Solid-state electrolyte material, preparation method thereof, positive electrode sheet and lithium ion battery

Abstract

The application provides a solid-state electrolyte material, a preparation method thereof, a positive electrode sheet and a lithium ion battery. The solid-state electrolyte material comprises a base material and a coating layer coated on the outer surface of the base material; wherein the structure of the base material is Li7La3Zr 2‑ x M x O 12 , wherein 0<=x<=2, M is selected from one or more of Ti, Nb, Al, Ga or Ta; the material of the coating layer has a porous structure, and the average pore size thereof is 5-50 nm; and the weight ratio of the coating layer to the base material is 0.05-2:1. According to the technical scheme, the battery has better safety performance and better electrochemical performance.

Description

Technical Field

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

[0002] In recent years, nickel-cobalt-manganese ternary cathode active materials have received widespread attention. For example, NCM811 cathode material has begun to be industrialized and applied in some electric vehicle models. However, as the nickel content in nickel-cobalt-manganese ternary cathode materials gradually increases, the probability of battery safety accidents also increases.

[0003] The main reason for the reduced battery safety performance is that as the nickel content in the positive electrode material increases, its thermal decomposition temperature and oxygen release temperature gradually decrease. During the phase change and oxygen release process of the positive electrode material, the electrolyte is oxidized and decomposed, releasing a large amount of heat. Under the action of oxygen as a combustion aid, the battery is highly susceptible to explosion, thus reducing its safety performance. Current methods to address this problem mainly include: firstly, coating and modifying the surface of the positive electrode material to reduce contact between the positive electrode material and the electrolyte, thereby reducing side reactions; secondly, using a high thermal stability separator to improve battery safety performance by enhancing the separator's thermal stability; and thirdly, adding solid electrolytes such as lithium lanthanum titanium oxide or lithium lanthanum zirconium oxide to the positive or negative electrode material to modify the positive electrode material and improve battery safety performance. However, on the one hand, the improvement effect of lithium lanthanum zirconium oxy-based solid electrolyte on battery safety performance is very limited; on the other hand, lithium lanthanum zirconium oxy-based solid electrolyte is strongly alkaline. When this solid electrolyte is added to a PVDF-containing solution to prepare electrode sheets, it causes the PVDF structure to degrade and fail, making it impossible to coat the slurry onto the current collector sheet, thus making the electrode sheet preparation process difficult. Therefore, there is an urgent need to provide a new solid electrolyte material to improve the above problems. Summary of the Invention

[0004] The main objective of this invention is to provide a solid electrolyte material to solve the following problems in the prior art of adding solid electrolytes such as lithium lanthanum titanium oxide or lithium lanthanum zirconium oxide to the cathode material: (1) the effect of lithium lanthanum zirconium oxide solid electrolyte on improving battery safety performance is very limited; (2) lithium lanthanum zirconium oxide solid electrolyte is strongly alkaline. When the solid electrolyte is added to the feed solution containing binder (such as PVDF) to prepare the electrode sheet, the binder structure will degrade and fail, making it impossible to coat the feed solution on the current collector, which makes the preparation process of the electrode sheet more difficult.

[0005] To achieve the above objectives, according to one aspect of the present invention, a solid electrolyte material is provided, comprising a matrix material and a coating layer covering the outer surface of the matrix material; wherein the matrix material has a structure of Li7La3Zr. 2-x M x O 12 Where 0≤x≤2, M is selected from one or more of Ti, Nb, Al, Ga or Ta; the coating material has a porous structure and its average pore size is 5 to 50 nm; the weight ratio of the coating material to the matrix material is 0.05 to 2:1.

[0006] Furthermore, the coating layer is made of a porous polymer with an average molecular weight of 100,000 to 400,000; more preferably, the porous polymer is selected from one or more of porous polydopamine, porous polypyrrole, porous polyaniline or porous polystyrene.

[0007] Furthermore, the weight ratio of the coating layer to the matrix material is 0.1 to 1:1.

[0008] Furthermore, the matrix material and the porous polymer are particulate; and the particle size of the matrix material is larger than that of the porous polymer, and the difference in particle size between the matrix material and the porous polymer is between 300 and 700 nm; preferably, the particle size D50 of the matrix material is 10 to 800 nm; preferably, the particle size D50 of the porous polymer is 10 to 500 nm.

[0009] To achieve the above objectives, according to one aspect of the present invention, a method for preparing the aforementioned solid electrolyte material is provided. The method includes: adding a matrix material and a coating layer material to a solvent for mechanical mixing, so that the coating layer material coats the outer surface of the matrix material; removing the solvent to obtain the solid electrolyte material; wherein the matrix material has a structure of Li7La3Zr. 2-x M x O 12 Where 0≤x≤2, M is selected from one or more of Ti, Nb, Al, Ga or Ta; the coating material has a porous structure and its average pore size is 5 to 50 nm.

[0010] Furthermore, during the mechanical mixing process, the stirring rate is 80–150 r / min, and the stirring time is 1–5 h.

[0011] Further, the matrix material and the coating material are added to a solvent to form a mixture with a solid content of 20-70%; preferably, the solvent is selected from N-methyl-2-pyrrolidone and / or anhydrous ethanol; preferably, the solvent is removed by drying, and more preferably the drying temperature is 70-90°C and the drying time is 12-24h.

[0012] According to another aspect of the present invention, a positive electrode sheet is provided, which includes a current collector and a positive electrode layer coated on the outer surface of the current collector. The positive electrode layer includes a positive electrode active material, a conductive agent, a binder, and a solid electrolyte material. The solid electrolyte material is the aforementioned solid electrolyte material, or a solid electrolyte obtained by the aforementioned method for preparing solid electrolyte material.

[0013] Furthermore, the binder in the positive electrode sheet is selected from one or more of PVDF, PTFE, CMC or SBR, more preferably PVDF; preferably, the positive electrode active material is selected from one or more of NCM811, NCM622, Ni92 or Ni90, more preferably NCM811; preferably, the conductive agent is selected from CNTs and / or SP, more preferably CNTs.

[0014] According to another aspect of the present invention, a lithium-ion battery is provided, the lithium-ion battery including the aforementioned positive electrode sheet.

[0015] Applying the technical solution of this invention, firstly, this invention uses the above-mentioned Li7La3Zr 2-x M x O 12 As a matrix material, it exhibits superior thermal stability, resulting in better safety performance of batteries composed of it. Secondly, this invention utilizes the aforementioned Li7La3Zr... 2- x M x O 12 When used as a matrix material, it was found that this matrix material exhibited strong alkalinity during subsequent electrode preparation, leading to the degradation and failure of the binder (such as PVDF), preventing the slurry from being coated and thus failing to obtain an electrode with complete performance. Therefore, this invention creatively coats the outer surface of the matrix material with a porous structure material with an average pore size of 5-50 nm. The porous structure material has a high specific surface area and high adsorption performance. On the one hand, it can quickly capture oxygen released during the phase transition of the cathode material, thereby further improving the safety performance of the battery. On the other hand, using a porous structure material as a coating layer for the matrix material can isolate the matrix material and the binder during the cathode preparation process, thereby effectively preventing the binder from structurally failing in a strong alkaline environment, and thus obtaining an electrode with excellent electrochemical performance. It should be noted that when the average pore size of the material is less than 5 nm, the coating layer cannot effectively and quickly capture oxygen released during the phase transition of the cathode material, and the safety performance of the battery cannot be significantly improved; while when the average pore size of the material is greater than 50 nm, the isolation effect on the binder and solid electrolyte is relatively poor. Furthermore, in order to further improve the rapid oxygen absorption performance of the electrolyte material, thereby enhancing the safety performance of the battery, and to further promote better synergy between the substrate material and the coating material, the weight ratio of the coating material to the substrate material is (0.05~2):1. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 The results of thermal runaway (ARC) tests on the batteries in Embodiments 1 and 2 and Comparative Example 1 of the present invention are shown in the figure. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] The following problems exist when adding solid electrolytes such as lithium lanthanum titanium oxide or lithium lanthanum zirconium oxide to the cathode material in the prior art: (1) The effect of lithium lanthanum zirconium oxide solid electrolyte on improving battery safety performance is very limited; (2) Lithium lanthanum zirconium oxide solid electrolyte is strongly alkaline. When the solid electrolyte is added to the feed solution containing binder (such as PVDF) to prepare the electrode sheet, the binder structure will degrade and fail, making it impossible to coat the feed solution on the current collector sheet, which makes the preparation process of the electrode sheet more difficult.

[0020] To address this problem, the present invention provides a solid electrolyte material comprising a matrix material and a coating layer covering the outer surface of the matrix material. The matrix material has a structure of Li7La3Zr. 2-x M x O 12 Where 0≤x≤2, M is selected from one or more of Ti, Nb, Al, Ga or Ta; the coating material has a porous structure and its average pore size is 5 to 50 nm, for example, it can be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm; the weight ratio of the coating material to the substrate material is 0.05 to 2:1, for example, it can be 0.05:1, 0.1:1, 0.5:1, 1:1, 1.5:1 or 2:1.

[0021] First, this invention uses the above-mentioned Li7La3Zr 2-x M x O 12 As a matrix material, it exhibits superior thermal stability, resulting in better safety performance of batteries composed of it. Secondly, this invention utilizes the aforementioned Li7La3Zr... 2-x M x O 12When used as a matrix material, it was found that this matrix material exhibited strong alkalinity during subsequent electrode preparation, leading to the degradation and failure of the binder (such as PVDF), preventing the slurry from being coated and thus failing to obtain an electrode with complete performance. Therefore, this invention creatively coats the outer surface of the matrix material with a porous structure material with an average pore size of 5-50 nm. The porous structure material has a high specific surface area and high adsorption performance. On the one hand, it can quickly capture oxygen released during the phase transition of the cathode material, thereby further improving the safety performance of the battery. On the other hand, using a porous structure material as a coating layer for the matrix material can isolate the matrix material and the binder during the cathode preparation process, thereby effectively preventing the binder from structurally failing in a strong alkaline environment, and thus obtaining an electrode with excellent electrochemical performance. It should be noted that when the average pore size of the material is less than 5 nm, the coating layer cannot effectively and quickly capture oxygen released during the phase transition of the cathode material, and the safety performance of the battery cannot be significantly improved; while when the average pore size of the material is greater than 50 nm, the isolation effect on the binder and solid electrolyte is relatively poor. Furthermore, in order to further improve the rapid oxygen absorption performance of the electrolyte material, thereby enhancing the safety performance of the battery, and to further promote better synergy between the substrate material and the coating material, the weight ratio of the coating material to the substrate material is (0.05~2):1.

[0022] To better improve the stability and chemical corrosion resistance of porous materials, and to better isolate the matrix material and binder when used as the outer surface of the matrix material, thereby effectively improving the difficult electrode preparation process, the preferred material for the coating layer is a porous polymer with an average molecular weight of 100,000 to 400,000.

[0023] In a preferred embodiment, the porous polymer is selected from one or more of porous polydopamine, porous polypyrrole, porous polyaniline, or porous polystyrene. These porous polymers are commercially available or can be prepared using methods known to those skilled in the art, which will not be elaborated upon here. Compared to other porous materials, the coating material of this application, selected from the above types, can more efficiently capture oxygen released during the phase transition of the cathode material, thereby significantly improving the safety performance of the battery. Simultaneously, such a porous structure material can more effectively isolate the matrix material and the binder, thereby effectively preventing structural failure of the binder in a strongly alkaline environment, and thus enabling the preparation of electrode sheets with excellent electrochemical performance.

[0024] More preferably, in order to enable the porous structure material to better coat the outer surface of the matrix material and promote better synergistic effects between the matrix material and the porous structure material, thereby improving the stability and high adsorption capacity of the electrolyte material, and further improving the safety performance of the battery, both the matrix material and the porous polymer are particulate. The particle size of the matrix material is larger than that of the porous polymer, and the difference in particle size between the matrix material and the porous polymer is between 300 and 700 nm. The particle size D50 of the matrix material is 10–800 nm, and the particle size D50 of the porous polymer is 10–500 nm.

[0025] To further improve the rapid oxygen absorption performance of the electrolyte material, thereby enhancing battery safety, and to further promote better synergy between the substrate material and the coating material, the preferred weight ratio of the coating material to the substrate material is (0.1-1):1, for example, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1 or 1:1.

[0026] Another aspect of the present invention provides a method for preparing a solid electrolyte material, comprising: adding a matrix material and a coating layer material to a solvent for mechanical mixing, so that the coating layer material coats the outer surface of the matrix material; removing the solvent to obtain the solid electrolyte material; wherein the matrix material has the structure Li7La3Zr. 2-x M x O 12 Where 0≤x≤2, M is selected from one or more of Ti, Nb, Al, Ga or Ta; the coating material has a porous structure and its average pore size is 5 to 50 nm.

[0027] For the reasons mentioned above, the solid electrolyte material prepared by this method can make the battery containing it have better safety performance and thermal stability. Moreover, the above preparation method is simple, easy to operate, and has mild conditions, and has broad prospects for industrial application.

[0028] In a preferred embodiment, during mechanical mixing, the stirring rate is 80–150 r / min, and the stirring time is 1–5 h. Under these stirring conditions, the agglomeration of porous polymers in the system can be effectively avoided, allowing them to be more uniformly coated on the outer surface of the matrix material, thereby improving the performance uniformity of the battery.

[0029] To further improve coating uniformity, in a preferred embodiment, the matrix material and the coating material are added to a solvent to form a mixture with a solid content of 20-70 wt%. This application does not impose specific limitations on the solvent, as long as it does not chemically react with the matrix material and the coating material. To further improve coating uniformity, in a preferred embodiment, the solvent is selected from NMP and / or anhydrous ethanol.

[0030] In a preferred embodiment, the solvent is removed by drying. This results in a solid electrolyte material with better structural stability and performance uniformity. More preferably, the drying temperature is 70–90°C and the drying time is 12–24 hours.

[0031] Another aspect of the present invention provides a positive electrode sheet, comprising a current collector and a positive electrode layer coated on the current collector. The positive electrode layer comprises a positive electrode active material, a conductive agent, a binder, and a solid electrolyte material. The solid electrolyte material is any of the aforementioned solid electrolyte materials, or a solid electrolyte obtained by any of the aforementioned solid electrolyte material preparation methods.

[0032] For the reasons mentioned above, during the coating process, the coating layer in the solid electrolyte material can effectively isolate the matrix material and the binder, thereby preventing the binder from structurally failing in a strongly alkaline environment.

[0033] In a preferred embodiment, to improve the adhesion and stability of the electrode sheet during preparation, thereby facilitating the preparation of the positive electrode sheet, the binder for the positive electrode sheet is preferably selected from one or more of PVDF, PTFE, CMC, or SBR, more preferably PVDF. To further improve the electrochemical performance of the positive electrode sheet, the positive electrode active material is preferably selected from one or more of NCM811, NCM622, Ni92, or Ni90, more preferably NCM811. To further increase the number of electron mobility channels in the positive electrode sheet, thereby improving the electrochemical performance of the battery, the conductive agent is preferably selected from CNTs and / or SP, more preferably CNTs.

[0034] To further improve the electrochemical performance and stability of the positive electrode, the preferred mass ratio of positive electrode active material, conductive agent, solid electrolyte material and binder in the positive electrode is 92-97:2-0.5:5-1.5:1.

[0035] Another aspect of the present invention provides a lithium-ion battery comprising the above-described solid electrolyte material, or a solid electrolyte material obtained by the above-described solid electrolyte material preparation method, or comprising the above-described positive electrode sheet. This lithium-ion battery exhibits excellent safety performance and thermal stability, and addresses the difficulty in improving its electrode sheet preparation process.

[0036] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0037] Example 1

[0038] Preparation methods of solid electrolyte materials:

[0039] 1.579 g of matrix material and 157.9 g of coating material were added to 605.3 g of NMP to form a mixture with a solid content of 21%. The mixture was stirred at 120 r / min for 2 h. The system was then placed in a vacuum oven to dry (drying temperature 90℃, treatment time 12 h) to remove NMP, yielding a solid electrolyte material.

[0040] The matrix material is lithium lanthanum zirconium oxide (LLZO), with the structural formula Li7La3Zr2O. 12 The particle size D50 is 350nm; the coating material is porous polydopamine PDA with a particle size D50 of 200nm and an average pore size of 25nm; the weight ratio of the coating material to the matrix material is 0.5:1.

[0041] Example 2

[0042] The only difference from Example 1 is that the average pore size of the coating material is 20 nm.

[0043] Example 3

[0044] The only difference from Example 1 is that the weight ratio of the coating layer to the substrate material is 0.1:1.

[0045] Comparative Example 1

[0046] The only difference from Example 1 is that the coating material is non-porous polydopamine PDA.

[0047] Comparative Example 2

[0048] The only difference from Example 1 is that the weight ratio of the coating layer to the substrate material is 3:1.

[0049] Performance characterization:

[0050] Preparation of the positive electrode sheet:

[0051] Take 51.5g of the solid electrolyte material from the examples and comparative examples respectively, and mix it with 51.5g of binder PVDF, 51.5g of conductive agent CNTs, 5000g of positive electrode active material NCM811 and 1000g of solvent to form a slurry.

[0052] The above slurry is coated on the surface of the current collector (aluminum foil) and dried in a vacuum oven at a temperature of 90°C for 12 hours to obtain the positive electrode sheet.

[0053] In the positive electrode sheet, the mass ratio of positive electrode active material, conductive agent, binder and solid electrolyte material is 95:1:3:1.

[0054] The fabrication of lithium-ion batteries:

[0055] Positive electrode: The positive electrode sheet prepared in the above embodiments and comparative examples;

[0056] Negative electrode: includes current collector (copper foil) and negative electrode layer coated on the current collector. The material of the negative electrode layer is C (graphite):CMC:SBR:SP = 96.2:1.2:1.8:0.8;

[0057] The diaphragm is made of single-sided ceramic with a diameter of 16+4μm.

[0058] A 10Ah pouch cell was fabricated by stacking.

[0059] (1) Battery electrical performance test

[0060] The battery's charge / discharge voltage range for electrical performance testing is 2.8–4.25V, and the current is 0.33C.

[0061] (2) Battery thermal runaway ARC energy test

[0062] The starting temperature is 40℃, the temperature rise step is 5℃, and the temperature rise rate is greater than 0.02℃ / min. The battery is judged to have self-heating and enters the adiabatic mode. The self-heating start temperature is T0. When the battery temperature rise rate reaches 1℃ / min, it can be considered as the start of thermal runaway. The temperature at this time is called Tc. The time from T0 to Tc is recorded as Δt. The highest temperature of thermal runaway is Tp.

[0063] The batteries prepared in the above embodiments and comparative examples were tested, and the results are shown in Tables 1 and 2 below.

[0064] Table 1

[0065]

[0066] Table 2

[0067] Example 1 68.6 142.6 30.8 656.0 Example 2 70.1 153.7 36.6 520.1 Example 3 68.0 150.8 29.3 610.3 Comparative Example 2 65.7 143.5 28.1 600.5 Comparative Example 1 65.5 142.3 28.2 602.3

[0068] As can be seen from the data in Table 1, the positive electrode sheets provided in Examples 1-3 of the present invention have better specific capacity and first-time efficiency compared with the positive electrode sheets in Comparative Examples 1-2.

[0069] from Figure 1As can be seen from the data in Table 2, the positive electrode sheets provided in Examples 1 and 2 of this invention, compared with the positive electrode sheet in Comparative Example 1, show an increased self-heating onset temperature and a significantly longer time to reach the critical temperature. Compared with the non-porous coating layer, the coating layer with a porous structure has a more significant effect on improving the thermal stability of the battery. Furthermore, the battery onset heat release temperature and the time to reach the critical temperature in Example 2 are better than those in Example 1. Therefore, the smaller the pore size of the porous material in the surface coating layer, the more significant the effect on improving battery thermal runaway. The lithium-ion battery prepared with the solid electrolyte material provided by this invention has superior battery thermal stability and safety performance, and the difficulties encountered in its electrode preparation process are improved.

[0070] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A positive electrode sheet, comprising a current collector and a positive electrode layer coated on the outer surface of the current collector, the positive electrode layer comprising a positive electrode active material, a conductive agent, a binder, and a solid electrolyte material, characterized in that, The solid electrolyte material includes a matrix material and a coating layer covering the outer surface of the matrix material; wherein, The matrix material has a structure of Li7La3Zr. 2-x M x O 12 Where 0≤x≤2, and M is selected from one or more of Ti, Nb, Al, Ga or Ta; The coating material has a porous structure and an average pore size of 5-50 nm; the weight ratio of the coating material to the substrate material is 0.05-2:

1. The coating layer is made of a porous polymer with an average molecular weight of 100,000 to 400,000. The porous polymer is selected from one or more of porous polydopamine, porous polypyrrole, porous polyaniline, or porous polystyrene; The binder in the positive electrode sheet is selected from one or more of PVDF, CMC, or SBR.

2. The positive electrode sheet according to claim 1, characterized in that, The weight ratio of the coating layer to the matrix material is 0.1 to 1:

1.

3. The positive electrode sheet according to claim 2, characterized in that, The matrix material and the porous polymer are granular; and the particle size of the matrix material is larger than the particle size of the porous polymer, and the difference in particle size between the matrix material and the porous polymer is between 300 and 700 nm. The particle size D50 of the matrix material is 10~800nm.

4. The positive electrode sheet according to claim 3, characterized in that, The particle size D50 of the porous polymer is 10~500nm.

5. The positive electrode sheet according to claim 1, characterized in that, The method for preparing the solid electrolyte material includes: adding a matrix material and a coating layer material to a solvent for mechanical mixing, so that the coating layer material coats the outer surface of the matrix material; and removing the solvent to obtain the solid electrolyte material. The matrix material has the structure Li7La3Zr. 2-x M x O 12 Where 0≤x≤2, M is selected from one or more of Ti, Nb, Al, Ga or Ta; the coating material has a porous structure and its average pore size is 5~50nm.

6. The positive electrode sheet according to claim 5, characterized in that, During the mechanical mixing process, the stirring rate is 80~150 r / min and the stirring time is 1~5 h.

7. The positive electrode sheet according to claim 5, characterized in that, The matrix material and the coating material are added to the solvent to form a mixture with a solid content of 20-70%; The solvent is selected from N-methyl-2-pyrrolidone and / or anhydrous ethanol.

8. The positive electrode sheet according to claim 7, characterized in that, The solvent is removed by drying.

9. The positive electrode sheet according to claim 8, characterized in that, The drying process is carried out at a temperature of 70-90°C for 12-24 hours.

10. The positive electrode sheet according to claim 9, characterized in that, The positive electrode active material is selected from NCM811 and / or NCM622; The conductive agent is selected from CNTs and / or SPs.

11. The positive electrode sheet according to claim 10, characterized in that, The binder in the positive electrode sheet is PVDF.

12. The positive electrode sheet according to claim 10, characterized in that, The positive electrode active material is NCM811.

13. The positive electrode sheet according to claim 10, characterized in that, The conductive agent is CNTs.

14. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet according to any one of claims 1 to 13.

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