Lithium ion battery electrolyte and lithium ion battery

Abstract

The invention discloses a lithium ion battery electrolyte and a lithium ion battery, and belongs to the technical field of lithium batteries. The lithium ion battery electrolyte comprises the following components in percentage by weight: 10-15% of lithium salt, 80-90% of organic solvent and 0-5% (not 0) of additive, the additive comprises a functional additive A, the structure of the functional additive A is shown as a formula I: in # imgabs0, R1, R2, R3, R4, R5 and R6 are the same or different, at least one of R1, R2, R3, R4, R5 and R6 is hydroxyl, and other R is respectively and independently hydrogen, straight-chain alkyl or alkoxy of C1 to C10 and branched-chain alkyl or alkoxy of C1 to C10. By correspondingly adjusting the components of the electrolyte and introducing the functional additive A, the four specific additives, the lithium salt and the organic solvent have a synergistic effect, so that the phenomenon of relatively fast capacitance attenuation or voltage attenuation in the charge-discharge cycle process of the lithium ion battery can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium ion battery electrolyte and a lithium ion battery. Background Art

[0002] The continuous development of computers, communications and consumer electronics has brought about the rapid development of the lithium-ion battery industry. In particular, the rise of new energy vehicles in recent years has not only promoted the development of power lithium-ion batteries, but also put forward higher energy density and safety performance. The endurance of electric vehicles has become one of the performance indicators that consumers pay most attention to, and the energy density of the battery determines the single mileage of the electric vehicle. How to improve the energy density of the battery under limited space and weight has become a hot topic in this field.

[0003] At present, increasing the working voltage of cathode materials is the main way to increase the energy density of lithium-ion batteries; high-voltage cathode materials such as LNMO, high-voltage ternary materials, high-voltage lithium cobalt oxide, layered lithium-rich oxide (LLO), etc. have become research hotspots. However, as the voltage of lithium-ion batteries continues to increase, cathode materials will have higher electrode potentials, and the oxidation decomposition of electrolytes at the cathode and the cathode interface reactions will become more intense; as the battery charge and discharge cycles continue, the internal resistance of the battery gradually increases, which in turn affects the battery performance and even causes failure.

[0004] To address the above problems, researchers mainly overcome these defects by modifying the positive electrode materials, such as surface coating, material microstructure design, element doping, etc.; among them, the material modification method has complex processes and high costs, while the use of suitable additives to improve the composition of the electrolyte is simple to operate and has obvious effects, which is conducive to industrial applications. Summary of the invention

[0005] The main purpose of the present invention is to provide a lithium ion battery electrolyte and a lithium ion battery to solve the problem of rapid cycle capacity decay and voltage decay of high voltage material system batteries in the prior art.

[0006] In order to achieve the above object, according to one aspect of the present invention, a lithium ion battery electrolyte is provided, which comprises the following components in weight percentage:

[0007] Lithium salt 10% to 15%, organic solvent 80% to 90%, additive 0 to 5% and not 0;

[0008] The additive includes a functional additive A, and the structure of the functional additive A is shown in Formula I:

[0009]

[0010] In Formula I, R1, R2, R3, R4, R5, and R6 are the same or different, at least one of R1, R2, R3, R4, R5, and R6 is a hydroxyl group, and the other Rs are each independently hydrogen, C1 to C 10 Straight chain alkyl or alkoxy, C1~C 10 A branched alkyl or alkoxy group.

[0011] Furthermore, in Formula I, R1, R2, R3, R4, R5, and R6 are the same or different, at least one of R1, R2, R3, R4, R5, and R6 is a hydroxyl group, and the other Rs are each independently hydrogen, a C1-C4 straight-chain alkyl or alkoxy group, or a C1-C4 branched alkyl or alkoxy group.

[0012] Furthermore, the functional additive A is a compound containing one hydroxyl group, a compound containing two hydroxyl groups, or a compound containing three hydroxyl groups in the structure of formula I.

[0013] Further, in Formula I, R5 is hydroxyl, and R1, R2, R3, R4, and R6 are all the same and are hydrogen; or, R3 is hydroxyl, R5 is hydroxyl, and R1, R2, R4, and R6 are all the same and are hydrogen; or, R4 is methyl, R5 is hydroxyl, and R1, R2, R3, and R6 are all the same and are hydrogen; or, R5 is hydroxyl, R6 is methyl, and R1, R2, R3, and R4 are all the same and are hydrogen.

[0014] Furthermore, the weight percentage of the lithium salt in the electrolyte is 10% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 0.5 to 5%.

[0015] Furthermore, the weight percentage of the lithium salt in the electrolyte is 10% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 2% to 5%.

[0016] Furthermore, the weight percentage of the lithium salt in the electrolyte is 13% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 3% to 4%.

[0017] Furthermore, the weight percentage of the functional additive A in the electrolyte is 0.3% to 1%, and more preferably 0.5% to 1%.

[0018] Furthermore, the additives include one or more of film-forming additives, lithium salt additives and sulfur-containing additives.

[0019] Furthermore, the film-forming additive is selected from vinylene carbonate and / or fluoroethylene carbonate.

[0020] Furthermore, the lithium salt additive is selected from one or more of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalatoborate) and lithium difluorobis(oxalatophosphate).

[0021] Further, the sulfur-containing additive is selected from one or more of 1,3-propane sultone, 1,3-propylene sultone and ethylene sulfate.

[0022] Furthermore, the additives also include vinylene carbonate, lithium difluorophosphate and 1,3-propane sultone.

[0023] Furthermore, the weight percentage of vinylene carbonate in the electrolyte is 0% to 1%, preferably 0.5% to 1%.

[0024] Furthermore, the weight percentage of lithium difluorophosphate in the electrolyte is 0.5% to 1%.

[0025] Furthermore, the weight percentage of 1,3-propane sultone in the electrolyte is 0.5% to 3%, preferably 2% to 3%.

[0026] Furthermore, the lithium salt is selected from lithium hexafluorophosphate.

[0027] Furthermore, the organic solvent is selected from one or more of cyclic carbonates, chain carbonates and chain carboxylates.

[0028] Furthermore, the mass ratio of the cyclic carbonate, the chain carbonate and the chain carboxylic acid ester is (1-15):(20-70):(5-20).

[0029] Further, the organic solvent includes fluoroethylene carbonate, ethylene carbonate, ethyl difluoroacetate and diethyl carbonate.

[0030] Furthermore, the weight percentage of fluoroethylene carbonate in the organic solvent is 10% to 12%; the weight percentage of ethylene carbonate in the organic solvent is 8% to 12%, the weight percentage of ethyl difluoroacetate in the organic solvent is 12 to 18%, and the weight percentage of diethyl carbonate in the organic solvent is 58% to 70%, totaling 100%.

[0031] According to a second aspect of the present invention, a method for preparing the above-mentioned lithium ion battery electrolyte is provided, comprising: adding a formulated amount of additives and electrolyte lithium salt to an organic solvent under an inert atmosphere, mixing at a temperature of 5 to 15° C., to obtain a lithium ion battery electrolyte.

[0032] According to a third aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode plate, a negative electrode plate, a separator, and an electrolyte; the electrolyte is the above-mentioned lithium-ion battery electrolyte or the electrolyte prepared by the above-mentioned method.

[0033] By applying the technical solution of the present invention, a lithium ion battery electrolyte is provided. By adjusting the electrolyte components accordingly and introducing a functional additive A, since the functional additive A contains unsaturated functional groups in its structure, it is easy to oxidize to form a dense and uniform CEI film, which effectively inhibits the dissolution of TMs metal ions and the release of oxygen, and at the same time reduces the acidic substances in the electrolyte and the LiF content in the SEI film, thereby reducing the interface side reactions and improving the film-forming quality of the negative electrode SEI film, thereby improving the high-voltage cycle process. DETAILED DESCRIPTION

[0034] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0035] In order to solve the problem of serious attenuation of electrochemical performance of lithium ion batteries in high voltage charge and discharge cycles, especially serious attenuation of battery cycle capacity and voltage, the present invention provides a lithium ion battery electrolyte, the electrolyte comprising the following components in weight percentage: 10% to 15% of lithium salt, 80% to 90% of organic solvent, and 0% to 5% of additives (not 0);

[0036] The additive includes a functional additive A, and the structure of the functional additive A is shown in Formula I:

[0037]

[0038] In Formula I, R1, R2, R3, R4, R5, and R6 are the same or different, at least one of R1, R2, R3, R4, R5, and R6 is a hydroxyl group, and the other Rs are each independently hydrogen, C1 to C 10 Straight chain alkyl or alkoxy, C1~C 10 A branched alkyl or alkoxy group.

[0039] The lithium salt in the electrolyte of the present invention is selected from any value among 10%, 11%, 12%, 13%, 14%, 15% or any range between two of them; the organic solvent is selected from any value among 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90% or any range between two of them; and the content of the additive is selected from any value among 0%, 1%, 2%, 3%, 4%, 5% or any range between two of them.

[0040] The present invention adjusts the electrolyte components accordingly and uses additives to form a film to protect the positive electrode interface, which can effectively reduce the side reactions at the electrolyte and positive electrode interface, and in situ regulates the physical structure and chemical composition of CEI through additives and solvents, providing a simple and effective method for improving battery performance.

[0041] The present invention selects the above compounds as film-forming agents for lithium batteries through a large number of experimental studies, which can significantly improve the phenomenon that the electrochemical performance of the battery decreases rapidly during the high-voltage charge and discharge cycle.

[0042] The electrolyte of the present invention introduces a new functional additive A, which is characterized in that the functional additive A contains unsaturated functional groups in its structure and is easily oxidized to form a dense and uniform CEI film; the dissolution of TMs metal ions and the release of oxygen are effectively inhibited, and at the same time, the acidic substances in the electrolyte are reduced, and the LiF content in the SEI film is reduced, thereby reducing the interface side reaction and improving the film formation quality of the negative electrode SEI film, and improving the high-voltage cycle process.

[0043] As a specific embodiment, in Formula I, R1, R2, R3, R4, R5, and R6 are the same or different, at least one of R1, R2, R3, R4, R5, and R6 is a hydroxyl group, and the other Rs are each independently hydrogen, a C1-C4 straight-chain alkyl or alkoxy group, or a C1-C4 branched alkyl or alkoxy group.

[0044] As a specific implementation, the functional additive A is a compound containing one hydroxyl group, a compound containing two hydroxyl groups, or a compound containing three hydroxyl groups in the structure of formula I.

[0045] As a preferred embodiment, in Formula I, R5 is a hydroxyl group, and R1, R2, R3, R4, and R6 are all the same and are hydrogen, and the structure is shown in Formula I-1:

[0046]

[0047] Alternatively, R3 is a hydroxyl group, R5 is a hydroxyl group, and R1, R2, R4, and R6 are all the same and are hydrogen, and the structure is shown in Formula I-2:

[0048]

[0049] Alternatively, R4 is methyl, R5 is hydroxy, and R1, R2, R3, and R6 are all the same and are hydrogen;

[0050]

[0051] Or, R5 is hydroxyl, R6 is methyl, and R1, R2, R3, and R4 are all the same and are hydrogen.

[0052]

[0053] As a preferred embodiment, the weight percentage of lithium salt in the electrolyte is 13% to 15%, the weight percentage of organic solvent in the electrolyte is 80% to 85%, and the weight percentage of additives in the electrolyte is 3% to 4%.

[0054] As a preferred embodiment, the weight percentage of the functional additive A in the electrolyte is 0.3% to 1%, and more preferably 0.5% to 1%.

[0055] In order to further improve the electrochemical performance of lithium batteries, the additives in the electrolyte also include one or more of film-forming additives, lithium salt additives and sulfur-containing additives.

[0056] The present invention adds the above-mentioned functional additive A having a film-forming effect in combination with the above-mentioned three different types of additives. Additive A forms a uniform and dense CEI film on the positive electrode, inhibits the dissolution of TMs metal ions and the release of oxygen, and inhibits their reduction on the negative electrode surface, thereby reducing interface side reactions.

[0057] As a specific embodiment, the film-forming additive is selected from vinylene carbonate and / or fluoroethylene carbonate.

[0058] As a specific embodiment, the lithium salt additive is selected from one or more of lithium bis(fluorosulfonyl)imide (LiFSI lithium salt), lithium difluorophosphate (LiPO2F2 additive), lithium bis(oxalatoborate) (LiBOB, film-forming additive) and lithium difluorobis(oxalatophosphate) (LiODFP, lithium salt).

[0059] As a specific embodiment, the sulfur-containing additive is selected from one or more of 1,3-propane sultone (PS), 1,3-propylene sultone (PST) and diethylene sulfate (DTD).

[0060] As a preferred embodiment, the additive specifically includes vinylene carbonate, lithium difluorophosphate and 1,3-propane sultone.

[0061] As a preferred embodiment, the weight percentage of vinylene carbonate in the electrolyte is 0% to 1%, preferably 0.5% to 1%.

[0062] As a preferred embodiment, the weight percentage of lithium difluorophosphate in the electrolyte is 0.5% to 1%.

[0063] As a preferred embodiment, the weight percentage of 1,3-propane sultone in the electrolyte is 0.5% to 3%, preferably 2% to 3%.

[0064] The vinylene carbonate (VC) of the present invention forms a film at the negative electrode. If the addition amount is too small, a dense SEI film cannot be formed. If the addition amount is too large, the impedance will be too large and high-temperature gas production will occur. 1,3-Propane sultone (PS) assists in film formation at the positive and negative electrodes and has high thermal stability. If the addition amount is too small, a dense SEI film cannot be formed at the negative electrode. If the addition amount is too large, the film impedance will be large, resulting in decreased cycle performance. Lithium difluorophosphate (LiPO2F2) participates in the film formation of the positive and negative electrodes. If the addition amount is too small, a dense SEI film cannot be formed. If the addition amount is too large, it cannot be completely dissolved. Functional additive A has a positive and negative electrode film-forming effect.

[0065] The above four specific additives and their specific ratios selected by the present invention can synergistically act with lithium salt and organic solvent to significantly improve the phenomenon of rapid capacity decay or voltage decay during the charge and discharge cycle of the lithium ion battery.

[0066] As a specific implementation, the lithium salt in the electrolyte of the present invention is selected from lithium hexafluorophosphate, and a suitable lithium salt electrolyte can also be selected according to actual needs.

[0067] As a specific embodiment, the organic solvent is selected from one or more of cyclic carbonates, chain carbonates and chain carboxylates; preferably, the organic solvent comprises a mixture of a cyclic carbonate, a chain carbonate and a chain carboxylate.

[0068] As a specific implementation, the mass ratio of cyclic carbonate, chain carbonate and chain carboxylic acid ester is (1-15): (20-70): (5-20).

[0069] As a specific implementation, the organic solvent includes fluoroethylene carbonate, ethylene carbonate, ethyl difluoroacetate and diethyl carbonate.

[0070] As a specific implementation manner, the weight percentage of fluoroethylene carbonate in the organic solvent is 10% to 12%; the weight percentage of ethylene carbonate in the organic solvent is 8% to 12%, the weight percentage of ethyl difluoroacetate in the organic solvent is 12 to 18%, and the weight percentage of diethyl carbonate in the organic solvent is 58% to 70%, totaling 100%.

[0071] In addition to using additives to form a film to protect the positive electrode interface, the electrolyte of the present invention can also effectively reduce side reactions at the electrolyte and positive electrode interface, and in situ regulate the physical structure and chemical composition of CEI through additives and solvents, thereby improving battery performance.

[0072] The present invention selects suitable organic solvents for compounding and limits the specific proportions of various organic solvents. The organic solvents, additives and lithium salts have good synergistic effects, which can further solve the problem of rapid battery performance degradation during high-voltage cycles and extend the battery life.

[0073] The present invention also provides a method for preparing the above-mentioned lithium ion battery electrolyte, comprising: adding a formulated amount of additives to an organic solvent under an inert atmosphere, then adding an electrolyte lithium salt, stirring and mixing at a temperature of 5 to 15° C., preferably at 10° C., to obtain a lithium ion battery electrolyte. The above-mentioned inert atmosphere can be selected from argon and other gases, and other suitable inert gases can be selected according to actual conditions.

[0074] The present invention further provides a lithium ion battery, comprising a positive electrode plate, a negative electrode plate, a separator, and an electrolyte; the electrolyte is the above-mentioned novel lithium ion battery electrolyte developed by the present invention.

[0075] As a specific embodiment, the preparation method of the above-mentioned negative electrode plate is as follows: the negative electrode material graphite, the conductive agent acetylene black and the binder CMC and SBR are prepared into a slurry in a mass percentage of 94:1:2:3, coated on the copper foil current collector, and vacuum dried to obtain the negative electrode plate.

[0076] As a specific embodiment, the preparation method of the positive electrode sheet is as follows: the positive electrode material 0.25Li2MnO3·0.75LiMn 0.375 Ni 0.375 Co 0.25 O2, conductive agent acetylene black and binder PVDF are prepared into a slurry in a mass ratio of 94:3:3, coated on an aluminum foil current collector, and vacuum dried to obtain a positive electrode sheet.

[0077] As a specific embodiment, the above-mentioned diaphragm is a Celgard2400 diaphragm.

[0078] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0079] Example 1

[0080] Step S1: The lithium-ion battery electrolyte includes the following components in weight percentage:

[0081] Lithium hexafluorophosphate 15%, organic solvent 81.5% (based on 100% by weight of the organic solvent, the organic solvent includes: 10% fluoroethylene carbonate, 10% ethylene carbonate, 15% ethyl difluoroacetate, 65% diethyl carbonate), 0.5% vinylene carbonate (VC), 0.5% lithium difluorophosphate (LiPO2F2), 2% 1,3-propane sultone (PS), and 0.5% functional additive A;

[0082] Among them, the structural formula of functional additive A is I-1:

[0083]

[0084] Step S2: Under an argon atmosphere, VC, PS, LiPO2F2 and functional additive A are added to an organic solvent according to a ratio, and then an electrolyte lithium salt is added, and the mixture is stirred and mixed at a temperature of 10° C. to obtain an electrolyte 1.

[0085] Example 2

[0086] Step S1: The lithium-ion battery electrolyte includes the following components in weight percentage:

[0087] Lithium hexafluorophosphate 10%, organic solvent 85% (based on 100% by weight of the organic solvent, the organic solvent includes: fluoroethylene carbonate 12%, ethylene carbonate 12%, ethyl difluoroacetate 12%, diethyl carbonate 64%), vinylene carbonate (VC) 1%, lithium difluorophosphate (LiPO2F2) 1%, 1,3-propane sultone (PS) 2%, functional additive A 1%;

[0088] Among them, the structural formula of functional additive A is I-2:

[0089]

[0090] Step S2: Under an argon atmosphere, VC, PS, LiPO2F2 and functional additive A are added to the organic solvent according to the ratio, and then electrolyte lithium salt is added, and the mixture is stirred and mixed at a temperature of 10° C. to obtain electrolyte 2.

[0091] Example 3

[0092] Step S1: The lithium-ion battery electrolyte includes the following components in weight percentage:

[0093] Lithium hexafluorophosphate 13%, organic solvent 83% (based on 100% by weight of the organic solvent, the organic solvent includes: fluoroethylene carbonate 10%, ethylene carbonate, 10%, ethyl difluoroacetate 12%, diethyl carbonate 68%), vinylene carbonate (VC) 0.8%, lithium difluorophosphate (LiPO2F2) 0.8%, 1,3-propane sultone (PS) 1.6%, functional additive A 0.8%;

[0094] Among them, the structural formula of functional additive A is I-3:

[0095]

[0096] Step S2: Under an argon atmosphere, VC, PS, LiPO2F2 and functional additive A are added to the organic solvent according to the ratio, and then electrolyte lithium salt is added, and the mixture is stirred and mixed at a temperature of 10° C. to obtain electrolyte 3.

[0097] Example 4

[0098] Step S1: The lithium-ion battery electrolyte includes the following components in weight percentage:

[0099] 10% lithium hexafluorophosphate, 88% organic solvent (based on 100% by weight of the organic solvent, the organic solvent includes: 10% fluoroethylene carbonate, 10% ethylene carbonate, 15% ethyl difluoroacetate, 65% diethyl carbonate), 0.5% vinylene carbonate (VC), 0.5% lithium difluorophosphate (LiPO2F2), 0.5% 1,3-propane sultone (PS), and 0.5% functional additive A;

[0100] Among them, the structural formula of functional additive A is I-4:

[0101]

[0102] Step S2: Under an argon atmosphere, VC, PS, LiPO2F2 and functional additive A are added to the organic solvent according to the ratio, and then electrolyte lithium salt is added, and the mixture is stirred and mixed at a temperature of 10° C. to obtain electrolyte 4.

[0103] Comparative Example 1

[0104] The difference between Comparative Example 1 and Example 1 is that the positive electrode film-forming additive compound 1 is not added to the electrolyte, and the rest is the same as Example 1.

[0105] Comparative Example 2

[0106] The difference between Comparative Example 2 and Example 1 is that the functional additive selected in the electrolyte is Formula I-5, and the rest is the same as Example 1.

[0107]

[0108] Application Examples

[0109] The electrolyte provided in each embodiment and comparative example was applied to a lithium ion battery, and the performance test was carried out using the lithium ion battery.

[0110] The specific preparation method of the lithium-ion battery used for the test includes: preparing a negative electrode material graphite, a conductive agent acetylene black and a binder CMC and SBR in a mass percentage of 94:1:2:3 into a slurry, coating it on a copper foil current collector, and vacuum drying to obtain a negative electrode sheet; preparing a positive electrode material 0.25Li2MnO3·0.75LiMn 0.375 Ni 0.375 Co 0.25 O2, conductive agent acetylene black and binder PVDF were prepared into slurry in a mass ratio of 94:3:3 and coated on the aluminum foil current collector, and vacuum dried to obtain the positive electrode sheet. The positive electrode sheet, negative electrode sheet, Celgard2400 separator and the electrolyte prepared in Examples 1 to 4 or Comparative Examples 1 to 2 were assembled into soft-pack batteries, respectively, and Sample 1, Sample 2, Sample 3, Sample 4, Comparative Sample 1 and Comparative Sample 2 were obtained in sequence; the electrochemical test was carried out using a Xinwei charge and discharge test cabinet, and the test results are shown in Table 1.

[0111] Test method:

[0112] (1) Normal temperature cycle performance test:

[0113] At 25°C, the lithium-ion battery is charged at a constant current of 0.5C (nominal capacity) to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current ≤ 0.05C, left for 10 minutes, and then discharged at a constant current of 1C to a cut-off voltage of 2.5V. The above is one charge and discharge cycle. The lithium-ion battery is charged and discharged 1000 times at 25°C under the above conditions.

[0114] The capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0115] The average voltage (V) of a lithium-ion battery after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, where N is the number of cycles of the lithium-ion battery.

[0116] (2) High temperature cycle performance test:

[0117] At 45°C, the lithium-ion battery is charged at a constant current of 1.0C (nominal capacity) to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current ≤ 0.05C, left for 10 minutes, and then discharged at a constant current of 1C to a cut-off voltage of 2.5V. The above is one charge and discharge cycle. The lithium-ion battery is subjected to 800 charge and discharge cycles at 45°C under the above conditions.

[0118] The capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0119] The average voltage (V) of a lithium-ion battery after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, where N is the number of cycles of the lithium-ion battery.

[0120] Table 1

[0121]

[0122] It can be seen from the test results in Table 1 that in the normal temperature (25°C) cycle test, the lithium ion batteries assembled using the electrolytes of Examples 1 to 4 showed a capacity retention rate of more than 87% and an average voltage of more than 3.7300V; while the capacity retention rate of Comparative Example 1 was 67.5% and the voltage was 3.6003V; it is obvious that Examples 1 to 4 of the present invention significantly improve the capacity retention rate of the lithium ion battery after 1000 cycles at room temperature, from the original 67.5% to 87.8%, and the voltage is increased from the original 3.6003V to 3.7344V; it shows that the present invention can significantly improve the serious problem of capacity attenuation and voltage attenuation in the normal temperature cycle of the high-voltage battery by adding the above-mentioned functional additive A to the electrolyte.

[0123] In the high temperature (45°C) cycle test, the lithium ion batteries assembled with the electrolytes of Examples 1 to 4 showed a capacity retention rate of more than 84% and an average voltage of more than 3.6500V; while the capacity retention rates of the comparative examples were 62.4% and 62.5%, and the voltages were 3.5798V and 3.5802V; it is obvious that Examples 1 to 4 of the present invention significantly improve the capacity retention rate of the lithium ion battery after 800 cycles at high temperature, from the original 62.4% to 84.7%, and the voltage is increased from the original 3.5798V to 3.6512V; this shows that the present invention can significantly improve the serious problem of capacity attenuation and voltage attenuation in high temperature cycles of high-voltage batteries by adding functional additive A to the electrolyte.

[0124] Compared with Comparative Example 2, although Examples 1 to 4 of the present invention are similar in structure, they are not as effective as the present invention in improving capacity decay and voltage decay in high-voltage battery cycles. This shows that the functional additive A selected by the present invention having a structure shown in the above formulas I-1, I-2, I-3, and I-4 containing one hydroxyl group or two hydroxyl groups can have better synergistic effects with other additives, organic solvents, and lithium salts when added to the lithium-ion battery electrolyte, and can more significantly improve the serious problems of capacity decay and voltage decay in high-voltage battery cycles, thereby improving the battery performance of lithium-ion batteries under high voltage.

[0125] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: The electrolyte comprises the following components in weight percentage: Lithium salt 10% to 15%, organic solvent 80% to 90%, additive 0 to 5% and not 0; Wherein, the additive includes a functional additive A, and the structure of the functional additive A is shown in Formula I: In Formula I, R1, R2, R3, R4, R5, and R6 are the same or different, at least one of R1, R2, R3, R4, R5, and R6 is a hydroxyl group, and the other Rs are each independently hydrogen, C1 to C 10 Straight chain alkyl or alkoxy, C1~C 10 A branched alkyl or alkoxy group.

2. The lithium ion battery electrolyte according to claim 1, characterized in that: In formula I, R1, R2, R3, R4, R5, and R6 are the same or different, at least one of R1, R2, R3, R4, R5, and R6 is a hydroxyl group, and the other Rs are each independently hydrogen, a C1-C4 straight-chain alkyl or alkoxy group, or a C1-C4 branched alkyl or alkoxy group.

3. The lithium ion battery electrolyte according to claim 1 or 2, characterized in that: The functional additive A is a compound containing one hydroxyl group, a compound containing two hydroxyl groups, or a compound containing three hydroxyl groups in the structure of formula I.

4. The lithium ion battery electrolyte according to any one of claims 1 to 3, characterized in that: In Formula I, R5 is hydroxyl, and R1, R2, R3, R4, and R6 are all the same and are hydrogen; Or, R3 is hydroxy, R5 is hydroxy, and R1, R2, R4, and R6 are all the same and are hydrogen; Or, R4 is methyl, R5 is hydroxy, and R1, R2, R3, and R6 are all the same and are hydrogen; or, R5 is hydroxy, R6 is methyl, and R1, R2, R3, and R4 are all the same and are hydrogen.

5. The lithium ion battery electrolyte according to any one of claims 1 to 4, characterized in that: The weight percentage of the lithium salt in the electrolyte is 10% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 0.5 to 5%; Preferably, the weight percentage of the lithium salt in the electrolyte is 10% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 2% to 5%; Preferably, the weight percentage of the lithium salt in the electrolyte is 13% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 3% to 4%; Preferably, the weight percentage of the functional additive A in the electrolyte is 0.3% to 1%, and more preferably 0.5% to 1%.

6. The lithium ion battery electrolyte according to any one of claims 1 to 5, characterized in that: The additives also include one or more of a film-forming additive, a lithium salt additive, and a sulfur-containing additive; Preferably, the film-forming additive is selected from vinylene carbonate and / or fluoroethylene carbonate; Preferably, the lithium salt additive is selected from one or more of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium dioxalatoborate and lithium difluorodioxalatophosphate; Preferably, the sulfur-containing additive is selected from one or more of 1,3-propane sultone, 1,3-propylene sultone and ethylene sulfate.

7. The lithium ion battery electrolyte according to any one of claims 1 to 6, characterized in that: The additives also include vinylene carbonate, lithium difluorophosphate and 1,3-propane sultone; Preferably, the weight percentage of the vinylene carbonate in the electrolyte is 0% to 1%, preferably 0.5% to 1%; Preferably, the weight percentage of the lithium difluorophosphate in the electrolyte is 0.5% to 1%; Preferably, the weight percentage of the 1,3-propane sultone in the electrolyte is 0.5% to 3%, preferably 2% to 3%.

8. The lithium ion battery electrolyte according to any one of claims 1 to 7, characterized in that: The lithium salt is selected from lithium hexafluorophosphate; and / or, the organic solvent is selected from one or more of cyclic carbonates, chain carbonates and chain carboxylates; Preferably, the mass ratio of the cyclic carbonate, the chain carbonate and the chain carboxylic acid ester is (1-15): (20-70): (5-20); Preferably, the organic solvent comprises fluoroethylene carbonate, ethylene carbonate, ethyl difluoroacetate and diethyl carbonate; Preferably, the weight percentage of the fluoroethylene carbonate in the organic solvent is 10% to 12%; the weight percentage of the ethylene carbonate in the organic solvent is 8% to 12%, the weight percentage of the ethyl difluoroacetate in the organic solvent is 12% to 18%, and the weight percentage of the diethyl carbonate in the organic solvent is 58% to 70%, totaling 100%.

9. The method for preparing a lithium ion battery electrolyte according to any one of claims 1 to 8, characterized in that: The method comprises: adding a formulated amount of additives and electrolyte lithium salt into an organic solvent under an inert atmosphere, mixing at a temperature of 5 to 15° C., and obtaining a lithium ion battery electrolyte.

10. A lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; characterized in that: The electrolyte is the lithium ion battery electrolyte according to any one of claims 1 to 8 or the electrolyte prepared by the method according to claim 9.

Images