Electrolyte suitable for dry-method graphite negative electrode interface and preparation method thereof
By adding N,N-diethyltrimethylsilane or N-(trimethylsilyl)acetamide as functional additives to the electrolyte of the dry graphite negative electrode, the poor interfacial performance of the dry graphite negative electrode was solved. The problem is that a dense SEI film is formed to remove HF, which improves the cycling performance and stability of the battery.
Patent Information
- Application Number
- CN202411734152.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-29
- Publication Date
- 2025-02-14
AI Technical Summary
The dry graphite negative electrode has a poor interfacial performance in lithium-ion batteries, mainly because polytetrafluoroethylene (PTFE) reacts at low potentials as a binder, resulting in corrosion of the negative interface.
Using an electrolyte containing lithium salt, a non-aqueous organic solvent and a functional additive, the functional additive is N,N-diethyltrimethylsilane or N-(trimethylsilyl)acetamide, which can A dense SEI film is formed on the surface of the negative electrode to remove the HF generated by the side reaction and protect the negative electrode.
By forming a dense SEI film and removing HF, the interface performance of the dry graphite negative electrode is significantly improved, and the cycle performance, stability and life of the battery are improved.
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Figure BDA0005161049470000251
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of lithium battery production, and in particular to an electrolyte suitable for a dry-process graphite negative electrode interface and a preparation method thereof. Background Art
[0002] In the field of lithium-ion batteries, dry-process graphite anodes have attracted attention due to their high loading and solvent-free properties. However, dry-process anodes have poor interfacial performance in practical applications. The main reason is that polytetrafluoroethylene (PTFE) as a binder undergoes a series of side reactions at low potentials, including the generation of HF during the reaction, which leads to corrosion of the anode interface. The hydrofluoric acid (HF) generated by PTFE during the electrochemical reduction process will further corrode other components of the battery, exacerbating the attenuation of battery performance. This problem limits the application of PTFE as a dry binder in high-loaded graphite anodes.
[0003] The commonly used methods in the prior art to inhibit the side reactions of polytetrafluoroethylene (PTFE) as a binder at low potential are generally to add a negative electrode coating, change the binder structure to inhibit its decomposition or add electrolyte additives for improvement. However, the prior art still has shortcomings, and the performance of dry-process batteries needs to be further improved to improve the negative electrode interface performance and increase the stability and life of the battery.
[0004] The market is in urgent need of a technical solution to solve the above problems. Summary of the invention
[0005] In order to solve the above problems, the present invention discloses an electrolyte suitable for the dry-process graphite negative electrode interface and a preparation method thereof. The technical solution of the present invention is implemented as follows:
[0006] The first aspect of the present invention provides an electrolyte suitable for a dry-process graphite negative electrode interface, the electrolyte comprising a lithium salt, a non-aqueous organic solvent and a functional additive, wherein the functional additive is dissolved in the non-aqueous organic solvent; the functional additive is N,N-diethyltrimethylsilylamine or N-(trimethylsilyl)acetamide.
[0007] Preferably, based on 100% of the mass of the electrolyte, the mass proportion of the functional additive is 0.1% to 3%.
[0008] Preferably, based on the mass of the electrolyte being 100%, the mass of the functional additive accounts for 1.5%.
[0009] Preferably, a film-forming additive is also included;
[0010] The film-forming additive includes at least one of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
[0011] Preferably, the non-aqueous organic solvent includes any one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), propyl acetate (PA), methyl acetate (MA), and methyl propionate (MP), or a combination of at least two or more in any proportion.
[0012] Preferably, the non-aqueous organic solvent includes ethylene carbonate (EC), dimethyl carbonate (DMC), or ethyl methyl carbonate (EMC).
[0013] Preferably, the lithium salt includes any one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiN(SO2F)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium fluorosulfonate (LiSO3F), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO2C2F5)2), lithium monofluorophosphate (Li2PO3F), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(oxalatofluoroborate) (LiODFB), or a combination of at least two or more thereof in any proportion.
[0014] Preferably, the lithium salt includes lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI).
[0015] Preferably, in the electrolyte, the concentration of the lithium salt is 0.8 mol / L to 1.5 mol / L.
[0016] Preferably, in the electrolyte, the concentration of the lithium salt is 1 mol / L.
[0017] A second aspect of the present invention provides a method for preparing an electrolyte, the preparation method comprising the following steps:
[0018] S1, adding lithium salt to a non-aqueous organic solvent and continuously stirring until completely mixed;
[0019] S2, adding film-forming additives and stirring again to mix;
[0020] S3, adding functional additives, stirring evenly, and completing the preparation of the electrolyte;
[0021] The functional additive includes at least one of N,N-diethyltrimethylsilylamine and N-(trimethylsilyl)acetamide.
[0022] The advantages of the present invention are as follows:
[0023] The present invention provides an electrolyte for a dry-process graphite negative electrode. The electrolyte contains a functional additive N,N-diethyltrimethylsilylamine or N-(trimethylsilyl)acetamide. The trimethylsilyl group and Si-N bond in the functional additives can ensure and form a dense SEI film on the surface of the negative electrode, and can remove HF generated by side reactions, so as to better protect the negative electrode, improve the negative electrode interface, and thus improve the cycle performance of the battery. DETAILED DESCRIPTION
[0024] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0025] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by technicians in the technical field to which the present invention belongs; the terms used in the specific implementation methods are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" in the specification and claims of the present invention and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.
[0026] In the description of the specific implementation methods of the present invention, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.
[0027] Reference to "embodiments" in the present invention means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present invention may be combined with other embodiments.
[0028] In the description of the embodiments of the present invention, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects before and after are in an "or" relationship.
[0029] Throughout the present invention, numerical values represent approximate measures or limits of ranges to cover minor deviations from given values as well as embodiments with about the values mentioned and embodiments with the exact values mentioned. Except for the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., amounts or conditions) in this specification (including the appended claims) should be understood to be modified by the term "about" in all cases, regardless of whether "about" actually appears before the numerical value. "About" indicates that the stated numerical value allows some minor imprecision (close to the exact value of the value to some extent; approximately or reasonably close to the value; almost). If the imprecision provided by "about" is not otherwise understood in this ordinary sense in the art, "about" as used in the present invention at least indicates the variation that can be produced by the ordinary methods of measuring and using such parameters. For example, "about" may include a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in some aspects, optionally less than or equal to 0.1%.
[0030] Additionally, disclosure of ranges includes disclosure of all values within the entire range and further divided ranges, including endpoints and sub-ranges given for such ranges.
[0031] The prior art adds a film-forming additive to the electrolyte of lithium-ion batteries containing lithium manganese oxide to form a CEI film on the positive electrode surface to protect the electrode surface. However, most CEI films are easily decomposed at high temperatures and cannot effectively prevent manganese from dissolving, and the high-temperature cycle performance of the battery is still poor. Therefore, the prior art still has shortcomings, and the battery cycle performance needs to be further improved.
[0032] In order to solve the above-mentioned shortcomings, the present invention proposes a technical solution.
[0033] The first aspect of the present invention provides an electrolyte suitable for a dry-process graphite negative electrode interface, the electrolyte comprising a lithium salt and a non-aqueous organic solvent, wherein a functional additive is dissolved in the non-aqueous organic solvent; the functional additive comprises at least one of N,N-diethyltrimethylsilylamine and N-(trimethylsilyl)acetamide.
[0034] The dry-process graphite negative electrode has the problem of poor interface performance in practical applications. The main reason is that polytetrafluoroethylene (PTFE) as an adhesive has a series of side reactions at low potential, which causes interface problems and hydrofluoric acid (HF) generated during the reaction causes corrosion of the negative electrode interface, resulting in poor interface and poor cycle performance of the dry-process graphite negative electrode. The electrolyte provided by the present invention contains functional additives N, N-diethyltrimethylsilylamine or N-(trimethylsilyl)acetamide, both of which include trimethylsilyl and Si-N bonds, which can ensure and form a dense SEI film on the negative electrode surface, and can remove HF generated by side reactions, better protect the negative electrode, improve the negative electrode interface, absorb fluoride ion free radicals generated by the decomposition of PTFE at high temperature and then form HF, improve the stability and life of the dry-process battery, and thus improve the cycle performance of the battery.
[0035] The "at least one" referred to in the present invention means that one can choose N,N-diethyltrimethylsilylamine, N-(trimethylsilyl)acetamide, or a mixture of the two. It should be noted that the above materials do not react with each other, so they do not affect their respective physicochemical properties when mixed and added. It can be understood by those skilled in the art that the above two materials both include trimethylsilyl and Si-N bonds, so whether one of them is used, or a mixture of several types, the same or similar technical effects can be achieved. The present invention does not impose any restrictions on this.
[0036] In some embodiments, based on the mass of the electrolyte being 100%, the mass of the functional additive accounts for 0.1% to 3%.
[0037] In specific applications, the mass percentage of the functional additives may be 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. The above values are only examples and are not limiting.
[0038] In some preferred embodiments, based on the mass of the electrolyte being 100%, the mass of the functional additive accounts for 1.5%.
[0039] When the mass proportion of functional additives in the electrolyte is 1.5%, the performance of the prepared lithium-ion battery is optimal.
[0040] In some embodiments, the electrolyte further comprises a film-forming additive;
[0041] The film-forming additive includes any one of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC) or a combination of at least two of them in any proportion.
[0042] The "at least two" referred to in the present invention means that any two, or a mixture of three or four, can be selected from the above materials. It should be noted that the above materials do not react with each other, so the physical and chemical properties of each are not affected when mixed and added. It can be understood by those skilled in the art that the same or similar technical effects can be achieved regardless of whether one of them is used or a mixture of several types is used. The present invention does not impose any limitation on this.
[0043] In some embodiments, the non-aqueous organic solvent includes any one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), propyl acetate (PA), methyl acetate (MA), and methyl propionate (MP), or a combination of at least two or more in any proportion.
[0044] The "at least two" referred to in the present invention means that any two materials can be selected from the above materials, or a mixture of two or more materials. It should be noted that the above materials do not react with each other, so the physical and chemical properties of each material will not be affected when mixed and added. It can be understood by those skilled in the art that the same or similar technical effects can be achieved regardless of whether one of them is used or a mixture of several types is used. The present invention does not impose any limitation on this.
[0045] In some preferred embodiments, the non-aqueous organic solvent includes ethylene carbonate (EC), dimethyl carbonate (DMC), or ethyl methyl carbonate (EMC).
[0046] In specific applications, when the non-aqueous organic solvent includes the above three, the performance of the electrolyte is the best, and thus the prepared lithium-ion battery has the best performance.
[0047] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bisfluorosulfonyl imide (LiN(SO2F)2), lithium bistrifluoromethanesulfonyl imide (LiN(SO2CF3)2), lithium fluorosulfonate (LiSO3F), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO2C2F5)2), lithium monofluorophosphate (Li2PO3F), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluorosulfonyl imide) (LiFSI), and lithium bis(oxalatofluoroborate) (LiODFB).
[0048] Those skilled in the art should know that in the electrolyte, the above-mentioned lithium salts do not react with each other. Therefore, without exceeding the scope of understanding of those skilled in the art, in specific applications, those skilled in the art may select any one or a combination of two or more thereof as needed, and the present invention does not impose any limitation on this.
[0049] In some preferred embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI).
[0050] In specific applications, the lithium salt is a mixture of lithium fluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI). When the electrolyte uses a mixed lithium salt, its performance is best, so the prepared lithium-ion battery has the best performance.
[0051] In some embodiments, in the electrolyte, the concentration of the lithium salt is 0.8 mol / L to 1.5 mol / L.
[0052] In specific applications, the concentration of the lithium salt can be 0.8 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc. The above values are only examples and are not limiting.
[0053] In some preferred embodiments, in the electrolyte, the concentration of the lithium salt is 1 mol / L.
[0054] When the lithium salt concentration is 1 mol / L, the electrolyte performance is optimal.
[0055] A second aspect of the present invention provides a method for preparing an electrolyte, the preparation method comprising the following steps:
[0056] S1, adding lithium salt to a non-aqueous organic solvent and continuously stirring until completely mixed;
[0057] S2, adding film-forming additives and stirring again to mix;
[0058] S3, adding functional additives, stirring evenly, and completing the preparation of the electrolyte;
[0059] The functional additive includes at least one of N,N-diethyltrimethylsilylamine and N-(trimethylsilyl)acetamide.
[0060] The third aspect of the present invention provides a lithium ion battery, the lithium ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises a positive electrode active material; the negative electrode comprises a negative electrode active material graphite;
[0061] The electrolyte includes a lithium salt and a non-aqueous organic solvent, in which a functional additive is dissolved; the functional additive includes at least one of N,N-diethyltrimethylsilylamine and N-(trimethylsilyl)acetamide.
[0062] In some embodiments, the positive electrode further includes a positive electrode conductor and a positive electrode binder.
[0063] The positive electrode active material can be mixed with a positive electrode binder such as poly(tetrafluoroethylene) (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), styrene ethylene butylene styrene copolymer (SEBS), styrene butadiene styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate, and combinations thereof. The positive electrode conductive agent may include a carbon-based material, powdered nickel or other metal particles, or a conductive polymer.
[0064] In some embodiments, the negative electrode active material may include a negative electrode binder.
[0065] The negative electrode binder improves the bonding between negative electrode active material particles and the bonding between the negative electrode active material and the current collector.
[0066] In specific applications, non-limiting examples of negative electrode binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin, nylon, etc.
[0067] The embodiments of the present invention will be described in detail below through examples and comparative examples. All examples and comparative examples are all solid-state battery sample groups prepared by the same process, and the number of samples in each group is 20.
[0068] It should be noted that the embodiments of the present invention are not limited to these examples.
[0069] Example 1
[0070] 1. Preparation of positive electrode:
[0071] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.
[0072] 2. Preparation of negative electrode:
[0073] 1. The negative electrode active material graphite, the binder polytetrafluoroethylene (PTFE) and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.
[0074] 2. The negative electrode active material layer and the copper foil are rolled and laminated.
[0075] 3. Preparation of electrolyte
[0076] S1, adding lithium salt to the non-aqueous organic solvent, and stirring continuously for 30 min until completely mixed;
[0077] Preparation method of non-aqueous organic solvent: Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are put into a container and mixed for 30 minutes.
[0078] Wherein, taking the total mass of the non-aqueous organic solvent as 100%, the mass of ethylene carbonate (EC) accounts for 30%, the mass of dimethyl carbonate (DMC) accounts for 35%, and the mass of ethyl methyl carbonate (EMC) accounts for 35%.
[0079] The lithium salt is a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), with a molar ratio of 4:1.
[0080] S2, add film-forming additives and stir again for 30 minutes to mix;
[0081] The film-forming additive is a mixture of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
[0082] S3, adding functional additives to the solution and stirring for 1 hour to complete the preparation of the electrolyte;
[0083] The functional additive is N,N-diethyltrimethylsilylamine.
[0084] In the prepared electrolyte, the concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.2 mol / L.
[0085] Taking the mass of the electrolyte as 100%, the mass of the film-forming additive accounts for 3%, and the mass of the functional additive accounts for 0.5%.
[0086] 4. Preparation of lithium-ion batteries
[0087] The positive electrode and negative electrode prepared above are stacked in order with the separator so that the separator is between the positive and negative electrodes to obtain a bare cell. The bare cell is placed in an outer packaging shell, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.
[0088] Example 2
[0089] 1. Preparation of positive electrode:
[0090] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.
[0091] 2. Preparation of negative electrode:
[0092] 1. The negative electrode active material graphite, the binder polytetrafluoroethylene (PTFE) and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.
[0093] 2. The negative electrode active material layer and the copper foil are rolled and laminated.
[0094] 3. Preparation of electrolyte
[0095] S1, adding lithium salt to the non-aqueous organic solvent, and stirring continuously for 30 min until completely mixed;
[0096] Preparation method of non-aqueous organic solvent: Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are put into a container and mixed for 30 minutes.
[0097] Wherein, taking the total mass of the non-aqueous organic solvent as 100%, the mass of ethylene carbonate (EC) accounts for 30%, the mass of dimethyl carbonate (DMC) accounts for 35%, and the mass of ethyl methyl carbonate (EMC) accounts for 35%.
[0098] The lithium salt is a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), with a molar ratio of 4:1.
[0099] S2, add film-forming additives and stir again for 30 minutes to mix;
[0100] The film-forming additive is a mixture of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
[0101] S3, adding functional additives to the solution and stirring for 1 hour to complete the preparation of the electrolyte;
[0102] The functional additive is N,N-diethyltrimethylsilylamine.
[0103] In the prepared electrolyte, the concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.2 mol / L.
[0104] Taking the mass of the electrolyte as 100%, the mass of the film-forming additive accounts for 3%, and the mass of the functional additive accounts for 1.5%.
[0105] 4. Preparation of lithium-ion batteries
[0106] The positive electrode and negative electrode prepared above are stacked in order with the separator so that the separator is between the positive and negative electrodes to obtain a bare cell. The bare cell is placed in an outer packaging shell, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.
[0107] Example 3
[0108] 1. Preparation of positive electrode:
[0109] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.
[0110] 2. Preparation of negative electrode:
[0111] 1. The negative electrode active material graphite, the binder polytetrafluoroethylene (PTFE) and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.
[0112] 2. The negative electrode active material layer and the copper foil are rolled and laminated.
[0113] 3. Preparation of electrolyte
[0114] S1, adding lithium salt to the non-aqueous organic solvent, and stirring continuously for 30 min until completely mixed;
[0115] Preparation method of non-aqueous organic solvent: Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are put into a container and mixed for 30 minutes.
[0116] Wherein, taking the total mass of the non-aqueous organic solvent as 100%, the mass of ethylene carbonate (EC) accounts for 30%, the mass of dimethyl carbonate (DMC) accounts for 35%, and the mass of ethyl methyl carbonate (EMC) accounts for 35%.
[0117] The lithium salt is a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), with a molar ratio of 4:1.
[0118] S2, add film-forming additives and stir again for 30 minutes to mix;
[0119] The film-forming additive is a mixture of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
[0120] S3, adding functional additives to the solution and stirring for 1 hour to complete the preparation of the electrolyte;
[0121] The functional additive is N,N-diethyltrimethylsilylamine.
[0122] In the prepared electrolyte, the concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.2 mol / L.
[0123] Taking the mass of the electrolyte as 100%, the mass of the film-forming additive accounts for 3%, and the mass of the functional additive accounts for 3%.
[0124] 4. Preparation of lithium-ion batteries
[0125] The positive electrode and negative electrode prepared above are stacked in order with the separator so that the separator is between the positive and negative electrodes to obtain a bare cell. The bare cell is placed in an outer packaging shell, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.
[0126] Example 4
[0127] 1. Preparation of positive electrode:
[0128] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.
[0129] 2. Preparation of negative electrode:
[0130] 1. The negative electrode active material graphite, the binder polytetrafluoroethylene (PTFE) and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.
[0131] 2. The negative electrode active material layer and the copper foil are rolled and laminated.
[0132] 3. Preparation of electrolyte
[0133] S1, adding lithium salt to the non-aqueous organic solvent, and stirring continuously for 30 min until completely mixed;
[0134] Preparation method of non-aqueous organic solvent: Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are put into a container and mixed for 30 minutes.
[0135] Wherein, taking the total mass of the non-aqueous organic solvent as 100%, the mass of ethylene carbonate (EC) accounts for 30%, the mass of dimethyl carbonate (DMC) accounts for 35%, and the mass of ethyl methyl carbonate (EMC) accounts for 35%.
[0136] The lithium salt is a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), with a molar ratio of 8:3.
[0137] S2, add film-forming additives and stir again for 30 minutes to mix;
[0138] The film-forming additive is a mixture of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
[0139] S3, adding functional additives to the solution and stirring for 1 hour to complete the preparation of the electrolyte;
[0140] The functional additive is N-(trimethylsilyl)acetamide.
[0141] In the prepared electrolyte, the concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.3 mol / L.
[0142] Taking the mass of the electrolyte as 100%, the mass of the film-forming additive accounts for 3%, and the mass of the functional additive accounts for 0.5%.
[0143] 4. Preparation of lithium-ion batteries
[0144] The positive electrode and negative electrode prepared above are stacked in order with the separator so that the separator is between the positive and negative electrodes to obtain a bare cell. The bare cell is placed in an outer packaging shell, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.
[0145] Example 5
[0146] 1. Preparation of positive electrode:
[0147] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.
[0148] 2. Preparation of negative electrode:
[0149] 1. The negative electrode active material graphite, the binder polytetrafluoroethylene (PTFE) and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.
[0150] 2. The negative electrode active material layer and the copper foil are rolled and laminated.
[0151] 3. Preparation of electrolyte
[0152] S1, adding lithium salt to the non-aqueous organic solvent, and stirring continuously for 30 min until completely mixed;
[0153] Preparation method of non-aqueous organic solvent: Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are put into a container and mixed for 30 minutes.
[0154] Wherein, taking the total mass of the non-aqueous organic solvent as 100%, the mass of ethylene carbonate (EC) accounts for 30%, the mass of dimethyl carbonate (DMC) accounts for 35%, and the mass of ethyl methyl carbonate (EMC) accounts for 35%.
[0155] The lithium salt is a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), with a molar ratio of 8:3.
[0156] S2, add film-forming additives and stir again for 30 minutes to mix;
[0157] The film-forming additive is a mixture of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
[0158] S3, adding functional additives to the solution and stirring for 1 hour to complete the preparation of the electrolyte;
[0159] The functional additive is N-(trimethylsilyl)acetamide.
[0160] In the prepared electrolyte, the concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.3 mol / L.
[0161] Taking the mass of the electrolyte as 100%, the mass of the film-forming additive accounts for 3%, and the mass of the functional additive accounts for 1.5%.
[0162] 4. Preparation of lithium-ion batteries
[0163] The positive electrode and negative electrode prepared above are stacked in order with the separator so that the separator is between the positive and negative electrodes to obtain a bare cell. The bare cell is placed in an outer packaging shell, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.
[0164] Example 6
[0165] 1. Preparation of positive electrode:
[0166] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.
[0167] 2. Preparation of negative electrode:
[0168] 1. The negative electrode active material graphite, polytetrafluoroethylene (PTFE) and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain a negative electrode active material layer.
[0169] 2. The negative electrode active material layer and the copper foil are rolled and laminated.
[0170] 3. Preparation of electrolyte
[0171] S1, adding lithium salt to the non-aqueous organic solvent, and stirring continuously for 30 min until completely mixed;
[0172] Preparation method of non-aqueous organic solvent: Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are put into a container and mixed for 30 minutes.
[0173] Wherein, taking the total mass of the non-aqueous organic solvent as 100%, the mass of ethylene carbonate (EC) accounts for 30%, the mass of dimethyl carbonate (DMC) accounts for 35%, and the mass of ethyl methyl carbonate (EMC) accounts for 35%.
[0174] The lithium salt is a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), with a molar ratio of 8:3.
[0175] S2, add film-forming additives and stir again for 30 minutes to mix;
[0176] The film-forming additive is a mixture of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
[0177] S3, adding functional additives to the solution and stirring for 1 hour to complete the preparation of the electrolyte;
[0178] The functional additive is N-(trimethylsilyl)acetamide.
[0179] In the prepared electrolyte, the concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.3 mol / L.
[0180] Taking the mass of the electrolyte as 100%, the mass of the film-forming additive accounts for 3%, and the mass of the functional additive accounts for 3%.
[0181] 4. Preparation of lithium-ion batteries
[0182] The positive electrode and negative electrode prepared above are stacked in order with the separator so that the separator is between the positive and negative electrodes to obtain a bare cell. The bare cell is placed in an outer packaging shell, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.
[0183] Comparative Example 1
[0184] 1. Preparation of positive electrode:
[0185] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.
[0186] 2. Preparation of negative electrode:
[0187] 1. The negative electrode active material graphite, the binder polytetrafluoroethylene (PTFE) and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.
[0188] 2. The negative electrode active material layer and the copper foil are rolled and laminated.
[0189] 3. Preparation of electrolyte
[0190] S1, adding lithium salt to the non-aqueous organic solvent, and stirring continuously for 30 min until completely mixed;
[0191] Preparation method of non-aqueous organic solvent: Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are put into a container and mixed for 30 minutes.
[0192] Wherein, taking the total mass of the non-aqueous organic solvent as 100%, the mass of ethylene carbonate (EC) accounts for 30%, the mass of dimethyl carbonate (DMC) accounts for 35%, and the mass of ethyl methyl carbonate (EMC) accounts for 35%.
[0193] The lithium salt is a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), with a molar ratio of 4:1.
[0194] S2, adding film-forming additives, stirring again for 30 minutes to mix well, and completing the preparation of the electrolyte.
[0195] The film-forming additive is a mixture of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
[0196] In the prepared electrolyte, the concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.2 mol / L.
[0197] Taking the mass of the electrolyte as 100%, the mass of the film-forming additive accounts for 3%.
[0198] 4. Preparation of lithium-ion batteries
[0199] The positive electrode and negative electrode prepared above are stacked in order with the separator so that the separator is between the positive and negative electrodes to obtain a bare cell. The bare cell is placed in an outer packaging shell, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.
[0200] Comparative Example 2
[0201] 1. Preparation of positive electrode:
[0202] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.
[0203] 2. Preparation of negative electrode:
[0204] 1. The negative electrode active material graphite, the binder polytetrafluoroethylene (PTFE) and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.
[0205] 2. The negative electrode active material layer and the copper foil are rolled and laminated.
[0206] 3. Preparation of electrolyte
[0207] S1, adding lithium salt to the non-aqueous organic solvent, and stirring continuously for 30 min until completely mixed;
[0208] Preparation method of non-aqueous organic solvent: Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are put into a container and mixed for 30 minutes.
[0209] Wherein, taking the total mass of the non-aqueous organic solvent as 100%, the mass of ethylene carbonate (EC) accounts for 30%, the mass of dimethyl carbonate (DMC) accounts for 35%, and the mass of ethyl methyl carbonate (EMC) accounts for 35%.
[0210] The lithium salt is a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), with a molar ratio of 4:1.
[0211] S2, add film-forming additives and stir again for 30 minutes to mix;
[0212] The film-forming additive is a mixture of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
[0213] S3, adding functional additives to the solution and stirring for 1 hour to complete the preparation of the electrolyte;
[0214] The functional additive is N,N-diethyltrimethylsilylamine.
[0215] In the prepared electrolyte, the concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.2 mol / L.
[0216] Taking the mass of the electrolyte as 100%, the mass of the film-forming additive accounts for 3%, and the mass of the functional additive accounts for 5%.
[0217] 4. Preparation of lithium-ion batteries
[0218] The positive electrode and negative electrode prepared above are stacked in order with the separator so that the separator is between the positive and negative electrodes to obtain a bare cell. The bare cell is placed in an outer packaging shell, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.
[0219] Comparative Example 3
[0220] 1. Preparation of positive electrode:
[0221] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.
[0222] 2. Preparation of negative electrode:
[0223] 1. The negative electrode active material graphite, the binder polytetrafluoroethylene (PTFE) and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.
[0224] 2. The negative electrode active material layer and the copper foil are rolled and laminated.
[0225] 3. Preparation of electrolyte
[0226] S1, adding lithium salt to the non-aqueous organic solvent, and stirring continuously for 30 min until completely mixed;
[0227] Preparation method of non-aqueous organic solvent: Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are put into a container and mixed for 30 minutes.
[0228] Wherein, taking the total mass of the non-aqueous organic solvent as 100%, the mass of ethylene carbonate (EC) accounts for 30%, the mass of dimethyl carbonate (DMC) accounts for 35%, and the mass of ethyl methyl carbonate (EMC) accounts for 35%.
[0229] The lithium salt is a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), with a molar ratio of 8:3.
[0230] S2, add film-forming additives and stir again for 30 minutes to mix;
[0231] The film-forming additive is a mixture of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).
[0232] S3, adding functional additives to the solution and stirring for 1 hour to complete the preparation of the electrolyte;
[0233] The functional additive is N-(trimethylsilyl)acetamide.
[0234] In the prepared electrolyte, the concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.3 mol / L.
[0235] Taking the mass of the electrolyte as 100%, the mass of the film-forming additive accounts for 3%, and the mass of the functional additive accounts for 5%.
[0236] 4. Preparation of lithium-ion batteries
[0237] The positive electrode and negative electrode prepared above are stacked in order with the separator so that the separator is between the positive and negative electrodes to obtain a bare cell. The bare cell is placed in an outer packaging shell, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.
[0238] Comparative experiment
[0239] A total of 9 groups of samples from the above embodiments 1-6 and comparative examples 1-3 were taken and the following tests were performed respectively. All test data were averaged and some values were rounded off.
[0240] 1. First efficiency test:
[0241] After the prepared lithium-ion battery was left to stand for 24 hours, it was charged to 3.0V at a constant current of 0.5C, and then charged to 4.2V at a constant current and constant voltage of 0.5C (cutoff current 0.05C) to obtain the charging capacity. After being left to stand for 1 hour, it was discharged to 3.0V at a constant current of 0.5C to obtain the discharge capacity. The first efficiency = discharge capacity / charging capacity.
[0242] 2. 500 cycles performance test at 25°C:
[0243] The battery was tested at 25°C as follows: the divided battery was charged to 4.2V with 1C constant current and constant voltage, with a cut-off rate of 0.05C; then discharged to 3V with 1C constant current. After such charge / discharge cycles, the capacity retention rate after the target number of cycles was calculated to evaluate its cycle performance. The target number of cycles at 25°C was 500 times.
[0244] The test results are shown in the following table:
[0245]
[0246] It can be seen from the above table:
[0247] Comparative Example 1 does not add the additive N,N-diethyltrimethylsilylamine or N-(trimethylsilyl)acetamide, and its rate performance, initial charge and discharge efficiency and capacity retention rate are not as good as those of the embodiment.
[0248] Comparative Example 2 adds an excessive amount of N,N-diethyltrimethylsilylamine, and Comparative Example 3 adds an excessive amount of N-(trimethylsilyl)acetamide. Their initial charge and discharge efficiency and capacity retention rate are not as good as those of the embodiment.
[0249] It can be seen from this that adding an appropriate amount of functional additives in the electrolyte can effectively improve the battery's rate performance, initial charge and discharge efficiency, and good capacity retention rate.
[0250] It should be pointed out that the above 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 in the protection scope of the present invention.
Claims
1. An electrolyte suitable for a dry-process graphite negative electrode interface, comprising a lithium salt, a non-aqueous organic solvent and a functional additive, characterized in that: The functional additive is N,N-diethyltrimethylsilylamine or N-(trimethylsilyl)acetamide.
2. The electrolyte according to claim 1, characterized in that Taking the mass of the electrolyte as 100%, the mass of the functional additive accounts for 0.1% to 3%.
3. The electrolyte according to claim 2, characterized in that Based on the mass of the electrolyte being 100%, the mass of the functional additive accounts for 1.5%.
4. The electrolyte according to claim 1, characterized in that Also included are film-forming additives; The film-forming additive includes at least one of lithium difluorophosphate, vinylene carbonate and fluoroethylene carbonate; The non-aqueous organic solvent includes any one of ethylene carbonate, ethyl methyl carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, propyl acetate, methyl acetate, and methyl propionate, or a combination of at least two or more thereof in any proportion.
5. The electrolyte according to claim 4, characterized in that The non-aqueous organic solvent includes ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.
6. The electrolyte according to claim 1, characterized in that The lithium salt includes any one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium fluorosulfonate, lithium bis(pentafluoroethanesulfonyl)imide, lithium monofluorophosphate, lithium bisoxalatoborate, lithium bisfluorosulfonyl imide, and lithium bisoxalatofluoroborate, or a combination of at least two or more thereof in any proportion.
7. The electrolyte according to claim 6, characterized in that The lithium salts include lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.
8. The electrolyte according to claim 1, characterized in that In the electrolyte, the concentration of the lithium salt is 0.8 mol / L to 1.5 mol / L.
9. The electrolyte according to claim 8, characterized in that In the electrolyte, the concentration of the lithium salt is 1 mol / L.
10. A method for preparing an electrolyte, characterized in that: The steps include: S1, adding lithium salt to a non-aqueous organic solvent and continuously stirring until completely mixed; S2, adding film-forming additives and stirring again to mix; S3, adding functional additives, stirring evenly, and completing the preparation of the electrolyte; The functional additive includes at least one of N,N-diethyltrimethylsilylamine and N-(trimethylsilyl)acetamide.