Electrodes, secondary batteries, battery packs and vehicles

Abstract

This invention relates to an electrode, a secondary battery, a battery pack, and a vehicle. It provides an electrode capable of suppressing gas generation and having high output performance, a secondary battery comprising the electrode, a battery pack comprising the secondary battery, and a vehicle comprising the battery pack. According to one embodiment, an electrode is provided. The electrode comprises a niobium-containing oxide and a carbon-containing material. The hydroxyl content of the niobium-containing oxide is 0.25 mmol / g or less. The functional group content of the carbon-containing material is 5 mmol / g or less.

Description

[Technical Field]

[0001] The embodiments of the present invention relate to electrodes, secondary batteries, battery packs, and vehicles. [Previous Technology]

[0002] In recent years, research and development of secondary batteries, such as non-aqueous electrolyte secondary batteries (e.g., lithium-ion secondary batteries), which are high-energy-density batteries, have been actively promoted. These secondary batteries are expected to serve as power sources for hybrid electric vehicles, electric vehicles, and uninterruptible power supplies for mobile phone base stations. Therefore, in addition to high energy density, secondary batteries are required to exhibit excellent performance in other areas such as rapid charge / discharge capabilities and long-term reliability. For example, secondary batteries capable of rapid charge / discharge can significantly shorten charging time, improve the power performance of vehicles such as hybrid electric vehicles, and effectively recover regenerative energy.

[0003] In order to achieve rapid charging and discharging, electrons and lithium ions need to move rapidly between the positive and negative electrodes. However, in batteries using carbon-based negative electrodes, when the system is repeatedly charged and discharged rapidly, lithium metal dendrites will be deposited on the electrodes, raising concerns about overheating or fire due to internal short circuits.

[0004] Therefore, batteries using metal composite oxides as negative electrodes to replace carbonaceous materials have been developed. Among them, battery systems using titanium oxide as negative electrodes have the characteristics of stable rapid charge and discharge, and longer lifespan than those using carbon-based negative electrodes.

[0005] However, titanium oxide-based materials have a higher potential for lithium metal compared to carbonaceous materials, meaning they are more expensive. Furthermore, titanium oxide-based materials have a lower capacity per unit weight. Therefore, battery systems using titanium oxide as the negative electrode suffer from low energy density.

[0006] For example, the electrode potential of titanium oxide is approximately 1.5V (vs. Li / Li+) relative to lithium metal, which is higher (and more expensive) than that of carbon-based anodes. The potential of titanium oxide is due to the redox reaction between Ti3+ and Ti4+ during the lithium electrochemical intercalation / deintercalation process, and is therefore electrochemically limited. Furthermore, even at a high electrode potential of 1.5V (vs. Li / Li+), rapid charging and discharging of lithium ions can be stably performed. Therefore, lowering the electrode potential to increase energy density has historically been difficult.

[0007] On the other hand, regarding capacity per unit weight, the theoretical capacity of titanium dioxide (anatase structure) is around 165 mAh / g, while the theoretical capacity of spinel-type lithium-titanium composite oxides such as Li4Ti5O12 is around 180 mAh / g. In comparison, the theoretical capacity of general graphite-based electrode materials is above 385 mAh / g. Thus, the capacity density of titanium oxide is significantly lower than that of carbon-based anodes. This is because the crystalline structure of titanium oxide has fewer sites for storing lithium (Li), and lithium is easily stabilized in the structure, leading to a decrease in actual capacity.

[0008] In view of this, novel electrode materials containing Nb are being researched. Such niobium-containing oxide materials are expected to have high charge-discharge capacity. In particular, composite oxides represented as TiNb2O7 have a high theoretical capacity exceeding 380 mAh / g. Therefore, the use of niobium-containing oxides as an alternative to Li4Ti5O12 is being considered. [Summary of the Invention]

[0009] The problem to be solved by the present invention is to provide an electrode capable of suppressing gas generation and having high output performance, a secondary battery including the electrode, a battery pack including the secondary battery, and a vehicle including the battery pack.

[0010] According to an embodiment, an electrode is provided. This electrode comprises a niobium-containing oxide and a carbon-containing material. The hydroxyl content of the niobium-containing oxide is 0.25 mmol / g or less. The functional group content of the carbon-containing material is 5 mmol / g or less.

[0011] According to other embodiments, a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte is provided. The negative electrode is the electrode in the above embodiments.

[0012] According to other embodiments, a battery pack including the secondary battery in the above embodiments is provided.

[0013] According to other embodiments, a vehicle is provided that includes the battery pack of the above embodiments.

[0014] The electrode constructed as described above can provide an electrode that suppresses gas generation and has high output performance.

Implementation Method

[0016] (First Embodiment) According to the first embodiment, an electrode is provided. The electrode system comprises a niobium-containing oxide and a carbon-containing material. The hydroxyl content of the niobium-containing oxide is 0.25 mmol / g or less. The functional group content of the carbon-containing material is 5 mmol / g or less.

[0017] Through careful research, the inventors have discovered that the lower the hydroxyl content of niobium oxides, the greater the tendency for gas generation in the electrode. Since the niobium oxide system containing the electrode in the embodiment has a hydroxyl content as low as 0.25 mmol / g or less, the amount of gas generated can be reduced. Furthermore, niobium oxide systems with low hydroxyl (hydroxyl) content have higher hydrophobicity.

[0018] Carbon-containing materials with a functional group content of 5 mmol / g or less exhibit high hydrophobicity. Therefore, they are less likely to repel niobium-containing oxides with a hydroxyl content of 0.25 mmol / g or less, which also possess high hydrophobicity. Consequently, the carbon-containing material and the niobium-containing oxide readily aggregate. This effectively maintains the conductive path within the electrode. Furthermore, delamination between the carbon-containing material and the niobium-containing oxide is less likely to occur. As a result, output performance can be improved.

[0019] The electrodes of the embodiment will be explained further.

[0020] This specification describes the composition, structure, and chemical formula of niobium oxides and carbon-containing materials. However, unless otherwise stated, the hydroxyl groups that may be present in niobium oxides and the elements contained in the functional groups that may be present in carbon-containing materials are not described in these descriptions. That is, niobium oxides may be substances in which hydroxyl groups have been additionally added to the composition shown in this specification. Carbon-containing materials may be substances in which functional groups have been additionally added to the composition shown in this specification.

[0021] Niobium containing oxides can be contained in the electrode in, for example, particle shape. The particles can be primary particles or secondary particles formed by the aggregation of primary particles.

[0022] Niobium oxide systems can contain crystalline and amorphous phases (defects). However, since amorphous phases readily attach hydroxyl groups, niobium oxides are preferably composed only of crystalline phases or have a small amount of amorphous phase. In other words, higher crystallinity of niobium oxides is preferred. Niobium oxides with low crystallinity, for example, in an amorphous phase, may have elemental ratios different from the atomic composition (elemental ratio) of the crystals constituting the niobium oxide. When particles containing niobium oxides have an amorphous phase, the surface of the particles may contain the amorphous phase.

[0023] The hydroxyl content of the niobium oxide can be, for example, 0.00 mmol / g or more and 0.25 mmol / g or less. The hydroxyl content of the niobium oxide can be expressed as the amount of hydroxyl groups (mmol) contained in each mass (g) of niobium oxide.

[0024] The carbon-containing material contains carbon atoms. Preferably, the carbon-containing material is composed of carbon atoms. The carbon-containing material may contain functional groups composed of atoms other than carbon atoms, but as mentioned above, it is preferable that the carbon-containing material has a low content of functional groups, and more preferably, it contains no functional groups. If the carbon-containing material does not contain functional groups, then the carbon-containing material system may consist only of carbon atoms.

[0025] The carbon-containing material system may contain a crystalline phase and an amorphous phase (defects). However, since the amorphous phase is prone to attaching functional groups, the carbon-containing material is preferably composed only of a crystalline phase or has a small amount of amorphous phase. In other words, the carbon-containing material system is preferably highly crystalline.

[0026] The functional group content of the carbon-containing material can be, for example, 0 mmol / g or more and 5 mmol / g or less. The functional group content of the carbon-containing material can be expressed as the amount of functional groups (mmol) contained in each mass (g) of carbon-containing material. Examples of functional groups that carbon-containing materials may contain include, for example, hydroxyl, carboxyl, carbonyl, ether bonds, and carbon-hydrogen bonds. These functional groups have high hydrophilicity. The higher the content of such functional groups, the lower the hydrophobicity of the carbon-containing material tends to be.

[0027] The carbon-containing material may include at least one type selected from the group consisting of fibrous carbon-containing materials, granular carbon-containing materials, and flat carbon-containing materials. The type of carbon-containing material may be one or more types.

[0028] The carbon-containing material is preferably a fibrous carbon-containing material. The fibrous carbon-containing material is a carbon-containing material with a high aspect ratio in one dimension. Among carbon-containing materials, those with an aspect ratio (the ratio of fiber length to fiber diameter) of 5 or more can be regarded as fibrous carbon-containing materials.

[0029] Examples of fibrous carbon-containing materials include carbon nanotubes (CNTs). Specific examples of CNTs include multi-walled carbon nanotubes (MWCNTs), carbon nanotubes with two or more layers (FWCNTs), single-walled carbon nanotubes (SWCNTs), vapor-grown carbon fibers (VGCFs), and carbon nanofibers (CNFs). The types of fibrous carbon-containing materials can be one or more.

[0030] The average fiber diameter of the fibrous carbon-containing material is preferably below 10 nm. A smaller average fiber diameter in the fibrous carbon-containing material facilitates higher crystallinity. Higher crystallinity of the carbon-containing material results in better hydrophobicity; therefore, a smaller average fiber diameter in the fibrous carbon-containing material facilitates aggregation with hydrophobic niobium oxides and maintains a good conductive path, which is preferable. Furthermore, it helps reduce side reactions in the electrode.

[0031] Examples of fibrous carbon-containing materials with an average fiber diameter of less than 10 nm include FWCNT and SWCNT. From the viewpoint of further reducing the average fiber diameter, nanocarbon nanotube systems with a cylindrical structure having a thin wall thickness are preferred, and the SWCNT system is the best.

[0032] The particulate carbon-containing material system can have a particle shape with a low aspect ratio. The particle shape can be amorphous. The particulate carbon-containing material system can include particles with a low aspect ratio, in a state where each particle exists individually, or in a state where two or more particles are connected together. Carbon-containing materials with a particle shape having an aspect ratio of 3 or less can be considered particulate carbon-containing materials. More specifically, for particles, if there is no combination with an aspect ratio greater than 3 among the three lengths obtained by measuring the lengths in the thickness direction, the longitudinal direction orthogonal to the thickness direction, and the transverse direction orthogonal to both the thickness direction and the longitudinal direction, then it can be called "aspect ratio of 3 or less".

[0033] Specific examples of granular carbon-containing materials include acetylene black and furnace black. From the viewpoint of reducing the functional group content of carbon-containing materials, crystalline carbon black is preferred. As an example of crystalline carbon black, acetylene black can be cited. A specific example of acetylene black is DenkaBlack (registered trademark).

[0034] A flat carbon-containing material system can have a two-dimensional structure. When measuring the lengths of the carbon-containing material in three directions—the thickness direction, the longitudinal direction orthogonal to the thickness direction, and the transverse direction orthogonal to both the thickness and longitudinal directions—if the ratio of the length in the thickness direction to the length in the longitudinal direction is 5 or more, and the ratio of the length in the thickness direction to the length in the transverse direction is 5 or more, then it can be considered a flat carbon-containing material. That is, a flat carbon-containing material system can have a plane with an aspect ratio of 5×5 or more relative to the thickness direction. The widest part of this plane is called the maximum width.

[0035] Examples of planar carbon-containing materials include multilayer graphene and graphite. Among them, multilayer graphene is preferred because its high crystallinity allows for a reduction in the content of functional groups.

[0036] When the carbon-containing material includes fibrous carbon-containing material and granular carbon-containing material, the average fiber diameter of the fibrous carbon-containing material and the average particle size of the granular carbon-containing material preferably satisfy the following formula A.

[0037] However, in Formula A, da-type fibrous carbon contains the average fiber diameter of the material, and db-type granular carbon contains the average particle size of the material.

[0038] When the carbon-containing material includes fibrous carbon-containing material and plate-shaped carbon-containing material, the average fiber diameter of the fibrous carbon-containing material and the average thickness of the plate-shaped carbon-containing material preferably satisfy the following formula B.

[0039] In formula B, da represents the average fiber diameter of the fibrous carbon material and ta represents the average thickness of the flat carbon material.

[0040] The fibrous carbon-containing materials and granular carbon-containing materials that satisfy Formula A are not easily aggregated with each other. Also, the fibrous carbon-containing materials and plate-shaped carbon-containing materials that satisfy Formula B are not easily aggregated with each other.

[0041] When granular carbon-containing materials and / or planar carbon-containing materials aggregate with fibrous carbon-containing materials, the fibrous carbon-containing materials can cover the granular carbon-containing materials and / or planar carbon-containing materials. In this case, the fibrous carbon-containing materials are difficult to disperse within the electrode, making it difficult to ensure the electrode conductive path of the fibrous carbon-containing materials, which may lead to a decrease in output and is therefore undesirable.

[0042] The electrodes of the embodiments will be described in detail.

[0043] In the electrode of the embodiment, niobium-containing oxide system may be included as an active material. Carbon-containing material system may be included as a conductive agent.

[0044] The electrode system may include a battery electrode containing niobium oxide as the active material for the battery. The electrode system is preferably a secondary battery electrode. Because the niobium oxide and carbon-containing materials in this electrode system are not easily peeled off, the conductive path within the electrode can be well maintained even after charge-discharge cycles. As a battery electrode, the electrode system may, for example, be a negative electrode containing niobium oxide as the negative electrode active material.

[0045] The relevant electrode system may include a current collector and an active material containing layer. The active material containing layer may be formed on one or both sides of the current collector. The active material containing layer may contain an active material, a conductive agent, and a binder.

[0046] The active material containing the layer system may contain niobium oxide alone, or may contain a mixture of niobium oxide and one or more other active materials.

[0047] Although the specific composition of niobium oxide is illustrated below, the hydroxyl groups that niobium oxide may contain are not considered in each composition formula.

[0048] Examples of niobium oxides include monoclinic niobium titanium oxide, niobium pentoxide (Nb₂O₅), and compounds represented by Nb₁₁₋ₓWₓO₂.₅₁₋₀.₅₋₀ (where x is, for example, 0 < x ≦ 0.₅). The number of niobium oxides may be one or more.

[0049] As an example of the above-mentioned monoclinic niobium titanium oxide, a compound represented by LixTi1-yM1yNb2-zM2zO7+δ can be cited. Here, M1 is selected from at least one of the groups consisting of Zr, Si, and Sn. M2 is selected from at least one of the groups consisting of V, Ta, and Bi. The added symbols in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3. As a specific example of monoclinic niobium titanium oxide, LixNb2TiO7 (0≦x≦5) can be cited.

[0050] As another example of monoclinic niobium titanium oxide, compounds represented by LixTi1-yM3y+zNb2-zO7-δ can be cited. Here, M3 is selected from at least one of Mg, Fe, Ni, Co, W, Ta, and Mo. The added symbols in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3.

[0051] Specific examples of compounds represented by Nb1-xWxO2.5+3x include Nb12WO33 and Nb16W5O55. These compositions are represented by Nb1-xWxO2.5+3x and satisfy 0 < x ≦ 0.5. In other words, the formulas Nb12WO33 and Nb16W5O55 are each compositional formulas satisfying Nb1-xWxO2.5+3x, expressed in integer form with each subscript being an integer.

[0052] When niobium-containing oxides are included as negative electrode active materials, other examples of active materials include lithium titanate with a straight manganese oxide structure (e.g., Li2+yTi3O7, O≦y≦3), lithium titanate with a spinel structure (e.g., Li4+xTi5O12, O≦x≦3), titanium dioxide (TiO2), anatase titanium dioxide, rutile titanium dioxide, manganese barite titanium composite oxides, and orthorhombic titanium composite oxides.

[0053] As an example of orthorhombic titanium containing composite oxides, compounds represented by Li2+aMI 2-bTi6-cMII dO14+σ can be cited. Here, MI is selected from at least one of the groups Sr, Ba, Ca, Mg, Na, Cs, Rb and K. MII is selected from at least one of the groups Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni and Al. The additive symbols in the composition formula are 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, and -0.5≦σ≦0.5. A specific example of orthorhombic titanium containing composite oxides is Li2+aNa2Ti6O14 (0≦a≦6).

[0054] The conductive agent is formulated to improve current collection performance and suppress the contact resistance between the active material and the current collector. Examples of conductive agents include the carbon-containing material described above. However, when the electrode in the embodiment is used as a negative electrode, the carbon-containing material is sometimes described as a negative electrode carbon-containing material. Besides using the carbon-containing material described above as a conductive agent, a carbon coating or an electronically conductive inorganic material coating can also be applied to the surface of the active material particles.

[0055] The adhesive is formulated to fill the gaps between dispersed active materials and to bond the active materials to the current collector. Examples of adhesives include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, polyacrylic acid compounds, amide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these can be used as an adhesive, or two or more can be combined as an adhesive.

[0056] The proportions of the active material, conductive agent, and binder in the active material containing layer can be appropriately varied depending on the application of the electrode. For example, when the electrode is used as the negative electrode of a secondary battery, the proportions of the active material (negative electrode active material), conductive agent, and binder are preferably 68% to 96% by mass, 2% to 30% by mass, and 2% to 30% by mass, respectively. By making the amount of conductive agent 2% or more by mass, the current-collecting performance of the active material containing layer can be improved. In addition, by making the amount of binder 2% or more by mass, the adhesion between the active material containing layer and the current collector is sufficient, and excellent cycle performance can be expected. On the other hand, it is preferable to make the conductive agent and binder 30% or less by mass respectively to achieve high capacity.

[0057] The current collector system uses 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 system 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 system with such a thickness achieves a balance between electrode strength and lightweight.

[0058] Furthermore, the current collector system may include a portion of its surface where no negative electrode active material layer is formed. This portion can function as a negative electrode current collector tongue.

[0059] (Manufacturing method) The manufacturing method of the electrode in the embodiment includes, for example, synthesizing niobium oxide, preparing a slurry containing niobium oxide and carbon material, and coating the slurry onto a current collector.

[0060] The following will describe the various projects that may be included in the above method.

[0061] The hydroxyl content of niobium oxides is affected by factors such as the synthesis conditions. For example, the synthesis of niobium oxides can generally be carried out by mixing starting materials and heating the resulting mixture. The mixing method or heating temperature in this synthesis may affect the hydroxyl content of the resulting niobium oxides. Furthermore, niobium oxide systems may contain residual alkali components from the starting materials as impurities. Examples of alkalis include potassium. Residual alkali components may also lead to an increase in the hydroxyl content of niobium oxides.

[0062] In order to obtain niobium-containing oxides with low hydroxyl content, it is preferred, for example, to synthesize niobium-containing oxides by annealing an intermediate obtained by a liquid-phase method.

[0063] The liquid-phase method refers to the method of synthesizing the target substance by melting, dissolving, or suspending the starting materials in a solvent, and then using a mixture (liquid mixture) that is homogeneous at the atomic level. Alternatively, granular precursors can be prepared from the liquid mixture, and the target substance can be synthesized from the precursors.

[0064] Examples of liquid-phase methods include spray drying, spray pyrolysis, and hydrothermal synthesis. Spray drying involves spraying a mixture of liquids, drying the sprayed droplets in hot air, and then heating the resulting intermediate to synthesize the target substance. Spray pyrolysis involves introducing the sprayed liquid droplets into a high-temperature environment such as a reactor using a carrier gas, heating them, and synthesizing the target substance through reaction with the gas or thermal decomposition. Hydrothermal synthesis involves heating and pressurizing a mixture using water as a solvent, and synthesizing the target substance in the presence of high-temperature, high-pressure hot water.

[0065] As starting materials, oxides or salts of niobium contained in the target niobium oxide and other metallic elements (e.g., titanium) can be used. Preferably, the salt system used as a starting material is a salt of carbonate or nitrate that decomposes to produce oxides at relatively low temperatures. These starting materials can be mixed according to the required molar ratio (molar ratio) for the target composition. Preferably, a starting material with a low alkali content is used.

[0066] Intermediates can also be obtained through methods other than the liquid-phase method described above. Examples of methods other than the liquid-phase method include the solid-phase method. The solid-phase method is a method of synthesizing the target substance by heating a mixture of starting materials such as metal oxides and mixing them in a solid phase.

[0067] From the viewpoint of obtaining niobium oxides with low hydroxyl content, the liquid phase method is preferable. Niobium oxides obtained by the liquid phase method are less prone to decrease in crystallinity and fluctuation in surface element ratio during the pulverization process described later, and are therefore preferable.

[0068] The intermediate system obtained as described above may contain niobium-containing oxides with low crystallinity. It is preferable to improve the crystallinity of the niobium-containing oxides by subjecting such intermediates to heat annealing treatment.

[0069] To obtain highly crystalline niobium-containing oxides, it is preferable to increase the annealing temperature. The higher the annealing temperature or the longer the annealing time, the more the crystalline phase of the niobium-containing oxide can develop. However, if the annealing temperature is too high or the time is too long, sintering may occur, resulting in the formation of coarse secondary particles in the niobium-containing oxide. To obtain niobium-containing oxides with the desired particle size, these secondary particles need to be pulverized using a ball mill or similar device. However, if the shear force during pulverization is too high, an amorphous phase may form on the surface of the niobium-containing oxide. As a result, the hydroxyl content may ultimately increase.

[0070] From the viewpoint of synthesizing highly crystalline niobium containing oxides, the annealing treatment is preferably carried out in the range of 400°C to 1100°C for 1 hour to 12 hours. The annealing temperature is more preferably 800°C or lower.

[0071] After annealing, niobium oxide can be pulverized to produce particles with the desired particle size. A ball mill can be used, for example, for pulverization. A dry ball mill is a specific example of a ball mill. The ball milling conditions can be set, for example, to a ball diameter of 1 mm to 10 mm, a rotation speed of 120 rpm to 450 rpm, and a milling time of 3 hours to 24 hours. The smaller the ball diameter, the lower the rotation speed, or the shorter the milling time, the lower the tendency for shear force during pulverization. The lower the shear force, the higher the crystallinity tendency of the niobium oxide particles obtained from pulverization.

[0072] After pulverization, a re-annealing treatment can be performed. The re-annealing treatment can be carried out by heating the pulverized niobium oxide particles at a temperature of 400°C to 700°C for 0.5 hours to 12 hours. The re-annealing time is preferably 6 hours or less. The pulverized niobium oxide particles may have decreased surface crystallinity due to pulverization, resulting in an amorphous phase on the particle surface. Re-annealing these niobium oxide particles increases the surface crystallinity, making it less likely for niobium oxides to adhere hydroxyl groups. As a result, the hydroxyl content of the niobium oxides can be reduced. If the crystallinity of the pulverized niobium oxide particles is already sufficiently high, the re-annealing treatment can be omitted.

[0073] However, ball milling at speeds exceeding 450 rpm causes a significant and rapid amorphization of niobium-containing oxides. As a result, the elemental composition of the niobium-containing oxide particles obtained after pulverization changes. Even after re-annealing such significantly amorphized niobium-containing oxides, the reduction in hydroxyl content is limited. Therefore, it is difficult to reduce the hydroxyl content of niobium-containing oxides to below 0.25 mmol / g, which is undesirable.

[0074] The niobium-containing oxide synthesized as described above is dispersed together with the carbon-containing material in a solvent. Specifically, the active material containing the niobium-containing oxide, the carbon-containing material, and the binder are dispersed in the solvent. Water can be used as a solvent, for example.

[0075] During dispersion, a glass bead mill can be used, for example. If the shear force of the glass bead mill is too high, the crystallinity of the carbon-containing material will decrease. Furthermore, the portion of the carbon-containing material with decreased crystallinity may react with the solvent. As a result, the carbon-containing material is prone to the adhesion of functional groups, which is undesirable. From the viewpoint of reducing the functional group content of the carbon-containing material, the dispersion conditions of the glass bead mill are preferably a low peripheral speed and a high flow rate. In glass bead mill dispersion, the peripheral speed can be set to, for example, 10 m / s or less. The peripheral speed is preferably, for example, 6 m / s. However, the peripheral speed is preferably, for example, 3000 rpm or less, for example, 2000 rpm. The flow rate can be set to 10 mL / min or more. The flow rate is, for example, 40 mL / min. Through the above methods, a slurry can be prepared.

[0076] Before dispersion in the glass bead mill, the active material containing niobium oxide, the carbon-containing material, and the binder can be pre-mixed. Pre-mixing allows for the preparation of an electrode slurry with sufficient material dispersion in the solvent without excessively increasing the shear force of the glass bead mill. For example, a planetary mixer can be used for pre-mixing. Excessive shear force in a planetary mixer reduces the crystallinity of the carbon-containing material, making it prone to functional group adhesion, which is detrimental. From the viewpoint of reducing the functional group content of the carbon-containing material, it is preferable to reduce the circumferential speed of the planetary mixer. The circumferential speed can be set to, for example, 3 m / s or less.

[0077] The slurry prepared as described above is coated onto one or both sides of the current collector. Next, the coated slurry is dried to obtain a laminate containing a positive electrode active material layer and a current collector. Then, pressure is applied to the laminate. Electrodes can be fabricated in this manner.

[0078] In addition to the method described above, the electrode can also be manufactured by the following method. First, niobium-containing oxide, carbon-containing material, and binder are mixed (kneaded) to obtain a mixture. At this time, a confined flow mixer (Henschel mixer) or the like can be used for kneading. At this time, if the shear force of the Henschel mixer is too high, the crystallinity of the carbon-containing material will decrease, and the carbon-containing material will easily attach functional groups, which is unfavorable. When mixing with a Henschel mixer, the kneading environment can be adjusted along with the shear force. From the viewpoint of reducing the functional group content of the carbon-containing material, it is preferable to adjust the speed and kneading atmosphere of the Henschel mixer as the kneading environment. For example, the speed can be set to 120 rpm or less. It is preferable to knead in an oxygen-free atmosphere as the kneading environment. Specifically, an argon atmosphere or the like can be selected. Next, the mixture is formed into granules. Then, by placing these granules on a current collector, an electrode can be obtained.

[0079] (Measurement Methods) The following will explain the measurement methods for the hydroxyl content of niobium oxides and the functional group content of carbon-containing materials. Furthermore, the methods for identifying the types of carbon-containing materials and measuring their dimensions will also be explained.

[0080] If the electrode of the object to be measured is already assembled in the battery, the battery should be disassembled in a glove box with a dew point management of -80°C or below before measurement, and the electrode of the object to be measured (e.g., the negative electrode) should be removed.

[0081] (Preparation of Samples for Measurement) From the electrodes of the object being measured, TG-MS samples for measuring the content of oxide hydroxyl groups in niobium and TPD-MS samples for measuring the content of material functional groups in carbon are prepared using the following methods.

[0082] First, using the electrode of the object being measured, assemble a button cell with Li metal as the counter electrode. By charging this button cell to 3.2V vs. Li at a current of 1mA / g, completely detach the Li from the electrode of the object being measured. Repeat this operation 3 times.

[0083] The button unit is disassembled in a glove box with a dew point management of -80°C or below, and the electrode of the object to be measured is removed. The active material containing layer of the electrode to be measured is peeled off from the current collector using a scraper to obtain a powdered active material containing layer (electrode powder). The obtained electrode powder is placed in water and ultrasonically dispersed. After dispersion, the precipitate is separated from the upper suspension. This ultrasonic dispersion and separation operation is repeated 3 times to obtain precipitate and suspension. Niobium oxide in the active material containing layer is prone to precipitation after ultrasonic dispersion. Therefore, the precipitate may contain niobium oxide. The suspension may contain carbon-containing materials.

[0084] (Measurement of hydroxyl content of niobium oxides) Thermogravimetry / mass spectrometry (TG-MS) samples used to measure the hydroxyl content of niobium oxides can be obtained by drying the precipitate obtained by the above method at 130°C for more than 24 hours and then letting it stand for 24 hours in an environment with a dew point of more than 10°C.

[0085] The hydroxyl content of niobium oxides can be measured by providing the TG-MS with the sample as described below.

[0086] Using a thermogravimetric / mass spectrometer, under inactive conditions, such as a nitrogen flow, measurements were performed up to 600°C at a heating rate of 3°C per minute. The hydroxyl groups were then quantified using MS analysis with m / z=18. The quantification of the hydroxyl groups was performed using an integrated value over a range of 150°C to 400°C.

[0087] (Measurement of Functional Group Content of Carbon-Containing Materials) A thermally programmed desorption-mass spectrometry (TPD-MS) sample for measuring the functional group content of carbon-containing materials can be obtained by the following method. First, the suspension obtained by the above method is centrifuged. The precipitate after centrifugation is then placed back into water, allowed to stand for 10 minutes, and the precipitate is removed. The resulting liquid is centrifuged again to precipitate the carbon-containing phase containing the carbon-containing material. Next, the obtained carbon-containing phase is washed. Washing is performed by placing the carbon-containing phase back into water, allowing it to stand for 10 minutes, removing the precipitate, and then centrifuging again to obtain the precipitate. After repeating the above washing process three times, the sample is dried at 150°C for at least 24 hours under an inactive atmosphere to obtain a TPD-MS sample.

[0088] The content of functional groups in carbon-containing materials can be measured by sending the sample to the TPD-MS in the following manner.

[0089] Using a heated desorption mass spectrometry analyzer, the quantities of CO, CO2, H2O, and H2 gases produced at temperatures above 200°C and below 800°C are quantified in an inert gas stream. These gases are produced when the carbon-containing material contains hydroxyl, carboxyl, carbonyl, ether, or hydrocarbon bonds.

[0090] The amount of gaseous matter obtained quantitatively is taken as the amount of functional groups contained in the carbon-containing material. Thermal desorption mass spectrometry analysis is preferably performed in a dehumidified environment to prevent moisture re-adsorption.

[0091] (Identification and Size Measurement of Carbon-Containing Materials) The type of carbon-containing material in the electrode can be determined by scanning electron microscopy (SEM). Among the particles, fibers, or plates observed in the secondary electron image of the electrode, the smallest in size (particle size, fiber length, or maximum width) is considered the carbon-containing material. The largest particles are considered the active material particles.

[0092] In the field of view containing both the aforementioned specific active material particles and carbon-containing materials, reflectance electron image analysis is performed. The conditions for obtaining the field of view are set such that the brightness of the specific active material particles and carbon-containing materials can be determined from the brightness using the above method. For example, measurements of 1kV-10uA in the reflectance electron image can be taken, but this is not limited to the type of active material, etc.

[0093] The fiber diameter of fibrous carbon-containing materials is defined as the distance between the perpendicular line drawn along one side of the fiber and the other side of the fiber. The average fiber diameter can be measured by randomly selecting 10 fibrous carbon-containing materials within the field of view, measuring their fiber diameters, and calculating their average value. The fiber length of fibrous carbon-containing materials can be measured by extrapolating a curve along one side of the fiber until it terminates within the field of view, and measuring the length of that curve. The average fiber length can be measured by selecting the 10 longest extrapolated curves and calculating their average length.

[0094] The thickness of the flat carbon-containing material is measured at the portion of the flat carbon-containing material with the smallest thickness. Specifically, when observing the thickness of the flat carbon-containing material, a straight line perpendicular to a plane with an aspect ratio of 5×5 or higher relative to the thickness direction is drawn at the portion with the smallest thickness. The distance between the two points where this straight line intersects the outline of the flat carbon-containing material is defined as the thickness of the flat carbon-containing material. The average thickness can be measured by randomly selecting 10 flat carbon-containing materials within the field of view, measuring their thickness, and calculating their average value.

[0095] The particle size of the granular carbon-containing material is the diameter of the largest circle inscribed in the particle. The average particle size can be measured by randomly selecting 10 granular carbon-containing materials within the field of view, measuring their diameters, and calculating their average value.

[0096] (Specification of Crystalline Carbon Black) Electrodes containing crystalline carbon black can be identified by transmission electron microscopy (TEM). A TEM sample is prepared from the electrode of the object being measured using the same method as for TPD-MS sample preparation. When the TEM sample is analyzed via TEM, a carbon-containing material with a layered structure of two or more layers can be identified, specifically crystalline carbon black.

[0097] Regarding the electrode of the first embodiment, it comprises a niobium-containing oxide and a carbon-containing material. The hydroxyl content of the niobium-containing oxide is 0.25 mmol / g or less. The functional group content of the carbon-containing material is 5 mmol / g or less. Therefore, an electrode that suppresses gas generation and has high output performance can be provided.

[0098] (Second Embodiment) According to the second embodiment, a secondary battery comprising a negative electrode, a positive electrode, and an electrolyte is provided. This secondary battery system includes, as the negative electrode, the electrode according to the first embodiment.

[0099] The relevant secondary battery system may further include a separator disposed between the positive and negative electrodes. The negative electrode, positive electrode, and separator system may constitute an electrode group. The electrolyte system may be maintained within the electrode group.

[0100] Furthermore, the relevant secondary battery system may further include an external component that houses the electrode group and the electrolyte.

[0101] Furthermore, the relevant secondary battery system may further include a negative terminal electrically connected to the negative electrode and a positive terminal electrically connected to the positive electrode.

[0102] The relevant secondary battery system may be, for example, a lithium secondary battery. Furthermore, the secondary battery system includes a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0103] The following will describe in detail the negative electrode, positive electrode, electrolyte, separator, external components, negative terminal and positive terminal.

[0104] 1) The negative electrode system may include a negative electrode current collector and a negative electrode active material containing layer. The negative electrode current collector and the negative electrode active material containing layer system may be a current collector and an active material containing layer comprising the electrode of the first embodiment, respectively.

[0105] In the detailed description of the negative electrode, the detailed and repetitive parts described in the first embodiment are omitted.

[0106] The density of the negative electrode active material containing the layer (excluding the current collector) is preferably 1.8 g / cm³ to 3.5 g / cm³. Negative electrodes with a negative electrode active material containing the layer density within this range exhibit excellent performance in terms of energy density and electrolyte retention. More preferably, the density of the negative electrode active material containing the layer is 2.1 g / cm³ to 3.0 g / cm³.

[0107] The negative electrode example can be manufactured by the same method as the electrode of the first embodiment.

[0108] 2) The positive electrode system may include a positive current collector and a positive active material containing layer. The positive active material containing layer system may be formed on one or both sides of the positive current collector. The positive active material containing layer system may include positive active material, and may also include conductive agents and binders.

[0109] As a positive electrode active material, for example, oxides or sulfides can be used. The positive electrode system, as a positive electrode active material, may contain only one type of compound, or may contain two or more compounds in combination. Among the examples of oxides and sulfides, compounds capable of inserting into and desorbing Li or Li ions are listed.

[0110] Such a compound system includes, for example, manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxides (e.g., LixMn2O4 or LixMnO2; 0 < x ≦ 1), lithium nickel composite oxides (e.g., LixNiO2; 0 < x ≦ 1), lithium cobalt composite oxides (e.g., LixCoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxides (e.g., LixNi1-yCoyO2; 0 < x ≦ 1, 0 < y < 1), and lithium manganese cobalt composite oxides (e.g., LixMnyCo1-yO2; 0 < x ≦ 1, 0 < y < 1). Lithium manganese nickel composite oxides with spinel structure (e.g., LixMn2-yNiyO4; 0<x≦1, 0<y<2), lithium phosphate with olivine structure (e.g., LixFePO4; 0<x≦1, LixFe1-yMnyPO4; 0<x≦1, 0<y≦1, LixCoPO4; 0<x≦1), ferric sulfate (Fe2(SO4)3), vanadium oxide (e.g., V2O5), and lithium nickel cobalt manganese composite oxides (LixNi1-y-zCoyMnzO2; 0<x≦1, 0<y<1, 0<z<1, y+z<1).

[0111] Examples of preferred positive electrode active materials in the above compounds include lithium manganese composite oxides (e.g., LixMn2O4; 0 < x ≦ 1), lithium nickel composite oxides (e.g., LixNiO2; 0 < x ≦ 1), lithium cobalt composite oxides (e.g., LixCoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxides (e.g., LixNi1-yCoyO2; 0 < x ≦ 1, 0 < y < 1), and compounds with a spinel-type structure. Lithium manganese nickel composite oxides with the following structures (e.g., LixMn2-yNiyO4; 0 < x ≦ 1, 0 < y < 2), lithium manganese cobalt composite oxides (e.g., LixMnyCo1-yO2; 0 < x ≦ 1, 0 < y < 1), lithium iron phosphate (e.g., LixFePO4; 0 < x ≦ 1), and lithium nickel cobalt manganese composite oxides (LixNi1-y-zCoyMnzO2; 0 < x ≦ 1, 0 < y < 1, 0 < z < 1, y + z < 1) can be used as positive electrode active materials to increase the positive electrode potential.

[0112] When a room-temperature molten salt is used as the electrolyte in the battery, it is preferable to use lithium iron phosphate, LixVPO4F (0≦x≦1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or mixtures thereof as the positive electrode active material. These compounds have low reactivity with room-temperature molten salt, thus improving cycle life. Detailed information about room-temperature molten salt will be provided later.

[0113] The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. Positive electrode active materials with a primary particle size of 100 nm or more are easy to handle in industrial production. Positive electrode active materials with a primary particle size of 1 μm or less enable smooth diffusion of lithium ions within the solid.

[0114] The specific surface area of ​​the positive electrode active material is preferably 0.1 m² / g or more and 10 m² / g or less. A positive electrode active material with a specific surface area of ​​0.1 m² / g or more can adequately ensure the adsorption and release sites of Li ions. A positive electrode active material with a specific surface area of ​​10 m² / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0115] The adhesive is used to fill the gaps between the dispersed positive electrode active materials and to bond the positive electrode active materials and the positive electrode current collector. Examples of adhesives include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, polyacrylic acid compounds, amide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these can be used as an adhesive, or two or more can be combined as an adhesive.

[0116] The conductive agent is formulated to improve current collection performance and suppress the contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include carbon black such as vapor-grown carbon fiber (VGCF), acetylene black, and carbonaceous materials such as graphite. One of these can be used as a conductive agent, or two or more can be combined as a conductive agent. Alternatively, the conductive agent can be omitted.

[0117] In the positive electrode active material containing layer, the positive electrode active material and the binder system are preferably combined in proportions of 80% to 98% by mass and 2% to 20% by mass, respectively.

[0118] Sufficient electrode strength can be obtained by making the amount of adhesive 2% by mass or more. Furthermore, the adhesive can act as an insulator. Therefore, when the amount of adhesive is 20% by mass or less, the amount of insulator contained in the electrode will be reduced, thereby reducing the internal resistance.

[0119] When adding a conductive agent, it is preferable that the positive electrode active material, binder and conductive agent are combined in proportions of 77% to 95% by mass, 0.2% to 20% by mass and 0.5% to 15% by mass, respectively.

[0120] The above-mentioned effects can be achieved by making the amount of conductive agent 0.5% by mass or more. Furthermore, by making the amount of conductive agent 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. When this proportion is low, the decomposition of the electrolyte can be reduced under high-temperature storage conditions.

[0121] The positive electrode current collector system is preferably aluminum foil, or aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu and Si.

[0122] The thickness of the aluminum foil or aluminum alloy foil is preferably 5μm to 20μm, and more preferably 15μm 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.

[0123] Furthermore, the positive electrode current collector system may include a portion of its surface where no positive electrode active material layer has been formed. This portion can function as a positive electrode current collector tongue.

[0124] The positive electrode system can be manufactured, for example, by the following method. First, a slurry is prepared by suspending the positive electrode active material, a conductive agent, and a binder in a solvent. This slurry is then coated onto one or both sides of the positive electrode current collector. Next, the coated slurry is dried to obtain a laminate containing the positive electrode active material layer and the current collector. Then, pressure is applied to the laminate. In this way, the positive electrode is manufactured.

[0125] Alternatively, the positive electrode system can also be manufactured by the following method. First, a positive electrode active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, the mixture is shaped into granules. Then, the positive electrode is obtained by disposing these granules on a positive electrode current collector.

[0126] 3) Electrolytes can be used as electrolytes, for example, non-aqueous electrolytes, aqueous electrolytes, or a combination of non-aqueous electrolytes and aqueous electrolytes.

[0127] As a non-aqueous electrolyte, a liquid non-aqueous electrolyte or a gel non-aqueous electrolyte can be used, for example. The 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 to 2.5 mol / L.

[0128] Examples of electrolyte salts include lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2) lithium salts, as well as mixtures thereof. Preferably, the electrolyte salt should be difficult to oxidize even at high potentials, with LiPF6 being the most suitable.

[0129] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); chain 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); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as mixed solvents.

[0130] The gel-like non-aqueous electrolyte is formulated by combining a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

[0131] Or as a non-aqueous electrolyte, in addition to liquid non-aqueous electrolytes and gel non-aqueous electrolytes, room temperature molten salts (ionic melts) containing lithium ions, polymeric solid electrolytes, and inorganic solid electrolytes can be used.

[0132] Room temperature molten salt (ionic melt) refers to a compound that exists as a liquid at room temperature (between 15°C and 25°C) within an organic salt composed of a combination of organic cations and anions. Room temperature molten salts include those existing as liquid monomers, those that become liquid by mixing with electrolyte salts, those that become liquid by dissolving in an organic solvent, or mixtures thereof. Generally, room temperature molten salts used in secondary batteries have a melting point below 25°C. Furthermore, organic cation systems generally possess a quadruple ammonium framework.

[0133] The polymer solid electrolyte system is prepared by dissolving the electrolyte salt in a polymer material and then solidifying it.

[0134] Inorganic solid electrolytes are solid substances that exhibit Li-ion conductivity. Li-ion conductivity, as referred to here, means a lithium-ion conductivity of 1 × 10⁻⁶ S / cm or higher at 25°C. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Specific examples of inorganic solid electrolytes are described below.

[0135] As an oxide-based solid electrolyte, a lithium phosphate solid electrolyte having a NASICON (sodium superionic conductor) type structure and represented by the general formula Li1+xMα2(PO4)3 is preferred. In the above general formula, Mα is, for example, one or more elements selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The additional character x is in the range of 0 ≤ x ≤ 2.

[0136] Specific examples of lithium phosphate solid electrolytes having a NASICON-type structure include LATP compounds represented by Li1+xAlxTi2-x(PO4)3 and 0.1≦x≦0.5; compounds represented by Li1+xAlyMβ2-y(PO4)3 and Mβ is selected from one or more of the groups Ti, Ge, Sr, Zr, Sn, and Ca, and 0≦x≦1 and 0≦y≦1; and compounds represented by Li1+xAlyMβ2-y(PO4)3 and Mβ is selected from one or more of the groups Ti, Ge, Sr, Zr, Sn, and Ca, and 0≦x≦1 and 0≦y≦1. Compounds represented by lxGe2-x(PO4)3 and 0≦x≦2; compounds represented by Li1+xAlxZr2-x(PO4)3 and 0≦x≦2; compounds represented by Li1+x+yAlxMγ2-xSiyP3-yO12 and Mγ is selected from one or more groups of Ti and Ge, and 0<x≦2 and 0≦y<3; compounds represented by Li1+2xZr1-xCax(PO4)3 and 0≦x<1.

[0137] Furthermore, as an oxide-based solid electrolyte, in addition to the aforementioned lithium phosphate solid electrolyte, the following compounds can be listed: amorphous LIPON compounds represented by LixPOyNz with 2.6≦x≦3.5, 1.9≦y≦3.8, and 0.1≦z≦1.3 (e.g., Li2.9PO3.3N0.46); compounds with a garnet-type structure represented by La5+xAxLa3-xMδ2O12 where A is selected from one or more of the groups Ca, Sr, and Ba, Mδ is selected from one or more of the groups Nb and Ta, and 0≦x≦0.5; Compounds represented as Li3Mδ2-xL2O12, where Mδ is selected from one or more species in the group consisting of Nb and Ta, and L may contain Zr with a 0 ≦ x ≦ 0.5 ; compounds represented as Li7-3xAlxLa3Zr3O12 with a 0 ≦ x ≦ 0.5 ; and LLZ compounds represented as Li5+xLa3Mδ2-xZrxO12, where Mδ is selected from one or more species in the group consisting of Nb and Ta with a 0 ≦ x ≦ 2 (e.g., Li7La3Zr2O12); and compounds with a perovskite structure represented as La2 / 3-xLixTiO3 with a 0.3 ≦ x ≦ 0.7 .

[0138] Of the above compounds, one or more may be used as a solid electrolyte. Two or more of the above solid electrolytes may also be used.

[0139] An aqueous electrolyte system comprises an aqueous solvent and an electrolyte salt. The aqueous electrolyte system is, for example, liquid. The liquid aqueous electrolyte system is a solution prepared by dissolving the electrolyte salt, which is a solute, in an aqueous solvent. Preferably, the solution has a volume of 1 mol of solute salt corresponding to 1 mol or more of aqueous solvent, more preferably 3.5 mol or more.

[0140] As an aqueous solvent, an aqueous solution can be used. The aqueous solution can be pure water or a mixture of water and an organic solvent. For example, the aqueous solvent contains water in a proportion of 50% by volume or more.

[0141] Aqueous electrolytes contain water, which can be confirmed by GC-MS (Gas Chromatography-Mass Spectrometry). Furthermore, the salt concentration and water content in aqueous electrolytes can be measured, for example, by ICP (Inductively Coupled Plasma) emission spectroscopy. By measuring a specified amount of aqueous electrolyte and calculating the salt concentration, the mole concentration (mol / L) can be calculated. Additionally, by measuring the specific gravity of the aqueous electrolyte, the mole count of the solute and solvent can be calculated.

[0142] The aqueous electrolyte system may be a gel-like electrolyte. The gel-like electrolyte system is prepared by mixing and combining the above-mentioned liquid aqueous electrolyte with a polymer material. As the polymer material, a polymer material described for gel-like non-aqueous electrolytes may be used.

[0143] Aqueous electrolytes may include, for example, lithium chloride (LiCl), lithium bromide (LiBr), lithium hydroxide (LiOH), lithium sulfate (Li2SO4), lithium nitrate (LiNO3), lithium acetate (CH3COOLi), lithium oxalate (Li2C2O4), lithium carbonate (Li2CO3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI; LiN(SO2F)2), and lithium bis(oxalatoborate)borate (LiBOB: LiB[(OCO)2]2), etc. The aqueous electrolyte may contain one or more types of electrolyte salts. It is preferable that the aqueous electrolyte contains LiCl. Using LiCl can increase the lithium-ion concentration of the aqueous electrolyte. Furthermore, in addition to LiCl, it is preferable that the lithium salt system contains at least one of LiSO4 and LiOH.

[0144] The molar concentration of lithium ions in the aqueous electrolyte can be 3 mol / L or higher, 6 mol / L or higher, or even 12 mol / L or higher. In one example, the molar concentration of lithium ions in the aqueous electrolyte was 14 mol / L or lower. A high lithium ion concentration in the aqueous electrolyte makes it less likely to suppress the electrolysis of the aqueous solvent on the negative electrode side, and reduces the tendency for hydrogen to be produced at the negative electrode.

[0145] The aqueous electrolyte system preferably contains at least one anionic species selected from chloride ion (Cl-), hydroxide ion (OH-), sulfate ion (SO4 2-), and nitrate ion (NO3-).

[0146] The pH value of the aqueous electrolyte is preferably between 3 and 14, and more preferably between 4 and 13. When different electrolytes are used for the negative electrode and the positive electrode, the pH value of the negative electrode electrolyte is preferably between 3 and 14, and the pH value of the positive electrode electrolyte is preferably between 1 and 8.

[0147] When the pH value of the electrolyte on the negative electrode side is within the above-mentioned range, the hydrogen generation potential of the negative electrode can be reduced, thereby suppressing hydrogen generation at the negative electrode. This improves the battery's storage performance and cycle life. When the pH value of the electrolyte on the positive electrode side is within the above-mentioned range, the oxygen generation potential of the positive electrode can be increased, thereby reducing oxygen generation at the positive electrode. This improves the battery's storage performance and cycle life. The pH value of the electrolyte on the positive electrode side is preferably in the range of 3 to 7.5.

[0148] Aqueous electrolyte systems may contain surfactants. Examples of surfactants include polyoxyalkylene ethers, polyethylene glycol, polyvinyl alcohol, thiourea, sodium 3,3'-dithiobis(1-propanephosphate)2, dimercaptothiadiazole, boric acid, oxalic acid, malonic acid, saccharin, sodium naphthalenesulfonate, gelatin, potassium nitrate, aromatic aldehydes, heterocyclic aldehydes, and other nonionic surfactants. Surfactants may be used alone or in combination of two or more.

[0149] 4) Separator Membrane The separator membrane is formed, for example, of a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a non-woven fabric made of synthetic resin. From a safety point of view, it is preferable to use a porous film formed of polyethylene or polypropylene. These porous films melt at a certain temperature and can interrupt the current.

[0150] 5) As an external component, for example, a container made of laminated film or a metal container can be used.

[0151] The thickness of the laminated film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

[0152] As a laminated film, a multilayer film containing multiple resin layers and a metal layer interposed between these resin layers can be used. The resin layer system includes polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). For weight reduction, the metal layer system is preferably made of aluminum foil or aluminum alloy foil. The laminated film is sealed by heat fusion and can be formed into the shape of an external component.

[0153] The wall thickness of the metal container is, for example, less than 1 mm, preferably less than 0.5 mm, and more preferably less than 0.2 mm.

[0154] The metal container is made of, for example, aluminum or aluminum alloy. It is preferable that the aluminum alloy contains elements such as magnesium, zinc, and silicon. When the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content is preferably below 100 ppm by mass.

[0155] The shape of the external component is not particularly limited. The shape of the external component may be, for example, flat (thin), square, cylindrical, coin-shaped, or button-shaped. The external component may be appropriately selected according to the battery size or the purpose of the battery.

[0156] 6) Negative Terminal System The negative terminal system may be formed of a material that is electrochemically stable and conductive at the absorption and release potential of the negative electrode active material Li. For example, the negative terminal system may be formed of a material that is electrically stable and conductive in a potential range (vs. Li / Li+) with a redox potential of lithium of 1V to 3V. Specifically, a series of materials for the negative terminal include copper, nickel, stainless steel or aluminum, or aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu and Si. Aluminum or aluminum alloys are preferably used as the material for the negative terminal. To reduce the contact resistance with the negative electrode current collector, the negative terminal system is preferably made of the same material as the negative electrode current collector.

[0157] 7) Positive Terminal The positive terminal system is electrically stable in a potential range of 3V to 4.5V relative to the redox potential of lithium (vs. Li / Li+) and is formed of a conductive material. Examples of materials for the positive terminal include aluminum, or aluminum alloys selected from at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. To reduce the contact resistance with the positive current collector, the positive terminal system is preferably formed of the same material as the positive current collector.

[0158] Next, the secondary battery of the embodiment will be described in more detail with reference to the drawings.

[0159] Figure 1 is a schematic cross-sectional view showing an example of a secondary battery. Figure 2 is an enlarged cross-sectional view of part A of the secondary battery shown in Figure 1.

[0160] The secondary battery 100 shown in Figures 1 and 2 includes a pouch-shaped outer casing 2 as shown in Figure 1, an electrode group 1 as shown in Figures 1 and 2, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the pouch-shaped outer casing 2. The electrolyte (not shown) is held in the electrode group 1.

[0161] The bag-shaped outer component 2 is made of a laminated film comprising two resin layers and a metal layer interposed therebetween.

[0162] As shown in Figure 1, electrode group 1 is a flat, wound electrode group. As shown in Figure 2, 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.

[0163] The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material containing layer 3b. In the negative electrode 3, the outermost part located in the wound electrode group 1 is as shown in FIG2, where the negative electrode active material containing layer 3b is formed only on the inner side of the negative electrode current collector 3a. In other parts 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.

[0164] The positive electrode 5 system includes a positive current collector 5a and a positive active material containing layer 5b formed on both sides thereof.

[0165] As shown in FIG. 1, the negative terminal 6 and the positive terminal 7 are located near the outer periphery of the wound electrode group 1. The negative terminal 6 is connected to the outermost part of the negative current collector 3a. The positive terminal 7 is connected to the outermost part of the positive current collector 5a. These negative terminals 6 and positive terminals 7 extend outward from the opening of the bag-shaped outer casing 2. A thermoplastic resin layer is provided on the inner surface of the bag-shaped outer casing 2, and the opening is closed by heat-welding it.

[0166] The secondary battery system of the embodiment is not limited to the secondary battery structure shown in FIG1 and FIG2, but may also be a battery structure shown in FIG3 and FIG4.

[0167] Figure 3 is a partial notch perspective view showing other examples of secondary batteries in a schematic manner. Figure 4 is an enlarged cross-sectional view of part B of the secondary battery shown in Figure 3.

[0168] The secondary battery 100 shown in Figures 3 and 4 includes an electrode group 1 as shown in Figures 3 and 4, an external component 2 as shown in Figure 3, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the external component 2. The electrolyte is held within the electrode group 1.

[0169] The outer component 2 is made of a laminated film comprising two resin layers and a metal layer interposed therebetween.

[0170] As shown in Figure 4, electrode group 1 is a laminated electrode group. The laminated electrode group 1 has a structure in which the negative electrode 3 and the positive electrode 5 are alternately laminated with an insulating membrane 4 inserted between them.

[0171] Electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 has 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. Electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 has 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.

[0172] The negative current collector 3a of each negative electrode 3 is a portion on one side of which does not support the negative electrode active material layer 3b on any surface. This portion functions as a negative current collector tongue 3c. As shown in FIG4, the negative current collector tongue 3c does not overlap with the positive electrode 5. Furthermore, the plurality of negative current collector tongues 3c are electrically connected to the strip-shaped negative terminal 6. The front end of the strip-shaped negative terminal 6 is led out to the outside of the outer component 2.

[0173] Furthermore, although not shown in the figure, the positive current collector 5a of each positive electrode 5 includes a portion on one side of which does not support the positive active material layer 5b on any surface. This portion can be used as a positive current collector tongue. The positive current collector tongue, like the negative current collector tongue 3c, does not overlap with the negative electrode 3. Furthermore, the positive current collector tongue is located on the opposite side of the electrode group 1 relative to the negative current collector tongue 3c. The positive current collector tongue is electrically connected to the strip-shaped positive terminal 7. The front end of the strip-shaped positive terminal 7 is located on the opposite side of the negative terminal 6 and is led out to the outside of the outer casing 2.

[0174] The secondary battery system associated with the second embodiment includes the electrodes associated with the first embodiment. Therefore, a secondary battery that suppresses gas generation and has high output performance can be provided.

[0175] (Third Embodiment) According to the third embodiment, a battery pack is provided. The battery pack includes a plurality of secondary batteries according to the second embodiment.

[0176] In the battery pack, each individual cell can be electrically connected in series or in parallel, or a combination of series and parallel connections.

[0177] Next, an example of the battery pack in the embodiment will be described with reference to the drawings.

[0178] Figure 5 is a perspective view schematically showing an example of a battery pack. The battery pack 200 shown in Figure 5 includes five individual cells 100a-100e, four busbars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five individual cells 100a-100e is a secondary battery with respect to the second embodiment.

[0179] Bus 21 connects, for example, the negative terminal 6 of a single cell 100a and the positive terminal 7 of an adjacent single cell 100b. Thus, five single cells 100 are connected in series by four bus 21s. That is, the battery pack 200 in Figure 5 is a battery pack of five connected in series. Although not shown in the example, in a battery pack containing multiple electrically parallel connected single cells, multiple single cells can be electrically connected, for example, by connecting multiple negative terminals to each other via bus 21, and simultaneously by connecting multiple positive terminals to each other via bus 21.

[0180] The positive terminal 7 of at least one of the five individual cells 100a to 100e is electrically connected to the positive terminal lead 22 for external connection. Also, the negative terminal 6 of at least one of the five individual cells 100a to 100e is electrically connected to the negative terminal lead 23 for external connection.

[0181] The secondary battery system associated with the third embodiment includes the battery pack associated with the second embodiment. Therefore, a battery pack that suppresses gas generation and has high output performance can be provided.

[0182] (Fourth Embodiment) According to the fourth embodiment, a battery pack is provided. The battery pack includes the battery pack of the third embodiment. The battery pack may also include a single secondary battery of the second embodiment, instead of the battery pack of the third embodiment.

[0183] The related battery pack system may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, the circuit contained in a device that uses the battery pack as a power source (e.g., electronic machine, automobile, etc.) may also be used as the protection circuit for the battery pack.

[0184] Furthermore, the relevant battery pack system may further include an external terminal for power supply. The external terminal for power supply is used to output current from the secondary battery to the outside and / or input 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 terminal for power supply. In addition, when the battery pack is charged, charging current (including regenerative energy from the power source of an automobile, etc.) is supplied to the battery pack through the external terminal for power supply.

[0185] Next, an example of the battery pack in the embodiment will be described with reference to the drawings.

[0186] Figure 6 is an exploded perspective view schematically showing an example of a battery pack. Figure 7 is a block diagram showing an example of the circuit of the battery pack shown in Figure 6.

[0187] The battery pack 300 shown in Figures 6 and 7 includes a housing 31, a cover 32, a protective sheet 33, a battery pack 200, a printed wiring board 34, wiring 35, and an insulating plate not shown.

[0188] The container 31 shown in Figure 6 is a rectangular container with a rectangular base. The container 31 is configured to house the protective sheet 33, the battery pack 200, the printed wiring board 34, and the wiring 35. The lid 32 is rectangular in shape. The lid 32 covers the container 31 to house the battery pack 200 and the like. Although the container 31 and the lid 32 are not shown, they are provided with openings or connection terminals for connecting to external machines or the like.

[0189] The battery pack 200 series includes multiple single cells 100, positive electrode side lead 22, negative electrode side lead 23 and adhesive tape 24.

[0190] At least one of the plurality of single cells 100 is a secondary battery according to the second embodiment. Each of the plurality of single cells 100 is electrically connected in series, as shown in FIG7. The plurality of single cells 100 can also be electrically connected in parallel, or a combination of series and parallel connections. When the plurality of single cells 100 are connected in parallel, the battery capacity increases compared to a series connection.

[0191] Adhesive tape 24 is used to secure the plurality of individual cells 100. Alternatively, heat shrinkable tape can be used to secure the plurality of individual cells 100 instead of adhesive tape 24. In this case, protective sheet 33 is placed on both sides of the battery pack 200, and the heat shrinkable tape is wrapped around the pack and then heat-shrinked to bind the plurality of individual cells 100.

[0192] One end of the positive electrode lead 22 is connected to the battery pack 200. One end of the positive electrode lead 22 is electrically connected to the positive terminal of one or more individual cells 100. One end of the negative electrode lead 23 is connected to the battery pack 200. One end of the negative electrode lead 23 is electrically connected to the negative terminal of one or more individual cells 100.

[0193] The printed wiring board 34 is disposed along one of the shorter sides of the inner surface of the receiving container 31. The printed wiring board 34 includes a positive-side connector 342, a negative-side connector 343, a thermistor 345, a protection circuit 346, wirings 342a and 343a, an external terminal 350 for power supply, a positive-side wiring 348a (positive side wiring), and a negative-side wiring 348b (negative side wiring). One main surface of the printed wiring board 34 faces one side of the battery pack 200. An insulating plate (not shown) is disposed between the printed wiring board 34 and the battery pack 200.

[0194] The other end 22a of the positive lead 22 is electrically connected to the positive side connector 342. The other end 23a of the negative lead 23 is electrically connected to the negative side connector 343.

[0195] Thermistor 345 is fixed on one main surface of printed wiring board 34. Thermistor 345 detects the temperature of each single cell 100 and sends the detection signal to protection circuit 346.

[0196] The external power-on terminal 350 is fixed to the other main surface of the printed wiring board 34. The external power-on terminal 350 is electrically connected to a machine located outside the battery pack 300. The external power-on terminal 350 includes a positive terminal 352 and a negative terminal 353.

[0197] The protection circuit 346 is fixed on the other main surface of the printed wiring 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. In addition, the protection circuit 346 is electrically connected to the positive connector 342 via wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the plurality of individual cells 100 via wiring 35.

[0198] The protective sheet 33 is disposed on the two inner sides of the long side of the housing 31, and on the inner side of the short side opposite to the printed wiring board 34 through the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0199] The protection circuit 346 controls the charging and discharging of the plurality of individual batteries 100. Furthermore, the protection circuit 346 disconnects the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for powering on an external machine based on the detection signal sent by the thermistor 345, or the detection signal sent by each individual battery 100 or battery pack 200.

[0200] The detection signal sent by the thermistor 345 may include, for example, a signal indicating that the temperature of a single cell 100 has reached or exceeded a predetermined temperature. The detection signal sent by each single cell 100 or the battery pack 200 may include, for example, a signal indicating overcharging, over-discharging, or overcurrent of a single cell 100. When detecting overcharging of a single cell 100, the battery voltage, positive electrode potential, or negative electrode potential may be detected. In the latter case, a lithium electrode serving as a reference electrode is inserted into each single cell 100.

[0201] In addition, as a protection circuit 346, a circuit included in a device that uses the battery pack 300 as a power source (e.g., electronic machine, automobile, etc.) may also be used.

[0202] Furthermore, as described above, the battery pack 300 includes an external power supply terminal 350. Therefore, the battery pack 300 can output current from the battery pack 200 to an external device via the external power supply terminal 350, and can also input current from an external device to the battery pack 200. 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 via the external power supply terminal 350. Additionally, when the battery pack 300 is charging, charging current from the external device is supplied to the battery pack 300 via the external power supply terminal 350. When this battery pack 300 is used as a vehicle battery, the vehicle's regenerative braking energy can be used as charging current from an external device.

[0203] However, the battery pack 300 series may include multiple battery packs 200. In this case, the multiple battery packs 200 series may be connected in series, in parallel, or in a combination of series and parallel connections. Furthermore, the printed wiring board 34 and wiring 35 series may be omitted. In this case, the positive electrode lead 22 and the negative electrode lead 23 may be used as the positive terminal 352 and negative terminal 353 of the external terminal 350 for power supply, respectively.

[0204] This type of battery pack is used, for example, in applications requiring excellent cycle performance under high current draw. Specifically, this battery pack can be used as a power source for electronic devices, a stationary battery, or an onboard battery for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for automotive batteries.

[0205] The battery pack of the fourth embodiment includes either the secondary battery of the second embodiment or the battery pack of the third embodiment. Therefore, a battery pack that suppresses gas generation and has high output performance can be provided.

[0206] (Fifth Embodiment) According to the fifth embodiment, a vehicle is provided. The vehicle is equipped with the battery pack of the fourth embodiment.

[0207] In vehicles, battery packs are used, for example, to recover regenerative energy from the vehicle's kinetic energy. The vehicle system may include a mechanism (regenerator) that converts the vehicle's kinetic energy into regenerative energy.

[0208] As examples of vehicles, the series includes two-wheeled to four-wheeled hybrid electric vehicles, two-wheeled to four-wheeled electric vehicles, electric bicycles, and railway vehicles.

[0209] There are no particular restrictions on the placement of the battery pack in the vehicle. For example, when mounting the battery pack in a car, it can be placed in the engine compartment, at the rear of the vehicle body, or under the seats.

[0210] The vehicle may be equipped with multiple battery packs. In this case, the batteries contained in each battery pack may be electrically connected in series, electrically connected in parallel, or a combination of series and parallel connections. For example, when each battery pack contains battery groups, the battery groups may be electrically connected in series, electrically connected in parallel, or a combination of series and parallel connections. Alternatively, when each battery pack contains a single battery, each battery may be electrically connected in series, electrically connected in parallel, or a combination of series and parallel connections.

[0211] Next, an example of the vehicle in the embodiment will be described with reference to the drawings.

[0212] Figure 8 is a partial perspective view that schematically shows an example of a vehicle.

[0213] The vehicle 400 shown in FIG8 includes a vehicle body 40 and a battery pack 300 in the fourth embodiment. In the example shown in FIG8, the vehicle 400 is a four-wheeled vehicle.

[0214] The 400 series vehicle can be equipped with multiple battery packs 300. In this case, the batteries (e.g., single cells or battery packs) contained in the battery pack 300 can be connected in series, in parallel, or in a combination of series and parallel connections.

[0215] Figure 8 illustrates an example where the battery pack 300 is mounted in the engine compartment in front of the vehicle body 40. As mentioned above, the battery pack 300 can also be mounted, for example, at the rear of the vehicle body 40 or under the seats. This battery pack 300 can be used as a power source for the vehicle 400. Furthermore, this battery pack 300 can recover regenerative energy from the power of the vehicle 400.

[0216] Next, referring to FIG9, the implementation mode of the vehicle in the embodiment will be described.

[0217] Figure 9 is a schematic diagram showing an example of a vehicle's electrical system and related control system. The vehicle shown in Figure 9 is a 400 series electric vehicle.

[0218] The vehicle 400 shown in Figure 9 includes a vehicle body 40, a vehicle power supply 41, a vehicle ECU (Electric Control Unit) 42 for the upper control device of the vehicle power supply 41, an external terminal (at the terminal connected to the external power supply) 43, an inverter 44 and a drive motor 45.

[0219] For example, the vehicle power supply 41 of the vehicle 400 series is mounted in the engine compartment, at the rear of the vehicle body, or under the seat. However, in the vehicle 400 shown in Figure 9, the mounting position of the vehicle power supply 41 is schematic.

[0220] The vehicle power supply 41 series includes a plurality of (e.g., 3) battery packs 300a, 300b and 300c, a battery management unit 411 (BMU), and a communication bus 412.

[0221] Battery pack 300a includes battery pack 200a and battery pack monitoring device 301a (e.g., VTM: Voltage Temperature Monitoring). Battery pack 300b includes battery pack 200b and battery pack monitoring device 301b. Battery pack 300c includes battery pack 200c and battery pack monitoring device 301c. Battery packs 300a to 300c are the same battery packs as the aforementioned battery pack 300, and battery packs 200a to 200c are the same battery packs as the aforementioned battery pack 200. Battery packs 200a to 200c are electrically connected in series. Battery packs 300a, 300b, and 300c can each be independently disassembled and replaced with other battery packs 300.

[0222] Each of the battery packs 200a to 200c comprises a plurality of single cells connected in series. At least one of the single cells is a secondary battery according to the second embodiment. Each of the battery packs 200a to 200c is charged and discharged through a positive terminal 413 and a negative terminal 414.

[0223] The battery management device 411 communicates with the battery pack monitoring devices 301a-301c to collect information such as the voltage and temperature of each individual cell 100 in the battery packs 200a-200c included in the vehicle power supply 41. In this way, the battery management device 411 collects information regarding the maintenance of the vehicle power supply 41.

[0224] The battery management device 411 and the battery pack monitoring devices 301a-301c are connected via a communication bus 412. In the communication bus 412, one set of communication lines is shared by multiple nodes (the battery management device 411 and one or more battery pack monitoring devices 301a-301c). The communication bus 412 is, for example, a communication bus based on the CAN (Control Area Network) standard.

[0225] The battery pack monitoring devices 301a to 301c measure the voltage and temperature of each individual cell constituting the battery packs 200a to 200c according to communication commands from the battery management device 411. However, the temperature only needs to be measured at several locations within a single battery pack; it is not necessary to measure the temperature of all individual cells.

[0226] The vehicle power supply 41 may also include an electromagnetic contactor (e.g., a switching device 415 shown in FIG. 9) that switches the electrical connection between the positive terminal 413 and the negative terminal 414. The switching device 415 includes a pre-charge switch (not shown) that is turned on when the battery packs 200a-200c are charging, and a main switch (not shown) that is turned on when the output of the battery packs 200a-200c supplies a load. The pre-charge switch and the main switch each have a relay circuit (not shown) that switches on or off by a signal supplied to a coil near the switching element. The electromagnetic contactor, such as the switching device 415, is controlled according to control signals from the battery management device 411 or the vehicle ECU 42 that controls the overall operation of the vehicle 400.

[0227] The inverter 44 converts the input DC voltage into a 3-phase AC high voltage for motor drive. The 3-phase output terminals of the inverter 44 are connected to the 3-phase input terminals of the drive motor 45. The inverter 44 is controlled according to control signals from the battery management device 411 or the vehicle ECU 42 for controlling the overall vehicle operation. The output voltage of the inverter 44 is adjusted by controlling the inverter 44.

[0228] The drive motor 45 is driven to rotate by electricity supplied by the inverter 44. The driving force generated by the rotation of the drive motor 45 is transmitted to the axle and drive wheel W, for example, through the differential gear unit.

[0229] Furthermore, although not shown in the figure, the vehicle 400 series is equipped with a regenerative braking mechanism (regenerator). The regenerative braking mechanism is a regenerative energy system that converts kinetic energy into electrical energy by rotating the drive motor 45 when the vehicle 400 brakes. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 44 and converted into direct current. The converted direct current is input to the vehicle power supply 41.

[0230] One terminal of the connecting line L1 is connected to the negative terminal 414 of the vehicle power supply 41. The other terminal of the connecting line L1 is connected to the negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 in the battery management device 411 is provided between the negative terminal 414 and the negative input terminal 417 in the connecting line L1.

[0231] The positive terminal 413 of the vehicle power supply 41 is connected to one terminal of the connecting line L2. The other terminal of the connecting line L2 is connected to the positive input terminal 418 of the frequency converter 44. A switching device 415 is provided between the positive terminal 413 and the positive input terminal 418 in the connecting line L2.

[0232] External terminal 43 is connected to battery management device 411. External terminal 43 can be connected to an external power source, for example.

[0233] The vehicle ECU 42, in response to input from the driver or other operators, coordinates with other management and control devices, including the battery management device 411, to control the vehicle power supply 41, switching device 415, and inverter 44, etc. Through the coordinated control of the vehicle ECU 42, the power output from the vehicle power supply 41 and the charging of the vehicle power supply 41 are controlled, and the overall management of the vehicle 400 is performed. The battery management device 411 and the vehicle ECU 42 communicate via a communication line to transmit data related to the maintenance of the vehicle power supply 41, such as the remaining capacity of the vehicle power supply 41.

[0234] The vehicle in the fifth embodiment is equipped with the battery pack of the fourth embodiment. Since gas generation in the battery pack is suppressed and output performance is high, a high-performance vehicle can be provided. [Example]

[0235] The present invention will be further described in detail below with examples. As long as it does not deviate from the spirit of the invention, the present invention is not limited to the disclosed embodiments.

[0236] (Example 1)

[0237] (Fabrication of the negative electrode) First, TiNb2O7, as the niobium-containing oxide, was synthesized by spray drying followed by annealing. The annealing treatment was carried out at 1100°C for 6 hours. Afterwards, it was pulverized in a dry ball mill at a ball diameter of 2 mm and a rotation speed of 200 rpm for 12 hours, and then subjected to a second annealing treatment at 600°C for 12 hours. The TiNb2O7 particles obtained in this way were used as the negative electrode active material.

[0238] As a carbon-containing material, acetylene black with a particle size of 31 nm was prepared. As an adhesive, a mixture of carboxymethyl cellulose and butadiene rubber in a 1:1 mass ratio was prepared.

[0239] Niobium oxide, acetylene black, and binder are mixed in a mass ratio of 96:2:2 and dispersed in water as a solvent. Preliminary mixing of the electrode materials is performed using a planetary mixer. Dispersion is carried out using a glass bead mill at 2000 rpm and a flow rate of 40 mL / min. The prepared negative electrode slurry is coated onto a negative electrode current collector made of aluminum foil and dried. This yields the negative electrode.

[0240] (Cathode Fabrication) 100 parts by weight of lithium nickel cobalt manganese composite oxide LiNi0.8Co0.1Mn0.1O2 (NCM811) was used as the cathode active material, 5 parts by weight of acetylene black was used as the conductive agent, and 5 parts by weight of polyvinylidene fluoride (PVdF) was used as the binder. These were mixed with N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was coated on both sides of a current collector made of 12 μm thick aluminum foil, dried, and pressurized to produce a cathode with an electrode density (excluding the current collector) of 3.2 g / cm3.

[0241] (Electrolyte preparation) Lithium hexafluorophosphate (LiPF6) was dissolved in propylene carbonate (PC) at a concentration of 1.0 mol / L under an argon atmosphere to prepare a liquid non-aqueous electrolyte (electrolyte).

[0242] (Battery Assembly) The above-prepared positive electrode, a 15 μm thick cellulose separator, the above-prepared negative electrode, and the separator are sequentially laminated, and then wound into a spiral shape with the negative electrode at the outermost periphery to form an electrode group. A flat electrode group with a width of 58 mm and a thickness of 3.0 mm is formed by heating and pressurizing it at 90°C. The resulting electrode group is housed in an outer casing made of a 0.1 mm thick laminated film composed of a 40 μm thick aluminum foil and polypropylene layers formed on both sides of the aluminum foil, and vacuum-dried at 120°C for 24 hours. After vacuum drying, electrolyte is injected into the electrode group housed in the laminated film under an argon atmosphere. Then, the upper part of the laminated film is sealed under reduced pressure to obtain a secondary battery.

[0243] (Example 2) Except that furnace black with a particle size of 45 nm was used as the carbon-containing material for the negative electrode, the secondary battery was made in the same manner as in Example 1.

[0244] (Example 3) A secondary battery was fabricated in the same manner as in Example 1, except that the negative electrode carbon-containing material was multilayer graphene with a thickness of 52 nm, which was used as the plate-shaped carbon-containing material.

[0245] (Example 4) A secondary battery was fabricated in the same manner as in Example 1, except that SWCNTs with a fiber diameter of 4 nm were used as the negative electrode carbon-containing material.

[0246] (Example 5) A secondary battery was fabricated in the same manner as in Example 1, except that SWCNT with a fiber diameter of 15 nm was used as the negative electrode carbon-containing material.

[0247] (Example 6) SWCNTs with a fiber diameter of 4 nm and acetylene black with a particle diameter of 31 nm were prepared as negative electrode carbon materials. In the preparation of the negative electrode slurry, the mass ratio of niobium oxide, SWCNTs, acetylene black, and binder was mixed at 96:1.99:0.01:2. Except as described above, a secondary battery was prepared in the same manner as in Example 1.

[0248] (Example 7) SWCNTs with a fiber diameter of 4 nm and multilayer graphene with a thickness of 55 nm were prepared as negative electrode carbon materials. In the preparation of the negative electrode slurry, the mass ratio of niobium oxide, SWCNTs, multilayer graphene, and binder was mixed at 96:0.1:1.9:2. Except as described above, a secondary battery was prepared in the same manner as in Example 1.

[0249] (Example 8) SWCNTs with a fiber diameter of 4 nm and acetylene black with a particle diameter of 49 nm were prepared as negative electrode carbon materials. In the preparation of the negative electrode slurry, the mass ratio of niobium oxide, SWCNTs, acetylene black, and binder was mixed at 96:1.99:0.01:2. Except as described above, a secondary battery was prepared in the same manner as in Example 1.

[0250] (Example 9) SWCNTs with a fiber diameter of 4 nm and graphite with a thickness of 582 nm were prepared as negative electrode carbon materials. Refined natural graphite was used as the graphite. In the preparation of the negative electrode slurry, the mass ratio of niobium oxide, SWCNTs, graphite, and binder was mixed at 96:0.1:1.9:2. Except as described above, a secondary battery was prepared in the same manner as in Example 1.

[0251] (Example 10) Niobium oxide was replaced with Nb2O5. Nb2O5 was synthesized by spray drying followed by annealing. The annealing was performed at 1100°C for 6 hours. Afterward, it was pulverized in a dry ball mill at a ball diameter of 2 mm and a rotation speed of 200 rpm for 12 hours, and then annealed again at 600°C for 12 hours. The Nb2O5 particles thus obtained were used as the negative electrode active material. Except as described above, a secondary battery was fabricated in the same manner as in Example 6.

[0252] (Example 11) The niobium oxide was replaced with Nb16W5O55. Nb16W5O55 was synthesized by spray drying followed by annealing. The annealing was performed at 1100°C for 6 hours. Afterwards, it was pulverized in a dry ball mill at a ball diameter of 2 mm and a rotation speed of 200 rpm for 12 hours, and then annealed again at 600°C for 12 hours. The Nb16W5O55 particles thus obtained were used as the negative electrode active material. Except as described above, a secondary battery was fabricated in the same manner as in Example 6.

[0253] (Example 12) The niobium oxide was replaced with FeNb11O29. FeNb11O29 was synthesized by spray drying followed by annealing. The annealing was performed at 1100°C for 6 hours. Afterwards, it was pulverized by dry ball milling at a ball diameter of 2 mm and a rotation speed of 200 rpm for 12 hours, and then annealed again at 600°C for 12 hours. The FeNb11O29 particles thus obtained were used as the negative electrode active material. Except as described above, a secondary battery was fabricated in the same manner as in Example 6.

[0254] (Comparative Example 1) In the synthesis of TiNb2O7, a niobium-containing oxide, the grinding conditions using a dry ball mill were changed to a ball diameter of 10 mm, a rotation speed of 300 rpm, and a grinding time of 48 hours. Furthermore, no re-annealing treatment was performed. Except as described above, a secondary battery was fabricated in the same manner as in Example 6.

[0255] (Comparative Example 2) In the preparation of the negative electrode slurry, except that the conditions of the glass bead mill used for dispersion were changed to 3600 rpm and the flow rate was 5 mL / min, the same as in Example 6 was used to prepare the secondary battery.

[0256] (Comparative Example 3) MWCNTs with a fiber diameter of 17 nm and furnace black with a particle diameter of 46 nm were prepared as negative electrode carbon materials. In the preparation of the negative electrode slurry, the mass ratio of niobium oxide, MWCNTs, furnace black, and binder was mixed at 92:2:4:2. Except as described above, a secondary battery was prepared in the same manner as in Example 6.

[0257] (Measurement) For the negative electrode contained in the secondary battery of each embodiment and comparative example, the hydroxyl content of niobium-containing oxide, the functional group content of carbon-containing material and the size of carbon-containing material (average fiber diameter of fibrous carbon, average thickness of plate-shaped carbon-containing material and average particle size of granular carbon-containing material) were measured according to the previously described method.

[0258] (Evaluation) For the secondary batteries of each embodiment and comparative example, the gas generation, 5C / 0.2C discharge capacity retention and cycle capacity retention were tested in the following manner.

[0259] (Gas Generation Amount) The secondary batteries of the Examples and Comparative Examples were kept at 100% State of Charge (SOC) and an ambient temperature of 80°C for 10 days. Afterwards, the gas generation amount (cc) within the secondary batteries was measured. The measured gas generation amount was divided by the battery capacity (Ah) to calculate the gas generation amount (cc / Ah) based on the battery capacity.

[0260] (5C / 0.2C Discharge Capacity Retention Rate) The secondary batteries of the Examples and Comparative Examples were charged and discharged within a potential range of 1.0V to 3.0V. To test the discharge rate performance, after confirming the 0.2C discharge capacity, the charging current was set to 0.2C again for charging, and the 5C rapid discharge capacity was confirmed at room temperature. Then, the 5C discharge capacity was divided by the 0.2C discharge capacity and multiplied by 100 to obtain the discharge capacity retention rate (%). The 5C / 0.2C discharge capacity retention rate (%) is an indicator for evaluating output performance.

[0261] (Cycle Capacity Retention Rate) The secondary batteries of the Examples and Comparative Examples were subjected to life tests at 25°C, with repeated 1C charge-discharge cycles within a potential range of 1.0V to 3.0V. Under these conditions, 1000 charge-discharge cycles were repeated (charge and discharge constitute one cycle), and the discharge capacity retention rate after 1000 cycles was investigated. To confirm the discharge capacity retention rate after 1000 cycles, a charge-discharge cycle was performed again at 0.2C (time-based discharge rate). The discharge capacity after 1000 cycles was divided by the initial discharge capacity and then multiplied by 100 to calculate the cycle capacity retention rate (%) with the initial discharge capacity as 100%. The discharge capacity retention rate after 1000 cycles is an indicator for evaluating cycle life performance.

[0262] The materials, measurement results, and test results of the various embodiments and comparative examples described above are summarized in the table. Table 1 shows the types of negative electrode active materials, the hydroxyl content of niobium-containing oxides, the types of carbon-containing materials, and the functional group content of carbon-containing materials. Table 2 shows the dimensions of carbon-containing materials (average fiber diameter of fibrous carbon-containing materials, average thickness of planar carbon-containing materials, and average particle size of granular carbon-containing materials), gas generation, 5C / 0.2C discharge capacity retention rate, and cycle capacity retention rate. In the dimensions of carbon-containing materials, carbon-containing materials not included in the secondary battery being measured are indicated by "-".

[0263] In Examples 1-12, the hydroxyl content of the niobium oxide contained in the negative electrode was all below 0.25 mmol / g, and the functional group content of the carbon-containing material was all below 5 mmol / g. These examples exhibited low gas generation and high 5C / 0.2C discharge capacity retention. In other words, the results showed suppressed gas generation and high output performance. This is believed to be because the low hydroxyl content of the niobium oxide contained in the electrode suppresses gas generation, and the low hydroxyl content of the niobium oxide and the low functional group content of the carbon-containing material allow for the formation of a good conductive path.

[0264] Furthermore, the secondary battery systems in the embodiments all exhibit high cycle capacity retention rates. This is believed to be because the niobium oxide in the electrodes has a low hydroxyl content and the carbon-containing material has a low functional group content. Therefore, even after charge-discharge cycles, the niobium oxide and carbon-containing material are not easily separated, thereby improving cycle life performance.

[0265] As can be seen from Examples 1 to 9, even if the types of carbon-containing materials vary or the carbon-containing materials with different shapes are combined, a secondary battery with low gas generation, high 5C / 0.2C discharge capacity retention rate, and high cycle capacity retention rate can be obtained.

[0266] Comparing Examples 1 and 2, which contain granular carbon-containing materials, Example 1, which contains acetylene black containing crystalline carbon black, shows superior performance in terms of gas generation, 5C / 0.2C discharge capacity retention, and cycle capacity retention.

[0267] Comparing Examples 4 and 5, which contain fibrous carbon materials, Example 4, which contains fibrous carbon materials with an average fiber diameter of less than 10 nm, shows better performance in terms of gas generation, 5C / 0.2C discharge capacity retention, and cycle capacity retention.

[0268] Comparing Examples 6 and 8, which contain fibrous carbon materials and granular carbon materials, Example 6, where the average fiber diameter of the fibrous carbon material is da and the average particle size of the granular carbon material is db (db < 10da), exhibits superior performance in terms of gas generation, 5C / 0.2C discharge capacity retention, and cycle capacity retention. This is believed to be because the average particle size of the granular carbon material is not too large relative to the average fiber diameter of the fibrous carbon material, thus preventing the fibrous carbon material from covering the granular carbon material, resulting in good dispersion of the fibrous carbon material in the electrode.

[0269] Comparing Examples 7 and 9, which contain fibrous carbon materials and plate-shaped carbon materials, Example 7, where the average fiber diameter of the fibrous carbon material is da and the average thickness of the plate-shaped carbon material is ta, shows superior performance in terms of gas generation, 5C / 0.2C discharge capacity retention, and cycle capacity retention. This is believed to be because the average thickness of the plate-shaped carbon material is not too large relative to the average fiber diameter of the fibrous carbon material, thus preventing the fibrous carbon material from covering the plate-shaped carbon material, resulting in good dispersion of the fibrous carbon material in the electrode.

[0270] As can be seen from Examples 1, 10 to 12, even if the type of niobium oxide contained in the negative electrode active material is changed, a secondary battery with low gas generation, high 5C / 0.2C discharge capacity retention rate, and high cycle capacity retention rate can be obtained.

[0271] Comparative Example 1 was similar to Example 6 in that it employed a liquid-phase spray drying method for the synthesis of niobium oxides. However, the shear force was higher under the dry ball milling conditions compared to Example 6, and the process lasted for 48 hours, resulting in excessive shear force. Consequently, the surface crystallinity of the niobium oxide particles decreased, leading to an increase in the hydroxyl content of the niobium oxides and an increase in gas production.

[0272] Although Comparative Example 2 used the same materials as Example 6 to fabricate the secondary battery, the carbon-containing material had a higher content of functional groups. This is believed to be due to excessively high circumferential speed and low flow rate of the glass bead mill used for dispersion during the preparation of the negative electrode slurry, resulting in excessive shear force, which reduced the crystallinity of the carbon-containing material, or due to the reaction between the solvent and the carbon-containing material, making it easier for functional groups to adhere to the carbon-containing material. Thus, Comparative Example 2 was inferior to the Example in terms of gas generation, 5C / 0.2C discharge capacity retention, and cycle capacity retention.

[0273] Comparative Example 3 was inferior to the Example in terms of gas generation, 5C / 0.2C discharge capacity retention, and cycle capacity retention. The negative electrode of the secondary battery in Comparative Example 3 contained MWCNT as a fibrous carbon-containing material and furnace black as granular carbon. Compared with SWCNT, which is also a fibrous carbon, the MWCNT system tended to have a higher functional group content. Compared with acetylene black, which is also a granular carbon, the furnace black system tended to have a higher functional group content. Due to the use of carbon-containing materials with high functional group content, the overall functional group content of the carbon-containing material exceeded 5 mmol / g, resulting in increased gas generation and decreased 5C / 0.2C discharge capacity retention and cycle capacity retention.

[0274] An electrode is provided according to at least one embodiment or example described above. The electrode system comprises niobium-containing oxide and carbon-containing material. The hydroxyl content of the niobium-containing oxide is 0.25 mmol / g or less. The functional group content of the carbon-containing material is 5 mmol / g or less. This electrode suppresses gas generation and has high output performance.

[0275] However, the above-mentioned implementation can be summarized as the following technical solution.

[0276] (Technical Case 1) An electrode comprising niobium oxide and carbon-containing material, wherein the hydroxyl content of the aforementioned niobium oxide is 0.25 mmol / g or less, and the functional group content of the aforementioned carbon-containing material is 5 mmol / g or less.

[0277] (Technical Case 2) The aforementioned carbon-containing material is an electrode described in Technical Case 1, which is selected from at least one of the group consisting of fibrous carbon-containing materials, granular carbon-containing materials and plate-shaped carbon-containing materials.

[0278] (Technical Case 3) The aforementioned carbon-containing material is the electrode described in Technical Case 1 or 2, which contains fibrous carbon-containing materials with an average fiber diameter of less than 10 nm.

[0279] (Technical Case 4) The aforementioned carbon-containing material is an electrode containing crystalline carbon black as described in any one of Technical Cases 1 to 3.

[0280] (Technical Case 5) The aforementioned carbon-containing material includes the aforementioned fibrous carbon-containing material and the aforementioned granular carbon-containing material, and satisfies Formula A. In Formula A, da is the average fiber diameter of the aforementioned fibrous carbon-containing material, and db is the average particle diameter of the aforementioned granular carbon-containing material. The electrode described in any one of Technical Cases 2 to 4.

[0281] (Technical Case 6) The aforementioned carbon-containing material includes the aforementioned fibrous carbon-containing material and plate-shaped carbon-containing material, and satisfies Formula B, in the aforementioned Formula B, da is the average fiber diameter of the aforementioned fibrous carbon-containing material, and ta is the average thickness of the aforementioned plate-shaped carbon-containing material. The electrode described in any one of Technical Cases 2 to 5.

[0282] (Technical Case 7) The aforementioned carbon-containing material further includes the aforementioned flat carbon-containing material and satisfies Formula B, in Formula B, where da is the aforementioned average fiber diameter and ta is the aforementioned average thickness of the flat carbon-containing material as recorded in the electrode of Technical Case 5.

[0283] (Technical Case 8) The aforementioned granular carbon containing material is an electrode containing crystalline carbon black as described in any one of Technical Cases 2 to 7.

[0284] (Technical Case 9) A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the aforementioned negative electrode is an electrode described in any one of Technical Cases 1 to 8.

[0285] (Technical Case 10) A battery pack comprising the secondary battery described in Technical Case 9.

[0286] (Technical Case 11) The battery pack further includes an external terminal for power supply and a protection circuit as described in Technical Case 10.

[0287] (Technical Case 12) Includes a plurality of the aforementioned secondary batteries, wherein the aforementioned secondary batteries are connected in series, parallel or a combination of series and parallel electrical connections as described in Technical Case 10 or 11.

[0288] (Technical Application 13) A vehicle equipped with a battery pack described in any one of Technical Applications 10 to 12.

[0289] (Technical Case 14) A vehicle described in Technical Case 13 that includes a mechanism for converting the kinetic energy of the aforementioned vehicle into regenerative energy.

[0290] Although several embodiments of the present invention have been described, these embodiments are provided 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, substitutions, or modifications can be made without departing from the spirit and scope of the invention. These embodiments or modifications are included in the scope or spirit of the invention, as well as the invention described in the patent claim and its equivalents. [Simplified Explanation of the Diagram]

[0015] [Fig. 1] A schematic cross-sectional view of an example of a secondary battery according to the embodiment. [Fig. 2] An enlarged cross-sectional view of part A of the secondary battery shown in Fig. 1. [Fig. 3] A partial notch perspective view of another example of a secondary battery according to the embodiment. [Fig. 4] An enlarged cross-sectional view of part B of the secondary battery shown in Fig. 3. [Fig. 5] A perspective view of an example of a battery pack according to the embodiment. [Fig. 6] An exploded perspective view of an example of a battery pack according to the embodiment. [Fig. 7] A block diagram showing an example of the circuit of the battery pack shown in Fig. 6. [Fig. 8] A partial perspective view of an example of a vehicle according to the embodiment. [Fig. 9] A schematic diagram of an example of the control system of the electrical system of the vehicle according to the embodiment.

Claims

1. An electrode characterized by comprising a niobium oxide and a carbon-containing material, wherein the hydroxyl content of the niobium oxide is less than 0.25 mmol / g, and the functional group content of the carbon-containing material is less than 5 mmol / g.

2. The electrode as described in claim 1, wherein, The aforementioned carbon-containing material is selected from at least one of the group consisting of fibrous carbon-containing materials, granular carbon-containing materials and flat carbon-containing materials.

3. The electrode as described in claim 2, wherein, The aforementioned carbon-containing materials include the aforementioned fibrous carbon-containing materials with an average fiber diameter of less than 10 nm.

4. The electrode as described in claim 1, wherein, The aforementioned carbon-containing materials include crystalline carbon black.

5. The electrode as described in claim 2 or 3, wherein, The aforementioned carbon-containing material includes the aforementioned fibrous carbon-containing material and the aforementioned granular carbon-containing material, and satisfies Formula A, in which da is the average fiber diameter of the aforementioned fibrous carbon-containing material and db is the average particle size of the aforementioned granular carbon-containing material.

6. The electrode as described in claim 2 or 3, wherein, The aforementioned carbon-containing material includes the aforementioned fibrous carbon-containing material and plate-shaped carbon-containing material, and satisfies Formula B, in Formula B, where da is the average fiber diameter of the aforementioned fibrous carbon-containing material and ta is the average thickness of the aforementioned plate-shaped carbon-containing material.

7. The electrode as described in claim 5, wherein, The aforementioned carbon-containing material further includes the aforementioned flat carbon-containing material and satisfies Formula B, in Formula B, where da is the aforementioned average fiber diameter and ta is the aforementioned average thickness of the flat carbon-containing material.

8. The electrode as described in claim 5, wherein, The aforementioned granular carbon contains materials including crystalline carbon black.

9. A secondary battery, characterized in that it comprises a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the electrode described in any one of claims 1 to 8.

10. A battery pack, characterized in that it comprises a secondary battery as described in claim 9.

11. The battery pack as described in claim 10, wherein, It also includes external terminals for power supply and protection circuitry.

12. The battery pack as described in claim 10 or 11, wherein, Includes a plurality of the aforementioned secondary batteries, wherein the aforementioned secondary batteries are electrically connected in series, parallel, or a combination of series and parallel connections.

13. A vehicle equipped with a battery pack as described in any one of claims 10 to 12.

14. The vehicle described in claim 13, wherein, It includes a mechanism for converting the kinetic energy of the aforementioned vehicle into regenerative energy.

Images