Electrodes, secondary batteries, and battery packs

Abstract

The present invention provides an electrode capable of realizing a secondary battery exhibiting excellent cycle life and low-temperature performance, a secondary battery containing this electrode, and a battery pack containing this secondary battery. [Solution] According to the embodiment, an electrode is provided comprising a current collector and an active material-containing layer supported on at least a portion of the current collector. The active material-containing layer comprises active material particles containing a lithium titanium-containing oxide having a spinel structure and an element-containing film covering at least a portion of the surface of the active material particles. The element is Al, or Al and Si. The ratio of the mass of the element to the mass of the active material particles is in the range of 0.1% by mass or more and 0.7% by mass or less. The electrode satisfies equation (1): 1.2 ≤ X 44 / X 18 ≤2.0 (1) However, X 18 This is the amount of volatilization of the substance corresponding to m / z=18 in the TPD-MS analysis of the electrode, calculated using the water equivalent method, and X 44 This represents the volatilization amount of the substance corresponding to m / z=44 in the TPD-MS analysis of the electrode, calculated using a water-equivalent method.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to electrodes, secondary batteries, and battery packs. [Background technology]

[0002] Recent rapid advancements in the field of electronics technology have led to the miniaturization and weight reduction of electronic devices. There is a strong demand for rechargeable batteries, which serve as power sources or backup power sources for such devices, that are also small, lightweight, and have high energy density. Furthermore, the recent demand for CO2 reduction has created an urgent need for the development of larger capacity energy storage systems for electric vehicles and for nighttime electricity storage in homes. To meet these demands, lithium-ion batteries with high volumetric density are attracting attention as a new type of rechargeable battery.

[0003] Lithium titanate with a spinel structure is known as an electrode material for lithium secondary batteries. However, lithium secondary batteries equipped with a negative electrode containing lithium titanate with a spinel structure as the negative electrode active material have challenges in terms of cycle life performance and low-temperature performance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-169276 [Patent Document 2] Japanese Patent Application Publication No. 2008-311067 [Patent Document 3] Japanese Patent Application Publication No. 2012-178327 [Patent Document 4] Japan Special Publication No. 2019-535110 [Patent Document 5] International Publication No. 2023 / 233692 [Overview of the project] [Problems that the invention aims to solve]

[0005] The problem that this invention aims to solve is to provide an electrode capable of realizing a secondary battery exhibiting excellent cycle life performance and low-temperature performance, a secondary battery including this electrode, and a battery pack including this secondary battery. [Means for solving the problem]

[0006] According to the embodiment, an electrode is provided comprising a current collector and an active material-containing layer supported on at least a portion of the current collector. The active material-containing layer comprises active material particles containing a lithium titanium-containing oxide having a spinel structure and an element-containing film covering at least a portion of the surface of the active material particles. The element is Al, or Al and Si. The ratio of the mass of the element to the mass of the active material particles is in the range of 0.1% by mass or more and 0.7% by mass or less. The electrode satisfies the following equation (1).

[0007] 1.2 ≤ X 44 / X 18 ≤2.0 (1) However, X 18 This is the amount of volatilization of the substance corresponding to m / z=18 in the TPD-MS analysis of the electrode, calculated using the water equivalent method, and X 44 This represents the volatilization amount of the substance corresponding to m / z=44 in the TPD-MS analysis of the electrode, calculated using a water-equivalent method.

[0008] According to one embodiment, a secondary battery is provided that comprises a positive electrode, a negative electrode consisting of the electrodes of the embodiment, and an electrolyte.

[0009] Furthermore, according to the embodiment, a battery pack comprising the secondary battery of the embodiment is provided. [Brief explanation of the drawing]

[0010] [Figure 1] A graph showing an example of the relationship between temperature and volatilization amount in TPD-MS analysis of the electrode of the embodiment. [Figure 2] A schematic cross-sectional view showing an example of a secondary battery according to this embodiment. [Figure 3] Figure 2 shows an enlarged cross-sectional view of section A of the secondary battery. [Figure 4] A schematic partial cutaway perspective view showing another example of a secondary battery according to the embodiment. [Figure 5] An enlarged cross-sectional view of section B of the secondary battery shown in Figure 4. [Figure 6] A schematic perspective view showing an example of a battery pack according to this embodiment. [Figure 7] An exploded perspective view schematically showing an example of a battery pack according to this embodiment. [Figure 8] A block diagram showing an example of the electrical circuit of the battery pack shown in Figure 7. [Modes for carrying out the invention]

[0011] Compared to lithium secondary batteries using carbon materials as the negative electrode active material, secondary batteries containing lithium titanium-containing oxides with a spinel structure, such as spinel-type lithium titanate, as the negative electrode active material exhibit less volume change during charging and discharging. Therefore, capacity reduction and negative electrode degradation due to lithium insertion and removal are less likely to occur. However, negative electrodes containing lithium titanium-containing oxides with a spinel structure have high self-discharge. Consequently, repeated charge-discharge cycles can cause the positive electrode potential to rise, potentially leading to cell (battery) swelling and positive electrode degradation due to the decomposition of electrolyte components.

[0012] Furthermore, the occurrence of self-discharge on the negative electrode surface is accompanied by film formation due to a side reaction between the active material particles and the electrolyte. When charge-discharge cycles are repeated, this film formation tends to increase the resistance at low temperatures compared to room temperature. In other words, negative electrodes containing lithium titanium oxide with a spinel structure are prone to deterioration in charge-discharge performance at low temperatures. This type of deterioration is due to the formation of a film caused by the reaction with the electrolyte on the negative electrode surface. By forming a layer containing Al or Si on the negative electrode surface using a metal alkoxide or the like, the film formation reaction on the negative electrode surface, which is a factor in resistance increase, is inhibited, making resistance increase less likely. Generally, the inventors have found that negative electrodes with a larger amount of Al or Si-containing layer coating tend to have slightly higher initial resistance, but they tend to have a higher effect in suppressing resistance increase after storage tests and cycle tests.

[0013] However, further research by the inventors revealed that even in secondary batteries using negative electrodes pre-coated with the same composition and amount of elements using metal alkoxides or the like, the resistance increase suppression effect varies depending on the conditions during negative electrode fabrication. In particular, while effective in suppressing resistance increase during storage, some negative electrodes do not exhibit much resistance increase suppression when subjected to charge-discharge cycle tests. This phenomenon was also found to be more pronounced in negative electrodes with a larger coating amount.

[0014] The electrodes of this embodiment make it possible to realize a secondary battery exhibiting excellent cycle life and low-temperature performance. The electrodes of this embodiment will be described below with reference to the drawings. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, each figure is a schematic diagram intended to explain the embodiment and facilitate understanding, and its shape, dimensions, ratios, etc., may differ from those of the actual device. These can be appropriately modified in consideration of the following explanation and known technology.

[0015] (First embodiment) The electrode of the first embodiment comprises a current collector and an active material-containing layer supported on at least a portion of the current collector. The active material-containing layer includes active material particles containing a lithium titanium-containing oxide having a spinel structure and an element-containing film covering at least a portion of the surface of the active material particles. The element-containing film may cover only a portion of the surface of the active material particles or the entire surface of the active material particles. The element (hereinafter referred to as the first element) is either Al or Al and Si. The ratio of the mass of the first element to the mass of the active material particles is in the range of 0.1% by mass or more and 0.7% by mass or less. The electrode also satisfies the following equation (1).

[0016] 1.2 ≤ X 44 / X 18 ≤2.0 (1) However, X 18This is the amount of volatilization of the substance corresponding to m / z=18 in the TPD-MS analysis (Temperature Programmed Desorption or Decomposition Mass-Spectrometry) of the electrode, calculated using the water equivalent method, and X 44 This represents the volatilization amount of the substance corresponding to m / z=44 in the TPD-MS analysis of the electrode, calculated using a water-equivalent method.

[0017] The electrodes of this embodiment are characterized by their resistance, which does not easily increase not only during storage but also during repeated charge-discharge cycles. The inventors have found that in secondary batteries where there is a difference in the resistance increase suppression effect between storage and charge-discharge cycles, the active material-containing layer of the electrodes contains a large amount of organic matter. It is presumed that the organic matter originates from the raw materials of the element-containing film. For example, organic matter such as metal alkoxides is used as the raw materials for the element-containing film. As the amount of element-containing film formed increases, the amount of organic matter used as a raw material also increases. As a result, some of the organic matter used as a raw material remains in the electrode. Due to this effect, when charge-discharge cycles are repeated, the residual organic matter in the electrode decomposes and moves outside the electrode, causing a structural change in the element-containing film on the surface of the active material particles. As a result, the residual organic matter detaches from the film present on the surface of the active material, making it impossible to sufficiently suppress the film formation reaction between the active material and the electrolyte. Therefore, it has been found that secondary batteries experience an increase in both room-temperature resistance and low-temperature resistance, accompanied by an increase in AC resistance.

[0018] The electrode of this embodiment reduces the amount of residual organic matter, which is an inhibiting factor in suppressing resistance increase. As a result, it is possible to provide an electrode that enables a secondary battery in which the resistance increase at room temperature accompanied by an increase in AC resistance is suppressed even after repeated charge-discharge cycles, and the increase in low-temperature resistance is also suppressed. Therefore, it is possible to realize a secondary battery with excellent charge-discharge cycle performance and low-temperature performance. Furthermore, by reducing the amount of residual organic matter, the initial resistance value can also be reduced even when the same amount of element-containing film is formed on the active material particles as before. The electrode of this embodiment will be described in detail below.

[0019] The ratio of the mass of the first element to the mass of the active material particles is preferably between 0.1% and 0.7% by mass. The reason for this is as follows: By setting the ratio to 0.7% by mass or less, the amount of organic matter used as a raw material for forming the element-containing film can be reduced, thereby reducing the amount of organic matter remaining in the electrode. Therefore, even after repeated charge-discharge cycles, it is possible to suppress the increase in resistance accompanied by an increase in AC resistance due to the detachment of residual organic matter from the active material surface coating layer. In addition, since the thickness of the element-containing film coating the surface of the active material particles becomes thinner, the Li ion conductivity during charge and discharge can be increased. As a result, the resistance at the beginning of the charge-discharge cycle can be kept low. Although a lower ratio of the mass of the contained (first) element to the mass of the active material particles reduces the amount of organic matter contained in the electrode, it is desirable to set the lower limit of the ratio to 0.1% by mass in order to ensure the suppression of resistance increase in harsh environments by the element-containing film. Therefore, by setting the ratio to 0.1% by mass or more and 0.7% by mass or less, it is possible to suppress the formation of a film caused by the reaction with the electrolyte on the surface of the active material, which is the cause of the increase in low-temperature resistance, while suppressing the increase in initial resistance and the increase in resistance due to the increase in AC resistance associated with the charge-discharge cycle. The preferred lower limit of the ratio of the mass of the contained (first) element to the mass of the active material particles is 0.12% by mass. The preferred upper limit of the ratio is 0.6% by mass. The even more preferred upper limit is 0.5% by mass.

[0020] The chemical structure of a film containing Al as the first element, i.e., an Al-containing film, is not yet clear, but it may exist, for example, in the form of aluminum oxide. An aluminum-containing film is, for example, a film made using organoaluminum compounds as the aluminum source.

[0021] In a film containing Al as the first element, it is desirable that the ratio of Al mass to the mass of active material particles be between 0.1% by mass and 0.7% by mass. The lower limit of this ratio is preferably 0.12% by mass. The upper limit of the ratio is preferably 0.6% by mass, and a more preferable range is 0.35% by mass. By setting the ratio within the range of 0.1% by mass and 0.35% by mass, it is possible to ensure the resistance increase suppression effect of the element-containing film, especially when used in harsh environments such as low-temperature environments, while maintaining good capacity and output performance of the secondary battery and minimizing the influence of residual organic matter associated with the formation of the element-containing film.

[0022] Element-containing films are advantageous over films made solely of Si in suppressing resistance increases in low-temperature, high-temperature, and high-state-of-charge (SOC) environments. They are particularly advantageous in suppressing resistance increases in low-temperature environments. Films containing both Al and Si as elements can lower initial resistance. The ratio of Si to Al in element-containing films should be determined considering the operating environment.

[0023] In a film containing Al and Si, Al and Si may or may not be chemically bonded to each other or via oxygen. Organic substituents contained in organoaluminum compounds may be bonded to or coordinated to the aluminum atoms in the Al-containing film. For example, a methoxy group may be bonded to the aluminum atoms, or an acetyl group may be coordinated to them. A metal alkoxide is used as the silicon raw material for the Al-Si-containing film. In this case, the raw material for the alkoxide used to prepare the Si-containing film is not particularly limited; either a monomeric silicon-based alkoxide, such as orthoethyl silicate, or a polymeric condensed silicate may be used.

[0024] In the film containing Al and Si as the first element, the more preferable range of the ratio of the total mass of Al and Si to the mass of the active material particles is within the range of 0.1% by mass or more and 0.5% by mass or less. By setting it within this range, the effect of suppressing the increase in resistance by the element-containing film, particularly the effect of suppressing the increase in resistance when used in harsh environments such as low-temperature environments, can be ensured, and while maintaining the capacity and output performance of the secondary battery well, the influence of residual organic substances accompanying the formation of the element-containing film can be reduced.

[0025] The element-containing film may contain substances other than Al and Si. Examples of such substances include organic substances and the like. Examples of organic substances include volatile organic substances and non-volatile organic substances.

[0026] The electrode satisfies equation (1). X in equation (1) 18 is the evaporation amount by the water conversion method of the substance corresponding to m / z = 18 in the TPD-MS analysis of the electrode. The substance corresponding to m / z = 18 contains H2O. X 18 is a constant amount regardless of the presence or absence of organic raw materials used in the element-containing film or the like, as long as the composition of the active material-containing layer of the electrode, the raw materials (e.g., active material, conductive agent, binder) used in the production of the active material-containing layer, and the production method of the electrode are constant. Therefore, X 18 is a value that serves as an index for determining the amount of organic substances contained in the electrode. On the other hand, X 44 is the evaporation amount by the water conversion method of the substance corresponding to m / z = 44 in the TPD-MS analysis of the electrode. The substance corresponding to m / z = 44 contains CO2. As a result of the intensive research by the present inventors, during battery use such as charge-discharge cycles, the residual organic substances in the coating layer on the surface of the active material particles gradually decompose, causing the contact between the active material particles and the conductive agent on the surface of the active material-containing layer to relax, resulting in an increase in room-temperature resistance accompanied by an increase in AC resistance, and a decrease in the effect of suppressing the reaction with the electrolyte components accompanied by the formation of a coating on the active material surface by the coating layer, leading to an increase in low-temperature resistance. It has been found that these increases in resistance are due to the decomposition of residual organic substances that gradually occur during charge-discharge cycles, and it is effective to reduce the volatile substances corresponding to the mass number 44 measured by TPD-MS analysis during cell production. X 44 / X18 By reducing the value of the ratio represented by to 2.3 or less, the increase in resistance associated with charge-discharge cycles can be suppressed. This is because the amount of organic matter present on the electrodes, derived from organic raw materials such as element-containing films and organic components that adhere to the electrodes through reactions with electrolytes, can be reduced. 44 / X 18 It is desirable to set the lower limit of the ratio value represented by to 1.2. The reason for this is explained below. After charging and discharging a secondary battery for capacity confirmation, the electrode (e.g., the negative electrode) is removed in an inert atmosphere and cleaned. On the surface of the cleaned electrode, there are organic components originating from the organic raw materials used to produce the element-containing film, and organic components originating from the electrolyte that adhered to the electrode surface due to reactions with the electrolyte during charging and discharging. Basically, the amount of organic components that adhere to the electrode due to reactions with the electrolyte during a few charge-discharge cycles is small compared to the amount of residual organic components originating from the raw materials of the element-containing film, so it hardly affects the resistance accompanied by an increase in AC resistance during the charge-discharge cycle. X 44 / X 18 Electrodes with a ratio value of less than 1.2 contain a relatively large amount of organic matter derived from organic components that adhere to the electrode through reactions with the electrolyte during charging and discharging, and organic matter derived from organic components in the slurry remaining after electrode fabrication, compared to the amount of residual organic components derived from the raw materials of the element-containing film. Such electrodes may not adequately cover the surface of the active material particles due to insufficient formation of the element-containing film, and may not adequately suppress resistance increase in harsh environments. Therefore, X 44 / X 18 By setting the value of the ratio represented by to between 1.2 and 2.0, it is possible to suppress the resistance increase associated with charge-discharge cycles while ensuring the effect of suppressing resistance increase in harsh environments. 44 / X 18 A more preferable range for the value of the ratio expressed is 1.4 or more and 2.0 or less. Volatility ratio (X 44 / X 18 These can be adjusted, for example, by the raw materials for the element-containing film, the method for manufacturing the electrode, and the method for storing the electrode.

[0027] Even in the electrode alone before being incorporated into the battery, the volatility ratio (X 44 / X 18 Controlling the volatility ratio (X) within a certain range is effective in suppressing resistance increase during charge-discharge cycles. 44 / X 18 The upper limit of ) is the volatility ratio (X) in the electrodes incorporated into the battery. 44 / X 18 It is acceptable for it to be greater than the upper limit of ). After being incorporated into the battery, some of the residual organic components in the electrode decompose due to charging and discharging, causing a decrease. Taking this decrease into account, the volatility ratio of the electrode alone (X 44 / X 18 ) can be between 1.2 and 2.3.

[0028] The electrodes of the embodiment will be described further below.

[0029] The electrode of the embodiment comprises a current collector and an active material-containing layer supported on at least a portion of the current collector. The electrode of the embodiment can be used as an electrode for a battery, an electrode for a secondary battery, or an electrode for a lithium secondary battery such as a lithium-ion secondary battery. The electrode of the embodiment may be a positive electrode or a negative electrode, but it is preferable that it be a negative electrode.

[0030] It is desirable that the active material-containing layer be supported on part or all of the surface intersecting the thickness direction of the current collector. An example of a surface intersecting the thickness direction of the current collector is the main surface of the current collector.

[0031] The active material-containing layer contains active material particles comprising a lithium titanium-containing oxide having a spinel structure. An example of a lithium titanium-containing oxide having a spinel structure is lithium titanate having a spinel structure. Lithium titanate having a spinel structure is, for example, a material with the general formula Li 4+a Ti5O 12This is a compound represented by (-1 ≤ a ≤ 3). The subscript 'a' in the general formula is a variable that can change within the above range depending on the charge state of lithium titanate. The lithium titanium-containing oxide may also be a lithium titanium composite oxide containing elements other than Li and Ti. Examples of elements other than Li and Ti include at least one selected from the group consisting of Mo, Nb, Ta, V, and W.

[0032] Lithium titanium-containing oxides having a spinel structure may exist in the form of primary particles or in the form of secondary particles formed by the aggregation of primary particles. Whether a lithium titanium-containing oxide with a spinel structure is in the form of secondary or primary particles can be determined by scanning electron microscopy (SEM) observation.

[0033] The average primary particle size (D50) of the spinel-structured lithium titanium-containing oxide is, for example, in the range of 0.1 μm to 30 μm, and preferably in the range of 1 μm to 10 μm.

[0034] The mass percentage of lithium titanium-containing oxide having a spinel structure in the active material particles may be 80% by mass or more. It may also be 90% by mass or more, or even 100% by mass. That is, the active material particles may consist solely of lithium titanium-containing oxide having a spinel structure. The type of active material particles may be one or more types.

[0035] Other active materials besides lithium titanium oxides with a spinel structure include, for example, lithium titanate (e.g., Li) having a ramsdelite structure. 2+yThere are several types of active materials: Ti3O7 (0≦y≦3), monoclinic titanium dioxide (TiO2), anatase titanium dioxide, rutile titanium dioxide, hollandite titanium composite oxide, monoclinic niobium titanium composite oxide, and orthorhombic titanium composite oxide. In batteries using these active materials as the negative electrode, a slight effect of suppressing the rise in room-temperature resistance due to surface coating is observed. However, in batteries using these active materials as the negative electrode, the element-containing film covering the surface of the active material is damaged by volume changes associated with charging and discharging. As a result, the formation of a film on the active material caused by side reactions with the electrolyte cannot be sufficiently suppressed, and the effect of suppressing the rise in low-temperature resistance is inferior to that of lithium titanium-containing oxides with a spinel structure. However, when using a cell (battery) under conditions where charging and discharging are infrequent, for example, under conditions where the storage time is long relative to the number of charge-discharge cycles in a constant temperature environment, the damage due to volume changes of the active material is small, and a resistance rise suppression effect can be expected.

[0036] The active material-containing layer may contain a binder. Examples of binders include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyimide, polyamide, polyvinylpyrrolidone (PVP), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyvinyl chloride (PVC), polyvinyl acetate (PVAC), and polyacrylic acid. The ratio of the binder's mass to the mass of the active material particles can be in the range of 1.5% by mass or more and 30.0% by mass or less.

[0037] From the viewpoint of minimizing the increase in battery resistance associated with increasing the amount of binder added, it is preferable that the binder contains PVDF. Furthermore, it is desirable that the ratio of the binder's mass to the mass of the active material particles be within the range of 1.5% by mass to 5.0% by mass, as this can suppress the increase in initial battery resistance due to the amount of binder added.

[0038] The active material-containing layer may also contain a conductive agent. The conductive agent is added to enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, fibrous carbon such as carbon nanotubes, and carbonaceous materials such as graphite. One of these may be used as a conductive agent, or two or more may be used in combination.

[0039] The proportions of active material particles, conductive agent, and binder in the active material-containing layer can be appropriately changed depending on the application of the electrode. For example, it is preferable to blend the active material particles, conductive agent, and binder in proportions of 68% to 96% by mass, 2% to 30% by mass, and 1.5% to 30% by mass, respectively. It is also desirable that the element-containing film be included in an amount of 0.1% to 0.6% by mass in the active material-containing layer. The total proportions of active material particles, conductive agent, and binder in the active material-containing layer may exceed 100% by mass.

[0040] The thickness of the active material-containing layer is not particularly limited, but can be, for example, in the range of 10 μm to 50 μm.

[0041] The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and removed from the active material. For example, when the active material is used as the negative electrode active material, the current collector is preferably made of copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm to 20 μm. A current collector with such a thickness can balance electrode strength and weight reduction.

[0042] Furthermore, the current collector may include portions on its surface where the active material-containing layer is not formed. These portions can function as current-collecting tabs.

[0043] The amount of organic matter present in the electrode can be set within the desired range by adjusting the type of organic raw material used for the element-containing film, the electrode manufacturing method, and especially the drying conditions of the electrode manufacturing method. For example, the electrode is obtained by mixing materials such as an active material, a conductive agent, and a binder with a solvent such as N-methyl-2-pyrrolidone (NMP) to make a slurry, coating the resulting slurry onto a current collector, and then drying it. After manufacturing, the electrode may be shaped to an appropriate electrode density by a pressing process, then dried, and finally placed inside the battery. The organic raw material used as the raw material for the element-containing film forms a film on the active material through decomposition or polymerization during the above series of processes. Some of the decomposition products generated during film formation remain inside the electrode. As will be described in detail later, in order to minimize the amount of organic matter remaining inside the electrode, it is useful to select organic raw materials that do not easily leave decomposition products during electrode manufacturing, or to perform a process to remove organic decomposition products from the electrode before or after placing the electrode inside the battery. The manufacturing method of the electrode according to the embodiment will be described below.

[0044] The electrode according to this embodiment can be manufactured, for example, by the following method.

[0045] First, a slurry is prepared by suspending active material particles containing a lithium titanium oxide having a spinel structure, a conductive agent, and a binder in a solvent. At this time, an organic aluminum compound is added to the slurry. The organic aluminum compound is added by, for example, diluting it using a solvent used when preparing slurries such as NMP, and then adding the solution or suspension containing the organic aluminum compound to the slurry. The solid content concentration in the resulting slurry is preferably in the range of, for example, 40% by mass or more and 65% by mass or less. The mixing ratio of active material particles, conductive agent, and binder is preferably as described above.

[0046] The prepared slurry is applied to a current collector such as aluminum foil using a coating machine to the desired weight, and the coating film is dried. For drying the coating film, depending on the material of the Al source used, it is desirable to perform vacuum drying at 120°C to 140°C for 12 hours or more. A preferred range for the vacuum drying temperature is 35 hours or more. Thus, a component comprising a current collector and an active material-containing layer formed on the current collector is produced. The resulting component is, for example, in the shape of a strip. This component is then pressed to achieve a predetermined electrode density. In this way, an electrode according to the first embodiment can be produced.

[0047] Examples of organic aluminum compounds include metal alkoxides such as aluminum (metal) alkoxides, and aluminum chelates (complexes).

[0048] Examples of aluminum chelates that can be used include aluminum trisacetylacetate (Al(C5H7O2)3), aluminum bisethylacetoacetate monoacetylacetate (Al(C5H7O2)(C6H9O3)2), aluminum trisethylacetoacetate (Al(C6H9O3)3), and aluminum monoacetylacetate bis(ethylacetoacetate) (Al(O2C5H7)2(O3C6H9)). These may be used individually or as a mixture of two or more. Aluminum monoacetylacetate bis(ethylacetoacetate) is desirable because it is easily volatile from the electrode during electrode fabrication. The structural formula of aluminum monoacetylacetate bis(ethylacetoacetate) is shown in Chemical Formula 1. An example of aluminum monoacetylacetate bis(ethylacetoacetate) is the product name Aluminum Chelate D (abbreviated as ACD) from Kawaken Fine Chemicals Co., Ltd.

[0049] [ka]

[0050] Examples of aluminum alkoxides that can be used include di-2-butoxyaluminum ethyl acetacetate (Al(C4H9O)2(C6H9O3)), aluminum tri-2-butoxide (Al(OC4H9)3), di-2-butoxyaluminum acetylacetate (Al(C4H9O)2(C5H7O2)), and aluminum secondary butoxide (Al(O-sec-C4H9)3). These may be used individually or as a mixture of two or more. Furthermore, it is desirable to select an appropriate material for coating the electrode active material with the organic Al compound. When using metal alkoxide-based raw materials, it is desirable to control the amount of organic matter in the electrode by controlling the electrode drying conditions. Specifically, when using metal alkoxide-based raw materials as the Al source, it is desirable to control the amount of organic matter in the electrode by increasing the electrode drying temperature or extending the drying time. In addition, the amount of organic matter in the electrode can also be controlled by controlling the aging treatment conditions, which also serve as degassing, performed on batteries before shipment.

[0051] When incorporating Si into a film, metal alkoxides can be used. Examples of Si-containing metal alkoxides include Si alkoxide monomers (silicate monomers) and Si alkoxide polymers (silicate oligomers). Examples of Si alkoxide monomers include ethyl orasilicate, propyl silicate, and butyl silicate. Si alkoxide polymers are often solid components formed by pre-condensing monomers. Examples of Si alkoxide polymers include polymers containing ethyl polysilicate (e.g., Silicate 40 (product name of Tama Chemical Industry Co., Ltd.), Ethyl Silicate 40 (product name of Colcoat Co., Ltd.), Ethyl Silicate 48 (product name of Colcoat Co., Ltd.)). These polymers are chemically stable condensed silicates.

[0052] Alkoxides containing condensed silicates as the main component can easily form Si-containing films on active material particles containing lithium titanium oxide having a spinel structure. A high degree of degeneracy of the condensed silicate is preferable because it helps reduce residual organic matter.

[0053] Furthermore, the electrode according to this embodiment may be manufactured by the following method. First, lithium titanium-containing oxide particles having a spinel structure, a conductive agent, and a binder are suspended in a suitable solvent to prepare a slurry. Using this slurry, an electrode structure free of Al components is obtained by coating, drying, and pressing in the same manner as the manufacturing method described above. Subsequently, this electrode structure is immersed in an ethanol solution containing an organic Al compound. The immersion treatment is preferably carried out by immersing the electrode structure at room temperature for 10 seconds to 30 seconds.

[0054] Subsequently, the electrode structure is removed from the organic Al compound-containing solution, and any excess solution adhering to the component is wiped off. Next, the electrode structure is subjected to drying. Drying is preferably carried out for at least 12 hours, more preferably 35 hours, in a vacuum dryer set to at least 120°C to 140°C, after which it is desirable to dry it in a vacuum dryer set to at least 120°C to 140°C. When using metal alkoxides as raw materials for the Al-containing film, residual organic matter tends to remain, so it is desirable to dry it in a vacuum dryer set to at least 120°C to 140°C for 35 hours or more. In this way, an Al-containing film can be formed on at least a portion of the surface of the active material particles.

[0055] It is desirable to select an aluminum chelate-based material as the organic aluminum compound. Aluminum chelate-based materials can reduce the amount of organic matter remaining on the electrode compared to alkoxide-based materials. Examples of organic aluminum compounds are as described above. Organic aluminum compounds containing aluminum monoacetylacetate bis(ethyl acetate) can form an aluminum-containing film on the surface of the active material-containing layer while reducing the amount of organic components remaining in the electrode.

[0056] While ethanol is given as an example of a solvent used for diluting organic aluminum compounds, the diluent is not limited to ethanol. The diluent should preferably be a solvent with a relatively low boiling point that does not remain in the electrode after drying and does not react easily with metal alkoxides or electrode components. Using a diluent that does not remain in the electrode prevents a decrease in efficiency due to residual solvent during battery charging and discharging. To prevent reactions with metal alkoxides and electrode components, a solvent with a low water content is desirable. Considering safety, cost, and ease of handling, ethanol is suitably used. Another example is methanol, but caution should be exercised when handling it due to its toxicity. Al or Al and Si present on the surface of the active material particles using the above method can be confirmed by analytical techniques such as TEM-EDX, SEM-EDX, or XPS.

[0057] The composition of the element-containing film, the volatility ratio (X) defined by equation (1) 44 / X 18 The following describes the methods for measuring the ratio of the mass of the first element to the mass of the active material particles, as well as the crystal structure and composition of the active material.

[0058] Scanning Electron Microscope - Energy Dispersive X-ray Spectroscopy (SEM-EDX) SEM-EDX can be used to confirm the presence of element-containing films on the surface of active material particles. A method for obtaining elemental mapping of an electrode cross-section using SEM-EDX is described below.

[0059] First, the rechargeable battery is brought to a completely discharged state. For example, the battery can be brought to a completely discharged state by repeatedly discharging it at a current of 0.1C in a 25°C environment until the rated cutoff voltage or battery voltage reaches 1.0V, and ensuring that the discharge current is less than 1 / 100 of the rated capacity. Even in a discharged state, residual lithium ions may still be present.

[0060] A secondary battery with an electrode in a fully discharged state (State of Charge: 0%) is disassembled in a glove box filled with argon. The electrode to be measured (for example, the negative electrode) is taken out from the disassembled secondary battery. This electrode is washed with an appropriate solvent. As the solvent used for washing, for example, ethyl methyl carbonate or the like may be used. If the washing is insufficient, it may be difficult to observe particles due to the influence of lithium carbonate, lithium fluoride, etc. remaining in the electrode. The electrode of the target taken out in this way is cut with an ion milling device. When cutting the electrode, the electrode is cut along the thickness direction. The cross-section of the cut electrode is attached to an SEM sample stage. At this time, treatment is performed using a conductive tape or the like so that the electrode does not peel off or float from the sample stage. The active material-containing layer of the electrode attached to the SEM sample stage is observed with an SEM to obtain an SEM image. Observation is performed at a magnification of 10,000 times during SEM measurement. Also, when introducing the electrode into the sample chamber, it is preferable to maintain an inert atmosphere.

[0061] Furthermore, an elemental mapping image corresponding to the above SEM image is obtained by EDX. By considering the combination of the above SEM image and the elemental mapping image, it can be confirmed that at least a part of the surface of the active material particles is covered with an element-containing film.

[0062] <TPD-MS (Temperature Programmed Desorption or Decomposition Mass-Spectrometry) analysis> The volatile ratio (X 44 / X 18 ) can be measured by TPD-MS analysis.

[0063] First, a method for taking out an electrode from a battery will be described.

[0064] After charging and discharging a battery to confirm its capacity, it is discharged to its rated discharge state (SOC 0%) and then disassembled in an inert atmosphere (e.g., in an Ar glove box or helium atmosphere). From the electrodes, the portion where the active material-containing layer is formed on both sides of the current collector is taken as a sample. The taken sample is washed with EMC (ethyl methyl carbonate) and then vacuum dried. The sample is loaded into a TPD-MS analyzer and heated to 25-500°C (e.g., at a heating rate of 10°C / min), and mass spectrometry of volatile components is performed. The amount of volatile components is obtained based on the water equivalent method (m / z=18,44) and the toluene equivalent method (m / z=99,132). Examples of volatile components obtained from the electrodes include components derived from moisture and organic components in the electrode (m / z=18,44), components derived from NMP used in electrode fabrication (m / z=99), and components derived from PVdF as a binder (m / z=132). The components originating from m / z=18, 99, and 132 will be approximately constant if the active material, conductive agent, and binder are constant. The components originating from m / z=44 may vary due to organic components adhering to the electrode through reaction with the electrolyte and organic components remaining after the formation of element-containing films. The specific method of mass spectrometry of volatile components is described below. First, a calibration curve is created using sodium tungstate dihydrate as a standard sample, between the peak intensity (integral value) of water (m / z=18) and the weight of the standard sample (the weight of water corresponding to the weight of the standard sample). The peak curves for each mass number of the sample (m / z=18, 44, 99, 132) are measured. An example of the peak curves for m / z=18 and 44 is shown in Figure 1. In Figure 1, the horizontal axis is the measurement temperature (°C), and the vertical axis is the abundance. The peak curve P(m / z18) for m / z=18 has a peak around 450°C. Furthermore, the peak curve P(m / z44) for m / z=44 has peaks around 200°C and 450°C.

[0065] The peak intensity (integral value) of each mass number in the sample is compared with the calibration curve described above to calculate the water equivalent content of each substance in the sample. Since the substances with m / z = 99 and 132 are organic substances, their water equivalent content is converted to toluene equivalent based on the ionization efficiency ratio. By calculating the toluene equivalent content of the substances with m / z = 99 and 132, the obtained volatility ratio (X 44 / X 18 ) can be verified. If the composition of the active material-containing layer is the same, the X measured in each sample 44 / X 18 If the toluene equivalent content of the substance with m / z = 99,132 is approximately the same across samples, the measurement accuracy is considered high. Specifically, for electrode samples with identical active material layer compositions, if the toluene equivalent content of the substance with m / z = 99,132 measured simultaneously exceeds 30% of the average value, the measurement should be repeated or the results should be discarded. In this way, the volatilization amount X 18 and volatilization amount X 44 Determine the volatility ratio (X 44 / X 18 ) obtain.

[0066] <Inductively coupled plasma emission spectroscopy measurement> The mass ratio of aluminum and silicon to the active material particles can be calculated by analysis using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0067] Specifically, the active material-containing layer to be measured is peeled off from the electrode current collector using an aqueous solvent or NMP, and a dispersion is prepared by dispersing the electrode components in the solvent. The solid components are extracted and recovered from this dispersion. The molten material obtained by methods such as acid decomposition or alkali melting is dissolved in an acidic aqueous solution. In the acid decomposition method, the solid components are dissolved in the acid by placing an appropriate acid and solid components in a pressurized container and heating it. In this way, a sample solution containing the electrode components is obtained. The electrode components may mainly include metal components that make up the active material-containing layer.

[0068] Quantitative analysis is performed on the sample solution using ICP analysis. The composition of the active material is determined from the ICP analysis results, powder X-ray diffraction measurement results, and compositional analysis results of the active material particles in the electrode by SEM-EDX. In addition, the mass ratio of silicon and aluminum to the active material particles is calculated from the analytical values ​​of at least one of the active material components, such as Ti, Si, and Al, and the active material composition.

[0069] The crystal structure and elemental composition of the active material (e.g., the negative electrode active material) can be confirmed, for example, by powder X-ray diffraction (XRD), inductively coupled plasma (ICP) emission spectroscopy, and SEM-EDX analysis of the electrodes, as described below.

[0070] <Powder X-ray diffraction measurement of active material> Powder X-ray diffraction measurements of active materials can be performed, for example, as follows: First, the sample is ground until the average particle size is approximately 5 μm. The ground sample is then packed into a holder portion with a depth of 0.2 mm formed on a glass sample plate. At this time, care should be taken to ensure that the sample is sufficiently packed into the holder portion. Care should also be taken to pack the correct amount of sample to avoid cracks, voids, etc. Next, another glass plate is pressed against the outside to flatten the surface of the sample packed into the holder portion. Care should be taken to ensure that there are no irregularities on the reference surface of the holder due to an excess or deficiency in the amount of packed sample.

[0071] Next, the glass plate filled with the sample is placed in a powder X-ray diffractometer, and a diffraction pattern (XRD pattern; X-Ray Diffraction pattern) is obtained using Cu-Kα rays.

[0072] Furthermore, the orientation of particles may increase depending on the particle shape of the sample. If the orientation of the sample is high, the position of the peak may shift or the intensity ratio may change depending on how the sample is packed. Samples with such significantly high orientation should be measured using a glass capillary. Specifically, the sample is inserted into the capillary, and this capillary is placed on a rotating sample stage for measurement. This measurement method can mitigate the orientation. As for the glass capillary, it is preferable to use a Lindemann glass capillary with a diameter of 1 mm to 6 mmφ.

[0073] When performing powder X-ray diffraction measurements on the active material contained in a secondary battery or electrode, the measurement can be carried out, for example, as follows. First, to understand the crystalline state of the active material, the lithium ions must be completely removed from the active material. For example, if the active material is used in the negative electrode, the battery must be completely discharged. For instance, the battery can be discharged by repeatedly discharging it at a current of 0.1C in a 25°C environment until the rated cutoff voltage or battery voltage reaches 1.0V, ensuring that the discharge current is less than 1 / 100th of the rated capacity. Even in the discharged state, residual lithium ions may still be present.

[0074] Next, disassemble the battery in a glove box filled with argon, take out the electrodes, and wash them with an appropriate solvent. As the appropriate solvent, for example, ethyl methyl carbonate can be used. If the electrode cleaning is insufficient, impurity phases such as lithium carbonate and lithium fluoride may be mixed in due to the influence of lithium ions remaining in the electrode. In that case, it is advisable to use an airtight container in which the measurement atmosphere can be in an inert gas. At this time, measure and grasp in advance the peaks derived from the metal foil as the current collector, the conductive agent, the binder, etc. using EDX. Of course, if these can be grasped in advance, this operation can be omitted. When the peak of the current collector overlaps with the peak of the active material, it is desirable to peel off the active material-containing layer from the current collector for measurement. This is to separate the overlapping peaks when quantitatively measuring the peak intensity. The active material-containing layer may be physically peeled off. The active material-containing layer is easily peeled off when ultrasonic waves are applied in an appropriate solvent. When ultrasonic treatment is performed to peel off the active material-containing layer from the current collector, the electrode body powder (including the active material, the conductive agent, and the binder) can be recovered by volatilizing the solvent. By filling the recovered electrode body powder into, for example, a capillary made of Lindemann glass and performing measurement, powder X-ray diffraction measurement of the active material can be performed. In addition, the electrode body powder recovered by ultrasonic treatment can also be used for various analyses other than powder X-ray diffraction measurement.

[0075] <Inductively Coupled Plasma (ICP) Emission Spectrometry> The composition of the active material can be analyzed, for example, using inductively coupled plasma (ICP) emission spectrometry. At this time, the abundance ratio (molar ratio) of each element depends on the sensitivity of the analytical apparatus used. Therefore, the measured molar ratio may deviate numerically from the actual molar ratio by the error of the measuring apparatus. However, even if the numerical value deviates within the error range of the analytical apparatus, the performance of the active material according to the embodiment can be sufficiently exhibited.

[0076] To measure the composition of the active material incorporated in the battery by ICP emission spectrometry, specifically, it is performed according to the following procedure.

[0077] First, according to the procedure described in the section on powder X-ray diffraction measurement, an electrode containing the active material to be measured is taken out from the secondary battery and washed. From the washed electrode, a portion containing the electrode active material, such as the active material-containing layer, is peeled off. For example, the portion containing the electrode active material can be peeled off by irradiating with ultrasonic waves. As a specific example, for instance, the electrode is placed in ethyl methyl carbonate contained in a glass beaker and vibrated in an ultrasonic cleaner to peel off the active material-containing layer containing the electrode active material from the electrode current collector.

[0078] Next, the peeled portion is heated in the air for a short time (for example, at about 500 °C for 1 hour) to burn off unnecessary components such as the binder component and carbon. By dissolving this residue in an acid, a liquid sample containing the active material can be prepared. At this time, hydrochloric acid, nitric acid, sulfuric acid, hydrogen fluoride, etc. can be used as the acid. By subjecting this liquid sample to ICP analysis, the composition in the active material can be known. <SEM-EDX Analysis> By performing SEM-EDX analysis on the electrode (negative electrode) or the negative electrode taken out from the disassembled cell, the composition of the negative electrode active material and Al or Al and Si present on the surface of the negative electrode active material can be confirmed. A part of the negative electrode to be measured is embedded in a curable resin, and an evaluation sample with the electrode cross-section exposed is obtained through a cutting and polishing process. By performing SEM-EDX analysis on this sample, the composition of the active material particles and Al or Al and Si present on the surface of the active material particles can be confirmed. When observing the electrode cross-section with SEM, the active material particles (containing Ti), conductive material, and binder constituting the electrode can be visually recognized. By performing SEM-EDX analysis on these active material particles, the components of the active material, that is, Ti excluding Li and other contained components, can be known. From this result and the result of powder X-ray diffraction measurement, the active material can be identified, and the composition containing Li and the crystal structure of the active material can be grasped. SEM-EDX analysis can be performed by the method described in <Scanning Electron Microscope - Energy Dispersive X-ray Spectroscopy: SEM-EDX>.

[0079] An electrode is provided according to the first embodiment described above. The electrode comprises active material particles containing a lithium titanium-containing oxide having a spinel structure, and an active material-containing layer comprising an element-containing film (the element (first element) is Al, or Al and Si) that covers at least a portion of the surface of the active material particles. The ratio of the mass of the element (first element) to the mass of the active material particles is in the range of 0.1% by mass or more and 0.7% by mass or less. Furthermore, the electrode has a volatility ratio (X 44 / X 18 The ratio is 1.2 or more and 2.0 or less. According to the electrode of the embodiment, even after repeated charge-discharge cycles, it is possible to realize a secondary battery in which the increase in resistance at room temperature accompanied by an increase in AC resistance is suppressed, and the increase in low-temperature resistance is also suppressed. Furthermore, by reducing the amount of organic matter contained in the electrode, the initial resistance value can also be reduced even when the same amount of element-containing film is formed on the active material particles as before.

[0080] (Second Embodiment) According to the second embodiment, a battery is provided. The battery is, for example, a secondary battery. The secondary battery may be, for example, a lithium secondary battery such as a lithium-ion secondary battery, or a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0081] The secondary battery of the embodiment includes a positive electrode, a negative electrode, and an electrolyte. The electrode of the embodiment is used for at least one of the positive or negative electrodes. It is preferable to use the electrode of the embodiment as the negative electrode. The secondary battery may further comprise a separator disposed between the positive electrode and the negative electrode. The negative electrode, positive electrode, and separator can constitute an electrode group. The electrolyte can be held in the electrode group. The secondary battery may further comprise an outer casing that houses the electrode group and the electrolyte. Furthermore, the secondary battery may further comprise a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the positive electrode.

[0082] The following provides a detailed explanation of the negative electrode, positive electrode, electrolyte, separator, outer casing, negative electrode terminal, and positive electrode terminal.

[0083] (1) Negative electrode As the negative electrode, it is desirable to use the negative electrode according to the embodiment.

[0084] The density of the negative electrode active material-containing layer (excluding the current collector) is 1.8 g / cm 3 or more and 2.8 g / cm 3 or less. A negative electrode with the density of the negative electrode active material-containing layer within this range is excellent in energy density and electrolyte retention. The density of the negative electrode active material-containing layer is 2.1 g / cm 3 or more and 2.6 g / cm 3 or less is more preferable.

[0085] (2) Positive electrode The positive electrode can include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer can be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer can include a positive electrode active material, and optionally a conductive agent and a binder.

[0086] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may contain one type of compound alone or a combination of two or more types of compounds as the positive electrode active material. Examples of the oxide and the sulfide include compounds into which Li or Li ions can be inserted and desorbed.

[0087] Examples of such compounds include manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (e.g., Li x Mn2O4 or Li x MnO2; 0 < x ≦ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co1-y O2; where 0 < x ≤ 1, 0 < y < 1), a lithium manganese nickel composite oxide having a spinel structure (e.g., LixMn 2-y Ni y O4; where 0 < x ≤ 1, 0 < y < 2), a lithium phosphate having an olivine structure (e.g., Li x FePO4; where 0 < x ≤ 1, Li x Fe 1-y Mn y PO4; where 0 < x ≤ 1, 0 < y < 1, Li x CoPO4; where 0 < x ≤ 1), iron sulfate (Fe2(SO4)3), vanadium oxide (e.g., V2O5), and a lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; where 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1) is included.

[0088] Among the above, examples of more preferable compounds as the positive electrode active material include a lithium manganese composite oxide having a spinel structure (e.g., Li x Mn2O4; where 0 < x ≤ 1), a lithium nickel composite oxide (e.g., Li x NiO2; where 0 < x ≤ 1), a lithium cobalt composite oxide (e.g., Li x CoO2; where 0 < x ≤ 1), a lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; where 0 < x ≤ 1, 0 < y < 1), a lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; where 0 < x ≤ 1, 0 < y < 2), a lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; where 0 < x ≤ 1, 0 < y < 1), lithium iron phosphate (e.g., Li x FePO4; where 0 < x ≤ 1), and a lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn zO2; where 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, and y + z < 1 is included. When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

[0089] When a room-temperature molten salt is used as the electrolyte of the battery, lithium iron phosphate, Li x VPO4F (0 ≤ x ≤ 1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or a positive electrode active material containing a mixture thereof is preferably used. Since these compounds have low reactivity with the room-temperature molten salt, the cycle life can be improved. Details of the room-temperature molten salt will be described later.

[0090] The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. A positive electrode active material with a primary particle size of 1 μm or less can allow the solid-state diffusion of lithium ions to proceed smoothly.

[0091] The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less. A positive electrode active material with a specific surface area of 0.1 m 2 / g or more can sufficiently secure the Li-ion insertion / extraction sites. A positive electrode active material with a specific surface area of 10 m 2 / g or less is easy to handle in industrial production and can ensure good charge / discharge cycle performance.

[0092] A binder is added to fill the gaps between dispersed positive electrode active materials and to bond the positive electrode active materials to the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0093] Conductive agents are added to enhance current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanofibers, and carbon nanotubes. One of these may be used as a conductive agent, or two or more may be used in combination. Conductive agents may also be omitted.

[0094] In the positive electrode active material-containing layer, it is preferable that the positive electrode active material and the binder are blended in proportions of 80% to 98% by mass and 2% to 20% by mass, respectively.

[0095] Sufficient electrode strength can be obtained by using a binder amount of 2% by mass or more. Furthermore, the binder can function as an insulator. Therefore, reducing the binder amount to 20% by mass or less reduces the amount of insulator contained in the electrode, thereby reducing internal resistance.

[0096] When a conductive agent is added, it is preferable that the positive electrode active material, binder, and conductive agent are blended in proportions of 77% to 95% by mass, 2% to 20% by mass, and 3% to 15% by mass, respectively.

[0097] The above-mentioned effects can be achieved by increasing the amount of conductive agent to 3% by mass or more. Furthermore, by reducing the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This lower proportion reduces the decomposition of the electrolyte under high-temperature storage conditions.

[0098] The positive electrode current collector is preferably an aluminum foil, or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

[0099] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0100] Furthermore, the positive electrode current collector may include portions on its surface where the positive electrode active material-containing layer is not formed. These portions can function as positive electrode current collector tabs.

[0101] A positive electrode can be manufactured, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of the active material-containing layer and the current collector. After that, this laminate is pressed. In this way, a positive electrode is manufactured.

[0102] Alternatively, the positive electrode may be manufactured by the following method: First, an active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Then, these pellets are placed on a current collector to obtain the positive electrode.

[0103] (3) Electrolyte As the electrolyte, for example, a liquid non-aqueous electrolyte or a gel-type non-aqueous electrolyte can be used. A liquid non-aqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0104] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonylimide (LiN(CF3SO2)2), as well as mixtures thereof. The electrolyte salt is preferably resistant to oxidation even at high potentials, with LiPF6 being the most preferred.

[0105] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); and γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as mixed solvents.

[0106] Gel-type non-aqueous electrolytes are prepared by compounding a liquid non-aqueous electrolyte with a polymer material. As the polymer material, at least one selected from the group consisting of polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, acrylic polymer, polyamide, and polyvinyl alcohol can be used. By using a gel-type electrolyte, metal elution from the positive electrode can be suppressed, and gas generation such as hydrogen can be inhibited. As a result, excellent cycle life performance can be obtained.

[0107] Alternatively, in addition to liquid nonaqueous electrolytes and gel-type nonaqueous electrolytes, room-temperature molten salts (ionic melts) containing lithium ions, polymer solid electrolytes, and inorganic solid electrolytes may be used as nonaqueous electrolytes.

[0108] Room temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as liquids at room temperature (15°C to 25°C). Room temperature molten salts include room temperature molten salts that exist as liquids on their own, room temperature molten salts that become liquid when mixed with an electrolyte salt, room temperature molten salts that become liquid when dissolved in an organic solvent, or mixtures thereof. Generally, the melting point of room temperature molten salts used in secondary batteries is 25°C or lower. Also, organic cations generally have a quaternary ammonium skeleton.

[0109] Polymeric solid electrolytes are prepared by dissolving an electrolyte salt in a polymer material and then solidifying it.

[0110] Inorganic solid electrolytes are solid materials that possess lithium ion conductivity.

[0111] (4) Separator The separator is positioned, in part or in whole, between the positive and negative electrodes. If part of the separator is positioned between the positive and negative electrodes, the other part of the separator may be in contact only with the positive electrode or only with the negative electrode.

[0112] The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin non-woven fabric. From the perspective of safety, it is preferable to use a porous film formed from polyethylene or polypropylene. This is because these porous films can melt at a certain temperature and interrupt the current.

[0113] As the separator, a solid electrolyte layer containing solid electrolyte particles can also be used. The solid electrolyte layer may contain one type of solid electrolyte particle or multiple types of solid electrolyte particles. The solid electrolyte layer may be a solid electrolyte composite membrane containing solid electrolyte particles. The solid electrolyte composite membrane is, for example, formed by shaping solid electrolyte particles into a film using a polymer material. The solid electrolyte layer may contain at least one selected from the group consisting of a plasticizer and an electrolyte salt. When the solid electrolyte layer contains an electrolyte salt, for example, the alkali metal ion conductivity of the solid electrolyte layer can be further increased.

[0114] Examples of the polymer material include polyether-based, polyester-based, polyamine-based, polyethylene-based, silicone-based, and polysulfide-based.

[0115] The lithium ion conductivity of the solid electrolyte is preferably 1×10 -10 S / cm or more at 25°C. When the lithium ion conductivity of the solid electrolyte at 25°C is 1×10 -10 S / cm or more, the lithium ion concentration near the surface of the solid electrolyte tends to be high, so the rate performance and life performance can be improved. The lithium ion conductivity of the solid electrolyte at 25°C is more preferably 1×10 -6 S / cm or more. According to one example, the upper limit value of the lithium ion conductivity of the solid electrolyte is 2×10 -2 S / cm.

[0116] Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and polymer solid electrolytes. Specifically, solid electrolytes include sulfide-based Li2SeP2S5 glass ceramics and lithium lanthanum titanium composite oxide (e.g., Li), which is an inorganic compound having a perovskite-type structure. 0.5 La 0.5 Inorganic compounds having a LISICON-type structure (e.g., Li O3), Li O3 3.6 Si 0.6 P 0.4 O4), inorganic compounds having a NASICON-type skeleton, amorphous LIPON(Li 2.9 PO 3.3 N 0.46 ), lithium calcium zirconium oxide (Li 1.2 Zr 1.9 Ca 0.1 The separator contains (PO4)3), and at least one selected from the group consisting of inorganic compounds having a garnet-type structure. The separator may contain one type of solid electrolyte, or it may contain two or more types of solid electrolytes.

[0117] Inorganic compounds having a NASICON-type skeleton are preferably inorganic compounds represented by the general formula LiM2(PO4)3 (where M is one or more selected from Ti, Ge, Sr, Zr, Sn, and Al). In particular, Li 1+x Al x Ge 2-x (PO4)3, Li 1+x Al x Zr 2-x (PO4)3, Li 1+x Al x Ti 2-x (PO4)3(LATP) is preferred because it has high ionic conductivity and high electrochemical stability in water. In the above, it is preferable that x satisfies 0 ≤ x ≤ 0.5.

[0118] Examples of inorganic compounds having a garnet-type structure include Li 5+x A y La 3-y M2O 12(A is at least one selected from the group consisting of Ca, Sr, and Ba, and M is at least one selected from the group consisting of Nb and Ta), Li3M 2-x Zr2O 12 (M is at least one selected from the group consisting of Ta and Nb), Li 7-3x Al x La3Zr3O 12 , and Li7La3Zr2O 12 Examples include the above. In the above, x is, for example, 0 ≤ x < 0.8, and preferably 0 ≤ x ≤ 0.5. y is, for example, 0 ≤ y < 2. The oxide having a garnet-type structure may consist of one of these compounds, or it may contain a mixture of two or more of these compounds. Among these, Li 6.25 Al 0.25 La3Zr3O 12 and Li7La3Zr2O 12 Because it has high ionic conductivity and is electrochemically stable, it has excellent discharge performance and cycle life performance.

[0119] If the solid electrolyte contains sulfur, it is undesirable because the sulfur component will dissolve in the organic electrolyte described later. It is preferable that the solid electrolyte does not contain sulfur.

[0120] A preferred solid electrolyte is LATP(Li) having a NASICON-type skeleton. 1+x Al x Ti 2-x (PO4)3), amorphous LIPON, garnet-type lithium lanthanum zirconium-containing oxide (e.g., Li7La3Zr2O 12 It is an oxide such as LLZ.

[0121] The lithium ion conductivity at 25°C of an inorganic compound represented by LiM2(PO4)3 having a NASICON-type skeleton is, for example, 1 × 10⁻⁶. -3 S / cm~1×10 -5 It is within the range of S / cm. 2.9 PO 3.3 N 0.46 The lithium-ion conductivity of ) at 25°C is 3 × 10⁻⁶.-6 It is S / cm. Garnet type LLZ(Li7La3Zr2O 12 The lithium-ion conductivity of ) at 25°C is 3 × 10⁻⁶. -4 It is S / cm.

[0122] Among these, the solid electrolyte is preferably LATP having a NASICON-type skeleton. LATP has high lithium-ion conductivity and is difficult to decompose in water, so it can exist stably even in air.

[0123] (5) Exterior components For example, the outer packaging material can be a container made of laminate film or a metal container.

[0124] The thickness of the laminating film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

[0125] As the laminate film, a multilayer film is used that includes multiple resin layers and a metal layer interposed between these resin layers. The resin layers include polymer materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably made of aluminum foil or aluminum alloy foil for weight reduction. The laminate film can be molded into the shape of an exterior component by sealing it by heat fusion.

[0126] The thickness of the metal container wall is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0127] Metal containers are made from, for example, aluminum or aluminum alloys. Aluminum alloys preferably contain elements such as magnesium, zinc, and silicon. If aluminum alloys contain transition metals such as iron, copper, nickel, and chromium, their content is preferably 100 ppm by mass or less.

[0128] The shape of the exterior components is not particularly limited. For example, the exterior components may be flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior components can be appropriately selected according to the battery dimensions and intended use.

[0129] (6) Negative terminal The negative electrode terminal can be formed from a material that is electrochemically stable at the Li absorption / release potential of the negative electrode active material described above, and is also conductive. Specifically, the material for the negative electrode terminal can be copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable to use aluminum or an aluminum alloy as the material for the negative electrode terminal. It is preferable that the negative electrode terminal be made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0130] (7) Positive terminal The positive terminal has a potential range of 3V to 5V relative to the oxidation-reduction potential of lithium (vs.Li / Li + The positive electrode terminal can be formed from an electrically stable and conductive material. Examples of positive electrode terminal materials include aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable that the positive electrode terminal be formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0131] Next, the secondary battery according to the embodiment will be described in more detail with reference to the drawings.

[0132] Figure 2 is a schematic cross-sectional view showing an example of a secondary battery according to the embodiment. Figure 3 is an enlarged cross-sectional view of part A of the secondary battery shown in Figure 2.

[0133] The secondary battery 100 shown in Figures 2 and 3 comprises a bag-shaped outer casing member 2 shown in Figures 2 and 3, an electrode group 1 shown in Figure 2, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the bag-shaped outer casing member 2. The electrolyte (not shown) is held by the electrode group 1.

[0134] The bag-shaped outer packaging member 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0135] As shown in Figure 2, electrode group 1 is a flat, wound electrode group. As shown in Figure 3, the flat, wound electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5. The separator 4 is interposed between the negative electrode 3 and the positive electrode 5.

[0136] The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material containing layer 3b. In the portion of the negative electrode 3 located in the outermost shell of the wound electrode group 1, the negative electrode active material containing layer 3b is formed only on the inner surface side of the negative electrode current collector 3a, as shown in Figure 3. In the other portions of the negative electrode 3, the negative electrode active material containing layer 3b is formed on both sides of the negative electrode current collector 3a.

[0137] The positive electrode 5 includes a positive electrode current collector 5a and positive electrode active material-containing layers 5b formed on both sides thereof.

[0138] As shown in Figure 2, the negative electrode terminal 6 and the positive electrode terminal 7 are located near the outer edge of the wound electrode group 1. The negative electrode terminal 6 is connected to the outermost part of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to the outermost part of the positive electrode current collector 5a. These negative electrode terminals 6 and positive electrode terminals 7 extend outward from the opening of the bag-shaped outer casing member 2. A thermoplastic resin layer is installed on the inner surface of the bag-shaped outer casing member 2, and the opening is closed by heat fusion of this layer.

[0139] The secondary battery according to this embodiment is not limited to the secondary battery with the configuration shown in Figures 2 and 3, but may also be a battery with the configuration shown in Figures 4 and 5, for example.

[0140] Figure 4 is a schematic partially cutaway perspective view showing another example of a secondary battery according to the embodiment. Figure 5 is an enlarged cross-sectional view of part B of the secondary battery shown in Figure 4.

[0141] The secondary battery 100 shown in Figures 4 and 5 comprises an electrode group 1 shown in Figures 4 and 5, an outer casing member 2 shown in Figure 4, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the outer casing member 2. The electrolyte is held within the electrode group 1.

[0142] The exterior component 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0143] As shown in Figure 5, electrode group 1 is a stacked electrode group. The stacked electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately stacked with separators 4 interposed between them.

[0144] The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 comprises a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 comprises a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a.

[0145] Each negative electrode 3's negative electrode current collector 3a includes a portion 3c on one side where the negative electrode active material-containing layer 3b is not supported on any surface. This portion 3c functions as a negative electrode current collector tab. As shown in Figure 5, the portion 3c acting as a negative electrode current collector tab does not overlap with the positive electrode 5. Furthermore, multiple negative electrode current collector tabs (portions 3c) are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 is extended to the outside of the outer casing member 2.

[0146] Although not shown in the diagram, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion functions as a positive electrode current collector tab. The positive electrode current collector tab, like the negative electrode current collector tab (part 3c), does not overlap with the negative electrode 3. Furthermore, the positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab (part 3c). The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side from the negative electrode terminal 6 and is extended to the outside of the outer casing member 2.

[0147] The structure of the electrode group is not limited; it may be a wound structure or a laminated structure. The laminated structure is not limited to the examples in Figures 4 and 5; for example, it may be fabricated by laminating a positive electrode and a negative electrode on a zigzag-fold separator, with the separator positioned between the positive and negative electrodes.

[0148] The secondary battery according to this embodiment is equipped with electrodes according to this embodiment. Therefore, even after repeated charge-discharge cycles, this secondary battery can suppress the increase in resistance at room temperature accompanied by an increase in AC resistance, and can also suppress the increase in low-temperature resistance. Furthermore, this secondary battery can also reduce its initial resistance value.

[0149] (Third embodiment) According to the third embodiment, a battery pack is provided. The battery pack according to the third embodiment comprises a plurality of secondary batteries according to the second embodiment.

[0150] In the battery pack according to this embodiment, each individual cell may be arranged in series or parallel connections, or a combination of series and parallel connections may be used.

[0151] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0152] Figure 6 is a schematic perspective view showing an example of a battery pack according to the embodiment. The battery pack 200 shown in Figure 6 comprises five single cells 100a to 100e, four busbars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five single cells 100a to 100e is a secondary battery according to the embodiment.

[0153] The busbar 21 connects, for example, the negative terminal 6 of one cell 100a to the positive terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four busbars 21. That is, the battery pack 200 in Figure 6 is a battery pack with five cells in series. Although not illustrated, in a battery pack containing multiple cells that are electrically connected in parallel, the multiple cells can be electrically connected, for example, by connecting multiple negative terminals to each other and multiple positive terminals to each other by busbars.

[0154] The positive terminal 7 of at least one of the five single cells 100a-100e is electrically connected to the positive lead 22 for external connection. In addition, the negative terminal 6 of at least one of the five single cells 100a-100e is electrically connected to the negative lead 23 for external connection.

[0155] The battery pack according to this embodiment comprises a secondary battery according to this embodiment. Therefore, even after repeated charge-discharge cycles, this battery pack can suppress the increase in resistance at room temperature accompanied by an increase in AC resistance, and can also suppress the increase in low-temperature resistance. Furthermore, this battery pack can also reduce its initial resistance value.

[0156] (Fourth Embodiment) According to the fourth embodiment, a battery pack is provided. This battery pack comprises a battery pack according to the third embodiment. The battery pack may also comprise a single secondary battery according to the third embodiment instead of the battery pack according to the third embodiment.

[0157] The battery pack according to this embodiment may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., an electronic device, an automobile, etc.) may be used as the protection circuit for the battery pack.

[0158] Furthermore, the battery pack according to this embodiment may also be further equipped with external terminals for power supply. These external terminals are for outputting current from the secondary battery to the outside and / or for inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals. Also, when charging the battery pack, the charging current (including regenerative energy from the power of an automobile, etc.) is supplied to the battery pack through the external terminals.

[0159] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0160] Figure 7 is an exploded perspective view schematically showing an example of a battery pack according to the embodiment. Figure 8 is a block diagram showing an example of the electrical circuit of the battery pack shown in Figure 7.

[0161] The battery pack 300 shown in Figures 7 and 8 comprises a housing 31, a lid 32, a protective sheet 33, a battery pack 200, a printed circuit board 34, wiring 35, and an insulating plate (not shown).

[0162] The container 31 shown in Figure 7 is a rectangular-bottomed rectangular container. The container 31 is configured to accommodate a protective sheet 33, a battery pack 200, a printed circuit board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the container 31, thereby housing the battery pack 200 and the other components. The container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices, etc., although these are not shown in the figures.

[0163] The battery pack 200 comprises multiple individual cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0164] At least one of the multiple single cells 100 is a secondary battery according to the third embodiment. Each of the multiple single cells 100 is electrically connected in series as shown in Figure 8. The multiple single cells 100 may also be electrically connected in parallel, or they may be connected in a combination of series and parallel connections. When the multiple single cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0165] The adhesive tape 24 fastens multiple single cells 100 together. Alternatively, heat-shrinkable tape may be used to secure the multiple single cells 100 instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both sides of the battery pack 200, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to bundle the multiple single cells 100 together.

[0166] One end of the positive lead 22 is connected to the battery pack 200. One end of the positive lead 22 is electrically connected to the positive terminal of one or more single cells 100. One end of the negative lead 23 is connected to the battery pack 200. One end of the negative lead 23 is electrically connected to the negative terminal of one or more single cells 100.

[0167] The printed circuit board 34 is installed along one of the shorter sides of the inner surface of the housing container 31. The printed circuit board 34 includes a positive terminal connector 342, a negative terminal connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for energization, a positive side wiring (positive wiring) 348a, and a negative side wiring (negative wiring) 348b. One main surface of the printed circuit board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed circuit board 34 and the battery pack 200.

[0168] The other end 22a of the positive lead 22 is electrically connected to the positive connector 342. The other end 23a of the negative lead 23 is electrically connected to the negative connector 343.

[0169] The thermistor 345 is fixed to one main surface of the printed circuit board 34. The thermistor 345 detects the temperature of each of the single cells 100 and transmits the detection signal to the protection circuit 346.

[0170] The external power supply terminal 350 is fixed to the other main surface of the printed circuit board 34. The external power supply terminal 350 is electrically connected to equipment located outside the battery pack 300. The external power supply terminal 350 includes a positive terminal 352 and a negative terminal 353.

[0171] The protection circuit 346 is fixed to the other main surface of the printed circuit board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive side wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative side wiring 348b. The protection circuit 346 is also electrically connected to the positive side connector 342 via wiring 342a. The protection circuit 346 is also electrically connected to the negative side connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the multiple single cells 100 via wiring 35.

[0172] The protective sheet 33 is positioned on both inner surfaces in the long-side direction of the housing container 31 and on the inner surface in the short-side direction facing the printed circuit board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0173] The protection circuit 346 controls the charging and discharging of multiple single cells 100. The protection circuit 346 also disconnects the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for supplying power to external devices, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from an individual single cell 100 or a battery pack 200.

[0174] An example of a detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of a single cell 100 is above a predetermined temperature. An example of a detection signal transmitted from an individual single cell 100 or a battery pack 200 is a signal indicating that overcharging, over-discharging, or overcurrent has been detected in a single cell 100. When detecting overcharging, etc., in an individual single cell 100, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode to be used as a reference electrode is inserted into each individual single cell 100.

[0175] Furthermore, the protection circuit 346 may be a circuit included in a device that uses the battery pack 300 as a power source (for example, an electronic device, an automobile, etc.).

[0176] Furthermore, as described above, the battery pack 300 is equipped with an external terminal 350 for power supply. Therefore, the battery pack 300 can output current from the battery pack 200 to an external device and input current from an external device to the battery pack 200 via the external terminal 350. In other words, when the battery pack 300 is used as a power source, current from the battery pack 200 is supplied to the external device through the external terminal 350. Also, when charging the battery pack 300, charging current from an external device is supplied to the battery pack 300 through the external terminal 350. When this battery pack 300 is used as an on-board battery, the regenerative energy of the vehicle's power can be used as the charging current from the external device.

[0177] The battery pack 300 may comprise multiple battery packs 200. In this case, the multiple battery packs 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed circuit board 34 and wiring 35 may also be omitted. In this case, the positive lead 22 and the negative lead 23 may be used as the positive and negative terminals of the external terminals for energization, respectively.

[0178] Such battery packs are used in applications where excellent cycle performance is required, for example, when drawing high currents. Specifically, these battery packs are used as power supplies for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. These battery packs are particularly suitable for use as on-board batteries.

[0179] The battery pack according to this embodiment comprises a secondary battery or a battery pack according to this embodiment. Therefore, even after repeated charge-discharge cycles, this battery pack can suppress the increase in resistance at room temperature accompanied by an increase in AC resistance, and can also suppress the increase in low-temperature resistance. Furthermore, this battery pack can also reduce its initial resistance value. [Examples]

[0180] Examples are described below, but the embodiments are not limited to those described below.

[0181] (Example 1-1) As shown below, a laminate battery was fabricated to be used as a secondary battery.

[0182] <Fabrication of the negative electrode> As the negative electrode active material, lithium titanate (Li4Ti5O) has a spinel structure with an average primary particle diameter D50 of 0.8 μm. 12 A powder containing acetylene black was prepared as the conductive agent, polyvinylidene fluoride (PVDF) as the binder, and aluminum monoacetylacetate bis(ethyl acetate) (product name Aluminum Chelate D (abbreviated as ACD) of Kawaken Fine Chemical Co., Ltd.) was prepared as the Al source to form an Al-containing coating layer on the lithium titanate surface. These materials were mixed so that the mass percentage of the resulting negative electrode active material-containing layer was active material (LTO):conductive agent:binder:Al = 100:3:3:0.2. This mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a negative electrode slurry. The solid content concentration in the negative electrode slurry was 58% by mass.

[0183] The prepared negative electrode slurry has a capacity of 1.05 mAh / cm³ per unit area on one side. 2 After coating both sides of the aluminum foil in this manner, the coating film was dried to obtain a laminate. Subsequently, the electrode density (electrode portion excluding aluminum foil) was 2.3 g / cm³. 3 After press molding the laminate to achieve the desired configuration, the negative electrode was fabricated by drying it in a vacuum at a temperature of 130°C for 12 hours.

[0184] <Fabrication of the positive electrode> Commercially available lithium nickel cobalt manganese composite oxide (LiNi 0.5 Co 0.2 Mn 0.3 A mixture was obtained by mixing 100 parts by mass of O2 with 5 parts by mass of acetylene black as a conductive agent. Next, this mixture was dispersed in NMP to obtain a dispersion. To this dispersion, PVdF as a binder was mixed at a ratio of 5 parts by mass relative to lithium nickel cobalt manganese composite oxide to prepare a positive electrode slurry. This slurry was applied to both sides of a current collector made of aluminum foil using a blade. After drying under vacuum at 130°C for 12 hours, the density of the positive electrode active material-containing layer (excluding the current collector) was 2.1 g / cm³. 3 The positive electrode was obtained by rolling the material in such a manner. The thickness of each electrode layer of the positive and negative electrodes was adjusted so that the negative electrode capacity / positive electrode capacity = 1.1.

[0185] <Fabrication of electrode groups> A strip-shaped separator, 19 μm thick and 76 mm wide, was prepared, consisting of 75% by weight of cellulose fiber and 25% by weight of polyester fiber (melting point 260°C). A rectangular negative electrode measuring 76 mm x 56 mm was cut from the previously prepared strip-shaped negative electrode. A rectangular positive electrode measuring 75 mm x 55 mm on one side was cut from the previously prepared strip-shaped positive electrode. An electrode group with a zigzag-fold separator was fabricated by alternately inserting the positive electrodes while folding the separator every 57 mm, so that the design capacity would be 2.5 Ah. The positive and negative electrode terminals were electrically connected to this electrode group.

[0186] <Preparation of liquid non-aqueous electrolytes> A mixed solvent of propylene carbonate and diethyl carbonate (volume ratio 1:2) was prepared. Lithium hexafluoride phosphate (LiPF6) was dissolved in this solvent at a concentration of 1 M. Thus, a liquid non-aqueous electrolyte was prepared.

[0187] <Making laminated batteries> The fabricated electrode group was incorporated into an outer casing made of a multilayer film containing multiple resin layers and metal layers interposed between these resin layers, and vacuum-dried for 8 hours at 120°C. Afterward, the previously prepared electrolyte was injected, the outer casing was sealed with heat seal, and a lithium-ion secondary battery with a design capacity of 2.5 Ah was fabricated.

[0188] (Examples 1-2 to 1-6) Laminate batteries were fabricated in the same manner as in Example 1-1, except that the Al content and vacuum drying conditions were changed as shown in Table 1. The Al content refers to the ratio of the mass of Al to the total mass of the active material particles.

[0189] (Examples 1-7 and 1-8) A negative electrode was prepared in the same manner as in Example 1-1, except that aluminum monoacetyl acetate bis(ethyl acetate) as the Al source was not added during negative electrode preparation. (The mass percentage in the negative electrode active material-containing layer was active material (LTO):conductive agent:binder:Al = 100:3:3) After preparation, the negative electrode was impregnated in a solution of ethanol and aluminum monoacetyl acetate bis(ethyl acetate) with a weight mixture ratio (aluminum tricetyl acetate / ethanol) of 0.1 to 0.6, and then vacuum-dried under the conditions shown in Table 2 to produce a negative electrode with Al coating on the surface of lithium titanate active material particles. The Al content is the ratio of the mass of Al to the total mass of the active material particles, as shown in Table 1. A laminate battery was prepared in the same manner as in Example 1-1, except that the obtained negative electrode was used.

[0190] (Examples 1-9 to 1-11) Laminate batteries were prepared in the same manner as in Example 1-1, except that the Al source was changed from aluminum monoacetylacetate bis(ethyl acetate) to di-2-butoxyaluminum acetylacetate (product name A-1033R, manufactured by Matsumoto Fine Chemical Co., Ltd.), the Al content was changed as shown in Table 1, and the vacuum drying conditions were changed as shown in Table 2. The Al content refers to the ratio of the mass of Al to the total mass of the active material particles.

[0191] (Comparative Example 1-1) A laminate battery was prepared in the same manner as in Example 1-1, except that aluminum monoacetylacetate bis(ethyl acetate) from the Al source was not added, and vacuum drying was not performed.

[0192] (Comparative Example 1-2) A laminate battery was prepared in the same manner as in Example 1-1, except for the Al source and Al content.

[0193] (Comparative Examples 1-3 to 1-7) Laminate batteries were fabricated in the same manner as in Example 1-1, except that the Al content was changed as shown in Table 1, and the Al source and vacuum drying conditions were changed as shown in Table 2.

[0194] (Example 2-1) A laminated battery was prepared in the same manner as in Example 1-1, except that the negative electrode slurry was prepared as follows.

[0195] As the negative electrode active material, lithium titanate (Li4Ti5O) has a spinel structure with an average primary particle diameter D50 of 0.8 μm. 12A powder was prepared. Acetylene black was prepared as the conductive agent. Polyvinylidene fluoride (PVDF) was prepared as the binder. Ethyl polysilicate (product name Silicate 40, Tama Chemical Industry Co., Ltd.) was prepared as the Si source. Aluminum monoacetylacetate bis (ethyl acetate) (product name Aluminum Chelate D (abbreviation ACD), Kawaken Fine Chemical Co., Ltd.) was prepared as the aluminum source. These materials were mixed so that the mass % (active material: conductive agent: binder: Si: Al) in the resulting negative electrode active material-containing layer was 100:3:3:0.15:0.1. This mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a negative electrode slurry. The solid content concentration in the negative electrode slurry was 58% by mass.

[0196] (Examples 2-2 to 2-7) The amount of ethyl polysilicate added as the Si source was changed so that the Si content was as shown in Table 3. Similarly, the amount of aluminum monoacetylacetate bis(ethyl acetate) added as the aluminum source was changed so that the Al content was as shown in Table 3. Furthermore, the vacuum drying conditions during negative electrode fabrication were set as shown in Table 4. Apart from these changes, the laminate battery was fabricated using the same method as in Example 2-1. Note that the Al content is the ratio of the mass of Al to the total mass of the active material particles. On the other hand, the Si content is the ratio of the mass of Si to the total mass of the active material particles.

[0197] (Comparative Examples 2-1 to 2-3) The amount of ethyl polysilicate added as the Si source was changed so that the Si content was as shown in Table 3. Similarly, the amount of aluminum monoacetylacetate bis(ethyl acetate) added as the aluminum source was changed so that the Al content was as shown in Table 3. Furthermore, the vacuum drying conditions during negative electrode fabrication were set as shown in Table 4. Apart from these changes, the laminated battery was fabricated using the same method as in Example 2-1.

[0198] <Negative electrode> The active material-containing layer of the fabricated negative electrode was extracted, and the amounts of Ti, Si, and Al were quantitatively analyzed using an ICP emission spectrometer under the aforementioned conditions. It was confirmed that the Si and Al content in the negative electrode was generally as designed for electrodes fabricated with the addition of Si-based alkoxides and organic Al compounds. Furthermore, SEM-EDX confirmed the presence of Si and Al on the electrode surface and the active material surface.

[0199] <Charge-discharge cycle test> The laminate batteries fabricated in each of the aforementioned examples were subjected to charge-discharge cycle tests under the following conditions.

[0200] The secondary battery was charged using constant current constant voltage (CCCV) charging at a voltage of 2.7V and a current of 1C (2.5A), and then discharged using constant current (CC) charging at a voltage of 1.5V and a current of 1C (2.5A) to confirm that it met the design capacity. After capacity confirmation, a portion of the battery was removed, disassembled in an inert atmosphere, and the negative electrode was extracted. The amount of volatile substances corresponding to mass number 18 and mass number 44 of the extracted negative electrode was measured using a TPD-MS analyzer, and the amount of volatile substances corresponding to mass number 18 and mass number 44 was measured using the water equivalent method as described above, and the ratio X 44 / X 18 We obtained the volatility ratio X. 44 / X 18 This is shown in Tables 1 and 3.

[0201] The fabricated secondary batteries were subjected to charge-discharge cycle tests at a 60°C environment to investigate the change in battery resistance at a 50% state of charge (SOC). Specifically, the change in resistance before and after 2,000 charge-discharge cycles under the aforementioned conditions was investigated at both 25°C and -20°C environments. When investigating the resistance after 2,000 cycles, each secondary battery was discharged at 1.5V and 1C at 25°C, then the SOC was adjusted to 50% by 1C charging, and then the discharge resistance for 10 seconds at 1C (2.5Ah) in constant temperature baths at 25°C and -20°C was investigated.

[0202] The results are shown in Tables 1-4 below. In Tables 1 and 3, for each example, the Si content, Al content, and the volatile content X calculated from the TPD-MS analysis results of the negative electrode removed after the battery was disassembled and the capacity was confirmed after assembly are shown. 44 / X 18 This is shown. Furthermore, the results of the charge-discharge cycle tests described above for each example are also shown.

[0203] In Tables 1 and 3, the percentage of Al present on the surface of the negative electrode active material particles relative to the mass of the active material particles (%), and the percentages of Al and Si present on the surface of the negative electrode active material particles relative to the mass of the active material particles (%) are shown as Al content and Si content, respectively. In Tables 1 and 3, the "Initial Resistance Ratio" column shows the initial resistance value of each example's secondary battery at a 25°C environment, expressed as a ratio to the initial resistance value of Comparative Example 1-1, which is set to 1. In Tables 1 and 3, the "25°C Resistance Increase Rate" column shows the resistance increase rate (ratio of resistance value after 2000 cycles to initial resistance value) for each example's secondary battery at a 25°C environment, and the "-20°C Resistance Increase Rate" column shows the resistance increase rate (ratio of resistance value after 2000 cycles to initial resistance value) for each example's secondary battery at a -20°C environment.

[0204] [Table 1]

[0205] [Table 2]

[0206] [Table 3]

[0207] [Table 4]

[0208] As shown in Examples 1-1 to 1-11, the active material particles contain lithium titanate having a spinel structure, contain Al in a predetermined amount, and in the negative electrode before the cycle test, the volatile matter corresponding to m / z = 18 in the TPD-MS mass measurement and the volatile matter corresponding to m / z = 44 The ratio X of the volatile amounts obtained by the respective water conversion methods 44 / X 18 In the secondary battery including a negative electrode having a predetermined value, the initial resistance in the environments of 25°C and -20°C was low, and the resistance increase rate was also suppressed low. That is, in Examples 1-1 to 1-11, excellent cycle life performance and low temperature performance could be realized.

[0209] On the other hand, in Comparative Examples 1-1, Comparative Example 1-2, and Comparative Example 1-7 in which Al was not formed on the surface of the active material or did not have a predetermined amount of Al, and in Comparative Examples 1-3 to Comparative Example 1-6 in which the amount of residual organic matter was large despite performing a predetermined Al coating, the resistance increase after cycling was large.

[0210] As shown in Comparative Example 1-7, as the Al content increased beyond 0.7 mass%, the initial resistance also increased, and even when the amount of residual organic matter was reduced to a predetermined value, the resistance increase rate tended to increase. Even in the case of a comparative example with a relatively low resistance increase rate, when the initial resistance was high, it could be read that the resistance value was high from the initial stage to after 2000 cycles. In Comparative Example 1-2 with a small coating amount, although the amount of residual organic matter was at a predetermined value, the Al coating amount was small and the resistance after cycling was large.

[0211] Also, as shown in Examples 2-1 to 2-7, the active material particles contain lithium titanate having a spinel structure, contain (Si + Al) in a predetermined amount, and in the negative electrode before the cycle test, the volatile matter corresponding to m / z = 18 in the TPD-MS mass measurement and the volatile matter corresponding to m / z = 44 The ratio X of the volatile amounts obtained by the respective water conversion methods 44 / X 18 In the secondary battery including a negative electrode having a predetermined value, the resistance increase rate in the environments of 25°C and -20°C was also suppressed low. That is, in Examples 2-1 to 2-7, excellent cycle life performance and low temperature performance could be realized.

[0212] As shown in Comparative Example 2-1, even when the content of (Si + Al) is within the range of 0.1% by mass to 0.7% by mass, in a battery with a large amount of residual organic matter, the resistance increase rate after the cycle test is large. On the other hand, in Comparative Example 2-2 where the content of (Si + Al) is less than 0.1% by mass and Comparative Example 2-3 where the content of (Si + Al) exceeds 0.7% by mass, the resistance increase rate also tended to increase.

[0213] According to at least one embodiment and example described above, an electrode is provided. The electrode includes an active material layer including active material particles containing a lithium titanium-containing oxide having a spinel structure, and an element-containing film (the element (the first element) is Al or Al and Si) covering at least a part of the surface of the active material particles. The ratio of the mass of the element (the first element) to the mass of the active material particles is within the range of 0.1% by mass or more and 0.7% by mass or less. Further, the electrode has a volatile amount ratio (X 44 / X 18 ) of 1.2 or more and 2.0 or less. According to the electrode of the embodiment, a secondary battery can be realized in which an increase in resistance at room temperature accompanied by an increase in AC resistance is suppressed even when charge-discharge cycles are repeated, and an increase in low-temperature resistance can also be suppressed. Therefore, a secondary battery excellent in charge-discharge cycle performance and low-temperature performance can be realized. Further, by reducing the amount of organic matter contained in the electrode, the initial resistance value can also be reduced even when an element-containing film of the same amount as before is formed on the active material particles.

[0214] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0215] 1…Electrode group, 2…Outer casing, 3…Negative electrode, 3a…Negative electrode current collector, 3b…Negative electrode active material-containing layer, 3c…Negative electrode current collector tab, 4…Separator, 5…Positive electrode, 5a…Positive electrode current collector, 5b…Positive electrode active material-containing layer, 6…Negative electrode terminal, 7…Positive electrode terminal, 21…Bus bar, 22…Positive electrode lead, 23…Negative electrode lead, 24…Adhesive tape, 31…Housing container, 32…Lid, 33…Protective sheet, 34…Printed wiring Circuit board, 35...wiring, 100...secondary battery, 100a-100e...single cell, 200...battery pack, 300...battery pack, 342...positive terminal connector, 343...negative terminal connector, 345...thermistor, 346...protection circuit, 342a...wiring, 343a...wiring, 350...external terminal for power supply, 352...positive terminal, 353...negative terminal, 348a...positive wiring, 348b...negative wiring.

Claims

1. An electrode comprising a current collector and an active material-containing layer supported on at least a portion of the current collector, The active material-containing layer comprises active material particles containing a lithium titanium-containing oxide having a spinel structure, and an element-containing film covering at least a portion of the surface of the active material particles, wherein the element is Al, or Al and Si. An electrode in which the ratio of the mass of the element to the mass of the active material particles is within the range of 0.1% by mass or more and 0.7% by mass or less, and satisfies the following equation (1). 1.2≦X 44 / X 18 ≦2.0 (1) However, X 18 This is the amount of volatilization of the substance corresponding to m / z = 18 in the TPD-MS analysis of the electrode, calculated using the water equivalent method, and X 44 This is the amount of volatilization of the substance corresponding to m / z = 44 in the TPD-MS analysis of the electrode, calculated using a water-equivalent method.

2. The lithium titanium-containing oxide having the spinel structure has the general formula Li 4+a Ti 5 O 12 The electrode according to claim 1, which is represented by (-1 ≤ a ≤ 3).

3. The substance corresponding to m / z = 18 contains H 2 O, and the substance corresponding to m / z = 44 contains CO 2 The electrode according to claim 1.

4. Positive electrode and, A negative electrode comprising the electrode described in any one of claims 1 to 3, A secondary battery comprising an electrolyte.

5. A battery pack comprising the secondary battery described in claim 4.

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