Electrolyte additive, lithium-ion battery electrolyte and lithium-ion battery

Abstract

The present invention discloses an electrolyte additive, a lithium ion battery electrolyte and a lithium ion battery, wherein the electrolyte additive comprises a compound A shown in structural formula 1, structural formula 2 or structural formula 3, wherein R1 is a hydrocarbon group with 1 to 6 carbon atoms, R2 is a hydrogen atom or a hydrocarbon group with 1 to 6 carbon atoms, R3, R5, R7 and R9 are each independently selected from a fluorine atom or a fluoroalkoxy group, and R4, R6, R8 and R9 are each independently selected from a fluorine atom or a fluoroalkoxy group. 10 Each is independently selected from a fluorine atom, a fluoroalkoxy group, an alkoxy group or a nitrogen-containing heterocyclic group. The electrolyte additive can not only ensure the high-temperature storage and high-temperature cycle performance of the lithium-ion battery under a high voltage (especially 4.5V) system, but also take into account the low-temperature performance of the lithium-ion battery.

Description

Technical Field

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

[0002] Lithium-ion batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and have been used in a wide range of applications. In lithium-ion batteries, high-voltage ternary cathode materials are widely used in portable electronic devices such as mobile phones and laptops, as well as large energy storage devices, due to their high energy density, environmental friendliness, and long cycle life. The rapid development of electronic information technology has put forward higher requirements for the high voltage and high energy density of lithium-ion batteries.

[0003] At present, the energy density of lithium-ion batteries is often improved by increasing the charging cut-off voltage, but there are also some problems with ternary positive electrode materials under high voltage: when the voltage reaches 4.5V, conventional electrolytes will undergo oxidative decomposition side reactions on the surface of the positive electrode materials, especially under high temperature conditions, which will accelerate the oxidative decomposition of the electrolyte, intensify the electrolyte side reactions, and promote the deterioration reaction of the ternary positive electrode materials; especially at low temperatures, the internal impedance of the lithium-ion battery increases, and the low-temperature discharge performance of the lithium-ion battery is obviously insufficient. Therefore, how to ensure the high and low temperature characteristics of lithium-ion batteries while increasing the cut-off voltage has become a research focus.

[0004] Therefore, there is an urgent need for an electrolyte additive, a lithium ion battery electrolyte and a lithium ion battery to solve the deficiencies of the prior art problems. Summary of the invention

[0005] The purpose of the present invention is to provide an electrolyte additive, which can not only ensure the high-temperature storage and high-temperature cycle performance of lithium-ion batteries under high voltage (especially 4.5V) systems, but also take into account the low-temperature performance of lithium-ion batteries.

[0006] Another object of the present invention is to provide a lithium-ion battery electrolyte, which can not only ensure the high-temperature storage and high-temperature cycle performance of the lithium-ion battery under a high voltage (especially 4.5V) system, but also take into account the low-temperature performance of the lithium-ion battery.

[0007] Another object of the present invention is to provide a lithium ion battery having good high temperature storage performance, high temperature cycle performance and low temperature discharge performance under a high voltage (especially 4.5V) system.

[0008] To achieve the above objectives, the present invention provides an electrolyte additive, comprising a compound A shown in structural formula 1, structural formula 2 or structural formula 3,

[0009]

[0010] wherein R1 is a hydrocarbon group having 1 to 6 carbon atoms, R2 is a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, R3, R5, R7, and R9 are each independently selected from a fluorine atom or a fluoroalkoxy group, and R4, R6, R8, and R 10 Each is independently selected from a fluorine atom, a fluoroalkoxy group, an alkoxy group or a nitrogen-containing heterocyclic group.

[0011] Compared with the prior art, the electrolyte additive of the present invention includes a compound A with a special structure, wherein the cyclic -SO2- structure on the compound A reacts at the positive electrode / electrolyte interface during the first charge to form an interface film containing S and O, which is relatively stable under high temperature conditions and can significantly improve the high temperature storage performance of lithium ion batteries. However, this type of interface film containing S and O is not very stable under continuous high voltage (especially at 4.5V), thereby affecting the high temperature cycle performance. The -PF or -PXF group on the fluorophosphate structure on the compound A has a high oxidation potential, so the fluorophosphate structure can improve the overall oxidation resistance of the compound A, which helps to inhibit the decomposition of the interface film containing S and O under continuous high voltage, thereby improving the high temperature cycle performance of the lithium ion battery. In addition, the cyclic -NC=ON- structure in formula 1 has high reactivity, which makes it easier to generate components such as Li3N and Li2CO3, thereby improving the ionic conductivity of the SEI film, effectively improving the DCR of the SEI film, and enhancing the low-temperature performance of lithium-ion batteries; the cyclic -NC=OCN- in formula 2 and the cyclic -NC=OC=ON- in formula 3 are conducive to the generation of uniform organic N x O y and inorganic Li2CO3, thereby improving the toughness of the interface film and the ionic conductivity of the SEI film, effectively improving the high-temperature cycle performance and low-temperature performance of lithium-ion batteries. x O y The components can also increase the ionic conductivity of the SEI film, thereby further improving the low-temperature performance of the lithium-ion battery. Therefore, the electrolyte additive of the present invention adds the compound A with a special structure, so that the lithium-ion battery has better high-temperature storage performance, high-temperature cycle performance and low-temperature discharge performance under a high voltage (especially 4.5V) system.

[0012] Preferably, compound A of the present invention is selected from any one of compound 1 to compound 9:

[0013]

[0014] Compound 1 is prepared by a substitution reaction between reaction substrate A and reaction substrate B under the action of potassium carbonate, and then purified by recrystallization or column chromatography. The reaction route is as follows:

[0015]

[0016] The reaction route from compound 2 to compound 9 is similar to the synthetic route of compound 1, and the corresponding reaction substrate A is shown below:

[0017]

[0018] The corresponding reaction substrate B is shown below:

[0019]

[0020] To achieve the above objectives, the present invention provides a lithium-ion battery electrolyte, comprising a lithium salt and an organic solvent, and also comprising the above electrolyte additive.

[0021] Compared with the prior art, the lithium ion battery electrolyte of the present invention includes a compound A containing a special structure, wherein structural formula 1 includes -SO2-, -NC=ON- and a fluorophosphate structure, structural formula 2 includes -SO2-, -NC=OCN- and a fluorophosphate structure, and structural formula 3 includes -SO2-, -NC=OC=ON- and a fluorophosphate structure. The lithium ion battery electrolyte is applied to a lithium ion battery, so that the lithium ion battery has better high-temperature storage performance, high-temperature cycle performance and low-temperature discharge performance under a high voltage (especially 4.5V) system.

[0022] Preferably, the mass percentage of the electrolyte additive of the present invention in the lithium ion battery electrolyte is 0.1-5%. More preferably, the mass percentage of the electrolyte additive in the lithium ion battery electrolyte is 0.5-2%, specifically but not limited to 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

[0023] Preferably, the mass percentage of the lithium salt of the present invention in the lithium ion battery electrolyte is 6.5-15.5%, specifically but not limited to 6.5%, 7%, 8%, 10%, 12%, 12.5%, 13%, 14%, 15%, 15.5%.

[0024] Preferably, the organic solvent of the present invention is selected from at least one of 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).

[0025] Preferably, the lithium salt of the present invention is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium bis(oxalatoborate) (C4BLiO8), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (C2BF2LiO4), lithium difluorobis(oxalatophosphate) (LiDFBP) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0026] To achieve the above objectives, the present invention provides a lithium ion battery, including a positive electrode material, a negative electrode material, and the above-mentioned lithium ion battery electrolyte, the positive electrode material is nickel cobalt manganese oxide or nickel cobalt aluminum oxide, and the maximum charging voltage is 4.5V.

[0027] Compared with the prior art, the lithium ion battery of the present invention includes a compound A containing a special structure, wherein structural formula 1 includes -SO2-, -NC=ON- and a fluorophosphate structure, structural formula 2 includes -SO2-, -NC=OCN- and a fluorophosphate structure, and structural formula 3 includes -SO2-, -NC=OC=ON- and a fluorophosphate structure, so that the lithium ion battery has better high-temperature storage performance, high-temperature cycle performance and low-temperature discharge performance under a high voltage (especially 4.5V) system.

[0028] Preferably, the chemical formula of the nickel-cobalt-manganese oxide of the present invention is LiNi x Co y Mn z M (1-x-y-z) O2, the chemical formula of nickel cobalt aluminum oxide is LiNi x Co y Al z N (1-x-y-z) O2, wherein M is at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, N is at least one of Mn, Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V and Ti, 0 <x<1,0<y<1,0<z<1,x+y+z≤1。

[0029] Preferably, 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 DESCRIPTION

[0030] The purpose, technical scheme and beneficial effects of the present invention are further illustrated by specific examples below, but do not constitute any limitation to the present invention. It should be noted that, if specific conditions are not specified in the embodiments and comparative examples, they can be carried out according to conventional conditions or conditions recommended by the manufacturer, and if the manufacturer of the reagents or instruments is not specified, they are all conventional products available on the market.

[0031] Example 1

[0032] (1) Preparation of non-aqueous electrolyte: The electrolyte is prepared in a vacuum glove box with an argon atmosphere and a moisture content of less than 1 ppm. In a dry argon atmosphere glove box, propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a weight ratio of PC:EMC:DEC=1:1:1, and then additives are added. After dissolving and stirring thoroughly, lithium salt is added and mixed evenly to obtain an electrolyte.

[0033] (2) Preparation of positive electrode: LiNi 0.5 Co 0.2 Mn 0.3 O2, adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 95:1:4 to form a lithium-ion battery positive electrode slurry with a certain viscosity. The mixed slurry is coated on both sides of an aluminum foil, and then dried and rolled to obtain a positive electrode sheet.

[0034] (3) Preparation of negative electrode: artificial graphite, conductive agent SuperP, thickener CMC, and adhesive SBR (styrene-butadiene rubber latex) are mixed in a mass ratio of 95:1.5:1.0:2.5 to make a slurry, mix them evenly, apply the mixed slurry on both sides of the copper foil, dry and roll-press to obtain a negative electrode sheet.

[0035] (4) Preparation of lithium-ion batteries: The positive electrode, the separator and the negative electrode are stacked to form a square battery cell, which is packaged with a polymer and filled with the lithium-ion battery non-aqueous electrolyte prepared above. After the steps of formation and capacity separation, a lithium-ion battery with a capacity of 1000 mAh is manufactured.

[0036] The electrolyte formulations of Examples 2 to 11 and Comparative Examples 1 to 3 are shown in Table 1. The steps of preparing the electrolyte and preparing the lithium-ion battery are the same as those of Example 1.

[0037] Table 1 Electrolyte composition

[0038]

[0039]

[0040] Compound 10 and compound 11 can be prepared by the following reaction:

[0041]

[0042] The lithium ion batteries prepared in Examples 1 to 11 and Comparative Examples 1 to 3 were subjected to low temperature discharge test, high temperature storage test and high temperature cycle test respectively. The specific test conditions are as follows. The performance test results are shown in Table 2.

[0043] (1) Low temperature discharge test of lithium-ion batteries

[0044] At room temperature (25°C), the lithium-ion battery is charged and discharged at 0.5C / 0.5C (the discharge capacity is recorded as C0), the upper limit voltage is 4.5V, and then the battery is charged to 4.5V under 0.5C constant current and constant voltage conditions. The lithium-ion battery is placed in a -20°C low temperature box for 4 hours and discharged at 0.5C at -20°C (the discharge capacity is recorded as C1). The low temperature discharge rate of the lithium-ion battery is calculated using the following formula:

[0045] Low temperature discharge rate = C1 / C0*100%

[0046] (2) Lithium-ion battery high temperature storage test

[0047] At room temperature (25°C), the lithium-ion battery is charged and discharged at 0.5C / 0.5C (the battery discharge capacity is recorded as C0), and the upper limit voltage is 4.5V; the battery is placed in a 60°C oven for 15 days, the battery is taken out, and the battery is placed in a 25°C environment for 0.5C discharge, and the discharge capacity is recorded as C1; then the lithium-ion battery is charged and discharged at 0.5C / 0.5C (the battery discharge capacity is recorded as C2), and the capacity retention rate and capacity recovery rate of the lithium-ion battery are calculated using the following formula.

[0048] Capacity retention rate = C1 / C0*100%

[0049] Capacity recovery rate = C2 / C0*100%

[0050] (3) High temperature cycle test of lithium-ion batteries

[0051] Place the lithium-ion battery in a 45℃ constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge at 1C constant current to a voltage of 4.5V, then charge at 4.5V constant voltage to a current of 0.05C, then discharge at 1C constant current to a voltage of 3.0V, and record the first cycle discharge capacity of the battery as C0. This is one charge and discharge cycle. Then, charge and discharge at 1C / 1C for 300 cycles at 45℃, and record the discharge capacity as C1.

[0052] Capacity retention rate = C1 / C0*100%

[0053] Table 2 Lithium-ion battery performance test results

[0054]

[0055] From the results in Table 2, it can be seen that the low-temperature discharge performance, high-temperature storage performance and high-temperature cycle performance of Examples 1 to 11 are all better than those of Comparative Examples 1 to 3. This is because the electrolyte additive of the present invention includes a compound A containing a special structure, wherein the -SO2- structure reacts at the positive electrode / electrolyte interface during the first charge to form an interface film containing S and O. The interface film is relatively stable under high temperature conditions and can significantly improve the high-temperature storage performance of lithium-ion batteries. However, this type of interface film containing S and O is not very stable under continuous high voltage (especially at 4.5V), thereby affecting the high-temperature performance. The -PF or -PXF group on the fluorophosphate structure has a high oxidation potential, so the fluorophosphate structure can improve the overall oxidation resistance of compound A, which helps to inhibit the decomposition of the interface film containing S and O under continuous high voltage, thereby improving the high-temperature cycle performance of lithium-ion batteries. In addition, the cyclic -NC=ON- structure has high reactivity, which makes it easier to generate components such as Li3N and Li2CO3, thereby improving the ionic conductivity of the SEI film, effectively improving the DCR of the SEI film, and enhancing the low-temperature performance of lithium-ion batteries; the cyclic -NC=OCN- and cyclic -NC=OC=ON- structures are conducive to the generation of uniform organic N x O y and inorganic Li2CO3, thereby improving the toughness of the interface film and the ionic conductivity of the SEI film, effectively improving the low-temperature performance and high-temperature cycle performance of lithium-ion batteries. x O y The components can also increase the ionic conductivity of the SEI film, thereby further improving the low-temperature performance of the lithium-ion battery. Therefore, the electrolyte additive of the present invention adds the compound A with a special structure, so that the lithium-ion battery has better high-temperature storage performance, high-temperature cycle performance and low-temperature discharge performance under a high voltage (especially 4.5V) system.

[0056] Comparing Example 8 with Comparative Examples 1 and 2, it can be seen that the lithium-ion battery of Example 8 has relatively better high-temperature cycle performance and low-temperature discharge performance. This is because although the additive of Comparative Example 2 contains -SO2- structure, which improves the high-temperature storage performance to a certain extent, it does not contain a cyclic -NC=OCN- structure, so the interface film does not contain uniform organic N x O yand inorganic Li2CO3 and other components, resulting in poor toughness of the interface film and easy rupture of the interface film, thus affecting the low-temperature performance and high-temperature cycle performance.

[0057] Comparing Example 8 with Comparative Examples 1 and 3, it can be seen that the lithium ion battery of Example 8 has relatively better high-temperature storage, high-temperature cycle performance and low-temperature discharge performance. Although the additive of Comparative Example 3 contains a cyclic -NC=ON- structure and a fluorophosphate structure, which improves the low-temperature performance and high-temperature cycle performance to a certain extent, the -SO2- structure is not on the heterocyclic structure, resulting in the formed S and O-containing interface film being less stable under high temperature conditions, thereby affecting the high-temperature storage performance, high-temperature cycle performance and low-temperature discharge performance.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. An electrolyte additive, characterized in that: Including compound 4, compound 5, compound 7 or compound A, wherein compound A is represented by structural formula 1, structural formula 2 or structural formula 3; wherein R1 is a hydrocarbon group having 1 to 6 carbon atoms, R2 is a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, R3, R5, R7, and R9 are each independently selected from a fluorine atom or a fluoroalkoxy group, and R4, R6, R8, and R 10 Each is independently selected from a fluorine atom, a fluoroalkoxy group, an alkoxy group or a nitrogen-containing heterocyclic group.

2. The electrolyte additive according to claim 1, characterized in that The compound A is selected from any one of compound 1 to compound 3, compound 6, compound 8, and compound 9:

3. A lithium ion battery electrolyte comprising a lithium salt and an organic solvent, characterized in that: It also includes the electrolyte additive as described in any one of claims 1 to 2.

4. The lithium ion battery electrolyte according to claim 3, characterized in that The mass percentage of the electrolyte additive in the lithium-ion battery electrolyte is 0.1-5%.

5. The lithium ion battery electrolyte according to claim 3, characterized in that: The mass percentage of the lithium salt in the lithium ion battery electrolyte is 6.5-15.5%.

6. The lithium ion battery electrolyte according to claim 3, characterized in that: The organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate and ethyl butyrate.

7. The lithium ion battery electrolyte according to claim 3, characterized in that: The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonyl imide, lithium bisoxalatoborate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium difluorobisoxalatophosphate and lithium bisfluorosulfonyl imide.

8. A lithium-ion battery comprising a positive electrode material and a negative electrode material, characterized in that: It also includes the lithium-ion battery electrolyte as described in any one of claims 3 to 7, wherein the positive electrode material is nickel cobalt manganese oxide or nickel cobalt aluminum oxide, and the maximum charging voltage is 4.5V.

9. The lithium ion battery according to claim 8, characterized in that The chemical formula of the nickel-cobalt-manganese oxide is LiNi x Co y Mn z M (1-x-y-z) O2, the chemical formula of the nickel cobalt aluminum oxide is LiNi x Co y Al z N (1-x-y-z) O2, wherein M is at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, N is at least one of Mn, Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V and Ti, 0 <x<1,0<y<1,0<z<1,x+y+z≤1。 10. The lithium ion battery according to claim 8, characterized in that The negative electrode material is selected from at least one of artificial graphite, natural graphite, lithium titanate, silicon-carbon composite material and silicon monoxide.

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