted alkyl group can be 1, 2, 3, 4, or 5; the number of carbon atoms in the unsubstituted C 1～5 alkyl group can be 1, 2, 3, 4, or 5; the number of carbon atoms in the unsubstituted C 2～5The unsaturated hydrocarbon group can be any one of an alkenyl group such as vinyl, propenyl, butenyl, and the like; or an alkynyl group such as ethynyl, propynyl, and the like; the number of carbon atoms in the substituted or unsubstituted aryl group can be 6, 7, 8, 9, 10; wherein the unsubstituted aryl group can be phenyl, naphthyl, and the like. In some embodiments, the hydrogen atom in the aryl group is substituted by an alkyl group, which is hereinafter referred to as "alkylaryl" for convenience of description, and the hydrogen atom in the alkylaryl group (including the hydrogen atom in the alkyl group and the hydrogen atom on the aryl ring) can be further substituted by other groups, in which case, the number of carbon atoms in the substituted or unsubstituted alkylaryl group is controlled to be 7-10, illustratively, the number of carbon atoms in the substituted or unsubstituted alkylaryl group is 7, 8, 9, 10; wherein the alkylaryl group can be benzyl, phenethyl, and the like.

[0032] In some embodiments of the present application, at least one of R1, R2, and R3 in the electrolyte additive is an alkylaryl group. In this way, the high-temperature performance of the battery is further improved.

[0033] In some embodiments of the present application, the substituents in the substituted alkyl group, the substituted unsaturated hydrocarbon group are each independently selected from at least one of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group; and the substituents in the substituted aryl group are selected from at least one of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group. It can be understood that in some embodiments, the hydrogen atom in the aryl group is substituted by an alkyl group, or the hydrogen atom in the alkyl group is substituted by an aryl group; that is, R1, R2, and R3 can each independently be a substituted or unsubstituted alkylaryl group, or each independently be a substituted or unsubstituted arylalkyl group; in which case, the hydrogen atom in the alkylaryl group or the arylalkyl group can be further substituted by at least one of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group. Illustratively, the substituted alkylaryl group can be a halobenzyl group. In some embodiments, the substituents are each independently selected from a halogen atom. The halogen atom can include a fluorine atom (F), a chlorine atom (Cl), a bromine atom (Br), and an iodine atom (I). The presence of the halogen atom in the CEI film can effectively improve the structural stability thereof, thereby further improving the cycle stability of the battery; at the same time, the halogenated end group with local strong polarity can improve the ionic conductivity of the electrolyte, thereby improving the rate performance of the battery, for example, facilitating the fast-charging performance of the battery.

[0034] In some embodiments of the present application, the substituted C 1～5 alkyl group, the substituted C 2～5 unsaturated hydrocarbon group, the substituted C 6～10 aryl group, the substituted C 7～10 The substituents in the alkylaryl group are each independently selected from at least one of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group.

[0035] The application further provides an electrolyte, comprising an organic solvent, an electrolyte salt, and at least one electrolyte additive as shown in formula (I):

[0036]

[0037] wherein x, y and n are each independently a natural number, and n≥1; R1, R2, R3 are each independently selected from at least one of a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted unsaturated hydrocarbon group, and a substituted or unsubstituted aryl group.

[0038] The electrolyte additive as shown in formula (I) is contained in the above electrolyte. During the charging and discharging process of the battery, part of the electrolyte additive can be oxidized prior to other components (e.g., the organic solvent) in the electrolyte, thereby generating a dense and relatively uniform CEI film on the surface of the positive electrode plate, improving the interface condition between the positive electrode and the electrolyte, effectively inhibiting the side reaction between the electrolyte and the positive electrode material, thereby alleviating the consumption of the electrolyte and the generation of gas, and reducing the swelling rate of the battery cell. At the same time, the cyan group in the electrolyte additive (mainly the undecomposed electrolyte additive) can inhibit the dissolution of transition metal ions in the positive electrode material (e.g., ternary positive electrode material), absorb the free water molecules in the battery and the HF molecules that may be generated during the cycle process, so that the above electrolyte can improve the safety performance and long cycle performance of the battery, especially the long cycle performance, high-temperature cycle performance, high-temperature storage performance and safety performance of the battery at high voltage. The detailed working principle of the electrolyte additive can be referred to the description of the electrolyte additive hereinbefore, which will not be described here again.

[0039] In some embodiments of the application, 1≤n≤3. Exemplarily, the value of n can be 1, 2 or 3. In some embodiments of the application, 0≤x≤5. Exemplarily, the value of x can be 0, 1, 2, 3, 4 or 5. In some embodiments of the application, 0≤y≤5. Exemplarily, the value of y can be 0, 1, 2, 3, 4 or 5. Controlling the values of x, y and n within the above ranges can achieve the effects described hereinbefore, which will not be described here again.

[0040] In some specific embodiments, in the electrolyte, the above electrolyte additive simultaneously satisfies 1≤n≤3, 0≤x≤5 and 0≤y≤5. At this time, the viscosity of the electrolyte is more conducive to the transmission of active ions.

[0041] In some embodiments of the application, R1, R2 and R3 in the electrolyte additive are each independently selected from at least one of a hydrogen atom, a halogen atom, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 unsaturated hydrocarbon group, and a substituted or unsubstituted C6-C20 aryl group. 1～5 In some embodiments of the application, R1, R2 and R3 in the electrolyte additive are each independently selected from at least one of a hydrogen atom, a halogen atom, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 unsaturated hydrocarbon group, and a substituted or unsubstituted C6-C20 aryl group. 2～5 In some embodiments of the application, R1, R2 and R3 in the electrolyte additive are each independently selected from at least one of a hydrogen atom, a halogen atom, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 unsaturated hydrocarbon group, and a substituted or unsubstituted C6-C20 aryl group. 6～10At least one of the aryl groups. Limiting the number of carbon atoms of the aforementioned hydrocarbon or aryl group to a certain range is beneficial for maintaining the viscosity of the electrolyte additive within a suitable range, thereby ensuring the wettability and ionic conductivity of the electrolyte. For example, the number of carbon atoms in the substituted or unsubstituted alkyl group can be 1, 2, 3, 4, or 5; the number of carbon atoms in the substituted or unsubstituted unsaturated hydrocarbon group can be 2, 3, 4, or 5; and the number of carbon atoms in the substituted or unsubstituted aryl group can be 6, 7, 8, 9, or 10. Similarly, each of R1, R2, and R3 can also independently be a substituted or unsubstituted C 7～10 alkylaryl, substituted or unsubstituted C 7～10 Arylalkyl groups, as described above, will not be repeated here.

[0042] In some embodiments of this application, similarly, the substituent groups in the substituted alkyl, substituted unsaturated hydrocarbon, substituted aryl, substituted arylalkyl, and substituted alkylaryl groups are each independently selected from at least one of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group. In some specific embodiments, the substituted C 1～5 Alkyl, substituted C 2～5 Unsaturated hydrocarbon groups, substituted C 6～10 Aryl and substituted C 7～10 The substituents in the alkyl aryl group are each independently selected from at least one of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group. In some specific embodiments, the substituents are each independently selected from a halogen atom. The halogen atom may include a fluorine atom (F), a chlorine atom (Cl), a bromine atom (Br), or an iodine atom (I). Locally highly polar halogenated end groups can improve the ionic conductivity of the electrolyte, which is beneficial for improving the rate performance of the battery, for example, enabling fast charging.

[0043] In some specific embodiments of this application, at least one of R1, R2, and R3 in the electrolyte additive is a C atom substituted with a halogen atom. 7～10 Alkyl aryl groups. This is more beneficial for the high-temperature performance of the battery.

[0044] In some embodiments of this application, the electrolyte contains at least one electrolyte additive represented by formula (A)-(F):

[0045]

[0046]

[0047] In some embodiments of the present application, the mass percentage of the electrolyte additive is 0.1%-20% based on the total weight of the electrolyte. Exemplarily, the mass percentage of the electrolyte additive in the electrolyte can be 0.1%, 0.2%, 0.5%, 1%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc. In some specific embodiments of the present application, the mass percentage of the electrolyte additive in the electrolyte can be in the range of 0.5%-5%. A part of the electrolyte additive can be used to form the CEI film, and a part of the electrolyte additive can still be free in the electrolyte. Therefore, an appropriate amount of electrolyte additive can form a complete and moderately thick CEI film on the surface of the positive electrode sheet, effectively reducing the problem of large-thickness CEI film affecting the performance of the battery; and greatly reducing the risk of excessive free electrolyte additive occupying the share of other necessary substances in the electrolyte, leading to the deterioration of battery performance.

[0048] In some embodiments of the present application, the electrolyte further comprises a negative electrode film-forming agent. The negative electrode film-forming agent can generate a stable solid electrolyte interface (SEI) film on the surface of the negative electrode sheet during the charging and discharging process of the battery, thereby improving the interface condition of the negative electrode / electrolyte, and being beneficial to further improving the cycle performance, storage performance and safety performance of the battery.

[0049] In some embodiments of the present application, the mass percentage of the negative electrode film-forming agent is 0.1%-15% based on the total weight of the electrolyte. Exemplarily, the mass percentage of the negative electrode film-forming agent in the electrolyte can be 0.1%, 0.2%, 0.5%, 1%, 2%, 5%, 8%, 10%, 12%, 15%, etc. In some specific embodiments, the mass percentage of the negative electrode film-forming agent in the electrolyte is 1%-5%. Controlling the content of the negative electrode film-forming agent in the above range can generate a complete and appropriately thick SEI film on the surface of the negative electrode, and will not occupy the content of other necessary substances in the electrolyte, which is beneficial to the normal performance of the battery.

[0050] In some embodiments of the present application, the negative electrode film-forming agent can be selected from materials well known to those skilled in the art. Exemplarily, the negative electrode film-forming agent can be one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 1,3-propene sultone, vinyl sulfate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate. In some specific embodiments, the negative electrode film-forming agent is selected from one or more of vinyl sulfate, lithium difluorobisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate. In this way, the negative electrode film-forming agent also has a synergistic effect with the electrolyte additive, which is conducive to further improving the overall electrochemical performance of the battery. In some embodiments of the present application, the organic solvent in the electrolyte includes, but is not limited to, one or more of vinyl carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, γ-butyrolactone, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, and butyl propionate.

[0051] In some embodiments of the present application, the electrolyte salt can be a material well known to those skilled in the art, specifically a lithium salt. The lithium salt includes, but is not limited to, one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorobisoxalate borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bisfluorosulfonylimide. In the present application, there is no special requirement for the content of the electrolyte salt in the electrolyte, which can refer to the conventional amount in the art.

[0052] The present application also provides a secondary battery including a positive electrode, a negative electrode, and the electrolyte provided by the present application. Due to the use of the electrolyte provided by the present application, the battery has good long cycle performance, high-temperature cycle performance, and high-temperature storage performance at a high working voltage.

[0053] In some specific embodiments of the present application, the secondary battery is a lithium ion battery.

[0054] In some embodiments of the present application, the positive electrode includes a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector. According to different secondary battery systems, the material of the positive electrode current collector is selected from any well-known material in the art that is suitable for the specific secondary battery system. The positive electrode active material includes a material that can realize reversible deintercalation / intercalation of active ions (e.g., lithium ions, sodium ions, potassium ions, magnesium ions, zinc ions, aluminum ions, etc.). Taking a lithium ion battery as an example, the positive electrode active material can be, but is not limited to, lithium cobaltate (LiCoO2), lithium iron phosphate (LiFePO4), LiNi 0.33 Co 0.33 Mn 0.33 O2(NCM111), LiNi 0.4 Co 0.2Mn 0.4 O2(NCM424), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811).

[0055] In some embodiments of the present application, the positive active material includes a high-nickel ternary material, the high-nickel ternary material includes a ternary nickel-cobalt-manganese material, and specifically can be LiNi 0.33 Co 0.33 Mn 0.33 O2(NCM111), LiNi 0.4 Co 0.2 Mn 0.4 O2(NCM424), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.075 Mn 0.075 O. The high-nickel ternary material has a high specific capacity, which can greatly improve the energy density of the battery.

[0056] In the present application, the negative electrode of the secondary battery can be any negative electrode known in the art.

[0057] In the present application, a separator is further clamped between the positive electrode and the negative electrode. The separator can be any separator known to those skilled in the art.

[0058] The present application also provides a power-using device, which includes the power-using device provided by the present application.

[0059] In some embodiments of the present application, the power-using device includes but is not limited to 3C electronic products, power vehicles, etc.

[0060] The technical solutions of the present application are further described in the following embodiments.

[0061] Embodiment 1

[0062] (1) Preparation of electrolyte: Vinyl carbonate (EC) and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 3:7, and then an electrolyte additive represented by formula (A), a negative electrode film former (specifically, vinylene carbonate, VC), and an electrolyte salt (specifically, lithium hexafluorophosphate, LiPF6) were added to the mixture to a molar concentration of 1.0 mol / L of the electrolyte salt, a mass percentage of 1% of the electrolyte additive, and a mass percentage of 2% of the negative electrode film former.

[0063] (2) Preparation of a positive electrode sheet, the preparation method of which is as follows: ternary positive electrode material (specifically, NCM622), Super-P (conductive agent), CNT (conductive agent), and binder (specifically, polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 96:1.5:1:1.5, and then they were dispersed in a solvent (specifically, N-methyl pyrrolidone, NMP) to obtain a positive electrode slurry by stirring the mixture in a vacuum stirrer until it was stable and uniform; the positive electrode slurry was uniformly coated on both sides of an aluminum foil with a thickness of 18 μm, and after being dried at room temperature, it was transferred to a 120°C air oven for drying for 2 h, and then it was subjected to cold pressing and slitting processes to obtain a positive electrode sheet.

[0064] (3) Preparation of a negative electrode sheet, the preparation method of which is as follows: artificial graphite, Super-P, binder (specifically, styrene butadiene rubber, SBR), and thickening agent (specifically, sodium carboxymethyl cellulose, CMC) were mixed in a mass ratio of 95.6:1.4:1:2, and then they were dispersed in a solvent (specifically, deionized water) to obtain a negative electrode slurry, and the negative electrode slurry was uniformly coated on both sides of a copper foil with a thickness of 8 μm, and after being dried at room temperature, it was transferred to a 120°C air oven for drying for 2 h, and then it was subjected to cold pressing and slitting processes to obtain a negative electrode sheet.

[0065] (4) Assembly and formation of the battery, the steps of which are as follows: the above-mentioned positive electrode sheet, separator, and negative electrode sheet were stacked in order in an argon glove box with a water content of less than 5 ppm to obtain a bare cell, the bare cell was loaded into a battery shell and welded, then 1.6 g of the above-mentioned electrolyte was injected into the battery shell, and the battery shell was sealed to obtain a lithium ion battery. The above-mentioned battery was first charged to 1.5 V at a current of 40 mA (0.05C), and then held at 1.5 V for 10 h to fully wet the battery electrode sheet. After the constant voltage was completed, the battery was initially charged at a small current of 8 mA (C / 100) for 10 h to form a stable and dense SEI film, and then charged to 4.35 V at a current of 40 mA (0.05C) and discharged to 3.0 V. A secondary battery of Example 1 was obtained.

[0066] Examples 2-16

[0067] On the basis of Example 1, the electrolyte part parameters in Example 1 and the composition of the electrolyte additive are replaced. For convenience of description, the parameters or substances changed in Examples 2-16 relative to Example 1 are summarized in Table 1.

[0068] To highlight the beneficial effects of the embodiments of the present application, Comparative Examples 1-3 are provided.

[0069] The parameters or substances changed in Comparative Examples 1-3 relative to Example 1 are also summarized in Table 1.

[0070] Table 1

[0071]

[0072]

[0073] In Table 1, the structural formula of the electrolyte additive in each example is as follows:

[0074]

[0075]

[0076] Electrochemical performance test

[0077] (1) Normal temperature cycle test

[0078] The secondary batteries prepared in each of the above examples and comparative examples were charged at 1C constant current to 4.4V at 25°C, then charged at constant voltage to the cutoff current of 0.05C, and then rested for 30min, and then discharged at 1C constant current to 2.5V, which was recorded as one charge-discharge cycle, and then cycled for 1000 weeks under the above conditions; wherein the capacity retention rate (%) of the secondary battery after 1000 weeks of cycling = (discharge capacity of the 1000th week cycle / first week discharge capacity) x 100%. The test results are summarized in Table 2.

[0079] (2) High temperature cycle performance test

[0080] The lithium ion batteries prepared in each of the above examples and comparative examples were charged at 1C constant current to 4.4V at 45°C, then charged at constant voltage to the cutoff current of 0.05C, and then rested for 30min, and then discharged at 1C constant current to 2.5V, which was recorded as one charge-discharge cycle, and then cycled for 500 weeks under the above conditions; wherein the capacity retention rate (%) of the secondary battery after 500 weeks of cycling = (discharge capacity of the 500th week cycle / first week discharge capacity) x 100%; the test results are summarized in Table 2.

[0081] (3) High temperature storage performance test

[0082] The secondary batteries prepared in each of the above examples and comparative examples were charged at 25°C at 1C constant current and constant voltage to 4.4V, cut off at 0.05C, and then left for 30 min, and then discharged at 1C constant current to 2.5V. The discharge capacity was taken as the initial capacity Co, the battery volume Vo before storage was measured, and the battery was transferred to a high-temperature test cabinet and stored at 55°C for 14 days. After storage, the test battery was taken out, left to stand at room temperature for 24 hours, the battery volume V1 after storage was measured, and then discharged at 1C constant current to 2.5V. The discharge capacity C1 was recorded, and then charged at 1C constant current and constant voltage to 4.4V, cut off at 0.05C, and then left for 30 min, and then discharged at 1C constant current to 2.5V. The discharge capacity C2 was recorded.

[0083] The capacity remaining rate (%) = C1 / C0 x 100%;

[0084] The capacity recovery rate (%) = C2 / C0 x 100%;

[0085] The battery volume expansion rate (%) = [(V1-V0) / V0] x 100%; and the test results are summarized in Table 2.

[0086] Table 2

[0087]

[0088] In combination with the parameters in Table 1 and the data in Table 2, in the case where the electrolyte of each secondary battery contains a negative electrode film former and an additive (the electrolyte additive of the examples or hexanedinitrile of Comparative Example 3) (Examples 1-14 and Comparative Examples 1-3), the room temperature / high temperature cycle performance and high temperature storage performance of the example batteries are significantly higher than those of the comparative example batteries.

[0089] In particular, as can be seen from the data of Comparative Examples 1-16, when the electrolyte provided by the present application is used (i.e., containing both a negative electrode film former and an electrolyte additive provided by the present application), the room temperature / high temperature cycle performance and high temperature storage performance of the battery are more favorable. As can be seen from the data of Comparative Example 7 and Example 8, when the negative electrode film former is selected from the further preferred substances such as vinyl sulfate, the performance of the battery is more favorable.

[0090] As can be seen from the data of Comparative Examples 1-6, when the content of the electrolyte additive in the electrolyte is within the range suggested by the present application (Examples 2-6), the performance of the battery is more favorable; and when the content of the electrolyte additive is within the further suggested range of the present application (Examples 3-5), the cycle performance and high temperature storage performance of the battery can be further improved.

[0091] The above is an example embodiment of the present application, it should be pointed out that, for those skilled in the art, without departing from the principles of the present application, can make several improvements and refinements, these improvements and refinements also regarded as the scope of protection of the present application.

Claims

1. An electrolyte additive characterized in that, The structure of the electrolyte additive is shown in formula (I): wherein x, y and n are each independently a natural number, and n≥1; R1, R2, R3 are each independently selected from at least one of a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted unsaturated hydrocarbon group, and a substituted or unsubstituted aryl group.

2. The electrolyte additive according to claim 1, characterized in that, 1≤n≤3。 3. The electrolyte additive according to claim 1, characterized in that, 0≤x≤5; 0≤y≤5.

4. The electrolyte additive according to claim 1, characterized in that, The substituted or unsubstituted alkyl group has 1-5 carbon atoms; the substituted or unsubstituted unsaturated hydrocarbon group has 2-5 carbon atoms; and the substituted or unsubstituted aryl group has 6-10 carbon atoms.

5. The electrolyte additive according to claim 1 or 4, characterized in that, The substituent in the substituted alkyl group, the substituted unsaturated hydrocarbon group is each independently selected from at least one of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group; and the substituent in the substituted aryl group is selected from at least one of a halogen atom, a cyano group, a carboxyl group, a sulfonic acid group, and an alkyl group.

6. The electrolyte additive according to claim 5, characterized in that The substituent in the substituted alkyl group, the substituted unsaturated hydrocarbon group, and the substituted aryl group is each independently selected from a halogen atom.

7. An electrolyte, characterized by The electrolyte comprises at least one electrolyte additive as claimed in any one of claims 1-6, an organic solvent, and an electrolyte salt.

8. The electrolyte according to claim 7, characterized in that The mass percentage of the electrolyte additive is 0.1%-20% based on the total weight of the electrolyte.

9. The electrolyte according to claim 7 or 8, characterized in that, The electrolyte further comprises a negative electrode film-forming agent; the mass percentage of the negative electrode film-forming agent is 0.1%-15% based on the total weight of the electrolyte.

10. A secondary battery characterized by comprising: The secondary battery comprises a positive electrode, a negative electrode, and an electrolyte; wherein the electrolyte comprises an electrolyte additive as claimed in any one of claims 1-6.

11. An electrical device, characterized by The electric device comprises the secondary battery as claimed in claim 10.

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