A solid electrolyte composition, a positive electrode sheet, a method for preparing the same, and a lithium-ion battery.

Abstract

This invention provides a solid electrolyte composition, a positive electrode sheet, a method for preparing the same, and a lithium-ion battery. The solid electrolyte composition includes a conductive agent, lithium dodecyl sulfate, a solid electrolyte, and lithium polyacrylate. A slurry formed from the solid electrolyte composition is coated onto the surface of a positive electrode current collector to form a solid electrolyte conductive coating. Subsequently, a positive electrode active material coating is coated onto the surface of the solid electrolyte conductive coating to obtain the positive electrode sheet. When this positive electrode sheet is used in the assembly of a lithium-ion battery, it not only ensures low ohmic resistance and low interfacial impedance between the positive electrode current collector and the positive electrode active material coating, but also optimizes the battery's overcharge voltage protection.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery material technology, specifically relating to a solid electrolyte composition, a positive electrode sheet and its preparation method, and a lithium-ion battery. Background Technology

[0002] Since their development, lithium-ion batteries have been increasingly widely used in various fields such as electric vehicles, consumer electronics, and energy storage. However, the safety hazards of lithium-ion batteries greatly limit their application, especially under adverse conditions such as overcharging, over-discharging, external pressure, and collisions. These conditions can lead to internal short circuits and significantly increase the risk of battery fire and explosion. Therefore, there is an urgent need for corresponding technical solutions to address this problem.

[0003] Solid electrolytes possess good chemical, electrochemical, and thermal stability, which can prevent internal short circuits during thermal runaway in lithium batteries and improve the battery's resistance to overcharge and overdischarge, thereby enhancing battery safety. Coating the surface of the positive electrode current collector with a solid electrolyte layer ensures battery safety while also giving the current collector both ionic and electronic conductivity, reducing electrode sheet resistance and facilitating the full utilization of the kinetic performance of high-rate positive electrode active materials. However, a single solid electrolyte coating only possesses lithium-ion conductivity and lacks electronic conductivity, thus failing to conduct electricity.

[0004] Existing technology CN116014231A provides a solid electrolyte coating prepared from an inorganic solid electrolyte, a conductive agent, and a binder. This coating is applied to both sides of the negative electrode current collector, followed by a negative electrode active material coating to obtain the negative electrode sheet. Applying this negative electrode sheet to lithium batteries can improve the battery's resistance to overcharge and over-discharge, and reduce the possibility of short circuits during safety tests such as nail penetration, impact, and compression, thereby improving the thermal safety of the lithium battery. However, the formulation of the aforementioned solid electrolyte coating only considers the ohmic internal resistance (sheet resistance) of the current collector and is mainly used for the negative electrode sheet. In actual applications, the interface impedance between the coating and the positive electrode is more significant in affecting the battery's internal resistance performance. This patent does not optimize the coating's interface impedance; therefore, after application to a battery, the excessively high interface impedance results in a large actual battery impedance. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a solid electrolyte composition, a positive electrode sheet, a method for preparing the same, and a lithium-ion battery. The coating formed by the solid electrolyte composition can improve the interfacial impedance between the current collector and the positive electrode active material coating, thereby optimizing the actual impedance of the current collector in the battery.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a solid electrolyte composition comprising, by mass fraction, 35-45% conductive agent, 5-8% lithium dodecyl sulfate, 20-30% solid electrolyte and 20-35% lithium polyacrylate.

[0008] Preferably, the solid electrolyte composition comprises, by mass fraction, 37-45% conductive agent, 5-7% lithium dodecyl sulfate, 20-28% solid electrolyte, and 20-30% lithium polyacrylate.

[0009] Preferably, the solid electrolyte is selected from any one or more of perovskite solid electrolyte, garnet solid electrolyte, NASICON solid electrolyte, ternary lithium fluoride salt or cryolite.

[0010] Preferably, the conductive agent is selected from any one or more of conductive carbon black, carbon black Surpe-P, CNT, acetylene black, Ketjen black, graphite KS-6, graphite KS-15, graphite SFG-6, or graphite SFG-15.

[0011] In a second aspect, the present invention provides a positive electrode sheet comprising a positive current collector, a coating formed by the above-mentioned solid electrolyte composition, and a positive active material coating, which are sequentially compounded together.

[0012] Preferably, the positive current collector is aluminum foil.

[0013] Preferably, the thickness of the solid electrolyte coating is 0.5 to 5 μm.

[0014] Preferably, the thickness of the positive electrode active material coating is 100–300 μm.

[0015] Preferably, the positive electrode active material coating includes a positive electrode active material, a conductive agent, and a binder.

[0016] Preferably, the positive electrode active material includes any one or more of lithium iron phosphate, lithium cobalt oxide, or lithium nickel cobalt manganese oxide.

[0017] Preferably, the conductive agent includes any one or more of conductive carbon black, carbon black Surpe-P, CNT, acetylene black, Ketjen black, graphite KS-6, graphite KS-15, graphite SFG-6, or graphite SFG-15.

[0018] Preferably, the adhesive comprises polyvinylidene fluoride (PVDF) and / or polytetrafluoroethylene (PTFE).

[0019] Thirdly, the present invention provides a method for preparing the above-mentioned positive electrode sheet, comprising the following steps:

[0020] A positive electrode active material, a conductive agent, and a binder are mixed evenly to prepare a positive electrode active material coating slurry; the positive electrode active material coating slurry is coated on the surface of the positive electrode current collector, and after drying, a positive electrode sheet is obtained;

[0021] The surface of the positive current collector contains a solid electrolyte conductive coating.

[0022] Preferably, the method for preparing the positive electrode current collector is as follows: mixing solid electrolyte, conductive agent, lithium polyacrylate and lithium dodecyl sulfate uniformly to prepare a solid electrolyte composition slurry; coating the solid electrolyte composition slurry onto the surface of the positive electrode current collector, and drying it to obtain a positive electrode current collector containing a solid electrolyte conductive coating.

[0023] Fourthly, the present invention provides a lithium-ion battery comprising the positive electrode sheet involved in the above-mentioned technical solution.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention provides a solid electrolyte composition comprising a conductive agent, lithium dodecyl sulfate, a solid electrolyte, and lithium polyacrylate. In this invention, a slurry formed from the solid electrolyte composition is coated onto the surface of a positive electrode current collector to form a solid electrolyte conductive coating. Subsequently, a positive electrode active material coating is coated onto the surface of the solid electrolyte conductive coating to obtain a positive electrode sheet. When this positive electrode sheet is used to assemble a lithium-ion battery, during use, the lithium dodecyl sulfate acts as a guiding agent. Under electrochemical conditions, through its own electrophoretic action, it can directionally induce the growth of an additional gel-state functional transition layer with high ionic conductivity on the surface of the solid electrolyte conductive coating, forming a second-order composite coating. The functional transition layer is a complex interface layer formed by lithium ions, lithium organic compounds, lithium metal compounds, and the electrolyte. It contains both lithium metal compounds (i.e., the solid electrolyte) that are affinity-bonded to the positive electrode active material coating and organic materials (lithium dodecyl sulfate and lithium polyacrylate) that are affinity-bonded to the first coating, thus exhibiting dual interfacial affinity. Simultaneously, it can wet the interfacial pores of the upper and lower layers through the porosity effect, increasing the effective contact area. Interface impedance can be optimized from both surface affinity and effective contact area perspectives. In this invention, lithium polyacrylate is chosen to avoid introducing non-lithium metal ions that would affect the functional transition layer's lithium ion transport capability. Simultaneously, lithium polyacrylate and lithium dodecyl sulfate can act as lithium replenishing materials, accumulating on the surface of the solid electrolyte conductive coating through potential and ion migration effects, forming the functional transition layer. This avoids the large-scale mixing of the solid electrolyte and lithium replenishing materials (both non-conductive materials) in the solid electrolyte conductive coating, which would negatively impact its conductivity.

[0026] The aforementioned functional transition layer, as a transition layer formed based on lithium-ion polymerization, significantly reduces the number of lithium ions inside the functional transition layer (moving towards the negative electrode) when the battery is overcharged or subjected to other abnormal potentials. This results in a change in the structure of the functional transition layer, weakening its ion conduction function and thus providing process protection. Excellent overcharge protection can be achieved through this mechanism.

[0027] In practical applications, the lithium-ion battery provided by this invention, through the combined effect of the solid electrolyte conductive coating and the functional transition layer, can simultaneously ensure low ohmic resistance and low interfacial impedance between the current collector and the positive electrode active material coating, thus optimizing the battery's overcharge voltage protection and offering more comprehensive advantages. Testing shows that the adhesion strength of the solid electrolyte conductive coating is above 40 N / m, and the internal resistance is below 3.5 Ω. Lithium-ion batteries using the positive electrode sheet provided by this invention can achieve an overcharge voltage above 40 V and an interfacial impedance below 2.5 Ω. Attached Figure Description

[0028] Figure 1 Here is a SEM image of the solid electrolyte conductive coating in Example 1;

[0029] Figure 2 SEM image of the functional transition layer formed under electrochemical conditions for assembling a lithium-ion battery using a positive electrode sheet including the solid electrolyte conductive coating from Example 1. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] In view of the problem that in the prior art, the risk of fire and explosion of lithium-ion batteries is greatly increased due to internal short circuits caused by overcharging, over-discharging, external pressure and impact, etc. The present invention provides a solid electrolyte composition comprising, by mass fraction, 35-45% conductive agent, 5-8% lithium dodecyl sulfate, 20-30% solid electrolyte and 20-35% lithium polyacrylate.

[0032] In this invention, the solid electrolyte composition comprises 35-45% conductive agent by mass fraction, more preferably 37-45%. In this invention, the conductive agent, used to provide conductivity, is selected from any one or more of conductive carbon black, carbon black Surpe-P, CNT, acetylene black, Ketjen black, graphite KS-6, graphite KS-15, graphite SFG-6, or graphite SFG-15, preferably carbon black Surpe-P. This invention does not have particular limitations on the source of the conductive agent; commercially available products are acceptable.

[0033] In this invention, the solid electrolyte composition comprises 5-8% lithium dodecyl sulfate by mass fraction, more preferably 5-7% lithium dodecyl sulfate. In this invention, the lithium dodecyl sulfate acts as a guiding agent, used to induce the growth of an additional gel-state functional transition layer with high ionic conductivity on the surface of the conductive coating of the solid electrolyte under formation conditions, after the positive electrode sheet comprising the coating formed by the above-mentioned solid electrolyte composition is installed in the battery. Preferably, the lithium dodecyl sulfate is used as a guiding agent in this invention, not only to guide the formation of the functional transition layer, but also because it contains lithium, it can be used as a lithium supplement material to improve lithium-ion transport capacity. This invention does not have particular restrictions on the source of lithium dodecyl sulfate; commercially available products are acceptable.

[0034] In this invention, the solid electrolyte composition comprises 20-30% solid electrolyte by mass fraction, more preferably 20-28% solid electrolyte. In this invention, the solid electrolyte provides lithium-ion conductivity to the current collector conductive coating and participates in the formation of a functional transition layer. Specifically, it can be selected from any one or more of perovskite solid electrolytes, garnet solid electrolytes, NASICON solid electrolytes, ternary lithium fluoride salts, or cryolite. In this invention, the aforementioned perovskite solid electrolytes, garnet solid electrolytes, NASICON solid electrolytes, or ternary lithium fluoride salts are substances well known to those skilled in the art. For example, the perovskite solid electrolyte can be selected from LLTO, such as lithium lanthanum titanium oxide (Li₂O₃). 3X La 2 / 3-X TiO3, a garnet-type solid electrolyte, can be selected from LLZO, such as lithium lanthanum zirconium oxide (Li7La3Zr2O). 12 NASICON-type solid electrolytes can be selected from LATP, such as lithium aluminum titanium phosphate (LiTi). 1+x Al x Ti 2-x (PO4)3, the ternary lithium fluoride salt can be selected from Li2ZrF6, Li3MCl6, and M is preferably any one or more of In, Y, Er, Zr, Fe or Sc. This invention does not have particular restrictions on the source of the solid electrolyte; commercially available products are sufficient.

[0035] In this invention, the solid electrolyte composition comprises 20-35% lithium polyacrylate by mass fraction, more preferably 20-30% lithium polyacrylate. In this invention, the lithium polyacrylate acts as a binder, satisfying the coating's adhesion requirements and remaining stable within the battery system without generating side reactions detrimental to secondary battery performance. Simultaneously, it contains lithium ions, which can participate in the formation of the functional transition layer, assisting the solid electrolyte in improving lithium-ion transport capacity. This invention does not impose any particular restrictions on the source of the lithium polyacrylate; commercially available products are acceptable.

[0036] In this invention, the slurry formed by the solid electrolyte composition is coated onto the surface of the positive electrode current collector to form a solid electrolyte conductive coating. Then, a positive electrode active material coating is coated onto the surface of the solid electrolyte conductive coating to obtain the positive electrode sheet. When this positive electrode sheet is used to assemble a lithium-ion battery, during use, the lithium dodecyl sulfate acts as a guide agent. Under electrochemical conditions, through its own electrophoretic action, it can directionally induce the growth of an additional gel-state functional transition layer with high ionic conductivity on the surface of the solid electrolyte conductive coating, forming a second-order composite coating. This functional transition layer is a complex interface layer formed by lithium ions, lithium organic compounds, lithium metal compounds, and the electrolyte. It contains both lithium metal compounds (i.e., the solid electrolyte) that are affinity-compatible with the positive electrode active material coating, and organic materials (lithium dodecyl sulfate and lithium polyacrylate) that are affinity-compatible with the first coating. Therefore, it has dual interfacial affinity. Simultaneously, it can wet the interfacial pores of the upper and lower layers through the pore effect, increasing the effective contact area. Interfacial impedance can be optimized from both surface affinity and effective contact area perspectives. In this invention, lithium polyacrylate is chosen to avoid introducing non-lithium metal ions that could affect the lithium-ion transport capability of the functional transition layer. Simultaneously, lithium polyacrylate and lithium dodecyl sulfate can serve as lithium-replenishing materials, concentrating on the surface of the solid electrolyte conductive coating through potential and ion migration effects, forming a functional transition layer. This avoids the large-scale mixing of the solid electrolyte and lithium-replenishing materials (both non-conductive materials) in the solid electrolyte conductive coating, which would negatively impact its conductivity.

[0037] In this invention, the thickness of the solid electrolyte conductive coating is 0.5–5 μm, preferably 1–3 μm. The functional transition layer is spontaneously formed during battery formation and has a thickness of approximately 30–60% of the solid electrolyte conductive coating, preferably 40–50%.

[0038] Tests showed that the adhesion of the solid electrolyte conductive coating was above 40 N / m and the internal resistance was below 3.5 Ω.

[0039] The present invention also provides a positive electrode sheet comprising a positive current collector, a coating formed by the above-mentioned solid electrolyte composition, and a positive active material coating sequentially laminated together. The solid electrolyte composition coating is applied to the surface of the positive current collector; the positive current collector is preferably an aluminum foil; the thickness of the solid electrolyte coating is preferably 0.5–5 μm, more preferably 1–3 μm. The positive active material coating is applied to the surface of the solid electrolyte composition coating; the thickness of the positive active material coating is preferably 100–300 μm, more preferably 150–200 μm.

[0040] In this invention, the positive electrode active material coating comprises a positive electrode active material, a conductive agent, and a binder. The positive electrode active material comprises any one or more of lithium iron phosphate, lithium cobalt oxide, or lithium nickel cobalt manganese oxide; the conductive agent comprises any one or more of conductive carbon black, carbon black Surpe-P, CNT, acetylene black, Ketjen black, graphite KS-6, graphite KS-15, graphite SFG-6, or graphite SFG-15; and the binder comprises PVDF and / or PTFE.

[0041] The present invention also provides a method for preparing the above-mentioned positive electrode sheet, comprising the following steps:

[0042] A positive electrode active material, a conductive agent, and a binder are mixed evenly to prepare a positive electrode active material coating slurry; the positive electrode active material coating slurry is coated on the surface of the positive electrode current collector, and after drying, a positive electrode sheet is obtained;

[0043] The surface of the positive current collector contains a solid electrolyte conductive coating.

[0044] According to this invention, a solid electrolyte, a conductive agent, lithium polyacrylate, and lithium dodecyl sulfate are first mixed uniformly to prepare a solid electrolyte composition slurry. The selection and amount of the solid electrolyte, conductive agent, lithium polyacrylate, and lithium dodecyl sulfate are as described in the relevant content of the above technical solution, and will not be repeated here. The mixing is preferably carried out under stirring conditions. Then, the solid electrolyte composition slurry is coated onto the surface of the positive electrode current collector, and after drying, a positive electrode current collector containing a solid electrolyte conductive coating is obtained. This invention does not impose any particular limitation on the above coating technique, and techniques well known to those skilled in the art can be used. In some embodiments of this invention, a transfer micro-grooving roller is preferably used for coating. The drying temperature is preferably 60-80°C. The above coating is preferably applied to one side of the positive electrode current collector.

[0045] Then, the positive electrode active material, conductive agent, and binder are mixed evenly to prepare a positive electrode active material coating slurry. The selection of the positive electrode active material, conductive agent, and binder is as described in the relevant content of the above technical solution, and will not be repeated here. In some embodiments of the present invention, it is preferred to mix the positive electrode active material, conductive agent, and binder evenly according to the mass ratio of 95% positive electrode, 2% conductive agent, and 3% binder to prepare a positive electrode active material coating slurry. The mixing is preferably carried out under stirring conditions. Then, the positive electrode active material coating slurry is coated on the surface of the positive electrode current collector, i.e., the surface of the solid electrolyte conductive coating, and dried to obtain a positive electrode sheet containing the solid electrolyte conductive coating and the positive electrode active material coating. The present invention does not have any particular limitation on the above coating technology, and technology known to those skilled in the art can be used. In some embodiments of the present invention, it is preferred to use a pressure coating device for coating. The drying temperature is preferably 50-70°C.

[0046] The method for preparing the above-mentioned positive electrode sheet provided by the present invention is simple, convenient, easy to implement, and conducive to large-scale production.

[0047] In some embodiments of the present invention, a positive electrode sheet is obtained according to the above method, using lithium iron phosphate as the positive electrode active material; conductive carbon black as the conductive agent; PVP K30 as the dispersant; PVDF as the binder; and NMP as the solvent. The mass ratio of the positive electrode active material, conductive agent, dispersant, and binder is (94-98):(0.5-1.5):(0.3-0.9):(0.3-0.9), specifically, for example, 96:1:0.6:0.6. The solvent is added and mixed to prepare a positive electrode slurry with a solid content of 45%-55%. The mixing is called stirring. The thickness of the positive electrode slurry coating is preferably 95-105 μm, more preferably 100 μm.

[0048] This invention also provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is as described in the relevant content of the above technical solution and will not be repeated here. The secondary battery may be a lithium-ion battery.

[0049] In some embodiments of the present invention, the method for preparing the negative electrode includes the following steps:

[0050] The negative electrode active material, conductive agent, binder, thickener and solvent are mixed to obtain the negative electrode slurry;

[0051] The negative electrode slurry is uniformly coated on the surface of the negative electrode current collector. After drying, the resulting film is cold-pressed and slit to obtain the negative electrode sheet.

[0052] The preferred anode active material is artificial graphite, the preferred conductive agent is conductive carbon black, the preferred binder is styrene-butadiene rubber (SBR), the preferred thickener is sodium carboxymethyl cellulose (CMC), and the preferred solvent is deionized water. The preferred mass ratio of the anode active material, conductive agent, binder, and thickener is (93–100):(0.4–1.2):(0.4–1.2):(0.8–1.6), specifically, for example, 96.2:0.8:0.8:1.2. Deionized water is added and mixed thoroughly to prepare a anode slurry with a solid content of 50%–60%. The mixing is performed by stirring.

[0053] The thickness of the negative electrode slurry coating is preferably 105-115 μm, more preferably 110 μm.

[0054] The negative electrode current collector is copper foil.

[0055] The diaphragm can be commercially available, including PE membrane, PE diaphragm with ceramic coating, PP membrane, PP diaphragm with ceramic coating, or non-woven fabric diaphragm. The thickness of the PE membrane (or PP diaphragm) is 5–20 μm; in the PE diaphragm and PP diaphragm with ceramic coating, the thickness of the PE membrane (or PP diaphragm) is 5–20 μm, and the thickness of the ceramic coating is 0.5–5 μm.

[0056] In some embodiments of the present invention, the electrolyte is a LiPF6 solution, wherein the solvent comprises ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7; and the mass concentration of the LiPF6 solution is 12.5%.

[0057] The present invention also provides a method for preparing the secondary battery described above, comprising the following steps:

[0058] The positive electrode, the separator, and the negative electrode are stacked and wound sequentially to obtain the electrode assembly;

[0059] The electrode assembly is placed in the outer packaging, electrolyte is added, and after sealing, standing, formation, and aging, a secondary battery is obtained.

[0060] The present invention does not impose any special restrictions on the source of the raw materials used above, and they can be commercially available products.

[0061] Taking lithium-ion batteries as an example, tests have shown that lithium-ion batteries using positive electrode sheets with a solid electrolyte conductive coating provided by this invention can achieve an overcharge voltage of over 40V and an interface impedance of less than 2.5Ω.

[0062] To further illustrate the present invention, the following embodiments provide a detailed description. The experimental materials used in the following embodiments of the present invention are all commercially available products.

[0063] Example 1

[0064] This embodiment provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0065] S1: 38wt% carbon black Surpe-P, 7wt% lithium dodecyl sulfate, 28wt% LATP, and 27wt% lithium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0066] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0067] The SEM image of the first coating of the solid electrolyte conductive coating formed above is shown below. Figure 1 As shown, a positive electrode sheet including the solid electrolyte conductive coating is used to assemble a lithium-ion battery. Under electrochemical conditions, the SEM image of the second-order composite coating of the solid electrolyte conductive coating is shown below. Figure 2 As shown, under electrochemical conditions, the solid electrolyte conductive coating will form a dense second coating that covers the surface of the first coating.

[0068] Example 2

[0069] This embodiment provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0070] S1: 35wt% carbon black Surpe-P, 7wt% lithium dodecyl sulfate, 28wt% LATP, and 30wt% lithium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0071] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0072] Example 3

[0073] This embodiment provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0074] S1: 45wt% carbon black Surpe-P, 7wt% lithium dodecyl sulfate, 23wt% LATP, and 25wt% lithium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0075] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0076] Example 4

[0077] This embodiment provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0078] S1: 43wt% carbon black Surpe-P, 5wt% lithium dodecyl sulfate, 28wt% LATP, and 24wt% lithium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0079] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0080] Example 5

[0081] This embodiment provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0082] S1: 43wt% carbon black Surpe-P, 7wt% lithium dodecyl sulfate, 20wt% LATP, and 30wt% lithium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0083] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0084] Comparative Example 1

[0085] This comparative example provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0086] S1: 38wt% carbon black Surpe-P, 7wt% lithium dodecyl sulfate, 28wt% LATP, and 27wt% sodium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0087] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0088] Comparative Example 2

[0089] This comparative example provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0090] S1: 38wt% carbon black Surpe-P, 7wt% lithium dodecyl sulfate, 28wt% LATP, and 27wt% polyvinyl alcohol are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0091] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0092] Comparative Example 3

[0093] This comparative example provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0094] S1: 38wt% carbon black Surpe-P, 7wt% lithium benzoate, 28wt% LATP, and 27wt% polyvinyl alcohol are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0095] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0096] Comparative Example 4

[0097] This comparative example provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0098] S1: 32wt% carbon black Surpe-P, 7wt% lithium dodecyl sulfate, 30wt% LATP, and 31wt% lithium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0099] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0100] Comparative Example 5

[0101] This comparative example provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0102] S1: 48wt% carbon black Surpe-P, 7wt% lithium dodecyl sulfate, 23wt% LATP, and 22wt% lithium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0103] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0104] Comparative Example 6

[0105] This comparative example provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0106] S1: 40wt% carbon black Surpe-P, 3wt% lithium dodecyl sulfate, 28wt% LATP, and 29wt% lithium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0107] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0108] Comparative Example 7

[0109] This comparative example provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0110] S1: 42wt% carbon black Surpe-P, 7wt% lithium dodecyl sulfate, 18wt% LATP, and 33wt% lithium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0111] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0112] Comparative Example 8

[0113] This comparative example provides a solid electrolyte conductive coating, the preparation method of which is as follows:

[0114] S1: 44wt% carbon black Surpe-P, 8wt% lithium dodecyl sulfate, 32wt% LATP, and 16wt% lithium polyacrylate are placed in deionized water and stirred to prepare a solid conductive paste A with a solid content of 15%.

[0115] S2: Solid conductive paste A is coated onto aluminum foil and dried to form a solid electrolyte conductive coating with a thickness of 2μm.

[0116] The solid electrolyte conductive coatings obtained in the examples and comparative examples were subjected to corresponding tests, and the test methods are as follows:

[0117] Overshoot voltage:

[0118] (1) Preparation of the positive electrode sheet:

[0119] 1-1) The positive electrode active material (lithium iron phosphate), conductive agent (conductive carbon black), dispersant (PVP K30), binder (PVDF) and solvent NMP are stirred and mixed to obtain a positive electrode slurry; the mass ratio of the positive electrode active material, conductive agent, dispersant and binder is 96:1:0.6:0.6, and NMP solvent is added to prepare a positive electrode slurry with a solid content of 50%;

[0120] 1-2) The positive electrode slurry is uniformly coated (the coating thickness is 100 μm) on the surface of the aluminum foil with the solid electrolyte conductive coating obtained in the examples and comparative examples. After drying, the resulting film is cold-pressed and slit to obtain the positive electrode sheet.

[0121] (2) Preparation of negative electrode sheet:

[0122] 2-1) The negative electrode active material (artificial graphite), conductive agent (conductive carbon black), binder (styrene-butadiene rubber), thickener (sodium carboxymethyl cellulose) and solvent (deionized water) are stirred and mixed to obtain a negative electrode slurry; the mass ratio of the negative electrode active material, conductive agent, binder and thickener is 96.2:0.8:0.8:1.2, and deionized water is added to prepare a negative electrode slurry with a solid content of 50%;

[0123] 2-2) The negative electrode slurry is uniformly coated (the coating thickness is 110 μm) on the surface of the copper foil. After drying, the resulting film is cold-pressed and slit to obtain the negative electrode sheet.

[0124] (3) Following the above method, the positive electrode, negative electrode, electrolyte, and separator are wound or stacked in a conventional manner to form a battery cell; the electrolyte is a LiPF6 solution, wherein the solvent includes ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7; the mass concentration of the LiPF6 solution is 12.5%; the separator is a PE film (12 μm thick);

[0125] (4) After the cells are encased, injected with electrolyte, sealed, formed, and tested for capacity, qualified batteries are selected as test samples.

[0126] (5) At room temperature and pressure, charge the qualified battery to the charging termination voltage at a rate of 0.5C, and then switch to constant voltage charging until the charging current rate drops to 0.02C. At this time, the battery capacity is fully charged.

[0127] (6) Install the battery on a DC withstand voltage tester, connect the power supply, adjust the voltage, and take the minimum voltage at which the battery does not show abnormal current and voltage fluctuations within 1 hour and does not short circuit or break down as the overshoot voltage.

[0128] Adhesion test:

[0129] 1. In the above embodiments and comparative examples, after obtaining a solid electrolyte conductive coating on the surface of aluminum foil, the current collector sample is cut into a width of 20 mm and a length of 220 mm using a cutter.

[0130] 2. Adhere the current collector sample to the test plate, ensuring the coating of the current collector sample (hereinafter referred to as the sample) is adhered to the test plate (sample width 20mm, length 220mm).

[0131] 3. Press back and forth three times with the pressure roller to ensure that the sample is precisely adhered to the test plate; fold one end of the sample 180° toward the side of the test plate where the test sample is adhered.

[0132] 4. Clamp one end of the test plate onto the upper fixture of the tensile testing machine, and clamp the free end of the test sample onto the lower fixture of the tensile testing machine. Then start the tensile testing machine to perform the test.

[0133] 5. Record the peel distance and peel force between the coating and the base film to obtain the peel strength. Interface impedance and ohmic internal resistance:

[0134] 1. Using IVIUM electrochemicals from the Netherlands, the battery EIS curves were tested according to industry standard procedures, and graphical fitting was performed.

[0135] 2. Based on the points where the fitted curves fall, the ohmic impedance and interface impedance of the battery can be obtained.

[0136] The test results are shown in Table 1 below:

[0137] Table 1

[0138]

[0139] As shown in Table 1, the solid electrolyte conductive coating provided by the present invention has an adhesion strength of over 40 N / m and an internal resistance of less than 3.5 Ω. A lithium-ion battery using a positive electrode sheet incorporating the solid electrolyte conductive coating provided by the present invention can achieve an overcharge voltage of over 40 V and an interface impedance of less than 2.5 Ω. This indicates that in the practical application of lithium-ion batteries, the combined effect of the solid electrolyte conductive coating and the functional transition layer can simultaneously ensure low ohmic resistance and low interface impedance between the positive current collector and the positive active material coating, and optimize the overcharge voltage protection of the battery.

[0140] A comparison of the data from Examples 1-5 with Comparative Examples 1-2 shows that replacing lithium polyacrylate with non-lithium salt organic binders such as sodium polyacrylate or polyvinyl alcohol can affect the formation of the functional transition layer because non-lithium salt organic binders do not contain lithium ions. This results in poor lithium ion transfer in the functional transition layer, manifested as an increase in internal resistance and interface impedance, as well as a decrease in overshoot voltage.

[0141] A comparison of the data from Examples 1-5 with Comparative Example 3 shows that replacing lithium dodecyl sulfate with lithium benzoate results in a poor guiding effect, failing to positively assist the enrichment and formation of the functional transition layer at the corresponding interface, leading to poor optimization of the battery's interface impedance and ohmic impedance, and a reduction in overcharge voltage.

[0142] A comparison of the data from Examples 1-5 with Comparative Example 4 shows that when there is too little conductive carbon black, the density of the solid electrolyte conductive coating network is insufficient, resulting in excessively high internal resistance.

[0143] A comparison of the data from Examples 1-5 with Comparative Example 5 shows that when there is too much conductive carbon black, the high specific surface area and adsorption capacity of the carbon material lead to the adsorption of too much lithium polyacrylate and lithium compound ions on the carbon surface, which affects the bonding effect of lithium polyacrylate and the participation of lithium polyacrylate in the formation of the functional transition layer. At the same time, it leads to the proportion of the material forming the functional transition layer being too small, resulting in a decrease in overshoot voltage and bonding force.

[0144] A comparison of the data from Examples 1-5 and Comparative Example 6 shows that when there is too little lithium dodecyl sulfate, some substances remain in the conductive coating during the formation of the functional transition layer, affecting the ohmic resistance of the conductive coating. Consequently, fewer functional transition layers are formed, resulting in poor overshoot voltage protection performance.

[0145] As can be seen from the comparison of the data of Examples 1-5 and Comparative Example 7, when the amount of solid electrolyte is too small, the functional transition layer is insufficient, resulting in insufficient interfacial affinity, high interfacial impedance, and poor protection of overshoot voltage by the functional transition layer.

[0146] A comparison of the data from Examples 1-5 with Comparative Example 8 shows that when the amount of lithium polyacrylate is too small, the coating peel strength is insufficient, making it prone to delamination and resulting in insufficient battery safety. Furthermore, increasing the proportion of lithium dodecyl sulfate does not optimize the interfacial impedance; therefore, lithium dodecyl sulfate should not be added excessively to avoid reducing the proportion of other effective substances.

[0147] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a solid electrolyte conductive coating, characterized in that, The solid electrolyte composition comprises, by mass fraction, 35-45% conductive agent, 5-8% lithium dodecyl sulfate, 20-30% solid electrolyte and 20-35% lithium polyacrylate; The slurry formed by the solid electrolyte composition is coated on the surface of the positive electrode current collector to form a solid electrolyte conductive coating.

2. The method for preparing a solid electrolyte conductive coating according to claim 1, characterized in that, The solid electrolyte composition comprises, by mass fraction, 37-45% conductive agent, 5-7% lithium dodecyl sulfate, 20-28% solid electrolyte, and 20-30% lithium polyacrylate.

3. The method for preparing a solid electrolyte conductive coating according to claim 1, characterized in that, The solid electrolyte is selected from any one or more of the following: perovskite solid electrolyte, garnet solid electrolyte, NASICON solid electrolyte, ternary lithium fluoride salt, or cryolite.

4. The method for preparing a solid electrolyte conductive coating according to claim 1, characterized in that, The conductive agent is selected from any one or more of the following: carbon black Surpe-P, CNT, acetylene black, Ketjen black, graphite KS-6, graphite KS-15, graphite SFG-6, or graphite SFG-15.

5. A positive electrode sheet, characterized in that, It includes a positive electrode current collector, a solid electrolyte conductive coating, and a positive electrode active material coating that are sequentially composited; The solid electrolyte conductive coating is prepared according to the preparation method of any one of claims 1 to 4.

6. The positive electrode sheet according to claim 5, characterized in that, The positive current collector is aluminum foil.

7. The positive electrode sheet according to claim 5, characterized in that, The thickness of the solid electrolyte conductive coating is 0.5~5 μm; The thickness of the positive electrode active material coating is 100~300μm.

8. The positive electrode sheet according to claim 5, characterized in that, The positive electrode active material coating includes a positive electrode active material, a conductive agent, and a binder; The positive electrode active material includes any one or more of lithium iron phosphate, lithium cobalt oxide, or lithium nickel cobalt manganese oxide. The conductive agent includes any one or more of the following: carbon black Surpe-P, CNT, acetylene black, Ketjen black, graphite KS-6, graphite KS-15, graphite SFG-6, or graphite SFG-15. The adhesive includes polyvinylidene fluoride and / or polytetrafluoroethylene.

9. A method for preparing a positive electrode sheet as described in any one of claims 5 to 8, characterized in that, Includes the following steps: A positive electrode active material, a conductive agent, and a binder are mixed evenly to prepare a positive electrode active material coating slurry; the positive electrode active material coating slurry is coated on the surface of the positive electrode current collector, and after drying, a positive electrode sheet is obtained; The surface of the positive current collector contains a solid electrolyte conductive coating.

10. The method for preparing the positive electrode sheet according to claim 9, characterized in that, The method for preparing the positive electrode current collector is as follows: a solid electrolyte, a conductive agent, lithium polyacrylate and lithium dodecyl sulfate are mixed evenly to prepare a solid electrolyte composition slurry; the solid electrolyte composition slurry is coated onto the surface of the positive electrode current collector and dried to obtain a positive electrode current collector containing a solid electrolyte conductive coating.

11. A lithium-ion battery, characterized in that, The positive electrode sheet comprising any one of the positive electrode sheets described in claims 5 to 8 or the positive electrode sheet prepared by the preparation method according to claim 9 or 10.

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