Positive electrode material for lithium ion battery, electrode and lithium ion battery

Abstract

To provide a lithium ion battery with little performance deterioration even under a high temperature environment, an electrode for constituting such a lithium ion battery, and a material constituting the electrode.SOLUTION: The positive electrode material of the lithium-ion battery is a sintered body containing lithium cobalt oxide as a main component and contains AgCoO2. A content ratio of AgCoO2 in the sintered body is 0. 02wt% or more and 3wt% or less. An electrode for a positive electrode of a lithium ion battery includes the material as a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and is an integrally sintered body in which the positive electrode, the negative electrode, and the separator are integrally sintered. A lithium ion battery includes an electrode including the material as a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, an electrolytic solution impregnated in the electrode, and an exterior body in which the electrode and the electrolytic solution are accommodated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode material for a lithium ion battery, an electrode, and a lithium ion battery. [Background technology]

[0002] Known lithium-ion batteries include a positive electrode layer made of a sintered body of lithium composite oxide, a negative electrode layer made of a sintered body containing titanium, and a ceramic separator disposed between the positive electrode layer and the negative electrode layer. Patent Document 1 discloses a lithium-ion battery that is made of an integrated sintered plate in which the positive electrode layer, ceramic separator, and negative electrode layer are bonded together and that is impregnated with an electrolyte.

[0003] Patent Document 2 discloses a lithium-ion battery including a battery element in which a power generation sheet including a ceramic positive electrode layer, a ceramic separator, a ceramic negative electrode layer, and a ceramic insulating layer is wound into a roll. The lithium-ion battery of Patent Document 2 has a feature in the spatial configuration of the power generation sheet, in which the rolled battery element is an integral sintered body. The positive electrode layer is made of a lithium composite oxide sintered body, and the lithium composite oxide may contain one or more elements selected from Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn, Sb, Te, Ba, Bi, and W. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 221140 [Patent Document 2] Japanese Patent Publication No. 2022-101165 Summary of the Invention [Problem to be solved by the invention]

[0005] The range of applications for lithium-ion batteries continues to expand, and there is a demand for batteries that exhibit minimal performance degradation during use in harsher environments, especially high-temperature environments.

[0006] In view of this situation, one of the objects of the invention according to the present disclosure is to provide a lithium ion battery that exhibits little performance degradation even in high-temperature environments, an electrode for constituting such a lithium ion battery, and a material for constituting such an electrode. [Means for solving the problem]

[0007] The positive electrode material according to the present disclosure is a sintered body primarily composed of lithium cobalt oxide. The sintered body contains AgCoO2, and the AgCoO2 content in the sintered body is 0.02 wt% or more and 3 wt% or less. The electrode according to the present disclosure includes the material as a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and is an integrated sintered body in which the positive electrode, the negative electrode, and the separator are sintered together. The lithium-ion battery according to the present disclosure includes an electrode including the material as a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, an electrolyte impregnated in the electrode, and an exterior housing containing the electrode and the electrolyte. [Effects of the Invention]

[0008] The lithium ion battery exhibits little performance degradation during use even in high-temperature environments. The electrode and the positive electrode material provide a lithium ion battery that exhibits little performance degradation during use even in high-temperature environments. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a lithium-ion battery according to the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view illustrating a lithium-ion battery according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Outline of implementation] First, embodiments of the present disclosure will be listed and described. The material disclosed herein is a positive electrode material for lithium-ion batteries, and is a sintered body primarily composed of lithium cobalt oxide. The sintered body also contains AgCoO2. The AgCoO2 content in the sintered body is 0.02 wt% or more and 3 wt% or less.

[0011] Aiming to further improve the performance of lithium-ion batteries, studies are underway on the components that make up the electrodes, such as the positive electrode, negative electrode, and separator. Among these, studies have focused on suppressing the degradation of battery characteristics with use for positive electrodes composed of sintered bodies primarily composed of lithium cobalt oxide (LCO). While previous studies have attempted to coat the surfaces of LCO particles with other materials, these efforts have not been satisfactory. Through extensive research, the inventors have found that when sintered bodies composed of LCO contain a small amount of silver (Ag), particularly AgCoO2 at a specific ratio, batteries incorporating these sintered bodies exhibit low battery resistance and minimize capacity loss even during repeated charge-discharge cycles in high-temperature environments. Without being bound by theory, it is believed that the inclusion of AgCoO2 in the LCO sintered body suppresses side reactions, such as the decomposition of the electrolyte, on the electrode surface, thereby suppressing the degradation of battery characteristics with long-term use.

[0012] In the sintered body, the abundance ratio of AgCoO2 at the end portion in the thickness direction of the sintered body may be higher than the abundance ratio of AgCoO2 at the center in the thickness direction of the sintered body. By localizing AgCoO2 at the end portion in the thickness direction, in other words, near the surface of the sintered body, the effects of the present disclosure can be more reliably obtained.

[0013] The electrode according to the present disclosure includes the positive electrode material as a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the separator may be an integrated sintered body. When the positive electrode, the negative electrode, and the separator are configured as an integrated sintered body, an electrode having the effects according to the present disclosure can be stably manufactured without significantly modifying known methods. Using the electrode according to the present disclosure, a lithium ion battery can be provided that exhibits little performance degradation during use even in high-temperature environments.

[0014] The lithium-ion battery according to the present disclosure includes electrodes including the positive electrode material as a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, an electrolyte solution impregnated in the electrodes, and an exterior housing containing the electrodes and the electrolyte solution. The lithium-ion battery according to the present disclosure has low battery resistance and is less susceptible to performance degradation during use even in high-temperature environments.

[0015] In the lithium-ion battery, the electrode may include a plurality of positive electrode layers, a plurality of negative electrode layers, and a separator disposed between the positive electrode layers and the negative electrode layers, and may include an integrated sintered body in which the plurality of positive electrode layers, the plurality of negative electrode layers, and the separator are sintered together. When the electrode is a multilayer stacked electrode, it is possible to construct a battery that is smaller in size and has a larger capacity.

[0016] [Specific examples of embodiments] Next, specific embodiments of the cathode material, electrode, and lithium-ion battery according to the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and their description will not be repeated.

[0017] (Lithium-ion battery) The lithium ion battery according to the present disclosure may be in any form, and may be, for example, a small coin-type battery or a pouch-type battery. FIG. 1 is a schematic cross-sectional view showing the structure of a coin-type lithium ion battery, which is an example of the lithium ion battery according to the present disclosure. Note that FIG. 1 shows the actual configuration with some parts enlarged, emphasized, and omitted for ease of understanding. The configuration shown in FIG. 1 does not necessarily reflect the actual dimensions.

[0018] Referring to FIG. 1, a lithium-ion battery 10 includes a positive electrode layer 12 serving as a positive electrode, a negative electrode layer 13 serving as a negative electrode, a separator 14, an electrolyte 19, and an exterior body 20. The positive electrode layer 12 is formed of a sintered body containing Ag and lithium cobalt oxide. In the sintered body, at least a portion of the Ag exists as AgCoO2. The negative electrode layer 13 is formed of a sintered body containing lithium titanate. The separator 14 is made of resin or ceramic and is interposed between the positive electrode layer 12 and the negative electrode layer 13. The electrolyte 19 is impregnated into the positive electrode layer 12, the negative electrode layer 13, and the separator 14. The electrode 11 in the lithium-ion battery 10 includes the positive electrode layer 12 serving as a positive electrode, the negative electrode layer 13 serving as a negative electrode, the separator 14, a positive electrode current collector 15, and a negative electrode current collector 17.

[0019] The exterior body 20 has a sealed space, and the positive electrode layer 12, the negative electrode layer 13, the separator 14, and the electrolyte solution 19 are accommodated in this sealed space. The positive electrode layer 12 and the negative electrode layer 13 are sintered bodies formed separately. In another embodiment, the positive electrode layer 12, the separator 14, and the negative electrode layer 13 may form a single integrated sintered body as a whole. That is, the positive electrode layer 12, the separator 14, and the negative electrode layer 13 may be bonded to each other. Note that "forming a single integrated sintered plate" means that the three layers of the positive electrode layer 12, the separator 14, and the negative electrode layer 13 are connected and bonded to each other without relying on other bonding methods such as adhesives. In another embodiment, the positive electrode layer 12 and the separator 14 may form a single integrated sintered plate, and the negative electrode layer 13 may be a sintered plate formed separately from the single integrated sintered plate.

[0020] The exterior body 20 includes a positive electrode can 21, a negative electrode can 22, and a gasket 23. The positive electrode can 21 and the negative electrode can 22 are crimped together via the gasket 23 to form a sealed space. The positive electrode can 21 and the negative electrode can 22 may be made of a metal such as stainless steel. The gasket 23 may be an annular member made of an insulating resin such as polypropylene, polytetrafluoroethylene, or PFA resin, and is not particularly limited. The specific dimensions of the exterior body 20 are not particularly limited, but, as an example, it is preferable that the diameter is 25 mm or less and the thickness is 6 mm or less.

[0021] Referring to FIG. 1 , a lithium-ion battery 10 includes a positive electrode current collector 15 and a negative electrode current collector 17. The positive electrode current collector 15 and the negative electrode current collector 17 are preferably, but not limited to, metal foils such as copper foil or aluminum foil. The positive electrode current collector 15 is preferably disposed between the positive electrode layer 12 and the positive electrode can 21. The negative electrode current collector 17 is preferably disposed between the negative electrode layer 13 and the negative electrode can 22. A positive electrode-side carbon layer 16 is preferably disposed between the positive electrode layer 12 and the positive electrode current collector 15 to reduce contact resistance. Similarly, a negative electrode-side carbon layer 18 is preferably disposed between the negative electrode layer 13 and the negative electrode current collector 17 to reduce contact resistance. Both the positive electrode-side carbon layer 16 and the negative electrode-side carbon layer 18 are preferably composed of conductive carbon. The carbon layers can be formed, for example, by applying a conductive carbon paste to the surface of a metal foil current collector using screen printing or the like.

[0022] The thickness of the positive electrode layer 12 is preferably 30 to 500 μm, more preferably 40 to 400 μm, and even more preferably 50 to 300 μm. The thickness of the negative electrode layer 13 is preferably 30 to 500 μm, preferably 40 to 400 μm, and more preferably 50 to 350 μm.

[0023] The separator 14 is a resin separator, specifically, for example, a cellulose porous monolayer membrane. The resin separator is not limited to a cellulose porous monolayer membrane, and may be a monolayer separator formed of a resin. Examples of resins that can be used include polyimide and polyester (e.g., polyethylene terephthalate (PET)). The thickness of the separator is, for example, 15 μm or more, preferably 18 μm or more, and more preferably 20 μm or more. The thickness of the separator is, for example, 31 μm or less, preferably 28 μm or less, and more preferably 26 μm or less. By making the separator thicker, even if lithium dendrites (tree-like crystals of lithium) precipitate, it is possible to prevent short-circuiting between the positive electrode and the negative electrode due to lithium dendrites. Furthermore, by making the separator thinner, it is possible to facilitate permeation of the electrolyte and lithium ions, thereby reducing the internal resistance of the battery.

[0024] The electrodes in the lithium-ion battery according to the present disclosure are not limited to those including one layer each of a positive electrode, a negative electrode, and a separator as described above. The electrodes in the lithium-ion battery according to the present disclosure may be multilayer electrodes in which multiple positive electrode layers and multiple negative electrode layers are stacked with separators interposed therebetween. Figure 2 is a schematic cross-sectional view showing the structure of a lithium-ion battery 110, which is an example of an embodiment according to the present disclosure.

[0025] Referring to FIG. 2, the lithium-ion battery 110 houses an electrode 111 inside an exterior body 20. The exterior body 20 is the same as that in the lithium-ion battery 10, and description thereof will be omitted. The electrode 111 includes a sintered body 109, and a positive electrode current collector 115 and a negative electrode current collector 117 attached to both side surfaces of the sintered body 109. The sintered body 109 includes a plurality of positive electrode layers 112, a plurality of negative electrode layers 113, and a separator 114, which are stacked on top of each other. The sintered body 109 is a single, integrated sintered body as a whole.

[0026] In the sintered body 109, the positive electrode layers 112 and the negative electrode layers 113 are alternately stacked in the stacking direction (thickness direction). A separator 114 is interposed between the positive electrode layers 112 and the negative electrode layers 113. The separator 114 separates the positive electrode layers 112 and the negative electrode layers 113 from each other. The positive electrode layers 112 are made of a sintered body containing lithium cobalt oxide and AgCoO2 according to the present disclosure. The negative electrode layers 113 are made of, for example, a titanium-containing sintered body. The separator 114 is made of ceramic.

[0027] The negative electrode layer 113 includes a negative electrode current collector layer 129 in contact with the negative electrode layer 113. By including the negative electrode current collector layer 129, it is possible to reduce the internal resistance of the sintered body 109, particularly the negative electrode layer 113. The negative electrode current collector layer 129 may be provided inside the negative electrode layer 113 in the thickness direction. Alternatively, the negative electrode current collector layer 129 may be formed so as to be exposed on one of the main surfaces of the negative electrode layer 113. The negative electrode current collector layer 129 is made of a material with excellent conductivity.

[0028] The electrode 111 includes a positive electrode current collector 115 arranged in contact with the sintered body 109 from the side surface to the bottom surface of the sintered body 109. The electrode 111 also includes a negative electrode current collector 117 arranged in contact with the sintered body 109 from the side surface to the top surface of the sintered body 109. The positive electrode current collector 115 and the negative electrode current collector 117 may be metal foils such as aluminum foils. The positive electrode current collector 115 may contain or be made of LiCoO2, which is the positive electrode active material constituting the positive electrode layer 112. The negative electrode current collector 117 may be copper foil, silver foil, or silver. From the viewpoint of reducing contact resistance, carbon layers (not shown) are preferably provided between the positive electrode current collector 115 and the negative electrode current collector 117 and the sintered body 109. The carbon layers are preferably made of conductive carbon. The carbon layer can be formed, for example, by applying a conductive carbon paste to the surface of a metal foil used as a current collector.

[0029] Separators 114 are exposed on the top and bottom surfaces of the sintered body 109. That is, the top and bottom layers of the sintered body 109 are both layers of the separators 114. In the sintered body 109, a positive electrode layer 112 and a negative electrode layer 113 that face each other with the separator 114 interposed therebetween form one cell. Five cells are formed in the electrode 111 shown in FIG. 2. The number of cells in the electrode of the lithium ion battery according to the present disclosure is not limited as long as the effects of the invention are maintained, but may be, for example, 3 to 200.

[0030] Although the lithium ion batteries 10 and 110 shown in FIGS. 1 and 2 are in the form of coin-type batteries, the form of the lithium ion battery according to the present disclosure is not limited to coin-type batteries. For example, other forms, such as thin secondary batteries including chip-type secondary batteries and pouch-type secondary batteries, may also be used. When the lithium ion battery is a chip-type battery that can be built into a card, the exterior body is preferably a resin substrate, and the electrodes and electrolyte are embedded within the resin substrate. When the lithium ion battery is a pouch-type secondary battery, the electrodes may be sandwiched between a pair of resin films. The pair of resin films may be bonded together with an adhesive. Furthermore, the pair of resin films may be heat-sealed together by a heat press. Furthermore, a separator made of a solid electrolyte may be used as the separator, and may not contain an electrolyte.

[0031] Next, each component included in the electrode of the lithium ion battery according to the present disclosure will be described in more detail.

[0032] (positive electrode) The positive electrode is composed of a sintered body mainly composed of lithium cobalt oxide. Here, "mainly composed of" means that 50 wt% or more of the sintered body is lithium cobalt oxide. In the sintered body constituting the positive electrode, the content ratio of lithium cobalt oxide is 50 wt% or more of the sintered body, preferably 75 wt% or more, more preferably 90% or more, and still more preferably 95 wt% or more. The positive electrode can be made to contain no binder or conductive aid. Specifically, examples of lithium cobalt oxide include LiCoO2 (hereinafter, may be abbreviated as LCO).

[0033] As the lithium cobalt oxide constituting the primary particles in the positive electrode, in addition to LCO, for example, Li x NiCoO2 (lithium nickel cobalt oxide), Li x CoNiMnO2 (lithium cobalt nickel manganese oxide), Li x CoMnO2 (lithium cobalt manganese oxide) and the like can be mentioned. Further, in addition to lithium cobalt oxide, other lithium composite oxides may be included. Examples of the lithium composite oxide include Li x MO2 (where 0.05 < x < 1.10, M is at least one kind of transition metal, and M typically includes one or more of Co, Ni, and Mn) can be mentioned.

[0034] When the positive electrode is composed of a plate-shaped sintered body containing LCO, the transition metal element among the elements constituting the positive electrode is Co. Further, when the positive electrode is composed of a sintered body containing Li x NiCoO2 (lithium nickel cobalt oxide), the transition metal elements among the elements constituting the positive electrode are Ni and Co. Further, when the positive electrode is composed of a sintered body containing Li x CoNiMnO2 (lithium cobalt nickel manganese oxide), the transition metal elements among the elements constituting the positive electrode are Ni, Co, and Mn.

[0035] The average particle size of the primary particles of the LCO constituting the positive electrode is preferably 5 μm or more. Specifically, the average particle size of the primary particles is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 12 μm or more. The particle size of the primary particles of the LCO is a value measured and calculated by particle size distribution measurement using a laser diffraction / scattering method.

[0036] The sintered body constituting the positive electrode may contain pores. When the sintered body contains pores, particularly open pores, and is incorporated into a battery as a positive electrode layer, the electrolyte can penetrate into the sintered body, thereby improving lithium ion conductivity. The porosity of the positive electrode is preferably 10 to 60%, more preferably 20 to 55%, and even more preferably 30 to 50%. The porosity of the sintered body can be measured according to a known method.

[0037] The average pore size of the sintered body constituting the positive electrode is preferably 0.1 to 10.0 μm, more preferably 0.2 to 5.0 μm, and even more preferably 0.25 to 3.0 μm. Within this range, localized stress concentration at large pores is suppressed, and stress within the sintered body is more easily released uniformly. Furthermore, the lithium ion conductivity can be more effectively improved by the internal penetration of the electrolyte solution through the pores.

[0038] The sintered body according to the present disclosure is primarily composed of lithium cobalt oxide and contains AgCoO2. The AgCoO2 content in the sintered body is 0.02 wt% or more and 3 wt% or less. The presence of AgCoO2 in the sintered body can be confirmed using high-angle annular dark-field scanning transmission microscopy (HAADF-STEM). The AgCoO2 content in the sintered body is calculated by image processing of the spherical Ag observed by SEM-EDS mapping and the layered AgCoO2 precipitated on the LCO surface.

[0039] The sintered body according to the present disclosure preferably has an AgCoO2 layer formed on the surface of the sintered body. In other words, the abundance ratio of AgCoO2 at the edge of the sintered body in the thickness direction is preferably greater than the abundance ratio of AgCoO2 at the center of the sintered body in the thickness direction. Here, the edge of the sintered body in the thickness direction refers to a region within 10% of the thickness of the sintered body from the surface. The center of the thickness direction refers to a region within 10% of the thickness of the sintered body from the center in the thickness direction. It is believed that the sintered body according to the present disclosure has a low-reactivity AgCoO2 layer on the surface, which suppresses side reactions such as decomposition of the electrolyte on the surface of the positive electrode. As a result, it is believed that deterioration of battery characteristics is suppressed even when used for long periods in high-temperature environments.

[0040] The sintered body according to the present disclosure may contain Ag particles in addition to AgCoO. The total amount of Ag constituting AgCoO and Ag present as Ag particles in the sintered body may be 0.01 wt% or more and 2.0 wt% or less with respect to the entire sintered body.

[0041] (separator) The separator in the lithium-ion battery according to the present disclosure may be a resin separator, a ceramic separator, or a laminate of two or more layers of ceramic and resin. It may also be a microporous membrane formed solely of ceramic. When the separator is a ceramic separator, it may be, for example, at least one selected from MgO, Al2O3, ZrO, SiC, Si3N4, AlN, and cogenerite. Preferably, it may be at least one selected from MgO, Al2O3, and ZrO2.

[0042] When the separator is a ceramic separator, it has the advantage of being excellent in heat resistance and being able to be manufactured as a single integrated sintered body together with the positive and negative electrodes. The thickness of the ceramic separator is preferably 3 to 40 μm, more preferably 5 to 35 μm, and even more preferably 10 to 30 μm. The porosity of the ceramic separator is preferably 30 to 85%, more preferably 40 to 80%.

[0043] (Negative electrode) The negative electrode is, for example, a plate-shaped sintered body containing a titanium-containing composition. The negative electrode may contain no binder or conductive additive. The titanium-containing sintered body is lithium titanate Li4Ti5O 12 It is preferable that the battery contains Li4Ti5O (hereinafter referred to as LTO) or niobium titanium composite oxide Nb2TiO7, and more preferably contains LTO. Although LTO is known to typically have a spinel structure, it can also adopt other structures during charge and discharge. For example, LTO can be Li4Ti5O 12 (spinel structure) and Li7Ti5O 12 The reaction proceeds in the coexistence of two phases, a spinel phase (rock salt structure) and a spinel phase (rock salt structure). Therefore, LTO is not limited to a spinel structure. LTO may be partially substituted with other elements. Examples of other elements include Nb, Ta, W, Al, and Mg. An LTO sintered body can be produced, for example, according to the method described in JP 2015-185337 A.

[0044] When the negative electrode is composed of a sintered body containing LTO, the transition metal element among the elements constituting the negative electrode is Ti. When the negative electrode is composed of a sintered body containing Nb2TiO7, the transition metal elements among the elements constituting the negative electrode are Nb and Ti. The negative electrode has a structure in which many primary particles are bonded together. It is preferable that these primary particles are composed of LTO or Nb2TiO7.

[0045] The primary particle size, which is the average particle size of the plurality of primary particles that make up the negative electrode, is preferably 1.2 μm or less, more preferably 0.02 to 1.2 μm, and even more preferably 0.05 to 0.7 μm.

[0046] The negative electrode layer, which is the negative electrode, preferably contains pores. By containing pores, particularly open pores, when the negative electrode is incorporated into a battery, the electrolyte can penetrate into the interior, resulting in improved lithium ion conductivity. The porosity of the negative electrode layer is preferably 20 to 60%, more preferably 30 to 55%, and even more preferably 35 to 50%. The average pore diameter of the negative electrode layer is preferably 0.08 to 5.0 μm, more preferably 0.1 to 3.0 μm, and even more preferably 0.12 to 1.5 μm.

[0047] (current collector) The current collector is, for example, a layer of metal foil made of a metal such as aluminum. The current collector may also include a conductive carbon layer laminated on the upper surface of the metal foil current collector in contact with the current collector. In other words, the main surface of the current collector facing the positive electrode layer or the negative electrode layer may be coated with a conductive carbon layer. The metal foil may be formed of various metals other than aluminum (e.g., copper, nickel, silver, gold, chromium, iron, tin, lead, tungsten, molybdenum, titanium, zinc, or alloys containing these). The current collector layer does not necessarily include a conductive carbon layer. The positive electrode current collector layer and the negative electrode current collector layer may have the same configuration or different configurations.

[0048] The negative electrode current collector can be made of a material with excellent conductivity. In the lithium-ion battery according to the present disclosure, the negative electrode current collector preferably contains Ag (silver). In addition to Ag, the negative electrode current collector may further contain one or more elements selected from the group consisting of Au (gold), Pt (platinum), Pd (palladium), Al (aluminum), Cu (copper), and Ni (nickel). The Ag content in the negative electrode current collector may be 30% or more, more preferably 50% or more, and even more preferably 100%.

[0049] (electrolyte) The lithium-ion battery according to the present disclosure includes an electrolyte. The electrolyte is not particularly limited, and any electrolyte known for use in lithium-ion batteries can be used. For example, the solvent can be one or a combination of two or more selected from ethylene carbonate (EC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and γ-butyrolactone (GBL). The electrolyte dissolved in the solvent can be, for example, a lithium salt compound such as lithium hexafluorophosphate (LiPF6) or lithium fluoroborate (LiBF4). The electrolyte 22 may further include at least one additive selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinylethylene carbonate (VEC), and lithium difluoro(oxalato)borate (LiDFOB).

[0050] The concentration of the electrolyte in the electrolytic solution is preferably 0.5 to 4.0 mol / L, more preferably 0.6 to 3.0 mol / L, even more preferably 0.7 to 2.5 mol / L, and particularly preferably 0.8 to 2.0 mol / L.

[0051] In addition to an electrolytic solution, a solid electrolyte or a polymer electrolyte can also be used as the electrolyte. In this case, as with an electrolytic solution, it is preferable that the electrolyte is impregnated at least into the pores of the separator. The impregnation method is not particularly limited, but examples include a method in which the electrolyte is melted and infiltrated into the pores of the separator, and a method in which a powder compact of the electrolyte is pressed against the separator.

[0052] (Manufacturing method) The method for producing the sintered body, electrode, and lithium ion battery according to the present disclosure is not particularly limited, but they can be produced, for example, by the following method.

[0053] (Method of manufacturing a sintered body for a positive electrode) The sintered body for a positive electrode according to the present disclosure can be manufactured through (a) preparing an Ag-containing LCO green sheet and (b) firing the Ag-containing LCO green sheet.

[0054] (a) Preparation of Ag-containing LCO green sheets Prepare lithium cobalt oxide (LCO) raw powder and Ag powder. The LCO raw powder may be commercially available or newly synthesized. The volumetric basis D of the LCO raw powder 50 The particle size is not particularly limited and may be, for example, 0.05 to 5.0 μm, preferably 0.1 to 2.0 μm. The LCO raw material powder may be pulverized to the desired particle size using, for example, a pot mill, a bead mill, or a jet mill. Larger particle sizes of the LCO raw material powder tend to result in larger pores in the sintered plate. Commercially available Ag powder can be used as is, or after pretreatment, if necessary. Examples of pretreatment for Ag powder include dispersion, washing, and pulverization. The LCO raw material powder and Ag powder are mixed with a dispersion medium and various additives (binder, plasticizer, dispersant, etc.) to form a slurry. The slurry is preferably stirred under reduced pressure to degas and adjusted to a viscosity of 4000 to 10000 cP. The resulting slurry is formed into a sheet to obtain an Ag-containing LCO green sheet. Sheet formation is achieved, for example, by applying the slurry to a resin film such as PET using a doctor blade method. The thickness of the Ag-containing LCO green sheet can be appropriately set taking into account the thickness after sintering. The Ag-containing LCO green sheet may be a single layer, or, for example, 2 to 30 green sheets may be stacked and pressure-bonded to form an integrated body. A single layer or a pressure-bonded green sheet of multiple layers can be cut to the desired shape. By combining multiple Ag-containing LCO green sheets with different Ag contents, or by combining an Ag-containing LCO green sheet with an Ag-free LCO green sheet, it is possible to produce sintered bodies with different Ag concentrations in the thickness direction.

[0055] (b) Firing of Ag-containing LCO green sheets An Ag-containing LCO green sheet is placed on a setter. The setter is made of ceramic, preferably zirconia or magnesia. The setter is preferably embossed. The green sheet placed on the setter is then placed in a sheath. The sheath is also made of ceramic, preferably alumina. After optional degreasing, the green sheet is fired to obtain an AgCoO2-containing LCO sintered body. Firing can be performed at 600 to 900°C for 0.1 to 50 hours, preferably at 700 to 800°C for 0.1 to 20 hours. The heating rate during firing can be 100 to 3000°C / h, preferably 200 to 2500°C / h. The heating rate may be constant throughout the heating process, or it may not be constant. For example, the heating rate may be varied depending on the temperature range and elapsed time.

[0056] By controlling the firing temperature, it is possible to control the ratio of Ag (Ag particles present as simple Ag) to AgCoO2 in the sintered body. The higher the firing temperature, the greater the ratio of AgCoO2 to Ag.

[0057] The Ag-containing LCO green sheet may be laminated with a separately prepared LTO green sheet or separator green sheet, and then compressed together and sintered to obtain an integrated sintered plate-type electrode in which the positive electrode, negative electrode, and separator are integrated.

[0058] (Lithium-ion battery manufacturing method) The method for producing a lithium ion battery according to the present disclosure can be appropriately selected depending on the form of the lithium ion battery and is not particularly limited. The sintered plate obtained by the above-mentioned production method is used as a positive electrode, and is combined with a negative electrode, a separator, and further a negative electrode current collector and a positive electrode current collector, and is housed in an outer casing, and an electrolyte is enclosed and sealed to obtain a lithium ion battery.

[0059] [Examples and Comparative Examples] The sintered body, electrode, and lithium-ion battery according to the present disclosure will be described in more detail below with reference to examples and comparative examples. Samples 1 to 8 are within the scope of the lithium-ion battery according to the present disclosure and are examples. Samples 9 to 11 are examples outside the scope of the lithium-ion battery according to the present disclosure and are comparative examples.

[0060] [Sample 1] A lithium ion battery was fabricated according to the methods described in 1 to 7 below.

[0061] 1. Preparation of the Positive Electrode Plate Co3O4 powder (manufactured by Seido Chemical Industry Co., Ltd.) and Li2CO3 powder (manufactured by Honjo Chemical Co., Ltd.) were weighed so that the molar ratio of Li / Co was 1.01, and then mixed. The mixture was kept at 780 °C for 5 hours. The obtained powder was milled in a pot mill to a volumetric standard of D 50 The powder was crushed to a particle size of 0.4 μm to obtain a powder consisting of LCO platelet particles. One hundred parts by weight of the resulting LCO powder was mixed with 2 parts by weight of Ag powder, 100 parts by weight of a dispersion medium (toluene:isopropanol = 1:1), 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), 2 parts by weight of a plasticizer (DOP: Di(2-ethylhexyl)phthalate, manufactured by Kurogane Kasei Co., Ltd.), and 4.5 parts by weight of a dispersant (product name Rheodol SP-O30, manufactured by Kao Corporation). The resulting mixture was stirred under reduced pressure to degas and the viscosity was adjusted to 4000 cP to prepare an LCO slurry. The prepared slurry was formed into a sheet on a PET film to form an LCO green sheet. The thickness of the positive electrode layer after firing was adjusted to 150 μm. The resulting green sheet was punched out to a diameter of 16.5 mm using a puncher, then heated from room temperature to 400°C and degreased for 5 hours. The temperature was then raised to 800°C and held there for 10 minutes for firing, after which the sheet was cooled to obtain a positive electrode plate. The Ag and AgCoO2 contents in the positive electrode plate were confirmed using SEM-EDS. The Ag content was 1.99 wt% and the AgCoO2 content was 0.02 wt%.

[0062] 2. Preparation of the Negative Electrode Plate LTO powder (volume basis D 50 100 parts by weight of a 0.6 μm particle size (manufactured by Ishihara Sangyo Kaisha, Ltd.), 100 parts by weight of a dispersion medium (toluene:isopropanol = 1:1), 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), 2 parts by weight of a plasticizer (DOP: Di(2-ethylhexyl)phthalate, manufactured by Kurogane Kasei Co., Ltd.), and 2 parts by weight of a dispersant (product name Rheodol SP-O30, manufactured by Kao Corporation) were mixed. The resulting negative electrode raw material mixture was stirred under reduced pressure to degas and the viscosity was adjusted to 4000 cP to prepare an LTO slurry. The prepared slurry was formed into a sheet on a PET film to form an LTO green sheet. The thickness of the negative electrode layer after firing was adjusted to 150 μm. The obtained green sheet was punched out to a diameter of 16.5 mm using a puncher, then heated from room temperature to 400°C and degreased for 5 hours, then heated to 800°C and held there for 10 minutes to be fired, and then cooled to obtain a negative electrode plate.

[0063] 3. Separator Preparation As a separator, a 25 μm thick cellulose porous single layer membrane (manufactured by Nippon Kodo Paper Industries Co., Ltd.) was prepared.

[0064] 4. Preparation of Conductive Carbon Paste A binder (CMC: MAC350HC, manufactured by Nippon Paper Industries Co., Ltd.) was weighed out to 1.2 wt% in pure water and dissolved using a stirrer to obtain a 1.2 wt% CMC solution. A carbon dispersion (product number: BPW-229, manufactured by Nippon Graphite Co., Ltd.) and a dispersant solution (product number LB-300, manufactured by Showa Denko K.K.) were prepared. Next, the carbon dispersion, dispersant solution, and 1.2 wt% CMC solution were weighed out to a ratio of 0.22:0.29:1, and these were mixed using a planetary mixer to prepare a conductive carbon paste.

[0065] 5. The positive electrode plate and aluminum foil are joined with conductive carbon paste The conductive carbon paste obtained in step 4 was screen-printed onto an aluminum foil serving as a positive electrode current collector. A positive electrode plate was placed so that it fit within the undried printed pattern (the area where the conductive carbon paste was applied), lightly pressed with a finger, and then vacuum-dried at 50°C for 60 minutes. In this way, the positive electrode plate and the positive electrode current collector were bonded via a conductive carbon adhesive layer. The thickness of the conductive carbon adhesive layer was 8 μm.

[0066] 6. The negative electrode plate and aluminum foil are joined with conductive carbon paste In the same manner as in 5., aluminum foil was adhered to the negative electrode plate as a negative electrode current collector via a conductive carbon adhesive layer.

[0067] 7. Fabrication of Lithium-ion Batteries The positive and negative cans that comprised the battery case were stacked in this order from the positive can to the negative can: positive current collector, positive plate, separator, negative plate, negative current collector, and wave washer. After filling the battery with electrolyte, the positive and negative cans were crimped together with a gasket to seal. This resulted in a coin-cell lithium-ion battery measuring 20 mm in diameter and 1.6 mm thick. The electrolyte was a 1.5 mol / L solution of LiPF6 in an organic solvent consisting of a 1:3 volumetric mixture of propylene carbonate (PC) and gamma-butyrolactone (GBL).

[0068] [Sample 2] A lithium-ion battery was fabricated in the same manner as Sample 1, except that the baking temperature of the positive electrode plate was set to 820°C. The Ag and AgCoO2 contents in the positive electrode plate were confirmed in the same manner as Sample 1. The Ag content in the positive electrode plate was 1.95 wt%, and the AgCoO2 content was 0.1 wt%.

[0069] [Sample 3] A lithium-ion battery was fabricated in the same manner as Sample 1, except that the baking temperature of the positive electrode plate was set to 830°C. The Ag and AgCoO2 contents in the positive electrode plate were confirmed in the same manner as Sample 1. The Ag content in the positive electrode plate was 1.90 wt%, and the AgCoO2 content was 0.2 wt%.

[0070] [Sample 4] A lithium-ion battery was fabricated in the same manner as Sample 1, except that the baking temperature of the positive electrode plate was set to 840°C. The Ag and AgCoO2 contents in the positive electrode plate were confirmed in the same manner as Sample 1. The Ag content in the positive electrode plate was 1.75 wt%, and the AgCoO2 content was 0.5 wt%.

[0071] [Sample 5] A lithium-ion battery was fabricated in the same manner as Sample 1, except that the baking temperature of the positive electrode plate was set to 850°C. The Ag and AgCoO2 contents in the positive electrode plate were confirmed in the same manner as Sample 1. The Ag content in the positive electrode plate was 1.50 wt%, and the AgCoO2 content was 1 wt%.

[0072] [Sample 6] A lithium-ion battery was fabricated in the same manner as Sample 1, except that the baking temperature of the positive electrode plate was set to 880°C. The Ag and AgCoO2 contents in the positive electrode plate were confirmed in the same manner as Sample 1. The Ag content in the positive electrode plate was 1.00 wt%, and the AgCoO2 content was 2 wt%.

[0073] [Sample 7] A lithium-ion battery was fabricated in the same manner as Sample 1, except that the baking temperature of the positive electrode plate was set to 900°C. The Ag and AgCoO2 contents in the positive electrode plate were confirmed in the same manner as Sample 1. The Ag content in the positive electrode plate was 0.50 wt%, and the AgCoO2 content was 3 wt%.

[0074] [Sample 8] Ag-containing LCO green sheets and LTO green sheets were produced in the same manner as in Sample 1. Separator green sheets were also prepared as follows. Magnesium carbonate powder (manufactured by Konoshima Chemical Co., Ltd.) was heat-treated at 900°C for 5 hours to obtain MgO powder. The obtained MgO powder and glass frit (manufactured by Nippon Frit Co., Ltd., CK0199) were mixed in a weight ratio of 7:3. The obtained mixed powder (volume basis D 50 100 parts by weight of powder (particle size 0.4 μm), 100 parts by weight of a dispersion medium (toluene:isopropanol = 1:1), 30 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), 6 parts by weight of a plasticizer (DOP: Di(2-ethylhexyl)phthalate, manufactured by Kurogane Kasei Co., Ltd.), and 2 parts by weight of a dispersant (product name Rheodol SP-O30, manufactured by Kao Corporation) were mixed. The resulting raw material mixture was stirred under reduced pressure to degas and the viscosity was adjusted to 4000 cP to prepare a slurry. The prepared slurry was formed into a sheet on a PET film to form a separator green sheet. The thickness of the separator layer after firing was adjusted to 25 μm. The prepared Ag-containing LCO green sheet, LTO green sheet, and separator green sheet were cut to be laminated and laminated by WIP (hot isostatic pressing). After that, they were punched out to φ16.5 mm with a puncher, degreased at 500°C for 5 hours in a dry environment, and then sintered at 900°C for 1 hour to obtain an electrode plate as an integrated sintered body. Using the obtained electrode plate, a lithium ion battery was fabricated in the same manner as in Sample 1. The contents of Ag and AgCoO2 in the positive electrode plate were confirmed in the same manner as in Sample 1. The contents of Ag in the positive electrode plate were 0.50 wt%, and the contents of AgCoO2 were 3 wt%.

[0075] [Sample 9] A lithium-ion battery was fabricated in the same manner as Sample 1, except that no Ag powder was added in the fabrication of the positive electrode plate and the firing temperature was set to 880°C. The Ag content in the positive electrode plate was 0 wt%, and the AgCoO2 content was also 0 wt%.

[0076] [Sample 10] A lithium-ion battery was fabricated in the same manner as Sample 1, except that the baking temperature of the positive electrode plate was set to 780°C. The Ag and AgCoO2 contents in the positive electrode plate were confirmed in the same manner as Sample 1. The Ag content in the positive electrode plate was 1.99 wt%, and the AgCoO2 content was 0.01 wt%.

[0077] [Sample 11] A lithium-ion battery was fabricated in the same manner as Sample 1, except that the baking temperature of the positive electrode plate was set to 920°C. The Ag and AgCoO2 contents in the positive electrode plate were confirmed in the same manner as Sample 1. The Ag content in the positive electrode plate was 0 wt%, and the AgCoO2 content was 4 wt%.

[0078] [evaluation] The obtained lithium ion batteries of Samples 1 to 11 were evaluated by the following method.

[0079] Evaluation 1. Battery resistance ratio The resistance value at 1 Hz at a state of charge (SOC) of 30% was measured by AC impedance measurement for each of the lithium-ion batteries of Samples 1 to 11. The resistance value of each of the lithium-ion batteries of Samples 1 to 8, 10, and 11 was calculated as a battery resistance ratio (%), assuming that the resistance value of the lithium-ion battery of Sample 9, which does not contain Ag, was 100%.

[0080] Evaluation 2: Capacity retention rate under high temperature conditions Each lithium-ion battery of Samples 1 to 11 was subjected to constant current / constant voltage (CCCV) charging (0.2C / 0.02C) in an 85°C environment until the voltage reached 2.7V. After charging, the battery was discharged (0.2C) in an 85°C environment, and the initial discharge capacity was calculated. This cycle was repeated 100 times, and the capacity retention rate (%) was calculated by dividing the discharge capacity at the 100th cycle by the initial discharge capacity.

[0081] The configurations of the lithium-ion batteries of Samples 1 to 11 and the results of Evaluations 1 and 2 are summarized in Table 1.

[0082] [Table 1]

[0083] As shown in Table 1, the lithium-ion batteries of Samples 1 to 8 had a capacity retention rate of 83 to 95%, which was higher than that of Sample 9, which did not contain AgCoO2. Furthermore, the lithium-ion batteries of Samples 1 to 8 had a battery resistance ratio of 100% to 120%, and the increase in battery resistance was not significant. In contrast, Sample 10, which contained 0.01 wt% AgCoO2, did not show an improvement in capacity retention rate compared to Sample 9, which did not contain AgCoO2. Furthermore, Sample 11, which contained 4 wt% AgCoO2, showed an improvement in capacity retention rate, but its battery resistivity was 200%, and it was determined that the battery resistance was excessive.

[0084] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present disclosure is defined not by the above description but by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0085] 10, 110 Lithium-ion battery, 11, 111 Electrode, 12, 112 Positive electrode layer, 13, 113 Negative electrode layer, 14, 114 Separator, 15, 115 Positive electrode current collector, 16 Positive electrode side carbon layer, 17, 117 Negative electrode current collector, 18 Negative electrode side carbon layer, 19 Electrolyte, 20 Exterior body, 21 Positive electrode can, 22 Negative electrode can, 23 Gasket, 109 Sintered body, 129 Negative electrode current collector layer.

Claims

1. A sintered body containing lithium cobalt oxide as a main component, AgCoO ２ Contains AgCoO in the sintered body ２ The content ratio is 0.02 wt% or more and 3 wt% or less, Positive electrode material for lithium-ion batteries.

2. AgCoO at the end of the sintered body in the thickness direction ２ The abundance ratio of AgCoO at the center in the thickness direction of the sintered body is ２ is greater than the abundance ratio of The positive electrode material for a lithium ion battery according to claim 1.

3. a positive electrode material according to claim 1 or 2 as a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; The electrode is an integrated sintered body in which the positive electrode, the negative electrode, and the separator are sintered together.

4. an electrode including the positive electrode material according to claim 1 or 2 as a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; an electrolyte impregnated in the electrode; and an exterior body that accommodates the electrodes and the electrolyte solution. Lithium-ion battery.

5. The electrode is a plurality of positive electrode layers, a plurality of negative electrode layers, and a separator disposed between the positive electrode layers and the negative electrode layers; the electrode includes an integrated sintered body in which the plurality of positive electrode layers, the plurality of negative electrode layers, and the separator are sintered together; The lithium ion battery of claim 4.

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