Electrolytes and high voltage electrochemical devices and electronic devices

Abstract

The application relates to an electrolyte, a high-voltage electrochemical device and an electronic equipment. The electrolyte is applied to the high-voltage electrochemical device, and the electrolyte comprises an organic solvent, a lithium salt and an additive. The additive comprises a polynitrile additive and a dinitrile additive. The polynitrile additive comprises at least three cyano groups. A condition that (A+B) / X >= 0.5 is met between the additive and the high-voltage electrochemical device, wherein A% is the mass percentage of the polynitrile additive in the electrolyte, B% is the mass percentage of the dinitrile additive in the electrolyte, and X V is the full charging voltage of the high-voltage electrochemical device. The scheme provided by the application can control the K value of the battery within a reasonable range, and the high-temperature cycle storage and high-temperature cycle performance of the battery under high voltage are considered.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrolyte, a high-voltage electrochemical device and an electronic device. BACKGROUND

[0002] The popularity of portable electronic devices such as mobile phones, tablets, and laptops has promoted the development of high-energy-density secondary batteries. In order to obtain higher battery capacity, the charge cut-off voltage is sometimes set to 4.4V or even higher. In this high-voltage environment, the oxidation of the positive electrode material increases, and the electrolyte is easily oxidized and decomposed on the positive electrode side. At the same time, transition metal ions are dissolved and reduced and deposited on the negative electrode side, hindering the migration of lithium ions. Therefore, it is particularly important to protect the surface of the positive electrode of the battery under high voltage.

[0003] In related technologies, by adding a polynitrile compound as an additive in the electrolyte, the cobalt atoms in the lithium cobalt oxide active material of the positive electrode can be effectively complexed, and the structural stability of the positive electrode active material under high voltage can be effectively improved.

[0004] However, the polynitrile compound can complex free copper ions in the electrolyte, and then be reduced to copper single element on the negative electrode surface, resulting in abnormal K value of the battery cell and affecting the electrochemical performance of the battery. SUMMARY

[0005] To solve or partially solve the problems in the related art, the present application provides an electrolyte, a high-voltage electrochemical device and an electronic device, which can control the K value of the battery within a reasonable range, and also consider the high-temperature cycle storage and high-temperature cycle performance of the battery under high voltage.

[0006] The first aspect of the present application provides an electrolyte applied to a high-voltage electrochemical device, the electrolyte comprising an organic solvent, a lithium salt and an additive, the additive comprising a polynitrile additive and a dinitrile additive, the polynitrile additive comprising at least three cyano groups; and the additive and the high-voltage electrochemical device satisfy the following relationship:

[0007] (A+B) / X≥0.5

[0008] In the relationship, the mass percentage of the polynitrile additive in the electrolyte is A%, the mass percentage of the dinitrile additive in the electrolyte is B%, and the full charge voltage of the high-voltage electrochemical device is X V.

[0009] As an optional embodiment, the additive and the high-voltage electrochemical device satisfy (A+B) / X≥0.556.

[0010] As an optional embodiment, 0.5≤A≤4.

[0011] As an optional embodiment, 0.5≤B≤4.

[0012] As an optional embodiment, 4≤X≤4.58.

[0013] As an optional embodiment, B / A≥0.5.

[0014] As an optional embodiment, the polycarbonitrile additive comprises at least one of 1,2,3,4,5-penta-oxygen-(2-cyanoethyl) and 1,3,6-hexanetricarbonitrile.

[0015] As an optional embodiment, the dinitrile additive comprises at least one of succinonitrile and adiponitrile.

[0016] As an optional embodiment, the additive further comprises a sulfur-containing additive, and the sulfur-containing additive has a structural formula as follows:

[0017]

[0018] In the structural formula I, n is 0 or 1, and X is selected from or R1, R2 and R3 are each independently selected from H, at least one of the above, and R1, R2 and R3 are not simultaneously selected from H, and at least one of X, R1, R2 and R3 contains a sulfur atom.

[0019] As an optional embodiment, the sulfur-containing additive accounts for C% of the mass percentage of the electrolyte, 0.5≤C≤4; and / or, C / (A+B)≥0.125.

[0020] As an optional embodiment, the sulfur-containing additive comprises at least one of the following compounds:

[0021]

[0022] The second aspect of the present application provides a high-voltage electrochemical device comprising the electrolyte described above.

[0023] The third aspect of the present application provides an electronic device comprising the electrochemical device described above.

[0024] The technical solution provided by the present application can include the following beneficial effects:

[0025] In the present application, the additive comprises a polycarbonitrile additive and a dinitrile additive, the polycarbonitrile additive can refer to a compound with a number of cyano functional groups not less than 3, and the content of the additive and the full charge voltage of the high-voltage electrochemical device satisfy (A+B) / X≥0.5, which can control the K value of the battery within a reasonable range, and also take into account the high-temperature cycle storage and high-temperature cycle performance of the battery at high voltage.

[0026] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application, as claimed. DETAILED DESCRIPTION

[0027] Embodiments of the present application will be described in more detail with reference to the drawings. Although embodiments of the present application are shown, it is to be understood that the present application can be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.

[0028] The terminology used in the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used in the description of the application and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0029] It should be understood that although the terms "first", "second", "third", etc. can be employed in this application to describe various information, such information should not be limited by these terms. These terms are only used to distinguish one piece of information from another. For example, a first information can also be referred to as a second information, and similarly, a second information can also be referred to as a first information without departing from the scope of the present application. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0030] In the related art, by adding a polycarbonyl compound as an additive in the electrolyte, the cobalt atoms in the positive active material lithium cobaltate can be effectively complexed, and the structural stability of the positive active material at high voltage can be effectively improved.

[0031] However, the polycarbonyl compound can complex free copper ions in the electrolyte, and then be reduced to copper single element on the negative electrode surface, resulting in abnormal K value of the battery cell, affecting the electrochemical performance of the battery.

[0032] To solve the above problems, the embodiments of the present application provide an electrolyte which can control the K value of the battery within a reasonable range, and also take into account the high-temperature cycle storage and high-temperature cycle performance of the battery at high voltage.

[0033] The electrolyte provided by the embodiment of the present application is applied to a high-voltage electrochemical device, and the electrolyte comprises an organic solvent, a lithium salt and an additive, the additive comprises a polynitrile additive and a dinitrile additive, the polynitrile compound contains at least three cyano groups, and the following relationship is satisfied between the additive and the high-voltage electrochemical device:

[0034] (A+B) / X≥0.5

[0035] In the relationship, the mass percentage of the polynitrile additive in the electrolyte is A%, the mass percentage of the dinitrile additive in the electrolyte is B%, the mass percentage of the sulfur-containing additive in the electrolyte is C%, and the full charging voltage of the high-voltage electrochemical device is X V.

[0036] In the embodiment of the present application, the lithium salt comprises one or more of lithium hexafluorophosphate LiPF6, lithium difluoro(oxalato)borate LiODFB, lithium bis(oxalato)borate LiBOB, lithium difluorophosphate LiPOF2, lithium tetrafluoroborate LiBF4, lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, and the concentration of the electrolyte salt is 0.4 mol / L-2.2 mol / L.

[0037] In the embodiment of the present application, the organic solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, methyl acetate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0038] In the embodiment of the present application, the full charging voltage of the high-voltage electrochemical device is a high voltage (4 V-4.58 V). The full charging voltage of the electrochemical device can refer to the voltage when the electrochemical device is fully charged, that is, the voltage value tested by a multimeter after charging the electrochemical device to the rated capacity marked on the battery cell. The full charging voltage can be the voltage marked on the battery after the battery is completed, and will not change due to the change of the additive.

[0039] In the embodiment of the present application, the additive comprises a polynitrile additive and a dinitrile additive, the polynitrile additive can refer to a compound with a number of cyano functional groups not less than 3, and the content of the additive and the full charging voltage of the high-voltage electrochemical device satisfy the relationship (A+B) / X≥0.5, which can control the K value of the battery within a reasonable range, and also consider the high-temperature cycle storage and high-temperature cycle performance of the battery at high voltage. This is due to the following reasons:

[0040] ① The nitrile additive can improve the high-voltage performance of the battery

[0041] The cyano functional groups in nitrile additives strongly complex with transition metals on the surface of the cathode material, forming a CEI film that protects the cathode active material and inhibits metal element dissolution, effectively improving the structural stability of the cathode active material at high voltages. Nitrile additives also have excellent oxidation resistance, inhibiting oxidative decomposition of the electrolyte on the cathode side at high voltages. Therefore, higher voltages require more nitrile additives to improve the battery's high-voltage performance.

[0042] ② Nitrile additives can improve the high-temperature storage performance of batteries

[0043] When batteries are stored at 85°C, the electrolyte is easily oxidized and decomposed to produce HF, which then undergoes side reactions at the electrode interface, leading to the generation of large amounts of gas. The cyano functional group in nitrile additives has the ability to remove water and acid, capturing the HF generated during high-temperature storage and inhibiting further side reactions in the electrolyte. Therefore, the addition of nitrile additives can effectively improve the high-temperature storage performance of batteries, and multi-nitrile additives are particularly effective in improving high-temperature storage performance.

[0044] ③Nitrile additives can synergistically control the battery K value within a reasonable range

[0045] Polynitrile compounds in nitrile additives, such as tetraether nitrile and HTCN, easily react with the electrolyte to produce copper precipitation, resulting in an increase in the battery K value. The reaction mechanism is as follows:

[0046] R1: 1LiPF6+H2O→POF3+LiF+2HF;

[0047] R2: 2H++CuO x →H2O+Cu 2+ ;

[0048] Cu 2+ / Cu (~3.3V vs.Li+ / Li); Cu + / Cu (~3.5V vs.Li+ / Li);

[0049] R3:Cu n+ +2CN-R+nPF.→Cu(CN-R)PF. / Cu(CN-R)PF;

[0050] Cu n+ +nF→CuF (slightly soluble);

[0051] Cu n+ +nPF→Cu(PF);

[0052] R4:Cu n+ +ne - →Cu↓(reduction and precipitation on the anode surface).

[0053] And the dinitrile additive such as SN and ADN in the nitrile additive can form a Cu(CN-R)·PF protective layer with Cu ions, inhibit the further corrosion of the copper foil, and improve the oxidation potential of Cu, so the dinitrile additive and the polynitrile additive have a synergistic effect, and the K value of the battery can be controlled in a reasonable range.

[0054] (4) The nitrile additive and the full charge voltage of the high-voltage electrochemical device satisfy (A+B) / X≥0.5, which can balance the high-temperature cycle performance at high voltage

[0055] Although the nitrile additive can improve the high-voltage performance of the battery, the nitrile additive has a high film-forming impedance on the positive electrode, which can easily lead to an increase in the polarization of the positive electrode side at high voltage, and deteriorate the high-temperature cycle performance. Therefore, the content of the nitrile additive needs to maintain a certain proportional relationship with the full charge voltage of the battery, so as to better balance the nitrile additive in improving the high-voltage performance of the battery, while considering the impedance on the positive electrode side and improving the high-temperature cycle performance. The inventors have found that when (A+B) / X≥0.5, a better balance can be achieved.

[0056] As an optional embodiment, the content of the additive and the full charge voltage of the high-voltage electrochemical device satisfy (A+B) / X≥0.556.

[0057] The inventors have further found that A+B can represent the total content of the polynitrile additive and the dinitrile additive, i.e., the total content of the nitrile additive. When the total content of the nitrile additive and the full charge voltage of the battery satisfy (A+B) / X≥0.556, the high-voltage performance and the high-temperature cycle performance can be further balanced.

[0058] As an optional embodiment, 0.5≤A≤4.

[0059] In the embodiments of the present application, A can be 0.5, 1, 2, 3, 4, or any value within the above defined range, which is not limited in the present application.

[0060] If the value of A is too low, the storage performance of the battery and the protection of the transition metal of the positive electrode are insufficient, and the high-voltage high-temperature cycle and the high-temperature storage performance are poor. If the value of A is too large, the viscosity of the electrolyte will increase.

[0061] As an optional embodiment, 0.5≤B≤4.

[0062] In the embodiments of the present application, B can be 0.5, 1, 2, 3, 4, or any value within the above defined range, which is not limited in the present application.

[0063] Similarly, if the value of B is too low, the K value of the battery will increase, and the high-voltage high-temperature cycle and the high-temperature storage performance are poor. If the value of B is too large, the viscosity of the electrolyte will increase.

[0064] As an optional embodiment, 4≤X≤4.58.

[0065] In the embodiments of the present application, X can be 4, 4.5, 4.58 or any value within the above defined range, which is not limited in the present application. The additive of the embodiments of the present application can achieve better effects when applied to the electrochemical device with the full charge voltage within the above range.

[0066] As an optional embodiment, B / A≥0.5.

[0067] B / A represents the ratio of the mass content of the dinitrile additive to the polynitrile additive, for example, B / A can be 0.5, 1, 3, 10, 20, etc. Since the polynitrile additive is a deteriorating factor for copper deposition, the more the content, the more obvious the deterioration, while the dinitrile compound can form a Cu(CN-R)·PF protective layer with Cu ions to inhibit the further corrosion of the copper foil and improve the oxidation potential of Cu. Therefore, when the content ratio of the dinitrile additive and the polynitrile additive is within the above range, the k value of the battery can be controlled within a reasonable range.

[0068] As an optional embodiment, the polynitrile additive includes at least one of 1,2,3,4,5-penta-oxy-(2-cyanoethyl) and 1,3,6-hexane trinitrile.

[0069] The polynitrile additive selected in the embodiments of the present application has more cyano functional groups, which is better for the transition metal complexation of the positive electrode, and has stronger oxidation resistance.

[0070] As an optional embodiment, the dinitrile additive includes at least one of succinonitrile and adiponitrile.

[0071] The dinitrile additive selected in the embodiments of the present application has lower cost, is more common, has relatively controllable viscosity and impedance, and has an effective effect of inhibiting corrosion of the copper foil.

[0072] As an optional embodiment, the additive further includes a sulfur-containing additive, and the structure formula of the sulfur-containing additive is as follows:

[0073]

[0074] In the structure formula one, n is 0 or 1, X is selected from or R1, R2 and R3 are each independently selected from H, at least one of the above, and R1, R2 and R3 are not simultaneously selected from H, and at least one of X, R1, R2 and R3 contains a sulfur atom.

[0075] The sulfur-containing additive of structural formula one can form a film on both the positive and negative electrode sides, and the electrode interface film formed by the sulfur-containing additive has good thermal stability, which can improve the high-temperature storage performance of the battery. At the same time, the CEI film formed by the sulfur-containing additive on the positive electrode side is rich in sulfur elements, which can reduce the impedance on the positive electrode side. Therefore, when the content of the nitrile-based additive is high, increasing the content of the sulfur-containing additive can reduce the impedance on the positive electrode, reduce polarization, and improve the high-voltage high-temperature cycle performance of the battery.

[0076] As a preferred embodiment, the mass percentage of the sulfur-containing additive in the electrolyte is C%, and 0.5≤C≤4.

[0077] In the embodiments of the present application, C can be 0.5, 1, 2, 3, 4, or any value within the above-mentioned range, which is not limited in the present application.

[0078] If the value of C is too low, the impedance on the positive electrode side cannot be reduced, which is not conducive to improving the high-voltage high-temperature cycle performance of the battery. If the value of C is too large, the viscosity of the electrolyte will increase, which will deteriorate the battery performance.

[0079] As a preferred embodiment, C / (A+B)≥0.125

[0080] C / (A+B) represents the ratio of the content of the sulfur-containing additive to the content of the nitrile-based additive. Since the sulfur-containing additive of the embodiments of the present application can form a film on both the positive and negative electrode sides, and the electrode interface film formed by the sulfur-containing additive has good thermal stability, which can improve the high-temperature storage performance of the battery. At the same time, the CEI film formed by the sulfur-containing additive on the positive electrode side is rich in sulfur elements, which can reduce the impedance on the positive electrode side. Therefore, when the content of the nitrile-based additive is high, increasing the content of the sulfur-containing additive can reduce the impedance on the positive electrode, reduce polarization, and improve the high-voltage high-temperature cycle performance of the battery. Controlling the content of the sulfur-containing additive and the nitrile-based additive within the above-mentioned range can effectively improve the high-voltage high-temperature cycle performance.

[0081] As a preferred embodiment, the sulfur-containing additive includes at least one of the following compounds:

[0082]

[0083] The sulfur-containing additive of the embodiments of the present application includes a five-membered cyclic carbonate group, a five-membered cyclic sulfate group, a six-membered cyclic carbonate group, or a six-membered cyclic sulfate group, and the sulfur-containing additive includes at least one cyclic sulfate group. The sulfate group or carbonate group in the sulfur-containing additive can participate in the formation of the interface film, improving the stability of the interface film. When the sulfur-containing additive is selected from the above-mentioned compounds, the sulfur-containing additive and the nitrile-based additive can better synergize to generate a CEI film with higher stability, thereby better alleviating the side reaction between the positive electrode additive and the positive electrode active material, and further improving the high-temperature cycle performance and high-temperature storage performance of the battery at high voltage.

[0084] In addition, the preparation method of the above-mentioned compound can be known by those skilled in the art according to the common knowledge in the field of chemical synthesis, on the basis of the structural formula of the compound shown in structural formula I.

[0085] Corresponding to the foregoing application function implementation method embodiments, the application further provides a high-voltage electrochemical device, an electronic device, and corresponding embodiments.

[0086] The application further provides a high-voltage electrochemical device, which comprises the foregoing electrolyte, a positive electrode, a negative electrode, and a separator.

[0087] As an optional embodiment, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, the positive electrode active material layer comprises a positive electrode active material, and the chemical formula of the positive electrode active material is LiNi a Co b Mn (1-a-b) M c O2, wherein 0.3≤a≤0.9, a+b<1, 0≤c<0.08, and M is at least one of Al, Mg, Zr, and Ti.

[0088] In the embodiments of the application, the type of the positive electrode current collector is not particularly limited, and it can be any material known to be suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector comprises metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and carbon materials such as carbon cloth and carbon paper. Preferably, the positive electrode current collector is a metal material.

[0089] In one embodiment, the positive electrode active material layer further comprises a conductive agent, a binder, and a solvent.

[0090] In one embodiment, the conductive agent comprises at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene.

[0091] In one embodiment, the binder comprises at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0092] In the embodiments of the application, the material and shape of the separator are not particularly limited, as long as they do not significantly impair the effects of the application.

[0093] In one embodiment, the separator comprises a substance in a porous sheet-like or non-woven cloth-like form with excellent liquid retention. The material of the resin or glass fiber separator includes, but is not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyether sulfone, and the like.

[0094] In some embodiments, the electrochemical device can include an outer package that can be used to encapsulate the electrode assembly and the electrolyte as described above.

[0095] In some embodiments, the outer package of the electrochemical device can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the electrochemical device can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0096] The shape of the electrochemical device is not particularly limited in the present application, and it can be cylindrical, square, or any other arbitrary shape.

[0097] The negative current collector in the embodiments of the present application is not particularly limited as long as it can achieve the purpose of the present application, and for example, it can be a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, or a composite current collector, or the like.

[0098] The embodiments of the present application also provide an electronic device including the electrochemical device as described above.

[0099] For example, the power consuming device as described above can include a mobile device (such as a mobile phone, a notebook computer, or the like), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, or the like), an electric train, a ship and a satellite, an energy storage system, or the like, but is not limited thereto.

[0100] In order to further understand the present application, the present application will be described below in conjunction with the embodiments, which are only used to illustrate the present application and do not limit the scope of the present application.

[0101] I. Preparation of the battery

[0102] 1. Preparation of the positive electrode sheet

[0103] The positive electrode active material lithium cobaltate, the conductive agent acetylene black Super P, and the polyvinylidene fluoride PVDF binder were mixed uniformly at a mass ratio of 97:1.5:1.5, and uniformly dispersed in 1-methyl-2-pyrrolidone NMP to prepare a uniform black slurry. After the mixed slurry was coated on both sides of the aluminum foil current collector, baking, rolling, and sheet cutting were performed to obtain the positive electrode sheet.

[0104] 2. Preparation of the negative electrode sheet

[0105] The negative electrode active material graphite, the conductive agent acetylene black Super P, the thickening agent CMC, and the binder SBR were mixed uniformly at a mass ratio of 94:2:1.2:2.8, and uniformly dispersed in deionized water to prepare a uniform black slurry. After the mixed slurry was coated on both sides of the aluminum foil current collector, baking, rolling, and sheet cutting were performed to obtain the negative electrode sheet.

[0106] 3. Preparation of electrolyte

[0107] a. Mixing, stirring and blending ethylene carbonate EC, propylene carbonate PC, propyl propionate PP and diethyl carbonate DEC according to a mass ratio of 10:20:40:30 to form a mixed solvent, removing water by using molecular sieve, adding 1M LiPF6 and uniformly mixing

[0108] b. Adding an additive (the type and amount of the additive are shown in Table 1) to the colorless transparent liquid obtained in step a to obtain electrolytes of each example and the comparative example.

[0109] 4. Preparation of battery

[0110] The prepared positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence with the separator between the positive and negative electrode sheets, and then wound and tab-welded to obtain a bare cell. The positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence with the separator between the positive and negative electrode sheets to play a separating role, and then wound to obtain a bare cell. The bare cell is placed in an aluminum plastic film for packaging to obtain a battery. The prepared positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence with the separator between the positive and negative electrode sheets, and then wound and tab-welded to obtain a bare cell. The bare cell is placed in an aluminum plastic film for packaging to obtain a battery. The prepared positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence with the separator between the positive and negative electrode sheets to play a separating role, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging bag, dried at high temperature until the water content of the electrode sheet is less than 100 ppm, and then injected with the electrolyte prepared in each example and the comparative example. After vacuum packaging, standing, formation and shaping, the preparation of lithium ion batteries of each example and the comparative example is completed, and the full charge voltage of each example and the comparative example is set according to Table 1.

[0111] II. Performance test of battery

[0112] The performance of each example and the comparative example is tested as follows:

[0113] 1. 45°C cycle test

[0114] The test method is as follows: the lithium ion battery is charged to the full charge voltage corresponding to each example and the comparative example at 1C in a 45±2°C constant temperature box, the cut-off current is 0.05C, and then discharged at 1C to 3V. The above conditions are repeated for multiple charge and discharge cycles, the capacity retention rate after 600 cycles is calculated, and each group has 5 batteries.

[0115] Capacity retention rate (%) = discharge capacity (mAh) corresponding to the cycle number / third week cycle discharge capacity (mAh) * 100%.

[0116] The capacity retention rate of each group of 5 batteries after different cycle times is averaged and recorded in Table 2.

[0117] 2. K value test

[0118] The test method is as follows: the lithium ion battery is charged in a 25±2℃ constant temperature box at 1C constant current and constant voltage to the full charge voltage corresponding to each example and comparative example, the cutoff current is 0.05C, and the full charge voltage of the test battery is recorded as V1; the full battery is left to stand at room temperature for 100h, and the voltage of the test battery is recorded as V2.

[0119] K=(V1-V2) / 100.

[0120] The average value of 5 batteries in each group is recorded in Table 2.

[0121] 3, 85℃ storage performance test:

[0122] The test method is as follows: the lithium ion battery is charged in a 25±2℃ constant temperature box at 1C constant current and constant voltage to the full charge voltage corresponding to each example and comparative example, the cutoff current is 0.05C, and the thickness of the lithium ion battery is tested (as the thickness before storage). The full charged battery is left to stand at (85±2)℃ for 18h, and is left to stand at room temperature for 2h after storage, the thickness after storage is tested, and the thickness expansion rate of the lithium ion battery is calculated:

[0123] Thickness expansion rate=[(thickness after storage-thickness before storage) / thickness before storage]×100%.

[0124] The average value of 5 batteries in each group is recorded in Table 2.

[0125] Table 1 formula and relationship

[0126]

[0127]

[0128]

[0129] Table 2 test results

[0130]

[0131]

[0132] According to the data in Table 1 and Table 2, by comparing the data of Example 1 to Example 5, and Comparative Example 3, Comparative Example 7 and Comparative Example 8, it can be known that when the content of the polycarbonyl additive increases, the high temperature storage performance of the battery is obviously improved, but when the content of the polycarbonyl additive is too large, the K value of the battery increases, resulting in poor high temperature cycle performance. This is because the pentaether nitrile is a copper precipitation deteriorating factor, and the more the content, the more obvious the deterioration. When 0.5≤A≤4 is satisfied, the high temperature storage performance of the battery can be improved.

[0133] It is found by comparing the data of Example 3, Example 6 to Example 9, and Comparative Example 2, Comparative Example 9 and Comparative Example 10 that the storage performance of the battery is slightly improved with the increase of the content of dinitrile additive, and the high-temperature storage performance of the battery can be better improved when 0.5≤B≤4 is met. It is further known from the data of Comparative Example 22 to Comparative Example 24 that when the content of dinitrile compound is too low relative to the content of polynitrile compound, the K value abnormally increases, and the high-temperature cycle is deteriorated due to the increase of the positive electrode impedance. When the content of dinitrile additive relative to the content of polynitrile additive meets B / A≥0.5, the abnormal K value and the high-temperature storage performance of the battery can be better improved.

[0134] It is found by comparing the data of Example 3, Example 10 to Example 13, and Comparative Example 1, Comparative Example 11 and Comparative Example 12 that when the sulfur-containing additive of structural formula I is added and the content of the sulfur-containing additive is increased, the high-temperature cycle performance and the storage performance of the battery are improved, but the content of the sulfur-containing additive should not be too high, otherwise the viscosity of the electrolyte will be increased and the cycle performance will be deteriorated. When 0.5≤C≤4 is met, the additive cost and the battery performance can be better balanced. It is further known from the data of Comparative Example 19 to Comparative Example 21 that when the content of the sulfur-containing additive and the content of the nitrile additive meet C / (A+B)≥0.125, the nitrile additive can better improve the deterioration of the positive electrode impedance, thereby improving the high-temperature cycle performance.

[0135] It is found by comparing the data of Example 13, Example 14 to Example 17, and Comparative Example 17 and Comparative Example 18 that when the full charge voltage of the battery is increased, the high-temperature storage and the high-temperature cycle performance of the battery are deteriorated. When the full charge voltage of the battery is decreased, the content of the polynitrile additive in the system is relatively too much, which affects the K value of the battery and deteriorates the high-temperature cycle performance. The higher the full charge voltage is, the more nitrile additive is needed to improve the high-voltage performance of the battery. It is further known from the data of Comparative Example 24 to Comparative Example 30 that the nitrile additive has a high film-forming impedance on the positive electrode, and under high voltage, it is easy to cause the polarization of the positive electrode to increase and the high-temperature cycle performance to deteriorate. Therefore, the content of the nitrile additive needs to be in a certain proportional relationship with the full charge voltage of the battery, so as to better balance the high-temperature storage and cycle performance of the nitrile additive. Further combining Example 1 and Example 6, when (A+B) / X≥0.556 is met, the above-mentioned effect can be achieved.

[0136] Although the present application has been described with reference to preferred embodiments, those skilled in the art will understand that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the present application. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the present application without departing from the essential scope thereof. Therefore, the present application is not intended to be limited to the particular embodiments by which the application is disclosed as the best mode contemplated for carrying out the application, but the application will include all embodiments falling within the scope of the appended claims.

[0137] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are combinable with each other.

[0138] Embodiments of the application have been described above with the intent to be illustrative rather than restrictive. Although not all embodiments of this technology have been described, alterations, permutations, combinations, and equivalents of those embodiments will become apparent to those skilled in the art once given the above description. Therefore, specific embodiments discussed above are not illustrative, but rather are meant to be illustrative of the broader principles of the application. The scope of the application should be interpreted in the broadest sense and be accorded the greatest of all possible equivalency. Many modifications and variations of this application can be made without departing from its spirit and scope, which is defined by the scope of the appended claims. It is the intent of the patent to cover all modifications and variations of this application that falls within the scope of the appended claims and their equivalents. It should be apparent that aspects of the application and components of the systems described herein can be implemented in hardware, software or a combination thereof.

Claims

1. An electrolyte, characterized by, The electrolyte applied to a high-voltage electrochemical device comprises an organic solvent, a lithium salt and an additive, the additive comprises a polynitrile additive and a dinitrile additive, the polynitrile additive comprises at least 3 cyano groups; and the following relationship is satisfied between the additive and the high-voltage electrochemical device: (A+B) / X≥0.5 In the relationship, the mass percentage of the polynitrile additive in the electrolyte is A%, the mass percentage of the dinitrile additive in the electrolyte is B%, the full charge voltage of the high-voltage electrochemical device is X V; 0.5≤A≤4, 0.5≤B≤4, 4≤X≤4.58, B / A≥0.5; the additive further comprises a sulfur-containing additive, the structure of the sulfur-containing additive is as follows: In structural formula one, n is 0 or 1, and X is selected from or; R1, R2and R3are each independently selected from H, at least one of X, R1, R2and R3is selected from H, and R1, R2and R3are not simultaneously selected from H, and at least one of X, R1, R2and R3contains a sulfur atom; the sulfur-containing additive comprises a mass percentage of the electrolyte of C%, 0.5≤C≤4, and C / (A+B)≥0.

125.

2. The electrolyte according to claim 1, characterized in that, The additive and the high-voltage electrochemical device satisfy the following relationship: (A+B) / X≥0.

556.

3. The electrolyte according to any one of claims 1 or 2, characterized in that, The polynitrile additive comprises at least one of pentaether nitrile and 1,3,6-hexanetricarbonitrile.

4. The electrolyte according to claim 1 or 2, characterized in that, The dinitrile additive comprises at least one of butanedinitrile and hexanedinitrile.

5. The electrolyte of claim 1, wherein The sulfur-containing additive comprises at least one of the following compounds:

6. A high voltage electrochemical device, characterized by, The electrolyte comprises the electrolyte according to any one of claims 1 to 5.

7. An electronic device, comprising: The electrochemical device comprises the electrolyte according to claim 6.

Images