Electrodes, batteries, and battery packs

Abstract

According to an embodiment of the present invention, provided is an electrode including an active material that contains a titanium-containing oxide and that has an average primary particle diameter in the range 200–600 nm. The ratio D90 / D10 in the particle diameter distribution of the electrode is in the range 17–27. At least part of a surface of the electrode contains aluminum. As regards the electrode, the value of the ratio IB / IA is in the range 3.5–9, said ratio being of the peak intensities of a peak A appearing in the range 1.1–1.5 Å and a peak B appearing in the range 2.8–3.2 Å in a radial distribution function based on a Fourier transform of a broad-spectrum X-ray absorbing microstructure spectrum at the aluminum K-edge with respect to the surface.

Description

[Technical Field]

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

[0002] Lithium-ion secondary batteries, which charge and discharge by the movement of lithium ions between the positive and negative electrodes, are widely applied in applications ranging from small devices such as portable electronic devices to large-scale applications such as electric vehicles and power supply and demand adjustment, taking advantage of their high energy density and high output.

[0003] Instead of carbon materials, the negative electrode active material has a lithium absorption / desorption potential of approximately 1.55V (vs.Li / Li) relative to the lithium electrode. + Non-aqueous electrolyte batteries using spinel-type lithium titanate, which has high performance, have also been put into practical use. Spinel-type lithium titanate has excellent cycle performance because it undergoes little volume change during charging and discharging. In addition, because lithium metal is not deposited during lithium absorption and release in negative electrodes containing spinel-type lithium titanate, secondary batteries equipped with this negative electrode can be charged at high currents and low temperatures. Attempts are being made to reduce the diameter of spinel-type lithium titanate particles in order to further improve high-current and low-temperature performance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2014-143004 [Patent Document 2] Japanese Patent Application Publication No. 2019-169276 [Non-patent literature]

[0005] [Non-Patent Document 1] B. Ravel and M. Newville, ATHENA, ARTHEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT, Journal of Synchrotron Radiation 12, 537-541 (2005) Summary of the Invention Problems to be Solved by the Invention

[0006] An object is to provide an electrode capable of realizing a battery having excellent high-current performance and storage performance at low temperatures and a high energy density, a battery including this electrode, and a battery pack including this battery. Means for Solving the Problems

[0007] According to an embodiment 、 having an average primary particle diameter of 200 nm or more and 600 nm or less Furthermore, it is made of lithium titanate having a spinel structure. an electrode containing an active material is provided. In the particle size distribution of the electrode by laser diffraction / scattering method, the particle size D at which the cumulative frequency from the small particle size side becomes 10% 10 and the particle size D at which the cumulative frequency from the small particle size side becomes 90% with respect to 90 the ratio D 90 / D 10 is from 17 to 27. The electrode Active material contains at least a part of the surface Aluminum alkoxide compounds . The electrode includes a peak A appearing in the range of 1.1 Å or more and 1.5 Å or less and a peak B appearing in the range of 2.8 Å or more and 3.2 Å or less in the radial distribution function obtained by Fourier transform of the wide-area X-ray absorption fine structure spectrum of the K absorption edge of Al with respect to the surface. The ratio Is B of the peak intensity Is A of peak A to the peak intensity Is A / I B of peak B has a value of 3.5 or more and 9 or less.

[0008] According to another embodiment, a battery including a positive electrode, a negative electrode, and an electrolyte is provided. The negative electrode includes the above electrode.

[0009] In yet another embodiment, a battery pack is provided, which includes the battery described above. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic plan view showing an example electrode according to the embodiment. [Figure 2] Figure 2 is a graph showing the particle size distribution for an example electrode according to the embodiment. [Figure 3] Figure 3 is a graph showing the radial distribution function obtained by the Fourier transform of the broadband X-ray absorption fine structure spectrum of Al at the K absorption edge for the surface of an example electrode according to the embodiment. [Figure 4] Figure 4 shows a cross-section of an example battery according to the embodiment, cut in the thickness direction. [Figure 5] Figure 5 is an enlarged cross-sectional view of section E in Figure 4. [Figure 6] Figure 6 is a partially cutaway perspective view of a battery in another example according to the embodiment. [Figure 7] Figure 7 is an exploded perspective view of an example battery pack according to the embodiment. [Figure 8] Figure 8 is a block diagram showing the electrical circuit of the battery pack shown in Figure 7. Embodiment

[0011] Input performance can be improved by reducing the particle size of the active material. On the other hand, when the particle size of the active material becomes smaller, a decrease in electrode density and an increase in resistance due to surface side reactions may become issues.

[0012] The embodiments will be described below with reference to the drawings. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted.

[0013] Furthermore, each figure is a schematic diagram intended to illustrate the embodiment and facilitate understanding of it. While the shape, dimensions, ratios, etc., may differ from those of the actual device, these can be appropriately modified in accordance with the following explanation and known technology.

[0014] (First embodiment) According to the first embodiment, an electrode is provided. The electrode includes an active material. The active material includes a titanium-containing oxide and has an average primary particle diameter of 200 nm to 600 nm. The particle diameter D at which the cumulative frequency from the small particle diameter side in the particle diameter distribution of the electrode is 10% 10 Particle size D where the cumulative frequency from the small particle size side is 90% 90 Ratio D 90 / D 10 The value is between 17 and 27. The electrode contains Al in at least a portion of its surface. The electrode has peak A and range between 2.8 Å and 3.2 Å in the radial distribution function obtained by the Fourier transform of the broad X-ray absorption fine structure spectrum of Al at the K absorption edge relative to the surface, which appear in the range between 1.1 Å and 1.5 Å. The area includes peak B. Peak intensity I of peak B B Peak intensity I of peak A A Ratio I A / I B The value is between 3.5 and 9.

[0015] The electrode according to the embodiment may be an electrode for a battery. Examples of batteries that may contain the electrode according to the embodiment include secondary batteries such as lithium-ion secondary batteries. Secondary batteries include non-aqueous electrolyte secondary batteries containing a non-aqueous electrolyte. The electrode may be, for example, a negative electrode for a battery.

[0016] Secondary batteries equipped with a negative electrode containing titanium oxide offer superior cycle life and storage performance, as well as the ability to charge and discharge at high currents and charge under low-temperature conditions. To further improve these high-current and low-temperature performance, attempts are being made to reduce the size of the active material particles. While reducing the size of the active material particles improves input / output performance, it also presents challenges such as decreased electrode density and increased resistance due to surface side reactions.

[0017] The present inventors have diligently conducted research to solve this problem concerning non-aqueous electrolyte batteries equipped with a negative electrode containing a titanium-containing oxide, and as a result have discovered an electrode according to the first embodiment. Specifically, they have found that by presenting a specific alkoxide compound on the surface of the titanium-containing oxide, the increase in resistance due to surface side reactions can be suppressed, and the decrease in electrode density can be suppressed by making it easier to adjust the titanium-containing oxide to a desired particle size distribution.

[0018] The electrode according to the first embodiment is an electrode containing a titanium-containing oxide with an average primary particle diameter of 200 nm to 600 nm as the electrode active material, wherein the particle diameter D is such that the cumulative frequency from the small particle diameter side in the particle diameter distribution of the electrode is 10%. 10 Particle size D where the cumulative frequency from the small particle size side is 90% 90 Ratio D 90 / D 10 The value is between 17 and 27. In addition, at least a portion of the electrode surface contains aluminum (Al). The radial distribution function obtained by the Fourier transform of the wide-field X-ray absorption fine structure (EXAFS) spectrum of Al at the K absorption edge relative to the electrode surface shows peak A appearing in the range of 1.1 Å to 1.5 Å and peak A appearing in the range of 2.8 Å to 3.2 Å. The range includes peak B. Peak intensity I of peak B. B Peak intensity I of peak A A Ratio I A / I B The value is between 3.5 and 9. By having such a configuration, the electrode can provide a battery with high electrode density and excellent low-temperature input performance due to suppressed resistance increase during low-temperature storage.

[0019] The mechanism by which such electrodes improve low-temperature storage performance is not fully understood, but it can be thought of as follows:

[0020] Reducing the primary particle size of the active material particles increases the specific surface area, thereby improving the lithium ion acceptance performance of the active material itself at low temperatures. However, as the primary particle size decreases, the proportion of active sites on the surface of the active material increases. As a result, side reactions between the active material and electrolytes increase, leading to an increase in electrical resistance during low-temperature storage.

[0021] The presence of an aluminum alkoxide compound in a specific state on the active material surface can suppress side reactions with the electrolyte, etc. Specifically, the radial distribution function obtained by the Fourier transform (FT-EXAFS) of the EXAFS spectrum of Al contains peak A in the range of 1.1 Å to 1.5 Å and peak B in the range of 2.8 Å to 3.2 Å, and the peak intensity ratio of these peaks is I A / I B In electrodes where the value is between 3.5 and 9, it is determined that the aluminum alkoxide compound is present on the active material surface in a state that is effective in suppressing the above-mentioned side reactions. At least a portion of the aluminum alkoxide compound is present on the active material surface. It is thought that the aluminum alkoxide compound condenses with functional groups that can act as active sites, thereby suppressing side reactions. Furthermore, it is thought that a portion of it is incorporated as a film on the surface of the active material, which facilitates the insertion and removal of lithium ions and reduces unevenness in charging and discharging, thereby reducing side reactions caused by localized overcharging. In addition, it is thought that the aluminum alkoxide compound enhances the interaction between active material particles, making it easier to obtain the desired particle size distribution, and thus enabling the achievement of high electrode density. Moreover, it is possible to provide a non-aqueous electrolyte secondary battery with excellent low-temperature performance.

[0022] In these electrodes, the average primary particle diameter of the active material particles is between 200 nm and 600 nm, thus enabling good input performance even under low-temperature conditions. Specifically, because the average primary particle diameter is 200 nm or more, the crystallinity of the active material can be increased, thereby improving the charge-discharge cycle performance and energy density of batteries using these electrodes. An average primary particle diameter of 600 nm or less allows for the creation of batteries with excellent low-temperature input performance.

[0023] In the particle size distribution of an electrode using laser diffraction and scattering methods, the average particle size D at which the cumulative frequency from the small particle size side reaches 10% 10 Particle size D where the cumulative frequency from the small particle size side is 90% 90 Ratio D 90 / D 10 The particle size distribution is between 17 and 27. Electrodes with this particle size distribution have an appropriate electrode density. Therefore, they are superior in terms of input / output performance and energy density.

[0024] The above particle size distribution may contain maximum values ​​in the range of 0.5 μm to 1 μm and in the range of 3 μm to 10 μm, respectively. In other words, the particle size distribution of the electrode may have a bimodal shape. When the peak with a maximum value in the range of 0.5 μm to 1 μm is taken as the first peak and the peak with a maximum value in the range of 3 μm to 10 μm is taken as the second peak, 1 The number of peaks relative to the frequency 2 It is preferable that the ratio of peak frequencies is between 0.18 and 0.35. Electrodes with a ratio of 0.18 or higher exhibit superior low-temperature storage performance. Electrodes with a ratio of 0.35 or lower exhibit superior energy density.

[0025] The pore specific surface area of ​​the electrode obtained by nitrogen adsorption method is 2 m². 2 / g or more 10m 2 It is preferable that the concentration is within the range of / g or less. The specific surface area of ​​the electrode pores is 2m². 2 A value of 10 / g or higher indicates good low-temperature input performance. 2 If the value is less than / g, side reactions between the electrode and electrolyte can be kept to a minimum.

[0026] For titanium-containing oxides in the active material, it is desirable that the full width at half maximum (FWHM) of the peak attributed to the (111) plane in the XRD spectrum, measured by powder X-ray diffraction (XRD) as described later, be 0.15 or less. When the FWHM of the (111) peak is 0.15 or less, the crystallinity of the titanium-containing oxide particles is high, and the diffusivity of lithium ions within the particles is good, resulting in high low-temperature input performance and reduced side reactions at the electrode surface. Alternatively, the FWHM can also be 0.15 or less when the crystallite size is large. In particles with a large crystallite size, there are fewer grain boundaries within the particles, and the diffusivity of lithium ions within the particles is improved, resulting in high low-temperature input performance. The (111) plane referred to here refers to the crystal lattice plane expressed in Miller indices.

[0027] Next, the electrode according to the first embodiment will be described in more detail.

[0028] The electrode may include a current collector and an active material-containing layer (electrode composite layer). The active material-containing layer may be formed, for example, on one side or both sides of a strip-shaped current collector. The active material-containing layer may include an active material and optionally a conductive agent and a binder.

[0029] The active material contains a titanium-containing oxide having an average primary particle diameter of 200 nm to 600 nm. Preferably, the titanium-containing oxide contains a lithium-titanium composite oxide. An electrode containing a titanium-containing oxide, such as a lithium-titanium composite oxide, exhibits a redox potential of 0.4 V (vs. Li / Li) relative to the oxidation-reduction potential of lithium. + Since it can exhibit a Li storage potential of ) or higher, it is possible to prevent the deposition of metallic lithium on the electrode surface when high current input and output are repeated. The titanium-containing oxide is particularly preferably a lithium titanium composite oxide having a spinel-type crystal structure. As a specific example of such a spinel-type lithium titanium composite oxide, Li 4+a Ti5O 12Lithium titanate having a spinel structure can be given as an example, where the value of the subscript a changes with charge and discharge within the range of 0 ≤ a ≤ 3.

[0030] The active material may include primary and secondary particles of the titanium-containing oxide described above. The primary particles of the titanium-containing oxide have the above-mentioned average primary particle diameter. The secondary particles of the titanium-containing oxide include a plurality of primary particles having the above-mentioned average primary particle diameter.

[0031] The average particle diameter of the secondary particles (average secondary particle diameter) is preferably between 1 μm and 100 μm. When the average particle diameter of the secondary particles is within this range, it is easier to handle in industrial production, and the mass and thickness of the coating film used to manufacture the electrodes can be made uniform. Furthermore, a decrease in the surface smoothness of the electrodes can be prevented. The average particle diameter of the secondary particles is more preferably between 2 μm and 30 μm.

[0032] The specific surface area of ​​secondary particles measured by the BET method is 3m 2 / g or more 50m 2 It is preferable that the specific surface area is 3 m² or less. 2 When the concentration is 50 m² or higher, it becomes possible to secure sufficient lithium ion intercalation and deintercalation sites. 2 When the amount is less than / g, it becomes easier to handle in industrial production. More preferably, the secondary particles have a specific surface area of ​​5 m² as measured by the BET method. 2 / g or more 50m 2 It is less than / g. The method for measuring specific surface area using the BET method will be described later.

[0033] The active material may contain additional active materials other than the titanium-containing oxide mentioned above. For convenience, the active material containing the titanium-containing oxide mentioned above will be referred to as the "first active material," and any other additional active materials will be referred to as the "second active material." If the second active material is further included in addition to the first active material, the second active material may be 0.4V(vs.Li / Li +It is desirable to use an active material that can exhibit a Li storage potential of ) or higher. If a 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.

[0034] Conductive agents can enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as acetylene black, carbon black, graphite, carbon nanofibers, and carbon nanotubes. These carbonaceous materials may be used individually or in combination.

[0035] A binder can have the effect of binding the active material, conductive agent, and current collector together. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, acrylic resin and its copolymers, polyacrylic acid, and polyacrylonitrile.

[0036] The mixing ratios of the active material, conductive agent, and binder are preferably within the following ranges: 70% to 97.5% by mass for the active material, 2% to 20% by mass for the conductive agent, and 0.5% to 10% by mass for the binder. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the active material-containing layer is improved, and excellent high-current performance and low-temperature performance can be expected. Furthermore, by setting the amount of binder to 0.5% by mass or more, sufficient bonding between the active material-containing layer and the current collector is achieved, and excellent lifespan performance can be expected.

[0037] On the other hand, from the viewpoint of increasing capacity, it is preferable that the conductive agent and the binder each be 20% by mass or less, and more preferably 10% by mass or less.

[0038] The current collector is preferably formed from aluminum foil or 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, and more preferably 15 μm or less.

[0039] Next, a specific example of the electrode according to the first embodiment will be described with reference to the drawings.

[0040] Figure 1 is a partially cutaway plan view schematically showing an example of an electrode according to the embodiment. Here, an example of a negative electrode is shown.

[0041] The negative electrode 4 shown in Figure 1 comprises 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.

[0042] Furthermore, the negative electrode current collector 4a includes a portion on its surface where the negative electrode active material-containing layer 4b is not provided. This portion functions, for example, as a negative electrode current collector tab 4c. In the illustrated example, the negative electrode current collector tab 4c is a narrow portion that is narrower than 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, or it may be the same width as the negative electrode active material-containing layer 4b. Instead of the negative electrode current collector tab 4c, which is 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).

[0043] [Electrode Manufacturing] The electrode in question can be manufactured as follows.

[0044] First, an active material containing titanium oxide is prepared. Titanium oxide can be synthesized, for example, by a solid-phase method. Titanium oxide can also be synthesized by other wet synthesis methods such as the sol-gel method and the hydrothermal method.

[0045] First, prepare a Ti source and a Li source according to the desired composition. These raw materials may be compounds such as oxides or salts. For the Li source, lithium hydroxide, lithium oxide, lithium carbonate, etc., can be used.

[0046] Next, the prepared raw materials are mixed in an appropriate stoichiometric ratio to obtain a mixture. For example, Li4Ti5O 12 When synthesizing the spinel-type lithium titanium composite oxide represented by [formula], titanium dioxide (TiO2) and lithium carbonate (Li2CO3) can be mixed such that the molar ratio of Li to Ti in the mixture is 4:5.

[0047] When mixing the raw materials, it is preferable to thoroughly grind them before mixing. Mixing thoroughly ground raw materials makes them more reactive with each other, which suppresses the generation of impurities when synthesizing titanium-containing oxides. In addition, more than the predetermined amount of Li may be mixed. In particular, since there is concern that Li may be lost during heat treatment, more than the predetermined amount may be added.

[0048] In the wet process, the raw materials are dissolved in pure water, and the resulting solution is dried while stirring to obtain a calcination precursor. Drying methods include spray drying, granulation drying, freeze-drying, or a combination thereof.

[0049] Next, the mixture obtained from the previous mixing or the calcination precursor is heat-treated at a temperature of 750°C to 1000°C for a period of 30 minutes to 24 hours. Below 750°C, sufficient crystallization is difficult to obtain. On the other hand, above 1000°C, grain growth progresses too much, resulting in coarse particles, which is undesirable. Similarly, if the heat treatment time is less than 30 minutes, sufficient crystallization is difficult to obtain. Also, if the heat treatment time is longer than 24 hours, grain growth progresses too much, resulting in coarse particles, which is undesirable. Calcination may be carried out in air. Alternatively, calcination may be carried out in an oxygen atmosphere, nitrogen atmosphere, or argon atmosphere.

[0050] It is preferable to heat-treat the mixture at a temperature of 800°C to 950°C for a period of 1 to 5 hours. By such heat treatment, a titanium-containing oxide can be obtained. Alternatively, pre-sintering may be performed before the main firing. Pre-sintering is carried out at a temperature of 450°C to 700°C for a period of 5 to 24 hours.

[0051] When using methods that involve water, such as the wet process, attention should be paid to the amount of residual moisture after firing. Residual moisture can react with the aluminum alkoxide compound added in a later stage to form a resistive component. Therefore, adjusting the firing temperature and firing time also contributes to controlling the radial distribution function of Al using FT-EXAFS.

[0052] The sample obtained by the calcination process can be subjected to grinding to break down aggregates (secondary particles) into primary particles. For example, grinding methods such as mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, bead mills, jet mills, counter-jet mills, and swirling airflow jet mills can be used. During grinding, wet grinding with liquid grinding aids such as water, ethanol, ethylene glycol, benzene, or hexane can also be used. These grinding aids are effective in improving grinding efficiency and increasing the amount of fine powder produced. A more preferred method is a ball mill using zirconia balls as the media, and wet grinding with a liquid grinding aid is preferred. Furthermore, organic substances such as polyols may be added as grinding aids to improve grinding efficiency. The type of polyol is not particularly limited, but pentaerythritol, triethylolethane, trimethylolpropane, etc., can be used alone or in combination.

[0053] Furthermore, re-calcination may be performed after the pulverization process. The average crystallite size of the titanium-containing oxide particles can be controlled by adjusting the calcination conditions. Re-calcination may be performed in air, or in an inert atmosphere using oxygen, nitrogen, argon, etc. Re-calcination should be performed at a temperature of 250°C to 900°C for about 1 minute to 10 hours. If the temperature is above 900°C, the calcination of the pulverized powder will progress, and even with a short heat treatment, the pores in the electrode may collapse due to sintering between the powder particles, which can reduce input / output performance. If the temperature is below 250°C, impurities (organic matter) that adhere during wet pulverization cannot be removed, and the battery performance will decrease. Preferably, re-calcination is performed at a temperature of 400°C to 700°C for 10 minutes to 3 hours. It is also preferable to wash with an aqueous solvent before re-calcination.

[0054] Furthermore, methods such as spray drying can be used to obtain secondary particles. Classification can be performed as needed to obtain primary or secondary particles with a specific particle size.

[0055] Next, an electrode slurry is prepared using the titanium-containing oxide active material prepared as described above. If a second active material other than the titanium-containing oxide is to be used, the electrode slurry is prepared using the second active material together with the titanium-containing oxide active material (first active material). Specifically, the active material, conductive agent, binder, and aluminum alkoxide compound are suspended in a solvent to prepare the slurry. For example, N-methylpyrrolidone (NMP) can be used as the solvent (dispersion medium).

[0056] It is preferable to use an alkoxide compound having substituents with 4 or more carbon atoms as the aluminum alkoxide compound added to the electrode slurry. For example, di-2-butoxyaluminum ethyl acetacetate (Al(C4H9O)2(C6H9O3)), aluminum tri-2-butoxide (Al(OC4H9)3), di-2-butoxyaluminum acetylacetate (Al(C4H9O)2(C5H7O2)), aluminum trisecondary butoxide (Al(O-sec-C4H9)3), etc., can be used. In electrodes to which the above aluminum alkoxide compounds are added, the peak intensity ratio I is measured in the radial distribution function of Al by FT-EXAFS. A / I B The above-described state, where the value is between 3.5 and 9, is easily obtained. In other words, the addition of these aluminum alkoxide compounds is effective in suppressing side reactions on the electrode. Other aluminum alkoxide compounds with fewer than 4 carbon atoms in the substituent include, for example, aluminum isopropoxide (Al(Oi-Pr)3). The added aluminum alkoxide compound may be one type or two or more types.

[0057] The particle size distribution of the electrode can be controlled by adjusting the content ratio and particle size of each component (active material, conductive agent, binder) included in the electrode, the content ratio of primary and secondary particles of the active material, and the type and amount of aluminum alkoxide compound added. Furthermore, the pore specific surface area of ​​the electrode can also be controlled by these adjustments. The particle size distribution reflects not only the primary and secondary particles of the active material, but also the content ratio of the conductive agent and whether or not aggregation occurs between the active material and the conductive agent. In other words, the particle size distribution and pore specific surface area of ​​the resulting electrode are influenced by the content ratio of each component in the electrode slurry, as well as the state and content ratio of the primary and secondary particles of the active material.

[0058] The particle size distribution at the electrode can also be controlled by the amount of aluminum alkoxide compound added. A higher amount of aluminum alkoxide tends to increase aggregation within the electrode. A lower amount tends to decrease aggregation. Therefore, the ratio D in the particle size distribution...90 / D 10 This is proportional to the amount of aluminum alkoxide added. The amount of aluminum alkoxide compound added may be, for example, 0.1% by mass or more and 1% by mass or less relative to the active material.

[0059] In preparing the slurry, when suspending the active material, conductive agent, binder, and aluminum alkoxide in the solvent, it is preferable to use a rotary-orbit mixer, planetary mixer, jet paster, homogenizer, etc., from the viewpoint of mixing uniformly without disturbing secondary particles. The solid content concentration of the slurry is preferably 40 wt% to 70 wt%. For the addition of the conductive agent, a paste in which the conductive agent is pre-dispersed in a solvent with a dispersant added may be used. Using such a paste can shorten the mixing time and suppress the disintegration of secondary particles.

[0060] The particle size distribution and pore specific surface area of ​​the resulting electrode can also be controlled by the stirring conditions during slurry preparation. For example, a higher stirring speed and longer stirring time result in a higher pore specific surface area and the aforementioned particle size distribution. 2 The frequency of the peak 1 The ratio to the frequency of the peak tends to be low. Lower stirring speeds and longer stirring times result in lower pore specific surface area. 2 The frequency of the peak 1 The ratio to the frequency of peaks tends to be high.

[0061] The slurry prepared as described above is applied to one or both sides of the current collector, and then the coating is dried. In this way, an electrode composite layer (active material-containing layer) can be formed. After that, the electrode composite layer is pressed. In this way, an electrode according to the first embodiment can be obtained.

[0062] <Electrode Measurement> This section describes various measurement methods for electrodes. Specifically, it explains methods for confirming the presence of titanium-containing oxides in the electrodes, measuring the average primary particle diameter of titanium-containing oxide particles, measuring the pore specific surface area by nitrogen adsorption, measuring the particle size distribution, and obtaining the radial distribution function by performing a Fourier transform on the EXAFS spectrum obtained from measuring the wide-field X-ray absorption fine structure (EXAFS) at the K absorption edge of Al.

[0063] If the electrode to be measured is incorporated into a battery, remove the electrode from the battery as follows: Discharge the battery and disassemble it in a glove box under an inert atmosphere such as an argon atmosphere to remove the electrode. Wash the electrode with diethyl carbonate and then vacuum dry it. This will obtain the measurement sample.

[0064] [Confirmation of titanium-containing oxides] The active material contained in the electrode can be identified as follows, and the presence or absence of titanium-containing oxides can be confirmed.

[0065] As described above, after cleaning and drying the electrodes removed from the battery, the obtained electrodes are attached to a glass sample plate. At this time, care should be taken to prevent the electrodes from peeling off or lifting by using double-sided tape or similar. If necessary, the electrodes may be cut to an appropriate size for attachment to the glass sample plate. In addition, a Si standard sample may be added to the electrodes to correct the peak position.

[0066] Next, the glass plate with the electrodes attached is placed in a powder X-ray diffraction (XRD) apparatus, and the diffraction pattern is acquired using Cu-Kα rays. Using Cu-Kα rays as the source, the X-ray diffraction pattern can be obtained by changing 2θ within the measurement range of 5° to 90°.

[0067] For powder X-ray diffraction measurements, for example, a SmartLab manufactured by Rigaku will be used. The measurement conditions will be as follows: X-ray source: Cu target Output: 45kV, 200mA Solar slit: 5° for both incident and received light. Step size: 0.02deg Scan speed: 20deg / min Semiconductor detector: D / teX Ultra 250 Sample plate holder: Flat glass sample plate holder (thickness 0.5 mm) Measurement range: 5° ≤ 2θ ≤ 90°.

[0068] If other equipment is used, measurements should be performed using standard Si powder for powder X-ray diffraction to obtain measurement results equivalent to those described above. The conditions under which the peak intensity and peak top position match those obtained with the above equipment should be found, and the sample should be measured under those conditions.

[0069] If the active material being measured contains a spinel-type lithium titanium composite oxide, X-ray diffraction measurements can confirm that an X-ray diffraction pattern belonging to the space group Fd-3m is obtained. Peaks in this X-ray diffraction pattern that are within the range of 2θ from 17° to 20° can be assigned to the (111) plane.

[0070] Next, the sample containing the active material is observed using a scanning electron microscope (SEM). Even during SEM observation, it is desirable to keep the sample from being exposed to air and to perform the observation in an inert atmosphere such as argon or nitrogen.

[0071] Using a 3000x SEM observation image, several particles with primary or secondary particle morphology are selected within the field of view. The selection is made to ensure the particle size distribution is as broad as possible. Energy dispersive X-ray spectroscopy (EDX) is then used to identify the types and composition of the active material elements present in the observed active material particles. This allows for the identification of the types and amounts of elements other than Li present in each selected particle. The same procedure is performed for each of the multiple active material particles to determine their mixing state.

[0072] Next, the active material-containing layer is separated from the current collector using, for example, a spatula, to obtain a powdered electrode mixture sample containing the active material. The collected powdered sample is washed with acetone and dried. The obtained powder is dissolved in hydrochloric acid, the conductive agent is filtered out, and then diluted with deionized water to prepare the measurement sample. The metal content ratio in the measurement sample is calculated using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0073] If there are multiple types of active materials, their mass ratios are estimated from the elemental content ratios specific to each active material. The ratio of the specific elements to the mass of the active material is determined from the composition of the constituent elements, which is obtained by energy-dispersive X-ray spectroscopy.

[0074] Thus, the active material contained in the electrode can be identified.

[0075] [Measurement of the average primary particle size of the active material] As described above, after cleaning and drying the electrodes removed from the battery, the active material-containing layer is separated from the current collector using, for example, a spatula, to obtain a powdered electrode composite sample containing the active material.

[0076] Next, the powdered sample is analyzed using the X-ray diffraction measurement and SEM-EDX described above to confirm the presence of the active material particles to be measured.

[0077] A magnification of approximately 5000x is desirable for SEM observation. If particle morphology is difficult to discern due to additives such as conductive agents, a SEM equipped with a focused ion beam (FIB-SEM) is used to acquire an image of the electrode cross-section (for example, the cross-section of the active material-containing layer) and observe it. The magnification should be adjusted so that an image containing 50 or more particles is obtained.

[0078] Next, the particle diameter of all particles contained in the obtained image is measured. For particles with secondary particle morphology, the particle diameter of each primary particle contained within the secondary particle is measured. If the particle is spherical, its diameter is taken as the particle diameter. If the particle has a shape other than spherical, first measure the length of the smallest diameter of the particle and the length of the largest diameter of the same particle. The average of these is taken as the average primary particle diameter.

[0079] [Measurement of pore specific surface area by nitrogen adsorption method] The pore specific surface area of ​​an electrode obtained by nitrogen adsorption corresponds to the BET specific surface area of ​​the electrode. BET specific surface area is the specific surface area determined by the BET method and is calculated using the nitrogen adsorption method. The analysis is performed, for example, by the following method.

[0080] As described above, the electrodes obtained by removing them from the battery, washing and drying them, are cut to the size of the measurement cell and used as the measurement sample. For the measurement cell, for example, a 1 / 2-inch glass cell is used. As a pretreatment method, the measurement cell is degassed by vacuum drying at a temperature of approximately 100°C or higher for 15 hours. As the measurement device, for example, a Cantasorb QS-20 manufactured by Cantachrome is used.

[0081] The cut electrode, to be used as the measurement sample, is placed in the measurement cell, and a mixed gas of 30% nitrogen and helium is flowed through it. While the gas is flowing, the glass cell is immersed in liquid nitrogen to adsorb nitrogen from the mixed gas onto the sample surface. Once adsorption is complete, the glass cell is returned to room temperature to desorb the adsorbed nitrogen. The nitrogen concentration in the mixed gas then increases, and the amount of increase is quantified. From this amount of nitrogen and the cross-sectional area of ​​the nitrogen molecules, the surface area of ​​the sample (m²) can be calculated. 2 Calculate the pore specific surface area (numerical unit: m²) by dividing this by the sample amount (g). 2 Calculate the value (per g).

[0082] [Measurement of particle size distribution] The particle size distribution of the electrode can be measured by the laser diffraction / scattering method described below.

[0083] After cleaning and drying the electrodes removed from the battery, the active material-containing layer is separated from the current collector using, for example, a spatula, to obtain a powdered electrode mixture sample containing the active material. Next, the powdered sample is added to a measuring cell filled with N-methylpyrrolidone (NMP) until a measurable concentration is reached. Note that the capacity of the measuring cell and the measurable concentration will vary depending on the particle size distribution analyzer.

[0084] Ultrasound is irradiated onto a measurement cell containing NMP and an electrode mixture sample dissolved in it for 5 minutes. The output of the ultrasound should be, for example, within the range of 35W to 45W. For example, if approximately 50 ml of NMP is used as the solvent, the solvent containing the measurement sample is irradiated with ultrasound at an output of approximately 40W for 300 seconds. Such ultrasound irradiation can dissolve the aggregation of conductive agent particles and active material particles.

[0085] The measurement cell is inserted into a particle size distribution analyzer using laser diffraction / scattering to measure the particle size distribution. Examples of particle size distribution analyzers include the Microtrac3100 and Microtrac3000II.

[0086] Thus, the particle size distribution of the electrodes can be obtained.

[0087] Figure 2 shows an example of the particle size distribution measured by laser diffraction and scattering for the electrode in question, as a graph. This graph corresponds to a histogram representing the particle size distribution of the particles contained in the electrode.

[0088] One example of particle size distribution is shown by the solid line 41, and the particle size distribution of another example is shown by the dashed line 42. The solid line 41 represents the particle size distribution for an electrode of a more preferred embodiment. The particle size distribution shown by the dashed line 42 includes a peak with a maximum value in the range of 0.5 μm to 1 μm, and does not include any other parts with maximum values. The particle size distribution shown by the solid line 41 has a bimodal shape, including a first peak with a maximum value in the range of 0.5 μm to 1 μm, and a second peak with a maximum value in the range of 3 μm to 10 μm.

[0089] [Measurement of broad-field X-ray absorption fine structure and Fourier transform] The measurement and Fourier transform of the broad-field X-ray absorption fine structure can be performed as follows.

[0090] After cleaning and drying the electrodes removed from the battery in an inert atmosphere, the sample is introduced into the vacuum chamber of the measuring instrument. The sample is irradiated with X-rays, and the amount of absorption is measured to determine the X-ray absorption fine structure (XAFS) spectrum (electron yield method). In the XAFS spectrum, the structure near the absorption edge is called XANES (X-ray Absorption Near Edge Structure), and the broad-spectrum X-ray absorption fine structure that appears at energies approximately 100 eV or more above the absorption edge is called EXAFS (Extended X-ray Absorption Fine Structure). Information about the valence and structure of the atom of interest can be obtained from XANES, and in EXAFS analysis, information about the local structure of the sample (atomic species, valence, and distance around the atom of interest) can be obtained by the Fourier transform of the real spectrum (FT-EXAFS; equivalent to the radial distribution function). The obtained spectral data is normalized before and after the absorption edge to derive the XANES spectrum.

[0091] The EXAFS oscillation (χ(k)) obtained from the EXAFS analysis is expressed by the following equation using plane wave simple scattering theory.

[0092]

number

[0093] Here, the subscript i is the number of the configuration circle, S0 2 is the damping factor, N i F is the number of atoms in the i-th coordination sphere. i (k i ) is the backscattering intensity, k i is the wave number, r i σ is the bond distance. i This is the Debye-Waller (DW) factor, φi(k i ) represents a phase shift.

[0094] In general, the number of atoms in each coordination sphere (N i As ) decreases, the amplitude of the EXAFS vibration (χ(k)) decreases. Also, from the above equation, the bond distance (r) with the measured atom decreases. i The shorter the atom's information, the greater the reflection of that information in the EXAFS vibration (χ(k)).

[0095] k for EXAFS oscillation (χ(k)) 3 The EXAFS function (k) is obtained by applying a weight to enhance the high-wavenumber vibrations. 3 This is the EXAFS function (k 3 By comparing the amplitudes of χ(k), the number of coordination atoms in the measured atom can be estimated.

[0096] In this embodiment, the EXAFS function (k 3 The radial distribution function is obtained by performing a Fourier transform on the EXAFS spectrum of χ(k) in the region 2.5 ≤ k ≤ 7 (corresponding to the EXAFS region). Athena (Non-Patent Literature 1) can be used as the analysis software.

[0097] An example of the radial distribution function obtained by FT-EXAFS for the electrodes in question is shown as a graph in Figure 3.

[0098] The spectrum obtained for the electrode is shown by the solid line 49, and the spectrum obtained for the aluminum alkoxide additive used in the electrode fabrication is shown by the dashed line 90. As shown in Figure 3, the shapes of the two spectra are similar. Therefore, it can be seen that the added aluminum alkoxide exists on the active material on the electrode surface in a form that largely maintains its chemical structure and has not been transformed into other components such as alumina.

[0099] Peak A, in the range of 1.1 Å to 1.5 Å, can be attributed to Al-O bonds. Peak B, in the range of 2.8 Å to 3.2 Å, can be attributed to Al-OC bonds. In electrodes where the Al-OC bonds inherent in elemental aluminum alkoxide are retained on the active material surface without being damaged, side reactions on the active material surface are suppressed.

[0100] The electrode according to the first embodiment includes an active material having an average primary particle diameter of 200 nm to 600 nm. The active material includes a titanium-containing oxide. The electrode has a particle diameter of D 90 Ratio D 90 / D 10 However, it has a particle size distribution between 17 and 27. The electrode surface contains Al, and the radial distribution function obtained by FT-EXAFS of the K absorption edge of Al shows peak intensity I of peak A appearing in the range of 1.1 Å to 1.5 Å and peak B appearing in the range of 2.8 Å to 3.2 Å. A and I B 3.5 ≤ I A / I B The relationship ≤ 9 is satisfied. This electrode excels in high current performance and storage performance at low temperatures, enabling the realization of a battery with high energy density. It is possible.

[0101] (Second embodiment) According to a second embodiment, a battery is provided. The battery comprises a positive electrode, a negative electrode, and an electrolyte. At least one of the positive electrode and the negative electrode includes an electrode according to the first embodiment.

[0102] The battery may further include a separator positioned between the positive and negative electrodes. The positive electrode, negative electrode, and separator can constitute an electrode group. The electrolyte can be held within the electrode group.

[0103] Furthermore, such a battery may further comprise an outer casing that houses the electrode group and the electrolyte.

[0104] Furthermore, such a battery may further comprise a positive terminal electrically connected to the positive electrode and a negative terminal electrically connected to the negative electrode. At least a portion of the positive terminal and at least a portion of the negative terminal may extend outside the outer casing.

[0105] The battery in question may be, for example, a lithium-ion secondary battery. The battery may also include, for example, a non-aqueous electrolyte battery containing a non-aqueous electrolyte as the electrolyte.

[0106] The following provides a detailed explanation of the negative electrode, positive electrode, electrolyte, separator, outer casing, positive electrode terminal, and negative electrode terminal.

[0107] (1) Negative electrode The negative electrode comprises a negative electrode current collector and a negative electrode active material-containing layer (negative electrode composite layer) supported on one side or both sides of the negative electrode current collector, which includes a negative electrode active material, a conductive agent, and a binder.

[0108] The negative electrode may be the electrode according to the first embodiment. In the negative electrode embodiment, the negative electrode current collector, negative electrode active material, and negative electrode active material containing layer correspond to the current collector, active material, and active material containing layer of the electrode according to the first embodiment, respectively. Since the electrode according to the first embodiment has been described in detail above, the description of the negative electrode will be omitted here.

[0109] (2) Positive electrode 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 side or both sides of the positive electrode current collector and containing a positive electrode active material, a conductive agent, and a binder.

[0110] The battery according to the second embodiment may include the electrode according to the first embodiment as a positive electrode. Alternatively, the battery may include a positive electrode having a configuration different from that of the electrode according to the first embodiment. Hereinafter, a positive electrode having a different aspect from the electrode according to the first embodiment will be described.

[0111] Examples of the positive electrode active material include lithium-containing nickel cobalt manganese oxide (for example, Li w Ni x Co y Mn z O2, where 0 < w ≦ 1 and x + y + z = 1; or Li 1-s Ni 1-t-u-v Co t Mn u M1 v O2, where M1 is one 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 such as lithium-containing cobalt oxide (for example, LiCoO2), manganese dioxide, lithium manganese composite oxide (for example, LiMn2O4, LiMnO2), lithium-containing nickel oxide (for example, LiNiO2), lithium-containing nickel cobalt oxide (for example, LiNi 0.8 Co 0.2 O2), lithium-containing iron oxide, vanadium oxide containing lithium, and chalcogen compounds such as titanium disulfide and molybdenum disulfide may be included. The type of positive electrode active material used can be one type or two or more types.

[0112] Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide, and polyamide. The binder can be one or more types.

[0113] Examples of conductive agents include carbon black such as acetylene black and Ketjenblack, graphite, carbon fiber, carbon nanotubes, and fullerenes. The number of conductive agents can be one or more.

[0114] In the positive electrode active material-containing layer, the preferred blending ratio of positive electrode active material, conductive agent, and binder is 80% to 95% by mass for the positive electrode active material, 3% to 18% by mass for the conductive agent, and 2% to 17% by mass for the binder.

[0115] As the current collector, aluminum foil or aluminum alloy foil is preferred, and its average crystal grain size is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 5 μm or less. A current collector made of aluminum foil or aluminum alloy foil having such an average crystal grain size can dramatically increase strength, making it possible to increase the density of the positive electrode with high pressing pressure, and thereby increasing the battery capacity.

[0116] Aluminum foil or aluminum alloy foil with an average grain size of 50 μm or less is complexly influenced by many factors, including material composition, impurities, processing conditions, heat treatment history, and annealing heating conditions. The diameter is adjusted during the manufacturing process by combining these various factors.

[0117] The thickness of the current collector is preferably 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% or higher. As for 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.

[0118] The positive electrode is manufactured, for example, by suspending a positive electrode active material, a conductive agent, and a binder in a suitable solvent, applying the resulting slurry to a current collector and drying it to create a positive electrode active material-containing layer, and then pressing it. Alternatively, the positive electrode active material, conductive agent, and binder may be formed into pellets and used as the positive electrode active material-containing layer.

[0119] The positive electrode active material-containing layer preferably has a porosity of 20% to 50%. A positive electrode equipped with such a positive electrode active material-containing layer is high-density and has excellent affinity with the electrolyte. A more preferable porosity is 25% to 40%.

[0120] The density of the positive electrode active material-containing layer is 2.5 g / cm³. 3 It is preferable to set it to the above.

[0121] (3) Electrolyte Examples of electrolytes include liquid non-aqueous electrolytes prepared by dissolving an electrolyte salt (solute) in a non-aqueous solvent, and gel-like non-aqueous electrolytes obtained by compounding a liquid non-aqueous electrolyte with a polymer material.

[0122] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonyliimide [LiN(CF3SO2)2]. These electrolyte salts may be used individually or in combination of two or more types.

[0123] It is preferable to dissolve the electrolyte salt in a non-aqueous solvent at a concentration of 0.5 mol / L to 2.5 mol / L.

[0124] Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC); linear carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC); cyclic ethers such as tetrahydrofuran (THF) and 2-methyl tetrahydrofuran (2MeTHF); linear ethers such as dimethoxyethane (DME); cyclic esters such as γ-butyrolactone (BL); linear esters such as methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate; and organic solvents such as acetonitrile (AN) and sulfolane (SL). These organic solvents can be used individually or as mixtures of two or more.

[0125] Examples of polymer materials used in gel-like non-aqueous electrolytes include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0126] (4) Separator Examples of separators include porous films containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), and nonwoven fabrics made of synthetic resins.

[0127] (5) Exterior components The exterior component may be formed from laminate film or made of a metal container. When a metal container is used, the lid may be integrated with the container or be a separate component. The wall thickness of the metal container is preferably 0.5 mm or less, and more preferably 0.2 mm or less. Examples of exterior component shapes include flat, rectangular, cylindrical, coin-shaped, button-shaped, sheet-shaped, and laminated types. The exterior component may be for small batteries mounted in portable electronic devices, as well as for large batteries mounted in two-wheeled or four-wheeled automobiles.

[0128] The thickness of the laminate film exterior component should preferably be 0.2 mm or less. Examples of laminate films include multilayer films containing a resin film and a metal layer placed between the resin films. For weight reduction, the metal layer is preferably aluminum foil or aluminum alloy foil. The resin film can be made of polymer materials such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET). The laminate film can be sealed by heat fusion and molded into the shape of the exterior component.

[0129] Metal containers are made from aluminum or aluminum alloys. As aluminum alloys, alloys containing elements such as magnesium, zinc, and silicon are preferred. In aluminum or aluminum alloys, it is preferable to keep the content of transition metals such as iron, copper, nickel, and chromium to 100 ppm or less in order to dramatically improve long-term reliability and heat dissipation in high-temperature environments.

[0130] The metal container made of aluminum or an aluminum alloy preferably has an average crystal grain size of 50 μm or less, more preferably 30 μm or less, and even more 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, making it possible to further thin the container. As a result, it is possible to realize a lightweight, high-output battery with excellent long-term reliability suitable for automotive applications and other uses.

[0131] An example of such a battery will be described with reference to Figures 4 and 5. The flat-type battery shown in Figure 4 comprises a flat-shaped wound electrode group 1, an outer casing member 2, a positive electrode terminal 7, a negative electrode terminal 6, and an electrolyte (not shown). The outer casing member 2 is a bag-shaped outer casing member made of laminate film. The wound electrode group 1 is housed in the outer casing member 2. As shown in Figure 5, the wound electrode group 1 includes a positive electrode 3, a negative electrode 4, and a separator 5, and is formed by spirally winding a laminate made by stacking the negative electrode 4, separator 5, positive electrode 3, and separator 5 from the outside in that order, and then press molding it.

[0132] 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 positive electrode active material. The positive electrode active material containing layer 3b is formed on both sides 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 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 side of the inner surface of the negative electrode current collector 4a. In the rest of the negative electrode 4, the negative electrode active material containing layer 4b is formed on both sides of the negative electrode current collector 4a.

[0133] As shown in Figure 4, near the outer edge of the wound electrode group 1, the positive electrode terminal 7 is connected to the positive electrode 3. The negative electrode terminal 6 is connected to the negative electrode 4 in the outermost layer. Both the positive electrode terminal 7 and the negative electrode terminal 6 extend to the outside through an opening in the outer casing member 2.

[0134] The battery in question is not limited to the configurations shown in Figures 4 and 5, but can also have a configuration like the one shown in Figure 6.

[0135] In the rectangular battery shown in Figure 6, the wound electrode group 11 is housed in a bottomed rectangular cylindrical metal container 12, which serves as the outer casing. A rectangular lid 13 is welded to the opening of the container 12. The flattened wound electrode group 11 may have a configuration similar to that of the wound electrode group 1 described with reference to Figures 3 and 4, for example.

[0136] The negative electrode tab 14 has one end electrically connected to the negative electrode current collector and the other end electrically connected to the negative electrode terminal 15. The negative electrode terminal 15 is fixed to the rectangular cover 13 with a hermetic seal interposed with a glass material 16. The positive electrode tab 17 has one end electrically connected to the positive electrode current collector and the other end electrically connected to the positive electrode terminal 18 fixed to the rectangular cover 13.

[0137] The negative electrode tab 14 is manufactured from a material such as aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, or Si. It is preferable that the negative electrode tab 14 be made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0138] The positive electrode tab 17 is manufactured from a material such as aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, or Si. It is preferable that the positive electrode tab 17 be made of the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0139] Although the illustrated battery uses a wound electrode group in which the separator is wound together with the positive and negative electrodes, a stacked electrode group may also be used in which the separator is folded in a zigzag pattern and the positive and negative electrodes are alternately arranged at the folded portions.

[0140] The battery according to the second embodiment includes the electrodes according to the first embodiment. Therefore, this battery can be used with high current even under low temperature conditions and can exhibit excellent storage performance even under low temperature conditions. Furthermore, the battery has a high energy density.

[0141] (Third embodiment) According to a third embodiment, a battery pack is provided, which comprises the battery according to the second embodiment.

[0142] The battery pack according to the third embodiment may comprise one or more of the batteries (single cells) according to the second embodiment described above. Multiple batteries that may be included in such a battery pack can be electrically connected to each other in series or parallel to form a battery pack. Such a battery pack may include multiple battery packs.

[0143] Next, an example of a battery pack according to the third embodiment will be described with reference to the drawings.

[0144] Figure 7 is an exploded perspective view of an example battery pack according to the second embodiment. Figure 8 is a block diagram showing the electrical circuit of the battery pack in Figure 7.

[0145] The battery pack 20 shown in Figures 7 and 8 comprises a plurality of individual cells 21. Each individual cell 21 may be a flat-type battery, an example of the second embodiment described with reference to Figure 6.

[0146] Multiple individual cells 21 are stacked so that their outwardly extending negative terminals 51 and positive terminals 61 are aligned in the same direction, and then fastened together with adhesive tape 22 to form a battery pack 23. These individual cells 21 are electrically connected in series with each other, as shown in Figure 8.

[0147] The printed circuit board 24 is positioned opposite the side from which the negative terminal 51 and positive terminal 61 of the single cell 21 extend. As shown in Figure 8, the printed circuit board 24 is equipped with a thermistor 25, a protection circuit 26, and terminals 27 for supplying power to external devices. An insulating plate (not shown) is attached to the side of the printed circuit board 24 that faces the battery pack 23 to avoid unnecessary connections with the wiring of the battery pack 23.

[0148] The positive lead 28 is connected to the positive terminal 61 located at the bottom layer of the battery pack 23, and its tip is inserted into the positive connector 29 of the printed circuit board 24 for electrical connection. The negative lead 30 is connected to the negative terminal 51 located at the top layer of the battery pack 23, and its tip is inserted into the negative connector 31 of the printed circuit board 24 for electrical connection. These connectors 29 and 31 are connected to the protection circuit 26 through wiring 32 and 33 formed on the printed circuit board 24.

[0149] The thermistor 25 detects the temperature of the individual cell 21, and the detection signal is transmitted to the protection circuit 26. The protection circuit 26 can interrupt the positive side wiring 34a and the negative side wiring 34b between the protection circuit 26 and the terminal 27 for supplying power to external devices under predetermined conditions. An example of a predetermined condition is when the temperature detected by the thermistor 25 exceeds a predetermined temperature. Another example of a predetermined condition is when overcharging, over-discharging, overcurrent, etc., of the individual cell 21 is detected. This detection of overcharging, etc., is performed for individual cell 21 or for the entire battery pack 23. When detecting individual cell 21, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each individual cell 21. In the battery pack 20 of Figures 7 and 8, wiring 35 for voltage detection is connected to each individual cell 21. Detection signals are transmitted to the protection circuit 26 through these wirings 35.

[0150] Protective sheets 36 made of rubber or resin are placed on three sides of the battery pack 23, excluding the side on which the positive terminal 61 and negative terminal 51 protrude.

[0151] The battery pack 23 is housed in a storage container 37 together with each protective sheet 36 and the printed circuit board 24. Specifically, the protective sheets 36 are placed on both inner surfaces in the long direction and on each inner surface in the short direction of the storage container 37, and the printed circuit board 24 is placed on the inner surface opposite to the short direction. The battery pack 23 is located in the space enclosed by the protective sheets 36 and the printed circuit board 24. The lid 38 is attached to the top surface of the storage container 37.

[0152] Alternatively, heat-shrinkable tape may be used instead of adhesive tape 22 to secure the battery pack 23. In this case, protective sheets are placed on both sides of the battery pack, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to secure the battery pack.

[0153] Figures 7 and 8 show a configuration in which the single cells 21 are connected in series, but they may be connected in parallel to increase the battery capacity. Furthermore, assembled battery packs can also be connected in series and / or in parallel.

[0154] Furthermore, the configuration of the battery pack can be appropriately modified depending on the application. Preferably, the battery pack is designed for applications where good cycle performance is desired when drawing high current. Specific applications include power supplies for digital cameras, and in-vehicle use in two-wheeled or four-wheeled hybrid electric vehicles, two-wheeled or four-wheeled electric vehicles, and electric assist bicycles. Such a battery pack is particularly suitable for in-vehicle use.

[0155] The battery pack according to the third embodiment comprises the battery according to the second embodiment. Therefore, this battery pack can be used with a high current even under low temperature conditions and can exhibit excellent storage performance even under low temperature conditions. Furthermore, the battery pack has a high energy density.

[0156] [Examples] Examples are described below, but the present invention is not limited to the examples listed below, unless it exceeds the spirit of the invention.

[0157] (Example 1) In Example 1, the non-aqueous electrolyte battery of Example 1 was prepared by following the procedure described below.

[0158] [Fabrication of the negative electrode] Follow these steps to use Li4Ti5O 12 A lithium titanium composite oxide powder having the following composition and spinel structure was prepared.

[0159] First, anatase-type titanium dioxide was added to a solution of lithium hydroxide dissolved in pure water, and the mixture was stirred and dried. These raw materials were mixed so that the molar ratio of Li:Ti in the mixture was 4:5. Prior to mixing, the raw materials were thoroughly pulverized.

[0160] The mixed raw materials were calcined at 870°C for 2 hours in an air atmosphere. The calcined material was then ground in a ball mill using zirconia balls as the media, and washed with water. After being subjected to heat treatment at 600°C for 30 minutes in an air atmosphere, it was classified. Thus, a powder product was obtained.

[0161] The average primary particle size of the obtained product powder was analyzed by SEM. As a result, it was found that the obtained product powder consisted of primary particulate particles with an average primary particle size of 400 nm.

[0162] A portion of the primary particles described above was granulated using a spray dryer. Thus, a powder in the form of secondary particles, which were aggregated from the primary particles, was obtained.

[0163] Furthermore, the composition and crystal structure of the obtained product were analyzed using ICP and X-ray diffraction measurements. As a result, the obtained product had a spinel-type crystal structure and was Li4Ti5O 12 It was found to be a lithium titanium composite oxide having the following composition. In the X-ray diffraction spectrum, the full width at half maximum of the peak attributed to the (111) plane was 0.15 or less, indicating that a product with high crystallinity was obtained. This product powder was used as the negative electrode active material.

[0164] 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 they were mixed with a Henschel mixer to obtain a mixture. To this mixture, polyvinylidene fluoride (PVdF) as a binder, N-methylpyrrolidone (NMP) as a dispersion medium, and aluminum alkoxide were added, and kneaded with a jet paster. As the aluminum alkoxide, di-2-butoxyaluminum ethyl acetoacetate was added. Thus, a slurry (slurry for producing a negative electrode) was obtained.

[0165] 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 would be 88 parts by mass:10 parts by mass:2 parts by mass. Also, the addition amount of the aluminum alkoxide was adjusted to 0.5 mass% with respect to the negative electrode active material.

[0166] This slurry was applied to both sides of a current collector made of an aluminum foil with a thickness of 15 μm, and the coating film was dried at 125°C. Next, the dried coating film was subjected to a roll press treatment. Further, vacuum drying was performed for 12 hours in an environment at 90°C. Thus, a negative electrode was produced which comprises a current collector and a negative electrode active material-containing layer formed on both surfaces of this current collector and having an electrode density (excluding the current collector) of 2.1 g / cm 3 The thickness of the negative electrode active material-containing layer formed on each surface of the current collector was 30 μm each.

[0167] [Production of Positive Electrode] First, lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3A powder of O2 was prepared. 90 parts by mass of positive electrode active material was mixed with 5 parts by mass of acetylene black as a conductive agent using a Henschel mixer to obtain 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 fixed ratio and mixed using a planetary mixer to obtain a slurry. This slurry was applied to both sides of a current collector made of 15 μm thick aluminum foil, and the coating was dried. Furthermore, the dried coating was subjected to a roll press treatment. Thus, the current collector and the electrode formed on both sides of the current collector with an electrode density (excluding the current collector) of 3.0 g / cm³ were obtained. 3 A positive electrode was fabricated comprising a positive electrode active material-containing layer.

[0168] [Fabrication of electrode groups] Two separators made of porous polyethylene film with a thickness of 20 μm were prepared.

[0169] Next, the previously fabricated positive electrode, one separator, the previously fabricated negative electrode, and another separator were stacked in this order to obtain a laminate. This laminate was then wound into a spiral shape. By heating and pressing this at 90°C, a group of flattened electrodes with a width of 30 mm and a thickness of 3.0 mm was fabricated.

[0170] The resulting electrode group was placed in a pack made of laminate film and vacuum-dried at 85°C for 24 hours. The laminate film was constructed by forming polypropylene layers on both sides of a 40 μm thick aluminum foil, with an overall thickness of 0.1 mm.

[0171] [Preparation of liquid non-aqueous electrolytes] A mixed solvent was prepared by mixing propylene carbonate (PC) and dimethyl carbonate (MEC) in a 1:1 volume ratio. A liquid non-aqueous electrolyte was prepared by dissolving LiPF6, the electrolyte, in 1 M of this mixed solvent.

[0172] [Manufacturing of non-aqueous electrolyte secondary batteries] A liquid non-aqueous electrolyte was injected into a laminate film pack containing an electrode group as described above. Then, the pack was completely sealed by heat sealing. Thus, a non-aqueous electrolyte secondary battery having the structure shown in FIGS. 4 and 5 above, with a width of 35 mm, a thickness of 3.2 mm, a height of 65 mm, and a rated capacity of 1 Ah was manufactured.

[0173] Next, the manufactured non-aqueous electrolyte secondary battery was charged at a charging rate of 1 A (1 C) in an environment of 25°C to adjust the SOC to 40%, and then subjected to heat treatment at a temperature of 70°C for 24 hours. Subsequently, the battery cooled to room temperature was discharged at 1 A to 1.5 V in an environment of 25°C, and then charged at 1 A to adjust the SOC to 50%.

[0174] [Measurement] For the non-aqueous electrolyte battery manufactured as described above, the pore specific surface area (BET specific surface area) of the negative electrode was measured by the nitrogen adsorption method described above. The obtained results are shown in Table 1 below.

[0175] For the negative electrode included in the battery, the particle size distribution was measured by the laser diffraction / scattering method described above. The ratio D 10 to D 90 in the obtained particle size distribution, D 90 / D<​​​​​​​​​​​​​​​​​​In Examples 2 and 3, non-aqueous electrolyte batteries were manufactured using the same procedure as in Example 1, except that the conditions for mixing with a jet paster during negative electrode slurry preparation were changed to obtain the negative electrode designs shown in Table 1 below. Specifically, in Example 2, the rotation speed and mixing time were reduced, while in Example 3, the rotation speed and mixing time were increased.

[0178] (Example 4) In Example 4, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the conditions of the ball mill used to prepare the negative electrode active material were changed so that the average primary particle size of the negative electrode active material was 200 nm. Specifically, the conditions were changed to increase the rotation speed and grinding time of the ball mill.

[0179] (Example 5) In Example 5, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the firing conditions for the raw materials were changed when preparing the negative electrode active material so that the average primary particle size of the negative electrode active material was 600 nm. Specifically, the firing temperature was increased and the firing time was extended.

[0180] (Example 6) In Example 6, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the aluminum alkoxide added to the slurry for negative electrode preparation was changed from di-2-butoxyaluminum ethyl acetacetate to aluminum trisec-butoxide.

[0181] (Example 7) In Example 7, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the heat treatment conditions after washing with water during the preparation of the negative electrode active material were changed to adjust the amount of residual moisture. Specifically, the heat treatment temperature was lowered and the heat treatment time was shortened.

[0182] (Examples 8 and 9) In Examples 8 and 9, non-aqueous electrolyte batteries were manufactured using the same procedure as in Example 1, except that the degree of aggregation of the negative electrode active material particles was controlled by the amount of aluminum alkoxide added to obtain the negative electrode design shown in Table 1 below. Specifically, in Example 8, the amount added was reduced to decrease aggregation, and in Example 9, the amount added was increased to increase aggregation.

[0183] (Examples 10 and 11) In Examples 10 and 11, non-aqueous electrolyte batteries were manufactured using the same procedure as in Example 1, except that the firing conditions for the negative electrode active material raw materials and the mixing conditions using a jet paster were changed to obtain negative electrodes with the designs shown in Table 1 below. Specifically, in Example 10, the firing temperature was increased and the firing time was extended, while the rotation speed and mixing time during mixing were both decreased. In Example 11, the firing temperature was lowered and the firing time was shortened, while the rotation speed and mixing time during mixing were both increased.

[0184] (Example 12) In Example 12, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the conditions for mixing with a jet paster during negative electrode slurry preparation were changed to obtain the negative electrode design shown in Table 1 below. Specifically, the rotation speed and mixing time were increased.

[0185] (Example 13) In Example 13, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the conditions of the ball mill used to prepare the negative electrode active material were changed so that the average primary particle size of the negative electrode active material was 300 nm, and the conditions of the jet paster used to mix the negative electrode slurry were changed so that a negative electrode with the design shown in Table 1 below could be obtained. Specifically, the conditions were changed to increase the rotation speed and grinding time of the ball mill, and to decrease the rotation speed and mixing time of the jet paster.

[0186] (Example 14) In Example 14, Li4Ti5O with a spinel structure was used as the negative electrode active material. 12 Li2Na2Ti6O has an orthorhombic crystal structure instead.14 A non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that a different material was used.

[0187] (Comparative Example 1) In Comparative Example 1, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the conditions of the ball mill used to prepare the negative electrode active material were changed so that the average primary particle size of the negative electrode active material was 100 nm. Specifically, the conditions were changed to increase the rotation speed and grinding time of the ball mill.

[0188] (Comparative Example 2) In Comparative Example 2, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the firing conditions for the raw materials were changed when preparing the negative electrode active material so that the average primary particle size of the negative electrode active material was 700 nm. Specifically, the firing temperature was increased and the firing time was extended.

[0189] (Comparative Example 3) In Comparative Example 3, a non-aqueous electrolyte secondary battery was manufactured using the same procedure as in Example 1, except that the aluminum alkoxide added to the slurry for negative electrode preparation was changed from di-2-butoxyaluminum ethyl acetacetate to aluminum isopropoxide (Al(Oi-Pr)3).

[0190] (Comparative Example 4) In Comparative Example 4, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the heat treatment conditions after washing with water during the preparation of the negative electrode active material were changed to adjust the amount of residual moisture. Specifically, the heat treatment temperature was made even lower and the heat treatment time was made even shorter than in Example 7.

[0191] (Comparative Example 5-6) In Comparative Examples 5 and 6, non-aqueous electrolyte batteries were manufactured using the same procedure as in Example 1, except that the degree of aggregation of the negative electrode active material particles was controlled by the amount of aluminum alkoxide added to obtain the negative electrode design shown in Table 1 below. Specifically, in Comparative Example 5, the amount of additive was reduced to decrease aggregation, while in Comparative Example 6, the amount of additive was increased to increase aggregation.

[0192] (Comparative Example 7) In Comparative Example 7, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the addition of aluminum alkoxide to the slurry for negative electrode preparation was omitted.

[0193] The same measurements were performed on each of the non-aqueous electrolyte batteries produced in Example 2-14 and Comparative Example 1-7 as were performed on the battery produced in Example 1. The results obtained are summarized in Table 1 below. Specifically, the composition and average primary particle diameter of the negative electrode active material, as well as the specific surface area of ​​the pores of the negative electrode and the ratio D determined from the particle size distribution of the negative electrode by nitrogen adsorption method, were measured. 90 / D 10 and 1 The number of peaks relative to the frequency 2 Ratio of peak frequencies ( 2 Peak frequency / number 1 Peak frequency, and peak intensity ratio I determined by FT-EXAFS A / I B This indicates.

[0194] [Table 1]

[0195] <Rating> The performance of each non-aqueous electrolyte battery manufactured in Example 1-14 and Comparative Example 1-7 was evaluated as follows. Specifically, the input performance and storage performance under low-temperature conditions, as well as the energy density, were evaluated for each battery.

[0196] (Low-temperature input performance) The input performance of the battery under low-temperature conditions was evaluated by measuring the low-temperature input resistance as described below.

[0197] First, the battery was charged at a constant current of 1A (1C) in a 25°C constant temperature bath until the battery voltage reached 2.7V. Then, it was charged at a constant voltage until the current value reached 50mA, followed by a 10-minute rest period. Next, it was discharged at a constant current of 200mA to 1.5V, followed by a 10-minute rest period. This charge-discharge cycle was repeated three times, and the discharge capacity during the third discharge was measured and used as the reference charge capacity.

[0198] Next, the battery was charged at a constant current rate of 1A (1C) until the battery voltage reached 2.7V, followed by constant voltage charging until the current value reached 50mA, and then discharged to 50% of its base capacity.

[0199] Subsequently, the temperature of the constant temperature bath was set to -20°C, and the battery was left in the bath for 3 hours. The voltage change was measured when the battery was charged with a constant current of 1A for 10 seconds in a low-temperature (-20°C) constant temperature bath. The low-temperature input resistance was calculated by dividing the voltage change during 10 seconds of charging under low-temperature conditions by the current value.

[0200] However, while the upper limit voltage per charge was set to 2.7V for Examples 1-13 and Comparative Examples 1-7, the upper limit voltage during charging was set to 2.9V only for Example 14, which used a different negative electrode active material.

[0201] (Low-temperature storage performance) The low-temperature storage performance of the batteries was evaluated as follows:

[0202] First, the battery was charged in a 25°C constant temperature bath at a charge rate of 1A (1C) until the battery voltage reached 2.7V. Then, it was charged at a constant voltage until the current value reached 50mA, followed by a 10-minute rest period. Next, it was discharged to 1.5V at a constant current of 200mA. The discharge capacity obtained at this time was measured. Subsequently, a capacity equivalent to 50% of the measured discharge capacity was charged at 200mA. After a 10-minute rest period, it was charged at 10A for 10 seconds. The charging resistance during the 10-second 10A charge was measured.

[0203] Next, the batteries were charged to a state of charge (SOC) of 100% and a battery voltage of 2.7V, and then stored in a constant temperature bath set to -20°C for 5 weeks. After that, the resistance increase rate was measured using the method described below.

[0204] The battery was removed from the -20°C constant temperature bath and left to stand at room temperature until its temperature reached room temperature. Next, the battery was placed in a 25°C constant temperature bath and discharged to 1.5V at 1A, followed by a 10-minute rest period. Then, the battery was charged to 2.7V at 1A in the 25°C constant temperature bath, and then charged at a constant voltage until the current reached 50mA at 2.7V. Afterward, a 10-minute rest period was observed. Next, the battery was discharged to 1.5V at a constant current of 200mA. The discharge capacity obtained at this time was measured and defined as the recovery capacity. Subsequently, a capacity equivalent to 50% of the recovery capacity was charged at 200mA. After a 10-minute rest period, charging was performed at 10A for 10 seconds. The charging resistance during the 10-second 10A charge was measured.

[0205] The ratio of the charging resistance measured after storage to the charging resistance measured before storage was calculated and defined as the resistance increase rate.

[0206] However, in Example 14 only, the upper limit voltage during charging was set to 2.9V.

[0207] (Energy density) The energy density of the battery was measured as follows:

[0208] First, the battery was charged at a constant current of 1A (1C) in a 25°C constant temperature bath until the battery voltage reached 2.7V. Then, it was charged at a constant voltage until the current value reached 50mA, followed by a 10-minute rest period. Next, it was discharged at a constant current of 200mA to 1.5V, followed by a 10-minute rest period. This charge-discharge cycle was repeated three times, and the discharge capacity obtained during the third discharge cycle was measured and used as the reference discharge capacity.

[0209] The battery energy was calculated by multiplying the reference discharge capacity by the average operating voltage during discharge. Next, the (volumetric) energy density of the battery was calculated by dividing the battery energy by the battery volume.

[0210] However, in Example 14 only, the upper limit voltage during charging was set to 2.9V.

[0211] Table 2 below summarizes the performance evaluation results for each non-aqueous electrolyte battery manufactured in Examples 1-14 and Comparative Examples 1-7. The performance evaluation results for low-temperature input resistance, resistance increase rate during low-temperature storage, and energy density are shown relative to the performance value / measured value for Example 1, which is set as a baseline of 100.

[0212] [Table 2]

[0213] As shown in Table 2, the negative electrode active material contains a titanium-containing oxide having an average primary particle diameter of 200 nm to 600 nm, and the ratio D in the particle size distribution for the negative electrode is 90 / D 10 The ratio of peak intensity I in the radial distribution function obtained from FT-EXAFS is between 17 and 27. A / I B In the batteries of Examples 1-14, where the resistance was between 3.5 and 9, both the low-temperature input resistance and the resistance increase during low-temperature storage were kept low, and a good energy density was obtained.

[0214] In contrast, in Comparative Example 1, the resistance increase rate when the battery was stored at low temperatures was high, and the energy density of the battery was low. In Comparative Example 1, the average primary particle size of the negative electrode active material was small. It is presumed that the small size of the negative electrode active material particles led to many side reactions between the active material and the electrolyte, resulting in poor storage performance and a low energy density of the battery.

[0215] In Comparative Example 2, the low-temperature input performance was low. In Comparative Example 2, the average primary particle diameter of the negative electrode active material was large. It is presumed that the input performance decreased due to the large negative electrode active material particles.

[0216] In Comparative Example 3, the resistance increase rate during low-temperature storage was high. In Comparative Example 3, the ratio I A / I B obtained from the Al FT-EXAFS for the negative electrode was low. For the aluminum isopropoxide added to the negative electrode in Comparative Example 3, the amount of Al-O-C bonds present on the surface of the active material was small, and it is presumed that the effect of reducing the side reaction between the active material and the electrolyte was small.

[0217] In Comparative Example 4, both the low-temperature input resistance and the resistance increase rate during low-temperature storage were high. In Comparative Example 4, the ratio I A / I B obtained from the Al FT-EXAFS for the negative electrode was high. During the preparation of the negative electrode active material (lithium titanate with a spinel structure) used in Comparative Example 4, the conditions of the heat treatment after washing with water were restricted, resulting in a relatively large amount of residual moisture. It is presumed that an excessive amount of components derived from aluminum alkoxide was formed on the surface of the active material.

[0218] In both Comparative Examples 5 and 6, the resistance increase rate during low-temperature storage was high. In Comparative Examples 5 and 6, the degree of aggregation in the negative electrode was increased or decreased by increasing or decreasing the addition amount of aluminum alkoxide. It is presumed that the side reaction in the negative electrode increased due to the extreme degree of aggregation of the negative electrode material.

[0219] In Comparative Example 7, the resistance increase rate during low-temperature storage was high. In Comparative Example 7, aluminum alkoxide was not added to the negative electrode, so the effect of reducing the side reaction between the active material and the electrolyte by the addition was not obtained.

[0220] Also, from the comparison between Example 1 and Example 14 where the battery designs other than the composition of the negative electrode active material are similar, it is found that the use of lithium titanate having a spinel structure tends to result in better low-temperature performance. The Li2Na2Ti6O with a orthorhombic structure used in Example 1414 The operating potential of 12 is lower than that of the operating potential used in Example 1, so the reactivity with the electrolyte is enhanced. From this, it can be seen that the reaction between the negative electrode active material and the electrolyte occurs even under low temperature conditions.

[0221] According to one or more of the embodiments and examples described above, an electrode including an active material containing a titanium-containing oxide is provided. The active material includes an active material having an average primary particle diameter of 200 nm or more and 600 nm or less. Regarding the electrode, for the particle diameter D in the particle size distribution 10 with respect to the particle diameter D 90 the ratio D 90 / D 10 is 17 or more and 27 or less. In addition, at least a part of the electrode surface contains Al, and the radial distribution function by FT-EXAFS of Al with respect to the electrode surface includes peak A in the range of 1.1 Å or more and 1.5 Å or less and peak B in the range of 2.8 Å or more and 3.2 Å or less, and the peak intensity I of peak A B with respect to the peak intensity I of peak B A the ratio I A / I B has a value of 3.5 or more and 9 or less. The electrode is excellent in high current performance and storage performance at low temperature, and can realize a battery and a battery pack with high energy density.

[0222] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0223] 1…Electrode group, 2…Outer casing, 3…Positive electrode, 3a…Positive electrode current collector, 3b…Positive electrode active material layer, 4…Negative electrode, 4a…Negative electrode current collector, 4b…Negative electrode active material layer, 4c…Negative electrode current collector tab, 5…Separator, 6…Negative electrode terminal, 7…Positive electrode terminal, 11…Electrode group, 12…Container, 13…Rectangular lid, 14…Negative electrode tab, 16…Glass material, 17…Positive electrode tab, 18…Positive electrode terminal, 20…Battery pack, 21…Single cell, 22…Adhesive tape P, 23...Battery pack, 24...Printed circuit board, 25...Thermistor, 26...Protection circuit, 27...Terminal for supplying power to external devices, 28...Positive lead, 29...Positive connector, 30...Negative lead, 31...Negative connector, 32...Wiring, 33...Wiring, 34a...Positive wiring, 34b...Negative wiring, 35...Wiring, 36...Protective sheet, 37...Storage container, 38...Lid, 51...Negative terminal, 61...Positive terminal.

Claims

1. The active material comprises lithium titanate having an average primary particle diameter of 200 nm or more and 600 nm or less and having a spinel structure, Particle size D at which the cumulative frequency from the small particle size side in the particle size distribution obtained by laser diffraction / scattering method reaches 10%. １０ Particle size D where the cumulative frequency from the small particle size side is 90% ９０ Ratio D ９０ / D １０ However, it is between 17 and 27. The surface of the active material contains an aluminum alkoxide compound in at least a portion thereof, and the radial distribution function obtained by the Fourier transform of the broad X-ray absorption fine structure spectrum of Al at the K absorption edge for the surface contains a peak A appearing in the range of 1.1 Å to 1.5 Å and a peak B appearing in the range of 2.8 Å to 3.2 Å, wherein the peak intensity of peak B is I B Peak intensity I of peak A A Ratio I A / I B An electrode whose value is between 3.5 and 9.

2. The electrode according to claim 1, wherein the pore specific surface area by the nitrogen adsorption method is in the range of 2 m ２ / g or more and 10 m ２ / g or less.

3. The electrode according to claim 1 or 2, wherein the particle size distribution includes a first peak having a maximum value in the range of 0.5 μm to 1 μm and a second peak having a maximum value in the range of 3 μm to 10 μm, and the ratio of the frequency of the second peak to the frequency of the first peak is 0.18 to 0.

35.

4. The electrode according to any one of claims 1 to 3, wherein the full width at half maximum of the (111) peak in the X-ray diffraction spectrum of the lithium titanate is 0.15 or less.

5. Positive electrode and, The negative electrode and, It is equipped with electrolytes, A battery wherein the negative electrode includes the electrode described in any one of claims 1 to 4.

6. A battery pack comprising the battery described in claim 5.

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