Electrode, Battery and Battery Pack

Abstract

According to an embodiment, an electrode containing an active material containing a titanium oxide is provided. The active material has an average primary particle size of 200 nm or more and 600 nm or less. Regarding the specific surface area S of the electrode based on the nitrogen adsorption method A and the pore specific surface area S based on the mercury intrusion method B satisfy the relationship of 0.3 ≤ S A / S B < 0.6.

Description

Technical Field

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

[0002] A lithium-ion secondary battery that charges and discharges by the movement of lithium ions between a positive electrode and a negative electrode has the advantages of high energy density and high output, and is widely used in small applications such as portable electronic devices and large applications such as electric vehicles and power supply and demand adjustment.

[0003] As a negative electrode active material, a non-aqueous electrolyte battery using spinel-type lithium titanate with a lithium insertion / extraction potential as high as about 1.55 V (vs. Li / Li + ) instead of a carbon material has also been put into practical use. Spinel-type lithium titanate has excellent cycle performance because of its small volume change during charge and discharge. In addition, since lithium metal does not precipitate during lithium insertion / extraction in the negative electrode containing spinel-type lithium titanate, a secondary battery having this negative electrode can be charged at high current and at low temperature. In order to further improve the high current performance and low temperature performance, attempts have been made to reduce the particle size of spinel-type lithium titanate.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-158396

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-105704

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 2007-18882

[0009] Patent Document 4: International Publication No. 2018 / 110708

[0010] Patent Document 5: Japanese Patent Application Laid-Open No. 2018-156865

[0011] Patent Document 6: Japanese Patent Application Laid-Open No. 2014-143004

[0012] Patent Document 7: Japanese Patent Application Laid-Open No. 9-161801

[0013] Non-Patent Documents

[0014] Non-Patent Document 1: "Fine Particle Handbook", Asakura Shoten (1991), written by Motoji Shinbo et al., pages 151-152

[0015] Non-Patent Document 2: "Powder Physical Property Measurement Methods", Asakura Shoten (1973), edited by Soichiro Hayakawa, pages 257-259 Summary of the Invention

[0016] Technical Problem to be Solved by the Invention

[0017] An object of the present invention is to provide an electrode for a battery that can achieve excellent large-current performance, cycle life performance, low gas generation, and high energy density at low temperatures, a battery including the electrode, and a battery pack including the battery.

[0018] Means for Solving the Technical Problem

[0019] According to an embodiment, an electrode containing an active material containing a titanium oxide is provided. The active material has an average primary particle size of 200 nm or more and 600 nm or less. Regarding the specific surface area S of the electrode based on the nitrogen adsorption method A and the pore specific surface area S based on the mercury intrusion method B satisfy the relationship of 0.3 ≤ S A / S B <0.6.

[0020] According to another embodiment, a battery including a positive electrode, a negative electrode, and an electrolyte is provided. At least one of the positive electrode and the negative electrode includes the above electrode.

[0021] Furthermore, according to another embodiment, a battery pack is provided. The battery pack includes the above battery. Brief Description of the Drawings

[0022] Figure 1 is a plan view schematically showing an example of an electrode according to an embodiment.

[0023] Figure 2 is a graph showing the particle size distribution of an electrode according to an example of an embodiment.

[0024] Figure 3 is a cross-section obtained by cutting a battery according to an example of an embodiment in the thickness direction.

[0025] Figure 4 is Figure 3 an enlarged cross-sectional view of part A of

[0026] Figure 5 is a partially cutaway perspective view of a battery according to another example of an embodiment.

[0027] Figure 6 is an exploded perspective view of a battery pack according to an example of an embodiment.

[0028] Figure 7 is showing Figure 6 a block diagram of the circuit of the battery pack shown in Detailed Description of the Embodiments

[0029] Hereinafter, embodiments will be described with reference to the drawings. In addition, the same reference numerals are given to the structures common to the embodiments, and redundant descriptions are omitted.

[0030] In addition, each figure is a schematic diagram for facilitating the explanation and understanding of the embodiments, and there are differences in its shape, size, ratio, etc. from the actual device, but they can be appropriately designed and changed with reference to the following description and known techniques.

[0031] (First Embodiment)

[0032] According to the first embodiment, an electrode is provided. The electrode contains an active material. The active material contains a titanium-containing oxide and has an average primary particle diameter of 200 nm or more and 600 nm or less. For the electrode, the specific surface area S obtained by the nitrogen adsorption method A and the pore specific surface area S obtained by the mercury intrusion method B satisfy the relationship of 0.3 ≤ S A / S B <0.6.

[0033] The electrode of the embodiment can be an electrode for a battery. As a battery that can include the electrode of the embodiment, for example, a secondary battery such as a lithium ion secondary battery can be cited. The secondary battery includes a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte. This electrode can be, for example, a negative electrode for a battery.

[0034] A secondary battery having a negative electrode containing a titanium-containing oxide has excellent cycle life performance and can be used at a large current and charged under low temperature conditions. However, when a secondary battery having a negative electrode containing a titanium-containing oxide is repeatedly charged and discharged under a large current and low temperature, a decrease in reversible capacity occurs. The inventors of the present invention conducted in-depth research to solve this problem related to a non-aqueous electrolyte battery having a negative electrode containing a titanium-containing oxide, and as a result, the electrode of the first embodiment was found.

[0035] The electrode of the first embodiment is an electrode containing a titanium-containing oxide having an average primary particle diameter of 200 nm or more and 600 nm or less as an electrode active material, and the specific surface area S measured by the nitrogen (N2) adsorption method A and the pore specific surface area S measured by the mercury intrusion method B satisfy the relationship of 0.3 ≤ S A / S B <0.6. By having such a configuration, this electrode can provide a battery that can suppress capacity reduction and has excellent life performance even when the battery is repeatedly subjected to charge and discharge cycles at a large current and low temperature.

[0036] The mechanism for improving the charge-discharge cycle performance in such an electrode is not fully understood, but is considered as follows. By reducing the primary particle size of the active material, the specific surface area increases, and thus the acceptance performance of lithium ions at high currents and low temperatures of the active material itself improves. However, by reducing the primary particle size, the volume of pores with relatively small pore diameters in the pores within the electrode increases. In pores with small pore diameters, it is difficult for lithium ions to diffuse at high currents and low temperatures, and thus the current distribution throughout the electrode becomes uneven. Therefore, it is considered that by repeatedly performing charge-discharge cycles, a decrease in capacity is likely to occur. In addition, the overvoltage increases in pores with small pore diameters, and thus gas is likely to be generated through side reactions. Furthermore, in the case of a material with a small primary particle size, it is difficult to obtain high crystallinity, and even in the initial state, the capacity of the active material decreases, and the energy density of the electrode may be low.

[0037] In this electrode, the average primary particle size of the active material particles is 200 nm or more and 600 nm or less, and thus good input performance can be exhibited even under high current conditions and low temperature conditions. Specifically, since the average primary particle size is 200 nm or more, the crystallinity of the active material can be improved, and thus the charge-discharge cycle performance and energy density of a battery using the electrode can be improved. By making the average primary particle size 600 nm or less, a battery with excellent low temperature input performance can be obtained.

[0038] In the specific surface area S measured by the nitrogen adsorption method for the electrode A mainly reflects the specific surface area of relatively small pores having a pore diameter on the order of 0.1 nm to 100 nm in the pores within the electrode. In contrast, in the pore specific surface area S measured for the electrode by mercury intrusion porosimetry B mainly reflects the specific surface area of relatively large pores having a pore diameter on the order of 1 nm to 1 mm in the pores within the electrode. That is, the ratio S A / S B becomes an index indicating the ratio of small pores to large pores in the electrode. In this electrode, the relationship 0.3 ≤ S A / S B <0.6 is satisfied, and thus in a battery using this electrode, cyclic degradation at high currents and low temperatures is suppressed, and the life performance is improved. The electrode can also achieve a battery with less gas generation and high energy density. Specifically, by making the ratio S A / S B 0.3 or more, the proportion of large pores in the electrode is not excessive, and thus the amount of active material per unit volume contained in the electrode can be sufficiently increased, and thus an electrode showing a high energy density can be obtained. In addition, if the ratio S A / S BIf it is less than 0.6, the proportion of small pores contained in the electrode is small, so the above-mentioned non-uniform current distribution and gas generation can be suppressed.

[0039] In the particle size distribution of the electrode based on the laser diffraction / scattering method, the average particle size D at a cumulative frequency of 90% starting from the small particle size side 90 Relative to the average particle size D at a cumulative frequency of 50% starting from the small particle size side 50 The ratio D 90 / D 50 Is preferably 5 or more and 10 or less. For an electrode having such a particle size distribution, the state of the fine pore diameter and the specific surface area of the fine pores is likely to be in the above-mentioned ratio S A / S B Range. Therefore, it is easier to obtain the effect of improving the cycle life performance.

[0040] Regarding the titanium-containing oxide contained in the active material, it is preferably that the half-peak width of the peak attributed to the (111) plane in the XRD pattern measured by powder X-ray diffraction (X-Ray Diffraction; XRD) described later is 0.15 or less. When the half-peak width of the (111) peak is 0.15 or less, the crystallinity of the particles of the titanium-containing oxide is high and the diffusivity of lithium ions in the particles is good, so the low-temperature input performance is high and the gas generation caused by overvoltage is reduced. Alternatively, when the crystallite diameter is large, the half-value width may also be 0.15 or less. In particles with a large crystallite diameter, there are few grain boundaries in the particles and the diffusivity of lithium ions in the particles is improved, so the low-temperature input performance is high and the gas generation caused by overvoltage is reduced. In addition, the (111) plane mentioned here refers to the lattice plane represented by Miller indices.

[0041] Next, the electrode of the first embodiment will be described in more detail.

[0042] The electrode may include a current collector and an active material-containing layer (electrode composite material layer). The active material-containing layer can be formed, for example, on one side or both sides of a strip-shaped current collector. The active material-containing layer may contain an active material and an optional conductive agent and binder.

[0043] The active material contains a titanium-containing oxide having an average primary particle size of 200 nm or more and 600 nm or less. The titanium-containing oxide preferably contains a lithium-titanium composite oxide. An electrode containing a titanium-containing oxide such as a lithium-titanium composite oxide can have an oxidation-reduction potential value of 0.4 V (vs. Li / Li +)The Li insertion potential is above the above value, so it can prevent the precipitation of metallic lithium on the electrode surface during repeated input and output at high current. The titanium-containing oxide particularly preferably contains a lithium-titanium composite oxide having a spinel-type crystal structure. As a specific example of such a spinel-type lithium-titanium composite oxide, there can be mentioned lithium titanate having a spinel structure represented by Li 4+a Ti5O 12 wherein the value of the subscript a varies during charge and discharge within the range of 0 ≤ a ≤ 3.

[0044] The active material may include primary particles and secondary particles of the above titanium-containing oxide. The primary particles of the titanium-containing oxide have the above average primary particle diameter. The secondary particles of the titanium-containing oxide include a plurality of primary particles having the above average primary particle diameter.

[0045] The average particle diameter (average secondary particle diameter) of the secondary particles is preferably 1 μm or more and 100 μm or less. If the average particle diameter of the secondary particles is within this range, it is easy to handle in industrial production. In addition, in the coating film for making an electrode, the quality and thickness can be made uniform. Furthermore, a decrease in the surface smoothness of the electrode can be prevented. The average particle diameter of the secondary particles is more preferably 2 μm or more and 30 μm or less.

[0046] The specific surface area of the secondary particles measured by the BET method is preferably 3 m 2 / g or more and 50 m 2 / g or less. When the specific surface area is 3 m 2 / g or more, the insertion and deinsertion sites of lithium ions can be sufficiently ensured. When the specific surface area is 50 m 2 / g or less, it is easy to handle in industrial production. More preferably, the specific surface area of the secondary particles measured by the BET method is 5 m 2 / g or more and 50 m 2 / g or less. The method for measuring the specific surface area by the BET method will be described later.

[0047] The active material may also contain a further active material other than the above titanium-containing oxide. Here, for convenience, the active material containing the above titanium-containing oxide is sometimes referred to as the "first active material", and the further active material other than this is referred to as the "second active material". When the second active material is contained in addition to the first active material, as the second active material, an active material material capable of exhibiting a Li insertion potential of 0.4 V (vs. Li / Li ` ) or more is preferably used. When the second active material is included, the mass ratio of the second active material to the first active material is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less.

[0048] The conductive agent can improve the current collection performance and inhibit the contact resistance between the active material and the current collector. Examples of the conductive agent include carbonaceous materials such as acetylene black, carbon black, graphite, carbon nanofibers, and carbon nanotubes. These carbonaceous materials can be used alone or multiple carbonaceous materials can be used.

[0049] The binder can bond the active material, the conductive agent, and the current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber, acrylic resin and its copolymer, polyacrylic acid, and polyacrylonitrile.

[0050] The mixing ratios of the active material, the conductive agent, and the binder are preferably as follows: the active material is in the range of 70% by mass or more and 96% by mass or less, the conductive agent is 2% by mass or more and 28% by mass or less, and the binder is 2% by mass or more and 28% by mass or less. By making the amount of the conductive agent 2% by mass or more, the current collection performance of the active material-containing layer can be improved, and excellent high-current performance and low-temperature performance are expected. In addition, by making the amount of the binder 2% by mass or more, the adhesion between the active material-containing layer and the current collector becomes sufficient, and excellent cycle performance can be expected.

[0051] On the other hand, from the viewpoint of high capacity, the conductive agent and the binder are preferably 28% by mass or less, respectively.

[0052] The thickness of the active material-containing layer is preferably 20 μm or more and 80 μm or less. When the active material-containing layer is provided on the main surfaces on both the front and back sides of the current collector, the thickness referred to here is the thickness of each side. If the thickness of the active material-containing layer is 20 μm or more, in the battery, the proportion of the active material-containing layer relative to the current collector or auxiliary components other than the active material-containing layer such as the separator in the battery becomes relatively large, so the energy density of the battery can be improved. By making the thickness 80 μm or less, the diffusion distance of lithium ions in the active material-containing layer becomes shorter, and the influence of the resistance of the electrolyte becomes smaller, so the current distribution in the electrode becomes more uniform. When the thickness of the active material-containing layer is relatively thick, at the end of charging, compared with the diffusion of lithium ions in the active material particles, the diffusion of lithium ions in the active material-containing layer is likely to become rate-limiting, and there is a tendency to show the influence of the resistance of the electrolyte.

[0053] The current collector is preferably formed of aluminum foil or an aluminum alloy foil containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 20 μm or less, more preferably 15 μm or less.

[0054] Next, a specific example of the electrode of the first embodiment will be described with reference to the accompanying drawings.

[0055] Figure 1 It is a partially cutaway top view schematically showing an example of the electrode of the embodiment. Here, as an example of the electrode, a negative electrode is illustrated.

[0056] Figure 1 The negative electrode 4 shown includes a negative electrode current collector 4a and a negative electrode active material-containing layer 4b provided on the surface of the negative electrode current collector 4a. The negative electrode active material-containing layer 4b is supported on the main surface of the negative electrode current collector 4a.

[0057] In addition, the negative electrode current collector 4a includes a portion where the negative electrode active material-containing layer 4b is not provided on its surface. This portion functions as a negative electrode current collector tab 4c, for example. In the illustrated example, the negative electrode current collector tab 4c becomes a narrow portion having a width narrower than that of the negative electrode active material-containing layer 4b. The width of the negative electrode current collector tab 4c may be narrower than the width of the negative electrode active material-containing layer 4b in this way, or may be the same as the width of the negative electrode active material-containing layer 4b. Instead of the negative electrode current collector tab 4c that is a part of the negative electrode current collector 4a, a separate conductive member may be electrically connected to the negative electrode 4 and used as an electrode current collector tab (negative electrode current collector tab).

[0058] [Manufacture of Electrode]

[0059] This electrode can be manufactured as follows.

[0060] First, an active material containing a titanium oxide is prepared. The titanium oxide can be synthesized by a solid-phase method, for example. The titanium oxide can also be synthesized by wet synthesis methods such as a sol-gel method or a hydrothermal method other than this.

[0061] First, according to the target composition, a Ti source and a Li source are prepared, for example. These raw materials can be compounds such as oxides or salts, for example. As the Li source, lithium hydroxide, lithium oxide, lithium carbonate, etc. can be used.

[0062] Next, the prepared raw materials are mixed in an appropriate stoichiometric ratio to obtain a mixture. For example, in the case of synthesizing a spinel-type lithium titanium composite oxide represented by the composition formula Li4Ti5O 12 TiO2 and Li2CO3 can be mixed so that the molar ratio of Li:Ti in the mixture is 4:5.

[0063] When mixing the raw materials, it is preferable to sufficiently pulverize and mix the raw materials. By mixing the sufficiently pulverized raw materials, the raw materials easily react with each other, and generation of impurities can be suppressed when synthesizing the titanium oxide. In addition, Li may be mixed in an amount more than the specified amount. In particular, since there is a concern that Li is lost during heat treatment, it may be added in an amount more than the specified amount.

[0064] In the case of using the wet method, the raw materials are dissolved in pure water, and the resulting solution is dried while being stirred to obtain a precursor for firing. Examples of the drying method include spray drying, granulation drying, freeze drying, or a combination thereof.

[0065] Next, the mixture or the precursor for firing obtained by the previous mixing is heat-treated at a temperature of 750°C or higher and 1000°C or lower for a time of 30 minutes or longer and 24 hours or shorter. When the temperature is lower than 750°C, it is difficult to obtain sufficient crystallization. On the other hand, when the temperature is higher than 1000°C, excessive grain growth occurs, resulting in coarse particles, which is not preferable. Similarly, when the heat treatment time is less than 30 minutes, it is difficult to obtain sufficient crystallization. In addition, if the heat treatment time is longer than 24 hours, excessive grain growth occurs, resulting in coarse particles, which is not preferable. The firing can be carried out in the air. In addition, the firing can also be carried out in an oxygen atmosphere, a nitrogen atmosphere, or an argon atmosphere.

[0066] It is preferable to heat-treat the mixture at a temperature of 800°C or higher and 950°C or lower for a time of 1 hour or longer and 5 hours or shorter. By such heat treatment, a titanium-containing oxide can be obtained. In addition, pre-firing can also be carried out before the formal firing. The pre-firing is carried out at a temperature of 450°C or higher and 700°C or lower for 5 hours or longer and 24 hours or shorter.

[0067] By subjecting the specimen obtained by the formal firing to a pulverization treatment, primary particles in which the aggregates (secondary particles) are broken can be produced. As the pulverization method, for example, a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a bead mill, a jet mill, a counter jet mill, a cyclone jet mill, etc. can be used. In the pulverization, wet pulverization in which a liquid pulverization aid such as water, ethanol, ethylene glycol, benzene, or hexane coexists can be used. The pulverization aid is effective for improving the pulverization efficiency and increasing the amount of fine powder generated. A more preferable method is a ball mill using zirconia balls as the medium, and wet pulverization in which a liquid pulverization aid is preferably added. Furthermore, an organic substance such as a polyol that improves the pulverization efficiency can also be added as the pulverization aid. The type of polyol is not particularly limited, but pentaerythritol, trihydroxyethyl ethane, trimethylolpropane, etc. can be used alone or in combination.

[0068] Alternatively, re-firing can be carried out after the pulverization treatment. By adjusting the firing conditions, the average crystallite diameter of the titanium-containing oxide particles can be controlled. The re-firing can be carried out in the atmosphere, or can also be carried out in an inert atmosphere such as an oxygen atmosphere, nitrogen, or argon. The re-firing can be carried out at a temperature of 250°C or higher and 900°C or lower for about 1 minute or more and 10 hours or less. If it is 900°C or higher, the firing of the pulverized powder progresses. Even for a short-time heat treatment, due to the sintering between the powder particles, the pores in the electrode are flattened, and it is difficult to obtain the above-mentioned relationship of the fine pore diameter. If it is lower than 250°C, the impurities (organic substances) attached during wet pulverization cannot be removed, and the battery performance is reduced. Preferably, the re-firing is carried out at a temperature of 400°C or higher and 700°C or lower for 10 minutes or more and 3 hours or less. Additionally, it is preferable to perform cleaning using an aqueous solvent before re-firing.

[0069] In addition, in order to obtain secondary particles, methods such as a spray dryer can be used. In order to obtain primary particles or secondary particles with a specific particle size, classification can be carried out as needed.

[0070] Next, an electrode paste is prepared using the active material containing the titanium-containing oxide prepared as above. In the case of further using a second active material other than the titanium-containing oxide, the second active material and the active material containing the titanium-containing oxide (first active material) are used together to prepare the electrode paste. Specifically, the active material, the conductive agent, and the binder are suspended in a solvent to prepare the paste. As the solvent (dispersion medium), for example, N-methylpyrrolidone (NMP) can be used.

[0071] By adjusting the content ratio, particle size, and the content ratio of the primary particles and secondary particles of each component (active material, conductive agent, binder) contained in the electrode, the state of the pores and the particle size distribution in the electrode can be controlled. In addition, the particle size distribution not only reflects the primary particles and secondary particles of the active material, but also reflects the content ratio of the conductive agent and the presence or absence of aggregation between the active material and the conductive agent. That is, the state of the pores and the particle size distribution of the obtained electrode are affected by the content ratio of each component in the electrode paste and the state and content ratio of the primary particles and secondary particles of the active material. For example, there is a tendency that the pores with a relatively small fine pore diameter are more numerous in the part with a smaller primary particle size of the contained particles, and there is a tendency that the ratio S A / S B of the specific surface area of the pores becomes larger. However, if the ratio of the secondary particles increases relative to the ratio of the primary particles, there is a tendency that the value of S A / S B becomes smaller. That is, even if the average primary particle size is small, by appropriately controlling the content ratio of the primary particles and secondary particles, an increase in the pores with a small fine pore diameter can be suppressed.

[0072] In the preparation of the slurry, from the viewpoint of not destroying the secondary particles and uniformly mixing when suspending the active material, conductive agent, and binder in the solvent, it is preferable to use a rotation-revolution mixer, planetary mixer, jet pump, homogenizer, etc. The solid component concentration of the slurry is preferably set to 40 wt% or more and 70 wt% or less. In the addition of the conductive agent, a paste in which the conductive agent is pre-dispersed in a solvent containing a dispersion material can also be used. By using such a paste, the kneading time can be shortened, and the breakage of secondary particles can be suppressed.

[0073] The particle size distribution obtained by measuring the slurry by the laser diffraction / scattering method is consistent with the particle size distribution obtained for the obtained electrode. Therefore, by measuring the particle size distribution in the slurry by the laser diffraction / scattering method, the particle size D can be confirmed in advance. 90 Relative to the particle size D 50 The ratio D 90 / D 50 Is 5 or more and 10 or less. Thereby, the ratio S A / S B Of 0.3 ≤ S A / S B <0.6 can be more reliably manufactured for the electrode within the range.

[0074] The slurry prepared as above is coated on one or both sides of the current collector, and then the coating film is dried. In this way, an electrode composite layer (including the active material layer) can be formed. Then, the electrode composite layer is pressed. In this way, the electrode of the first embodiment can be obtained.

[0075] <Measurement of Electrode>

[0076] Various measurement methods for the electrode will be described. Specifically, a method for confirming the presence of titanium-containing oxide in the electrode, a method for measuring the average primary particle size of the particles of the titanium-containing oxide, a method for measuring the pore specific surface area S A Based on the nitrogen adsorption method, a method for measuring the pore specific surface area S B Based on the mercury intrusion method, a method for measuring the particle size distribution, and a method for measuring the thickness of the active material layer will be described respectively.

[0077] When the electrode to be measured is assembled in the battery, the electrode as the measurement sample is taken out of the battery as follows. The battery is discharged, disassembled in a glove box under an argon atmosphere, and the electrode is taken out. After washing the electrode with diethyl carbonate, it is dried under vacuum. In this way, the measurement sample is obtained.

[0078] [Confirmation of Titanium-Containing Oxide]

[0079] As described below, by identifying the active material contained in the electrode, the presence or absence of the titanium-containing oxide can be confirmed.

[0080] As described above, after cleaning and drying the electrode taken out from the battery, the obtained electrode is pasted on a glass test plate. At this time, pay attention to using double-sided tape or the like for disposal so that the electrode does not peel off or float. If necessary, the electrode can also be cut into a size suitable for pasting on the glass test plate. In addition, a Si standard sample for correcting the peak position can also be applied to the electrode.

[0081] Next, the glass plate with the electrode pasted thereon is set in a powder X-ray diffraction (XRD) apparatus, and a diffraction pattern is obtained using Cu-Kα rays. Using Cu-Kα rays as the radiation source and measuring while changing 2θ in the measurement range of 5 to 90°, an X-ray diffraction pattern can be obtained.

[0082] As the apparatus for powder X-ray diffraction measurement, for example, SmartLab manufactured by Rigaku Corporation is used. The measurement conditions are as follows:

[0083] X-ray source: Cu target

[0084] Output: 45 kV, 200 mA

[0085] Soller slit: 5° for both incidence and light reception

[0086] Step size: 0.02 deg

[0087] Scanning speed: 20 deg / minute

[0088] Semiconductor detector: D / teX Ultra 250

[0089] Test plate holder: Flat glass test plate holder (thickness 0.5 mm)

[0090] Measurement range: Range of 5° ≤ 2θ ≤ 90°.

[0091] In the case of using other apparatuses, in such a way as to obtain measurement results equivalent to the above, measurement using a standard Si powder for powder X-ray diffraction is carried out, and conditions where the peak intensity and peak top position equivalent to those obtained by the above apparatus are consistent are found, and the sample is measured under these conditions.

[0092] In the case where the active material to be measured contains a spinel-type lithium titanium composite oxide, an X-ray diffraction pattern belonging to the space group Fd-3m can be confirmed by X-ray diffraction measurement. The peak existing in the range of 2θ of 17 to 19° in this X-ray diffraction pattern can be attributed to the (111) plane.

[0093] Next, observe the sample containing the active material with a Scanning Electron Microscope (SEM). In the SEM observation, it is also preferable to keep the sample from contacting the atmosphere and conduct the observation in an inert atmosphere such as argon or nitrogen.

[0094] In the SEM observation image at 3000 times magnification, select several particles with the morphology of primary particles or secondary particles confirmed within the field of view. At this time, select them in such a way that the particle size distribution of the selected particles becomes as wide as possible. For the observable active material particles, use Energy Dispersive X-ray spectroscopy (EDX) to determine the types and compositions of the constituent elements of the active material. Thereby, the types and amounts of elements other than Li among the elements contained in each of the selected particles can be determined. Perform the same operation on multiple active material particles respectively to judge the mixing state of the active material particles.

[0095] Next, for example, use a spatula or the like to separate the active material-containing layer from the current collector, thereby obtaining a powdery electrode composite material sample containing the active material. Wash the collected powdery sample with acetone and dry it. Dissolve the obtained powder in hydrochloric acid, filter out the conductive agent, and then dilute it with ion-exchanged water to prepare a measurement sample. Calculate the metal content ratio in the measurement sample by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES).

[0096] In the case where there are multiple active materials, estimate their mass ratios based on the content ratios of the elements inherent to each active material. The ratio of the inherent element to the mass of the active material is judged based on the composition of the constituent elements obtained by energy dispersive X-ray spectroscopy.

[0097] In this way, the active materials contained in the electrode can be identified.

[0098] [Measurement of the average primary particle size of the active material]

[0099] As described above, after cleaning and drying the electrode taken out from the battery, for example, use a spatula or the like to separate the active material-containing layer from the current collector, thereby obtaining a powdery electrode composite material sample containing the active material.

[0100] Next, analyze the powdery sample using the X-ray diffraction measurement and SEM-EDX described above to confirm the presence of the active material particles to be measured.

[0101] The magnification during SEM observation is preferably about 5000 times. In cases where it is difficult to distinguish the particle morphology due to additives such as conductive agents, use an SEM equipped with a focused ion beam (FIB) (FIB-SEM), etc., to obtain an image of the electrode cross-section (for example, the cross-section including the active material layer) and observe it. The magnification is adjusted to obtain an image containing 50 or more particles.

[0102] Next, measure the particle sizes of all the particles contained in the obtained image. For particles having a secondary particle morphology, measure the particle sizes of each primary particle contained in the secondary particle. In the case where the particle is spherical, set its diameter as the particle size. In the case where the particle has a shape other than spherical, first, measure the length of the minimum diameter of the particle and the length of the maximum diameter of the same particle. Take their average as the average primary particle size.

[0103] [Measurement of Pore Specific Surface Area Based on Nitrogen Adsorption Method]

[0104] Regarding the pore specific surface area S of the electrode based on the nitrogen adsorption method A Corresponds to the BET specific surface area of the electrode. The BET specific surface area refers to the specific surface area determined by the BET method and is calculated by the nitrogen adsorption method. The analysis is carried out, for example, by the following method.

[0105] The electrode obtained by washing and drying after being taken out of the battery as described above is cut according to the size of the measurement cell and used as a measurement sample. For the measurement cell, a 1 / 2-inch glass cell is used, for example. As a pretreatment method, perform a degassing treatment on this measurement cell by carrying out a reduced-pressure drying at a temperature of about 100 °C or higher for 15 hours. As a measurement device, for example, use Quadrasorb QS-20 manufactured by Quantachrome Instruments.

[0106] Put the cut electrode as the measurement sample into the measurement cell and flow a mixed gas of 30% nitrogen - helium balance. While making the gas flow, immerse the glass cell in liquid nitrogen to adsorb the nitrogen in the mixed gas on the sample surface. After the adsorption ends, return the glass cell to room temperature to desorb the adsorbed nitrogen. Then, since the nitrogen concentration in the mixed gas increases, quantify the increase amount. Based on this nitrogen amount and the cross-sectional area of nitrogen molecules, calculate the surface area of the sample (m 2 ). Divide it by the sample amount (g) to calculate the specific surface area (pore specific surface area S A ; numerical unit: m 2 / g).

[0107] [Measurement of Pore Specific Surface Area Based on Mercury Intrusion Method]

[0108] The following describes the method for measuring the specific surface area S of pores of an electrode based on the mercury intrusion method. B

[0109] As the measuring device, a pore size distribution measuring device, the fully automatic mercury porosimeter 9520 type manufactured by Shimadzu Corporation, or a device having an equivalent function can be used. As the specimen, a specimen piece obtained by cutting the washed and dried electrode into a strip of about 12.5 mm × 25 mm is used.

[0110] Sixteen specimen pieces are used for the standard large piece unit, and the measurement is carried out under the conditions of an initial pressure of 20 kPa (equivalent to about 3 psia, pore diameter of about 60 μm) and a final pressure of 414000 kPa (equivalent to about 60000 psia, pore diameter of about 0.003 μm). The specific surface area of pores (specific surface area S B ; numerical unit: m 2 / g) calculates the shape of the pores as cylindrical.

[0111] In addition, the analysis principle of the mercury intrusion method is based on the following Washburn's formula (1).

[0112] D = -4γcosθ / P (1)

[0113] Here, D is the pore diameter, γ is the surface tension of mercury (480 dyne·cm -1 ), θ is the contact angle between mercury and the pore wall surface (140°), and P is the applied pressure. Since γ and θ are constants, the relationship between the applied pressure P and the pore diameter D is obtained according to Washburn's formula (1), and by measuring the mercury intrusion volume at this time, the pore diameter and its volume distribution can be derived. For details of the measurement method, principle, etc., reference can be made to Non-Patent Document 1 or Non-Patent Document 2, etc.

[0114] [Measurement of particle size distribution]

[0115] The particle size distribution of the electrode can be measured by the laser diffraction / scattering method described below.

[0116] After washing and drying the electrode taken out from the battery, for example, using a spatula or the like, the active material layer is separated from the current collector, and thus a powdery electrode composite material specimen containing the active material is obtained. Then, the powdery specimen is put into a measurement unit filled with N-methylpyrrolidone (NMP) until it reaches a measurable concentration. In addition, the capacity of the measurement unit and the measurable concentration vary depending on the particle size distribution measuring device.

[0117] ​For the measurement unit of the electrode composite material sample added with NMP and dissolved therein, ultrasonic waves are irradiated for 5 minutes. The output of the ultrasonic waves is, for example, in the range of 35 W to 45 W. For example, when using NMP as a solvent in an amount of about 50 ml, ultrasonic waves with an output of about 40 W are irradiated to the solvent mixed with the measurement sample for 300 seconds. According to such ultrasonic irradiation, conductive agent particles and active material particles can be uniformly dispersed in the solvent.

[0118] Insert the measurement unit into a particle size distribution measuring device using the laser diffraction / scattering method to measure the particle size distribution. Examples of the particle size distribution measuring device include Microtrac3100 and Microtrac3000 II.

[0119] In this way, the particle size distribution of the electrode can be obtained.

[0120] An example of the particle size distribution measured by the laser diffraction / scattering method for this electrode is shown as a curve in Figure 2 . This curve graph corresponds to a histogram representing the particle size distribution of the particles contained in the electrode.

[0121] [Measurement of the thickness of the active material layer]

[0122] The thickness of the active material layer can be measured by SEM observation. As described above, after cleaning and drying the electrode taken out from the battery, the thickness of the active material layer after removing the current collector is measured using SEM.

[0123] The electrode of the first embodiment includes an active material having an average primary particle size of 200 nm or more and 600 nm or less. The active material includes titanium oxide-containing. The specific surface area S of the electrode obtained by the nitrogen adsorption method A and the pore specific surface area S of the electrode obtained by the mercury intrusion method B satisfy the relationship of 0.3 ≤ S A / S B <0.6. This electrode can achieve a battery with excellent high-current performance, cycle life performance, less gas generation, and high energy density at low temperatures.

[0124] (Second Embodiment)

[0125] According to the second embodiment, a battery is provided. The battery includes a positive electrode, a negative electrode, and an electrolyte. At least one of the positive electrode and the negative electrode includes the electrode of the first embodiment.

[0126] The battery may further include a separator disposed between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the separator may form an electrode assembly. The electrolyte may be held in the electrode assembly.

[0127] In addition, the battery may further include an outer packaging member for housing the electrode assembly and the electrolyte.

[0128] Furthermore, the battery may further include a positive electrode terminal electrically connected to the positive electrode and a negative electrode terminal electrically connected to the negative electrode. At least a part of the positive electrode terminal and at least a part of the negative electrode terminal can extend to the outside of the outer packaging member.

[0129] The battery may be, for example, a lithium ion secondary battery. In addition, the battery includes, for example, a non-aqueous electrolyte battery containing a non-aqueous electrolyte as the electrolyte.

[0130] Hereinafter, the negative electrode, the positive electrode, the electrolyte, the separator, the outer packaging member, the positive electrode terminal, and the negative electrode terminal will be described in detail.

[0131] (1) Negative electrode

[0132] The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer (negative electrode composite material layer) carried on one or both sides of the negative electrode current collector and containing a negative electrode active material, a conductive agent, and a binder.

[0133] The negative electrode may be the electrode of the first embodiment. In the case of the negative electrode, the negative electrode current collector, the negative electrode active material, and the negative electrode active material-containing layer of the negative electrode correspond to the current collector, the active material, and the active material-containing layer of the electrode of the first embodiment, respectively. Since the electrode of the first embodiment has been described in detail above, the description of the negative electrode here is omitted.

[0134] (2) Positive electrode

[0135] The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer (positive electrode composite material layer) carried on one or both sides of the positive electrode current collector and containing a positive electrode active material, a conductive agent, and a binder.

[0136] The battery of the second embodiment may include the electrode of the first embodiment as the positive electrode. Alternatively, the battery may include a positive electrode having a structure different from that of the electrode of the first embodiment. Hereinafter, the positive electrode in a manner different from that of the electrode of the first embodiment will be described.

[0137] Examples of the positive electrode active material include lithium-containing nickel cobalt manganese oxide (for example, represented by Li w Ni x Co y Mn z O2, where 0 < w ≤ 1 and x + y + z = 1; or represented by Li 1-s Ni 1-t-u-v Co t Mn u M1 vO2 represents a compound in which M1 is 1 or more selected from the group consisting of Mg, Al, Si, Ti, Zn, Zr, Ca, and Sn, -0.2 < s < 0.5, 0 < t < 0.5, 0 < u < 0.5, 0 ≤ v < 0.1, and t + u + v < 1). In addition, various oxides can also be included, such as lithium-containing cobalt oxides (e.g., LiCoO2), manganese dioxide, lithium manganese composite oxides (e.g., LiMn2O4, LiMnO2), lithium-containing nickel oxides (e.g., LiNiO2), lithium-containing nickel cobalt oxides (e.g., LiNi 0.8 Co 0.2 O2), lithium-containing iron oxides, lithium-containing vanadium oxides, chalcogen compounds such as titanium disulfide and molybdenum disulfide, etc. The type of the positive electrode active material used can be one type or two or more types.

[0138] Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide, polyamide, etc. The type of the binder can be one type or two or more types.

[0139] Examples of the conductive agent include carbon blacks such as acetylene black and Ketjen black, graphite, carbon fiber, carbon nanotube, fullerene, etc. The type of the conductive agent can be one type or two or more types.

[0140] The mixing ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer is preferably 80% by mass or more and 95% by mass or less for the positive electrode active material, 3% by mass or more and 18% by mass or less for the conductive agent, and 2% by mass or more and 17% by mass or less for the binder.

[0141] As the current collector, an aluminum foil or an aluminum alloy foil is preferred. Its average crystal grain diameter is preferably 50 μm or less, more preferably 30 μm or less, and further preferably 5 μm or less. The current collector composed of an aluminum foil or an aluminum alloy foil having such an average crystal grain diameter can remarkably increase the strength, can densify the positive electrode at a high pressing pressure, and can increase the battery capacity.

[0142] The aluminum foil or the aluminum alloy foil with an average crystal grain diameter of 50 μm or less is complexly affected by many factors such as material composition, impurities, processing conditions, heat treatment history, and heating conditions of annealing. In the manufacturing process, the above-mentioned (diameter) is adjusted by combining the above factors.

[0143] The thickness of the current collector is preferably 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% or more. As the aluminum alloy, an alloy containing elements such as magnesium, zinc, and silicon is preferred. On the other hand, the content of transition metals such as iron, copper, nickel, and chromium is preferably 1% or less.

[0144] The positive electrode is produced, for example, by suspending a positive electrode active material, a conductive agent, and a binder in an appropriate solvent, coating the resulting slurry on a current collector, and drying it. After producing a positive electrode active material layer-containing product in this way, pressing is carried out. In addition, the positive electrode active material, the conductive agent, and the binder may be formed into particles and used as the positive electrode active material layer-containing product.

[0145] The positive electrode active material layer-containing product preferably has a porosity of 20% or more and 50% or less. The positive electrode having a positive electrode active material layer-containing product with such a porosity is high-density and has excellent affinity with the electrolyte. A more preferable porosity is 25% or more and 40% or less.

[0146] The density of the positive electrode active material layer-containing product is preferably 2.5 g / cm 3 or more.

[0147] (3) Electrolyte

[0148] Examples of the electrolyte include a liquid non-aqueous electrolyte prepared by dissolving an electrolyte salt (solute) in a non-aqueous solvent, and a gel-like non-aqueous electrolyte obtained by compounding a liquid non-aqueous electrolyte with a polymer material.

[0149] Examples of the electrolyte salt include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bis(trifluoromethanesulfonyl)imide [LiN(CF3SO2)2]. These electrolyte salts may be used alone or in combination of two or more.

[0150] The electrolyte salt is preferably dissolved in a range of 0.5 mol / L or more and 2.5 mol / L or less with respect to the non-aqueous solvent.

[0151] As non-aqueous solvents, for example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), etc.; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc.; cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), etc.; chain ethers such as dimethoxyethane (DME), etc.; cyclic esters such as γ-butyrolactone (BL), etc.; chain esters such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, etc.; acetonitrile (AN); organic solvents such as sulfolane (SL), etc. These organic solvents can be used alone or in the form of a mixture of two or more kinds.

[0152] As the polymer materials used in the gel-like non-aqueous electrolyte, for example, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), etc. can be cited.

[0153] (4)Separator

[0154] As the separator, for example, porous membranes containing polyethylene (PE), polypropylene (PP), cellulose or polyvinylidene fluoride (PVdF), non-woven fabrics made of synthetic resin, etc. can be cited.

[0155] (5)Outer packaging component

[0156] The outer packaging component can be formed of a laminated film or can be composed of a metal container. In the case of using a metal container, the lid can be integrated with the container or be a separate component. The wall thickness of the metal container is more preferably 0.5 mm or less, 0.2 mm or less. As the shape of the outer packaging component, flat type, square type, cylindrical type, coin type, button type, sheet type, laminated type, etc. can be cited. The outer packaging component can be not only for small batteries mounted on portable electronic devices, etc., but also for outer packaging components for large batteries mounted on two-wheeled or four-wheeled vehicles.

[0157] The wall thickness of the outer packaging component made of the laminated film is preferably 0.2 mm or less. As an example of the laminated film, a multilayer film including a resin film and a metal layer disposed between the resin films can be cited. For weight reduction, the metal layer is preferably an aluminum foil or an aluminum alloy foil. As the resin film, a polymer material such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET) can be used. The laminated film can be sealed by heat welding and formed into the shape of the outer packaging component.

[0158] The metal container is made of aluminum or an aluminum alloy. As the aluminum alloy, an alloy containing elements such as magnesium, zinc, and silicon is preferred. In aluminum or an aluminum alloy, the content of transition metals such as iron, copper, nickel, and chromium is 100 ppm or less, which is preferred in terms of dramatically improving the long-term reliability and heat dissipation in a high-temperature environment.

[0159] For a metal container made of aluminum or an aluminum alloy, the average crystal grain size is preferably 50 μm or less, more preferably 30 μm or less, and further preferably 5 μm or less. By setting the average crystal grain size to 50 μm or less, the strength of the metal container made of aluminum or an aluminum alloy can be dramatically increased, and further thinning of the container can be achieved. As a result, a lightweight, high-output, and long-term reliability-excellent battery suitable for in-vehicle use or the like can be realized.

[0160] Refer to Figure 3 and Figure 4 An example of this battery will be described. Figure 3 The flat battery shown includes a flat wound electrode group 1, an outer packaging component 2, a positive terminal 7, a negative terminal 6, and an electrolyte (not shown). The outer packaging component 2 is a bag-shaped outer packaging component made of a laminated film. The wound electrode group 1 is housed in the outer packaging component 2. As Figure 4 shown, the wound electrode group 1 includes a positive electrode 3, a negative electrode 4, and a separator 5, and is formed by winding a laminate laminated in the order of the negative electrode 4, the separator 5, the positive electrode 3, and the separator 5 from the outside into a spiral shape and press-forming it.

[0161] The positive electrode 3 includes a positive electrode current collector 3a and a positive electrode active material-containing layer 3b. The positive electrode active material-containing layer 3b contains a positive electrode active material. The positive electrode active material-containing layer 3b is formed on both surfaces of the positive electrode current collector 3a. The negative electrode 4 includes a negative electrode current collector 4a and a negative electrode active material-containing layer 4b. The negative electrode active material-containing layer 4b contains a negative electrode active material. In the outermost part of the negative electrode 4, the negative electrode active material-containing layer 4b is formed only on one surface, the inner surface side of the negative electrode current collector 4a. In other parts of the negative electrode 4, the negative electrode active material-containing layer 4b is formed on both surfaces of the negative electrode current collector 4a.

[0162] like Figure 3 As shown, a positive electrode terminal 7 is connected to the positive electrode 3 near the outer peripheral end of the wound electrode group 1. A negative electrode terminal 6 is connected to the outermost negative electrode 4. The positive electrode terminal 7 and the negative electrode terminal 6 extend to the outside through the opening of the outer casing 2.

[0163] The battery is not limited to the above Figure 3 and Figure 4 The structure shown can be, for example, Figure 5 The structure shown.

[0164] exist Figure 5 In the rectangular battery shown in FIG. 1 , a wound electrode group 11 is contained in a metal bottomed rectangular cylindrical container 12 as an outer packaging member. A rectangular cover 13 is welded to the opening of the container 12. The flat wound electrode group 11 may have, for example, the same shape as in FIG. Figure 3 and Figure 4 The structure is the same as the wound electrode group 1 described above.

[0165] One end of the negative electrode tab 14 is electrically connected to the negative electrode collector, and the other end is electrically connected to the negative electrode terminal 15. The negative electrode terminal 15 is fixed to the rectangular cover 13 via a hermetic seal of a glass material 16. One end of the positive electrode tab 17 is electrically connected to the positive electrode collector, and the other end is electrically connected to the positive electrode terminal 18 fixed to the rectangular cover 13.

[0166] The negative electrode tab 14 is made of, for example, aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. To reduce contact resistance with the negative electrode collector, the negative electrode tab 14 is preferably made of the same material as the negative electrode collector.

[0167] The positive electrode tab 17 is made of aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, Si, etc. The positive electrode tab 17 is preferably made of the same material as the positive electrode collector in order to reduce the contact resistance with the positive electrode collector.

[0168] The illustrated battery uses a wound electrode group in which a separator is wound together with positive and negative electrodes, but a stacked electrode group in which a separator is folded ninety-nine times and positive and negative electrodes are alternately arranged at the folded portions may be used.

[0169] The battery pack of the second embodiment includes the electrode of the first embodiment. Therefore, the battery can show excellent cycle life performance even when used at a large current and under low temperature conditions. In addition, the gas generated in the battery is small, and the battery has a high energy density.

[0170] (Third Embodiment)

[0171] According to the third embodiment, a battery pack is provided. The battery pack includes the battery of the second embodiment.

[0172] The battery pack of the third embodiment may include one or more of the batteries (single cells) of the second embodiment described above. The multiple batteries that can be included in the battery pack can be electrically connected in series or in parallel with each other, and can also form a battery pack. The battery pack may also include multiple battery groups.

[0173] Next, a battery pack according to an example of the third embodiment will be described with reference to the drawings.

[0174] Figure 6 FIG. is an exploded perspective view of a battery pack according to an example of the second embodiment. Figure 7 It shows Figure 6 a block diagram of the circuit of the battery pack.

[0175] Figure 6 and Figure 7 The battery pack 20 shown includes a plurality of single cells 21. The single cells 21 may be flat batteries according to an example of the second embodiment described with reference to Figure 5 above.

[0176] The plurality of single cells 21 are stacked in such a manner that the negative electrode terminals 51 and the positive electrode terminals 61 extending to the outside are aligned in the same orientation, and are formed into a battery group 23 by being fastened with an adhesive tape 22. These single cells 21 are electrically connected in series with each other as shown in Figure 7 FIG.

[0177] The printed wiring board 24 is disposed opposite to the sides where the negative electrode terminals 51 and the positive electrode terminals 61 of the single cells 21 extend. As shown in Figure 7 FIG., a thermistor 25, a protection circuit 26, and power supply terminals 27 for supplying power to an external device are mounted on the printed wiring board 24. In addition, an insulating plate (not shown) is mounted on the surface of the printed wiring board 24 that faces the battery group 23 to prevent unnecessary connection with the wiring of the battery group 23.

[0178] The positive electrode side lead 28 is connected to the positive electrode terminal 61 located at the lowermost layer of the battery group 23, and its tip is inserted into the positive electrode side connector 29 of the printed wiring board 24 for electrical connection. The negative electrode side lead 30 is connected to the negative electrode terminal 51 located at the uppermost layer of the battery group 23, and its tip is inserted into the negative electrode side connector 31 of the printed wiring board 24 for electrical connection. These connectors 29 and 31 are connected to the protection circuit 26 through wirings 32 and 33 formed on the printed circuit wiring board 24.

[0179] The thermistor 25 detects the temperature of the single cell 21 and sends the detection signal to the protection circuit 26. The protection circuit 26 can cut off the positive-side wiring 34a and the negative-side wiring 34b between the protection circuit 26 and the power supply terminal 27 for an external device under specified conditions. An example of the specified conditions is when the detected temperature of the thermistor 25 becomes equal to or higher than a specified temperature. Additionally, other examples of the specified conditions are when overcharging, overdischarging, overcurrent, etc. of the single cell 21 are detected. The detection of overcharging, etc. is performed for each single cell 21 or the entire battery pack 23. In the case of detecting each single cell 21, the battery voltage can be detected, or the positive electrode potential or the negative electrode potential can be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each single cell 21. In Figure 6 and Figure 7 for the battery pack 20, wirings 35 for voltage detection are respectively connected to the single cells 21. Detection signals are sent to the protection circuit 26 through these wirings 35.

[0180] On three sides of the battery pack 23 other than the sides where the positive terminal 61 and the negative terminal 51 protrude, protection sheets 36 made of rubber or resin are respectively arranged.

[0181] The battery pack 23, together with each protection sheet 36 and the printed circuit wiring board 24, is housed in a housing container 37. That is, the protection sheets 36 are respectively arranged on two inner sides in the long side direction and the inner side in the short side direction of the housing container 37, and the printed wiring board 24 is arranged on the inner side on the opposite side in the short side direction. The battery pack 23 is located in the space surrounded by the protection sheets 36 and the printed wiring board 24. A lid 38 is installed on the upper surface of the housing container 37.

[0182] Additionally, in fixing the battery pack 23, a heat shrink tape can be used instead of the adhesive tape 22. In this case, protection sheets are arranged on both sides of the battery pack, and after the heat shrink tape is wound around, the heat shrink tape is heat-shrunk to bundle the battery pack.

[0183] In Figure 6 and Figure 7 , a method of connecting the single cells 21 in series is shown, but in order to increase the battery capacity, they can also be connected in parallel. Furthermore, the assembled battery packs can be connected in series and / or in parallel.

[0184] Additionally, the form of this battery pack is appropriately changed according to the use. As the use of the battery pack, it is preferable to expect good cycle performance during the period of drawing a large current. As specific uses, power supply for digital cameras, on-vehicle use such as two-wheeled to four-wheeled hybrid electric vehicles, two-wheeled to four-wheeled electric vehicles, and assist bicycles can be cited. This battery pack is particularly suitable for on-vehicle use.

[0185] The battery pack of the third embodiment includes the battery of the second embodiment. Therefore, this battery pack can exhibit excellent cycle life performance even when used under high current and low temperature conditions. In addition, the gas generation in the battery pack is less, and the battery pack has a high energy density.

[0186] [Examples]

[0187] Hereinafter, the above embodiments will be further described in detail based on examples. Although the examples will be described, the present invention is not limited to the examples described below as long as it does not exceed the gist of the present invention.

[0188] (Example 1)

[0189] In Example 1, a non-aqueous electrolyte secondary battery of Example 1 was produced through the following steps.

[0190] [Fabrication of negative electrode]

[0191] Powder of lithium titanium composite oxide having a composition of Li4Ti5O 12 and a spinel structure was prepared in the following order.

[0192] First, anatase-type titanium oxide was added to a solution in which lithium hydroxide was dissolved in pure water, followed by stirring and drying. These raw materials were mixed so that the molar ratio of Li:Ti in the mixture was 4:5. Before mixing, the raw materials were sufficiently pulverized.

[0193] The mixed raw materials were subjected to heat treatment at 870 °C for 2 hours in an air atmosphere. Then, the fired product was pulverized using a ball mill with zirconia balls as the medium and washed with water. After heat treatment at 600 °C for 30 minutes in an air atmosphere, classification was performed. Thus, the powder of the product was obtained.

[0194] The average primary particle size of the obtained product powder was analyzed using SEM. As a result, it was found that the obtained product powder was primary particle-shaped particles with an average primary particle size of 400 nm.

[0195] A part of the above primary particles was granulated using a spray dryer. Thus, a powder in the form of secondary particles formed by aggregation of primary particles was obtained.

[0196] In addition, the composition and crystal structure of the obtained product were analyzed using ICP and X-ray diffraction measurement. As a result, it was found that the obtained product was a lithium titanium composite oxide having a spinel-type crystal structure and a composition of Li4Ti5O 12 In the X-ray diffraction spectrum, the half-value width of the peak attributed to the (111) plane was 0.15 or less, and thus it was found that a product with high crystallinity was obtained. The powder of this product was used as the negative electrode active material.

[0197] Next, acetylene black as a conductive agent was added to the powder of spinel-type lithium titanium composite oxide as a negative electrode active material, and the mixture was mixed using a Henschel mixer to obtain a mixture. At this time, adjustment was made so that the ratio of primary particles to secondary particles of the spinel-type lithium titanium composite oxide was 2 to 3 by weight (primary particles: secondary particles = 2:3). Next, polyvinylidene fluoride (PVdF) as a binder and N-methylpyrrolidone (NMP) as a dispersion medium were added to this mixture, and kneading was performed using a jet pump. Thus, a slurry (slurry for producing a negative electrode) was obtained.

[0198] In the above mixing, the addition amounts of acetylene black and PVdF were adjusted so that the ratio of the negative electrode active material: acetylene black: PVdF in the obtained slurry became 85 parts by mass: 10 parts by mass: 5 parts by mass.

[0199] This slurry was coated on both sides of a current collector composed of an aluminum foil with a thickness of 15 μm, and the coating film was dried at 125°C. Further, the dried coating film was subjected to a roll pressing treatment. Thus, a negative electrode having a current collector and a negative electrode active material layer formed on both sides of the current collector with an electrode density (excluding the current collector) of 2.1 g / cm3 was produced. The thickness of the negative electrode active material layer formed on each side of the current collector was 60 μm.

[0200] [Fabrication of Positive Electrode]

[0201] First, a powder of lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) was prepared as a positive electrode active material. 5 parts by mass of acetylene black as a conductive agent was added to 90 parts by mass of the positive electrode active material, and the mixture was mixed using a Henschel mixer to prepare a mixed positive electrode active material. Next, 5 parts by mass of PVdF and N-methylpyrrolidone (NMP) were added to this mixed positive electrode active material in a certain ratio, and kneading was performed using a planetary mixer to prepare a slurry. This slurry was coated on both sides of a current collector composed of an aluminum foil with a thickness of 15 μm, and the coating film was dried. Further, the dried coating film was subjected to a roll pressing treatment. Thus, a positive electrode having a current collector and a positive electrode active material layer formed on both sides of the current collector with an electrode density (excluding the current collector) of 3.0 g / cm 3 was produced.

[0202] [Fabrication of Electrode Assembly]

[0203] Two separator films made of a porous polyethylene film with a thickness of 20 μm were prepared.

[0204] Next, stack the previously fabricated positive electrode, one separator, the previously fabricated negative electrode, and another separator in sequence to obtain a stacked body. Wind the stacked body into a vortex shape. Heat and press it at 90 °C to fabricate a flat electrode group with a width of 30 mm and a thickness of 3.0 mm.

[0205] Place the obtained electrode group in a package made of a laminated film and perform vacuum drying at 85 °C for 24 hours. The laminated film is composed of polypropylene layers formed on both sides of an aluminum foil with a thickness of 40 μm, and the overall thickness is 0.1 mm.

[0206] [Preparation of Liquid Non-aqueous Electrolyte]

[0207] Mix propylene carbonate (PC) and dimethyl carbonate (MEC) in a volume ratio of 1:1 to make a mixed solvent. Prepare a liquid non-aqueous electrolyte by dissolving 1 M of LiPF6 as an electrolyte in the mixed solvent.

[0208] [Manufacture of Non-aqueous Electrolyte Secondary Battery]

[0209] Inject the liquid non-aqueous electrolyte into the package of the laminated film containing the electrode group as described above. Then, hermetically seal the package completely by heat sealing. In this way, a non-aqueous electrolyte secondary battery with the structure shown above, a width of 35 mm, a thickness of 3.2 mm, a height of 65 mm, and a rated capacity of 1 Ah is manufactured. Figure 3 and Figure 4 Next, charge the fabricated non-aqueous electrolyte secondary battery at a charging rate of 1 A (1 C) in a 25 °C environment to adjust it to SOC 50%, and subject it to heat treatment at 70 °C for 48 hours. Then, discharge the battery that has naturally cooled to room temperature at 1 A to 1.5 V in a 25 °C environment and then charge it at 1 A to adjust it to SOC 50%.

[0210] (Example 2)

[0211] (Example 3)

[0212] When preparing the powder of spinel-type lithium titanium composite oxide as the negative electrode active material, adjust the firing conditions to set the primary particle size to 200 nm, and adjust the ratio of primary particles to secondary particles in the slurry for fabricating the negative electrode to 1 to 2 (primary particles: secondary particles = 1:2). Except for this, manufacture the non-aqueous electrolyte secondary battery in the same steps as in Example 1. In addition, the roll pressing treatment is performed at the same line pressure as in Example 1.

[0213] (Example 3)

[0214] When preparing the powder of the spinel-type lithium titanium composite oxide as the negative electrode active material, the firing conditions were adjusted to set the primary particle size to 600 nm, and the ratio of primary particles to secondary particles in the slurry for manufacturing the negative electrode was adjusted to 3:2. Otherwise, a non-aqueous electrolyte secondary battery was manufactured in the same steps as in Example 1. In addition, the roll pressing treatment was carried out at the same line pressure as in Example 1.

[0215] (Example 4)

[0216] A non-aqueous electrolyte secondary battery was manufactured in the same steps as in Example 1, except that the ratio of primary particles to secondary particles in the slurry for manufacturing the negative electrode was adjusted to 1:2. In addition, the roll pressing treatment was carried out at the same line pressure as in Example 1.

[0217] (Comparative Example 1)

[0218] A non-aqueous electrolyte secondary battery was manufactured in the same steps as in Example 1, except that the ratio of primary particles to secondary particles in the slurry for manufacturing the negative electrode was adjusted to 1:4. In addition, the roll pressing treatment was carried out at the same line pressure as in Example 1.

[0219] (Comparative Example 2)

[0220] A non-aqueous electrolyte secondary battery was manufactured in the same steps as in Example 1, except that the ratio of primary particles to secondary particles in the slurry for manufacturing the negative electrode was adjusted to 3:2. In addition, the roll pressing treatment was carried out at the same line pressure as in Example 1.

[0221] (Comparative Example 3)

[0222] When preparing the powder of the spinel-type lithium titanium composite oxide as the negative electrode active material, the firing conditions were adjusted to set the primary particle size to 100 nm, and the ratio of primary particles to secondary particles in the slurry for manufacturing the negative electrode was adjusted to 1:20. Otherwise, a non-aqueous electrolyte secondary battery was manufactured in the same steps as in Example 1. In addition, the roll pressing treatment was carried out at the same line pressure as in Example 1.

[0223] (Comparative Example 4)

[0224] When preparing the powder of the spinel-type lithium titanium composite oxide as the negative electrode active material, the firing conditions were adjusted to set the primary particle size to 100 nm, and the ratio of primary particles to secondary particles in the slurry for manufacturing the negative electrode was adjusted to 1:4. Otherwise, a non-aqueous electrolyte secondary battery was manufactured in the same steps as in Example 1. In addition, the roll pressing treatment was carried out at the same line pressure as in Example 1.

[0225] (Comparative Example 5)

[0226] When preparing the powder of the spinel-type lithium titanium composite oxide as the negative electrode active material, the firing conditions were adjusted to set the primary particle size to 100 nm, and the ratio of primary particles to secondary particles in the slurry for manufacturing the negative electrode was adjusted to 1:2. Except for this, a non-aqueous electrolyte secondary battery was manufactured in the same steps as in Example 1. In addition, the roll pressing treatment was carried out at the same line pressure as in Example 1.

[0227] (Comparative Example 6)

[0228] When preparing the powder of the spinel-type lithium titanium composite oxide as the negative electrode active material, the firing conditions were adjusted to set the primary particle size to 700 nm, and the ratio of primary particles to secondary particles in the slurry for manufacturing the negative electrode was adjusted to 1:20. Except for this, a non-aqueous electrolyte secondary battery was manufactured in the same steps as in Example 1. In addition, the roll pressing treatment was carried out at the same line pressure as in Example 1.

[0229] (Comparative Example 7)

[0230] When preparing the powder of the spinel-type lithium titanium composite oxide as the negative electrode active material, the firing conditions were adjusted to set the primary particle size to 700 nm, and the ratio of primary particles to secondary particles in the slurry for manufacturing the negative electrode was adjusted to 4:1. Except for this, a non-aqueous electrolyte secondary battery was manufactured in the same steps as in Example 1. In addition, the roll pressing treatment was carried out at the same line pressure as in Example 1.

[0231] (Comparative Example 8)

[0232] When preparing the powder of the spinel-type lithium titanium composite oxide as the negative electrode active material, the firing conditions were adjusted to set the primary particle size to 700 nm, and the ratio of primary particles to secondary particles in the slurry for manufacturing the negative electrode was adjusted to 9:1. Except for this, a non-aqueous electrolyte secondary battery was manufactured in the same steps as in Example 1. In addition, the roll pressing treatment was carried out at the same line pressure as in Example 1.

[0233] <Measurement>

[0234] For each non-aqueous electrolyte secondary battery manufactured in Examples 1-4 and Comparative Examples 1-8, the pore specific surface area S of the negative electrode was measured by the nitrogen adsorption method described above A (BET specific surface area). In addition, for each battery, the pore specific surface area S of the negative electrode was measured by the mercury intrusion method described above B . The ratio S of the former to the latter was calculated A / S B . The calculation results are shown in Table 1 below.

[0235] For the negative electrode included in each battery, the particle size distribution was measured by the laser diffraction / scattering method described above. D in the calculated particle size distribution90 Relative to D 50 Ratio to D 90 / D 50 . The calculation results are shown in Table 1 below.

[0236] <Evaluation>

[0237] For each non-aqueous electrolyte secondary battery manufactured in Examples 1-4 and Comparative Examples 1-8, the performance evaluation was carried out as follows. Specifically, the input performance of each battery at low temperature, the measurement of energy density, the cycle life test, and the measurement of the gas generation amount during the cycle life test were carried out respectively.

[0238] (Low-temperature input performance)

[0239] The input performance of the battery under low-temperature conditions was evaluated as follows.

[0240] First, in a constant-temperature bath at 25°C, the battery was charged with a constant current at a charging rate of 1 A (1 C) until the battery voltage reached 2.7 V. Then, constant-voltage charging was carried out until the current value reached 50 mA, and a pause time of 10 minutes was set. Then, it was discharged with a constant current of 200 mA to 1.5 V, and a pause time of 10 minutes was set. After repeating this charge-discharge cycle 3 times, the charging capacity obtained when charging to 2.7 V with a constant current of 1 A was measured as the reference charging capacity.

[0241] Then, it was discharged with a constant current of 200 mA to 1.5 V, and a pause time of 10 minutes was set. The previous charge-discharge cycle was carried out once again. The temperature of the constant-temperature bath was set to -20°C, and the battery was allowed to standby in the constant-temperature bath for 3 hours. The charging capacity obtained when charging the battery to 2.7 V with a constant current of 1 A in the constant-temperature bath at low temperature (-20°C) was measured. The value obtained by dividing the charging capacity under low-temperature conditions by the reference charging capacity was used as the low-temperature input performance.

[0242] (Energy density)

[0243] The energy density of the battery was measured as follows.

[0244] First, in a constant-temperature bath at 25°C, the battery was charged with a constant current at a charging rate of 1 A (1 C) until the battery voltage reached 2.7 V. Then, constant-voltage charging was carried out until the current value reached 50 mA, and a pause time of 10 minutes was set. Then, it was discharged with a constant current of 200 mA to 1.5 V, and a pause time of 10 minutes was set. This charge-discharge cycle was repeated 3 times, and the discharge capacity obtained during the discharge of the third cycle was measured as the reference discharge capacity.

[0245] The battery energy is obtained by multiplying the reference discharge capacity by the average working voltage during discharge. Then, the (volume) energy density of the battery is calculated by dividing the battery energy by the volume of the battery.

[0246] (Cycle life performance)

[0247] The following cycle life test is carried out to evaluate the cycle life performance of the battery.

[0248] The battery is placed in a constant temperature bath at 25°C and charged at a constant current of 1 A (1 C) until the battery voltage reaches 2.7 V. Then, constant voltage charging is carried out until the current value reaches 50 mA, and a 10-minute pause time is set. Then, it is discharged at a constant current of 200 mA to 1.5 V, and a 10-minute pause time is set. This charge-discharge cycle is repeated 3 times, and the discharge capacity obtained during the discharge of the third cycle is measured as the reference discharge capacity.

[0249] The battery is placed in a constant temperature bath at 45°C and charged at a constant current of 8 A until the battery voltage reaches 2.7 V. Then, constant voltage charging is carried out until the current value reaches 50 mA, and a 5-minute pause time is set. Then, it is discharged at a constant current of 5 A to 1.5 V, and a 5-minute pause time is set. This charge-discharge cycle is repeated 1000 times.

[0250] The battery after being repeatedly charged and discharged 1000 times is charged at a constant current of 1 A to 2.7 V in a constant temperature bath at 25°C, and then constant voltage charging is carried out until the current value reaches 50 mA, and a 10-minute pause time is set. Then, the discharge capacity obtained when discharging at a constant current of 200 mA to 1.5 V is measured as the recovery capacity. The capacity retention rate is calculated by dividing the recovery capacity by the reference discharge capacity. For the discharge capacity (reference discharge capacity) before the cycle life test obtained in this way, the ratio (capacity retention rate) of the discharge capacity (recovery capacity) maintained after the test is used as an index to evaluate the cycle life performance.

[0251] (Gas generation amount)

[0252] As described below, the amount of gas generated during the cycle life test is measured.

[0253] The battery before the cycle life test is immersed in a rectangular graduated container filled with water, and the volume of the battery is read according to the change in the water surface position. The volume of the battery after the cycle life test is also read in the same way, and the change amount compared with the volume of the battery before the test is calculated as the gas generation amount.

[0254] In Table 1 below, the design and performance evaluation results of the negative electrodes are summarized for each non-aqueous electrolyte secondary battery manufactured in Examples 1-4 and Comparative Examples 1-8. As the design of the negative electrode, the average primary particle diameter of the spinel-type lithium titanium composite oxide contained as the negative electrode active material, and the specific surface area S of the pores of the negative electrode measured by the nitrogen adsorption method and the mercury intrusion method respectively A and S B The ratio S A / S B between, and D in the particle size distribution measured by the laser diffraction / scattering method 90 The ratio D 50 relative to D 90 / D 50 are shown. As the result of the performance evaluation, the evaluation results of the above-mentioned low-temperature input performance, energy density, cycle life performance, and gas generation amount are used as the performance values of Example 1, and the measured values are used as the reference value 100, indicating the relative values with respect to this reference value.

[0255] [Table 1]

[0256]

[0257] As shown in Table 1, a titanium-containing oxide (lithium titanate having a spinel structure) having an average primary particle diameter of 200 nm or more and 600 nm or less is contained as the negative electrode active material, and for the specific surface area S of the negative electrode based on the nitrogen adsorption method A and the pore specific surface area S of the pores based on the mercury intrusion method B The ratio S A / S B For the batteries of Examples 1-4 that are 0.3 or more and less than 0.6, good low-temperature input performance is shown, good energy density and good cycle life performance are obtained, and the gas generation amount is suppressed.

[0258] On the other hand, in Comparative Example 1, the energy density of the battery is low. In Comparative Example 1, since the ratio S A / S B is low, it can be seen that the proportion of large pores relative to the small pores in the negative electrode is large. It is speculated that: due to the large number of large pores in the negative electrode, the energy density of the battery is low.

[0259] In Comparative Example 2, the low-temperature input performance is low, and in addition, the gas generation amount is large. In Comparative Example 2, since the ratio S A / S B is high, it can be seen that a large number of small pores are present in the negative electrode. It is speculated that: due to the large number of small pores in the negative electrode, the input performance becomes low and the gas generation amount becomes large.

[0260] In Comparative Examples 3-5, the energy density and cycle life performance were low, and the gas generation amount was large. It is speculated that in Comparative Examples 3-5, since the primary particle size of the negative electrode active material was small, the crystallinity was low, and thus the energy density and cycle life performance were low. In addition, it is speculated that since the primary particle size was small, the size of the pores in the negative electrode was small, and thus the cycle life performance was also low. Furthermore, it is speculated that since the primary particle size was small, the specific surface area of the active material particles was large, and thus the side reaction between the active material and the electrolyte on the side with good low-temperature input performance increased, and the gas generation amount increased.

[0261] In Comparative Examples 6-8, the low-temperature input performance was low. It is speculated that in Comparative Examples 6-8, since the primary particle size of the negative electrode active material was large and the specific surface area of the active material particles was small, the lithium ion acceptance performance was low.

[0262] According to one or more of the embodiments and examples described above, an electrode containing an active material containing a titanium-containing oxide is provided. The active material contains an active material having an average primary particle size of 200 nm or more and 600 nm or less. For the electrode, the specific surface area S A obtained by the nitrogen adsorption method and the pore specific surface area S B obtained by the mercury intrusion method satisfy the relationship of 0.3 ≤ S A / S B < 0.6. This electrode can achieve a battery and a battery pack with excellent high-current performance, cycle life performance, less gas generation, and high energy density at low temperatures.

[0263] Several embodiments of the present invention have been described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope or gist of the invention, and are also included in the invention described in the claims and its equivalents.

Claims

1. An electrode, comprising an active material, the active material containing a titanium-containing oxide having a spinel structure and having an average primary particle diameter of 200 nm or more and 600 nm or less, Regarding the electrode, the specific surface area S based on the nitrogen adsorption method A and the pore specific surface area S based on the mercury intrusion method B satisfy the relationship of 0.3 ≤ S A / S B <0.

6. wherein the half-value width of the (111) peak in the X-ray diffraction spectrum of the titanium-containing oxide is 0.15 or less.

2. The electrode according to claim 1, wherein, In the particle size distribution of the electrode, the particle size D at which the cumulative frequency starting from the small particle size side is 90% 90 relative to the particle size D at which the cumulative frequency starting from the small particle size side is 50% 50 the ratio D 90 / D 50 is 5 or more and 10 or less.

3. The electrode according to claim 1 or 2, wherein, the electrode comprises an active material-containing layer, the active material-containing layer containing the active material and having a thickness of 20 μm or more and 80 μm or less.

4. The electrode according to claim 1 or 2, wherein, the titanium-containing oxide comprises lithium titanate having a spinel structure.

5. A battery, comprising: a positive electrode; a negative electrode; and an electrolyte, wherein at least one of the positive electrode and the negative electrode comprises the electrode according to any one of claims 1 to 4.

6. A battery pack comprising the battery according to claim 5.

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