A lithium-ion battery

Abstract

The application relates to a lithium ion battery in the technical field of lithium battery production, which comprises a positive electrode, a liquid electrolyte and an inorganic solid electrolyte film, wherein the inorganic solid electrolyte film is located on the surface of the positive electrode active material layer; the liquid electrolyte comprises a fluorinated additive; the mass percentage of the fluorinated additive in the liquid electrolyte is 0.5%<=a<=10%; the percentage of the inorganic solid electrolyte film in the total mass of the solid-liquid electrolyte in the battery is 1%<=b<=99%; the porosity of the inorganic solid electrolyte film is c>=20%, and the tortuosity is d=1-10. The fluorinated additive is matched with the inorganic solid electrolyte film, the porosity and capillary structure of the positive and negative electrode surfaces are increased, the surface tension of the electrolyte and the electrode sheet is reduced, the electrolyte is uniformly distributed on all parts of the battery under the capillary action, the low-temperature Rct (charge transfer resistance) is significantly reduced, a protective film rich in inorganic components is formed on the positive and negative electrode surfaces, and the low-temperature Rsei film impedance is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery production, in particular to a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have been widely used in electronic products and new energy vehicles due to their green environmental protection, high energy density, long cycle life and other characteristics. The main components of lithium ion batteries include positive electrode, negative electrode, electrolyte and separator. Among them, the electrolyte plays a role in conducting ions in the battery and is a key component of lithium ion batteries. Traditional commercial lithium ion electrolyte is usually composed of non-aqueous organic solvent, electrolyte salt and additive. Existing solutions mainly improve the performance of lithium ion batteries by improving the electrolyte. For example, some studies improve the performance of the electrolyte by adding fluorinated additives. In addition, some studies use inorganic solid electrolyte membranes to replace traditional liquid electrolytes. Although the existing solutions improve the performance of lithium ion batteries to some extent, there are still some problems. For example, the interfacial transmission impedance and concentration polarization impedance of traditional commercial lithium ion electrolyte at low temperature will significantly increase, resulting in rapid attenuation aging of battery capacity reduction, internal resistance increase and voltage drop. In addition, the thickness of the negative electrode side SEI film will significantly thicken at low temperature, resulting in inability to charge and discharge at high rate. These problems limit the use performance of lithium ion batteries in low temperature environment.

[0003] There is an urgent need for a technical solution to solve the above problems. SUMMARY

[0004] To solve the above problems, a lithium ion battery is disclosed in the present application. The technical solution of the present application is implemented as follows:

[0005] A lithium ion battery, comprising a positive electrode, a liquid electrolyte and an inorganic solid electrolyte membrane, wherein the inorganic solid electrolyte membrane is located on the surface of the positive electrode active material layer;

[0006] The liquid electrolyte comprises a fluorinated additive;

[0007] The mass percentage of the fluorinated additive in the liquid electrolyte is 0.5%≤a≤10%;

[0008] The percentage of the inorganic solid electrolyte membrane in the total mass of the solid-liquid electrolyte inside the battery is 1%≤b≤99%;

[0009] The porosity c of the inorganic solid electrolyte membrane is ≥20%, and the tortuosity d is 1-10.

[0010] Preferably, the liquid electrolyte further comprises a non-aqueous organic solvent and an electrolyte salt;

[0011] The non-aqueous organic solvent includes at least one of a carbonate solvent, a carboxylate solvent, and a phosphate solvent; and the electrolyte salt includes at least one of a fluorine-containing inorganic lithium salt and a fluorine-containing organic lithium salt.

[0012] Preferably, the inorganic solid electrolyte film has a tortuosity d of 1.5 to 3.

[0013] Preferably, the inorganic solid electrolyte film has a thickness of 5 μm to 20 μm.

[0014] Preferably, the inorganic solid electrolyte film has a thickness of 10 μm.

[0015] Preferably, the inorganic solid electrolyte film includes at least one of a halide solid electrolyte, a sulfide solid electrolyte, and an oxide solid electrolyte.

[0016] Preferably, the inorganic solid electrolyte includes at least one of a lithium zirconium chloride electrolyte (LZC), a lithium lanthanum zirconate electrolyte (LLZO), and a lithium titanium aluminum phosphate electrolyte (LATP).

[0017] Preferably, the fluorinated additive has a structural formula as follows:

[0018]

[0019] In the above formula, R1 is selected from at least one of H, F, and a fluorinated hydrocarbon group having 1 to 3 carbons; and R2 is selected from at least one of H, F, and a fluorinated hydrocarbon group having 1 to 3 carbons.

[0020] Preferably, the fluorinated additive includes at least one of fluorinated ethylene carbonate (FEC), difluorinated ethylene carbonate (DFEC), and tetrafluorinated ethylene carbonate (TFEC).

[0021] Preferably, the lithium ion battery further includes a separator and a negative electrode, the separator being disposed between the positive electrode and the negative electrode.

[0022] Preferably, the negative electrode includes a negative electrode active material.

[0023] Preferably, the negative electrode active material includes at least one of graphite, a single-crystal silicon composite, soft carbon, and hard carbon.

[0024] Advantages of the present application are as follows:

[0025] The present application adds fluorinated additives in liquid electrolyte to match inorganic solid electrolyte membrane, the fluorinated additives have the function of surfactant, reduce the surface tension of electrolyte and pole piece, can make electrolyte evenly distributed in each part of the battery up and down left and right under the capillary action. Significantly reduce the low temperature Rct(charge transfer resistance), combined with inorganic solid electrolyte membrane, the fluorinated additives on the positive and negative electrode surface form a protective film rich in inorganic components, which can also reduce the low temperature Rsei membrane impedance;

[0026] The present application uses inorganic solid electrolyte membrane to replace the traditional diaphragm, the inorganic solid electrolyte membrane has higher ion conductivity and better thermal stability, which can effectively improve the safety performance of lithium ion battery. This technical scheme effectively solves the safety problem of the traditional liquid electrolyte in the prior art, and improves the use safety of the lithium ion battery. DETAILED DESCRIPTION

[0027] The technical solutions of the present application will be described clearly and completely below by combining with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0028] Unless otherwise defined, all technical and scientific terms used in the present application have the same meanings as those commonly understood by those skilled in the art to which the present application belongs; the terms used in the specific embodiments are only for the purpose of describing the specific embodiments, not intended to limit the present application; the terms in the specification and claims of the present application and the above description, and any modification thereof, are intended to cover non-exclusive inclusion.

[0029] In the description of the specific embodiments of the present application, 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 application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0030] In the present application, the phrase "embodiment" means that the specific features, structures or properties described in combination with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the described embodiments of the present application can be combined with other embodiments.

[0031] In the description of the embodiments of the present application, the term "and / or" is merely an association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A existing alone, A and B existing together, and B existing alone. In addition, the character " / " in the present application generally represents an "or" relationship between the front and rear associated objects.

[0032] Throughout the present application, numerical values represent approximate measures or limits of ranges to encompass minor deviations from given values and embodiments with about the mentioned values and embodiments with the mentioned exact values. Except for the working examples provided at the end of the specific embodiments, all numerical values of parameters (e.g., amounts or conditions) in the present specification (including the appended claims) should be understood in all cases as being modified by the term "about", whether or not the term "about" actually appears before the numerical value. "About" indicates that the stated numerical value allows for some minor inaccuracy (is close to the exact value of the stated value to some extent; is approximately or reasonably close to the stated value; is almost). If the inaccuracy provided by "about" is not otherwise understood in the art in this ordinary meaning, "about" as used in the present application at least indicates the variation that can be produced by ordinary methods of measuring and using such parameters. For example, "about" can 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 certain aspects, optionally less than or equal to 0.1%.

[0033] In addition, the disclosure of a range includes all values within the range and further partitioned ranges, including the endpoints and subranges given for these ranges.

[0034] The interface transmission impedance and concentration polarization impedance of conventional commercial lithium ion electrolyte at low temperature will significantly increase, resulting in rapid aging of reduced battery capacity, increased internal resistance and voltage drop. In addition, the thickness of the SEI film on the negative electrode side will significantly increase at low temperature, resulting in the inability to charge and discharge at high rate. These problems limit the use performance of lithium ion batteries in low temperature environments.

[0035] The present application proposes a technical solution to solve the above problems. Specifically as follows:

[0036] A lithium ion battery, comprising a positive electrode, a liquid electrolyte and an inorganic solid electrolyte film, wherein the inorganic solid electrolyte film is located on the surface of the positive electrode active material layer;

[0037] The liquid electrolyte comprises a fluorinated additive;

[0038] The fluorinated additive accounts for 0.5%≤a≤10% of the mass percentage of the liquid electrolyte;

[0039] The percentage of the inorganic solid-state electrolyte film in the total mass of the solid-liquid electrolyte inside the battery is 1%≤b≤99%;

[0040] The porosity c of the inorganic solid-state electrolyte film is ≥20%, and the tortuosity d is 1-10.

[0041] The present application adds a fluorinated additive to the liquid electrolyte to match the inorganic solid-state electrolyte film. The fluorinated additive has the function of a surfactant, reduces the surface tension of the electrolyte and the electrode sheet, and can make the electrolyte uniformly distributed in all parts of the battery under capillary action. Significantly reduce the low temperature Rct (charge transfer resistance), combined with the inorganic solid-state electrolyte film, it is also beneficial to the formation of a protective film rich in inorganic components on the surface of the positive and negative electrodes, and can also reduce the low temperature Rsei membrane impedance.

[0042] In specific applications, the mass percentage of the fluorinated additive in the liquid electrolyte can be selected as: 0.5%, 0.8%, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, etc. The above listed percentage values are only examples and are not limited, as long as they are within the understanding range of those skilled in the art, the present application can freely implement any percentage value within the range of 0.5%≤a≤10%.

[0043] In specific applications, the percentage of the inorganic solid-state electrolyte film in the total mass of the solid-liquid electrolyte inside the battery can be selected as: 1%, 2%, 5%, 8%, 10%, 11%, 12%, 15%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc. The above listed percentage values are only examples and are not limited, as long as they are within the understanding range of those skilled in the art, the present application can freely implement any percentage value within the range of 0.5%≤a≤10%.

[0044] In specific applications, the porosity c of the inorganic solid-state electrolyte film can be selected as 20%, 22%, 25%, 28%, 30%, 35%, etc. The tortuosity d of the inorganic solid-state electrolyte film can be selected as: 1, 2, 4, 5, 7, 10, etc. The above listed values are only examples and are not limited, as long as they are within the understanding range of those skilled in the art and the above limited value range, those skilled in the art can freely implement.

[0045] In some embodiments, the liquid electrolyte further comprises a non-aqueous organic solvent and an electrolyte salt;

[0046] The non-aqueous organic solvent includes at least one of a carbonate solvent, a carboxylic acid ester solvent, and a phosphate solvent; and the electrolyte salt includes at least one of a fluorine-containing inorganic lithium salt and a fluorine-containing organic lithium salt.

[0047] The carbonate solvent includes at least one of ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and propylene carbonate (PC).

[0048] The carboxylic acid ester solvent includes at least one of ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), and propyl acetate (PA).

[0049] The phosphate solvent includes at least one of triethyl phosphate (TEP), triphenyl phosphate (TPP), and trioctyl phosphate (TOP).

[0050] The fluorine-containing inorganic lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, and lithium fluoroborate.

[0051] The fluorine-containing organic lithium salt includes at least one of lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium bis-oxalato-borate, and lithium difluoro-oxalato-borate.

[0052] The "at least one" in the present application refers to that any one element in the list can be selected as a technical solution, or a combination of two or more elements can be adopted as a technical solution, and the combination does not exceed the understanding of those skilled in the art, so that the combination form can be freely selected as needed, and the combination of all the listed elements is not more than the maximum.

[0053] In some preferred embodiments, the tortuosity d of the inorganic solid-state electrolyte film is 1.5-3.

[0054] In specific applications, the tortuosity d of the inorganic solid-state electrolyte film can be selected as 1.5, 1.8, 2, 2.1, 2.2, 2.5, 2.8, 3, etc. The above listed values are only examples and are not limited, and do not exceed the understanding of those skilled in the art and the above limited numerical range.

[0055] In some embodiments, the thickness of the inorganic solid-state electrolyte film is 5-20 μm.

[0056] In specific applications, the thickness of the inorganic solid electrolyte membrane can be selected as: 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, etc. The above-listed values are only examples and not limitations, within the understanding scope of those skilled in the art and within the above-defined numerical range.

[0057] In some preferred embodiments, the thickness of the inorganic solid electrolyte membrane is 10μm.

[0058] When the thickness of the inorganic solid electrolyte membrane is about 10μm, the comprehensive performance of the inorganic solid electrolyte membrane is optimal.

[0059] In some embodiments, the inorganic solid electrolyte membrane includes at least one of halide solid electrolytes, sulfide solid electrolytes, and oxide solid electrolytes.

[0060] In some embodiments, the halide solid electrolyte includes at least one of chloride, bromide, and iodide solid electrolytes;

[0061] In some embodiments, the sulfide solid electrolyte includes at least one of vitreous sulfide, glass-ceramic sulfide, and crystalline sulfide solid electrolytes;

[0062] In some embodiments, the oxide solid electrolyte includes at least one of fluorite-type oxides, perovskite-structured oxides, lithium lanthanum zirconium oxides, lithium lanthanum titanium oxides, and lithium aluminum titanium phosphorus oxides solid electrolytes;

[0063] In specific applications, the halide solid electrolyte can be selected from: Li2CdC l4 , Li2MgC l4 , Li2Cd I4 , Li2ZnI4, Li3OCl, LiI, Li5ZnI4, Li3OCl 1-x Br x (where 0 < x < 1) of at least one.

[0064] In specific applications, the sulfide solid electrolyte can be selected from: Li2S-P2S5, Li2S-P2S5-MS x (where M is Si, Ge, and Sn and 0 ≤ x ≤ 2), Li 3.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.3 、Li 9.6 P3S 12 、Li7P3S11 Li9P3S9O3, Li 10.35 Si 1.35 P 1.65 S 12 Li 9.81 Sn 0.81 P 2.19 S 12 Li 10 (Si 0.5 Ge 0.5 )P2S 12 Li(Ge 0.5 Sn 0.5 )P2S 12 Li(Si 0.5 Sn 0.5 )PsS 12 Li 10 GeP2S 12 (LGPS), Li6PS5X (where X is CI, Br or I), Li7P2S8I, Li 10.35 Ge 1.35 P 1.65 S 12 Li 3.25 Ge 0.25 P 0.75 S4, Li 10 SnP2S 12 Li 10 SiP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 C l0.3 Li2S (where 0.5 < x < 0.7). (1-x) P2S 5-x Li2S (where 0.5 < x < 0.7).

[0065] In a specific application, the oxide solid electrolyte can be selected from: perovskite type, garnet type, LISICON type, NASICON type, wherein the perovskite type solid electrolyte material is preferably LLTO (lithium lanthanum titanium oxide / lithium titanate, Li 0.33 La 0.56 TiO3), the garnet type solid electrolyte material is preferably LLZO (lithium lanthanum zirconium oxide / lithium zirconate, Li7La3Zr2O 12 ), the NASICON (sodium superionic conductor) type solid electrolyte material is preferably lithium titanium aluminum phosphate

[0066] LATP Li 1.3 Al 0.3 Ti 1.7 (PO4)3).

[0067] In some preferred embodiments, the inorganic solid-state electrolyte comprises at least one of lithium zirconium chloride (LZC), lithium lanthanum zirconate (LLZO), lithium aluminum titanium phosphate (LATP).

[0068] The inorganic oxide solid-state electrolyte with fluorinated additives at low temperature helps to form SEI film of inorganic oxide components, the impedance of inorganic oxide SEI film components at low temperature is significantly lower than that of organic components. Mainly because the inorganic components usually have higher mechanical strength and chemical stability, while having higher ionic conductivity and lower lithium ion diffusion barrier, which can inhibit the growth of lithium dendrites at low temperature, thereby improving the cycle stability and safety of the battery; while the organic component SEI film shows higher impedance at low temperature, mainly because its ionic conductivity is low, and it is easy to form a crystalline state at low temperature, resulting in blocked lithium ion transport.

[0069] In some preferred embodiments, the fluorinated additive has a structural formula as follows:

[0070]

[0071] In the above formula, R1 is selected from at least one of H, F, C1-C3 fluorinated hydrocarbon groups; R2 is selected from at least one of H, F, C1-C3 fluorinated hydrocarbon groups.

[0072] In some embodiments, the fluorinated additive comprises at least one of fluorinated ethylene carbonate (FEC), difluorinated ethylene carbonate (DFEC), tetrafluorinated ethylene carbonate (DFEC).

[0073] In some embodiments, the lithium ion battery further comprises a separator and a negative electrode sheet, the separator is disposed between the positive electrode and the negative electrode.

[0074] In some embodiments, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, a positive electrode conductive agent and a positive electrode binder.

[0075] In specific applications, the positive electrode active material can be selected to include any one or a combination of at least two of lithium cobaltate, lithium nickel cobalt manganese acid, lithium nickel cobalt aluminum acid, lithium manganate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium iron phosphate, lithium titanate or lithium-rich manganese elastic base material. The above are all common positive electrode active materials in the art, which are only examples and are not limited.

[0076] In particular applications, the positive electrode conductive agent can include any conductive material so long as it does not cause chemical changes. Conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof. The above are all common conductive agents in the art, and are merely examples, not limitations.

[0077] In particular applications, the positive electrode binder can include at least one of polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyethylene oxide, poly(p-phenylene oxide), poly(methyl methacrylate), polyacrylonitrile, or polyvinyl chloride (PVC). The above are all common binders in the art, and are merely examples, not limitations.

[0078] The separator includes one or more of a polyolefin-based separator, a coating-treated polyester film, a cellulose film, a polyimide film and a polyamide film, a spandex or aramid film, a nonwoven fabric separator, an inorganic nanocomposite film.

[0079] In some embodiments, the negative electrode includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0080] In some embodiments, the negative electrode active material includes at least one of graphite, a single-crystal silicon composite, soft carbon, and hard carbon.

[0081] In particular applications, the negative electrode conductive agent can include any conductive material so long as it does not cause chemical changes. Conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof. The above are all common conductive agents in the art, and are merely examples, not limitations.

[0082] In particular applications, non-limiting examples of the negative electrode binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride-1,1, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, etc.

[0083] The positive electrode binder can improve the binding of the positive electrode active material particles to each other, and also improve the binding of the positive electrode material layer to the positive electrode current collector; the negative electrode binder improves the binding of the negative electrode active material particles to each other and the binding of the negative electrode active material to the current collector.

[0084] The embodiments of the present application will be specifically described below by examples and comparative examples. Among them, all the examples and comparative examples are full solid-state battery sample groups prepared by the same process, and the number of samples in each group is 20.

[0085] Example 1:

[0086] I. Preparation of liquid electrolyte

[0087] 1) Mix non-aqueous organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and triethyl phosphate (TEP) according to the volume ratio of 1:1:1, and stir for 30 minutes to obtain a mixed organic solvent.

[0088] 2) Add fluorine-containing inorganic lithium salt LiPF6 and fluorine-containing organic lithium salt LiFSI (molar ratio of two lithium salts is 1:1) to the mixed non-aqueous organic solvent, and the molar ratio of non-aqueous organic solvent to lithium salt is 15:1. After stirring for 60 minutes, it is placed in a low-temperature environment at 0°C for 4 hours to obtain an electrolyte with a lithium salt mass concentration of 15%.

[0089] 3) Add 5% by mass of fluoroethylene carbonate (FEC), and stir for 30 minutes to obtain the liquid electrolyte.

[0090] II. Preparation of inorganic solid electrolyte film

[0091] 1) Select inorganic solid electrolyte lithium zirconium chloride electrolyte (LZC) and lanthanum zirconate lithium electrolyte (LLZO) according to the mass ratio of 9:1, and stir for 30 minutes to mix uniformly.

[0092] 2) Mix the mixed inorganic solid electrolyte with polyvinylidene fluoride (PVDF) according to the mass ratio of 4:3, then add N-methyl pyrrolidone (NMP) solvent, and stir for 60 minutes to obtain a uniform slurry. Coating on a glass plate by a flow coating machine, drying to obtain an inorganic solid electrolyte film with a thickness of 10 μm.

[0093] 3) The percentage b of the inorganic solid electrolyte film in the total mass of the solid-liquid electrolyte inside the battery is 50%, the porosity c is 47%, and the tortuosity d is 1.8.

[0094] III. Assembly of lithium ion battery

[0095] 1) Mix the positive electrode material (LMO), the binder PVDF and the conductive agent conductive carbon SP according to the mass ratio of 97:2:1, add NMP solvent and stir uniformly, and stir for 60 minutes to obtain a positive electrode slurry. Then, the positive electrode slurry is coated on an aluminum foil, dried, pressed into a sheet, and a positive electrode sheet is obtained.

[0096] 2) The negative electrode material graphite, binder PVDF and conductive agent conductive carbon SP are mixed in a mass ratio of 94:3:3, deionized water is added and stirred uniformly, and stirring is performed for 60 minutes to obtain a negative electrode slurry. Then, the negative electrode slurry is coated on a copper foil, dried, pressed into a sheet, and a negative electrode sheet is obtained.

[0097] 3) The positive electrode sheet, inorganic solid electrolyte film, separator, inorganic solid electrolyte film, negative electrode sheet are stacked in order, liquid electrolyte is injected, and packaged to obtain a lithium ion battery.

[0098] Example 2: The process for preparing a lithium ion battery in this example is basically the same as that in Example 1, except that the mass percentage of the additive fluoroethylene carbonate (FEC) in the liquid electrolyte is 0.5%.

[0099] Example 3: The process for preparing a lithium ion battery in this example is basically the same as that in Example 1, except that the mass percentage of the additive fluoroethylene carbonate (FEC) in the liquid electrolyte is 2%.

[0100] Example 4: The process for preparing a lithium ion battery in this example is basically the same as that in Example 1, except that the mass percentage of the additive fluoroethylene carbonate (FEC) in the liquid electrolyte is 8%.

[0101] Example 5: The mass percentage of the additive fluoroethylene carbonate (FEC) in the liquid electrolyte is 10%.

[0102] Example 6: The process for preparing a lithium ion battery in this example is basically the same as that in Example 1, except that the porosity of the inorganic solid electrolyte film is 20%.

[0103] Example 7: The process for preparing a lithium ion battery in this example is basically the same as that in Example 1, except that the porosity of the inorganic solid electrolyte film is 30%.

[0104] Example 8: The process for preparing a lithium ion battery in this example is basically the same as that in Example 1, except that the porosity of the inorganic solid electrolyte film is 40%.

[0105] Example 9: The process for preparing a lithium ion battery in this example is basically the same as that in Example 1, except that the porosity of the inorganic solid electrolyte film is 60%.

[0106] Example 10: The process for preparing a lithium ion battery in this example is basically the same as that in Example 1, except that the tortuosity of the inorganic solid electrolyte film is 1.5.

[0107] Example 11: The process for preparing a lithium ion battery in this example is basically the same as that in Example 1, except that the tortuosity of the inorganic solid electrolyte film is 2.

[0108] Example 12: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that the tortuosity of the inorganic solid-state electrolyte membrane is 3.

[0109] Example 13: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that the percentage of the inorganic solid-state electrolyte membrane to the total mass of the solid-liquid electrolyte inside the battery is 1%.

[0110] Example 14: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that the percentage of the inorganic solid-state electrolyte membrane to the total mass of the solid-liquid electrolyte inside the battery is 20%.

[0111] Example 15: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that the percentage of the inorganic solid-state electrolyte membrane to the total mass of the solid-liquid electrolyte inside the battery is 99%.

[0112] Comparative Example 1: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that the mass percentage of fluoroethylene carbonate (FEC) added to the liquid electrolyte is 0.05%.

[0113] Comparative Example 2: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that the mass percentage of fluoroethylene carbonate (FEC) added to the liquid electrolyte is 20%.

[0114] Comparative Example 3: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that no fluoroethylene carbonate (FEC) is added to the electrolyte.

[0115] Comparative Example 4: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that the porosity of the inorganic solid-state electrolyte membrane is 10%.

[0116] Comparative Example 5: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that the tortuosity of the inorganic solid-state electrolyte membrane is 0.01.

[0117] Comparative Example 6: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that the tortuosity of the inorganic solid-state electrolyte membrane is 12.

[0118] Comparative Example 7: The process for preparing the lithium ion battery of this example is substantially the same as that of Example 1, except that the percentage of the inorganic solid-state electrolyte membrane to the total mass of the solid-liquid electrolyte inside the battery is 0.1%.

[0119] Comparative Example 8: The process for preparing lithium ion batteries in this comparative example is basically the same as that in Example 1, the only difference being that no inorganic solid-state electrolyte film is used, only a common separator is used, i.e. no unique capillary effect and low impedance film forming effect.

[0120] Take 23 groups of samples in total in Examples 1-15 and Comparative Examples 1-8, respectively, and perform the following tests, all test results are taken as the average, and some results are rounded off.

[0121] 1) Interface impedance EIS test:

[0122] I. Turn on the power of the electrochemical workstation, when the green indicator light is on, it means it has been turned on;

[0123] II. Open the ETC-lab software on the computer; find the Config option on the homepage, and a drop-down menu appears;

[0124] III. When Connect appears, click directly; if it is Disconnent, do not click;

[0125] IV. Select the channel (1-16); click New;

[0126] V. Set the scan frequency to 0.01 Hz to 1 KHz; start the high-low temperature box;

[0127] VI. After setting the parameters, connect the red, white and blue lines of each example and comparative example battery, and put them into the high-low temperature box to start cooling to -20℃ and constant temperature for 4h to reach thermodynamic equilibrium;

[0128] VII. Start EIS software to start testing.

[0129] 2) Low temperature DCR test:

[0130] I. Prepare each example and comparative example battery at 25℃±2℃ room temperature, and adjust the load to 50% SOC at 1C rate;

[0131] II. Put the battery into the high-low temperature box and cool to -40℃ and constant temperature for 4h to reach thermodynamic equilibrium;

[0132] III. Discharge the battery at 1C rate current I, duration 10s,

[0133] IV. Record the voltage value V1 at the start of discharge and the voltage value V2 at the end of discharge.

[0134] V. Calculate the discharge DCR=(V1-V2) / I.

[0135] 3) Low temperature discharge test:

[0136] I. The prepared batteries of each example and the comparative example were subjected to 1C constant volume 3 cycles (voltage range 3.0V-4.2V) at room temperature 25℃±2℃, and the discharge energy of the 3rd cycle was recorded as E0;

[0137] II. The battery was placed in a high-low temperature box and cooled to -10℃ and kept constant for 4h to reach thermodynamic equilibrium;

[0138] III. The battery was discharged to 3.0V at a current of 1C rate, and the discharge energy was recorded as E1;

[0139] IV. After the battery was restored to room temperature in the high-low temperature box, it was charged to 4.2V at a constant current and constant voltage of 1C rate;

[0140] V. The temperature was lowered to -20℃ and kept constant for 4h to reach thermodynamic equilibrium; the battery was discharged to 3.0V at a current of 1C rate, and the discharge energy was recorded as E2;

[0141] VI. After the battery was restored to room temperature in the high-low temperature box, it was charged to 4.2V at a constant current and constant voltage of 1C rate;

[0142] VII. The temperature was lowered to -40℃ and kept constant for 4h to reach thermodynamic equilibrium; the battery was discharged to 3.0V at a current of 1C rate, and the discharge energy was recorded as E3;

[0143] VIII. The -10℃ / 1C discharge energy retention rate was calculated as E1 / E0; the -20℃ / 1C discharge energy retention rate was calculated as E2 / E0; and the -40℃ / 1C discharge energy retention rate was calculated as E3 / E0;

[0144] 4) Low-temperature fast-charging time test:

[0145] I. The prepared examples and comparative example three-electrode batteries were subjected to 3.0V-4.2V charge-discharge test at room temperature 25℃±2℃, relative humidity 45%-75%, with lithium-plated copper wire as the reference electrode;

[0146] II. First, room temperature IC constant volume three times, 1C rate constant voltage and constant current charging to 4.2V;

[0147] Rest for 10 minutes, 1C constant current discharge to 3.0V;

[0148] III. The battery was placed in a high-low temperature box and cooled to -10℃ and kept constant for 4h to reach thermodynamic equilibrium, and charged to the reference electrode potential of 0V at a constant current of 2C rate, and the charging time T1 was recorded;

[0149] IV. After the battery was restored to room temperature in the high-low temperature box, it was discharged to 3.0V at a constant current of 1C rate;

[0150] V. Cool to -20℃ and keep for 4h to reach thermodynamic equilibrium, charge to the reference electrode potential of 0V at 1C rate, and record the charging time T2;

[0151] 5) Test of the porosity of the electrode sheet (solid-state electrolyte film):

[0152] I. Dry the electrode sheet of the sample battery at 100℃ for 2h to remove surface moisture for pretreatment;

[0153] II. Select a gas adsorption instrument and calibrate and debug, put the pretreated sample into the sample tube of the gas adsorption instrument and seal;

[0154] III. Degassing the sample, remove air and residual moisture in the pores at high temperature;

[0155] IV. Under different pressures, a certain amount of adsorbed gas (such as nitrogen) is introduced into the sample tube, and after adsorption equilibrium, the amount of gas adsorption is measured;

[0156] V. Gradually reduce the pressure to desorb the gas adsorbed on the surface of the sample, and measure the desorption amount under different pressures;

[0157] VI. According to the adsorption and desorption data, use BET theory, BJH model, etc. to calculate the specific surface area, pore volume, tortuosity and other pore structure parameters.

[0158] The test results of the comparative test are shown in the following table:

[0159]

[0160]

[0161] According to the above table, we can know that:

[0162] Examples 1-5: Keep the percentage b of the total mass of the inorganic solid-state electrolyte film in the battery internal solid-liquid electrolyte as 50%, the porosity c of the inorganic solid-state electrolyte film as 47%, and the tortuosity d as 1.8. With the increase of the mass of the additive fluoroethylene carbonate (FEC) in the liquid electrolyte, the -20℃ interface impedance, the -40℃ low-temperature DCR first decreases and then increases, the discharge capacity retention rate tested at low temperature (-10℃, -20℃, -40℃) presents a trend of first increasing and then decreasing, and at -10℃ and -20℃ low temperature, the charging time first becomes fast and then slow. When the mass percentage of FEC in the liquid electrolyte is 5%, the performance of the battery reaches the peak. Therefore, appropriate addition of FEC can improve the impedance, capacity retention rate and charging time of the battery.

[0163] Embodiment 1 and Embodiments 6-9: keeping the mass percentage a of the additive FEC in the liquid electrolyte as 5%, the percentage b of the inorganic solid-state electrolyte film in the total mass of the solid-liquid electrolyte in the battery as 50%, and the tortuosity d as 1.8, as the porosity of the inorganic solid-state electrolyte film increases, the interface impedance at-20℃, the low-temperature DCR at-40℃ first decrease and then increase, the discharge capacity retention rate tested at low temperatures (-10℃, -20℃, -40℃) all show a trend of first increasing and then decreasing, at the same time, the charging time at-10℃ and-20℃ low temperature first becomes fast and then slow, and when the porosity of the inorganic solid-state electrolyte film is 47%, the various performances of the battery reach the peak value. Therefore, the porosity of the inorganic solid-state electrolyte film can optimize the impedance, capacity retention rate and charging time of the battery.

[0164] Embodiment 1 and Embodiments 10-12: keeping the mass percentage a of the additive FEC in the liquid electrolyte as 5%, the percentage b of the inorganic solid-state electrolyte film in the total mass of the solid-liquid electrolyte in the battery as 50%, and the porosity c of the inorganic solid-state electrolyte film as 47%, as the tortuosity increases, the interface impedance at-20℃, the low-temperature DCR at-40℃ also increase, the discharge capacity retention rate tested at low temperatures (-10℃, -20℃, -40℃) all decrease, at the same time, the charging time at-10℃ and-20℃ low temperature gradually becomes long. This is because the larger the tortuosity, the longer the ion transport path, the lower the transmission efficiency, which leads to the increase of the internal resistance of the battery and affects the discharge capacity of the battery; at the same time, high tortuosity will lead to the decrease of the energy density and power density of the battery, affecting the overall performance of the battery. Therefore, according to the experiment, it is concluded that Embodiment 10 is the best embodiment of the present application, so that the comprehensive performance of the battery is optimal.

[0165] Embodiment 1 and Embodiments 13-15: keeping the mass percentage a of the additive FEC in the liquid electrolyte as 5%, the porosity c of the inorganic solid-state electrolyte film as 47%, and the tortuosity d as 1.8, as the percentage b of the inorganic solid-state electrolyte film increases, the interface impedance at-20℃, the low-temperature DCR at-40℃ first decrease and then increase, the discharge capacity retention rate tested at low temperatures (-10℃, -20℃, -40℃) all show a trend of first increasing and then decreasing, at the same time, the charging time at-10℃ and-20℃ low temperature first becomes short and then long, and when the percentage of the inorganic solid-state electrolyte film in the total mass of the solid-liquid electrolyte is 50%, the various performances of the battery are optimal. Therefore, the percentage of the inorganic solid-state electrolyte in the battery has an effect on the impedance, capacity retention rate and charging time of the battery.

[0166] Comparative Example 1 and Comparative Examples 1-3: As can be seen from Comparative Examples 1-2, when the mass percentage of fluoroethylene carbonate (FEC) in the liquid electrolyte is too low or too high, or no FEC is added, the impedance, capacity retention rate and charging time of the battery are all poor, and it is obvious that the battery performance without FEC is worse than that with FEC. Comparative Example 1 and Comparative Example 4: When the porosity of the inorganic solid electrolyte membrane is too low, the performance of the battery at low temperature is only slightly improved. Comparative Example 1 and Comparative Examples 5-6: When the tortuosity of the inorganic solid electrolyte membrane is too small or too large, the interface impedance of the battery is obviously increased, thereby causing the capacity retention rate to decrease and the charging time to be prolonged. Comparative Example 1 and Comparative Examples 7-8: When the inorganic solid electrolyte membrane accounts for too little of the internal solid-liquid electrolyte of the battery or no inorganic solid electrolyte membrane is used, only a common separator is used, i.e., there is no unique capillary effect and low-impedance membrane forming effect, at this time the comprehensive performance of the battery at low temperature is in the worst state, indicating that the inorganic solid electrolyte membrane has a great influence on the battery and plays an important role in the battery.

[0167] It should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A lithium-ion battery, characterized by, The battery comprises a positive electrode, a liquid electrolyte and an inorganic solid electrolyte film, wherein the inorganic solid electrolyte film is located on the surface of the positive electrode active material layer; The liquid electrolyte comprises a fluorinated additive; The fluorinated additive accounts for 0.5%≤a≤10% of the mass percentage of the liquid electrolyte; The inorganic solid electrolyte film accounts for 1%≤b≤99% of the total mass percentage of the solid-liquid electrolyte inside the battery; The inorganic solid electrolyte film has a porosity c≥20% and a tortuosity d of 1.5-3; The inorganic solid electrolyte film comprises at least one of a lithium zirconium chloride electrolyte LZC, a lithium lanthanum zirconate electrolyte LLZO and a lithium titanium aluminum phosphate electrolyte LATP; The fluorinated additive comprises at least one of a fluorinated ethylene carbonate, a bis-fluorinated ethylene carbonate and a tetra-fluorinated ethylene carbonate.

2. The lithium-ion battery of claim 1, wherein, The liquid electrolyte further comprises a non-aqueous organic solvent and an electrolyte salt; The non-aqueous organic solvent comprises at least one of a carbonate solvent, a carboxylic acid ester solvent and a phosphoric acid ester solvent; and the electrolyte salt comprises at least one of a fluorine-containing inorganic lithium salt and a fluorine-containing organic lithium salt.

3. The lithium-ion battery of claim 1, wherein, The inorganic solid electrolyte film has a thickness of 5 μm-20 μm.

4. The lithium-ion battery of claim 3, wherein, The inorganic solid electrolyte film has a thickness of 10 μm.

5. The lithium-ion battery of claim 1, wherein, The battery further comprises a separator and a negative electrode.

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