Lithium ion battery electrolyte and application thereof

Abstract

The invention belongs to the field of batteries, and particularly relates to a lithium ion battery electrolyte and application thereof. The lithium ion battery electrolyte provided by the invention comprises the following components: an organic solvent, a lithium salt and an additive, the additive comprises a compound with a structure as shown in a formula I and / or a compound with a structure as shown in a formula II. The electrolyte provided by the invention can be used for optimizing SEI membrane components of the lithium ion battery, improving the cycle coulombic efficiency of the lithium ion battery, improving the high-voltage tolerance of an SEI membrane and improving the high-temperature and high-voltage cycle performance of the lithium ion battery. # imgabs0 #

Description

Technical Field

[0001] The invention belongs to the field of batteries, and in particular relates to a lithium ion battery electrolyte and an application thereof. Background Art

[0002] With the rapid development of portable electronic devices and the electric vehicle industry, the demand for lithium-ion batteries is growing, especially in terms of energy density and cycle stability. To meet this demand, researchers are committed to developing electrode materials and electrolyte systems that can support higher operating voltages to increase the energy density of batteries. However, under high-voltage operation, batteries face problems such as electrolyte decomposition, instability of the solid electrolyte interface (SEI) film, and dissolution of transition metals, which can lead to battery capacity decay and reduced safety.

[0003] At present, lithium-ion batteries generally adopt a variety of strategies to enhance their performance under high voltage, including: (1) Solvent optimization: By optimizing the high-voltage resistant solvent components, the electrochemical window of the electrolyte is improved to improve the electrolyte voltage tolerance and reduce the high-voltage decomposition side reaction. (2) SEI film optimization: By adding specific additives to the electrolyte, a stable SEI film can be formed on the surface of the positive and negative electrodes. This film needs to be both conductive and able to prevent further electrolyte decomposition to improve coulombic efficiency and cycle life; however, traditional SEI films may become unstable under high voltage, resulting in continuous electrolyte decomposition and reversible lithium loss. (3) Modification of positive electrode materials: Under high voltage conditions, transition metal ions of the positive electrode material may dissolve into the electrolyte, deposit at the negative electrode, and catalyze the decomposition of the electrolyte into a film at the negative electrode, which not only reduces the capacity of the battery, but may also cause internal short circuits; therefore, a lot of work has been done on the modification of positive electrode materials to prevent the dissolution and migration of transition metals.

[0004] Although the above methods have improved the performance of lithium-ion batteries to a certain extent, they still have some limitations, and higher voltage and longer cycle of batteries are still challenges. For example, in the lithium nickel manganese oxide system, the platform voltage is 4.7V, and the traditional additive-modified SEI film may not be able to effectively passivate the positive electrode interface under high voltage and cannot completely inhibit the dissolution of transition metal ions. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a lithium ion battery electrolyte and its application. The electrolyte provided by the present invention can be used to optimize the SEI membrane components of lithium ion batteries, improve the cycle coulomb efficiency of lithium ion batteries, improve the high-voltage tolerance of SEI membranes, and enhance the high-temperature and high-pressure cycle performance of lithium ion batteries.

[0006] The present invention provides a lithium ion battery electrolyte, the components of which include an organic solvent, a lithium salt and an additive;

[0007] The additives include a compound of formula I and / or a compound of formula II:

[0008]

[0009] Preferably, the content of the compound of formula I in the electrolyte is 0.1-2 wt%.

[0010] Preferably, the content of the compound of formula II in the electrolyte is 0.1-2 wt%.

[0011] Preferably, the additive also includes a basic additive, and the basic additive is one or more of sulfonate compounds, sulfate compounds, unsaturated cyclic carbonate compounds, borate compounds, trimethylsilyl ester compounds and nitrile compounds; the content of the basic additive in the electrolyte is 0.1 to 8 wt%.

[0012] Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate and lithium bis(oxalatoborate); and the content of the lithium salt in the electrolyte is 0.5 to 2 mol / L.

[0013] Preferably, the organic solvent is one or more of propylene carbonate, ethylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate and γ-butyrolactone.

[0014] The present invention provides a lithium ion battery, wherein the electrolyte in the lithium ion battery is the lithium ion battery electrolyte described in the above technical solution.

[0015] Preferably, the positive electrode active material in the lithium ion battery is lithium nickel manganese oxide and / or lithium cobalt oxide; the negative electrode active material in the lithium ion battery is one or more of graphite, silicon carbon and metallic lithium.

[0016] The present invention provides a method for preparing a lithium ion battery, comprising the following steps:

[0017] Assembling the positive electrode of the lithium-ion battery, the separator and the negative electrode of the lithium-ion battery to obtain a battery assembly to be injected with liquid;

[0018] The lithium-ion battery electrolyte described in the above technical solution is injected into the battery assembly to be injected, and the injection method is one injection or multiple injections to obtain a lithium-ion battery.

[0019] Preferably, the injection method is a double injection, the lithium ion battery electrolyte used in the first injection contains the compound of formula I, and the lithium ion battery electrolyte used in the second injection contains the compound of formula II.

[0020] Compared with the prior art, the present invention provides a lithium ion battery electrolyte and its application. The components of the lithium ion battery electrolyte provided by the present invention include an organic solvent, a lithium salt and an additive; the additive includes a compound of formula I and / or a compound of formula II. The present invention adds a specific type of electrical performance improving additive to the lithium ion battery electrolyte; wherein, the addition of the compound of formula I structure can form a SEI film rich in Li2O and LiF in the formation stage of lithium ion battery preparation, increase the proportion of Li2O in the SEI film, improve the ion migration capacity of the SEI film, and effectively inhibit the growth of lithium dendrites, improve the cycle coulomb efficiency of the lithium ion battery, thereby significantly improving the cycle stability and safety of the lithium ion battery; the compound of formula II structure can provide a higher lithium replenishment capacity, replenish the active lithium lost in the formation stage of lithium ion battery preparation, and improve the initial efficiency of the lithium ion battery; at the same time, the isohydroxamate radical of the lithium replenisher after lithium removal has strong coordination, can coordinate with transition metal ions, thereby can form a complex interface on the positive electrode surface of the lithium ion battery, inhibit the dissolution of transition metal ions, and further improve the problem of positive electrode structure destruction of the lithium ion battery under high temperature and high pressure. In addition, in the preferred technical scheme of the present invention, a secondary injection process is used to prepare a lithium-ion battery, aiming to form a SEI film with a high Li2O content on the surface of the negative electrode in the first injection, and introduce a lithium supplement additive in the second injection to replenish the active lithium lost by formation, while further optimizing the positive electrode interface. The two injections can reduce the crosstalk of the additives on the interface film components and directionally regulate the positive and negative electrode interfaces; the secondary injection method can bring into play the synergistic effect of the compound of structure I and the compound of structure II, greatly improving the high-voltage and high-temperature cycle performance of the lithium-ion battery. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] The present invention provides a lithium ion battery electrolyte, the components of which include an organic solvent, a lithium salt and an additive;

[0023] The additives include a compound of formula I and / or a compound of formula II:

[0024]

[0025] In the lithium ion battery electrolyte provided by the present invention, the content of the compound of formula I in the electrolyte is preferably 0.1-2wt%, specifically 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt% or 2wt%.

[0026] In the lithium ion battery electrolyte provided by the present invention, the content of the compound of formula II in the electrolyte is preferably 0.1-2wt%, specifically 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt% or 2wt%.

[0027] In the lithium ion battery electrolyte provided by the present invention, the additive preferably also includes a basic additive, and the basic additive is preferably one or more of a sulfonate compound, a sulfate compound, an unsaturated cyclic carbonate compound, a borate compound, a trimethylsilyl ester compound and a nitrile compound, more preferably tris(trimethylsilyl) phosphate (TMSP) and / or 1,3-propane sultone (1,3-PS); the content of the basic additive in the electrolyte is preferably 0.1-8wt%, specifically 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%. %, 6.5wt%, 7wt%, 7.5wt% or 8wt%; the content of tris(trimethylsilyl)phosphate in the electrolyte is preferably 0.1-2wt%, specifically 0.1wt%, 0.2wt%, 0.4wt%, 0.8wt%, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt% or 2wt%; the content of 1,3-propane sultone in the electrolyte is preferably 0.2-4wt%, specifically 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt% or 4wt%.

[0028] In the lithium ion battery electrolyte provided by the present invention, the lithium salt is preferably one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate and lithium bis(oxalatoborate); the content of the lithium salt in the electrolyte is preferably 0.5-2 mol / L, specifically 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2 mol / L.

[0029] In the lithium ion battery electrolyte provided by the present invention, the organic solvent is preferably one or more of propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate, dimethyl carbonate (DMC), diethyl carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate and γ-butyrolactone, more preferably propylene carbonate, ethylene carbonate, fluoroethylene carbonate and dimethyl carbonate, and the mass ratio of propylene carbonate, ethylene carbonate, fluoroethylene carbonate and dimethyl carbonate is preferably 1:(0.5-2):(0.5-2):(2-8), more preferably 1:1:1:4.

[0030] The present invention also provides a lithium ion battery, comprising: a lithium ion battery positive electrode, a lithium ion battery negative electrode, a separator and an electrolyte, wherein the electrolyte is the lithium ion battery electrolyte described in the above technical solution.

[0031] In the lithium-ion battery provided by the present invention, the active material of the positive electrode is preferably lithium nickel manganese oxide and / or lithium cobalt oxide.

[0032] In the lithium-ion battery provided by the present invention, the active material of the negative electrode is preferably one or more of graphite, silicon carbon and metallic lithium.

[0033] The present invention also provides a method for preparing a lithium ion battery, comprising the following steps:

[0034] Assembling the positive electrode of the lithium-ion battery, the separator and the negative electrode of the lithium-ion battery to obtain a battery assembly to be injected with liquid;

[0035] The lithium-ion battery electrolyte described in the above technical solution is injected into the battery assembly to be injected, and the injection method is one injection or multiple injections to obtain a lithium-ion battery.

[0036] In the preparation method provided by the present invention, the injection method is preferably a double injection, the lithium ion battery electrolyte used in the first injection contains the compound of formula I, and the lithium ion battery electrolyte used in the second injection contains the compound of formula II.

[0037] In the preparation method provided by the present invention, in the secondary injection method, the lithium ion battery electrolyte used in the first injection does not contain the compound of formula II structure, and preferably also contains the basic additive; the lithium ion battery electrolyte used in the second injection does not contain the compound of formula I structure; the mass ratio of the injection amount of the first injection to the second injection is preferably (2 to 8):1, specifically 2:1, 3:1, 4:1, 5:1, 6:1, 7:1 or 8:1.

[0038] In the preparation method provided by the present invention, in the secondary injection method, since the component content and injection volume of the electrolyte used for the first injection and the second injection can be different, the preferred component content of the electrolyte used for each injection may not be within the preferred content range of the electrolyte component introduced above, as long as the final content of each component in the electrolyte after the secondary injection is guaranteed to be consistent with the preferred content range introduced above. In one embodiment provided by the present invention, the content of the compound of formula II structure in the lithium ion battery electrolyte used for the second injection is preferably 1 to 10wt%, specifically 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt% or 10wt%.

[0039] In the preparation method provided by the present invention, in the secondary liquid injection method, the formation and aging processes are performed after the first liquid injection, and the packaging and volume separation processes are performed after the second liquid injection.

[0040] The technical solution provided by the present invention adds a specific type of electrical performance improving additive to the lithium ion battery electrolyte; wherein, the addition of the compound of formula I structure can form a SEI film rich in Li2O and LiF in the formation stage of lithium ion battery preparation, increase the proportion of Li2O in the SEI film, improve the ion migration ability of the SEI film, and effectively inhibit the growth of lithium dendrites, improve the cycle coulomb efficiency of the lithium ion battery, thereby significantly improving the cycle stability and safety of the lithium ion battery; the compound of formula II structure can provide a higher lithium replenishment capacity, replenish the active lithium lost in the formation stage of lithium ion battery preparation, and improve the initial efficiency of the lithium ion battery. At the same time, the isohydroxamate radical of the lithium replenisher after delithiation has strong coordination, can coordinate with transition metal ions, and can be directed to the positive electrode surface of the lithium ion battery, inhibit the dissolution of transition metal ions, and further improve the problem of positive electrode structure destruction of the lithium ion battery under high temperature and high pressure. In addition, in the preferred technical scheme of the present invention, a secondary injection process is used to prepare a lithium-ion battery, aiming to form a SEI film with a high Li2O content on the surface of the negative electrode in the first injection, and introduce a lithium supplement additive in the second injection to replenish the active lithium lost by formation, while further optimizing the positive electrode interface. The two injections can reduce the crosstalk of the additives on the interface film components and directionally regulate the positive and negative electrode interfaces; the secondary injection method can bring into play the synergistic effect of the compound of structure I and the compound of structure II, greatly improving the high-voltage and high-temperature cycle performance of the lithium-ion battery.

[0041] For the purpose of greater clarity, the present invention is described in detail with reference to the following examples and comparative examples.

[0042] In the following examples and comparative examples of the present invention, the compound of formula I is commercially available; the compound of formula II is prepared according to the following method:

[0043] In a 500mL flask, add 274mg (1mmol) of 3,4-dihydroxybenzohydroxamic acid to an appropriate amount of methanol and stir until completely dissolved to form a saturated solution. Separately, in another container, add 74.4mg (3.1mmol) of lithium hydroxide to an appropriate amount of methanol and stir until completely dissolved to form a saturated solution. Slowly add the solution containing lithium hydroxide to the solution containing 3,4-dihydroxybenzohydroxamic acid and stir for 12h at 25°C using a magnetic stirrer to allow the reaction to proceed fully. After the reaction is completed, filter the reaction mixture and collect the obtained white solid. Wash the white solid with cold methanol, ethanol, acetone and ethyl acetate in sequence to remove residual solvent and unreacted raw materials. Transfer the white solid to a clean flask, add an appropriate amount of methanol, and heat to 40°C until completely dissolved. Slowly cool the solution to recrystallize the product. Filter and collect the recrystallized product. Place the recrystallized white powder in a vacuum drying oven and dry it at a suitable temperature overnight to completely remove the residual solvent to obtain the target product.

[0044] Example 1

[0045] (1) Preparation of electrolyte: In a glove box filled with argon (water content <0.1 ppm, oxygen content <0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC) were mixed at a mass ratio of 10:10:40:10, and lithium hexafluorophosphate (LiPF6) was slowly added to the solution, with a molar concentration of LiPF6 of 1 mol / L. Tris(trimethylsilyl) phosphate (TMSP) accounting for 0.8% of the total mass of the electrolyte, 1,3-propane sultone (1,3-PS) accounting for 1.6% of the total mass of the electrolyte, and a compound of formula I accounting for 0.8% of the total mass of the electrolyte were added to the electrolyte to obtain an electrolyte.

[0046] (2) Preparation of positive electrode sheet: The positive electrode active material is lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), lithium nickel manganese oxide, conductive carbon black, carbon nanotubes and polytetrafluoroethylene are evenly coated on a 12 μm aluminum foil in a mass ratio of 97:1.2:0.8:1, and the double-sided coating surface density is 300 g / m 2 , compacted density is 3.0g / cm 3 .

[0047] (3) Preparation of negative electrode sheet: The negative electrode active material is graphite. Artificial graphite, conductive carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose are uniformly coated on a 6 μm copper foil in a mass ratio of 95:2.5:1.2:1.3. The double-sided coating surface density is 121 g / m 2 , compacted density is 1.65g / cm 3 .

[0048] (4) Preparation of batteries: The positive electrode sheet, separator and negative electrode sheet are wound together into a core, sealed with an aluminum plastic film and then baked to ensure that the electrode moisture meets the requirements. After baking, the battery cell is injected with electrolyte at a rate of 4.5 Ah / g, and then subjected to formation, aging and capacity separation steps to obtain a finished soft-pack battery cell; wherein, the formation conditions are: charging to 4.0 V at 0.02 C and leaving for 5 min; the aging conditions are: charging to 4.6 V at 0.05 C and aging at 45° C. for 24 h; and capacity separation is performed at a rate of 0.1 C.

[0049] Example 2

[0050] Referring to Example 1, the only difference is that the compound of formula I accounting for 0.8% of the total mass of the electrolyte is replaced by the compound of formula II accounting for 1% of the total mass of the electrolyte.

[0051] Example 3

[0052] Refer to Example 1, the only difference is that: the compound of formula II is added to the electrolyte in an amount of 1% of the total mass of the electrolyte.

[0053] Example 4

[0054] (1) Preparation of electrolyte:

[0055] (1.1) First electrolyte: In a glove box filled with argon (water content <0.1ppm, oxygen content <0.1ppm), ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 10:10:40:10, and lithium hexafluorophosphate (LiPF6) was slowly added to the solution. The molar concentration of LiPF6 was 1 mol / L. Tris(trimethylsilyl) phosphate (TMSP) accounting for 1% of the total mass of the electrolyte, 1,3-propane sultone (1,3-PS) accounting for 2% of the total mass of the electrolyte, and a compound of formula I accounting for 1% of the total mass of the electrolyte were added to the electrolyte to obtain a first electrolyte.

[0056] (1.2) Second electrolyte: In a glove box filled with argon (water <0.1ppm, oxygen <0.1ppm), ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC) are mixed in a mass ratio of 10:10:40:10, and lithium hexafluorophosphate (LiPF6) is slowly added to the solution. The molar concentration of LiPF6 is 1 mol / L. The compound of formula II is added to the electrolyte in an amount of 5% of the total mass of the electrolyte to obtain a second electrolyte.

[0057] (2) Preparation of positive electrode sheet: same as in Example 1.

[0058] (3) Preparation of negative electrode sheet: same as in Example 1.

[0059] (4) Preparation of batteries: The positive electrode sheet, the separator and the negative electrode sheet are wound together into a core, sealed with an aluminum-plastic film and then baked to ensure that the moisture content of the electrodes meets the requirements. After baking, the battery cell is injected with electrolyte, and the injection coefficient is 4.5Ah / g; more specifically, the electrolyte is injected twice, the electrolyte injected for the first time is the above-mentioned first electrolyte, and the injection amount of the first injection is 80wt% of the total injection amount. After the battery cell is soaked with the electrolyte, it is charged to 4.0V at 0.02C, left for 5min, and then charged to 4.6V at 0.05C, aged at 45°C for 24h, and then injected for the second time. The electrolyte injected for the second time is the above-mentioned second electrolyte, and the injection amount of the second injection is 20wt% of the total injection amount. After the injection is completed, the injection port is sealed and the capacity is divided at a rate of 0.1C.

[0060] Example 5

[0061] Refer to Example 4, the only difference is that the content of the compound of formula I in the first electrolyte is adjusted to 0.5% of the total mass of the electrolyte.

[0062] Example 6

[0063] Refer to Example 4, the only difference is that the content of the compound of formula II in the second electrolyte is adjusted to 10% of the total mass of the electrolyte.

[0064] Comparative Example 1

[0065] Refer to Example 1, the only difference is that the electrolyte does not contain the compound of formula I.

[0066] In order to more intuitively compare the differences between Examples 1 to 6 and Comparative Example 1, the electrolyte components and injection conditions of Examples 1 to 6 and Comparative Example 1 are summarized in the following table:

[0067]

[0068]

[0069] Battery Test

[0070] The performance tests of the batteries prepared in Examples 1 to 6 and Comparative Example 1 were carried out as follows:

[0071] (1) First effect: The first effect of different formulations is obtained by dividing the fractional capacity by the sum of the fractional charge capacity and the formation charge capacity.

[0072] (2) AC internal resistance (ACR): The AC internal resistance meter performs ACR test on the battery.

[0073] (3) Room temperature cycle performance: At room temperature (25±2°C), the above-mentioned battery was charged to 4.85V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C; left for 5 minutes, then discharged to 3.0V at 1C constant current, left for 5 minutes, and the charge and discharge cycle was repeated in this way to obtain the capacity retention rate of different formulations.

[0074] (4) High temperature cycle performance: Under high temperature (45°C) conditions, the above batteries were charged to 4.85V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C; left for 5 minutes, and then discharged to 3.0V at 1C constant current, left for 5 minutes, and the charge and discharge cycle was repeated in this way to obtain the capacity retention rates of different formulations.

[0075] The test results are shown in the following table:

[0076]

[0077] From the comparison between Comparative Example 1 and Example 1, it can be seen that the compound of formula I can optimize the composition of the interface film, improve the first efficiency of the battery, and improve the cycle coulombic efficiency, thereby effectively improving the battery cycle capacity retention rate.

[0078] By comparing Comparative Example 1 with Example 2, it can be seen that the compound of formula II can replenish the active lithium lost in film formation during the formation and capacity division stage, thereby improving the initial efficiency and capacity division capacity of the battery. Because the structure after delithiation has strong coordination with transition metal ions, it effectively protects the positive electrode structure and improves the capacity retention rate of normal temperature and high temperature cycles.

[0079] From the comparison between Comparative Example 1 and Example 3, it can be seen that the compound of formula II structure will increase the battery ACR. When used with the low-impedance compound of formula I structure, the battery impedance can be reduced, the battery first efficiency and differential capacity can be further improved, and the battery cycle efficiency can be improved.

[0080] It can be seen from the data of Example 2 and Example 4 that the secondary injection method can maximize the synergistic effect of the two additives (the compound of formula I and the compound of formula II). The first injection preferentially forms a stable low-impedance interface film, and the second injection replenishes the lost active lithium. The structure after delithiation passivates the positive electrode interface, effectively improving the battery performance.

[0081] It can be seen from Examples 4, 5 and 6 that the battery performance is optimal when the total content of the compound of formula I in the electrolyte is 0.8 wt % and the total content of the compound of formula II in the electrolyte is 1 wt %.

[0082] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: The components of the lithium-ion battery electrolyte include an organic solvent, a lithium salt and an additive; The additive comprises a compound of formula I and / or a compound of formula II:

2. The lithium ion battery electrolyte according to claim 1, characterized in that: The content of the compound of formula I in the electrolyte is 0.1-2 wt%.

3. The lithium ion battery electrolyte according to claim 1, characterized in that The content of the compound of formula II in the electrolyte is 0.1-2 wt %.

4. The lithium ion battery electrolyte according to claim 1, characterized in that: The additives also include basic additives, which are one or more of sulfonate compounds, sulfate compounds, unsaturated cyclic carbonate compounds, borate compounds, trimethylsilyl ester compounds and nitrile compounds; the content of the basic additives in the electrolyte is 0.1-8wt%.

5. The lithium ion battery electrolyte according to claim 1, characterized in that: The lithium salt is one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate and lithium bis(oxalatoborate); and the content of the lithium salt in the electrolyte is 0.5-2 mol / L.

6. The lithium ion battery electrolyte according to claim 1, characterized in that: The organic solvent is one or more of propylene carbonate, ethylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate and γ-butyrolactone.

7. A lithium ion battery, characterized in that: The electrolyte in the lithium ion battery is the lithium ion battery electrolyte according to any one of claims 1 to 6.

8. The lithium-ion battery according to claim 7, characterized in that: The positive electrode active material in the lithium ion battery is lithium nickel manganese oxide and / or lithium cobalt oxide; the negative electrode active material in the lithium ion battery is one or more of graphite, silicon carbon and metallic lithium.

9. A method for preparing a lithium ion battery, characterized in that: The following steps are involved: Assembling the positive electrode of the lithium-ion battery, the separator and the negative electrode of the lithium-ion battery to obtain a battery assembly to be injected with liquid; The lithium ion battery electrolyte according to any one of claims 1 to 6 is injected into the battery assembly to be injected, and the injection method is one injection or multiple injections to obtain a lithium ion battery.

10. The preparation method according to claim 9, characterized in that: The injection method is a double injection, the lithium ion battery electrolyte used in the first injection contains the compound of formula I, and the lithium ion battery electrolyte used in the second injection contains the compound of formula II.

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