Non-aqueous electrolyte and lithium ion battery

Abstract

The application discloses a nonaqueous electrolyte and a lithium ion battery containing the nonaqueous electrolyte, and the nonaqueous electrolyte comprises a lithium salt, a nonaqueous organic solvent and an additive, wherein the additive is a compound as shown in a structural formula 1, Ag x M structural formula 1 wherein M represents any one of hexafluorophosphate, tetrafluoroborate, oxalate, perchlorate, nitrate, fluorine anion and bistrifluoromethylsulfonate, and x represents the chemical valence of the anion. The additive Ag x The negative ion structure in M can improve the cycle performance of the battery at high voltage, and the silver positive ion can optimize the composition of a solid electrolyte interface film; through the adsorption of the silver ion, a certain degree of adsorption is formed, and thus the high-temperature cycle performance of the battery is improved. Therefore, the lithium ion battery prepared by using the nonaqueous electrolyte has good high-temperature storage performance, high-temperature cycle performance and low-temperature discharge performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a non-aqueous electrolyte and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in 3C digital products, power tools, aerospace, energy storage, and electric vehicles due to their advantages such as high specific energy, no memory effect, and long cycle life. Existing lithium cobalt oxide and ternary materials, with their high energy density and gravimetric energy density, have become the preferred materials for the positive electrode active material of lithium-ion batteries. To meet the needs of large mobile electrical equipment, the development of high-capacity lithium-ion batteries has become urgent. The most common method is to increase the voltage of lithium-ion batteries, but all high-voltage positive electrode materials face a common problem: electrolyte decomposition at high voltages. For example, at a high voltage of 4.535V, conventional electrolytes oxidize and decompose faster on the surface of the battery positive electrode, especially under high temperature conditions, which further accelerates the oxidation and decomposition of the electrolyte and promotes the deterioration of the positive electrode material. Currently, the technical approach to changing this situation mainly focuses on the structural design of electrolyte additives. For example, Chinese patent CN114597490A designed a sulfate ester-based substance that significantly improves the high-temperature storage performance and high-temperature cycle performance of ternary and lithium iron phosphate batteries. These technical solutions mainly focus on the research and development of organic electrolyte additives, while the development of inorganic salt electrolyte additives is relatively limited. This is because inorganic salts have low solubility in carbonates, and so far, the improvement effect of inorganic salt electrolyte additives has been limited. Therefore, developing inorganic salt additives suitable for electrolytes under high voltage conditions remains a challenging task. Summary of the Invention

[0003] The purpose of this invention is to provide a non-aqueous electrolyte that can improve the high-temperature storage performance and high-temperature cycle performance of lithium-ion batteries under high voltage (especially at 4.535V) systems, while also improving the low-temperature discharge performance of lithium-ion batteries.

[0004] To achieve the above objectives, the present invention provides a non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent, and an additive, wherein the additive is a compound represented by structural formula 1.

[0005] Ag x M-structure 1

[0006] Where M represents any one of hexafluorophosphate, tetrafluoroborate, oxalate, perchlorate, nitrate, fluoride anion, and bis(trifluoromethanesulfonate), and x represents the chemical valence state of the anion.

[0007] Compared with the prior art, the non-aqueous electrolyte of the present invention includes a lithium salt, a non-aqueous organic solvent, and an additive, wherein the additive is Ag.x M represents hexafluorophosphate, tetrafluoroborate, oxalate, perchlorate, nitrate, fluoride anion, and bis(trifluoromethanesulfonate). These negative ion structures can improve the cycle performance of batteries under high voltage, while silver positive ions can optimize the composition of the solid electrolyte interface film. Through the adsorption of silver ions, a certain degree of adsorption is formed, thereby improving the high-temperature cycle performance of lithium-ion batteries. Simultaneously, the additive Ag formed by the combination of these positive and negative ions... x M can optimize the cathode / electrolyte interface, reduce electrode surface activity, and thus inhibit electrolyte oxidative decomposition, ensuring electrolyte stability under sustained high voltage. This improves the high-temperature storage and cycling performance of lithium-ion batteries at high voltages (especially at 4.535V). Simultaneously, silver ions exhibit strong electrochemical conductivity and show higher redox activity with increasing valence. Ag... x The addition of M can significantly improve the ionic conductivity of the electrolyte, thus improving cycle performance and coulombic efficiency when used as an electrolyte in lithium-ion batteries. The addition of this additive can also improve the low-temperature discharge performance of lithium-ion batteries.

[0008] In some embodiments, the additive Ag x M is one of silver tetrafluoroborate, silver oxalate, silver nitrate, and silver bis(trifluoromethanesulfonate). Among them, Ag is used as an additive to achieve better high-temperature storage performance in lithium-ion batteries. x M uses silver nitrate, while Ag is added to improve the high-temperature cycle performance of lithium-ion batteries. x M uses silver oxalate.

[0009] In some embodiments, the mass percentage of the additive of the present invention in the non-aqueous electrolyte is 0.1% to 3%, preferably 0.1% to 2%. As an example, the mass percentage of the additive in the non-aqueous electrolyte may be, but is not limited to, 0.1%, 0.2%, 0.5%, 1%, 1.5%, or 2%.

[0010] In some embodiments, the mass percentage of the lithium salt in the non-aqueous electrolyte is 6.5% to 15.5%. For example, the mass percentage of the lithium salt in the non-aqueous electrolyte may be, but is not limited to, 6.5%, 7%, 8%, 9%, 10%, 12%, 12.5%, 13%, 14%, or 15%.

[0011] In some embodiments, the lithium salt of the present invention is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate, lithium difluorooxalatoborate, lithium difluorodi(oxalato)phosphate, and lithium bis(fluorosulfonyl)imide. As an example, the lithium salt is lithium hexafluorophosphate (LiPF6) or lithium bis(oxalato)borate (LiBOB). In a preferred embodiment, the lithium salt is a mixture of two or more compounds, such as a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(oxalato)borate (LiBOB), or a mixture of lithium hexafluorophosphate and lithium trifluoromethanesulfonate, which can achieve better high-temperature cycling performance.

[0012] In some embodiments, the non-aqueous organic solvent of the present invention is at least one selected from chain carbonates, cyclic carbonates, and carboxylic acid esters. Further, the non-aqueous organic solvent is selected from at least one selected from ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butyl acetate (n-Ba), γ-butyrolactone (γ-Bt), propyl propionate (n-PP), ethyl propionate (EP), and ethyl butyrate (Eb).

[0013] In some embodiments, the non-aqueous organic solvent of the present invention comprises 60-90% by mass in the non-aqueous electrolyte; preferably, the non-aqueous organic solvent comprises 70-88% by mass in the non-aqueous electrolyte; more preferably, the non-aqueous organic solvent comprises 80-88% by mass in the non-aqueous electrolyte. As an example, the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte may be, but is not limited to, 80%, 82%, 85%, 86%, 87%, or 88%.

[0014] Correspondingly, the present invention also provides a lithium-ion battery, including a positive electrode material, a negative electrode material and the above-mentioned non-aqueous electrolyte. Because the lithium-ion battery contains the non-aqueous electrolyte, it has good high-temperature storage performance, high-temperature cycle performance, and low-temperature discharge performance.

[0015] In some embodiments, the cathode material contains cobalt. Preferably, the cathode material is at least one of lithium cobalt oxide, nickel cobalt manganese oxide, or nickel cobalt aluminum oxide. These cathode materials all contain cobalt ions, possess catalytic properties, and can significantly enhance the adsorption of silver ions, forming a strong adsorption and thus greatly improving the high-temperature cycle performance of the battery.

[0016] Among them, the chemical formula of nickel-cobalt-manganese oxide is LiNi x Co y Mn z M (1-x-y-z) O2; the chemical formula of nickel-cobalt-aluminum oxide is LiNi xCo y Al z N (1-x-y-z) O2, where M and N are each independently selected from at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z ≤ 1; the chemical formula of lithium cobaltate is LiCoO2.

[0017] In some embodiments, the negative electrode material of the present invention is selected from at least one of artificial graphite, natural graphite, lithium titanate, silicon-carbon composite material, and silicon monoxide. Detailed Embodiments

[0018] To better illustrate the purpose, technical solution, and beneficial effects of the present invention, the following specific examples are used to further illustrate the purpose, technical solution, and beneficial effects of the present invention, but do not constitute any limitation to the present invention. For those not specified in the examples, conventional conditions or conditions recommended by the manufacturer can be followed. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial channels.

[0019] Example 1

[0020] (1) Preparation of non-aqueous electrolyte

[0021] In a glove box filled with argon (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed according to a weight ratio of EC:EMC:DEC = 1:1:1 to prepare 87 g of non-aqueous organic solvent. Then, 0.5 g of silver tetrafluoroborate was added as an additive. After dissolving and stirring well, 12.5 g of lithium hexafluorophosphate was added, and after mixing evenly, a non-aqueous electrolyte was obtained.

[0022] (2) Preparation of positive electrode

[0023] LiCoO2, binder PVDF, and conductive agent SuperP were mixed evenly according to a mass ratio of 95:1:4 to prepare a lithium-ion battery positive electrode slurry with a certain viscosity. After coating the mixed slurry on both sides of the aluminum foil, it was dried and roll-pressed to obtain a positive electrode sheet.

[0024] (3) Preparation of negative electrode

[0025] Artificial graphite, conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) were made into a slurry according to a mass ratio of 95:1.5:1.0:2.5, mixed evenly, and after coating the mixed slurry on both sides of the copper foil, it was dried and roll-pressed to obtain a negative electrode sheet.

[0026] (4) Preparation of separator

[0027] A single-layer PE porous polymer film was used as the separator (S), with a thickness of 5 micrometers and a porosity of 39%. The inorganic coating was Al2O3, and the organic particles were polyvinylidene fluoride.

[0028] (5) Preparation of lithium-ion batteries

[0029] The positive electrode, separator, and negative electrode are wound together to form a soft-pack battery cell, which is then packaged in a polymer aluminum-plastic film and filled with the prepared non-aqueous electrolyte for lithium-ion batteries. After formation, capacity testing, and other processes, a lithium-ion battery with a capacity of 4000mAh is produced.

[0030] The non-aqueous electrolyte formulations for Examples 2-7 and Comparative Example 1 are shown in Table 1. The steps for preparing the electrolyte and manufacturing the battery are the same as in Example 1.

[0031] Table 1 Formulation of non-aqueous electrolyte

[0032]

[0033] The lithium-ion batteries prepared in Examples 1-7 and Comparative Example 1 were subjected to low-temperature discharge performance tests, high-temperature storage tests, and high-temperature cycling tests, respectively. The specific test conditions are as follows, and the performance test results are shown in Table 2.

[0034] Low temperature discharge performance test of lithium ion battery

[0035] Under normal temperature (25℃) conditions, a lithium-ion battery is subjected to a 0.5C / 0.5C charge and discharge cycle (discharge capacity denoted as C0), with an upper limit voltage of 4.535V. Then, the battery is charged to 4.535V under constant current and constant voltage conditions at 0.5C. The lithium-ion battery is then placed in a -20℃ low-temperature chamber for 4 hours and discharged at -20℃ at 0.5C (discharge capacity denoted as C1). The low-temperature discharge rate of the lithium-ion battery is calculated using the following formula:

[0036] Low-temperature discharge rate = (C1 / C0) * 100%

[0037] High temperature storage performance test of lithium ion battery

[0038] Under normal temperature (25℃) conditions, a lithium-ion battery was subjected to one 0.3C / 0.3C charge and discharge cycle (battery discharge capacity recorded as C0), with an upper limit voltage of 4.535V. The battery was then placed in a 60℃ oven for 7 days, removed, and placed in a 25℃ environment for a 0.3C discharge, with the discharge capacity recorded as C1. Finally, the lithium-ion battery was subjected to another 0.3C / 0.3C charge and discharge cycle (battery discharge capacity recorded as C2). The capacity retention rate and capacity recovery rate of the lithium-ion battery were calculated using the following formulas:

[0039] Capacity retention rate = (C1 / C0) * 100%

[0040] Capacity recovery rate = (C2 / C0) * 100%

[0041] High temperature cycle performance test of lithium ion battery

[0042] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1C until the voltage reached 4.535V, followed by constant voltage charging at 4.535V until the current reached 0.05C. Next, it was discharged at a constant current of 1C until the voltage reached 3.0V. The first discharge capacity was recorded as C0. This constitutes one charge-discharge cycle. Then, 300 cycles of 1C / 1C charging and discharging were performed at 45°C, and the discharge capacity was recorded as C1. The capacity retention rate of the lithium-ion battery was calculated using the following formula.

[0043] Capacity retention rate = (C1 / C0) * 100%

[0044] Table 2. Performance test results of lithium-ion batteries

[0045]

[0046] As shown in Table 2, the lithium-ion batteries of Examples 1-7 exhibit better high-temperature storage performance, high-temperature cycle performance, and low-temperature discharge performance than Comparative Example 1. In Examples 1-3, the silver ion content was added in a gradient manner, and the differences in experimental data were not significant, indicating that the silver ion content in the non-aqueous organic electrolyte described in Example 1 was already saturated when 0.5g of silver tetrafluoroborate was added. The non-aqueous electrolyte of this invention uses Ag as an additive. x M represents hexafluorophosphate, tetrafluoroborate, oxalate, perchlorate, nitrate, fluoride anion, and bis(trifluoromethanesulfonate). These negative ion structures can improve the cycle performance of batteries under high voltage, while silver ions can optimize the composition of the solid electrolyte interface film. Through the adsorption of silver ions, a certain degree of adsorption is formed, thereby improving the high-temperature cycle performance of the battery. Simultaneously, the additive Ag formed by the combination of these positive and negative ions... x M can optimize the cathode / electrolyte interface, reduce the surface activity of the electrode and thus inhibit the oxidative decomposition of the electrolyte, so that the electrolyte remains stable under continuous high voltage, thereby improving the high-temperature storage performance and high-temperature cycle performance of lithium-ion batteries under high voltage (especially at 4.535V). At the same time, it was also found in the actual research and development process that the addition of this additive can also improve the low-temperature discharge performance of lithium-ion batteries.

[0047] Data from Example 5 illustrates that the additive Ag xM uses silver nitrate, and the battery's high-temperature cycling capacity retention rate is higher than other embodiments. After silver ions dissolve in the non-aqueous electrolyte described in Embodiment 1, the silver ions can be oxidized in advance to participate in the formation of a dense and uniform SEI film with a flat surface free of lithium dendrites. This is due to the effect of nitrate, which can reduce the risk of lithium plating under fast-charging conditions and reduce the catalytic reaction between metallic lithium and cyclic molecules such as electrolyte solvent EC. At the same time, the cationic silver ions can change the solvation effect of lithium ions entering the positive electrode interface and reduce the steric hindrance at the electrolyte interface. On the other hand, the intrinsic adsorption effect of silver ions reduces the dissolution of cobalt ions into the electrolyte during high-voltage cycling of lithium cobalt oxide, enhances the stability of the CEI interface, and indirectly improves the stability of the battery interface. The combined effect of silver nitrate on both aspects enables the lithium-ion battery to achieve better high-temperature cycling and high-temperature storage performance.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode material, a negative electrode material, and a non-aqueous electrolyte, characterized in that, The lithium-ion battery has a maximum charging voltage of 4.535V. The positive electrode material is lithium cobalt oxide, and the negative electrode material is selected from at least one of artificial graphite, natural graphite, lithium titanate, silicon-carbon composite material, and silicon suboxide. The non-aqueous electrolyte includes lithium salt, non-aqueous organic solvent, and additives. The non-aqueous organic solvent is at least one of chain carbonate, cyclic carbonate, and carboxylic acid ester. The additives are compounds as shown in structural formula 1. Ag x M-structure 1 Where M represents any one of hexafluorophosphate, tetrafluoroborate, oxalate, perchlorate, nitrate, fluoride anion, and bis(trifluoromethanesulfonate), and x represents the chemical valence state of the anion.

2. The lithium-ion battery as described in claim 1, characterized in that, The additive constitutes 0.1% to 2% of the non-aqueous electrolyte by mass.

3. The lithium-ion battery as described in claim 1, characterized in that, The lithium salt constitutes 6.5% to 15.5% of the mass of the non-aqueous electrolyte.

4. The lithium-ion battery as described in claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate-borate), lithium difluorophosphate, lithium difluorooxalate-borate, lithium difluorodioxalate-phosphate, and lithium bis(oxalate-imide).

5. The lithium-ion battery as described in claim 1, characterized in that, The non-aqueous organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate, and ethyl butyrate.

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