A solid electrolyte interface film and a preparation method thereof, a positive electrode sheet containing the solid electrolyte interface film, and a lithium ion battery

Abstract

The application provides a solid electrolyte film and a preparation method thereof, a positive electrode sheet containing the solid electrolyte interface film and a lithium ion battery, and the preparation method of the solid electrolyte film comprises the following steps: (1) configuring an electrolyte containing tris(trimethylsilyl) phosphate; (2) assembling a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte containing tris(trimethylsilyl) phosphate in step (1) to obtain a lithium ion battery precursor; (3) irradiating the positive electrode sheet area of the lithium ion battery precursor prepared in step (2) with a laser through the electrolyte, so that the solid electrolyte film is formed on the surface of the positive electrode sheet. In the preparation method of the application, the electrolyte outside the laser irradiation area does not participate in the film formation reaction and decomposition, the time required for the formation process is short, the reaction is efficient, and the hydrolysis of tris(trimethylsilyl) phosphate is avoided. The battery prepared by the preparation method of the application has excellent discharge capacity, coulomb efficiency, cycle performance and AC impedance performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and particularly relates to a solid electrolyte interface film, a preparation method thereof, a positive electrode sheet containing the solid electrolyte interface film and a lithium ion battery. BACKGROUND

[0002] Tris(trimethylsilyl)phosphate (TMSP) is a kind of solid-state interface film-forming additive with wide application prospects in lithium ion batteries, which has the advantage of forming films on both positive and negative electrodes. In the existing technical solutions, TMSP film formation depends on the formation process, and the film formation principle of TMSP mainly depends on direct electron transfer in the electrochemical process.

[0003] In the negative electrode, TMSP can silanize the electrolyte and improve the performance of the solid electrolyte interface film (SEI). The reaction equation of TMSP forming SEI film in the negative electrode is as follows:

[0004] [(CH3)9O4PSi3Li + ]+RO - →(CH3)6O3PSi2Li+ROSi(CH3)3(1)

[0005] wherein R is determined by electrolyte components and additive components, and ROSi(CH3)3 is the main organic component of TMSP as SEI film.

[0006] In the positive electrode, not only the silicon atoms in TMSP can accept fluoride ions as electron acceptors, but also the phosphorus atoms can accept hydrogen protons as electron donors. Both of the above combinations can further react with the electrolyte to form the cathode electrolyte interface film (CEI). Benefiting from the advantage of double active sites of TMSP, the film formation in the positive electrode is very efficient; at the same time, it can also effectively remove HF in the electrolyte to prevent swelling and corrosion. The reaction equation of TMSP forming CEI film in the positive electrode is as follows:

[0007] (CH3)6O2PSi2F+C3H4O3→(CH3)6O2PSi2O(CH2)2O(CH2)2F+CO2(2)

[0008] (CH3)9O4PSi3+HF→(CH3)8O3PSi3F+CH3OH(3)

[0009] (CH3)6O3PSi2 . +C3H4O3→(CH3)6O3PSi2O(CH2)2OCOO . (4)

[0010] Wherein, formula (2) and formula (4) are reactions involving phosphorus as active center, formula (3) is a reaction involving silicon as active center, and the formed product itself or in the form of dimer constitutes the main component of the positive CEI film.

[0011] However, the poor hydrolytic stability of TMSP limits its application. TMSP is extremely easy to hydrolyze to form trimethylsilanol and phosphoric acid, which leads to the failure of the additive, limits its application in long-term storage, and causes the film forming effect to not meet the expected effect. The reaction equation of TMSP and trace water in the electrolyte is as follows:

[0012] (CH3)9O4PSi3+H2O→H3PO4+(CH3)3SiOH(5)

[0013] The existing process cannot completely remove the water introduced in the production process, so that the film forming of TMSP is strictly dependent on the operation interval and storage time, which limits the process.

[0014] Currently, the film forming of TMSP often needs to shorten the time interval between feeding and formation, and must strictly ensure that the system is in a water-free and oxygen-free state. Although the literature and patents report the film forming method of TMSP in formation, there is no relevant report on how to avoid the direct regulation of TMSP film forming by electrochemical process.

[0015] In fact, TMSP can decompose at 120-250℃, it can react with the electrolyte in the form of P-O and Si-O bonds to form a solid electrolyte interface film, and this technology is often not considered because such high temperature will cause the decomposition of the electrolyte, eventually causing serious capacity decay and damage to the active material. The adverse effects of high temperature on the electrolyte are far greater than the positive effects brought by film forming.

[0016] Therefore, it is urgent to develop a solid electrolyte interface film forming method that can prepare a lithium ion battery with excellent battery discharge capacity, coulomb efficiency, cycle performance and AC impedance performance, while avoiding most of the electrolyte participating in the film forming reaction and decomposition, shortening the formation process time, improving the reaction efficiency, avoiding TMSP hydrolysis. SUMMARY

[0017] The application provides a forming method of a solid electrolyte interface film, which realizes local temperature concentration on the surface of an electrode by locally irradiating the electrode area with a laser, promotes the decomposition of TMSP on the surface of the electrode and the reaction of the electrolyte to form a solid electrolyte interface film, and the other areas of the electrolyte still remain at room temperature and do not participate in the film forming reaction and decomposition. The method does not need a long formation process, the reaction is efficient, the hydrolysis of TMSP caused by long storage time is avoided, and the battery prepared by the method has excellent discharge capacity, coulomb efficiency, cycle performance and AC impedance performance.

[0018] Specifically, the application provides a method for preparing a solid electrolyte film, which comprises the following steps:

[0019] (1) configuring an electrolyte containing tris(trimethylsilyl) phosphate;

[0020] (2) assembling a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte containing tris(trimethylsilyl) phosphate in step (1) to obtain a lithium ion battery precursor;

[0021] (3) irradiating the positive electrode sheet area of the lithium ion battery precursor prepared in step (2) with a laser through the electrolyte, so that the solid electrolyte film is formed on the surface of the positive electrode sheet to obtain a lithium ion battery intermediate.

[0022] In one or more embodiments, the electrolyte contains an organic solvent, a lithium salt and an additive; in the electrolyte, the content of the organic solvent is 77wt%-89wt% by mass percentage, the content of the lithium salt is 10wt%-18wt%, and the content of the additive is 1wt%-5wt%, and the additive contains tris(trimethylsilyl) phosphate; preferably, the mass of tris(trimethylsilyl) phosphate is 33wt%-100wt% of the total mass of the additive.

[0023] In one or more embodiments, the organic solvent is ethylene carbonate and / or methyl ethyl carbonate.

[0024] In one or more embodiments, the additive further contains vinylene carbonate.

[0025] In one or more embodiments, the lithium salt is LiPF6.

[0026] In one or more embodiments, the positive electrode sheet contains a current collector and a positive electrode material layer on at least one surface of the current collector, and the positive electrode material layer contains a positive electrode active material, a conductive agent and a binder; preferably, the conductive agent is conductive carbon black, the binder is polyvinylidene fluoride, and the positive electrode active material is selected from one or more of lithium nickel cobalt manganese oxide, lithium iron manganese phosphate and LiCO2.

[0027] In one or more embodiments, the pulse power of the laser irradiation is 20-200 mJ / pulse / cm 2 , preferably 20-60 mJ / pulse / cm 2 .

[0028] In one or more embodiments, the pulse frequency of the laser irradiation is 8-12 Hz.

[0029] In one or more embodiments, the pulse width of the laser irradiation is 8-12 ns.

[0030] In one or more embodiments, the beam diameter of the laser irradiation is 8-12 mm.

[0031] In one or more embodiments, the wavelength of the laser irradiation is 1060-1070 nm.

[0032] In one or more embodiments, the time of the laser irradiation is 150-210 s.

[0033] In one or more embodiments, in step (3), after using the laser irradiation, the laser is removed and the lithium ion battery precursor is left to stand for a period of time, and the standing time is 25-35 min.

[0034] The present application provides a solid electrolyte interface film prepared by the method of the present application.

[0035] The present application provides a positive electrode sheet having a solid electrolyte interface film of the present application on the surface.

[0036] The present application provides a lithium ion battery comprising a positive electrode sheet of the present application.

[0037] The present application provides a method for preparing a lithium ion battery, which comprises: forming the lithium ion battery intermediate prepared by the method of the present application at 40-50°C to obtain the lithium ion battery; preferably, the forming time is 35-60 min.

[0038] The present application provides a lithium ion battery prepared by the method of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 A schematic diagram of the decomposition of tris(trimethylsilyl) phosphate under laser beam high temperature in some embodiments of the present application.

[0040] Figure 2 A schematic diagram of the local temperature rise and film formation of tris(trimethylsilyl) phosphate under laser irradiation in some embodiments of the present application. DETAILED DESCRIPTION

[0041] To enable persons skilled in the art to understand the features and effects of the present application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used herein are in the usual meaning understood by those skilled in the art of the present application, and in the event of a conflict, the definition in the present specification shall prevail.

[0042] Theories and mechanisms described and disclosed herein, whether correct or not, should not be considered limiting on the scope of the present application, which can be practiced without regard to any particular theory or mechanism.

[0043] In the present text, "comprise", "include", "contain" and similar words are intended to cover the meaning of "consist essentially of" and "consist of", e.g. if the present text states that a structure "comprises" a component, it should be considered that the structure "consists essentially of" and "consists of" the component, and vice versa.

[0044] In the present text, "comprise", "include", "contain" and similar words are intended to cover the meaning of "consist essentially of" and "consist of", e.g. if the present text states that a structure "comprises" a component, it should be considered that the structure "consists essentially of" and "consists of" the component, and vice versa.

[0045] In the present text, all features defined by a numerical range or a percentage range, such as values, amounts, contents and concentrations, are intended to cover only the numerical range or the percentage range for the sake of brevity and convenience. Accordingly, the description of the numerical range or the percentage range should be considered to cover and specifically disclose all possible sub-ranges and individual values within the range, including integers and fractions.

[0046] In the present text, unless otherwise specified, percentages are intended to mean mass percentages and ratios are intended to mean mass ratios.

[0047] In the present text, when describing embodiments or examples, it should be understood that they are not intended to limit the present application to these embodiments or examples. On the contrary, all alternatives, modifications, and equivalents of the methods and materials described herein, which are intended to be within the scope of the present application, are to be included.

[0048] In the present text, for the sake of brevity, all possible combinations of the technical features in each embodiment or example are not described. Therefore, as long as the combinations of the technical features do not contradict each other, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered to be within the scope of the present specification.

[0049] The present application provides a method for preparing a solid electrolyte membrane, the method comprising the steps of:

[0050] (1) preparing an electrolyte solution comprising tris(trimethylsilyl) phosphate;

[0051] (2) Assembling the positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte containing the tris(trimethylsilyl) phosphate of step (1) to obtain a lithium ion battery precursor;

[0052] (3) Using a laser to irradiate the positive electrode sheet region of the lithium ion battery precursor prepared in step (2) through the electrolyte, so that a solid electrolyte film is formed on the surface of the positive electrode sheet, and a lithium ion battery intermediate is obtained.

[0053] The method for preparing the solid electrolyte film in the present application is shown in Figure 2 The method for preparing the solid electrolyte film in the present application is shown in

[0054] In the present application, the tris(trimethylsilyl) phosphate in the electrolyte is decomposed at a high temperature under laser irradiation, and the principle is shown in Figure 1

[0055] In the present application, the electrolyte contains an organic solvent, a lithium salt, and an additive.

[0056] In the electrolyte of the present application, the content of the organic solvent can be 77wt% to 89wt%, for example, 77wt%, 78wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, or 89wt%, in terms of mass percentage.

[0057] In the electrolyte of the present application, the content of the lithium salt can be 10wt% to 18wt%, for example, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, or 18wt%, in terms of mass percentage.

[0058] In the electrolyte of the present application, the content of the additive can be 1wt% to 5wt%, for example, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, or 5.0wt%, in terms of mass percentage.

[0059] In the present application, the mass of the tris(trimethylsilyl) phosphate can be 33wt% to 100wt% of the total mass of the additive, for example, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, or 100wt%.

[0060] ​In the present application, the organic solvent can be ethylene carbonate and / or methyl ethyl carbonate.

[0061] In the present application, the additive can further comprise vinylene carbonate. In some embodiments, the total mass of vinylene carbonate and tris(trimethylsilyl)phosphate is 1wt% to 5wt% of the mass of the electrolyte, for example 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt%. In some embodiments, the mass of tris(trimethylsilyl)phosphate is 33wt% to 100wt% of the total mass of vinylene carbonate and tris(trimethylsilyl)phosphate, for example 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, 100wt%. In some embodiments, the additive consists of vinylene carbonate and tris(trimethylsilyl)phosphate.

[0062] In the present application, the lithium salt can be LiPF6.

[0063] In the present application, the positive electrode tab comprises a current collector and a positive electrode material layer on at least one surface of the current collector, and the positive electrode material layer comprises a positive electrode active material, a conductive agent, and a binder.

[0064] In the present application, the conductive agent can be conductive carbon black.

[0065] In the present application, the binder can be polyvinylidene fluoride.

[0066] In the present application, the positive electrode active material can be one or more selected from lithium nickel cobalt manganese oxide, lithium iron manganese phosphate, and LiCO2.

[0067] In the present application, the lithium nickel cobalt manganese oxide can be one selected from LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523).

[0068] In the present application, the lithium iron manganese phosphate can be LiMn 0.7 Fe 0.3 PO4.

[0069] In the present application, the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector. The negative electrode current collector can be a material commonly used in the art with excellent conductivity, such as a copper foil. The negative electrode material layer comprises a negative electrode active material, a conductive agent and a binder. The negative electrode material layer is coated on the negative electrode current collector by a negative electrode slurry comprising a negative electrode active material, a conductive agent, a binder and a solvent, and then dried and pressed to obtain. The negative electrode active material, the conductive agent and the binder can be added to the solvent to prepare the negative electrode slurry. The solvent of the negative electrode slurry can be a conventional solvent in the art, such as deionized water. The negative electrode active material can be one or more selected from graphite (including artificial graphite, natural graphite), silicon-carbon negative electrode, hard carbon and lithium titanate, the conductive agent is preferably one or more selected from conductive carbon black (such as acetylene black, ketjen black), carbon fiber, graphene and carbon nanotube, and the binder is preferably one or more selected from fluorine-containing resin, polypropylene resin, fiber type binder, rubber type binder and polyimide type binder. The negative electrode material layer and the negative electrode slurry can also contain a thickening agent, such as sodium carboxymethyl cellulose (CMC-Na).

[0070] The separator in the lithium ion battery of the present application can be a polymer separator, a ceramic separator or a polymer / ceramic composite separator. The polymer separator includes a polyethylene (PE) separator, a polypropylene (PP) separator and a polyethylene terephthalate (PET) separator.

[0071] In the present application, the lithium ion battery precursor is prepared by sequentially rolling, die cutting, drying, winding, assembling, placing in a PET separator, injecting the prepared electrolyte and sealing the positive electrode sheet and the negative electrode sheet.

[0072] In the present application, the pulse power of laser irradiation can be 20-200 mJ / pulse / cm 2 , preferably 20-60 mJ / pulse / cm 2 . In the present application, when the laser beam irradiation step is not used, the local temperature does not rise, the TMSP does not reach the film-forming potential, and the CEI film is not formed at this time. However, in the lithium ion battery prepared under the condition of laser beam irradiation, the CEI film is formed on the positive electrode, and the overall capacity, coulombic efficiency and cycle life of the lithium ion battery are improved. The film thickness of the CEI film is reduced compared to the film thickness of the conventional process, and the film-forming resistance is reduced. However, if the pulse power of the laser is too high, the overall capacity, coulombic efficiency and cycle life of the lithium ion battery decrease. This is because although the beam heating does not diffuse into the electrolyte, it diffuses into the electrode interior. Higher power causes high temperature to destroy the internal structure of the electrode material, and ultimately the active material is affected, and the positive electrode sheet cracks. Therefore, in the present application, the pulse power of laser irradiation is controlled within the preferred range described above, which is beneficial to maintaining excellent overall capacity, coulombic efficiency, cycle life, AC impedance and electrode morphology of the lithium ion battery.

[0073] In the present application, the pulse frequency of laser irradiation can be 8-12 Hz, for example 8 Hz, 9 Hz, 10 Hz, 11 Hz, 12 Hz.

[0074] In the present application, the pulse width of laser irradiation can be 8-12 ns, for example 8 ns, 9 ns, 10 ns, 11 ns, 12 ns.

[0075] In the present application, the beam diameter of laser irradiation can be 8-12 mm, for example 8 nm, 9 nm, 10 nm, 11 nm, 12 nm.

[0076] In the present application, the wavelength of laser irradiation can be 1060-1070 nm, for example 1060 nm, 1062 nm, 1064 nm, 1068 nm, 1070 nm.

[0077] In the present application, the time of laser irradiation can be 150-210 s, for example 150 s, 160 s, 170 s, 180 s, 190 s, 200 s, 210 s. In the present application, the longer the time of laser irradiation, the more complete the film-forming reaction, and the longer the time of laser irradiation, the higher the temperature, which can damage the electrode and the active material. Therefore, controlling the time of laser irradiation within the above range is beneficial to balancing the capacity and cycle life of the battery.

[0078] In step (3) of the present application, after laser irradiation, the laser is removed and the lithium ion battery precursor is left for a period of time, which can be 25-35 min, for example 25 min, 27 min, 29 min, 30 min, 31 min, 33 min, 35 min.

[0079] The present application provides a solid electrolyte interface film prepared by the method of the present application.

[0080] The present application provides a positive electrode sheet having a solid electrolyte interface film of the present application on its surface.

[0081] The present application provides a lithium ion battery comprising a positive electrode sheet of the present application. The lithium ion battery of the present application has excellent overall capacity, coulombic efficiency, cycle life, AC impedance, and electrode morphology.

[0082] The present application provides a method for preparing a lithium ion battery, which comprises: using the lithium ion battery intermediate prepared by the method of the present application to perform formation at 40-50℃ to prepare a lithium ion battery; preferably, the time of formation can be 35-60 min, for example 35 min, 40 min, 45 min, 50 min, 55 min, 60 min.

[0083] The present application also provides a lithium ion battery prepared by the method of the present application.

[0084] Compared with the prior art, the present application has the following beneficial effects:

[0085] (1) In the present application, the TMSP film is formed by local overheating of the electrode area in situ by laser irradiation;

[0086] (2) In the present application, other components of the electrolyte do not participate in the film formation reaction and remain stable;

[0087] (3) Compared with the conventional formation process, the capacity retention rate and the capacity recovery rate are maintained or improved;

[0088] (4) Compared with the conventional formation process, the AC impedance is maintained or decreased;

[0089] (5) The reaction time of laser irradiation in the present application is controlled within 5 minutes, which significantly improves the film formation efficiency and saves time cost compared with the formation process of more than 5 hours.

[0090] The present application will be described below in the manner of specific examples. It should be understood that these examples are merely illustrative and are not intended to limit the scope of the present application. The methods, reagents and materials used in the examples are conventional in the art unless otherwise specified. The raw material compounds in the examples can be purchased through commercial channels.

[0091] Example 1

[0092] (1) Preparation of electrolyte: In a glove box (moisture <0.01 ppm, oxygen content <0.01 ppm), ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were uniformly mixed in a mass ratio of 3:7, and then vinylene carbonate (VC), a film-forming additive, and tris(trimethylsilyl) phosphate, a film-forming additive, were added thereto. After uniform mixing, a basic electrolyte was obtained, with the mass fraction of VC being 2wt% and the mass fraction of TMSP being 1wt%. The basic electrolyte and LiPF6 were uniformly mixed in a mass ratio of 86:14 to prepare the electrolyte;

[0093] (2) Preparation of positive electrode sheet: 210g of polyvinylidene fluoride (PVDF) powder was dissolved in 2791g of N-methyl pyrrolidone (NMP) to prepare a PVDF glue solution with a solid content of 7wt%, which was used as prepared. 10g of positive active material LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811) and 0.3g of conductive carbon black were dry-mixed and stirred uniformly, and then the prepared PVDF glue solution was added to the mixed dry materials. After uniform stirring, the solid content of the slurry was adjusted to 60wt% with NMP, and then coated on a 9μm thick aluminum foil current collector to prepare a positive electrode sheet;

[0094] (3) Preparation of negative electrode sheet: Dissolve 72g of carboxymethyl cellulose (CMC) powder in 3928g of deionized water to prepare CMC adhesive solution with a solid content of 1.8wt% for later use. Mix 5g of hard carbon and 0.17g of conductive agent in dry materials and stir evenly. Then add 6.3g of the aforementioned CMC adhesive solution and 0.51g of styrene-butadiene rubber (SBR) to the mixed dry materials and stir evenly. Adjust the solid content of the slurry to 52.5wt% with deionized water and then coat it on a 6μm thick copper foil current collector to obtain the negative electrode sheet.

[0095] (4) Assembly of lithium-ion battery precursor: The positive electrode sheet and the negative electrode sheet are rolled, die-cut, dried, wound, assembled, placed in a PET separator, injected with the prepared electrolyte, and sealed to obtain the lithium-ion battery precursor.

[0096] (5) Laser film formation: using 20mJ / pulse / cm 2 A laser beam with a pulse frequency of 10Hz, a pulse width of 10ns, a beam diameter of 10mm, and a wavelength of 1064nm is used to irradiate the positive electrode sheet through the electrolyte. After irradiation for 180s, the electrode is left to stand for 30min to obtain a lithium-ion battery intermediate, and the surface of the positive electrode sheet has a solid electrolyte film.

[0097] (6) High-temperature formation: Under the condition of 45°C, the lithium-ion battery intermediate is placed for 20 minutes, charged to 3.45V with a constant current of 0.02C, placed for 5 minutes, charged to 3.45V with a constant current of 0.05C, placed for 5 minutes, charged to 3.65V with a constant current of 0.1C, placed for 5 minutes, and charged to 3.65V with a constant current of 0.2C to obtain the lithium-ion battery.

[0098] Example 2

[0099] All other conditions are the same as in Example 1, except that the laser pulse power is changed from 20 mJ / pulse / cm 2 Replace with 40mJ / pulse / cm 2 .

[0100] Example 3

[0101] All other conditions are the same as in Example 1, except that the laser pulse power is changed from 20 mJ / pulse / cm 2 Replace with 100mJ / pulse / cm 2 .

[0102] Example 4

[0103] All other conditions are the same as in Example 1, except that the laser pulse power is changed from 20 mJ / pulse / cm 2 Replace with 200mJ / pulse / cm 2.

[0104] Example 5

[0105] The other conditions are the same as Example 1, only the positive active material in the preparation of the positive electrode sheet is replaced by LiCO2 from NCM811, and the laser pulse power is replaced by 40 mJ / pulse / cm from 20 mJ / pulse / cm 2 . 2 .

[0106] Example 6

[0107] The other conditions are the same as Example 1, only the positive active material in the preparation of the positive electrode sheet is replaced by LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523) from NCM811, and the laser pulse power is replaced by 40 mJ / pulse / cm from 20 mJ / pulse / cm 2 . 2 .

[0108] Example 7

[0109] The other conditions are the same as Example 1, only the positive active material in the preparation of the positive electrode sheet is replaced by LiMn 0.7 Fe 0.3 PO4 from NCM811, and the laser pulse power is replaced by 40 mJ / pulse / cm from 20 mJ / pulse / cm 2 . 2 .

[0110] Example 8

[0111] The other conditions are the same as Example 1, only the laser pulse power is replaced by 60 mJ / pulse / cm from 20 mJ / pulse / cm 2 . 2 .

[0112] Comparative Example 1

[0113] The other conditions are the same as Example 1, only step (5) is not included, that is, the high-temperature formation process of step (6) is directly performed on the lithium ion battery precursor prepared in step (4).

[0114] Comparative Example 2

[0115] (1) Preparation of the precursor solution: 1wt% tris(trimethylsilyl) phosphate, 2wt% vinylene carbonate, 29.1wt% ethylene carbonate, and 67.9wt% methyl ethyl carbonate are mixed to prepare the precursor solution;

[0116] (2) Preparation of the positive electrode sheet: 210 g of polyvinylidene fluoride (PVDF) powder was dissolved in 2791 g of N-methyl pyrrolidone (NMP) to prepare a PVDF glue solution with a solid content of 7 wt%. The positive electrode active material (LiNi

[0117] The PVDF glue solution was prepared and 10 kg of positive electrode active material (LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811) and 0.3 kg of conductive carbon black were dry-mixed and stirred uniformly. Then the prepared PVDF glue solution was added to the mixed dry materials, and the slurry was stirred uniformly. The solid content of the slurry was adjusted to 60 wt% with NMP, and then coated on a 9 μm thick aluminum foil current collector to prepare a positive electrode sheet.

[0118] (3) Laser film forming: a laser beam with a power of 40 mJ / pulse / cm 2 was irradiated on the positive electrode sheet immersed in the precursor solution through the electrolyte at a pulse frequency of 10 Hz, a pulse width of 10 ns, a beam diameter of 10 mm, and a wavelength of 1064 nm. After irradiation for 180 s, the sample was rested for 30 min to prepare a positive electrode sheet with a solid electrolyte film on the surface.

[0119] (4) Preparation of the electrolyte: in a glove box (moisture <0.01 ppm, oxygen content <0.01 ppm), ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were uniformly mixed in a mass ratio of 3:7. Film-forming additive vinylene carbonate (VC) and film-forming additive tris(trimethylsilyl) phosphate were added to the mixture, and the mixture was stirred uniformly to obtain a base electrolyte. The mass fraction of VC in the base electrolyte was 2 wt%, and the mass fraction of TMSP was 1 wt%. The base electrolyte and LiPF6 were uniformly mixed in a mass ratio of 86:14 to prepare an electrolyte.

[0120] (5) Preparation of the negative electrode sheet: 72 g of carboxymethyl cellulose (CMC) powder was dissolved in 3928 g of deionized water to prepare a CMC glue solution with a solid content of 1.8 wt%. 5 g of hard carbon and 0.17 g of conductive agent were dry-mixed and stirred uniformly. Then 6.3 g of the prepared CMC glue solution and 0.51 g of styrene-butadiene rubber (SBR) were added to the mixed dry materials, and the slurry was stirred uniformly. The solid content of the slurry was adjusted to 52.5 wt% with deionized water, and then coated on a 6 μm thick copper foil current collector to prepare a negative electrode sheet.

[0121] (6) Assembly of the lithium ion battery intermediate: the positive electrode sheet and the negative electrode sheet were sequentially subjected to rolling, die cutting, drying, winding, assembly, PET separation film, injection of the prepared electrolyte, and sealing to prepare a lithium ion battery intermediate.

[0122] (7) high-temperature formation: the lithium-ion battery intermediate was left to stand at 45 °C for 20 min, charged at 0.02 C to 3.45 V, left to stand for 5 min, charged at 0.05 C to 3.45 V, left to stand for 5 min, charged at 0.1 C to 3.65 V, left to stand for 5 min, and charged at 0.2 C to 3.65 V to obtain the lithium-ion battery.

[0123] Test Example

[0124] Cycle test: the battery was left to stand at 25 °C for 30 min, charged at 1 P to 3.65 V, left to stand for 5 min, discharged at 1 P to 2.00 V, left to stand for 5 min, and the above steps were repeated for 50, 100, and 500 cycles, and the discharge capacity data after 50 cycles, the coulombic efficiency data after 100 cycles, and the cycle capacity retention rate data after 500 cycles were collected.

[0125] 100% SOC AC impedance test: the lithium-ion battery was left to stand at 25 °C for 30 min, and the AC impedance data were obtained after charging to 100% SOC.

[0126] CEI film average thickness and electrode morphology test: the electrode morphology was observed using a transmission scanning electron microscope, the CEI film average thickness within 500 nm was calculated, and the cracking condition was related to the morphology.

[0127] The discharge capacity after 50 cycles, the coulombic efficiency after 100 cycles, the cycle capacity retention rate after 500 cycles, the 100% SOC AC impedance, the CEI film average thickness, and the electrode morphology of Test Examples 1-8 and Comparative Examples 1-2 were tested, and the results are shown in Table 1.

[0128] Table 1: Discharge capacity, coulombic efficiency, cycle performance, AC impedance, CEI film average thickness, and electrode morphology of lithium-ion batteries of Examples 1-8 and Comparative Examples 1-2

[0129]

[0130] From the comparison of Comparative Example 1 of the present application with Examples 1, 2, 3, 4, 5, 6, and 7, it can be seen that when the laser beam irradiation step is not used, the TMSP does not reach the film-forming potential and does not decompose to form a CEI film due to the absence of local heating, and the cycle capacity retention rate sharply decreases, thereby verifying the effectiveness of the laser irradiation film-forming method.

[0131] From the comparison of Example 1 and Comparative Example 1 in Table 1, compared with the lithium ion battery prepared without the laser film forming operation step in Comparative Example 1, the lithium ion battery prepared under the laser beam irradiation condition of laser pulse power of 20 mJ / pulse / cm 2 in Example 1 formed a CEI film on the positive electrode, improved the capacity and coulombic efficiency of the whole battery, and the better film forming stability improved the cycle life; in addition, the film thickness of the CEI film was reduced compared with the film thickness of the conventional process, so that it had lower film forming impedance.

[0132] From the comparison of the lithium ion battery prepared under the laser beam irradiation condition of laser pulse power of 20 mJ / pulse / cm 2 in Example 1 and the lithium ion battery prepared under the laser beam irradiation condition of laser pulse power of 20 mJ / pulse / cm 2 in Example 2 in Table 1, increasing the laser pulse power from 20 mJ / pulse / cm 2 to 40 mJ / pulse / cm 2 was beneficial to improve the capacity, coulombic efficiency and cycle life of the whole battery, because the temperature increase caused by higher power was more significant, and the film forming reaction of TMSP and electrolyte was more complete; in addition, the film thickness was also further reduced, which reduced the film forming impedance.

[0133] From the comparison of the lithium ion battery prepared under the laser beam irradiation condition of laser pulse power of 40 mJ / pulse / cm 2 in Example 2 and the lithium ion battery prepared under the laser beam irradiation condition of laser pulse power of 100 mJ / pulse / cm 2 in Example 3 in Table 1, increasing the laser pulse power from 40 mJ / pulse / cm 2 to 100 mJ / pulse / cm 2 was not conducive to the capacity, coulombic efficiency and cycle life of the whole battery. This is because although the beam heating does not diffuse into the electrolyte, it will diffuse into the electrode, and higher power will destroy the internal structure of the electrode material at high temperature, eventually affecting the active material, which reflects the performance decline, and the cracking phenomenon of the positive electrode under the microscope further verifies this conclusion.

[0134] From the comparison of the lithium ion battery prepared under the laser beam irradiation condition of laser pulse power of 100 mJ / pulse / cm 2 in Example 3 and the lithium ion battery prepared under the laser beam irradiation condition of laser pulse power of 200 mJ / pulse / cm 2The data in Table 1 shows that the lithium ion battery prepared under the condition of laser beam irradiation with a laser pulse power of 100 mJ / pulse / cm 2 was raised to 200 mJ / pulse / cm 2 was not conducive to the capacity, coulombic efficiency and cycle life of the battery. This is because although the beam heating does not diffuse into the electrolyte, it diffuses into the electrode interior, and higher power can cause high temperature to destroy the internal structure of the electrode material, ultimately affecting the active material and reflecting the decline in performance, with many obvious cracks appearing in the positive electrode under a microscope.

[0135] The battery performance in Examples 1, 2, 3 and 4 is summarized, and it is concluded that the optimal laser power should be controlled at about 40 mJ / pulse / cm 2 .

[0136] The data in Table 1 shows that the lithium ion battery prepared under the condition of laser beam irradiation with a laser pulse power of 100 mJ / pulse / cm 2 was raised to 200 mJ / pulse / cm 2 was not conducive to the capacity, coulombic efficiency and cycle life of the battery. This is because although the beam heating does not diffuse into the electrolyte, it diffuses into the electrode interior, and higher power can cause high temperature to destroy the internal structure of the electrode material, ultimately affecting the active material and reflecting the decline in performance, with many obvious cracks appearing in the positive electrode under a microscope.

[0137] The data in Table 1 shows that the lithium ion battery prepared under the condition of laser beam irradiation with a laser pulse power of 100 mJ / pulse / cm 2 was raised to 200 mJ / pulse / cm 2 was not conducive to the capacity, coulombic efficiency and cycle life of the battery. This is because although the beam heating does not diffuse into the electrolyte, it diffuses into the electrode interior, and higher power can cause high temperature to destroy the internal structure of the electrode material, ultimately affecting the active material and reflecting the decline in performance, with many obvious cracks appearing in the positive electrode under a microscope.

[0138] The data in Table 1 shows that the lithium ion battery prepared under the condition of laser beam irradiation with a laser pulse power of 100 mJ / pulse / cm 2 was raised to 200 mJ / pulse / cm 2 was not conducive to the capacity, coulombic efficiency and cycle life of the battery. This is because although the beam heating does not diffuse into the electrolyte, it diffuses into the electrode interior, and higher power can cause high temperature to destroy the internal structure of the electrode material, ultimately affecting the active material and reflecting the decline in performance, with many obvious cracks appearing in the positive electrode under a microscope.241680

[0139] The data in Table 1 shows that the lithium ion battery prepared under the condition of laser beam irradiation with a laser pulse power of 100 mJ / pulse / cm 2 was raised to 200 mJ / pulse / cm 2 was not conducive to the capacity, coulombic efficiency and cycle life of the battery. This is because although the beam heating does not diffuse into the electrolyte, it diffuses into the electrode interior, and higher power can cause high temperature to destroy the internal structure of the electrode material, ultimately affecting the active material and reflecting the decline in performance, with many obvious cracks appearing in the positive electrode under a microscope.

[0140] Examples 5, 6 and 7 are summarized to verify the applicability of the laser TMSP decomposition film forming technology, which can be further extended to positive electrode active materials in different application fields.

[0141] From the data comparison in Table 1 of the in-situ laser irradiation positive electrode film forming method in the electrolyte environment in Example 2 and the method of first soaking the positive electrode tab in the precursor solution and then locally laser irradiating to form a film in Comparative Example 2, and then preparing a battery, it can be seen that the in-situ laser irradiation positive electrode film forming method in the electrolyte environment is superior to the method of first soaking the positive electrode tab in the precursor solution and then locally laser irradiating to form a film, and then preparing a battery in improving the battery cycle performance and coulomb efficiency. This is mainly because the in-situ film forming process in the electrolyte is accompanied by changes in the electrolyte components. After the positive electrode is first locally laser irradiated to form a film, the composition of the liquid injected is different from the composition after the consumption of the precursor solution, which affects the compatibility of the film forming in the subsequent formation process. Based on this experimental phenomenon, it is proved that the in-situ laser irradiation positive electrode method is more effective than the method of first forming a positive electrode film in a precursor solution and then preparing a battery in improving the battery cycle performance.

Claims

1. A method for producing a solid electrolyte membrane, characterized by, The method comprises the following steps: (1) configuring an electrolyte containing tris (trimethylsilyl) phosphate; (2) assembling a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte containing tris (trimethylsilyl) phosphate in step (1) to obtain a lithium ion battery precursor; (3) irradiating the positive electrode sheet region of the lithium ion battery precursor prepared in step (2) with laser through the electrolyte, so that the solid electrolyte film is formed on the surface of the positive electrode sheet, and a lithium ion battery intermediate is obtained; The pulse power of the laser irradiation is 20-60 mJ / pulse / cm 2 ; The laser irradiation time is 150-210s.

2. The method of claim 1, wherein, The electrolyte comprises an organic solvent, a lithium salt, and an additive; in the electrolyte, the content of the organic solvent is 77wt%-89wt%, the content of the lithium salt is 10wt%-18wt%, and the content of the additive is 1wt%-5wt%, and the additive comprises tris (trimethylsilyl) phosphate.

3. The method of claim 1, wherein, The mass of tris (trimethylsilyl) phosphate is 33wt%-100wt% of the total mass of the additive.

4. The method of claim 2, wherein, The method has one or more of the following characteristics: The organic solvent is ethylene carbonate and / or methyl ethyl carbonate; The additive further comprises vinylene carbonate; The lithium salt is LiPF6.

5. The method of claim 1, wherein, The positive electrode sheet comprises a current collector and a positive electrode material layer on at least one surface of the current collector, and the positive electrode material layer comprises a positive electrode active material, a conductive agent, and a binder.

6. The method of claim 5, wherein, The conductive agent is conductive carbon black, the binder is polyvinylidene fluoride, and the positive electrode active material is selected from one or more of lithium nickel cobalt manganese oxide, lithium iron manganese phosphate, and LiCO2.

7. The method of claim 1, wherein, The method has one or more of the following characteristics: The pulse frequency of the laser irradiation is 8-12Hz; The pulse width of the laser irradiation is 8-12ns; The beam diameter of the laser irradiation is 8-12mm; The wavelength of the laser irradiation is 1060-1070nm; In step (3), after laser irradiation, the laser is removed, and the lithium ion battery precursor is left to stand for a period of time, and the standing time is 25-35min.

8. A solid electrolyte interface film prepared by the method of any one of claims 1-7.

9. A positive electrode sheet characterized by comprising: The surface of the positive electrode sheet has the solid electrolyte interface film of claim 8.

10. A lithium-ion battery, characterized by, The lithium ion battery comprises the positive electrode sheet of claim 9.

11. A method of making a lithium-ion battery, characterized in that, The method comprises: forming the lithium ion battery intermediate prepared by the method of any one of claims 1-7 at 40-50℃ to obtain the lithium ion battery.

12. The method of claim 11, wherein, The formation time is 35-60min.

13. A lithium ion battery prepared by the method of claim 11 or 12.

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