A high-voltage lithium cobalt oxide battery additive combination

Abstract

The present application provides a battery additive combination, which comprises a fluorinated aromatic ether compound and an aromatic sulfone compound. An electrolyte containing the additive combination can sequentially generate a double-layer positive electrode / electrolyte interface film on the surface of the positive electrode. The inner layer is formed by the adsorption of the oxidation fragments of the fluorinated ether compound on the surface of the positive electrode, and is a flexible layer. The outer layer is a rigid layer generated by the aromatic sulfone derivative. The present application effectively inhibits the oxidative decomposition of the electrolyte under high pressure, and improves the stability of the interface between the electrolyte and the electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, and particularly relates to an electrolyte additive of high-voltage lithium cobalt oxide battery. BACKGROUND

[0002] The high-voltage lithium cobalt oxide battery is the most widely used energy storage device in modern mobile electronic devices, and the performance thereof directly affects the peak performance and endurance time of the electronic device. However, the existing commercial electrolyte system is difficult to cope with the problems of electrolyte oxidation decomposition and interface layer instability on the electrode surface under high voltage. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application provides a high-voltage lithium cobalt oxide battery additive combination, which effectively inhibits the oxidation decomposition of the electrolyte under high voltage and improves the stability of the interface between the electrolyte and the electrode.

[0004] The battery additive combination of the present application comprises a fluorinated aromatic ether compound and an aromatic sulfone compound. The fluorinated aromatic ether compound has better affinity by fluorination, is more easily bonded and coated on the surface of the positive electrode, the ether bond has better flexibility, promotes the formation of the inner coating layer, and the presence of the aromatic ring introduces a relatively rigid group in the flexible chain, which is easy to form a transition with the outer aromatic sulfone compound; the aromatic sulfone compound forms a rigid coating layer on the outer layer, the presence of the sulfone group can balance the electron cloud density on the aromatic ring, and as a rigid interface layer, it can further promote the stability of the interface layer under high voltage operation and promote the cycle performance.

[0005] The fluorinated aromatic ether compound is selected from one or more of the following compounds:

[0006] R1-Ph-R5-O-R2

[0007] Ph is a benzene ring, R1 is a fluorinated alkyl group with not more than 3 carbon atoms, R2 is an alkyl group or a fluorinated alkyl group with not more than 6 carbon atoms, R5 is an alkyl group or a fluorinated alkyl group with not more than 3 carbon atoms, and R1 and R5 are located at the ortho position or the para position of Ph, respectively.

[0008] Preferably, Ph is a benzene ring, R1 is a fluorinated methyl group, R2 is an alkyl group or a fluorinated alkyl group with not more than 6 carbon atoms, R5 is a fluorinated methylene group, and R1 and R5 are located at the meta position or the para position of Ph, respectively.

[0009] The aromatic sulfone compound is selected from one or more of the following compounds:

[0010] R3-Ph-SO2-Ph-R4

[0011] Ph is a benzene ring, R3 and R4 are each independently H or alkyl or fluoroalkyl having a carbon atom number of no more than 6, and R3 and R4 are each independently located at the meta or para position of the connected Ph relative to the sulfone group.

[0012] The molar ratio of the fluoroaromatic ether compound and the aromatic sulfone compound can be 1:50-50:1, preferably 1:5-5:1, and more preferably 2:1-1:1.

[0013] In the present application, "fluoro" means that at least one hydrogen atom in a substituent is replaced by a fluorine atom, and preferably all hydrogen atoms are replaced by fluorine atoms.

[0014] The above battery additive combination of the present application can be added to a base electrolyte as an additive to obtain a high-pressure-resistant electrolyte product. The additive amount of the battery additive combination in the base electrolyte is 1 mM-100 mM; preferably, the additive amount of the fluoroaromatic ether compound in the base electrolyte is 1 mM-50 mM, and the additive amount of the aromatic sulfone compound in the base electrolyte is 1 mM-50 mM; more preferably, the additive amount of the fluoroaromatic ether compound in the base electrolyte is 20-40 mM, the additive amount of the aromatic sulfone compound in the base electrolyte is 10-20 mM, and the ratio of the additive amount of the fluoroaromatic ether compound to the additive amount of the aromatic sulfone compound in the base electrolyte is 2:1-1:1.

[0015] The above battery additive combination or high-pressure-resistant electrolyte product of the present application, due to its excellent high-pressure-resistant performance, can be particularly suitable for high-voltage lithium cobalt oxide batteries. Therefore, the present application also provides a high-voltage lithium cobalt oxide battery comprising an electrolyte containing the above battery additive combination, and a lithium cobalt oxide positive electrode and a negative electrode. The lithium cobalt oxide positive electrode can comprise a lithium cobalt oxide material doped in the bulk phase and / or modified on the surface, the bulk phase doping comprises doping with Ni, Mn, Ti, Mg, Zn, etc., and the surface modification comprises coating with Al2O3, ZrO2, LiF, etc.; the negative electrode comprises one of lithium metal, graphite, lithium titanate, and silicon-carbon composite material.

[0016] By the present application, a positive electrode / electrolyte interface structure is also provided, which has an inner interface layer and an outer interface layer on the surface of the positive electrode in sequence, the inner interface layer is composed of oxidation fragments of the fluoroaromatic ether compound, and the outer interface layer is composed of the aromatic sulfone compound. The interface structure can be formed on the positive electrode material by the above battery additive combination.

[0017] The thickness of the inner interface layer and the outer interface layer can be independently formed to be 1-100 nm, and preferably 3-20 nm.

[0018] The method for forming the above positive electrode / electrolyte interface structure comprises the following steps: firstly, the battery containing the electrolyte with the above battery additive combination is forcedly polarized at the positive electrode potential of 3.6-3.75 V, and then charged to the cut-off potential. The forced polarization at the positive electrode potential can make the fluorine-substituted aromatic ether compound fully oxidize and decompose and be deposited on the positive electrode surface to form an inner interface layer; and the charging to the cut-off potential can make the aromatic sulfone compound electrochemically polymerize and be deposited on the surface of the aforementioned inner interface layer to form an outer interface layer.

[0019] The battery is a high-voltage lithium cobalt oxide battery; the forced polarization time is 3-10 h; and the cut-off potential is between 4.2 V and 4.6 V.

[0020] The present application has the beneficial effect that: by virtue of the difference in the oxidation decomposition / polymerization potential of each component, a double-layer positive electrode / electrolyte interface film is sequentially generated on the positive electrode surface. The inner layer is formed by the adsorption of the oxidation fragments of the fluorine-substituted ether compound on the positive electrode surface, i.e. the oxidation product of the aromatic fluorine-substituted ether, and the outer layer is a rigid layer generated by the aromatic sulfone derivative. In the double-layer interface film, the inner layer is resistant to high voltage and provides a buffer space for the volume change of the electrode particles during the working process, and the outer layer is relatively rigid, wraps the electrode particles, suppresses the contact of the electrolyte components with the inner layer / electrode surface, and maintains the integrity of the inner layer interface film. BRIEF DESCRIPTION OF DRAWINGS

[0021] The technical solutions of the embodiments of the present application are described in further detail below with reference to the drawings and examples.

[0022] Figure 1 TEM characterization of the positive electrode surface of the battery 3a after cycling.

[0023] Figure 2 The surface AFM test result graph of the stainless steel sheet / Li battery assembled with the electrolyte 17.

[0024] Figure 3 The surface AFM test result graph of the stainless steel sheet / Li battery assembled with the electrolyte 15. DETAILED DESCRIPTION

[0025] The present application is further described below with reference to the drawings and specific examples, but it should be understood that these examples are merely used for more detailed description and should not be understood as limiting the present application in any form, i.e. not intended to limit the protection scope of the present application.

[0026] I. Preparation of high-voltage-resistant electrolyte

[0027] The combination of fluoro aromatic ether compounds and aromatic sulfone compounds in different concentrations added to the base electrolyte can obtain different high pressure resistant electrolyte products, and Table 1 provides 14 different electrolyte products 1-14, and 4 electrolyte products 15-18 obtained by adding fluoro aromatic ether compounds or aromatic sulfone compounds alone. The base electrolyte is PC+DMC+EMC (volume ratio 1:1:3), and LiPF61.1 mol / L.

[0028] Table 1

[0029]

[0030]

[0031] II. Preparation of the battery

[0032] The lithium cobaltate is used as the active material, and the conductive agent activated carbon (Super P) and the binder polyvinylidene fluoride (PVDF) are uniformly mixed in the N-methyl pyrrolidone (NMP) solution, and the mass ratio of the active material, activated carbon (Super P) and binder is 8:1:1, then coated on the aluminum foil and pressed into a sheet to obtain the positive electrode.

[0033] The metal lithium sheet is used as the negative electrode, the PP / PE separator is used, and the electrolyte 1-14 is used to assemble CR2032 type button lithium batteries 1a-14a. The electrolyte 15-18 is used to assemble CR2032 type button lithium batteries, which are marked as control batteries 1b-4b. The base electrolyte is used to assemble button batteries CR2032, which is marked as control battery 5b.

[0034] III. Performance characterization

[0035] (1) Electrochemical performance test

[0036] The above battery is subjected to electrochemical performance test on a LAND-CT2001A charge-discharge tester. Specifically, in the range of 3-4.6 V, the battery is first charged to 3.7 V at 0.2C, polarized for 4h, then charged to 4.6 V at 0.5C and static for 30s, then discharged at 1C constant current, and the cut-off voltage is 3V. Take this as one cycle, and cycle for 100 weeks under the same conditions. The results are shown in Table 2 (mAhg -1 ).

[0037]

[0038] Wherein, n is the cycle number, and the initial discharge capacity is the discharge capacity of the first week of the cycle.

[0039] Table 2

[0040]

[0041] As can be seen from Table 2, the additives of the present invention can significantly improve the cycle capacity of the battery under high voltage compared with ordinary electrolytes and additives with a single component. Furthermore, under the optimized ratio (addition amount 2:1 to 1:1, concentrations of 20-40mM and 10-20mM, respectively), the capacity retention rate is higher.

[0042] (2) Interface characterization

[0043] Figure 1 The image shows an electron microscope (EM) image of the cathode / electrolyte interface structure obtained by this invention. As can be seen from the image, two interface layers, inner and outer, are formed on the surface of the cathode material, with a smooth interface transition and a thickness of approximately 5 nm for each layer.

[0044] To verify the rigidity of the interface layer formed by the electrolyte of this invention on the surface of the battery positive electrode, stainless steel / Li batteries were assembled using electrolytes 15 and 17 respectively for AFM testing. The batteries were subjected to a constant voltage of 4.5 V vs. Li+ / Li for 2 hours. The stainless steel sheet was then removed and cleaned with dimethyl carbonate (DMC) solvent. The Young's modulus of the film on the stainless steel sheet was measured using an atomic force microscope (AFM). The results are as follows: Figures 2-3 As shown, the Young's modulus comparison reveals that the CEI film formed using electrolyte 17 has a modulus of only 4 GPa. This is mainly due to the oxidation products of aromatic fluoroethers, which exhibit good elasticity. In contrast, the film formed using electrolyte 15, composed of aromatic sulfone derivatives, has a modulus of 18.6 GPa, demonstrating better rigidity. This indicates that the additive combination of the present invention can form two layers of film with complementary flexibility and rigidity, effectively promoting the interfacial stability between the electrode and the electrolyte.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A battery additive combination comprising a fluorinated aromatic ether compound and an aromatic sulfone compound. The fluorinated aromatic ether compound is selected from one or more of the following compounds: R1-Ph-R5-O-R2 Ph is a benzene ring, R1 is a fluorinated alkyl group with a carbon number of no more than 3, R2 is an alkyl group or a fluorinated alkyl group with a carbon number of no more than 6, R5 is an alkyl group or a fluorinated alkyl group with a carbon number of no more than 3, R1 and R5 are located at the ortho position or the para position of Ph, respectively. The aromatic sulfone compound is selected from one or more of the following compounds: R3-Ph-SO2-Ph-R4 Ph is a benzene ring, R3 and R4 are each independently H or an alkyl group or a fluorinated alkyl group with a carbon number of no more than 6, R3 and R4 are each independently located at the meta position or the para position of the connected Ph with respect to the sulfone group.

2. The battery additive combination of claim 1, wherein, The fluorinated aromatic ether compound is selected from one or more of the following compounds: R1-Ph-R5-O-R2 Ph is a benzene ring, R1 is a fluorinated alkyl group with a carbon number of no more than 3, R2 is an alkyl group or a fluorinated alkyl group with a carbon number of no more than 6, R5 is an alkyl group or a fluorinated alkyl group with a carbon number of no more than 3, R1 and R5 are located at the ortho position or the para position of Ph, respectively.

3. The battery additive combination of claim 1, wherein, The molar ratio of the fluorinated aromatic ether compound and the aromatic sulfone compound is 1:50-50:

1.

4. The battery additive combination of claim 1, wherein, The molar ratio of the fluorinated aromatic ether compound and the aromatic sulfone compound is 1:5-5:

1.

5. The battery additive combination of claim 1, wherein, The molar ratio of the fluorinated aromatic ether compound and the aromatic sulfone compound is 2:1-1:

1.

6. A high-voltage electrolyte solution comprising the battery additive combination of any one of claims 1-5.

7. The high pressure resistant electrolyte according to claim 6, characterized in that The amount of the battery additive combination added to the base electrolyte solution is 1 mM-100 mM.

8. The high pressure resistant electrolyte according to claim 6, characterized in that The amount of the fluorinated aromatic ether compound in the battery additive combination added to the base electrolyte solution is 1 mM-50 mM, and the amount of the aromatic sulfone compound in the battery additive combination added to the base electrolyte solution is 1 mM-50 mM.

9. The high pressure resistant electrolyte according to claim 6, characterized in that The amount of the fluorinated aromatic ether compound in the battery additive combination added to the base electrolyte solution is 20-40 mM, and the amount of the aromatic sulfone compound in the battery additive combination added to the base electrolyte solution is 10-20 mM, and the ratio of the amount of the fluorinated aromatic ether compound to the amount of the aromatic sulfone compound added to the base electrolyte solution is 2:1-1:

1.

10. A high-voltage lithium cobalt oxide battery comprising the battery additive combination of any one of claims 1-5 or the high-voltage electrolyte solution of claim 6.

11. The high-voltage lithium cobalt oxide battery of claim 10, wherein, Further comprising a lithium cobalt oxide positive electrode and a negative electrode, the lithium cobalt oxide positive electrode comprising a lithium cobalt oxide material that is phase-doped and / or surface-modified, the phase-doping comprising doping with one or more of Ni, Mn, Ti, Mg, Zn, and the surface modification comprising coating with one or more of Al2O3, ZrO2, LiF; and the negative electrode comprising one of lithium metal, graphite, lithium titanate, and silicon-carbon composite material.

12. A positive electrode / electrolyte interface structure, which has an inner interface layer and an outer interface layer successively on the surface of a positive electrode, the inner interface layer being composed of oxidized fragments of a fluorinated aromatic ether compound, and the outer interface layer being composed of an aromatic sulfone compound, the interface structure being formed by the battery additive combination of any one of claims 1 to 5 on the positive electrode material.

13. The positive electrode / electrolyte interface structure according to claim 12, characterized by The thickness of the inner interface layer and the outer interface layer is independently 1-100 nm.

14. The positive electrode / electrolyte interface structure according to claim 12, wherein The thickness of the inner interface layer and the outer interface layer is independently 3-20 nm.

15. The positive electrode / electrolyte interface structure according to claim 12, wherein The positive electrode is a lithium cobalt oxide positive electrode.

16. The positive electrode / electrolyte interface structure according to claim 15, wherein The positive electrode is a lithium cobalt oxide positive electrode which is phase-doped and / or surface-modified, the phase-doping comprising doping with any one or more of Ni, Mn, Ti, Mg, Zn, and the surface-modification comprising coating with any one or more of Al2O3, ZrO2, LiF.

17. A method for forming the positive electrode / electrolyte interface structure of claim 12, comprising the steps of: first subjecting a battery containing the electrolyte containing the above-mentioned battery additive combination to forced polarization at a positive electrode potential of 3.6-3.75 V, and then charging to a cut-off potential.

18. The method for forming a cathode / electrolyte interface structure according to claim 17, wherein The battery is a high-voltage lithium cobalt oxide battery; the forced polarization time is 3-10 h; and the cut-off potential is between 4.2 and 4.6 V.

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