The positive electrode of a lithium-ion battery and its manufacturing method, and lithium-ion batteries

Abstract

This invention provides a positive electrode for a lithium-ion battery capable of suppressing the generation of carbon dioxide gas while increasing the battery capacity of the lithium-ion battery, a method for manufacturing the same, and the lithium-ion battery itself. The positive electrode of the lithium-ion battery has a positive current collector and a positive active material layer. The positive electrode is characterized in that the positive active material layer has a positive electrode additive comprising the positive active material, and the positive electrode additive contains lithium carbonate in a range of 9% by mass or more and 20% by mass relative to the total weight.

Description

Technical Field

[0001] This invention relates to the positive electrode of a lithium-ion battery, a lithium-ion battery, and a method for manufacturing the positive electrode of a lithium-ion battery. Background Technology

[0002] Vehicles such as EVs (Electric Vehicles) and HEVs (Hybrid Electric Vehicles) are equipped with energy storage devices that supply power to motors and other components. Typically, these energy storage devices contain multiple secondary batteries.

[0003] Lithium-ion batteries (LIBs) are widely used as secondary batteries in EVs and HEVs. Due to their lightweight nature and high energy density, lithium-ion batteries are preferred as high-output power sources for vehicles.

[0004] To enable vehicles to travel long distances on a single charge, it is desirable to maximize battery capacity and improve energy efficiency.

[0005] As one method to increase the battery capacity of such lithium-ion batteries, a scheme is proposed to use lithium carbonate (Li2CO3) in one of the materials constituting the positive electrode active material (for example, see Patent Documents 1 and 2).

[0006] According to Patent Documents 1 and 2, a non-aqueous electrolyte secondary battery is disclosed that uses lithium carbonate in the positive electrode active material of a lithium-ion battery, thereby suppressing the decrease in battery capacity caused by changes over time and ensuring a large battery capacity over a long period of time.

[0007] Prior technology literature

[0008] [Patent Documents]

[0009] Patent Document 1: Japanese Patent Application Publication No. 2001-167767

[0010] Patent Document 2: Japanese Patent Application Publication No. 2002-117843 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, in the non-aqueous electrolyte secondary batteries disclosed in Patent Documents 1 and 2, since the upper limit of the amount of lithium carbonate added to the positive electrode is 8.0% by mass, there is a problem that the effect of increasing battery capacity is limited.

[0013] In view of the above-mentioned problems, the present invention proposes a solution, the purpose of which is to provide a positive electrode of a lithium-ion battery, a lithium-ion battery, and a method for manufacturing the positive electrode of a lithium-ion battery that can increase the battery capacity of a lithium-ion battery and improve energy efficiency while suppressing the generation of carbon dioxide.

[0014] Solution for solving the problem

[0015] Based on the above background, the inventors have discovered new knowledge related to the appropriate addition ratio of lithium carbonate to the cathode agent, which can increase the battery capacity of lithium-ion batteries and suppress the generation of carbon dioxide gas.

[0016] That is, a positive electrode of a lithium-ion battery of the present invention has a positive current collector and a positive active material layer, wherein the positive electrode of the lithium-ion battery is characterized in that the positive active material layer has a positive electrode compound containing the positive active material, and the positive electrode compound contains lithium carbonate in a range of 9% by mass or more and 20% by mass or less relative to its total weight.

[0017] According to the present invention, by including lithium carbonate in the positive electrode compound constituting the positive electrode active material layer at a range of 9% by mass and 20% by mass relative to the total weight of the positive electrode compound, the battery capacity of the lithium-ion battery can be increased. Furthermore, even when lithium carbonate is added to the positive electrode compound within the aforementioned range, the increase in the amount of carbon dioxide produced due to the battery reaction can be reduced.

[0018] Alternatively, in this invention, the positive electrode mixture may include the lithium carbonate, ternary cathode material (NMC), carbon black, and resin binder.

[0019] The lithium-ion battery of the present invention is characterized in that the lithium-ion battery has: a positive electrode of the lithium-ion battery as described in the preceding claims; a negative electrode having a negative electrode current collector and a negative electrode active material layer and being opposite to the positive electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode.

[0020] The method for manufacturing the positive electrode of a lithium-ion battery according to the present invention is a method for manufacturing the positive electrode of a lithium-ion battery as described in the foregoing claims, characterized in that the method comprises: a mixing step of adding the lithium carbonate, the ternary cathode material (NMC), the carbon black, the resin binder, and an organic solvent and mixing them to obtain a mixture; and a positive electrode active material layer forming step of coating the mixture onto the positive electrode current collector and causing the organic solvent to evaporate to form the positive electrode active material layer.

[0021] Invention Effects

[0022] According to the present invention, a positive electrode of a lithium-ion battery, a lithium-ion battery, and a method for manufacturing the positive electrode of a lithium-ion battery are provided, which can increase the battery capacity of the lithium-ion battery and improve energy efficiency while suppressing the generation of carbon dioxide gas. Attached Figure Description

[0023] Figure 1 This is a schematic cross-sectional view showing an example of the layer structure of the lithium-ion battery according to this embodiment.

[0024] Figure 2 This is a graph showing the measurement results (verification example) of the capacity density of lithium-ion batteries.

[0025] Figure 3 This is a graph showing the measurement results (verification example) of the amount of carbon dioxide generated in the positive electrode of a lithium-ion battery.

[0026] Explanation of reference numerals in the attached figures:

[0027] 10…Lithium-ion batteries

[0028] 11…Positive current collector

[0029] 12… Positive electrode active material layer

[0030] 13… Positive electrode

[0031] 14… Negative current collector

[0032] 15…Negative electrode active material layer

[0033] 16… Negative electrode

[0034] 17…Electrolyte layer. Detailed Implementation

[0035] Hereinafter, a positive electrode of a lithium-ion battery, a lithium-ion battery, and a method for manufacturing the positive electrode of a lithium-ion battery according to an embodiment of the present invention will be described with reference to the accompanying drawings. It should be noted that the embodiments shown below are described in detail to better understand the gist of the invention, and unless otherwise specified, the invention is not limited thereto. Furthermore, in the accompanying drawings used in the following description, to facilitate understanding of the features of the invention, some portions that would otherwise be key parts are sometimes shown enlarged, and the dimensions and proportions of the constituent elements may not be the same as in reality.

[0036] (Positive electrode of lithium-ion battery, lithium-ion battery)

[0037] The structure of a lithium-ion battery including the positive electrode of a lithium-ion battery according to an embodiment of the present invention will be described.

[0038] Figure 1 This is a schematic cross-sectional view illustrating an example of the layered structure of a lithium-ion battery.

[0039] The lithium-ion battery (LIB) 10 is formed by stacking a positive electrode 13, a negative electrode 16, and an electrolyte layer 17. The positive electrode 13 has a positive current collector 11 and a positive active material layer 12 located on one side of the positive current collector 11. The negative electrode 16 is opposite to the positive electrode 13 and has a negative current collector 14 and a negative active material layer 15 located on one side of the negative current collector 14. The electrolyte layer 17 is located between the positive electrode 13 and the negative electrode 16.

[0040] The positive electrode active material layer 12 is a layer containing a positive electrode additive. The positive electrode additive includes a positive electrode active material, lithium carbonate, conductive additives, and a binder.

[0041] Positive electrode active materials can use ions that enable ion adsorption and release, ion detachment and insertion (intercalation), or ion-ion equilibrium anions (e.g., PF6). - Electrode active materials that can be reversibly doped and dedoped between )

[0042] Specific examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), lithium manganese spinel (LiMn2O4), and those derived from the general formula: LiNi x Co y Mn z M a O2 (x+y+z+a=1, 0≤x<1, 0≤y<1, 0≤z<1, 0≤a<1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr) represents a composite metal oxide (ternary compound), lithium vanadium compound (LiV2O5), olivine-type LiMPO4 (where M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr or VO), lithium titanate (Li4Ti5O) 12 LiNi x Co y Al z O2 (0.9 < x + y + z < 1.1) and other composite metal oxides, polyacetylene, polyaniline, polypyrrole, polythiophene, polybenzoxene, etc.

[0043] In this embodiment, a ternary compound containing Ni, Co, and Mn is used as the positive electrode active material contained in the positive electrode mixture.

[0044] The positive electrode additive constituting the positive electrode active material layer 12 of this embodiment includes lithium carbonate (Li2CO3). Lithium carbonate can increase the battery capacity of the lithium-ion battery 10. In this embodiment, the positive electrode additive contains lithium carbonate in a range of 9% by mass or more and 20% by mass or less relative to the total weight of the positive electrode additive.

[0045] When the lithium carbonate content is less than 9% by mass, the increase in battery capacity, i.e., capacity density, of the lithium-ion battery 10 is limited. Such a capacity density is preferably, for example, 180 mAh / g or higher.

[0046] In addition, when the content of lithium carbonate exceeds 20% by mass, the capacity density begins to decrease significantly.

[0047] In addition, the one with a higher amount of lithium carbonate in the positive electrode mixture suppresses the generation of carbon dioxide gas.

[0048] As in this embodiment, by adding lithium carbonate to the positive electrode compound within the above-mentioned range, in addition to the lithium ions in the electrolyte layer, the lithium contained in the lithium carbonate also helps the battery reaction, thereby increasing the capacity density.

[0049] The binder included in the positive electrode binder of the positive electrode active material layer 12 can be a known binder. Examples include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF) and other fluoropolymers.

[0050] The conductive additives included in the positive electrode active material layer 12 include, for example, carbon powders such as carbon black, carbon nanotubes, carbon materials, metal powders such as copper, nickel, stainless steel, and iron, mixtures of carbon materials and metal powders, and conductive oxides such as ITO.

[0051] The positive electrode agent constituting the positive electrode active material layer 12 of this embodiment is Ketjen black, which has particularly excellent conductivity among carbon blacks.

[0052] It should be noted that if sufficient conductivity can be ensured using only the positive electrode agent, the conductive additive may not be included in the positive electrode agent.

[0053] The negative electrode active material layer 15 serves as a negative electrode binder, containing both a negative electrode active material and a binder, and may contain conductive additives as needed. Known negative electrode active materials can be used. Examples of negative electrode active materials include: graphite (natural graphite, artificial graphite) capable of absorbing and releasing metallic lithium and lithium ions; carbon materials such as carbon nanotubes, difficult-to-graphitize carbon, easily-graphitize carbon, and low-temperature sintered carbon; metals capable of combining with lithium, such as aluminum, silicon, and tin; and SiO₂. x (0 < x < 2), amorphous compounds mainly composed of oxides such as tin dioxide, and lithium titanate (Li4Ti5O) 12 Particles including ) and others.

[0054] The conductive additives and binders included in the negative electrode mixture can be the same as those used in the positive electrode active material layer 12. In addition to the binders mentioned in the positive electrode active material layer 12, other binders used in the negative electrode mixture may include carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyimide (PI), polyamide-imide (PAI), and polyacrylic acid (PAA).

[0055] When the lithium-ion battery 10 is charged, the potential of the negative electrode 16, which includes such a negative electrode active material layer 15, changes as lithium ions enter the interlayer of the carbon material, which is an example of a negative electrode active material.

[0056] The positive electrode 13 of the lithium-ion battery 10 of this embodiment, and the lithium-ion battery 10 using the positive electrode 13, contain lithium carbonate in the positive electrode compound constituting the positive electrode active material layer 12 in a range of 9% by mass or more and 20% by mass or less relative to the total weight of the positive electrode compound. As a result, the battery capacity of the lithium-ion battery 10 can be increased compared with the case where no lithium carbonate is added.

[0057] Furthermore, even if lithium carbonate is added to the cathode compound within the range described above, there is no increase in the amount of carbon dioxide produced by the battery reaction, and there is no need for a structure for gas release.

[0058] This type of lithium carbonate is relatively inexpensive, thus enabling the realization of a positive electrode for lithium-ion batteries that increases battery capacity, as well as lithium-ion batteries using this positive electrode, with a low-cost and simple structure.

[0059] (Manufacturing method of the positive electrode of lithium-ion battery)

[0060] An embodiment of a method for manufacturing the positive electrode of a lithium-ion battery with the structure described above will be described.

[0061] When manufacturing the positive electrode of a lithium-ion battery using the manufacturing method of the positive electrode of the lithium-ion battery of this embodiment, firstly, a positive electrode mixture is prepared.

[0062] For example, LiCoNiMnO6 (NMC) and lithium carbonate are used as ternary oxides as positive electrode active materials, Ketjen black is used as a conductive additive, and polyvinylidene fluoride (PVdF) is used as a binder. N-methyl-2-pyrrolidone (NMP) is added to their powders as an organic solvent and they are mixed to obtain a compound (mixing process).

[0063] Next, a paste-like compound is coated onto a positive electrode current collector, such as an aluminum thin film. Then, the material obtained by coating the aluminum thin film with the compound is dried to evaporate the organic solvent, thereby obtaining the positive electrode of the lithium-ion battery of this embodiment (positive electrode active material layer formation process).

[0064] The embodiments of the present invention have been described above, but such embodiments are given as examples and are not intended to limit the scope of the invention. Such embodiments can be implemented in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and are similarly included in the invention described in the technical solution and its equivalents.

[0065]

Example

[0066] [Verification of Capacity Density]

[0067] As an embodiment of the present invention, the relationship between the content of lithium carbonate in the positive electrode mixture and the capacity density of the lithium-ion battery was verified.

[0068] In the lithium-ion battery used in the verification, aluminum films were used for the positive electrode current collector and the negative electrode current collector, respectively, and positive electrode additives and negative electrode additives were coated onto the aluminum films to form positive electrode active material layers and negative electrode active material layers, respectively.

[0069] (positive electrode)

[0070] As positive electrode agents, LiCoNiMnO6 (NMC), lithium carbonate, Ketjen black (KB), and polyvinylidene fluoride (PVdF) were used respectively.

[0071] The following shows the content ratios (A∶B∶C∶D (mass%)) of NMC (A), KB (B), PVdF (C), and lithium carbonate (C) used in the verification.

[0072] Example 1∶81∶5∶5∶9

[0073] Example 2∶75∶5∶5∶15

[0074] Example 3∶70∶5∶5∶20

[0075] Comparative Example 1: 90: 5: 5: 0

[0076] Comparative Example 2: 87: 5: 5: 3

[0077] Comparative Example 3: 60: 5: 5: 30

[0078] Each of these positive electrode mixtures in different ratios was added to 100 μL of NMP as an organic solvent, and the mixtures were repeatedly kneaded for 3 minutes four times at a speed of 1000 rpm using a degassing mixer (Defoaming Rentarō: THINKY Co., Ltd.). Then, NMP was added again to bring the total addition to 400 μL, and the mixtures were kneaded once more at a speed of 1000 rpm for 3 minutes to obtain the mixtures for each sample.

[0079] Next, the obtained slurry-like mixture was coated onto an aluminum film using a doctor blade coating machine (doctor blade coating machine) with a 100 μm coating gap. Then, the aluminum film coated with the mixture was dried at 80°C and atmospheric pressure for 2 hours, and then vacuum dried at 120°C for 12 hours to evaporate the organic solvent. After that, it was punched into a circular plate with a diameter of 16 mm to obtain the positive electrode of each sample.

[0080] (negative electrode)

[0081] Lithium metal foil was used as the negative electrode.

[0082] (Electrolyte layer)

[0083] An electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) in a solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 3:7 to obtain an electrolyte concentration of 1 M / L. The electrolyte was then impregnated in a sheet-like porous substrate to obtain an electrolyte layer.

[0084] The lithium-ion battery used in the verification was fabricated by stacking the positive electrode, negative electrode, and electrolyte layers as described above.

[0085] exist Figure 2 The results of capacity density measurements of lithium-ion batteries manufactured using the positive electrodes of Examples 1-3 and Comparative Examples 1-3 of the present invention are shown in the figure.

[0086] according to Figure 2 The results show that the lithium-ion batteries using the cathodes of Examples 1 to 3, which contain lithium carbonate in the range of 9% to 20% by mass relative to the total weight of the cathode compound, all have a capacity density of 180 mAh / g or higher, and can achieve high battery capacity.

[0087] On the other hand, the capacity density of lithium-ion batteries using cathodes that do not contain lithium carbonate and those using cathodes that contain 3% by mass and 30% by mass relative to the total weight of the cathode compound are all less than 175 mAh / g, and the effect of increasing battery capacity is non-existent or minimal.

[0088] Based on the above results, the increased battery capacity of the present invention can be confirmed.

[0089] [Verification of the amount of carbon dioxide gas produced due to the addition of lithium carbonate]

[0090] As an embodiment of the present invention, the relationship between the content of lithium carbonate in the positive electrode mixture and the amount of carbon dioxide gas produced, which is a representative example of carbon dioxide gas, was verified.

[0091] The positive electrodes of the lithium-ion batteries used in the verification were the same as those used in Example 1 and Comparative Examples 1 and 2 in the capacity density verification described above. Furthermore, voltages of 3.8V (below the decomposition voltage of lithium carbonate) and 4.3V (4.2V, the decomposition voltage of lithium carbonate) were applied to the positive electrodes of each lithium-ion battery, and the concentration of the generated carbon dioxide gas was measured. The carbon dioxide gas concentration was measured using gas chromatography.

[0092] exist Figure 3 The relationship between the amount of lithium carbonate added and the amount of carbon dioxide gas produced is shown in a graph.

[0093] according to Figure 3 The results show that, under an applied voltage of 4.3V, the amount of carbon dioxide produced in Example 1, which had 9% by mass of lithium carbonate added, was lower than that in Comparative Example 1, which did not add lithium carbonate to the positive electrode mixture, and Comparative Example 2, which had 3% by mass of lithium carbonate added.

[0094] Therefore, according to the present invention, it can be confirmed that when a cathode containing lithium carbonate in the range of 9% by mass or more and 20% by mass or less relative to the total weight of the cathode compound is used in order to increase the battery capacity, the amount of carbon dioxide gas generated can also be suppressed.

[0095] [Industry Applicability]

[0096] The positive electrode of the lithium-ion battery, the lithium-ion battery itself, and the method for manufacturing the positive electrode of the lithium-ion battery of the present invention balance the increase in battery capacity with the suppression of carbon dioxide gas production. When used as a secondary battery in vehicles such as EVs and HEVs, lithium-ion batteries can achieve long-distance driving on a single charge, improving energy efficiency. Therefore, they have industrial applicability.

Claims

1. A positive electrode for a lithium-ion battery, comprising a positive current collector and a positive active material layer, wherein the positive electrode of the lithium-ion battery is characterized in that... The positive electrode active material layer has a positive electrode mixture containing positive electrode active material. The cathode mixture comprises lithium carbonate, ternary cathode material (NMC), carbon black, and resin binder. The positive electrode mixture contains lithium carbonate in an amount ranging from 15% to 20% by mass relative to its total weight, in order to suppress the generation of carbon dioxide gas. The ternary cathode material (NMC) is composed of the general formula: LiNi x Co y Mn z M a O2 represents a composite metal oxide, in which... x+y+z+a=1, 0<x<1, 0<y<1, 0<z<1, 0<a<1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr. The mass ratio of the ternary cathode material (NMC), the carbon black, the resin binder, and the lithium carbonate is 75:5:5:15 or 70:5:5:

20.

2. A lithium-ion battery, characterized in that, The lithium-ion battery comprises: a positive electrode of the lithium-ion battery according to claim 1; a negative electrode having a negative current collector and a negative active material layer and being opposite to the positive electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode.

3. A method for manufacturing the positive electrode of a lithium-ion battery, which is the method for manufacturing the positive electrode of a lithium-ion battery as described in claim 1, characterized in that, The method for manufacturing the positive electrode of the lithium-ion battery includes: A mixing process in which the lithium carbonate, the ternary cathode material (NMC), the carbon black, the resin binder, and the organic solvent are added and mixed to obtain a compound; and The positive electrode active material layer formation process involves coating the compound onto the positive electrode current collector and allowing the organic solvent to evaporate to form the positive electrode active material layer.

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