Coating material manufacturing method, electrode material manufacturing method, and battery manufacturing method

Abstract

A coating material manufacturing method according to the present disclosure is a method for manufacturing a coating material of an electrode material containing a lithium oxide, the method comprising: a biomass mixing step for obtaining a slurry by mixing a plant-based biomass with a solvent; a heating step for heating the slurry obtained in the biomass mixing step; a solid-liquid separation step for subjecting the slurry heated in the heating step to solid-liquid separation; and a distillation step for distilling a liquid phase obtained in the solid-liquid separation step.

Description

Coating material manufacturing method, electrode material manufacturing method, and battery manufacturing method

[0001] The present disclosure relates to a method for manufacturing a coating material, a method for manufacturing an electrode material, and a method for manufacturing a battery.

[0002] As the need to move away from fossil fuels grows and the market for electric vehicles and other products expands, there is a growing demand for higher capacity and higher output lithium-ion batteries. Electrode materials for lithium secondary batteries are required to have high potential and high capacity. For example, LiCoO ２ Cobalt (Co) is widely used as a high-capacity positive electrode material, but there are issues with supply chain and cost stability due to the bias in the countries where it is produced, as well as safety issues such as instability during charging. To address this issue, ternary (NCM-based) positive electrode materials in which part of the cobalt is replaced with nickel (Ni) or manganese (Mn), and cobalt-free iron phosphate-based positive electrode materials have been developed.

[0003] The performance of electrode materials requires not only high potential and high capacity but also cycle characteristics. For example, NCM-based positive electrode materials deteriorate in cycle characteristics due to contact with the electrolyte, decomposition of the electrolyte, and an increase in surface resistance. In addition, iron phosphate-based positive electrode materials such as LiFePO ４ (LFP) has relatively low electrical conductivity (10 －１０ ~10 －５ S / cm), and at high current rates, the potential and capacity decrease, resulting in poor performance during high-speed charge and discharge. ２ Even in (LCO), the magnitude of its electrical conductivity (about 10 －３ S / cm) is not necessarily sufficient.

[0004] LiNi ０．５ Mn １．５ O ４ (LNMO) has a relatively large theoretical capacity and a high operating potential (about 4.7 V vs. Li / Li ＋ ) and is free of the rare metal cobalt, so it is expected to be a new high energy density cathode material. On the other hand, due to the high voltage, the cycle characteristics are significantly reduced due to the reaction with the electrolyte, and the electrical conductivity is low (10 －６S / cm), the potential and capacity tend to decrease during high-speed charging and discharging.

[0005] To solve these problems, coatings are being carried out on the surface of cathode materials. For example, by adding polysilazane, a type of inorganic polymer, to cathode active materials such as LFP, LCO, and LNMO, SiO ２ A method has been proposed in which a coating is applied to prevent the electrolyte from reacting with the positive electrode (see Patent Document 1).In addition, a method has been proposed in which an organic solvent such as glycerol or an organic compound such as glucose or sucrose is mixed with an LFP precursor as a carbon source, and the mixture is then fired under an inert atmosphere to produce a carbon-coated LFP nanopowder (see Patent Documents 2-4).

[0006] Japanese Patent Application Laid-Open No. 2022-071406 Special Publication No. 2015-530965 Special Publication No. 2016-509564 Special Publication No. 2015-530344

[0007] However, coating with inorganic materials cannot be expected to improve electronic conductivity. Furthermore, when coating with carbon, the carbon reduces Co, Ni, and Mn in the positive electrode active material during mixed firing under an inert atmosphere. Materials containing Co have limitations in their application to positive electrode materials. Materials containing Ni and Mn are prone to destabilizing the crystal structure. Therefore, firing must be performed in air (in the presence of oxygen), but due to the catalytic action of Ni, carbon reduces to CO in an air atmosphere. ２ As a result, it becomes difficult to obtain a good coating. ２ Emissions of CO2 will also go against the worsening problem of global warming.

[0008] The present disclosure has been made based on the above-mentioned circumstances, and aims to provide a coating material manufacturing method that can suitably coat an electrode material, a method for manufacturing an electrode material using the coating material manufactured by this coating material manufacturing method, and a method for manufacturing a battery.

[0009] A coating material production method according to one embodiment of the present disclosure is a coating material production method for an electrode material containing lithium oxide, and includes a biomass mixing step of mixing plant biomass with a solvent to obtain a slurry, a heating step of heating the slurry obtained in the biomass mixing step, a solid-liquid separation step of performing solid-liquid separation of the slurry heated in the heating step, and a distillation step of distilling the liquid phase obtained in the solid-liquid separation step.

[0010] A method for producing an electrode material according to another aspect of the present disclosure includes a coating step of coating an electrode material precursor containing lithium oxide with a coating material, and the coating material is produced by the method for producing a coating material according to the present disclosure.

[0011] A battery manufacturing method according to yet another aspect of the present disclosure includes a positive electrode material manufacturing step of manufacturing a positive electrode material, and the positive electrode material manufacturing step uses the electrode material manufacturing method of the present disclosure.

[0012] The coating material manufacturing method of the present disclosure can suitably coat electrode materials. Furthermore, the electrode material manufacturing method and battery manufacturing method of the present disclosure, which use a coating material manufactured by the coating material manufacturing method of the present disclosure, produce electrodes with excellent properties.

[0013] FIG. 1 is a flow diagram showing a method for producing a coating material according to one embodiment of the present disclosure. FIG. 2 is a block diagram showing the configuration of a thermal extraction device used in the coating material production method of FIG. 1. FIG. 3 is a flow diagram showing a method for producing an electrode material according to another embodiment of the present disclosure. FIG. 4 is a block diagram showing the configuration of a thermal extraction device different from that shown in FIG. 2. FIG. 5 is a graph showing XRD measurement results for batteries No. 10 and No. 11 according to the examples. FIG. 6 is a graph showing evaluation results (up to 500 cycles) of the charge-discharge characteristics of batteries No. 10 and No. 11 according to the examples. FIG. 7 is a graph showing evaluation results (up to 5,000 cycles) of the charge-discharge characteristics of batteries No. 10 and No. 11 according to the examples. FIG. 8 is an SEM image of LNMO of LNMO of No. 11 according to the examples. FIG. 9 is an SEM image of LNMO of No. 10 on the same scale as FIG. 8. FIG. 10 is an SEM image of LNMO of No. 14 according to the examples. Fig. 11 is an SEM image of LNMO No. 10 on the same scale as Fig. 10. Fig. 12 is a graph showing the results of evaluation of the charge-discharge characteristics of batteries No. 20 and No. 22 in the examples. Fig. 13 is a graph showing the results of evaluation of the charge-discharge characteristics of batteries No. 30 and No. 32 in the examples.

[0014] [Explanation of an embodiment of the present disclosure] (1) A coating material production method according to one aspect of the present disclosure is a coating material production method for an electrode material containing lithium oxide, and includes a biomass mixing step of mixing plant biomass with a solvent to obtain a slurry, a heating step of heating the slurry obtained in the biomass mixing step, a solid-liquid separation step of separating the slurry heated in the heating step into solid and liquid, and a distillation step of distilling the liquid phase obtained in the solid-liquid separation step.

[0015] This coating material manufacturing method produces a coating material obtained by solvent-modifying plant biomass. The coating material obtained by solvent-modifying plant biomass undergoes gradual carbonization during coating on electrode materials, enabling electronic conductivity to be achieved through carbonization treatment at relatively low temperatures. Furthermore, good contact with the electrode active material during the coating treatment allows for good coating.

[0016] (2) In the coating material manufacturing method of (1), the lithium oxide may include lithium nickel manganese oxide. Lithium nickel manganese oxide is an electrode material with a high theoretical capacity and a high operating potential, and by combining it with the coating material manufactured by the coating material manufacturing method, it is possible to improve electronic conductivity and obtain an electrode with excellent cycle characteristics and battery characteristics.

[0017] (3) In the coating material production method of (1) or (2) above, the heating temperature in the heating step is preferably 280° C. or higher and 400° C. or lower. By setting the heating temperature in the heating step within the above range, it is possible to prevent an increase in heating energy, while suppressing the coating material (extract) from becoming lighter, and to prevent a decrease in yield during the coating process.

[0018] (4) A method for producing an electrode material according to another aspect of the present disclosure includes a coating step of coating an electrode material precursor containing lithium oxide with a coating material, and the coating material is produced by any one of the coating material production methods (1) to (3) above.

[0019] The method for producing the electrode material uses the coating material of the present disclosure, and therefore can improve electronic conductivity in particular, and can provide an electrode with excellent cycle characteristics and battery characteristics.

[0020] (5) In the method for producing an electrode material according to (4), the coating step may include a coating material mixing step of mixing the coating material with the electrode material precursor, and a firing step of firing the mixture obtained in the coating material mixing step in an oxygen-containing atmosphere. By firing in such an oxygen-containing atmosphere, it is possible to improve the electronic conductivity and prevent a decrease in potential and capacity at a high current rate.

[0021] (6) In the method for producing an electrode material according to (5), the firing temperature in the firing step is preferably 280°C or higher and 450°C or lower. By setting the firing temperature in the firing step within the above range, carbonization of the coating material of the present disclosure can be promoted while preventing an increase in heating energy. As a result, the electron conductivity of the coating is improved, and the coating material becomes carbon, thereby reducing the migration resistance of lithium ions within the coating layer.

[0022] (7) In the method for producing an electrode material according to (4), the lithium oxide may include lithium iron phosphate, and the coating step may include a coating material mixing step of mixing the coating material with the electrode material precursor, and a firing step of firing the mixture obtained in the coating material mixing step under an inert atmosphere. By firing under an inert atmosphere in this manner, it is possible to improve electronic conductivity and prevent a decrease in potential and capacity at a high current rate.

[0023] (8) In the method for producing an electrode material according to (7), the firing temperature in the firing step is preferably 400°C or higher and 900°C or lower. By setting the firing temperature in the firing step within the above range, carbonization of the coating material of the present disclosure can be promoted while preventing an increase in heating energy. As a result, the electron conductivity of the coating is improved, and the coating material becomes carbon, thereby reducing the migration resistance of lithium ions within the coating layer.

[0024] (9) In the method for producing an electrode material according to any one of (5) to (8), the mixing ratio in the coating material mixing step may be adjusted so that the carbon content after the firing step is 0.1% by mass or more and 3.0% by mass or less. By adjusting the carbon content after the firing step to 0.1% by mass or more and 3.0% by mass or less in this way, it is possible to prevent coating defects due to a lack of carbon and to suppress the inhibition of diffusion of lithium ions into the active material.

[0025] (10) A method for manufacturing a battery according to yet another aspect of the present disclosure includes a cathode material manufacturing step for manufacturing a cathode material, and the cathode material manufacturing step uses any one of the electrode material manufacturing methods (5) to (9) above.

[0026] The method for producing an electrode material according to the present disclosure is particularly suitable for use as a coating material for the positive electrode material of a battery.

[0027] [Details of Embodiments of the Present Disclosure] Hereinafter, a method for producing a coating material, a method for producing an electrode material, and a method for producing a battery according to an embodiment of the present disclosure will be described in detail.

[0028] [Coating Material] A method for producing a coating material according to an embodiment of the present disclosure is a method for producing a coating material for an electrode material containing lithium oxide. Here, in this specification, "lithium oxide" refers to a metal oxide containing lithium as the metal (lithium-containing metal oxide).

[0029] The lithium oxide is not particularly limited, but examples include those containing oxides of cobalt (Co), nickel (Ni), manganese (Mn), etc., such as lithium nickel manganese oxide, lithium iron phosphate, and lithium cobalt oxide. Among these, lithium nickel manganese oxide or lithium iron phosphate is preferred from the viewpoint of being cobalt-free, and lithium nickel manganese oxide is more preferred. Lithium nickel manganese oxide is an electrode material with a high theoretical capacity and a high operating potential, and by combining it with a coating material produced by the coating material production method, electronic conductivity can be improved, resulting in an electrode with excellent cycle characteristics and battery characteristics.

[0030] As shown in FIG. 1, the coating material production method includes a biomass mixing step S1, a heating step S2, a solid-liquid separation step S3, and a distillation step S4.

[0031] The coating material production method can be carried out using, for example, a thermal extraction apparatus 1 shown in Fig. 2. The thermal extraction apparatus 1 includes a solvent supply tank 10, an extraction tank 20, a distillation apparatus 30, a condenser 40, and a recovered solvent tank 50.

[0032] <Biomass Mixing Step> In the biomass mixing step S1, a slurry is obtained by mixing plant biomass with a solvent.

[0033] The biomass mixing step S1 can be performed in the extraction tank 20 of the thermal extraction apparatus 1. Specifically, plant biomass is charged into the extraction tank 20, and the solvent stored in the solvent supply tank 10 is supplied and mixed to form a slurry.

[0034] The plant biomass may be agricultural biomass, forestry biomass, etc. Examples of the plant biomass include rice straw, rice husks, herbaceous plants, bamboo, coconut shells, thinned wood, pruned branches, wood chips, and wood pellets.

[0035] The solvent is not particularly limited as long as it is stable in the heating temperature range of the heating step S2 described below, does not react with the plant biomass, and can be separated from the extracted components by distillation in the distillation step S4 described below. Examples of the solvent include bicyclic aromatic compounds such as methylnaphthalene oil and naphthalene oil, which are industrial organic solvents.

[0036] <Heating Step> In the heating step S2, the slurry obtained in the biomass mixing step S1 is heated.

[0037] Heating step S2 can be carried out in extraction tank 20. Extraction tank 20 has a stirrer 21 and a heater 22, and while the contents of extraction tank 20 are sufficiently stirred by agitator 21, heater 22 heats the contents to a predetermined temperature (heating temperature) and maintains the temperature for a predetermined period of time, thereby eluting the extracted components from the plant biomass.

[0038] The lower limit of the heating temperature in the heating step S2 is preferably 280°C, more preferably 300°C. On the other hand, the upper limit of the heating temperature is preferably 400°C, more preferably 380°C. By setting the heating temperature at or above the lower limit, it is possible to prevent the coating material, which is an extract, from becoming lighter and to prevent a decrease in yield during the coating process. Furthermore, if the heating temperature is below the lower limit, the bonds between the molecules that make up the plant biomass may not be sufficiently weakened, resulting in a decrease in the extraction rate. Conversely, by setting the heating temperature at or below the upper limit, it is possible to prevent an unnecessary increase in heating energy.

[0039] The average rate of temperature rise up to the heating temperature and the time for which the heating temperature is maintained are not particularly limited, but the lower limit of the average rate of temperature rise up to the heating temperature is preferably 1°C / min, more preferably 3°C / min. On the other hand, the upper limit of the average rate of temperature rise up to the heating temperature is preferably 100°C / min, more preferably 10°C / min. Furthermore, the lower limit of the time for which the heating temperature is maintained is preferably 10 min, more preferably 30 min. On the other hand, the upper limit of the time for which the heating temperature is maintained is preferably 100 min, more preferably 60 min.

[0040] <Solid-Liquid Separation Step> In the solid-liquid separation step S3, the slurry heated in the heating step S2 is subjected to solid-liquid separation.

[0041] The solid-liquid separation step S3 can be performed, for example, by filtering using a filter 23 provided in the extraction tank 20. The pore size of the filter 23 can be set to 0.1 μm or more and 50 μm or less.

[0042] The solid-liquid separation step S3 may be carried out while maintaining the temperature at the temperature heated in the heating step S2.

[0043] <Distillation Step> In the distillation step S4, the liquid phase obtained in the solid-liquid separation step S3 is distilled.

[0044] The distillation step S4 can be carried out using a distillation apparatus 30. The liquid phase is distilled at atmospheric pressure until no more distillate is produced, thereby removing the solvent and obtaining a coating material that is a solvent-modified product of the plant biomass.

[0045] On the other hand, the solvent after distillation can be liquefied by a condenser 40 and recovered in a recovered solvent tank 50. The recovered solvent can be supplied to the solvent supply tank 10 and reused.

[0046] <Advantages> This coating material manufacturing method produces a coating material obtained by solvent-modifying plant biomass. The coating material obtained by solvent-modifying plant biomass undergoes gradual carbonization when coated onto an electrode material, enabling electronic conductivity to be achieved through a relatively low-temperature carbonization process. Furthermore, good contact with the electrode active material during the coating process allows for good coating.

[0047] [Method for Producing Electrode Material] As shown in FIG. 3 , a method for producing an electrode material according to another embodiment of the present disclosure includes a coating step S5 of coating an electrode material precursor containing lithium oxide with a coating material, and the coating material is produced by the method for producing a coating material according to the present disclosure.

[0048] The electrode material precursor may be a commercially available product or may be synthesized before the coating step S5. The electrode material precursor is an active material before coating, such as lithium nickel manganese oxide, lithium iron phosphate, or lithium cobalt oxide.

[0049] The coating step S5 includes a coating material mixing step S51 and a baking step S52.

[0050] <Coating Material Mixing Step> In the coating material mixing step S51, the coating material is mixed with the electrode material precursor.

[0051] In the coating material mixing step S51, it is preferable to adjust the mixing ratio so that the carbon content after the firing step S52 described below falls within a predetermined range. The lower limit of the predetermined range is preferably 0.1 mass %, more preferably 0.5 mass %. On the other hand, the upper limit of the predetermined range is preferably 3.0 mass %, more preferably 2.0 mass %. By setting the predetermined range to a value equal to or greater than the lower limit, coating defects due to insufficient carbon can be prevented. Conversely, by setting the predetermined range to a value equal to or less than the upper limit, it is possible to prevent excessive carbon from causing the coating film to become too thick, thereby inhibiting the diffusion of lithium ions into the active material.

[0052] <Baking Step> In the baking step S52, the mixture obtained in the coating material mixing step S51 is baked.

[0053] [First Embodiment] In the first embodiment, the firing step S52 is performed in an oxygen-containing atmosphere. By firing in such an oxygen-containing atmosphere, it is possible to improve the electronic conductivity and prevent a decrease in potential and capacity at a high current rate.

[0054] The lower limit of the baking temperature in the baking step S52 is preferably 280°C, more preferably 300°C, and even more preferably 330°C. Meanwhile, the upper limit of the baking temperature is preferably 450°C, more preferably 400°C. It is presumed that the coating material of the present disclosure carbonizes more slowly than conventional coating materials, and that a carbonization treatment at a relatively low temperature within the above range increases lithium diffusibility and electronic conductivity within the coating layer, thereby enabling efficient coating in an air atmosphere. Furthermore, it is presumed that the coating material softens and melts at temperatures in the 100°C range, providing good contact with the active material during the coating treatment, enabling good coating. Therefore, baking at an appropriate temperature promotes carbonization of the coating material, thereby improving the electronic conductivity of the coating, and reducing the resistance to lithium ion migration within the coating layer by converting the coating material into carbon.

[0055] Furthermore, by setting the baking temperature to the above upper limit or less, a coating film is formed on the surface of the electrode active material particles, and the reaction with the electrolyte is suppressed, thereby reducing deterioration of cycle characteristics.

[0056] Furthermore, by keeping the firing temperature as low as possible, CO ２ This reduces the amount of carbon lost and the amount of heat required for heating.

[0057] [Second Embodiment] In a second embodiment, the calcination step S52 is performed in an inert atmosphere. The electrode material is not particularly limited as long as it is not destabilized by calcination with carbon in an inert atmosphere. For example, this method can be applied when the lithium oxide contains lithium iron phosphate. By calcining in an inert atmosphere in this way, electronic conductivity can be improved, preventing a decrease in potential and capacity at high current rates.

[0058] The lower limit of the baking temperature in the baking step S52 is preferably 400°C, more preferably 450°C. On the other hand, the upper limit of the baking temperature is preferably 900°C, more preferably 800°C, and even more preferably 550°C. By baking at such an appropriate temperature, carbonization of the coating material can be promoted. As a result, the electronic conductivity of the coating is improved, and the coating material becomes carbon, thereby reducing the migration resistance of lithium ions within the coating layer. Furthermore, by lowering the baking temperature, the amount of heat required for heating can be reduced.

[0059] <Advantages> The method for producing the electrode material uses the coating material of the present disclosure, and therefore, it is possible to improve the electronic conductivity in particular, and to obtain an electrode with excellent cycle characteristics and battery characteristics.

[0060] [Method for Manufacturing Battery] A method for manufacturing a battery according to yet another aspect of the present disclosure includes a positive electrode material manufacturing step for manufacturing a positive electrode material, and the method for manufacturing an electrode material according to the present disclosure is used in the positive electrode material manufacturing step.

[0061] The method for producing an electrode material according to the present disclosure is particularly suitable for use as a coating material for the positive electrode material of a battery.

[0062] [Other Embodiments] The above-described embodiments do not limit the configuration of the present disclosure. Therefore, the above-described embodiments may include omissions, substitutions, or additions of components based on the description in this specification and common general technical knowledge, and all of these should be construed as belonging to the scope of the present disclosure.

[0063] In the above embodiment, the solid-liquid separation step is performed by filtration. However, the solid-liquid separation method is not limited to filtration, and other methods such as gravity settling or centrifugation may also be used.

[0064] In the above embodiment, a method for recovering the solvent after distillation has been described, but recovery of the solvent after distillation is not an essential configuration and can be omitted. If recovery of the solvent after distillation is not performed, new solvent is always supplied to the solvent supply tank. This configuration can prevent unavoidable impurities that may remain in the solvent after distillation from being mixed into the solvent.

[0065] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0066] [No. 1] The plant biomass and extraction solvent of the type and amount shown in Table 1 were charged into the extraction tank 20 of the thermal extraction apparatus 1 (volume 13 L) shown in Figure 2 and mixed to form a slurry. The extraction tank 20 was heated to 350 °C at an average temperature increase rate of 3 °C / min while stirring thoroughly, and then maintained for 60 minutes to elute the extracted components from the plant biomass. Then, while maintaining the temperature, the mixture was filtered through a filter 23 with a pore size of 0.5 μm, thereby performing solid-liquid separation. The filtered post-biomass extraction solvent was subjected to atmospheric distillation (heater temperature 320 °C) using a distillation apparatus 40 until no distillate remained, thereby removing the solvent, and coating material No. 1 was obtained.

[0067] [No. 2, No. 3] The plant biomass and extraction solvent of the type and amount shown in Table 1 were charged into the extraction tank 20 of the thermal extraction apparatus 2 (0.5 L capacity) shown in Figure 4 and mixed to form a slurry. The extraction tank 20 was heated to 350 °C at an average temperature increase rate of 5 °C / min while stirring thoroughly, and then maintained for 40 minutes to elute the extracted components from the plant biomass. The mixture was then filtered through a 0.5 μm pore size filter 23 while maintaining the temperature, and the filtrate was collected in a receiver 60, thereby performing solid-liquid separation. The filtered post-biomass extraction solvent was subjected to reduced pressure distillation (30 mmHg or less, oil bath temperature 150 °C) using an experimental evaporator to remove the solvent, and further vacuum dried in a dryer at 150 °C / 4 hours to obtain coating materials No. 2 and No. 3.

[0068]

[0069] [Coating on LNMO and evaluation of charge / discharge characteristics] LiOH·H ２ O, Ni(CH ３ COO) ２ ・4H ２ O, Mn(CH ３ COO) ２ ・4H ２ O was added to deionized water in a stoichiometric ratio and mixed. The mixture was heated to remove moisture, then heat-treated in an air atmosphere at 400°C for 10 hours, pulverized in a ball mill (100 rpm / 1 hour), and further heat-treated in an air atmosphere at 800°C for 6 hours to obtain LNMO before carbon coating.

[0070] The LNMO was mixed with coating material No. 1 or No. 3 at a predetermined ratio. The mixture was heated to a predetermined temperature at a temperature increase rate of 5°C / min under air flow (100 mL / min) and maintained for 60 minutes to obtain carbon-coated LNMO. After coating, the carbon content was measured using a C / S analyzer (HORIBA EMIA-220V).

[0071] The LNMO (No. 11, No. 13) or uncoated LNMO (No. 10) was mixed with acetylene black (a conductive additive) and polyvinylidene fluoride (PVDF) (a binder), and a few drops of N-methylpyrrolidone were added. The mixture was mixed using a stirring and degassing device to obtain a slurry-like mixture. The weight ratio of LNMO:acetylene black:PVDF was 8:1:1.

[0072] The slurry was applied to an aluminum foil to a thickness of 100 μm and thoroughly dried in a vacuum dryer at 55° C. After pressing at 10 MPa for 10 minutes, the coating was dried to a thickness of 1 cm. ２ The cathode was prepared by cutting the aluminum foil into a circular shape.

[0073] Batteries were assembled using a galvanic cell in a glove box filled with Ar gas. The positive electrode was the same as above, and metallic Li (Honjo Metals Co., Ltd.) was used as the negative electrode. Other conditions are shown in Table 2. In this manner, batteries No. 10, No. 11, and No. 13 were obtained.

[0074] (Evaluation) Figure 5 shows the results of XRD measurement of LNMO before the above-mentioned carbon coating (LMNO (No. 10) in Figure 5) and LNMO after the No. 11 coating (LMNO (No. 11) in Figure 5). The peak position of the synthesized LNMO (No. 10) was consistent with that of lithium nickel manganese oxide (PDF: 01-080-2162) (see Figure 5). Furthermore, the peak position of LNMO (No. 11) after coating was also unchanged from that of LNMO (No. 10), indicating that the crystal structure was not changed by the coating.

[0075] The charge-discharge characteristics of batteries No. 10, No. 11, and No. 13 were evaluated. A charge-discharge measuring device (2141-PFX2011S SPEC20796, KIKUSUI) was used for the measurements. After the first cycle, the batteries were charged and discharged at a 1C rate, and thereafter, charge-discharge cycle tests were performed at a 10C rate for 80 to 5,000 cycles. The measurement voltage range was 3.5-4.9V vs. Li / Li. ＋Here, the "1 C rate" refers to a current value that fully discharges the battery capacity in one hour, and the "10 C rate" refers to a current value that is 10 times the 1 C rate.

[0076] Table 2 shows the evaluation results of the maximum discharge capacities of batteries No. 10, No. 11, and No. 13. Here, the maximum discharge capacity is the maximum discharge capacity observed from the second cycle onwards, because the charge / discharge rate is different between the first cycle and the second cycle onwards. The batteries coated with the coating material of the present disclosure (No. 11 and No. 13) recorded a higher maximum discharge capacity than the uncoated battery (No. 10). This is thought to be due to the coating improving the apparent electronic conductivity of LNMO.

[0077]

[0078] The results of evaluating the charge-discharge characteristics of batteries No. 10 and No. 11 are shown in Figures 6 and 7. In the case of battery No. 10 without a coating, the discharge capacity rapidly decreased with increasing cycle count, whereas battery No. 11 coated with the coating material maintained approximately 80% of its maximum capacity at 2,000 cycles and approximately 60% of its maximum capacity even at 5,000 cycles, demonstrating extremely high cycle characteristics. This is thought to be because the LNMO particles were protected by the coating material of the present disclosure, suppressing their reaction with the electrolyte.

[0079] Furthermore, to compare with conventional coating materials, LNMO was coated with sucrose (No. 14) using the same procedure as in No. 11. The sucrose content was 5.0% by mass, and the treatment temperature was 290°C.

[0080] To confirm the presence or absence of coating, an SEM image of LNMO No. 11, which was coated with the coating material of the present disclosure, is shown in Figure 8. For comparison, an SEM image of LNMO No. 10, which was uncoated, is shown at the same scale in Figure 9. Similarly, an SEM image of LNMO No. 14, which was coated with sucrose, is shown in Figure 10, and an SEM image of LNMO No. 10, which was also coated with sucrose, is shown in Figure 11.

[0081] In the case of LNMO No. 11, what appeared to be carbon was observed on the LNMO surface, whereas no clear difference was observed in the case of sucrose compared to the case without a coating. In other words, due to the catalytic action of nickel contained in LNMO, most of the sucrose disappeared when fired together with LMNO in an air atmosphere, whereas LNMO No. 11, which used the coating material of the present disclosure, had a high yield even when fired in an air atmosphere, and it can be said that the LNMO surface was effectively coated.

[0082] [Coating on LFP and evaluation of charge / discharge characteristics] LiOH·H ２ O, 85% by mass H ３ P.O. ４ Aqueous solution, FeSO ４ ・7H ２ The mixture was added to polyethylene glycol so that the molar ratio of 0:1:1 was obtained, and hydrothermal synthesis was carried out at a temperature of 150°C, a pressure of 12 MPa, and a stirring speed of 200 rpm. The mixture was then filtered and dried, and then dehydrated with N ２ The resulting mixture was subjected to a heat treatment at 400° C. for 1 hour in a 500° C. atmosphere to obtain LFP (No. 20).

[0083] The LFP was mixed with coating material No. 2 at a predetermined ratio. The mixture was heated to a predetermined temperature at a rate of 5°C / min in an Ar atmosphere and maintained at that temperature for 60 minutes to obtain carbon-coated LFP (No. 22). After coating, the carbon content was measured using a C / S analyzer (HORIBA EMIA-220V).

[0084] The LFP (No. 22) or uncoated LFP (No. 20) was mixed with acetylene black (a conductive additive) and polyvinylidene fluoride (PVDF) (a binder), and a few drops of N-methylpyrrolidone were added. The mixture was mixed using a stirring and degassing device to obtain a slurry-like mixture. The mixing ratio by weight was LFP:acetylene black:PVDF = 7:2:1.

[0085] The slurry was applied to an aluminum foil to a thickness of 100 μm and thoroughly dried in a vacuum dryer at 55° C. After pressing at 10 MPa for 10 minutes, the coating was dried to a thickness of 1 cm. ２The cathode was prepared by cutting the aluminum foil into a circular shape.

[0086] Batteries were assembled using a galvanic cell in a glove box filled with Ar gas. The positive electrode was the same as above, and metallic Li (Honjo Metals Co., Ltd.) was used as the negative electrode. Other conditions are shown in Table 3. In this manner, batteries No. 20 and No. 22 were obtained.

[0087] (Evaluation) The charge / discharge characteristics of batteries No. 20 and No. 22 were evaluated. A charge / discharge measuring device (2141-PFX2011S SPEC20796, KIKUSUI) was used for the measurement, and two sets of nine cycles were performed: two cycles at a 0.2 C rate, two cycles at a 0.5 C rate, and five cycles at a 1 C rate. The measurement voltage range was 2.5-4.0 V vs. Li / Li. ＋ was set to.

[0088] Table 3 shows the evaluation results of the maximum discharge capacity of batteries No. 20 and No. 22. The evaluation results of the charge / discharge characteristics are shown in Figure 12. In Table 3, the maximum discharge capacity is the maximum discharge capacity observed at each rate.

[0089]

[0090] The results in Table 3 and Figure 12 show that coating increases the maximum discharge capacity at 0.5C and 1C. At 0.2C, the maximum discharge capacity is the same; however, this is because LFP has a redox rate sufficient for charge / discharge at this current rate, and therefore the effect of increasing electronic conductivity was not observed. From the above, it can be said that coating improved the apparent electronic conductivity of LFP. Furthermore, since the difference in discharge capacity between the coated and uncoated batteries increases as the charge / discharge rate increases, it is expected that the reduction in potential and capacity at high current rates will be reduced.

[0091] [Coating on LCO and Evaluation of Charge / Discharge Characteristics] LCO was mixed with Coating Material No. 2 at a predetermined ratio. The mixture was heated to a predetermined temperature at a temperature increase rate of 5°C / min in an air atmosphere and maintained at that temperature for 60 minutes to obtain a carbon-coated LCO.

[0092] The LCO (No. 32) or uncoated LCO (No. 30) was mixed with acetylene black (a conductive additive) and polyvinylidene fluoride (PVDF) (a binder), and a few drops of N-methylpyrrolidone were added. The mixture was mixed using a stirring and degassing device to obtain a slurry-like mixture. The weight ratio of LCO:acetylene black:PVDF was 75:18:7.

[0093] The slurry was applied to an aluminum foil to a thickness of 100 μm and thoroughly dried in a vacuum dryer at 55° C. After pressing at 10 MPa for 10 minutes, the coating was dried to a thickness of 1 cm. ２ The cathode was prepared by cutting the aluminum foil into a circular shape.

[0094] Batteries were assembled using a galvanic cell in a glove box filled with Ar gas. The positive electrode was the same as above, and metallic Li (Honjo Metals Co., Ltd.) was used as the negative electrode. Other conditions are shown in Table 4. In this manner, batteries No. 30 and No. 32 were obtained.

[0095] (Evaluation) The charge / discharge characteristics of batteries No. 30 and No. 32 were evaluated. A charge / discharge measuring device (2141-PFX2011S SPEC20796, KIKUSUI) was used for the measurement, and two sets of 30 cycles were performed: 10 cycles at 1C rate, 10 cycles at 5C rate, and 10 cycles at 10C rate. The measurement voltage range was 3.0-4.3V vs. Li / Li. ＋ was set to.

[0096] Table 4 shows the evaluation results of the maximum discharge capacity of batteries No. 30 and No. 32. The evaluation results of the charge / discharge characteristics of the batteries are shown in Figure 13. In Table 4, the maximum discharge capacity is the largest discharge capacity observed at each rate.

[0097]

[0098] From the results in Table 4 and Figure 13, it is believed that the coating increased the discharge capacity, and that the coating improved the apparent electronic conductivity of the LCO. Since the capacity improved even at a high rate of 10 C, it can be said that it is possible to reduce the decrease in potential and capacity at high current rates.

[0099] The coating material manufacturing method of the present disclosure can suitably coat electrode materials. Furthermore, the electrode material manufacturing method and battery manufacturing method of the present disclosure, which use a coating material manufactured by the coating material manufacturing method of the present disclosure, produce electrodes with excellent properties.

[0100] 1, 2 Heat extraction device 10 Solvent supply tank 20 Extraction tank 21 Stirrer 22 Heater 23 Filter 30 Distillation device 40 Condenser 50 Recovered solvent tank 60 Receiver

Claims

1. A method for producing a coating material for an electrode material containing lithium oxide, comprising: a biomass mixing step of mixing plant biomass with a solvent to obtain a slurry; a heating step of heating the slurry obtained in the biomass mixing step; a solid-liquid separation step of separating the slurry heated in the heating step into solid and liquid; and a distillation step of distilling the liquid phase obtained in the solid-liquid separation step.

2. The method for producing a coating material according to claim 1, wherein said lithium oxide comprises lithium nickel manganese oxide.

3. A method for producing a coating material according to claim 1 or 2, wherein the heating temperature in the heating step is 280°C or higher and 400°C or lower.

4. A method for producing an electrode material, comprising a coating step of coating an electrode material precursor containing lithium oxide with a coating material, wherein the coating material is produced by the coating material production method described in claim 1.

5. The method for producing an electrode material according to claim 4, wherein the coating step comprises: a coating material mixing step of mixing the coating material with the electrode material precursor; and a firing step of firing the mixture obtained in the coating material mixing step in an oxygen-containing atmosphere.

6. The method for producing an electrode material according to claim 5, wherein the firing temperature in the firing step is 280°C or higher and 450°C or lower.

7. The method for producing an electrode material according to claim 4, wherein the lithium oxide contains lithium iron phosphate, and the coating step comprises: a coating material mixing step of mixing the coating material with the electrode material precursor; and a firing step of firing the mixture obtained in the coating material mixing step in an inert atmosphere.

8. The method for producing an electrode material according to claim 7, wherein the firing temperature in the firing step is 400°C or higher and 900°C or lower.

9. A method for manufacturing an electrode material according to any one of claims 5 to 8, wherein in the coating material mixing step, the mixing ratio is adjusted so that the carbon content after the firing step is 0.1 mass % or more and 3.0 mass % or less.

10. A method for manufacturing a battery, comprising a cathode material manufacturing process for manufacturing a cathode material, wherein the cathode material manufacturing method according to claim 4 is used in the cathode material manufacturing process.

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