Secondary battery

Abstract

Space probes used on planets other than Earth and on asteroids need to withstand severe environmental conditions. One aspect of the present invention provides a space probe to which is mounted a secondary battery that can be used over a wide temperature range and is hardly affected by environmental temperatures. In addition, the present invention provides a secondary battery that is suitable for the space probe and is very safe. According to the present invention, an electrolyte is put in a container such as a bag and is sealed. The electrolyte is kept sealed in an airtight manner in the bag from Earth to a target planet, and is subjected to an impact at the time of landing on the target planet and after a while, the secondary battery is supplied with the electrolyte and functions as a secondary battery. A battery reaction does not occur until a portion of the bag of the electrolyte is broken by the impact.

Description

secondary battery

[0001] One embodiment of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One embodiment of the present invention relates to a power storage device including a secondary battery, a semiconductor device, a display device, a light-emitting device, a lighting device, an electronic device, or a manufacturing method thereof.

[0002] In this specification, the term "electronic device" refers to any device having a power storage device, and includes electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like.

[0003] In this specification, the term "electricity storage device" refers to elements and devices in general that have an electricity storage function, including, for example, lithium ion secondary battery electricity storage devices (also called secondary batteries), lithium ion capacitors, and electric double layer capacitors.

[0004] In recent years, the development of various power storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries, has been actively pursued. Demand for high-power, high-energy-density lithium-ion secondary batteries has been rapidly expanding in conjunction with the development of portable information terminals, such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical devices, next-generation clean-energy automobiles, such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs), and the semiconductor industry. These batteries have become indispensable in the modern information society as a rechargeable energy source.

[0005] There is also an increasing demand for electronic devices that can withstand harsh environments, specifically low temperatures (e.g., −50° C.) or high temperatures (e.g., 100° C.), and are intended for use over a wide range of operating temperatures. Examples include observation equipment around the Antarctic or Arctic, seismometers installed around the craters of active volcanoes, artificial satellites orbiting the Earth, and probes intended for use in investigating other planets.

[0006] It is also desirable for the seismometer or probe to be highly resistant to shocks such as those caused by being dropped. It would be convenient if the seismometer could be dropped from an unmanned aircraft and installed near a crater where it would be dangerous for humans to carry the measuring device. There are also plans to drop a penetrator from a satellite orbiting the planet to install a seismometer from the planet's surface to its interior. A penetrator is an exploration probe equipped with a dual-axis seismometer.

[0007] Conventionally, 18650 type cylindrical can batteries have been used as power sources for such electronic devices. Conventionally, primary batteries have been used for one-time use, and are disposable after a short period of use and function as a power source.

[0008] However, when considering long-term measurements or weight restrictions during transportation, it is desirable to use secondary batteries that can be charged using solar cells. It is also desirable to be able to collect the measuring equipment after installation and reuse it.

[0009] The present applicant has disclosed in Patent Documents 1 and 2 a strong secondary battery that can bend even when an external force is applied thereto.

[0010] Patent Document 3 discloses a cylindrical primary battery in which a conventional electrolyte is placed in an electrolyte container, and when an impact of an acceleration of 5 G or more is applied, the electrolyte container breaks, releasing the electrolyte and initiating a battery reaction.

[0011] JP 2020-198318 A JP 2020-188030 A JP 2008-262738 A

[0012] Probes used on planets and asteroids other than Earth must withstand harsh environmental conditions, specifically large temperature changes. For example, the temperature range on the surface of Mars is between -140°C and 20°C, and it is preferable for the secondary battery placed inside the housing to be able to operate sufficiently even at an internal temperature of -40°C or -30°C. The -40°C or -30°C refers to the internal temperature of the secondary battery; the temperature around the secondary battery, i.e., the environmental temperature, is even lower.

[0013] It is also preferable to make the secondary battery usable even if the temperature drops below -40°C and the battery or the electrolyte inside the battery freezes, by heating it with a heater to thaw it.

[0014] One type of astronomical observation device is a rocket-shaped probe called a penetrator, which performs autonomous observations. The secondary batteries installed in penetrators are expected to have high impact resistance. Surrounding the secondary batteries with thick metal plates is one way to provide impact resistance, but this would significantly increase the total weight. Using all-solid-state batteries is also an option, but solids made by sintering powder under pressure may crack due to the impact of a fall, making them unable to charge or discharge.

[0015] Conventional 18650-type cylindrical lithium-ion batteries are filled with electrolyte inside a cylindrical can, and the wound body inside the can is connected to the external terminals. Because a large amount of electrolyte is filled into the can, there is a risk that the wound body may shift position due to impact. Temperature changes also pose a risk of electrolyte expansion or gasification. Batteries using conventional cylindrical cans are vulnerable to drop impacts and are at risk of leakage.

[0016] Furthermore, because all-solid-state batteries are at least partially made of ceramics, they are brittle when subjected to impact, and if they crack, they lose conductivity and may become unusable.

[0017] The secondary battery has an area in which an electrolyte is contained between an exterior body and a positive electrode or a negative electrode, and when subjected to an impact of a predetermined impact value or greater, a part of the boundary of the area is destroyed, bringing the electrolyte into contact with the positive electrode and / or negative electrode, causing a battery reaction in the secondary battery.

[0018] In the above configuration, the boundary between the regions is formed by a diaphragm or a film. For example, the electrolyte is placed in a film bag and sealed. The diaphragm may be, for example, an ion exchange membrane. The diaphragm or film may be made of a material that has the function of separating the electrolyte from the positive electrode so that they do not come into contact with each other, or separating the electrolyte from the negative electrode so that they do not come into contact with each other.

[0019] A typical example of a secondary battery is one that uses a laminate film as an exterior body, rather than a cylindrical or coin-shaped body. Under reduced pressure, a bag containing an electrolyte, a positive electrode, a separator, or a negative electrode is sealed with the exterior body.

[0020] The electrolyte is separated from the positive or negative electrode by a diaphragm, or a container or bag containing the electrolyte is placed between the exterior body and the positive or negative electrode.

[0021] Conventionally, the internal space of a secondary battery is filled with an electrolyte solution, and the battery is sealed in a state where the electrolyte solution is in contact with the positive electrode or the negative electrode.

[0022] On the other hand, in the present invention, the electrolyte is placed in a container such as a bag and sealed. Therefore, the electrolyte is sealed under reduced pressure, the internal space is not filled with the electrolyte, and in this state the electrolyte is not in contact with the positive electrode (or negative electrode), so charging and discharging are not possible.

[0023] When a secondary battery of the present invention, which uses a laminate film for its exterior, is subjected to impact or deformation, such as bending, a portion of the electrolyte bag located in the internal space of the secondary battery is torn, and the electrolyte is supplied to the gaps inside the secondary battery or to the separator, etc., and contacts the positive or negative electrode. When used as a penetrator, the electrolyte is kept sealed in the bag from Earth to the target planet, and after an impact upon landing on the target planet, the electrolyte is supplied and the battery functions as a secondary battery. No battery reaction occurs until a portion of the electrolyte bag is torn upon impact. Only after a portion of the electrolyte bag is torn and the electrolyte is released does the battery function. Therefore, the secondary battery does not self-discharge or leak until landing. Furthermore, there is no risk of malfunction or short circuit until landing.

[0024] Furthermore, even if the electrolyte freezes during long travel in space, it can be thawed after landing using a heater or the like, allowing it to function as a secondary battery. It is also preferable to use a mixed organic solvent or ionic liquid with a low melting point to prevent the electrolyte from freezing. Secondary batteries using a laminate film as their exterior (also called laminated type) can withstand the impact of landing, and the container or bag containing the electrolyte can also function as a shock absorber, dispersing the impact. The laminate film exterior itself can also deform to a certain extent to absorb the impact. Secondary batteries using a laminate film as their exterior can be charged and discharged even if they are deformed by impact.

[0025] Furthermore, the bag after being torn can also function as a protective layer, and since it is between the inner laminate and the outer body, they can slide easily against each other.

[0026] Secondary batteries using laminate films as exteriors are connected to the positive or negative electrodes using lead wires. There is a risk that the positive or negative electrode lead wires may break due to impact. Therefore, the current collector is constructed from a material with rubber elasticity. A current collector constructed from a material with rubber elasticity is also called a rubber-like current collector. Using a material with rubber elasticity as the current collector prevents the positive or negative electrode lead wires from breaking. Furthermore, by modifying the shape of the rubber-like current collector to connect the current collector and the lead wire, and having it function as a tab portion and lead wire, a secondary battery with high shock resistance can be produced. In this case, the ultrasonic bonding process between the tab portion and the lead wire can be omitted, thereby reducing the number of processes.

[0027] The current collector may be made of metal, and the metal tab may be protected from the outside with conductive rubber, and then hardened with an adhesive layer using epoxy resin, etc. When epoxy resin is used for sealing, it is not limited to thermocompression bonding, and metal foil may also be used as the exterior body.

[0028] Rubber elasticity refers to the unique elasticity exhibited by materials such as rubber. Rubber elasticity is characterized by a high elastic limit (the stress at the limit at which the material will not return to its original shape after an external force is removed) and a low Young's modulus (0.1 MPa to 10 MPa). Materials that exhibit rubber elasticity are known to have a network molecular structure in which chain molecules are crosslinked (also known as vulcanization).

[0029] The rubber-like current collector may be made of one or more rubber materials selected from the group consisting of styrene-butadiene rubber, styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, butyl rubber, ethylene-propylene rubber, fluororubber, silicone rubber, and urethane rubber, and a particulate or fibrous conductive material (also called a conductive filler).

[0030] The physical properties of the rubber-like current collector may be, for example, tensile strength, elongation at break, and volume resistivity within the following ranges. The tensile strength is preferably 0.1 MPa to 30 MPa, more preferably 1 MPa to 20 MPa, and even more preferably 1 MPa to 10 MPa. The elongation at break is preferably greater than 100% to 300%, and even more preferably 130% to 200% (the length when no external force is applied is defined as 100%). The volume resistivity is preferably 0.1 Ω·m to 30 Ω·m, more preferably 0.1 Ω·m to 20 Ω·m, more preferably 0.1 Ω·m to 10 Ω·m, and even more preferably 0.1 Ω·m to 5 Ω·m.

[0031] The conductive material contained in the rubber-like current collector can be one or more of a conductive carbon material and a metal material such as aluminum, titanium, stainless steel, gold, platinum, zinc, iron, copper, etc. As the conductive carbon material, for example, one or more of the following can be used: carbon black such as acetylene black and furnace black; graphite such as artificial graphite and natural graphite; carbon fiber such as carbon nanofiber and carbon nanotube; graphene; and graphene compounds.

[0032] Examples of carbon fibers that can be used include mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers. Carbon nanofibers and carbon nanotubes can also be used as carbon fibers. Carbon nanotubes can be produced by vapor phase growth, for example.

[0033] When a rubber-like current collector is used as the positive electrode current collector, it may further contain an antioxidant such as a hindered phenol-based material.

[0034] When a rubber-like current collector is used as a negative electrode current collector, it is preferable that the metal material used as the conductive material is a material that does not alloy with carrier ions such as lithium.

[0035] The conductive material contained in the rubber-like current collector may have an average particle size of 10 nm or more and 10 μm or less, and preferably 30 nm or more and 5 μm or less.

[0036] The rubber current collector has a thickness of 5 μm or more and 200 μm or less, preferably 5 μm or more and 100 μm or less, more preferably 5 μm or more and 50 μm or less, and more preferably 5 μm or more and 30 μm or less.

[0037] The present invention also includes a penetrator equipped with a secondary battery, which has an acceleration measurement unit, a sensor unit, a battery compartment unit, and a communication unit, and the battery compartment unit has multiple secondary batteries, and the secondary battery has a bag containing an electrolyte between the outer casing and the positive electrode or negative electrode, and the outer casing surrounding the positive electrode, negative electrode, and bag is a laminate film.

[0038] Furthermore, although a battery reaction does not occur before a part of the electrolyte bag is ruptured by an impact, a laminate at a stage before a battery reaction occurs also constitutes one aspect of the present invention. The laminate includes a bag containing an electrolyte, a sheet-like positive electrode, a separator, and a sheet-like negative electrode, the sheet-like positive electrode and the separator are stacked in contact with each other, the separator and the sheet-like negative electrode are stacked in contact with each other, the bag containing the electrolyte is stacked in contact with the sheet-like positive electrode or the sheet-like negative electrode, and one or both of the sheet-like positive electrode and the sheet-like negative electrode is a rubber current collector.

[0039] According to one embodiment of the present invention, a secondary battery that can withstand harsh environmental conditions in which the internal temperature of the secondary battery reaches −40° C. or −30° C. can be provided.

[0040] Alternatively, according to one embodiment of the present invention, a secondary battery can be realized that is brought into a chargeable and dischargeable state by utilizing the impact generated when the battery lands on a target planet.

[0041] According to one embodiment of the present invention, a secondary battery with a novel structure can be provided. Specifically, a secondary battery with a novel flexible structure can be provided. Alternatively, according to one embodiment of the present invention, a novel power storage device, an electronic device including the novel secondary battery, or the like can be provided.

[0042] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc.

[0043] FIG. 1A is a cross-sectional schematic diagram illustrating one embodiment of the present invention, FIG. 1B is a top view of a bag containing an electrolyte solution, FIG. 1C is a top view of a negative electrode, and FIG. 1D is a top view of a positive electrode. FIGS. 2A and 2B are top views of a laminate illustrating one embodiment of the present invention, and FIG. 2C is a top view of a secondary battery. FIG. 3A is a top view of a secondary battery illustrating one embodiment of the present invention, and FIGS. 3B and 3C are cross-sectional views thereof. FIG. 4A is a top view of a positive electrode illustrating one embodiment of the present invention, FIG. 4B is a cross-sectional view thereof, FIG. 4C is a top view of a positive electrode illustrating one embodiment of the present invention, and FIG. 4D is a cross-sectional view thereof. FIGS. 5A and 5B are top views illustrating one embodiment of the present invention, and FIG. 5C is an example cross-sectional view. FIG. 6 is a cross-sectional schematic diagram of a measuring device (penetrator) illustrating one embodiment of the present invention. FIG. 7 is a cross-sectional schematic diagram of a measuring device (penetrator) illustrating one embodiment of the present invention. FIGS. 8A to 8D are views illustrating a manufacturing process of a positive electrode active material. 9A to 9D are diagrams showing an example of space equipment.

[0044] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0045] In this embodiment, a secondary battery 10 having two bags containing an electrolyte solution will be described with reference to Figures 1 and 2. Although it is called a secondary battery 10, in reality it does not function as a battery when in the state shown in Figure 1A, but for convenience, the laminate surrounded by an exterior body 23 is referred to as the secondary battery 10.

[0046] 1A shows a state in which a first bag 40a containing an electrolyte solution, a second bag 40b containing an electrolyte solution, a negative electrode 41, a separator 42, a positive electrode 43, and a gap 45 are housed in an exterior body 23. In FIG. 1A, the negative electrode 41, the separator 42, the positive electrode 43, and the gap 45 are dry, and the gap 45 in the exterior body 23 is a reduced-pressure space. Because the bags 40a and 40b are located on the outside of the internal structure of the secondary battery 10, they are most susceptible to stress when the battery is bent and are also susceptible to external impacts, making the bags prone to tearing. Note that tearing the bags does not necessarily mean making a hole in the film, but also includes weakening the sealed portion and allowing the electrolyte solution inside to leak through the sealed portion.

[0047] FIG. 1B shows a schematic top view of a first bag 40a containing an electrolyte solution. The first bag 40a uses a laminate film. The laminate film has a layered structure, and may be, for example, a laminate of multiple resin films with a metal foil as an intermediate layer. The resin film in the laminate film uses a nylon layer and a polypropylene layer, with the polypropylene layer positioned on the inside. A predetermined amount of electrolyte solution is injected under reduced pressure and sealed. The polypropylene layer is a thermoplastic resin, and the polypropylene layers can be bonded together by thermocompression bonding. The laminate film can be formed into a bag shape by sealing the adhesive area 48 around the periphery by thermocompression bonding. While a transparent laminate film is used in this embodiment, this is not particularly limited, and any suitable material may be used as long as the electrolyte solution does not leak from the bag or container upon subsequent impact. While an example in which two electrolyte solutions are contained in the bag is shown here, one or three or more electrolyte solutions may be contained in the bag. In addition, one or more weak spots in the seal may be intentionally provided to promote leakage of the electrolyte from the bag or container upon subsequent impact, or protrusions for rupturing the bag or container may be provided as appropriate.

[0048] 1C shows a schematic top view of a positive electrode 43. As shown in FIG. 1C, the positive electrode 43 has a positive electrode current collector 24 and a positive electrode active material layer 25 containing a positive electrode active material. The positive electrode active material layer contains a positive electrode active material, and may further contain a conductive material and a binder. A first positive electrode active material layer and a second positive electrode active material layer may be provided on both sides of the positive electrode current collector 24.

[0049] In this specification, the positive electrode active material refers to a compound containing a transition metal and oxygen, capable of inserting and extracting lithium. Carbonates, hydroxyl groups, and the like adsorbed after the preparation of the positive electrode active material are not included in the positive electrode active material. Lithium salts, organic solvents, binders, conductive materials, and compounds derived from these that are attached after the preparation of the positive electrode active material are also not included in the positive electrode active material.

[0050] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the lithium that can be inserted and removed from the positive electrode active material is removed. For example, LiCoO ２ The theoretical capacity of LiNiO is 274 mAh / g. ２ The theoretical capacity of LiMn is 275mAh / g. ２ O ４ The theoretical capacity of the battery is 148 mAh / g.

[0051] In this specification, the amount of lithium remaining in the positive electrode active material relative to the theoretical capacity is determined by the x in the composition formula, for example, Li ｘ CoO ２ x in, or Li ｘ MO ２ In this specification, M is a transition metal that is oxidized and reduced with the insertion and desorption of lithium. ｘ CoO ２ Li as appropriate ｘ MO ２ In the case of a positive electrode active material in a secondary battery, x can be expressed as x = (theoretical capacity - charging capacity) / theoretical capacity. For example, LiCoO ２ When a secondary battery using this as the positive electrode active material is charged to 219.2 mAh / g, Li ０．２ CoO ２ Or we can say x = 0.2. ｘ CoO ２ In the above formula, "x" is small, for example, when 0.1<x≦0.24. The extent to which lithium has been released from the positive electrode active material relative to the theoretical capacity is sometimes referred to as the depth of charge. In this specification and elsewhere, the depth of charge corresponds to 1−x.

[0052] Li ｘ CoO２ The charge capacity and discharge capacity used to calculate x in the table should preferably be measured under conditions where there is no short circuit and where there is little or no effect of lithium salt decomposition. For example, data from a secondary battery that has experienced a sudden change in capacity that may be due to a short circuit should not be used to calculate x.

[0053] When the lithium cobalt oxide satisfies the stoichiometric ratio, LiCoO ２ The occupancy rate of Li on the lithium site is x = 1. The lithium cobalt oxide contained in the secondary battery after discharge is also LiCoO ２ In this case, x = 1. The end of discharge here refers to the state where the voltage is 2.5 V (lithium counter electrode) or less at a current of 100 mA / g, for example. In a lithium ion secondary battery, when the occupancy rate of lithium in the lithium site reaches x = 1 and no more lithium can enter, the voltage drops sharply. At this point, discharge can be said to be complete. Generally, LiCoO ２ In a lithium ion secondary battery using LiCoO, the discharge voltage drops rapidly until it reaches 2.5 V, so discharge is considered to have ended under the above conditions. Furthermore, when the positive electrode after discharge is analyzed using an XRD pattern, it is found to be a typical LiCoO ２ It can be confirmed that the crystal structure is

[0054] In this specification, "homogeneous" refers to a phenomenon in which a certain element (e.g., A) is distributed with similar characteristics in a specific region in a solid composed of multiple elements (e.g., A, B, C). It is sufficient that the concentration of the element in each specific region is substantially the same. For example, it is sufficient that the difference in element concentration between each specific region is within 10%. Examples of specific regions include a surface layer, a surface, a convex portion, a concave portion, and a bulk.

[0055] In this specification and the like, uneven distribution refers to the concentration of an element in a certain region being different from that in other regions, and is synonymous with segregation, precipitation, non-uniformity, bias, or the mixture of areas with high concentration and areas with low concentration.

[0056] In this specification and the like, when describing the characteristics of a positive electrode active material, not all of the positive electrode active materials in a secondary battery need to have that characteristic. For example, when describing the characteristics of a coating of a positive electrode active material, for example, if 50% or more, preferably 70% or more, and more preferably 90% or more of the total number of three or more randomly selected positive electrode active materials have the characteristic of a coating (specifically, the surface on which the coating is formed occupies 50% or more, preferably 70% or more, and more preferably 90% or more of the positive electrode active material), it can be said that there is a sufficient effect of improving the characteristics of the positive electrode active material and a secondary battery having the same.

[0057] Unless otherwise specified, in this specification, the materials (positive electrode active material, negative electrode active material, lithium salt, etc.) contained in a secondary battery are described in their pre-degradation state. Note that a decrease in discharge capacity due to aging and burn-in treatments during the secondary battery manufacturing stage is not referred to as degradation. For example, a secondary battery having a discharge capacity of 97% or more of its rated capacity can be said to be in its pre-degradation state. The rated capacity conforms to JIS C 8711:2019. Note that in this specification, the pre-degradation state of the materials contained in a secondary battery is sometimes referred to as an initial product or initial state, and the post-degradation state (a state in which the secondary battery has a discharge capacity of less than 97% of its rated capacity) is sometimes referred to as an in-use product or in-use state, or a used product or used state.

[0058] In this specification, a lithium ion secondary battery refers to a battery that uses lithium ions as carrier ions, but the carrier ions of the present invention are not limited to lithium ions. For example, alkali metal ions or alkaline earth metal ions can be used as carrier ions of the present invention, and specifically, sodium ions can be used. In this case, the present invention can be understood by replacing lithium ions with sodium ions. Furthermore, when there is no limitation on the carrier ions, the battery may be referred to as a secondary battery.

[0059] In this specification, a full cell refers to a battery cell assembled with different electrodes positioned on both sides, such as a positive electrode / negative electrode unit cell, and a half cell refers to a battery cell assembled with a positive electrode and lithium metal as the positive electrode and negative electrode, respectively.

[0060] Other examples of the positive electrode active material include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, LiFePO ４ , LiFeO ２ , LiNiO ２ , LiMn ２ O ４ , V ２ O ５ , Cr ２ O ５ , MnO ２ and the like compounds.

[0061] Other positive electrode active materials include LiMn ２ O ４ Lithium-containing materials having a spinel-type crystal structure containing manganese, such as lithium nickel oxide (LiNiO ２ or LiNi １−ｘ M ｘ O ２ It is preferable to mix (0<x<1) (M=Co, Al, etc.) This configuration can improve the characteristics of the secondary battery.

[0062] In addition, as another positive electrode active material, the composition formula Li ａ Mn ｂ M ｃ O ｄA lithium-manganese composite oxide that can be expressed by the formula (1) can be used. Here, element M is preferably a metal element selected from among lithium and manganese, or silicon or phosphorus, and more preferably nickel. Furthermore, when measuring the entire lithium-manganese composite oxide particle, it is preferable that 0<a / (b+c)<2, c>0, and 0.26≦(b+c) / d<0.5 (where a, b, c, and d are excluding 0) are satisfied during discharge. The composition of metals, silicon, phosphorus, etc. in the entire lithium-manganese composite oxide particle can be measured, for example, using an inductively coupled plasma mass spectrometer (ICP-MS). The oxygen composition in the entire lithium-manganese composite oxide particle can be measured, for example, using energy dispersive X-ray spectroscopy (EDX). Furthermore, the composition can be determined by valence evaluation using fusion gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICP-MS analysis. The lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain one or more elements selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, phosphorus, and the like.

[0063] [Positive Electrode Current Collector] The positive electrode current collector 24 can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not leach out due to the potential of the positive electrode. In this embodiment, a first rubber-like current collector is used as the positive electrode current collector 24.

[0064] 1D is a schematic top view of the negative electrode 41. As shown in FIG. 1D, the negative electrode 41 has a negative electrode current collector 34 and a negative electrode active material layer 35 containing a negative electrode active material.

[0065] [Negative Electrode Active Material] As the negative electrode active material, for example, an alloy material and / or a carbon material can be used.

[0066] As the negative electrode active material, an element capable of undergoing a charge-discharge reaction by alloying / dealloying reaction with lithium can be used. In this specification and the like, an element capable of undergoing a charge-discharge reaction by alloying / dealloying reaction with lithium, and a compound containing such an element, may be referred to as an alloy material. For example, as the alloy material, a material containing one or more selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger charge-discharge capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use a negative electrode active material containing silicon. For example, as a negative electrode active material containing silicon, SiO, Mg ２ Si, Mg ２ Ge, SnO, SnO ２ , Mg ２ Sn, SnS ２ , V ２ Sn ３ , FeSn ２ , CoSn ２ , Ni ３ Sn ２ , Cu ６ Sn ５ , Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ , LaSn ３ , La ３ Co ２ Sn ７ , CoSb ３ , InSb, SbSn, etc.

[0067] The conductive material and binder that can be contained in the negative electrode active material layer 35 can be the same as the conductive material and binder that can be contained in the positive electrode active material layer.

[0068] [Negative electrode current collector] The negative electrode current collector 34 can be made of the same material as the positive electrode current collector. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium. In this embodiment, a second rubber-like current collector is used as the negative electrode current collector 34.

[0069] [Separator] The secondary battery preferably includes a separator. Examples of the separator include fibers containing cellulose, such as paper, nonwoven fabrics, glass fibers, ceramics, and synthetic fibers such as nylon (polyamide), polyimide, vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably formed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0070] The separator may have a multilayer structure. For example, an organic film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0071] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide-based materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0072] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0073] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0074] [Electrolyte] In this embodiment, a material is used in which lithium ions in the electrolyte function as carrier ions when the internal temperature of the secondary battery is −40° C. or −30° C. As such a material, an ionic liquid, or an organic solvent containing a fluorinated cyclic carbonate (sometimes referred to as a fluorinated cyclic carbonate), or a fluorinated chain carbonate (sometimes referred to as a fluorinated chain carbonate) is used.

[0075] Examples of fluorinated cyclic carbonates that can be used include fluoroethylene carbonate (fluorinated ethylene carbonate, fluoroethylene carbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), and tetrafluoroethylene carbonate (F4EC). DFEC includes isomers such as cis-4,5 and trans-4,5. Since all of these fluorinated cyclic carbonates have electron-withdrawing substituents, they are believed to have low solvation energies for lithium ions.

[0076] Common organic solvents used in lithium ion batteries, such as ethylene carbonate (EC) or diethyl carbonate (DEC), may freeze at -20°C, making it difficult to fabricate lithium ion batteries that can be charged and discharged at -40°C, preferably -50°C. The organic solvent described as an example in this embodiment allows the freezing point to be -40°C or lower, preferably -50°C or lower, making it possible to realize a lithium ion battery that can be charged and discharged even in sub-zero environments of -40°C or lower. As a result, a lithium ion battery that can be charged and discharged over a wide temperature range, including at least sub-zero temperatures, can be realized. Note that sub-zero temperatures are values ​​on Earth, and will differ on other planets, but for convenience, they are converted to sub-zero temperatures on Earth.

[0077] Ionic liquids that can be used in one embodiment of the present invention will be described. Ionic liquids, sometimes referred to as room-temperature molten salts, have cations and anions. The basic skeleton of the cation is imidazolium-based, ammonium-based, pyrrolidinium-based, piperidinium-based, pyridinium-based, or phosphonium-based. Ionic liquids with an imidazolium-based cation basic skeleton have lower viscosity than ammonium-based ionic liquids. Low viscosity tends to increase the conductivity of carrier ions. Furthermore, physical properties such as viscosity can be controlled by the alkyl group or the like on the side chain of the cation.

[0078] <Anion> The anion of the ionic liquid according to one embodiment of the present invention will be described below. Examples of the anion include a halide ion, tetrafluoroborate, hexafluorophosphate, bis(trifluoromethylsulfonyl)amide, and bis(fluorosulfonyl)imide.

[0079] Specific anions that can be used include one or more of a monovalent amide anion, a monovalent methide anion, a fluorosulfonate anion, a perfluoroalkylsulfonate anion, a tetrafluoroborate anion, a perfluoroalkylborate anion, a hexafluorophosphate anion, a perfluoroalkylphosphate anion, and a tetrafluoroborate anion.

[0080] The monovalent amide anion is represented by the general formula (C ｎ F ２ｎ＋１ SO ２ ) ２ N − (n is 0 or more and 3 or less).

[0081] In the above general formula, when n is 0, it is a bis(fluorosulfonyl)imide anion. The abbreviation for bis(fluorosulfonyl)imide anion is FSI or FSA.

[0082] <Cation> The cation of the ionic liquid that can be used in one embodiment of the present invention will be described below. A specific example of the cation is the 1-ethyl-3-methylimidazolium cation, abbreviated as EMI.

[0083] Since such ionic liquids are composed solely of ions, they exhibit strong electrostatic interactions and excellent thermal stability, making it possible to realize secondary batteries that can be charged and discharged even in subzero temperatures of −40°C or below.

[0084] <Lithium Salt> The lithium salt dissolved in the non-aqueous solvent of one embodiment of the present invention is preferably a lithium salt having a halogen. More preferably, it is a fluorine-containing imide lithium salt. The fluorine-containing imide lithium salt is Li(CF ３ SO ２ ) ２ N (hereinafter, also referred to as "LiTFSI" or "LiTFSA"), Li(C ２ F ５ SO ２ ) ２ N (hereinafter also referred to as "LiBETI"), or Li(SO ２ F) ２ N (hereinafter, also referred to as "LiFSI" or "LiFSA"), etc. can be used.

[0085] Another example of a halogen-containing lithium salt is LiPF ６ , LiBF ４ , LiClO ４ etc. can be used.

[0086] Furthermore, LiBOB (lithium bis(oxalato)borate) may be used as another halogen-free lithium salt.

[0087] These lithium salts may be used alone or in combination.

[0088] The electrolyte can be introduced into the bag, for example, by sealing three of the four sides by thermocompression, then introducing the electrolyte, and then sealing the remaining side by thermocompression. Alternatively, as described below, the four sides can be sealed after the electrolyte is injected. For example, a solution containing an ionic liquid and a salt having carrier ions can be used as the electrolyte, and the electrolyte can be introduced by, for example, dropping the solution.

[0089] The above-described electrolyte solution is sealed in a bag, and multiple laminated bodies are stacked to fabricate a laminate-type secondary battery. Fig. 2A shows a top view of a laminated body in which a positive electrode current collector 24 is stacked on a first bag 40a containing the electrolyte solution, a separator 42 is stacked on the positive electrode current collector 24, and a negative electrode current collector 34 is stacked on top of that.

[0090] FIG. 2B is a top view of the second bag 40b containing the electrolyte layer 40a placed on top of the first bag 40b.

[0091] The laminated secondary battery was then sealed under reduced pressure. The top view of the battery is shown in Figure 2C, and the cross-sectional view taken along the chain line A1-A2 in Figure 2C corresponds to Figure 1A. In Figure 1A, the laminated body has four negative electrode active material layers, four positive electrode active material layers, and two separators, but this is not particularly limited. The laminated body may have one or more of each of a bag containing an electrolyte solution, a negative electrode active material layer, a separator, and a positive electrode active material layer.

[0092] Furthermore, the use of a laminate film is not limited thereto, and as shown in Figures 3A, 3B, and 3C, the metal foil that forms the exterior body 23 can be sealed with a resin layer 49 (e.g., epoxy resin) in the adhesive region 48. To prevent oxidation or damage to the metal foil, a nylon resin may be coated on the surface of the metal foil. Figure 3A shows an example of a secondary battery, and Figure 3B shows a cross section taken along chain line A3-A4, and Figure 3C shows a cross section taken along chain line A5-A6.

[0093] The conductive rubber used as the current collector in Figures 1, 2, and 3 may have various shapes. For example, three extension portions may be provided as shown in Figure 4A. Figure 4A shows an example of a top view of a positive electrode, and Figure 4B shows a schematic cross-sectional view taken along the chain line C1-C2 in Figure 4A. A positive electrode active material layer 25 is provided on a positive electrode current collector 24 made of conductive rubber. As shown in Figure 4A, three or more protruding portions may be provided so that any one of them may break upon impact. Furthermore, slits may be provided in the conductive rubber to provide flexibility.

[0094] 1, 2, 3, 4A and 4B show examples in which conductive rubber is used as the positive electrode current collector 24, but this is not particularly limited, and conductive rubber may be used in part.

[0095] 4C and 4D show an example in which a metal foil (gold, silver, copper, or aluminum) is used as the positive electrode current collector 24, conductive rubber is used as the lead wire 36, and the periphery is fixed with epoxy resin 37. Fig. 4D shows a schematic cross-sectional view taken along the chain line C3-C4 in Fig. 4C.

[0096] FIG. 5 also shows an example in which a single bag containing an electrolyte is used, conductive metal foil current collectors are used as the positive and / or negative electrode current collectors instead of conductive rubber, and lead wires are used. FIG. 5A shows a top view of a laminated secondary battery 500, and the cross section taken along the chain line B1-B2 corresponds to FIG. 5C. As shown in FIG. 5C, a positive electrode 43, a separator 42, and a negative electrode 41 are laminated, and an adhesive region 48 may be provided on the outer periphery or edge of the exterior body 23. The laminated secondary battery 500 shown in FIG. 5A has a bag 540 containing an electrolyte and is overlapped with the laminated body. The lead wire is connected to the bag 540 via a tab. The position of the lead wire is not particularly limited, and a laminated secondary battery 501 such as that shown in FIG. 5B may also be used.

[0097] When the bag, which is part of the laminate thus obtained, is subjected to an impact, for example, by dropping a laminated secondary battery, the pressure caused by the impact of the drop causes the electrolyte to leak from the thermocompression-bonded part of the bag, filling the gap 45 with the electrolyte.

[0098] 5 shows a modified example having a configuration partially different from that of FIG. 1. FIG. 5C is a cross-sectional view taken along the chain line B1-B2 in FIG. 5A. As shown in FIG. 5C, there is only one bag 540 containing the electrolyte, and the same reference numerals will be used for the same parts in the following description.

[0099] 5A and 5B show a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511 without using a rubber-like current collector. Although an adhesive region 48 is shown to fix a portion of the exterior body 509, the exterior body 509 may also be fixed with an adhesive. When an adhesive is used, the gap 45 may be filled. The positive electrode 503 has a protruding region (also referred to as a tab region) where no positive electrode active material layer is formed. Ultrasonic welding is used to join the tab region of the positive electrode 503 and the positive electrode lead electrode 510.

[0100] 5A shows a secondary battery 500 in which a positive electrode lead electrode 510 and a negative electrode lead electrode 511 are led out of the exterior of the outer casing from the same side. A secondary battery 501 shown in FIG. 5B can also be produced by leading the positive electrode lead electrode 510 and the negative electrode lead electrode 511 out of the exterior of the outer casing from opposite sides.

[0101] 5A and 5B, when an impact such as a drop is applied, a portion of the bag 540 containing the electrolyte is torn, allowing the electrolyte to leak out and causing a battery reaction. Furthermore, the secondary battery 500 shown in Fig. 5A and the secondary battery 500 shown in Fig. 5B can be bent, and when a bending force is applied, a portion of the bag 540 containing the electrolyte is torn, allowing the electrolyte to leak out and causing a battery reaction.

[0102] (Embodiment 2) An example in which the secondary battery shown in Embodiment 1 is mounted on a measuring device, specifically, an example in which it is mounted on a penetrator, will be described below.

[0103] An example of the configuration of a penetrator is shown in Figure 6. As shown in Figure 6, the tip shape of the penetrator is conical, ogive, or parabolic. The shape of the penetrator casing 21 other than the tip is cylindrical.

[0104] In this embodiment, the tip of the penetrator is used as the vertical reference, and devices or power sources are sequentially arranged above the tip inside the housing 21.

[0105] An accelerometer 22 is provided inside the conical tip of the penetrator, and a first battery compartment 27a or a second battery compartment 27b serves as a power source for driving the accelerometer 22. The space at the tip where no equipment is located is irregular in shape and therefore prone to becoming dead space. Therefore, by deforming a bendable secondary battery and arranging it along the curved surface of the inner wall, the space can be effectively utilized.

[0106] Furthermore, a seismometer 33 is disposed above the accelerometer 22. Above the seismometer 33, a third battery compartment 27c is disposed.

[0107] The communication circuit unit 26 is disposed on the third battery compartment 27c. The power supply disposed in the third battery compartment 27c supplies power to both the seismometer 33 and the communication circuit unit 26.

[0108] To prevent the penetrator from becoming unstable when it falls, the devices and secondary batteries are placed so that their weights are balanced and they can withstand the vibrations that occur during rocket launch.

[0109] In addition, to cushion the impact of a fall, the penetrator is equipped with a parachute-like component called an aeroshell, as well as solar cells for generating electricity. Although not shown, the penetrator is also equipped with insulation or a heater for cold weather protection. The secondary battery may be heated by a heater while monitoring its internal temperature. A T terminal (temperature detection terminal) inside the secondary battery is an analog signal output terminal of a temperature sensor. A thermistor is connected between the negative terminal and the T terminal, and the resistance value of the thermistor is detected by a circuit, and the temperature is calculated from the resistance value. The temperature around the secondary battery (also called the ambient temperature) may be measured with a thermometer, and the internal temperature of the secondary battery may be adjusted by adjusting the ambient temperature with a heater. For example, if the internal temperature of the secondary battery is set to approximately -30°C, the heater may be used to adjust the temperature so that the internal temperature is within a range of -30°C plus or minus 5°C. Power to the heater may be supplied from either the secondary battery located in the first battery compartment 27a or the secondary battery located in the second battery compartment 27b, or both. Furthermore, either the first battery compartment 27a or the second battery compartment 27b may use a primary battery.

[0110] Additionally, cushioning material may be placed in gaps where no tip or equipment is provided to cushion the impact when landing.

[0111] A penetrator incorporating the above-mentioned device or a secondary battery is dropped and pierced into the planet's surface to be fixed underground, and the results of measuring the planet's seismic waves and the like are transmitted to Earth via the communication circuit unit 26. A system in which the signal from the communication circuit unit 26 is received by an artificial satellite and transmitted to Earth via the artificial satellite may also be used.

[0112] 7 shows an example of an arrangement of multiple laminated secondary batteries. As shown in FIG. 7 , a secondary battery 10 is placed in the first battery compartment 27a, and multiple secondary batteries 500 are placed on the curved inner wall of the second battery compartment 27b. Furthermore, a secondary battery 501 is placed side by side in the third battery compartment 27c, and multiple secondary batteries 500 are stacked on top of each other. When the secondary battery 10 is dropped, the electrolyte-containing bag inside the secondary battery 10 breaks, causing the electrolyte to leak, filling the interior of the secondary battery 10 and allowing it to function as a secondary battery. Furthermore, the secondary batteries 501 are closely arranged in the third battery compartment 27c, and when pressure is applied due to the propagation of an impact from the housing 21 or temporary deformation of the housing, the electrolyte fills the interior of the secondary battery 501, allowing it to function as a secondary battery. In addition, multiple secondary batteries 500 are stacked on top of each other, and when they are dropped and hit, they bend and the bag containing the electrolyte inside is broken, allowing the electrolyte to be filled inside the secondary battery 500 and for it to function as a secondary battery.

[0113] Of course, if the laminated secondary battery itself is damaged by the impact of being dropped, it may malfunction, so the laminated secondary battery may be sealed with a strong adhesive layer to prevent leakage rather than by thermocompression bonding.

[0114] Furthermore, the battery characteristics of the laminated secondary battery are hardly deteriorated by radiation exposure, and the laminated secondary battery can supply power to other devices that may be attached to the penetrator.

[0115] Furthermore, the laminated secondary battery is not limited to the configuration shown in FIG. 7 , and any one of the secondary batteries 10, 500, and 501 shown in embodiment 1 may be used and placed in either or both of the first battery compartment 27 a and the second battery compartment 27 b.

[0116] Furthermore, considering Mars, it is desirable to have a battery that can be charged and discharged at low temperatures. In storage tests at -40°C, ethylene carbonate (EC) or diethyl carbonate (DEC) may at least partially solidify. If these materials are used as electrolytes, the battery reaction is difficult to occur at low temperatures, and the battery function cannot be fully demonstrated.

[0117] Therefore, the electrolyte to be used is preferably an ionic liquid, or an organic solvent containing a fluorinated cyclic carbonate (sometimes referred to as a fluorinated cyclic carbonate), or a fluorinated chain carbonate (sometimes referred to as a fluorinated chain carbonate).

[0118] <Example of Method for Manufacturing Positive Electrode Active Material> An example of a method for manufacturing a positive electrode active material that can be used as one embodiment of the present invention (an example of a method for manufacturing a positive electrode active material) will be described with reference to FIGS. 8A to 8D .

[0119] <Step S10> First, in step S10, lithium cobalt oxide is prepared as a starting material. The lithium cobalt oxide preferably has a median diameter of 10 μm or less, and more preferably 8 μm or less. Commercially available lithium cobalt oxide can be used as the lithium cobalt oxide with a median diameter of 10 μm or less. A representative example of commercially available lithium cobalt oxide is lithium cobalt oxide manufactured by Nippon Chemical Industry Co., Ltd. (product name "CellSeed C-5H"). In this specification, CellSeed C-5H will be simply referred to as "C-5H." C-5H has a median diameter of approximately 7 μm.

[0120] The lithium cobalt oxide having a median diameter of 10 μm or less can be lithium cobalt oxide produced through steps S11 to S14 shown in Fig. 8B. The production method of steps S11 to S14 will be described.

[0121] <Step S11> In step S11 shown in FIG. 8B, a lithium source (referred to as Li source in the drawing) and a cobalt source (referred to as Co source in the drawing) are prepared as starting materials for lithium and transition metal, respectively.

[0122] As the lithium source, it is preferable to use a compound containing lithium, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. It is preferable that the lithium source has high purity, and it is preferable to use a material with a purity of, for example, 99.99% or higher.

[0123] As the cobalt source, it is preferable to use a compound containing cobalt, such as tricobalt tetroxide or cobalt hydroxide. The cobalt source preferably has a high purity, for example, a material with a purity of 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, impurities in the positive electrode active material can be controlled. As a result, the capacity of the secondary battery is increased, and the reliability of the secondary battery is improved.

[0124] <Step S12> Next, in step S12 shown in FIG. 8B , the lithium source and the cobalt source are pulverized and mixed to prepare a mixed material. The pulverization and mixing can be performed in a dry or wet manner. Wet pulverization and mixing allows for smaller pulverization, which is preferable for obtaining lithium cobalt oxide with a median diameter of 10 μm or less as a starting material. When performing the wet method, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). However, it is preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. It is preferable to mix the lithium source and the transition metal source in dehydrated acetone with a purity of 99.5% or higher, with a water content reduced to 10 ppm or less, and then pulverize and mix the mixture. Using dehydrated acetone with the above purity reduces the amount of impurities that may be present.

[0125] A ball mill, a bead mill, or the like can be used as a means for pulverization and mixing. When using a ball mill, aluminum oxide balls or zirconium oxide balls are preferably used as the pulverization media. Zirconium oxide balls are preferred because they emit less impurities. When using a ball mill, a bead mill, or the like, the peripheral speed should be set to 100 mm / s or more and 2000 mm / s or less to suppress contamination from the pulverization media.

[0126] <Step S13> Next, in step S13 shown in FIG. 8B, the mixed material is heated.

[0127] The temperature increase rate in the temperature increase step of the heat treatment depends on the temperature to be reached, but is preferably 80° C. / h or more and 250° C. / h or less. For example, if the temperature in the temperature holding step is 1000° C., the temperature increase rate should be 200° C. / h.

[0128] It is preferable that the temperature rise rate in the processing chamber of the heat treatment device is within the above-mentioned range. Note that the temperature rise rate set in the heat treatment device and the temperature rise rate in the processing chamber may not match. For example, the temperature rise rate in the processing chamber may be lower than the set temperature rise rate. The set temperature rise rate may be adjusted so that the temperature rise rate in the processing chamber is within the above-mentioned range. Note that if the temperature in the processing chamber cannot be measured, the set temperature rise rate of the heat treatment device may be set to the above-mentioned range. If the temperature of the workpiece can be measured, it is even more preferable that the temperature rise rate of the workpiece be within the above-mentioned range.

[0129] The temperature of the temperature holding step is preferably 800°C or higher and 1100°C or lower, more preferably 900°C or higher and 1000°C or lower, and even more preferably 950°C. If the temperature is too low, the decomposition and melting of the lithium source and the cobalt source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to lithium evaporation from the lithium source and / or excessive reduction of cobalt. For example, cobalt may change from trivalent to divalent, causing oxygen defects.

[0130] It is preferable that the temperature in the treatment chamber of the heat treatment device is within the above-mentioned range. Note that the temperature set in the heat treatment device and the temperature inside the treatment chamber may not match. For example, the temperature inside the treatment chamber may be lower than the set temperature. The set temperature may be adjusted so that the temperature inside the treatment chamber is within the above-mentioned range. Note that if the temperature inside the treatment chamber cannot be measured, the set temperature of the heat treatment device may be set to the above-mentioned range. If the temperature of the workpiece can be measured, it is even more preferable that the temperature of the workpiece is within the above-mentioned range.

[0131] After the temperature increase step, a phenomenon (also called an overshoot) may occur in which the temperature inside the processing chamber exceeds the set temperature at the beginning of the temperature holding step. Even when an overshoot occurs, it is preferable to adjust the temperature increase rate so that the temperature inside the processing chamber falls within the temperature range of the temperature holding step described above. Multiple temperature increase steps with different temperature increase rates may be provided. For example, a first temperature increase step and a second temperature increase step following the first temperature increase step may be provided, and the temperature increase rate of the second temperature increase step may be set lower than that of the first temperature increase step. This can suppress the occurrence of an overshoot. Note that, if the temperature temporarily falls outside the temperature range of the temperature holding step described above due to an overshoot, the period is preferably short.

[0132] If the time for the temperature holding step is too short, lithium cobalt oxide may not be synthesized, and if it is too long, productivity decreases. For example, the time is preferably 1 hour or more and 100 hours or less, and more preferably 2 hours or more and 20 hours or less.

[0133] It is not necessary to strictly distinguish between the temperature-raising step, the temperature-holding step, and the cooling step. In the heat treatment, the length of the period during which the temperature is within the aforementioned range may be within the aforementioned time range. Therefore, in this specification and the like, the temperature of the aforementioned temperature-holding step may be referred to as the heat treatment temperature or heating temperature, and the time of the temperature-holding step may be referred to as the heat treatment time or heating time.

[0134] The atmosphere in the temperature-raising step and the temperature-holding step preferably contains oxygen. Examples of the oxygen-containing atmosphere include an oxygen atmosphere, a dry air atmosphere, an air atmosphere, and an atmosphere containing oxygen mixed with other gases (e.g., one or more selected from nitrogen and noble gases). Examples of noble gases include argon. Alternatively, the atmosphere may be a mixture of nitrogen, a noble gas, or two or more selected from nitrogen and noble gases.

[0135] The atmosphere in the temperature increasing step and the temperature maintaining step preferably contains little moisture. The dew point of the atmosphere is preferably, for example, -50°C or less, more preferably -80°C or less. Dry air can be suitably used in the temperature increasing step and the temperature maintaining step. In addition, the CH ４, CO, CO ２ , and H ２ By setting the impurity concentrations of the above to 5 ppb (parts per billion) or less, it may be possible to suppress impurities that may be mixed into the material.

[0136] There is a method of continuously introducing gas into the processing chamber used for the heat treatment. This method can also be said to be a gas flow in the processing chamber. In this case, the gas flow rate may be, for example, 0.1 L / min or more and 0.7 L / min or less per 1 L of the processing chamber volume. When the processing chamber volume is 40 L, the gas flow rate is preferably 10 L / min or approximately 10 L / min. Note that, for example, oxygen gas, dry air, nitrogen gas, noble gas, or a mixture of two or more selected from these gases can be used as the gas.

[0137] A method of replacing the atmosphere in the processing chamber with a desired gas and then preventing the gas from entering or leaving the processing chamber may be used. For example, the atmosphere in the processing chamber may be replaced with a gas containing oxygen to prevent the gas from entering or leaving the processing chamber. Alternatively, the processing chamber may be depressurized before introducing the gas. Specifically, for example, the processing chamber may be depressurized until a differential pressure gauge indicates -970 hPa, and then the gas may be introduced until the pressure reaches 50 hPa.

[0138] After the temperature holding step, the workpiece is cooled in the cooling step. The cooling step may be performed for, for example, 15 minutes to 50 hours. The cooling step may be performed by allowing the workpiece to cool naturally. Furthermore, the workpiece does not necessarily have to be cooled to room temperature, as long as it is cooled to a temperature acceptable for the next step.

[0139] The atmosphere used in the cooling step preferably contains oxygen. Examples of oxygen-containing atmospheres include an oxygen atmosphere, a dry air atmosphere, an air atmosphere, and an atmosphere containing oxygen mixed with other gases (e.g., one or more selected from nitrogen and noble gases). Alternatively, the atmosphere may be nitrogen, a noble gas, or a mixture of two or more selected from nitrogen and noble gases.

[0140] In the cooling step, a gas may be introduced into the processing chamber. Alternatively, a gas may be continuously introduced into the processing chamber. The gas may include oxygen gas, dry air, nitrogen gas, a noble gas, a mixture of two or more selected from these gases, and the like.

[0141] In the cooling step, the temperature can be gradually lowered from the temperature in the temperature holding step by controlling the temperature inside the treatment chamber using a heater or the like. In addition, in the cooling step, the temperature may be heated to a temperature lower than the temperature in the temperature holding step but higher than room temperature.

[0142] In the cooling step, cooling may be performed at room temperature without heating using a heater or the like.

[0143] The gas used in the cooling step may be heated to a temperature higher than room temperature. Alternatively, the gas used in the cooling step may be cooled to a temperature lower than room temperature. Alternatively, one or both of the heat treatment device and the treatment chamber may be cooled using a cooling solvent such as cooling water. For example, cooling may be performed by circulating cooling water around the periphery of the treatment chamber.

[0144] In the heat treatment, the temperature increasing step, the temperature maintaining step, and the cooling step may be performed in the same treatment chamber, or the temperature increasing step, the temperature maintaining step, and the cooling step may be performed in different treatment chambers.

[0145] When a rotary kiln is used for the heat treatment, the temperature increasing step, the temperature holding step, and the cooling step can be carried out consecutively within the rotary kiln. Alternatively, the cooling step, or a part of the cooling step, can be carried out outside the rotary kiln.

[0146] The use of a roller hearth kiln will be described below. The roller hearth kiln preferably has at least three zones: a zone for performing a temperature-raising process (hereinafter referred to as the temperature-raising zone), a zone for performing a temperature-maintaining process (hereinafter referred to as the temperature-maintaining zone), and a zone for performing a cooling process (hereinafter referred to as the cooling zone). The mixed material prepared in step S12 is placed in a heating container such as a sheath and moved sequentially through the temperature-raising zone, the temperature-maintaining zone, and the cooling zone of the roller hearth kiln.

[0147] The container used for heating is preferably an aluminum oxide crucible or an aluminum oxide sheath. An aluminum oxide crucible is a material that is almost free of impurities. In this embodiment, an aluminum oxide sheath with a purity of 99.9% is used. Note that it is preferable to place a lid on the crucible or sheath before heating, as this prevents the material from volatilizing.

[0148] After heating, the material may be crushed and sieved as necessary. When recovering the heated material, it may be transferred from the crucible to a mortar and then recovered. It is preferable to use a mortar made of zirconium oxide or agate. Heating conditions equivalent to those of step S13 can also be applied to heating steps other than step S13, which will be described later.

[0149] <Step S14> By the above steps, lithium cobalt oxide (LiCoO ２ ) can be synthesized. ２ After step S13, a crushing step and a classification step are carried out to adjust the particle size distribution, and then lithium cobalt oxide (LiCoO ２ ) may be obtained.

[0150] Although the composite oxide is produced by the solid phase method in steps S11 to S14, the composite oxide may be produced by a coprecipitation method or a hydrothermal method.

[0151] 8A, the lithium cobalt oxide starting material is heated. The heating in step S15 is sometimes referred to as initial heating in this specification, etc., because it is the first heating of the lithium cobalt oxide. Alternatively, because it is performed before step S31 described below, it is sometimes referred to as preheating or pretreatment.

[0152] The initial heating causes lithium compounds and the like unintentionally remaining on the surface of the lithium cobalt oxide to be desorbed. It is also expected to have the effect of enhancing the internal crystallinity. Although impurities may be present in the lithium source and / or cobalt source prepared in step S11, etc., the initial heating can reduce the impurities from the lithium cobalt oxide starting material. The effect of enhancing the internal crystallinity is, for example, the effect of alleviating distortion, misalignment, and the like resulting from differential shrinkage of the lithium cobalt oxide prepared in step S14.

[0153] In addition, the initial heating has the effect of smoothing the surface of the lithium cobalt oxide, and also has the effect of reducing cracks, crystal defects, and the like that the lithium cobalt oxide has.

[0154] For this initial heating, it is not necessary to separately prepare a material that functions as a lithium source, an additive element source, or a flux.

[0155] If the heating time in this step is too short, sufficient effects will not be obtained, but if it is too long, productivity will decrease. An appropriate heating time range can be selected, for example, from the heating conditions described in step S13. The heating temperature in step S15 is preferably lower than the temperature in step S13 in order to maintain the crystalline structure of the complex oxide. Furthermore, the heating time in step S15 is preferably shorter than the time in step S13 in order to maintain the crystalline structure of the complex oxide. For example, heating is preferably performed at a temperature of 700°C or higher and 1000°C or lower (more preferably, 800°C or higher and 900°C or lower) for 1 hour or higher and 20 hours or lower (more preferably, 1 hour or higher and 5 hours or lower).

[0156] The heating in step S13 can cause a temperature difference between the surface and the interior of the lithium cobalt oxide. This temperature difference can induce a shrinkage difference. It is also thought that the temperature difference causes a difference in fluidity between the surface and the interior, resulting in a shrinkage difference. The energy associated with the shrinkage difference causes a difference in internal stress in the lithium cobalt oxide. This difference in internal stress is also called strain, and this energy is sometimes called strain energy. It is thought that the internal stress is removed by the initial heating in step S15; in other words, the strain energy is homogenized by the initial heating in step S15. When the strain energy is homogenized, the strain in the lithium cobalt oxide is relaxed. This smooths the surface of the lithium cobalt oxide. Alternatively, it can be said that the surface is improved. In other words, by going through step S15, the shrinkage difference that occurred in the lithium cobalt oxide is alleviated, resulting in a smooth surface for the composite oxide.

[0157] Furthermore, the shrinkage difference may cause microscopic misalignment, such as crystal misalignment, in the lithium cobalt oxide. To reduce this misalignment, it is preferable to perform step S15. By performing step S15, it is possible to equalize the misalignment of the composite oxide (alleviate the misalignment of crystals, etc., that has occurred in the composite oxide, or align the crystal grains). As a result, the surface of the composite oxide becomes smooth.

[0158] When lithium cobalt oxide, which has a smooth surface, is used as the positive electrode active material, it increases the safety of the secondary battery, reduces deterioration during charging and discharging, and also prevents cracking of the positive electrode active material.

[0159] Note that step S15 is not an essential configuration in one aspect of the present invention, and therefore an aspect in which step S15 is omitted is also included in one aspect of the present invention.

[0160] <Step S20> Next, details of step S20 for preparing the additional element A as the A source will be described with reference to FIGS. 8C and 8D.

[0161] <Step S21> Step S20 shown in FIG. 8C includes steps S21 to S23. In step S21, an additive element A is prepared. Specific examples of the additive element A include one or more elements selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron. FIG. 8C illustrates a case where a magnesium source (referred to as an Mg source in the drawing) and a fluorine source (referred to as an F source in the drawing) are prepared. In step S21, a lithium source may be separately prepared in addition to the additive element A.

[0162] When magnesium is selected as the additional element A, the source of the additional element A can be called a magnesium source. As the magnesium source, magnesium fluoride (MgF ２ ), magnesium oxide (MgO), magnesium hydroxide (Mg(OH) ２ ), or magnesium carbonate (MgCO ３ ) etc. A plurality of magnesium sources may be used.

[0163] When fluorine is selected as the additional element A, the source of the additional element A can be called a fluorine source. Examples of the fluorine source include lithium fluoride (LiF) and magnesium fluoride (MgF ２ ), aluminum fluoride (AlF ３ ), titanium fluoride (TiF ４ ), cobalt fluoride (CoF ２ , CoF ３ ), nickel fluoride (NiF ２ ), zirconium fluoride (ZrF ４ ), vanadium fluoride (VF ５ ), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF ２ ), calcium fluoride (CaF ２ ), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF ２ ), cerium fluoride (CeF ３ , CeF ４ ), lanthanum fluoride (LaF ３), or sodium aluminum hexafluoride (Na ３ AlF ６ Among them, lithium fluoride is preferable because it has a relatively low melting point of 848°C and is easily melted in the heating step described below. In other words, lithium fluoride can function as a flux (also called a fluxing agent).

[0164] Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source. Other lithium sources that can be used in step S21 include lithium carbonate.

[0165] The fluorine source may also be a gas, such as fluorine (F ２ ), fluorocarbon, sulfur fluoride, or oxygen fluoride (OF ２ , O ２ F ２ , O ３ F ２ , O ４ F ２ , O ５ F ２ , O ６ F ２ , O ２ F) or the like may be used and mixed into the atmosphere in the heating step described below. A plurality of fluorine sources may be used.

[0166] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF) is prepared as the fluorine source and magnesium source. ２ Lithium fluoride and magnesium fluoride are prepared as LiF:MgF ２ When the ratio of lithium fluoride to magnesium fluoride is mixed at a ratio of 65:35, the effect of lowering the melting point is maximized. In addition, if the ratio of lithium fluoride is too high, there is a concern that the lithium will be excessive, which may deteriorate the cycle characteristics. Therefore, the molar ratio of lithium fluoride to magnesium fluoride is set to LiF:MgF ２ =x:1 (0≦x≦1.9), and LiF:MgF ２ =x:1 (0.1≦x≦0.5) is more preferable, and LiF:MgF ２= x: 1 (x = near 0.33) is more preferable. In this specification and the like, unless otherwise specified, "near" refers to a value that is greater than 0.9 times and smaller than 1.1 times the value.

[0167] 8C, the magnesium source and the fluorine source are pulverized and mixed. This step can be performed under pulverization and mixing conditions selected from those described in step S12.

[0168] 8C, the pulverized and mixed materials are collected to obtain a source of the additional element A. The source of the additional element A shown in step S23 includes a plurality of starting materials and can also be called a mixture.

[0169] The particle size of the mixture is preferably 100 nm or more and 10 μm or less, more preferably 300 nm or more and 5 μm or less in median diameter. Even when a single material is used as the source of the additional element A, the median diameter is preferably 100 nm or more and 10 μm or less, more preferably 300 nm or more and 5 μm or less.

[0170] The mixture (including the case where only one kind of additive element is contained) pulverized in step S22 is likely to be uniformly adhered to the surface of the lithium cobalt oxide when mixed with the lithium cobalt oxide in a later step. If the mixture is uniformly adhered to the surface of the lithium cobalt oxide, the additive element can be easily distributed or diffused uniformly in the surface layer portion of the composite oxide after heating, which is preferable.

[0171] <Step S21a> A process different from that shown in Fig. 8C will be described with reference to Fig. 8D. Step S20 shown in Fig. 8D includes steps S21a to S23.

[0172] In step S21a shown in Fig. 8D, four types of additive element A sources to be added to lithium cobalt oxide are prepared. That is, Fig. 8D differs from Fig. 8C in the types of additive element A sources. In addition to the additive element A sources, a lithium source may also be prepared separately.

[0173] As sources of four types of additive elements A, a magnesium source (referred to as Mg source in the drawing), a fluorine source (referred to as F source in the drawing), a nickel source (referred to as Ni source in the drawing), and an aluminum source (referred to as Al source in the drawing) are prepared. The magnesium source and the fluorine source can be selected from the compounds described in FIG. 8C . Nickel oxide, nickel hydroxide, etc. can be used as the nickel source. Aluminum oxide, aluminum hydroxide, etc. can be used as the aluminum source.

[0174] <Step S22> and <Step S23> Next, step S22 and step S23 shown in FIG. 8D are the same as step S22 and step S23 described with reference to FIG. 8C.

[0175] <Step S31> Next, in step S31 shown in Fig. 8A, the lithium cobalt oxide that has been subjected to step S15 (initial heating) is mixed with a source of the additional element A. Here, the number of cobalt atoms A in the lithium cobalt oxide that has been subjected to step S15 is Ｃｏ and the number of magnesium atoms A contained in the additive element A. Ｍｇ The ratio of A Ｃｏ : A Ｍｇ = 100:y (0.1 ≦ y ≦ 6), and A Ｃｏ : A Ｍｇ = 100:y (0.3≦y≦3) is more preferable. Since the surface of lithium cobalt oxide that has undergone initial heating is smooth, the additional element A can be added evenly. For this reason, it is preferable to add the additional element A after the initial heating (step S15), rather than adding the additional element A and then performing the initial heating (step S15).

[0176] Furthermore, when nickel is selected as the additional element A, it is preferable to perform the mixing in step S31 so that the number of nickel atoms in the nickel source is 0.05% or more and 4% or less of the number of cobalt atoms in the lithium cobalt oxide that has undergone step S15. Furthermore, when aluminum is selected as the additional element A, it is preferable to perform the mixing in step S31 so that the number of aluminum atoms in the aluminum source is 0.05% or more and 4% or less of the number of cobalt atoms in the lithium cobalt oxide that has undergone step S15.

[0177] The mixing in step S31 is preferably performed under milder conditions than the pulverization and mixing in step S12 so as not to destroy the shape of the lithium cobalt oxide. For example, it is preferable to perform the mixing under conditions of a lower rotation speed or a shorter time than in step S12. It can also be said that the dry method provides milder conditions than the wet method. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconium oxide balls as the medium.

[0178] In this embodiment, dry mixing is performed in a ball mill using zirconium oxide balls with a diameter of 1 mm at 150 rpm for 1 hour in a dry room with a dew point of −100° C. or higher and −10° C. or lower.

[0179] <Step S32> Next, in step S32 of FIG. 8A, the mixed materials are collected to obtain a mixture 903.

[0180] <Step S33> Next, in step S33 shown in FIG. 8A, the mixture 903 is heated. The heating temperature in step S33 is preferably 800°C or higher and 1100°C or lower, more preferably 800°C or higher and 950°C or lower, and even more preferably 850°C or higher and 900°C or lower. The heating time in step S33 may be 1 hour or higher and 100 hours or lower, and preferably 1 hour or higher and 10 hours or lower. The lower limit of the heating temperature in step S33 needs to be equal to or higher than the temperature at which the reaction between the lithium cobalt oxide and the additive element A source proceeds. The temperature at which the reaction proceeds may be any temperature at which interdiffusion of elements contained in the lithium cobalt oxide and the additive element A source occurs, and may be lower than the melting temperature of these materials. For example, taking an oxide as an example, the melting temperature T ｍ 0.757 times (Tammann temperature T ｄ ) solid-phase diffusion occurs, so the heating temperature in step S33 may be 500° C. or higher.

[0181] For example, LiF and MgF are used as the source of the additive element A. ２ When LiF and MgF ２6, the eutectic point of the mixture 903 is around 742° C. Therefore, the lower limit of the heating temperature in step S33 is preferably set to 742° C. or higher. Note that the reaction proceeds more easily when the temperature is equal to or higher than the melting point of one or more of the starting materials of the mixture 903.

[0182] Also, LiCoO ２ :LiF:MgF ２ In a mixture 903 obtained by mixing the components so that the molar ratio was 100:0.33:1, an endothermic peak was observed around 830°C in differential scanning calorimetry (DSC measurement) as shown in Fig. 7. Therefore, the lower limit of the heating temperature is more preferably 830°C or higher.

[0183] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0184] The upper limit of the heating temperature is set to be lower than the melting point (1130°C) of lithium cobalt oxide. At temperatures near the melting point, there is a concern that lithium cobalt oxide may decompose, albeit only slightly. Therefore, the upper limit of the heating temperature is preferably 1000°C or lower, more preferably 950°C or lower, and even more preferably 900°C or lower.

[0185] Furthermore, when the mixture 903 is heated, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source or the like within an appropriate range.

[0186] In the manufacturing method described in this embodiment, some materials, for example, LiF as a fluorine source, may function as a flux, which allows the heating temperature to be lowered to a temperature lower than the melting point of lithium cobalt oxide, for example, 742° C. to 950° C., and allows additive elements such as magnesium to be distributed in the surface layer, thereby enabling the manufacture of a positive electrode active material with excellent characteristics.

[0187] Incidentally, since LiF has a lower specific gravity in a gaseous state than oxygen, there is a possibility that LiF will volatilize when heated, and if it volatilizes, the amount of LiF in the mixture 903 will decrease. In this case, the function as a flux will be weakened. Therefore, it is preferable to heat while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, etc., LiCoO ２There is a possibility that Li on the surface reacts with F in the fluorine source to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, it is still necessary to suppress volatilization.

[0188] Therefore, it is preferable to heat the mixture 903 by, for example, placing a lid on the container of the mixture 903. By heating in this manner, volatilization of LiF in the mixture 903 can be suppressed.

[0189] Furthermore, the heating in this step is preferably performed so as not to stick together the mixture 903. If the mixture 903 sticks together during heating, the contact area with oxygen in the atmosphere decreases, and the route along which the added element (for example, fluorine) diffuses is blocked, which may result in a poor distribution of the added element (for example, magnesium and fluorine) in the surface layer portion.

[0190] Furthermore, when the additive element (e.g., fluorine) is uniformly distributed in the surface layer portion, a smooth cathode active material with few irregularities can be obtained. Therefore, in order to maintain or further smooth the surface after the heating in step S15 in this process, it is preferable that the mixture 903 does not stick to each other.

[0191] <Step S34> Next, in step S34 shown in FIG. 8A , the heated material is recovered to obtain a positive electrode active material according to one embodiment of the present invention, which contains the additional element A. The recovered material may be crushed as needed. It is also preferable to sieve the recovered material. Through the above steps, the positive electrode active material according to one embodiment of the present invention can satisfy the median diameter of 12 μm or less (preferably 10.5 μm or less, more preferably 8 μm or less).

[0192] In this embodiment, graphite and silicon particles are used as the negative electrode active material. Silicon particles are silicon powder used as the negative electrode active material for lithium-ion secondary batteries. Silicon particles refer to particles with an average particle size distribution, i.e., an average particle size of approximately 100 nm, and are sometimes called nanosilicon particles. The silicon particles used are preferably prepared by pulverizing silicon raw materials to a uniform particle size. The silicon particles may contain at least one of silicon, silicon oxide, and silicon alloy. The weight ratio of graphite to silicon particles in the negative electrode active material layer is 9:1. The negative electrode active material layer preferably contains graphite in an amount at least nine times the weight of the silicon particles. A binder and a conductive additive are also added to prepare a slurry, which is then applied and dried. When a negative electrode active material layer containing a mixture of graphite and silicon particles is used as a negative electrode, charging and discharging at −40°C or −30°C is possible.

[0193] In the above configuration, the average particle diameter of the graphite particles mixed with the silicon particles is preferably 1 μm or more, and more preferably 5 μm or more and 30 μm or less. The particle size can be measured typically by laser diffraction particle size distribution measurement, but is not limited to laser diffraction particle size distribution measurement. The major axis of the particle cross section may also be measured by analysis using a SEM (scanning electron microscope) or a TEM (transmission electron microscope).

[0194] In this specification, the negative electrode active material contains at least both graphite particles and silicon particles. Since the silicon particles are mixed and used in the negative electrode, a secondary battery with high energy density can be realized.

[0195] When lithium ions are absorbed into silicon particles, they expand, resulting in a volumetric expansion. Because there are voids between adjacent graphite particles and silicon particles between the graphite particles, the expansion caused by the absorption of lithium ions has almost no effect on the negative electrode active material layer as a whole. The silicon particles are present between the graphite particles, and are aggregated in some of the voids. These voids exist when the negative electrode active material layer is formed on the negative electrode current collector, but are filled with an electrolyte solution during the subsequent secondary battery fabrication process.

[0196] The weight ratio in this specification refers to the compounding ratio when preparing the electrode slurry described below, i.e., the weight ratio (wt%) of each active material and conductive additive in the total weight (mixed powder) of the active material and conductive additive. Therefore, it may not match the weight ratio of each active material and conductive additive after the secondary battery is made.

[0197] Specifically, the weight ratio of silicon to the total weight of the powder material constituting the negative electrode active material is set to 7.5 wt % or more and 37.5 wt % or less. Another feature is that the weight ratio of graphite particles in the negative electrode active material layer is higher than the weight ratio of silicon particles.

[0198] Acetylene black (AB) may also be used as a type of conductive additive. The acetylene black (AB) is attached or adsorbed to the surface of the graphite or the surface of the silicon particles, or chemically bonded to the surface of the graphite or the surface of the silicon particles.

[0199] Furthermore, a resin material may be mixed with the negative electrode active material. Since the resin binder is an insulator, it is preferable to use a small amount of resin material. In this specification, the resin material refers to a polymeric organic material with high insulating properties.

[0200] <Binder> A binder is preferably provided to bind various components, such as active materials together, conductive materials together, and active materials and current collectors. Furthermore, the binder should be thermally stable and electrochemically stable at the positive electrode potential or the negative electrode potential. For example, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer as the binder. Fluorine rubber can also be used as the binder.

[0201] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0202] Alternatively, polymer materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose are preferably used as binders. Polymer materials are preferred because they are flexible and therefore make it easy to increase electrode density. PVDF has C—H bonds and C—F bonds, but is not polar overall, making it easy to disperse appropriately within the positive electrode.

[0203] The binder may be a combination of two or more of the above. In addition, since the binder is not a material that directly contributes to the battery characteristics, the binder may be unnecessary.

[0204] In this embodiment, an example is shown in which the internal space of the housing 21 is divided into several areas and devices or secondary batteries are placed in those areas, but this is not particularly limited, and it is sufficient that the desired measurements can be performed and the measurement results can be transmitted to an artificial satellite or the Earth.

[0205] Embodiment 3 In this embodiment, an example in which a lithium-ion battery according to one embodiment of the present invention is mounted in space equipment will be described.

[0206] 9A shows an artificial satellite 6800 as an example of space equipment. The artificial satellite 6800 has a body 6801, a solar panel 6802, an antenna 6803, and a lithium-ion battery 6805. The solar panel may be called a solar cell module.

[0207] When sunlight is irradiated onto the solar panel 6802, the power required for the satellite 6800 to operate is generated. However, for example, in a situation where sunlight is not irradiated onto the solar panel or where the amount of sunlight irradiating the solar panel is low, the generated power is reduced. Therefore, there is a possibility that the power required for the satellite 6800 to operate will not be generated. To operate the satellite 6800 even in a situation where the generated power is low, it is preferable to provide the satellite 6800 with a lithium ion battery 6805. The lithium ion battery 6805 of this embodiment has a bag containing an electrolyte therein. After the rocket launch, an impact or external force is applied to break the bag containing the electrolyte, causing a battery reaction. Furthermore, the lithium ion battery 6805 is expected to operate for a long period of time even at sub-zero temperatures.

[0208] The satellite 6800 can generate a signal. The signal is transmitted via the antenna 6803, and can be received by, for example, a receiver installed on the ground or another satellite. By receiving the signal transmitted by the satellite 6800, the position of the receiver that received the signal can be measured, for example. As described above, the satellite 6800 can constitute, for example, a satellite positioning system.

[0209] Alternatively, the artificial satellite 6800 may be configured to include a sensor. For example, by including a visible light sensor, the artificial satellite 6800 may have the function of detecting sunlight reflected from an object on the ground. Alternatively, by including a thermal infrared sensor, the artificial satellite 6800 may have the function of detecting thermal infrared rays emitted from the earth's surface. As described above, the artificial satellite 6800 may function as, for example, an earth observation satellite.

[0210] 9B shows a probe 6900 with a solar sail (also called a solar sail) as an example of space equipment. The probe 6900 has a body 6901, a solar sail 6902, and a lithium-ion battery 6905. When photons emitted from the sun hit the surface of the solar sail 6902, momentum is transferred to the solar sail 6902. Therefore, the surface of the solar sail 6902 should preferably have a thin film with high reflectivity, and should preferably face the sun.

[0211] The solar sail 6902 may also be designed to remain folded up until it leaves the atmosphere, and then unfold into a large sheet once outside the Earth's atmosphere (outer space), as shown in Figure 9B. The lithium-ion battery 6905 of this embodiment has a bag containing an electrolyte inside, and the impact of unfolding it ruptures the bag containing the electrolyte, causing a battery reaction. The lithium-ion battery 6905 is also expected to provide excellent long-term operation even at temperatures below freezing.

[0212] FIG. 9C shows a spacecraft 6910 as an example of space equipment. The spacecraft 6910 has a body 6911, a solar panel 6912, and a lithium-ion battery 6913. When the organic solvent and positive electrode active material of the present invention are used in the lithium-ion battery, excellent charge / discharge characteristics can be expected over a wide temperature range, including temperatures from below freezing to high temperatures. The body 6911 can have, for example, a pressurized compartment and a non-pressurized compartment. The pressurized compartment may be designed to accommodate a crew member. Electricity generated by sunlight irradiating the solar panel 6912 can be charged into the lithium-ion battery 6913.

[0213] FIG. 9D shows a rover 6920 as an example of space equipment. The rover 6920 includes a body 6921 and a lithium-ion battery 6923. The lithium-ion battery 6923 of this embodiment includes a bag containing an electrolyte, and the impact of landing is used to break the bag containing the electrolyte, causing a battery reaction. The lithium-ion battery 6923 is also expected to operate for a long period of time even at sub-zero temperatures. The rover 6920 may also include a solar panel 6922.

[0214] The rover 6920 may be designed to accommodate a crew member. The lithium ion battery 6923 may be charged with electricity generated by sunlight irradiating the solar panel 6912, or the lithium ion battery 6923 may be charged with electricity generated by other power sources, such as a fuel cell, a radioisotope thermoelectric converter, or the like.

[0215] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0216] 10: Secondary battery, 21: Housing, 22: Accelerometer, 23: Exterior body, 24: Positive electrode current collector, 25: Positive electrode active material layer, 26: Communication circuit section, 27a: First battery compartment, 27b: Second battery compartment, 27c: Third battery compartment, 33: Seismometer, 34: Negative electrode current collector, 35: Negative electrode active material layer, 36: Conductive rubber, 37: Epoxy resin, 40a: First bag, 40b: Second bag, 41: Negative electrode, 42: Separator, 43: Positive electrode, 45: Gap, 48: Adhesive region, 49: Adhesive layer, 500: Secondary battery, 501: Secondary battery, 503: Positive electrode, 506: Negative electrode, 507: Separator rover, 509: exterior body, 510: positive lead electrode, 511: negative lead electrode, 540: bag, 903: mixture, 6800: satellite, 6801: airframe, 6802: solar panel, 6803: antenna, 6805: lithium ion battery, 6900: probe, 6901: airframe, 6902: solar sail, 6905: lithium ion battery, 6910: spacecraft, 6911: airframe, 6912: solar panel, 6913: lithium ion battery, 6920: rover, 6921: airframe, 6922: solar panel, 6923: lithium ion battery

Claims

The battery has a region in which an electrolyte is contained between the exterior body and the positive electrode or the negative electrode, A secondary battery in which, upon receiving an impact of a predetermined impact value or more, a part of the boundary of the region is destroyed, causing the electrolyte to come into contact with the positive electrode or the negative electrode, thereby causing a battery reaction in the secondary battery.

2. The secondary battery according to claim 1, wherein the boundary of the region is formed by a separator or a film.

2. The secondary battery according to claim 1, wherein the positive electrode comprises a first rubber-like current collector and a positive electrode active material layer formed on the first rubber-like current collector.

2. The secondary battery according to claim 1, wherein the negative electrode comprises a second rubber-like current collector and a negative electrode active material layer formed on the second rubber-like current collector.

2. The secondary battery according to claim 1, wherein the region containing the electrolyte is a plurality of regions.

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