Electrolyte, lithium ion battery and electric equipment

Abstract

The embodiment of the invention discloses an electrolyte, a lithium ion battery and electric equipment, the electrolyte comprises an electrolyte lithium salt and a silicon-containing organic additive, the molecular structure of the silicon-containing organic additive is as shown in formula (I) # imgabs0 #, L1 is a nitrogen atom or a phosphorus atom; m1 is selected from a halogenated alkyl group, an alkoxy group or a halogenated alkoxy group; r1, R2, R3, R4, R5 and R6 are independently selected from any one of a hydrogen atom, a halogenated alkyl group, an alkoxy group, a halogenated alkoxy group and a halogen-substituted or non-substituted heterocyclic group, and the halogen-substituted or non-substituted heterocyclic group contains one or more heteroatoms of oxygen, nitrogen and sulfur. The silicon-containing organic additive can inhibit hydrolysis of electrolyte lithium salt and enhance the interface stability of a battery electrode, and can effectively improve the cycling stability of a battery when being applied to the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the field of lithium - ion batteries, and particularly to an electrolyte, a lithium - ion battery, and an electrical device using the same. Background Art

[0002] With the rapid development of electric vehicles, portable electronic devices, and large - scale energy storage, the demand for high - energy - density lithium - ion batteries is more urgent. Silicon - based materials have a high theoretical specific capacity, a low working potential, low cost, can provide channels for lithium - ion insertion and extraction in all directions, and have excellent fast - charging performance. They are considered ideal anode materials for the next - generation high - energy - density lithium - ion batteries. However, silicon - based materials have a serious volume effect during the lithium - insertion and extraction process, which will cause fresh surfaces to continuously form on the silicon - based materials during charge and discharge. Therefore, the electrolyte is continuously consumed to form a solid electrolyte interface film (SEI film), reducing the cycle performance of the silicon anode.

[0003] To address the problem of poor cycle performance of silicon anodes, a common method in the industry is to add various additives to the electrolyte for silicon anodes. However, the existing additives have limited improvement in the cycle stability of silicon anodes. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide an electrolyte, a lithium - ion battery, and an electrical device using the same. The electrolyte includes a silicon - containing organic additive. As an electrolyte additive for lithium - ion batteries, the silicon - containing organic additive can effectively inhibit the hydrolysis of electrolyte lithium salts, reduce the internal resistance of the battery during operation, and is beneficial to the formation of a stable SEI film on the surface of the battery electrode, improving the long - cycle stability of the electrode and thus enhancing the cycle performance of the battery.

[0005] In a first aspect, embodiments of the present invention provide an electrolyte, which includes an electrolyte lithium salt and a silicon - containing organic additive. The molecular structure of the silicon - containing organic additive is shown in formula (I):

[0006]

[0007] In formula (I), L1 is a nitrogen atom or a phosphorus atom;

[0008] M1 is selected from a haloalkyl group, an alkoxy group, or a haloalkoxy group;

[0009] R1, R2, R3, R4, R5, and R6 are each independently selected from any one of a hydrogen atom, a haloalkyl group, an alkoxy group, a haloalkoxy group, a halogen - substituted or unsubstituted heterocyclic group, and the halogen - substituted or unsubstituted heterocyclic group contains one or more heteroatoms of oxygen, nitrogen, or sulfur.

[0010] In an embodiment of the present invention, the haloalkyl group includes an alkyl group substituted by halogen with C 1-30 The alkoxy group includes C1-30 alkoxy group, and the haloalkoxy group includes a halogen-substituted C 1-30 alkoxy group.

[0011] In an embodiment of the present invention, the halogen-substituted or unsubstituted heterocyclic group includes any one of a halogen-substituted or unsubstituted furyl group, a halogen-substituted or unsubstituted pyranyl group, a halogen-substituted or unsubstituted pyrrolyl group, a halogen-substituted or unsubstituted imidazolyl group, a halogen-substituted or unsubstituted pyridyl group, a halogen-substituted or unsubstituted pyrazinyl group, a halogen-substituted or unsubstituted pyrimidinyl group, a halogen-substituted or unsubstituted pyridazinyl group, a halogen-substituted or unsubstituted tetrazinyl group, a halogen-substituted or unsubstituted thiophenyl group, a halogen-substituted or unsubstituted thiopyranyl group, a halogen-substituted or unsubstituted quinolinyl group, and a halogen-substituted or unsubstituted oxazolyl group.

[0012] In an embodiment of the present invention, at least one of M1, R1, R2, R3, R4, R5, and R6 is a halogen-containing group.

[0013] In an embodiment of the present invention, the silicon-containing organic additive includes one or more of the compounds represented by formula (II) to formula (VI),

[0014]

[0015] In an embodiment of the present invention, in the electrolyte, the mass percentage of the silicon-containing organic additive is 0.1% - 10%; the mass percentage of the electrolyte lithium salt is 12.6% - 30%.

[0016] In an embodiment of the present invention, the electrolyte lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalato)phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0017] In an embodiment of the present invention, the electrolyte further includes a film-forming additive. In the electrolyte, the mass percentage of the film-forming additive is 1% - 30%; the film-forming additive includes one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), propylene sultone (PST), tris(trimethylsilyl) borate (TMSB), and tris(trimethylsilyl) phosphate (TMSP).

[0018] In an embodiment of the present invention, the film-forming additive includes fluoroethylene carbonate (FEC), and one or more of vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), propylene sultone (PST), tris(trimethylsilyl) borate (TMSB), and tris(trimethylsilyl) phosphate (TMSP).

[0019] In an embodiment of the present invention, the electrolyte further includes an organic solvent, and the organic solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and fluoroethyl carbonate (FDEC); in the electrolyte, the mass percentage of the organic solvent is 35% - 85.5%.

[0020] In an embodiment of the present invention, in the electrolyte, the mass percentage of fluoroethylene carbonate is 0.5% - 20%.

[0021] The electrolyte provided in the first aspect of the embodiment of the present invention includes a silicon-containing organic additive, which can react with water and acid, reduce the content of water and acid in the electrolyte, effectively inhibit the hydrolysis of the electrolyte lithium salt, and can be used as a protective additive for the battery electrode to promote the formation of a stable SEI film on the electrode surface, avoiding irreversible loss of active lithium caused by electrode swelling and excessive consumption of Li in the electrolyte + When it is applied to a lithium-ion battery, it can reduce the increase in the DC internal resistance during the cycling of the battery and extend the service life of the battery.

[0022] In a second aspect, the embodiment of the present invention provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte, and the electrolyte includes the electrolyte described in the first aspect of the embodiment of the present invention.

[0023] In an embodiment of the present invention, after the first charge and discharge of the lithium-ion battery, there is an interfacial layer on the surface of the negative electrode, and the interfacial layer contains LiF.

[0024] In an embodiment of the present invention, within a depth range of 260 nm from the surface of the interfacial layer inward, the atomic percentage of F atoms is 25% - 45%; in the fine spectrum of Li 1s X-ray photoelectron spectroscopy measured from the surface of the interfacial layer to a depth of 260 nm, the average content of the LiF peak fitting is 10% - 40%.

[0025] In an embodiment of the present invention, the negative electrode includes a silicon-based negative electrode material, and the silicon-based negative electrode material includes one or more of nano-silicon and silicon-carbon composite materials.

[0026] The lithium-ion battery provided in the second aspect of the embodiments of the present invention adopts the electrolyte provided in the first aspect. By using a silicon-containing organic additive as a protective additive for the battery electrode, a stable SEI film is formed on the electrode surface, enabling the electrode to remain stable after long-term cycling, having good cycle stability, and being applicable to electrical devices with high energy density requirements.

[0027] In the third aspect, the embodiments of the present invention provide an electrical device, which includes the lithium-ion battery described in the second aspect of the embodiments of the present invention.

[0028] The electrical device provided in the third aspect of the embodiments of the present invention uses the lithium-ion battery provided in the second aspect as a power source. The electrode structure of this lithium-ion battery is stable and has a long cycle life, and it can stably provide electrical energy with high energy density for the electrical device for a long time, improving the performance of the electrical device. Description of the Drawings

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the background art, the following will describe the drawings required to be used in the embodiments of the present invention or the background art.

[0030] Figure 1 It is a process diagram of the continuous hydrolysis reaction of lithium hexafluorophosphate (LiPF6);

[0031] Figure 2 It is a process diagram of the hydrolysis reaction (a) and ring-opening reaction (b) of fluoroethylene carbonate (FEC);

[0032] Figure 3 It is a distribution diagram of the element content of the negative electrode sheet after battery formation provided in Embodiment 1 and Comparative Example 1 of the present invention;

[0033] Figure 4 It is a peak fitting diagram of the X-ray photoelectron spectroscopy fine spectrum of Li 1s measured at a depth of 260 nm from the surface of the interface layer on the surface of the negative electrode sheet after battery formation provided in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Embodiments

[0034] The following describes the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention.

[0035] Silicon, as a material with advantages such as rich resources, environmental protection, low cost, high capacity, and low working potential, is considered to be one of the most promising negative electrode materials for high energy density lithium-ion batteries. However, during the lithiation and delithiation processes of silicon, there is a huge volume expansion (up to 400%), which will cause the silicon-based electrode material to continuously form fresh surfaces during the charge and discharge processes. Therefore, the electrolyte is continuously consumed to generate a new SEI film. An overly thick SEI film will lead to irreversible loss of active lithium and Li in the electrolyte +Problems such as excessive consumption reduce the cycling performance of the electrode material. The electrolyte plays an important role in protecting the SEI film during the initial lithiation process. Salts, solvents, and additives in the electrolyte have a profound impact on the solvation structure, interfacial stability, electrode dissolution, cost, safety, and overall electrochemical performance. However, the existing electrolytes cannot effectively alleviate the problems of continuous electrolyte consumption, loss of active lithium, and performance degradation caused by the volume expansion of silicon anodes. In order to passivate the interfacial layer protective film and reduce the repeated lithiation and delithiation processes, it is necessary to develop functional additives for use in the corresponding electrolytes to stabilize the SEI film and alleviate the continuous side reactions between silicon and the electrolyte, thereby improving the cycling stability of the battery.

[0036] Based on this, an embodiment of the present invention provides an electrolyte, including an electrolyte lithium salt and a silicon-containing organic additive, and the molecular structure of the silicon-containing organic additive is shown in formula (Ⅰ):

[0037]

[0038] In formula (Ⅰ), L1 is a nitrogen atom or a phosphorus atom;

[0039] M1 is selected from a haloalkyl group, an alkoxy group, or a haloalkoxy group;

[0040] R1, R2, R3, R4, R5, and R6 are each independently selected from any one of a hydrogen atom, a haloalkyl group, an alkoxy group, a haloalkoxy group, a halogen-substituted or unsubstituted heterocyclic group, and the halogen-substituted or unsubstituted heterocyclic group contains one or more heteroatoms of oxygen, nitrogen, or sulfur.

[0041] The electrolyte provided by the embodiment of the present invention includes a silicon-containing organic additive, which can improve the interfacial stability of the battery electrode and enhance the cycling performance of the battery. On the one hand, the silicon-containing organic additive can react with water and acid, reduce the content of water and acid in the electrolyte, effectively inhibit the hydrolysis of the electrolyte lithium salt, and extend the service life of the electrolyte. On the other hand, after adding the silicon-containing organic additive to the electrolyte, a dense, uniform, and stable SEI film can be formed in-situ on the surface of the battery electrode, and it can maintain the stability of the interfacial environment and assist in locking the components in the SEI film, such as the stability of LiF. The stable SEI film can weaken the influence brought by the volume change of the battery electrode. The battery electrode, especially the silicon-based anode, has a serious volume effect during the lithium insertion and extraction process. If the SEI film is not stable enough, the battery electrode will continuously consume the electrolyte during charge and discharge to form a new SEI film. Therefore, the stable SEI film can reduce the loss of the electrolyte and the loss of active lithium, and can reduce the increase in the DC internal resistance of the battery during cycling, thereby enhancing the cycling performance of the battery.

[0042] In the embodiment of the present invention, the haloalkyl group includes a C substituted by a halogen 1-30For the alkyl group, i.e., the number of carbon atoms in the haloalkyl group is 1 - 30; the halogen includes fluorine, chlorine or bromine, and the halogenation is either fully halogenated or partially halogenated. In some embodiments, the number of carbon atoms in the haloalkyl group can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 16, 17, 20, 22, 25, 28, 30. In some examples, the haloalkyl group can be monofluoromethyl, difluoromethyl, trifluoromethyl, trifluoroethyl, tetrafluoroethyl, pentafluoroethyl, trifluoropropyl, tetrafluoropropyl, hexafluoroisopropyl, nonafluorobutyl, chloromethyl, dichloromethyl, trichloromethyl, chloroethyl, dichloroethyl, trichloroethyl, chloropropyl, dichloropropyl, dichloroisopropyl, chlorobutyl, bromomethyl, tribromomethyl, bromoethyl, dibromoethyl, bromopropyl, bromoisopropyl, dibromopropyl or bromobutyl.

[0043] In the embodiments of the present invention, the alkoxy group includes C 1-30 of the alkoxy group, i.e., the number of carbon atoms in the alkoxy group is 1 - 30. In some embodiments, the number of carbon atoms in the alkoxy group can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 16, 17, 20, 22, 25, 28, 30. In some examples, the alkoxy group can be methoxy, ethoxy, propoxy, butoxy, isobutoxy or tert - butoxy.

[0044] In the embodiments of the present invention, the haloalkoxy group includes a halogen - substituted C 1-30 of the alkoxy group, i.e., the number of carbon atoms in the haloalkoxy group is 1 - 30; the halogen includes fluorine, chlorine or bromine, and the halogenation is either fully halogenated or partially halogenated. In some embodiments, the number of carbon atoms in the haloalkoxy group can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 16, 17, 20, 22, 25, 28, 30. In some examples, the haloalkoxy group can be monofluoromethoxy, difluoromethoxy, trifluoromethoxy, trifluoroethoxy, tetrafluoroethoxy, pentafluoroethoxy, hexafluoropropoxy, perfluorotert - butoxy, chloromethoxy, dichloromethoxy, trichloromethoxy, chloroethoxy, trichloroethoxy, chloropropoxy, chlorobutoxy, bromomethoxy, bromoethoxy, bromopropoxy, bromobutoxy or bromoisobutoxy.

[0045] In the embodiments of the present invention, the halogen - substituted or unsubstituted heterocyclic group includes any one of a halogen - substituted or unsubstituted furyl group, a halogen - substituted or unsubstituted pyranyl group, a halogen - substituted or unsubstituted pyrrolyl group, a halogen - substituted or unsubstituted imidazolyl group, a halogen - substituted or unsubstituted pyridyl group, a halogen - substituted or unsubstituted pyrazinyl group, a halogen - substituted or unsubstituted pyrimidinyl group, a halogen - substituted or unsubstituted pyridazinyl group, a halogen - substituted or unsubstituted tetrazinyl group, a halogen - substituted or unsubstituted thiophenyl group, a halogen - substituted or unsubstituted thianyl group, a halogen - substituted or unsubstituted quinolinyl group and a halogen - substituted or unsubstituted oxazolyl group.

[0046] In an embodiment of the present invention, at least one of M1, R1, R2, R3, R4, R5, and R6 is a halogen-containing group. The halogenated group has a relatively high polarity and electrophilicity, and various reactions are easily triggered, which easily leads to the decomposition of the silicon-containing organic additive and is conducive to the formation of a stable SEI film.

[0047] In an embodiment of the present invention, the silicon-containing organic additive includes one or more of the compounds shown in Formula (II) to Formula (VI).

[0048]

[0049] In an embodiment of the present invention, in the electrolyte, the mass percentage of the silicon-containing organic additive is 0.1% - 10%. In some embodiments of the present invention, the mass percentage of the silicon-containing organic additive in the electrolyte can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 1.75%, 2%, 3%, 4%, 5%, 6%, 8%, 10%. Adding the silicon-containing organic additive to the electrolyte according to the above dosage requirements can not only effectively remove water and inhibit acid, inhibit the decomposition of the lithium salt in the electrolyte, but also ensure the good dissolution of the silicon-containing organic additive in the electrolyte. Under specific high-voltage working conditions, the solvent in the electrolyte is oxidized by the high-voltage positive electrode to generate active hydrogen, increasing the acidification of the electrolyte and severely deteriorating the cycle. The introduction of the silicon-containing organic additive solves this problem by fixing HF.

[0050] In an embodiment of the present invention, in the electrolyte, the mass percentage of the electrolyte lithium salt can be 12.6% - 30%. In some embodiments of the present invention, the mass percentage of the electrolyte lithium salt in the electrolyte can be, for example, 12.6%, 14%, 15%, 18%, 20%, 22%, 25%, 28%, 30%. Adding the electrolyte lithium salt provided in the embodiments of the present invention to the electrolyte according to the above addition amount of the electrolyte lithium salt can better provide more LiF for the SEI film. In combination with the use of the silicon-containing organic additive, the structure of the formed SEI film can be made more stable, and the conductivity of the electrolyte can also be improved, enhancing the electrochemical performance of the electrolyte.

[0051] In an embodiment of the present invention, the electrolyte lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalato)phosphate (LiPF2(C2O4)2), lithium tetrafluoroxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0052] In some embodiments, the electrolyte lithium salt is lithium hexafluorophosphate (LiPF6). As Figure 1 shown, LiPF6 is easily decomposed into LiF and PF5. PF5 decomposes under the action of moisture to produce POF3 and HF. POF3 further continuously decomposes with chain carbonates (such as organic solvents DMC, DEC, EMC) to generate products such as alkyl phosphates, phosphoric acid, fluoroalkanes, CO2 and HF. The alkyl groups in the electrolyte solvent continuously replace F atoms, and LiPF6 is continuously hydrolyzed and converted into alkyl phosphates, resulting in intense side reactions and gas generation hazards. When LiPF6 is used in combination with a silicon-containing organic additive, the silicon-containing organic additive can react with the decomposition products PF5 and HF of LiPF6, fix PF5 and HF, so that they can no longer participate in the hydrolysis reaction, block the continuous hydrolysis reaction of LiPF6, inhibit the acidification of the electrolyte, and prolong the battery stability. Further, since LiF mainly comes from LiPF6 during SEI film formation, using LiPF6 as the electrolyte lithium salt can better in-situ form a dense, uniform and LiF-rich SEI film on the surface of the battery electrode, so that the formed SEI film structure is more stable, more effectively prevents the decomposition of the electrolyte, reduces the loss of the electrolyte and the loss of active lithium, improves the interfacial stability of the electrode, and thus improves the cycle performance of the battery.

[0053] In the embodiments of the present invention, the electrolyte further includes a film-forming additive. In the electrolyte, the mass percentage of the film-forming additive can be 1%-30%; the film-forming additive includes one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), propylene sultone (PST), tris(trimethylsilyl) borate (TMSB) and tris(trimethylsilyl) phosphate (TMSP). In some embodiments, the mass percentage of the film-forming additive in the electrolyte can be, for example, 1%, 3%, 5%, 6.15%, 8%, 10%, 13.18%, 15%, 17%, 20%, 23%, 25%, 28% or 30%. The film-forming additive provided by the embodiments of the present invention can promote the formation of a stable and effective SEI film on the surface of the electrode material. When used in combination with a silicon-containing organic additive, it is beneficial to further improve the rate performance and cycle life of the battery.

[0054] In the embodiments of the present invention, the film-forming additive may include fluoroethylene carbonate (FEC), and one or more of vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), propylene sultone (PST), tris(trimethylsilyl) borate (TMSB), and tris(trimethylsilyl) phosphate (TMSP). The film-forming additive in the embodiments of the present invention includes FEC. When FEC is used in combination with the electrolyte lithium salt, it can provide more LiF for SEI film formation, make the formed SEI film structure more stable, and effectively prevent the decomposition of the electrolyte. FEC usually undergoes hydrolysis reaction and ring-opening reaction in the electrolyte. As shown in (a) of Figure 2 , the presence of Lewis acids PF5 or HF will promote the de-HF reaction of FEC, generating VC, HF and other acids, such as H3OPF6, HPO2F2, H2PO3F and H3PO4. Also as shown in (b) of Figure 2 , Lewis acid PF5 will also catalyze the ring-opening of FEC to generate partially fluorinated polymers, increasing the acidity of the electrolyte and exacerbating the decomposition of the electrolyte. However, since the silicon-containing organic additive in the electrolyte provided by the present invention can solidify PF5 and HF in the electrolyte, it will inhibit the hydrolysis reaction and ring-opening reaction of FEC, and FEC can exist stably in the electrolyte, effectively improving the service life of the electrolyte.

[0055] In the embodiments of the present invention, the electrolyte further includes an organic solvent, and the organic solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and fluoroethyl carbonate (FDEC). In the electrolyte, the mass percentage of the organic solvent can be 35%-85.5%, which can not only ensure the transmission rate of lithium ions in the electrolyte, but also reduce the risk of battery combustion and explosion. In some embodiments, the mass percentage of the organic solvent in the electrolyte can be, for example, 35%, 40%, 45%, 50%, 60%, 70%, 80%, or 85.5%. The organic solvent provided by the present invention has good solubility for the electrolyte lithium salt, and has high conductivity and low corrosivity, making the prepared battery have high energy density and long service life.

[0056] In the embodiments of the present invention, in the electrolyte, the mass percentage of fluoroethylene carbonate (FEC) can be 0.5%-20%, which can not only improve the structural stability of the SEI film, but also avoid the increase of electrolyte impedance. In some embodiments, the mass percentage of FEC in the electrolyte can be, for example, 0.5%, 1%, 2%, 5%, 7%, 9%, 10%, 12%, 14%, 16%, 19%, or 20%.

[0057] In any of the above embodiments of the present invention, the electrolyte can form a stable SEI structure on the surface of the battery electrode, avoiding irreversible loss of active lithium caused by electrode swelling and excessive consumption of Li in the electrolyte, and can remove water and suppress acid, reducing the hydrolysis of electrolyte lithium salts. When applied to a lithium-ion battery, it can reduce the increase in DC internal resistance during the cycling process of the battery and extend the service life of the battery. +

[0058] An embodiment of the present invention also provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator and an electrolyte located between the positive electrode and the negative electrode, and the electrolyte includes the electrolyte in any of the above embodiments.

[0059] In the embodiment of the present invention, after the first charge and discharge of the lithium-ion battery, there is an interface layer on the surface of the negative electrode, and LiF is included in the interface layer. As an ion conductor, LiF can provide good ion conductivity, which helps to improve the migration and cycling stability of lithium ions in the battery.

[0060] In the embodiment of the present invention, within the depth range of 260 nm from the surface of the interface layer inward, the atomic percentage of F atoms is 25%-45%; specifically, it can be 25%, 30%, 35%, 40%, 45%. A high content of F atoms in the interface layer is beneficial to better controlling the O content in the interface layer at a lower level, thereby improving the stability of the interface layer. In the embodiment of the present invention, in the fine spectrum of Li 1s X-ray photoelectron spectroscopy measured from the surface of the interface layer to a depth of 260 nm, the average content of the LiF peak fitting is 10%-40%; specifically, it can be 10%, 20%, 27%, 30%, 40%. The high content of LiF in the interface layer of the lithium-ion battery provided by the embodiment of the present invention helps to reduce the impedance of the interface layer, thereby being beneficial to the improvement of the battery power performance.

[0061] In the embodiment of the present invention, the negative electrode may include a silicon-based negative electrode material, and the silicon-based negative electrode material may include one or more of nano-silicon and silicon-carbon composite materials. In some embodiments, the silicon-carbon composite material may be a silicon-carbon composite material formed by compounding SiO w with graphite, where 1 < w < 2.

[0062] In the embodiment of the present invention, the positive electrode may be made of various lithium-ion battery positive electrode materials, for example, it may be one or more of lithium iron phosphate materials and ternary nickel cobalt manganese lithium materials.

[0063] The lithium-ion battery provided by the embodiment of the present invention adopts the above-mentioned electrolyte of the present invention. By using a silicon-containing organic additive as a protective additive for the battery electrode, especially the silicon-based negative electrode, a stable and dense SEI film is formed on the electrode surface, so that the electrode remains stable after long-term cycling, has good cycle stability, and can be applied to electrical equipment with high energy density requirements.

[0064] The embodiment of the present invention also provides an electrical equipment, and the electrical equipment includes the lithium-ion battery in any of the above embodiments.

[0065] The electrical equipment provided by the embodiment of the present invention uses a lithium-ion battery as a power source. The electrode structure of the lithium-ion battery is stable and has a long cycle life, and can stably provide electrical energy with high energy density for the electrical equipment for a long time, improving the performance of the electrical equipment.

[0066] The embodiments of the present invention will be further described in multiple embodiments below.

[0067] Example 1

[0068] (1) Preparation of electrolyte

[0069] In a glove box filled with argon, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are weighed as electrolyte solvents according to the mass percentages of 19.73 wt%, 38.99 wt%, and 6.52 wt% of the total mass of the electrolyte. Lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) are weighed as electrolyte lithium salts according to the mass percentages of 12.93 wt% and 1 wt% of the total mass of the electrolyte, and continuously stirred until dissolved. Finally, fluoroethylene carbonate (FEC), the silicon-containing organic additive shown in formula (II), vinylene carbonate (VC), and methylene methanedisulfonate (MMDS) are weighed as electrolyte additives according to the mass percentages of 13.18 wt%, 0.5 wt%, 6.15 wt%, and 1 wt% of the total mass of the electrolyte, and continuously stirred evenly to prepare an electrolyte, denoted as E1.

[0070]

[0071] (2) Preparation of soft-pack battery

[0072] The negative electrode sheet of the battery is made of a silicon-carbon composite material with a surface density of 160 g / m² -2 and a tap density of 1.58 g / cm³ -3 as the battery negative electrode. In the silicon-carbon composite material, the active substance is SiO W(1 < w < 2) has a mass percentage of 10%, graphite has a mass percentage of 86%, conductive agent acetylene black has a mass percentage of 2%, and binder polyacrylic acid (PAA) has a mass percentage of 2%. The positive electrode sheet made of lithium iron phosphate is used as the battery positive electrode (lithium iron phosphate, conductive agent epoxy, binder polyvinylidene fluoride are in a mass ratio of 96:1:3). The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets, and wound to obtain a bare battery cell; the bare battery cell is placed in an aluminum-plastic film package, and electrolyte E1 is injected into the dried battery, and left standing at room temperature to prepare the lithium-ion soft-pack battery B1 corresponding to Example 1.

[0073] Example 2

[0074] The difference between Example 2 and Example 1 is only that the silicon-containing organic additive shown in formula (II) added in step (1) of Example 1 is replaced with an equal mass of the silicon-containing organic additive shown in formula (III). It is configured into an electrolyte, denoted as E2, and the lithium-ion soft-pack battery B2 corresponding to Example 2 is prepared.

[0075]

[0076] Example 3

[0077] The difference between Example 3 and Example 1 is only that the silicon-containing organic additive shown in formula (II) added in step (1) of Example 1 is replaced with an equal mass of the silicon-containing organic additive shown in formula (IV). It is configured into an electrolyte, denoted as E3, and the lithium-ion soft-pack battery B3 corresponding to Example 3 is prepared.

[0078]

[0079] Example 4

[0080] The difference between Example 4 and Example 1 is only that the silicon-containing organic additive shown in formula (II) added in step (1) of Example 1 is replaced with an equal mass of the silicon-containing organic additive shown in formula (V). It is configured into an electrolyte, denoted as E4, and the lithium-ion soft-pack battery B4 corresponding to Example 4 is prepared.

[0081]

[0082] Example 5

[0083] The difference between Example 5 and Example 1 is only that the silicon-containing organic additive shown in formula (II) added in step (1) of Example 1 is replaced with an equal mass of the silicon-containing organic additive shown in formula (VI). It is configured into an electrolyte, denoted as E5, and the lithium-ion soft-pack battery B5 corresponding to Example 5 is prepared.

[0084]

[0085] Example 6

[0086] (1) Preparation of electrolyte

[0087] In a glove box filled with argon, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were weighed according to the mass percentages of 26.21 wt%, 42.4 wt%, and 8.8 wt% of the total mass of the electrolyte as the electrolyte solvents. Lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) were weighed according to the mass percentages of 12.93 wt% and 1 wt% of the total mass of the electrolyte as the electrolyte lithium salts, and continuously stirred until dissolved. Finally, the silicon-containing organic additive shown in formula (II), vinylene carbonate (VC), and methylene methanedisulfonate (MMDS) were weighed according to the mass percentages of 0.5 wt%, 7.02 wt%, and 1.14 wt% of the total mass of the electrolyte as the electrolyte additives, and continuously stirred evenly to prepare the electrolyte, denoted as E6.

[0088] (2) Preparation of soft-pack battery

[0089] Same as Example 1, to obtain the lithium-ion soft-pack battery B6.

[0090] Example 7

[0091] (1) Preparation of electrolyte

[0092] In a glove box filled with argon, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were weighed according to the mass percentages of 20.57 wt%, 33.27 wt%, and 6.9 wt% of the total mass of the electrolyte as the electrolyte solvents. Lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) were weighed according to the mass percentages of 12.93 wt% and 1 wt% of the total mass of the electrolyte as the electrolyte lithium salts, and continuously stirred until dissolved. Finally, fluoroethylene carbonate (FEC), the silicon-containing organic additive shown in formula (II), vinylene carbonate (VC), and methylene methanedisulfonate (MMDS) were weighed according to the mass percentages of 13.18 wt%, 5 wt%, 6.15 wt%, and 1 wt% of the total mass of the electrolyte as the electrolyte additives, and continuously stirred evenly to prepare the electrolyte, denoted as E7.

[0093] (2) Preparation of soft-pack battery

[0094] Same as Example 1, to obtain the lithium-ion soft-pack battery B7.

[0095] Example 8

[0096] (1) Preparation of electrolyte

[0097] In a glove box filled with argon, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were weighed according to the mass percentages of 18.87 wt%, 30.53 wt%, and 6.34 wt% of the total mass of the electrolyte as the electrolyte solvents. Lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) were weighed according to the mass percentages of 12.93 wt% and 1 wt% of the total mass of the electrolyte as the electrolyte lithium salts, and continuously stirred until dissolved. Finally, fluoroethylene carbonate (FEC), the silicon-containing organic additive shown in formula (II), vinylene carbonate (VC), and methylene methanedisulfonate (MMDS) were weighed according to the mass percentages of 13.18 wt%, 10 wt%, 6.15 wt%, and 1 wt% of the total mass of the electrolyte as the electrolyte additives, and continuously stirred and uniformly mixed to prepare an electrolyte, denoted as E8.

[0098] (2) Preparation of soft-pack battery

[0099] Same as Example 1, lithium-ion soft-pack battery B8 was obtained.

[0100] Example 9

[0101] (1) Preparation of electrolyte

[0102] In a glove box filled with argon, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were weighed according to the mass percentages of 19.92 wt%, 38.94 wt%, and 6.79 wt% of the total mass of the electrolyte as the electrolyte solvents. Lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) were weighed according to the mass percentages of 12.93 wt% and 1 wt% of the total mass of the electrolyte as the electrolyte lithium salts, and continuously stirred until dissolved. Finally, fluoroethylene carbonate (FEC), the silicon-containing organic additive shown in formula (II), vinylene carbonate (VC), and methylene methanedisulfonate (MMDS) were weighed according to the mass percentages of 13.18 wt%, 0.1 wt%, 6.15 wt%, and 1 wt% of the total mass of the electrolyte as the electrolyte additives, and continuously stirred and uniformly mixed to prepare an electrolyte, denoted as E8.

[0103] (2) Preparation of soft-pack battery

[0104] Same as Example 1, lithium-ion soft-pack battery B8 was obtained.

[0105] Comparative Example 1

[0106] The difference between Comparative Example 1 and Example 1 is only that the silicon-containing organic additive shown in formula (II) added in step (1) of Example 1 is not added. An electrolyte was prepared, denoted as DE1, and the corresponding lithium-ion soft-pack battery DB1 of Comparative Example 1 was prepared.

[0107] Comparative Example 2

[0108] The difference between Comparative Example 2 and Example 1 is only that the silicon-containing organic additive shown in formula (II) added in step (1) of Example 1 is replaced with an equal mass of lithium difluoro(oxalato)phosphate (LiDFOP). An electrolyte was prepared and denoted as DE2, and the corresponding lithium-ion soft-pack battery DB2 of Comparative Example 2 was prepared.

[0109] Comparative Example 3

[0110] The difference between Comparative Example 3 and Example 1 is only that the silicon-containing organic additive shown in formula (II) added in step (1) of Example 1 is replaced with an equal mass of vinylene sulfate (DTD). An electrolyte was prepared and denoted as DE3, and the corresponding lithium-ion soft-pack battery DB3 of Comparative Example 3 was prepared.

[0111] Comparative Example 4

[0112] The difference between Comparative Example 4 and Example 1 is only that the silicon-containing organic additive shown in formula (II) added in step (1) of Example 1 is replaced with an equal mass of lithium difluoro(oxalato)borate (LiDFOB). An electrolyte was prepared and denoted as DE4, and the corresponding lithium-ion soft-pack battery DB4 of Comparative Example 4 was prepared.

[0113] Comparative Example 5

[0114] The difference between Comparative Example 5 and Example 6 is only that the silicon-containing organic additive shown in formula (II) added in step (1) of Example 6 is replaced with an equal mass of lithium difluoro(oxalato)borate (LiDFOB). An electrolyte was prepared and denoted as DE5, and the corresponding lithium-ion soft-pack battery DB5 of Comparative Example 5 was prepared.

[0115] The lithium-ion soft-pack batteries prepared in Examples 1-9 and Comparative Examples 1-5 of the present invention were subjected to the following tests:

[0116] (1) X-ray photoelectron spectroscopy (XPS) analysis

[0117] The lithium-ion soft-pack batteries prepared in Examples 1-9 and Comparative Examples 1-5 were formed. After the formation was completed, the complete negative electrode sheet was disassembled in a glove box; the negative electrode sheet was immersed in anhydrous dimethyl carbonate (DMC) for 5 minutes and then taken out to obtain the electrode sheet; the electrode sheet was subjected to ion sputtering, and the sputtering depth of the electrode sheet was controlled according to different sputtering times. XPS analysis was performed on the electrode sheets at different depths to obtain the atomic percentages of the negative electrode sheet at different depths, and the content of LiF was obtained by peak fitting of the Li 1s fine spectrum. The average content of LiF obtained by peak fitting in the Li 1s XPS energy spectrum of the negative electrode sheet interface layer (within a depth range of 260 nm) of Examples 1-9 and Comparative Examples 1-5 is shown in Table 1. The element content distributions of the negative electrode sheets of the batteries of Example 1 and Comparative Example 1 after formation are asFigure 3 As shown, the peak fitting diagram of the X-ray photoelectron spectroscopy fine spectrum of Li 1s measured at a depth of 260 nm from the surface inward of the interface layer on the surface of the negative electrode sheet after formation of the batteries provided in Example 1 and Comparative Example 1 is as Figure 4 shown.

[0118] From Figure 3 it can be seen that in the interface layer of the negative electrode sheet (within a depth range of 260 nm), the proportion of F atoms in Example 1 is higher than 35% in this depth range, while the proportion of F atoms in Comparative Example 1 is about 25%, that is, the F content in the interface layer of the negative electrode sheet in Example 1 is significantly higher than that in Comparative Example 1. From Figure 4 it can be seen that the peak fitting result of Example 1 shows that the content of the peak area of LiF is higher than that of Comparative Example 1. Among them, the proportion of LiF in Example 1 is 27%, and the proportion of LiF in Comparative Example 1 is 12%, indicating that the silicon-containing organic additive provided in the embodiments of the present invention can increase the content of LiF in the surface interface layer of the battery negative electrode sheet, which helps to reduce the impedance of the surface interface layer of the battery negative electrode, and thus is beneficial to the improvement of the battery power performance.

[0119] (2) Battery cycle performance test

[0120] The lithium-ion soft-pack batteries prepared in Examples 1-9 and Comparative Examples 1-5 were formed. After formation, the batteries were charged at a constant current and constant voltage to 3.8 V under a current condition of 0.5C, the cut-off current for constant voltage charging was 0.05C, and they were left standing for 10 minutes, and then discharged at a constant current to 2.0 V under a current condition of 0.5C. This is recorded as one cycle, and then they were cycled 500 times in sequence, and the capacity retention rate of the batteries was detected. The test results of the capacity retention rate are shown in Table 1.

[0121] Table 1 Detection results of LiF content and test results of cycle performance

[0122] Group LiF Content (%) Capacity Retention Rate (%) Example 1 27 93.25 Example 2 28 93.89 Example 3 31 93.21 Example 4 35 92.77 Example 5 25 92.39 Example 6 20 88.12 Example 7 29 93.10 Example 8 38 91.67 Example 9 22 90.21 Comparative Example 1 12 84.52 Comparative Example 2 11 85.67 Comparative Example 3 12 82.28 Comparative Example 4 10 84.93 Comparative Example 5 9 80.3

[0123] It can be seen from Table 1 that the content of LiF in the interface layer of the negative electrode sheets of the batteries in Examples 1-9 is higher than that in Comparative Examples 1-5, and the capacity retention rate of the batteries in Examples 1-9 after 500 cycles is also higher than that in Comparative Examples 1-5, indicating that the silicon-containing organic additive provided in the embodiments of the present invention can effectively increase the content of LiF in the negative electrode interface layer of the battery and can improve the cycle performance of the battery. It can be known from Examples 1 and Examples 7-9 that when the addition amount of the silicon-containing additive is 0.5%-5%, it can better increase the content of LiF in the interface layer of the battery negative electrode sheet and better improve the cycle performance of the battery. It can be seen from Examples 1-6 that when the silicon-containing organic additive provided in the embodiments of the present invention is used in combination with FEC, it can better increase the content of LiF in the interface layer of the battery negative electrode sheet and better improve the cycle performance of the battery.

[0124] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, It includes an electrolyte lithium salt and a silicon-containing organic additive, and the molecular structure of the silicon-containing organic additive is shown in formula (Ⅰ): In formula (Ⅰ), L1 is a nitrogen atom or a phosphorus atom; M1 is selected from a haloalkyl group, an alkoxy group or a haloalkoxy group; R1, R2, R3, R4, R5, and R6 are each independently selected from any one of a hydrogen atom, a haloalkyl group, an alkoxy group, a haloalkoxy group, a halogen-substituted or unsubstituted heterocyclic group, and the halogen-substituted or unsubstituted heterocyclic group contains one or more heteroatoms of oxygen, nitrogen, and sulfur.

2. The electrolyte according to claim 1, wherein The haloalkyl group includes an alkyl group substituted with halogen and having C 1-30 ; the alkoxy group includes an alkoxy group having C 1-30 ; and the haloalkoxy group includes an alkoxy group substituted with halogen and having C 1-30 .

3. The electrolyte according to claim 1, wherein The halogen-substituted or unsubstituted heterocyclic group includes any one of a halogen-substituted or unsubstituted furyl group, a halogen-substituted or unsubstituted pyranyl group, a halogen-substituted or unsubstituted pyrrolyl group, a halogen-substituted or unsubstituted imidazolyl group, a halogen-substituted or unsubstituted pyridyl group, a halogen-substituted or unsubstituted pyrazinyl group, a halogen-substituted or unsubstituted pyrimidinyl group, a halogen-substituted or unsubstituted pyridazinyl group, a halogen-substituted or unsubstituted tetrazinyl group, a halogen-substituted or unsubstituted thiophenyl group, a halogen-substituted or unsubstituted thianyl group, a halogen-substituted or unsubstituted quinolinyl group, and a halogen-substituted or unsubstituted oxazolyl group.

4. The electrolyte according to claim 1, wherein At least one of M1, R1, R2, R3, R4, R5, and R6 is a halogen-containing group.

5. The electrolyte according to claim 1, wherein The silicon-containing organic additive includes one or more of the compounds shown in formula (II) to formula (VI), 6. The electrolyte according to claim 1, wherein, In the electrolyte, the mass percentage of the silicon-containing organic additive is 0.1% - 10%; the mass percentage of the electrolyte lithium salt is 12.6% - 30%.

7. The electrolyte according to claim 1 or 6, characterized in that, The electrolyte lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium oxalato(phosphate), lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

8. The electrolyte according to claim 1, characterized in that, It further includes a film-forming additive. In the electrolyte, the mass percentage of the film-forming additive is 1% - 30%; the film-forming additive includes one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, ethylene sulfate, methylene methanedisulfonate, propene sultone, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate.

9. The electrolyte according to claim 8, wherein, The film-forming additive includes fluoroethylene carbonate, and one or more of vinylene carbonate, 1,3-propane sultone, ethylene sulfate, methylene methanedisulfonate, propene sultone, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate.

10. The electrolyte according to claim 1, characterized in that, The electrolyte further includes an organic solvent, and the organic solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, fluoroethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and fluoroethyl carbonate; in the electrolyte, the mass percentage of the organic solvent is 35% - 85.5%.

11. The electrolyte according to any one of claims 8-10, characterized in that, In the electrolyte, the mass percentage of fluoroethylene carbonate is 0.5% - 20%.

12. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, and the electrolyte includes the electrolyte according to any one of claims 1 - 11.

13. The lithium ion battery according to claim 12, characterized in that, After the first charge and discharge of the lithium-ion battery, there is an interface layer on the surface of the negative electrode, and LiF is included in the interface layer.

14. The lithium-ion battery according to claim 13, wherein Within a depth range of 260 nm from the surface of the interface layer inward, the atomic percentage of F atoms is 25%-45%; in the Li1s X-ray photoelectron spectroscopy fine spectrum measured from the surface of the interface layer to a depth of 260 nm, the average content of the LiF peak fitting is 10%-40%.

15. The lithium-ion battery according to any one of claims 12-14, characterized in that, The negative electrode includes a silicon-based negative electrode material, and the silicon-based negative electrode material includes one or more of nano-silicon and silicon-carbon composite materials.

16. An electrical device, characterized in that, The electrical device includes the lithium-ion battery according to any one of claims 12-15.

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