Electrode, non-aqueous electrolyte battery and battery pack

Abstract

One embodiment of the present invention provides an electrode. This electrode is provided with an active material-containing layer. The active material-containing layer contains isolated particles of an active material that is represented by formula (1). With respect to the cumulative distribution of the circularity of the active material-containing layer, the average circularity at 25% of the cumulative distribution is from 0.05 to 0.60, and the average circularity at 90% of the cumulative distribution is from 0.3 to 0.85. The void fraction of the active material-containing layer is from 10% to 25% as determined by a mercury intrusion method. (1): LiaNi(1-b-c-d)CobMncMdO2 In the formula, 1 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.1, and M represents one or more elements that are selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga and V.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The present invention relates to an electrode, a nonaqueous electrolyte battery, and a battery pack. [Background technology]

[0002] In recent years, with the spread of electric vehicles (EVs) and electric buses (EV buses), there is a need to increase the driving distance per charge. For the lithium-ion batteries that power these vehicles, there is a strong demand for high energy density lithium-ion batteries from the perspective of increasing the charging capacity per pack and reducing weight. One method of increasing the energy density is to increase the capacity of the battery. To increase the capacity of a battery, LNCM (lithium, nickel, manganese, cobalt) composite oxides, which have a large capacity per unit mass, are promising as positive electrode active materials. In order to increase the capacity of a battery using this LNCM positive electrode active material, if a high positive electrode potential of 4.2 V or more is used, at which a large capacity can be extracted, resistance increases significantly due to gas generation caused by a side reaction between the surface of the positive electrode active material particles and the electrolyte. This causes a problem of significant deterioration in life characteristics during cycles and calendaring (storage). In other words, it has been difficult to achieve both resistance suppression and high capacity. In addition, conventional LNCM positive electrode active materials are generally polycrystalline, which form secondary particles formed by aggregation of fine primary particles. These particles have a circularity close to 1, and when filled into the positive electrode composite layer, they create many voids, which prevents the positive electrode density from increasing. In lithium-ion secondary batteries, where the positive electrode and negative electrode must be stored in a limited space, it is difficult to increase the battery capacity because the positive electrode area cannot be increased. Furthermore, because the particles are spherical, with a circularity close to 1, the contact points between the particles and the conductive additive are point contacts. As a result, the conductivity decreases due to the expansion and contraction of the positive electrode active material caused by cycling, and the AC resistance increases. In addition, during cycling or calendaring (storage) at high potentials, the oxidation reaction between the positive electrode and the electrolyte in the high SOC (State of Charge) region causes the formation of a positive electrode film in the polycrystalline system with a large specific surface area, which also increases the DC resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2008-186753 [Patent Document 2] Japanese Patent Publication No. 2020-87879 [Patent Document 3] International Publication No. WO2018-088320 [Patent Document 4] International Publication No. WO2019-150559 [Patent Document 5] International Publication No. WO2020-110486 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide an electrode, a nonaqueous electrolyte battery, and a battery pack in which an increase in resistance during cycling or calendaring at a high potential is suppressed. [Means for solving the problem]

[0005] According to an embodiment, there is provided an electrode including a current collector and an active material-containing layer formed on the current collector. The active material-containing layer includes single particles of an active material represented by the following formula (1). In the cumulative distribution of circularity of the active material-containing layer, the average circularity at 25% of the cumulative distribution is 0.05 to 0.60, and the average circularity at 90% of the cumulative distribution is 0.3 to 0.85. The active material-containing layer has a porosity of 10% or more and 25% or less as measured by mercury intrusion porosimetry. Li a Ni (1-b-c-d) Co b Mn c M d O2(1) Here, 1≦a≦1.2, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V. According to an embodiment, there is provided an electrode including a current collector and an active material-containing layer formed on the current collector. The active material-containing layer includes single particles of an active material represented by the following formula (1) and a conductive agent. The unit particle containing the single particle and the conductive agent includes a single particle of the active material and an aggregate in which the single particle of the active material is composited with the conductive agent. In the cumulative distribution of circularity for the single particle and the unit particle containing the conductive agent, the average circularity at 25% of the cumulative distribution is 0.05 to 0.60, and the average circularity at 90% of the cumulative distribution is 0.3 to 0.85. The active material-containing layer has a porosity of 10% or more and 25% or less as measured by mercury intrusion porosimetry. Li a Ni (1-b-c-d) Co b Mn c M d O2(1) Here, 1≦a≦1.2, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V. According to another embodiment, a non-aqueous electrolyte battery is provided. The non-aqueous electrolyte battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode is an electrode according to the embodiment.

[0006] According to another embodiment, a battery pack is provided, the battery pack including a nonaqueous electrolyte battery according to the embodiment. [Brief description of the drawings]

[0007] [Figure 1] FIG. 4 is a graph showing a cumulative distribution of circularity for a positive electrode according to an embodiment. [Diagram 2] FIG. 2 is an exploded perspective view of an example of a nonaqueous electrolyte battery according to the embodiment. [Diagram 3] 3 is a partially exploded perspective view of an electrode group used in the nonaqueous electrolyte battery shown in FIG. 2. [Figure 4]FIG. 2 is a block diagram showing an example of an electric circuit of the battery pack according to the embodiment. Embodiment

[0008] In order to improve the high-output characteristics, it has been proposed that the particle diameter of the positive electrode active material containing secondary particles is 1 μm to 10 μm, and the average circularity is 0.05 or more and 0.6 or less. However, when the positive electrode contains such secondary particles, cracks occur at the particle boundaries of the positive electrode active material during electrode pressing, and a film is formed on the crack surface due to a side reaction with the electrolyte during charge-discharge cycles. Therefore, the resistance increase becomes significant. In addition, in order to improve the volume capacity and volume capacity retention rate, it has been proposed that the positive electrode active material contains secondary particles and single particles, has an average particle diameter of 2 μm to 20 μm, has a first peak in the circularity range of 0.4 to 0.7, and has a second peak in the circularity range of 0.75 to 0.95. However, since such a particle configuration contains secondary particles, it is not possible to suppress the increase in resistance during cycling for the same reason as described above.

[0009] As a result of intensive research, the present inventors have found for the first time that the relationship between the circularity and porosity in the active material-containing layer is important in suppressing the increase in resistance at high potential. Even if the circularity of the active material-containing layer is specified, if the porosity is not appropriate for that circularity, the electrode density will be low or the contact between the particles will not be sufficiently secured, causing the AC (alternating current) resistance to increase during cycles and calendaring (storage, preservation), and at high potentials, the oxidation reaction of the electrolyte will be promoted on the surfaces of the separated particles, so that the DC (direct current) resistance will also increase. By using single particles of the positive electrode active material that have no particle boundaries and do not crack, and optimizing the average circularity of the active material and the positive electrode porosity, the contact between particles in the positive electrode is sufficiently maintained, and the increase in AC resistance and DC resistance during cycling and calendaring (storage, preservation) at high potential can be suppressed. That is, in an active material-containing layer containing single particles of the active material represented by the following formula (1), the average circularity at 25% of the cumulative distribution, determined from the cumulative distribution when the circularity is measured, is set to 0.05 to 0.60, and the average circularity at 90% of the cumulative distribution is set to 0.3 to 0.85. In addition, the porosity of the active material-containing layer measured by mercury intrusion porosity is set to 10% to 25%. This makes it possible to provide a positive electrode for a nonaqueous electrolyte battery in which the increase in DC resistance and AC resistance is suppressed even during cycling and calendaring at high potential. Li a Ni (1-b-c-d) Co b Mn c M d O2(1) Here, 1≦a≦1.2, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V. (First embodiment) The following describes in detail the electrodes of the first embodiment. The electrodes can be applied to, for example, a positive electrode, a negative electrode, or both a positive electrode and a negative electrode.

[0010] The electrode includes a current collector and an active material-containing layer formed on at least one surface of the current collector. When the current collector has, for example, a sheet shape, the active material-containing layer can be supported on at least one main surface of the current collector. The active material-containing layer contains single particles of the active material represented by the above formula (1). The active material-containing layer can contain materials other than the active material, such as a conductive agent and a binder.

[0011] The lithium-containing metal oxide represented by the above formula (1) has a large capacity per unit mass and a voltage of 4.2V (vs. Li / Li +By using up to the above positive electrode potential, a large capacity can be obtained. The molar ratio a in formula (1) can vary as the positive electrode intercalates and deintercalates lithium ions. A more preferable range is 1.05 ≦ a ≦ 1.15.

[0012] By setting the molar ratio b in formula (1) to 0 < b ≦ 0.4 and the molar ratio c to 0 < c ≦ 0.4, since the lithium-containing metal oxide further contains Co and Mn in addition to Ni as the transition metal, the capacity per unit mass increases. A more preferable range for the molar ratio b and the molar ratio c is 0.05 ≦ b ≦ 0.2, 0.05 ≦ c ≦ 0.2.

[0013] A more preferable range for the molar ratio d of the element M in formula (1) is 0.01 ≦ d ≦ 0.05. By including the element M, for example, when M = Al, the lattice strain decreases and the Li ion diffusivity improves. When M = Mg, the bulk electron conductivity improves and the apparent discharge capacity improves. Furthermore, the cycle stability under high voltage improves. When M = Zr, the cycle characteristics improve. When M = Ti, the cycle characteristics improve due to the alleviation of the phase change under high voltage charge and discharge. When M = Ga, the bulk electron conductivity improves and the cycle characteristics improve.

[0014] The single particles of the active material represented by formula (1) do not contain grain boundaries inside. Therefore, the specific surface area of the single particles is small, and cracks due to the expansion and contraction of the particles are unlikely to occur. Therefore, this single particle is advantageous for suppressing the increase in AC resistance caused by the reduction of contact points or gas generation, and the increase in DC resistance caused by the side reaction with the non-aqueous electrolyte at the particle interface. The average particle diameter (D50) of the single particles can be in the range of 1 μm or more and 8 μm or less. If the average particle diameter is less than 1 μm, it may be difficult to handle the particles. On the other hand, if the average particle diameter exceeds 8 μm, the input / output performance of the electrode may decrease.

[0015] The circularity is the circularity of the unit particles constituting the active material-containing layer. The unit particles are the smallest unit particles obtained when the active material-containing layer is crushed under specified conditions. The crushing conditions are as described below. Most of the unit particles are single particles of the active material, but they may also include aggregates in which other substances are attached or bound to the single particles of the active material. The unit particles obtained by crushing the active material-containing layer under the conditions described below reflect the shape of the single particles of the active material. Examples of substances contained in the aggregates include conductive agents, binders, etc.

[0016] The cumulative distribution of circularity is a cumulative distribution of the number of particles arranged from smallest to largest circularity. In the electrode of the embodiment, the average circularity at 25% of the cumulative distribution is 0.05 to 0.60, and the average circularity at 90% of the cumulative distribution is 0.3 to 0.85. The average circularity at 90% of the cumulative distribution is greater than the average circularity at 25% of the cumulative distribution. When the average circularity is close to 1, the particles become close to a perfect circle, so that the filling property of the active material decreases and the battery capacity decreases significantly. By reducing the average circularity, the particles become close to an ellipse, flattened shape, plate-like, square or fibrous shape, or the surface irregularities become large. As a result, the contact points between active materials and the contact points between the active material and the conductive agent become surfaces rather than points, and the electrode density is easily increased. The reason why the lower limit of the average circularity is set to 0.05 is that the circularity of active materials that can be produced with current technology is around 0.05. The upper limit of the average circularity at 25% cumulative is preferably 0.55. This can enhance the effect of suppressing the increase in resistance during cycling at high potential. A more preferable range of the average circularity at 25% cumulative is 0.4 or more and 0.55 or less. This can further enhance the effect of suppressing the increase in resistance during cycling at high potential. A more preferable range is 0.5 or more and 0.55 or less. On the other hand, it is preferable that the upper limit of the average circularity at 90% cumulative is 0.81. This can enhance the effect of suppressing the increase in resistance during cycling at high potential. A more preferable range of the average circularity at 90% cumulative is 0.5 or more and 0.81 or less. This can further enhance the effect of suppressing the increase in resistance during cycling at high potential. A more preferable range of the average circularity at 90% cumulative is 0.5 or more and 0.80 or less. In addition, in order to suppress the increase in resistance during cycling at high potential, it is preferable that the lower limit of the average circularity at 90% cumulative is 0.75. It is desirable to set the average circularity at 10% accumulation to 0.4 or more and 0.47 or less, which can enhance the effect of suppressing the increase in resistance during cycles at high potential. It is desirable to set the average circularity at 75% of the cumulative length to 0.65 or more and 0.73 or less, which can enhance the effect of suppressing the increase in resistance during cycles at a high potential. When the average circularity at 25% of the cumulative total is 0.05 to 0.60 and the average circularity at 90% of the cumulative total is 0.3 to 0.85, it is desirable to set the average circularity at 10% of the cumulative total to 0.4 to 0.47 and the average circularity at 75% of the cumulative total to 0.65 to 0.73. This is expected to suppress the resistance in both cycles at high potential and calendaring at high potential. Furthermore, it is desirable to set the average circularity at 10% cumulative to 0.4 or more and 0.47 or less, the average circularity at 25% cumulative to 0.5 or more and 0.55 or less, the average circularity at 75% cumulative to 0.65 or more and 0.73 or less, and the average circularity at 90% cumulative to 0.75 or more and 0.81 or less. A cumulative distribution that satisfies this condition may have a peak of the average circularity at about 0.6, and may have a distribution that is almost symmetrical around the peak, as shown in FIG. 1, for example. As a result, the electrode density, contact between particles, contact between particles and electrolyte, etc., when the porosity is set to 10% or more and 25% or less, can be made appropriate, so that the resistance increase in both the cycle at high potential and the calendar at high potential can be suppressed.

[0017] The reason for setting the porosity of the active material-containing layer in the range of 10% to 25% will be explained. In order to prevent the liquid from drying up due to the reaction consumption between the active material and the electrolyte, it is desirable to ensure a porosity of about 30%. However, if the porosity of the electrode containing the above single particles and having the average circularity of cumulative 25% and 90% specified as described above exceeds 25%, the density is low and the contact between the particles cannot be sufficiently ensured, so that the AC resistance increases due to expansion and contraction due to cycling, and further, in high potential cycles and calendaring, the oxidation reaction of the electrolyte is promoted on the separated particle surfaces, so that the DC resistance also increases. Therefore, the battery capacity is greatly reduced. In order to suppress the increase in resistance at high potential, the porosity is set to 25% or less. Since the reaction with the electrolyte is suppressed, the consumption of the electrolyte is small even with such a small porosity, and the liquid from drying up can be prevented. However, if the porosity is set to less than 10%, the electrode's ability to absorb the electrolyte decreases, so the resistance increase increases and the cycle also deteriorates. The porosity is more preferably in the range of 20% to 24%.

[0018] The conductive agent can improve the current collecting performance and suppress the contact resistance between the active material and the current collector. The conductive agent preferably contains a carbon material. Examples of the carbon material include acetylene black, ketjen black, furnace black, graphite, carbon nanotubes, and carbon nanofibers. The active material-containing layer can contain one or more of the above carbon materials.

[0019] The conductive agent has, for example, a particle or fiber shape. The average particle size of the conductive agent particles is preferably 20 nm or more and 100 nm or less. The proportion of the conductive agent in the active material-containing layer is preferably, for example, 3 mass % or more and 20 mass % or less.

[0020] Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber. The type of binder used may be one or more. The proportion of the binder in the active material-containing layer is preferably 1% by mass or more and 1.8% by mass or less.

[0021] The density of the active material-containing layer is 3.2 g / cm 3 More than 3.8g / cm 3 It is preferable that:

[0022] The current collector may be, for example, a metal foil or an alloy foil. Examples of the metal foil include aluminum foil, stainless steel foil, and nickel foil. Examples of the alloy foil include aluminum alloy, copper alloy, and nickel alloy.

[0023] The electrode is produced, for example, by the following method. An active material, a conductive agent, and a binder are kneaded together with a solvent (e.g., N-methylpyrrolidone (NMP)) to prepare a slurry. The obtained slurry is applied to a current collector, dried, and then pressed to obtain an electrode. The voids in the active material-containing layer can be adjusted by pressing with a load according to the composition of the active material-containing layer. If necessary, a cutting step to a predetermined width may be performed before or after pressing. The cumulative distribution of circularity for single particles and unit particles containing a conductive agent can be adjusted to a target distribution by, for example, adjusting the conditions of a process for preparing a slurry (also called a paste). The preparation process is performed, for example, by the following method. An active material and a conductive agent are mixed to form a composite material (compound) of the active material and the conductive agent. The composite material and the binder obtained are dispersed in a solvent and kneaded using a planetary mixer. The kneaded material is then mixed in a bead mill device to prepare a slurry (paste). A target cumulative distribution can be obtained by comprehensively considering the shapes of the active material and the conductive agent, the affinity between the active material and the solvent, the kneading conditions, and the like. The affinity between the active material and the solvent can be affected, for example, by the active material composition, the distance between the active material, the conductive agent, and the binder, and the like. When the affinity between the active material and the solvent is high, the active material is easily dispersed uniformly in the slurry (paste). When the affinity between the active material and the solvent is different, it is possible to obtain a different cumulative distribution even if the subsequent kneading conditions are the same. Furthermore, when the rotation speed of the beads in the bead mill is high, the circularity of the unit particle tends to approach 1. When the solids concentration of the slurry (paste) during kneading is high, shear forces are more likely to be applied to the processed materials (active material, conductive agent, etc.). By adjusting the affinity between the active material and the solvent and the solids concentration, it is possible to make the dispersibility of the active material and conductive agent appropriate without applying large shear forces, making it easier to reduce the circularity of the unit particle.

[0024] The methods for measuring the circularity, porosity, average particle size, and composition of the active material are described below. First, the method for removing the electrode from the battery is described.

[0025] First, prepare a battery to be measured. The battery to be measured must have a discharge capacity of 80% or more of its rated capacity. In other words, batteries that have deteriorated excessively are not to be measured.

[0026] Next, the prepared battery is discharged until the open circuit voltage is 2.0 to 2.2 V. Next, the discharged battery is transferred into a glove box filled with argon, the dew point of the internal atmosphere being −70° C. The battery is opened in such a glove box. The electrode group is removed from the cut-open battery. If the removed electrode group includes a positive electrode lead and a negative electrode lead, the positive electrode lead and the negative electrode lead are cut off, taking care not to short-circuit the positive electrode and the negative electrode.

[0027] Next, the electrode group is disassembled into a positive electrode, a negative electrode, and a separator. The electrode (e.g., the positive electrode) thus obtained is washed using diethyl carbonate as a solvent. In this washing, the disassembled members are completely immersed in the diethyl carbonate solvent and left in that state for 60 minutes.

[0028] After cleaning, the electrodes are subjected to vacuum drying. During vacuum drying, the pressure is reduced from atmospheric pressure to -97 kPa or more in a 25°C environment, and this state is maintained for 10 minutes. The electrodes taken out in this manner are measured using the following method.

[0029] Circularity measurement method For example, a flow-type image analysis particle size / shape measurement device (Particle Insight by Shimadzu Corporation) is used as the device. The active material-containing layer is drawn from the electrode with a spatula to obtain peeled powder. The peeled powder is crushed in an agate mortar or the like, collected in a 50 ml beaker, and about 10 ml of ethanol is added. After that, the measurement sample is subjected to dispersion treatment for 1 minute in a 200 W ultrasonic bath. About 1 g of the measurement sample is placed in a beaker containing 60 ml of pure water, and the measurement is performed while stirring with a stirrer. The stirrer speed in the beaker is set to 350 rpm. The circulation flow rate of the sample solution to the device is set to a pump rotation speed of 70 rpm (circulation flow rate: about 100 ml / min). The circularity obtained from the image analysis of about 9,000 particles is plotted as a cumulative distribution for the number of particles, and the average circularity in a predetermined cumulative distribution is tallied. For example, the average circularity at 25% cumulative is the sum of the circularities up to 25% cumulative distribution divided by the cumulative number up to 25% cumulative distribution. The average circularities at 10%, 75%, and 90% cumulative can be calculated in the same way. An example of a cumulative distribution is shown in Figure 1. In Figure 1, the horizontal axis is the circularity of the particles, and the vertical axis is the frequency (%). The frequency (%) is the percentage of the number of particles at each circularity out of the total number.

[0030] porosity A plurality of rectangular measurement samples are cut out from the electrode. The dimensions of the measurement samples are, for example, 1.25 cm x 2.50 cm. Next, the mass of the cut out measurement samples is measured. Next, 16 measurement samples are placed in the cell of the measurement device. These measurement samples are measured under conditions of an initial pressure of about 10 kPa (about 1.5 psia, equivalent to a pore diameter of about 120 μm) and a maximum pressure of 414 MPa (about 59986 psia, equivalent to a pore diameter of about 0.003 μm) to obtain a pore distribution curve of the electrode. As the measurement device, for example, a Shimadzu Micromeritics pore distribution measurement device Autopore 9520 is used.

[0031] Next, the active material-containing layer is peeled off from another measurement sample cut out from the same electrode, for example, using a spatula, to obtain a collector piece. Next, the mass of this collector piece is measured. Next, the mass of the active material-containing layer contained in the measurement sample is obtained by subtracting the mass of the collector piece from the mass of the measurement sample. Next, the pore distribution curve of the electrode obtained by the above method is recalculated and converted into the pore distribution curve of the active material-containing layer. In this way, the pore distribution curve of the active material-containing layer is obtained. From the pore distribution obtained as above and the mass of the active material-containing layer, the pore volume per 1 g of the active material-containing layer can be obtained. The pore volume obtained (mL / g) is divided by the volume per 1 g of the active material-containing layer to obtain the porosity.

[0032] Average particle size The active material-containing layer is peeled off from the electrode using, for example, a spatula, ultrasonically crushed, and measured with a particle size distribution measuring device (for example, a laser diffraction type particle size distribution measuring device SALD-2300 (manufactured by Shimadzu Corporation)).

[0033] Active material composition The composition of the active material can be obtained by measuring the surface of the electrode removed from the battery using X-ray fluorescence (XRF) using the method described above.

[0034] The electrode according to the first embodiment described above includes an active material-containing layer containing a single particle of the active material represented by the formula (1). In the cumulative distribution of circularity of the active material-containing layer, the average circularity at 25% of the cumulative distribution is 0.05 to 0.60, and the average circularity at 90% of the cumulative distribution is 0.3 to 0.85. The porosity of the active material-containing layer measured by mercury intrusion porosimetry is 10% to 25%. According to the electrode of the embodiment, increases in both AC resistance and DC resistance can be suppressed even during cycling or calendaring at high potential.

[0035] Second embodiment According to the second embodiment, a nonaqueous electrolyte battery is provided. The nonaqueous electrolyte battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The electrode according to the first embodiment can be used as the positive electrode.

[0036] Next, the nonaqueous electrolyte battery according to the second embodiment will be described in detail. The nonaqueous electrolyte battery according to the second embodiment may include an electrode group. The electrode group includes a positive electrode and a negative electrode. The electrode group may further include a separator located between the positive electrode and the negative electrode. The positive electrode may include a positive electrode current collector tab electrically connected to the electrode group. The negative electrode may include a negative electrode current collector tab electrically connected to the electrode group. The nonaqueous electrolyte battery according to the second embodiment may further include an exterior member. The electrode group may be housed in this exterior member. The exterior member may further house a nonaqueous electrolyte. The nonaqueous electrolyte may be impregnated into the electrode group housed in the exterior member. The nonaqueous electrolyte battery according to the second embodiment may further include a positive electrode terminal and a negative electrode terminal electrically connected to the exterior member. The positive electrode terminal may be electrically connected to the positive electrode current collector tab of the positive electrode. The negative electrode terminal may be electrically connected to the negative electrode current collector tab of the negative electrode.

[0037] The negative electrode, the positive electrode, the electrolyte, the separator, the exterior member, the negative electrode terminal, and the positive electrode terminal will be described in detail below. (1) Positive electrode As the positive electrode, the electrode according to the above-mentioned first embodiment can be used. (2) Negative electrode The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer formed on the negative electrode current collector. The negative electrode active material-containing layer may include a conductive agent and a binder in addition to the negative electrode active material.

[0038] The negative electrode active material, the conductive agent, the binder, and the negative electrode current collector will be described below.

[0039] <Negative electrode active material> The negative electrode active material is 0.4V (vs. Li / Li + ) or more. The nonaqueous electrolyte battery according to the second embodiment, which includes such a negative electrode, can suppress the deposition of lithium due to charging and discharging. Therefore, such a nonaqueous electrolyte battery has excellent rapid charging and discharging characteristics. Examples of the negative electrode active material include Li4+x Ti5O 12 (x varies in the range of -1 ≦ x ≦ 3 due to charge and discharge reactions), spinel-type lithium titanate represented by Li 2+x Lithium titanate of the ramsdellite type represented by Ti3O7 (x varies in the range of -1 ≦ x ≦ 3 due to charge and discharge reactions), niobium titanium composite oxide represented by Nb2TiO7, or a metal composite oxide containing at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe and Ti is used. The metal composite oxide containing at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe and Ti is, for example, TiO2-P2O5, TiO2-V2O5, TiO2-P2O5-SnO2, or TiO2-P2O5-MO (M is at least one element selected from the group consisting of Cu, Ni, and Fe). These metal composite oxides change into lithium titanium composite oxides by inserting lithium upon charging. Among the lithium titanium composite oxides, spinel-type lithium titanate is excellent in cycle characteristics and is preferable.

[0040] The negative electrode active material may contain, for example, a carbonaceous material or a metal compound. Examples of the carbonaceous material include natural graphite, artificial graphite, coke, vapor-grown carbon fiber, mesophase pitch-based carbon fiber, spherical carbon, or resin-fired carbon. More preferable carbonaceous materials include vapor-grown carbon fiber, mesophase pitch-based carbon fiber, or spherical carbon. The carbonaceous material preferably has an interplanar spacing d of the (002) plane by X-ray diffraction 002 of 0.34 nm or less.

[0041] As the metal compound, a metal sulfide or a metal nitride can be used. Examples of the metal sulfide include titanium sulfide such as TiS2, molybdenum sulfide such as MoS2, and iron sulfide such as FeS, FeS2, or Li x FeS2. As the metal nitride, lithium cobalt nitride (for example, Li s Co t N, 0 < s < 4, 0 < t < 0.5) can be used.

[0042] <Conductive agent> Examples of conductive agents include carbonaceous materials such as acetylene black, carbon black, and graphite.

[0043] <Binding agent> Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, and styrene-butadiene rubber.

[0044] <Negative electrode current collector> When the negative electrode active material is a material capable of absorbing and releasing lithium ions, the negative electrode current collector can be made of a material that is electrochemically stable at the lithium ion absorbing and releasing potential of the negative electrode active material. The negative electrode current collector is preferably a metal foil made of at least one selected from copper, nickel, stainless steel, and aluminum, or an alloy foil made of an aluminum alloy containing at least one element selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The shape of the negative electrode current collector can be various depending on the application of the battery.

[0045] <Manufacturing method> The negative electrode can be produced, for example, by the following method. First, the negative electrode active material, the binder, and, if necessary, the conductive agent are suspended in a commonly used solvent, such as N-methylpyrrolidone, to prepare a slurry for producing the negative electrode. The obtained slurry is applied onto the negative electrode current collector. The applied slurry is dried, and the dried coating film is pressed to obtain a negative electrode including the negative electrode current collector and the negative electrode active material-containing layer formed on the negative electrode current collector.

[0046] (3) Separator The separator is not particularly limited as long as it has insulating properties, and may be a porous film or nonwoven fabric made of a polymer such as polyolefin, cellulose, polyethylene terephthalate, or vinylon. The separator may be made of one type of material or a combination of two or more types. The thickness of the separator can be from 5 μm to 20 μm.

[0047] (4) Electrode group The electrode group may have a wound structure in which a positive electrode, a separator, and a negative electrode are laminated and wound, or a stacked structure in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated with separators interposed therebetween, or may have another structure.

[0048] (5) Nonaqueous electrolyte The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous electrolyte include a non-aqueous electrolyte solution and a gel-like non-aqueous electrolyte.

[0049] The electrolyte salt may be, for example, LiPF6, LiBF4, Li(CF3SO2)2N (lithium bistrifluoromethanesulfonylamide; commonly known as LiTFSI), LiCF3SO3 (commonly known as LiTFS), Li(C2F5SO2)2N (lithium bispentafluoroethanesulfonylamide; commonly known as LiBETI), LiClO4, LiAsF6, LiSbF6, lithium bisoxalatoborate {LiB(C2O4)2, commonly known as LiBOB}, or lithium difluoro(trifluoro-2-oxide-2-trifluoro-methylpropionato(2-)-0,0)borate {LiBF2OCOOC(CF3)2, commonly known as LiBF2(HHIB)}. These electrolyte salts may be used alone or in combination of two or more. As the electrolyte salt, it is preferable to use LiPF6, LiBF4, or a mixture thereof.

[0050] The electrolyte salt concentration in the non-aqueous electrolyte is preferably in the range of 1 mol / L to 3 mol / L. When the electrolyte salt concentration is in this range, it is possible to further improve performance when a high load current is applied while suppressing the effect of an increase in viscosity due to an increase in the electrolyte salt concentration in the non-aqueous electrolyte.

[0051] The non-aqueous solvent is not particularly limited. For example, the non-aqueous solvent may be a cyclic carbonate such as propylene carbonate (PC) or ethylene carbonate (EC), a chain carbonate such as diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), or dipropyl carbonate (DPC), 1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeHF), 1,3-dioxolane, sulfolane, or acetonitrile (AN). These solvents may be used alone or in combination of two or more. As the non-aqueous solvent, a non-aqueous solvent containing a cyclic carbonate and / or a chain carbonate is preferred.

[0052] (6) Exterior materials The exterior member may be, for example, a laminate film or a metal container. The thickness of the laminate film and the metal container may each be 0.5 mm or less. The exterior member may be a resin container made of polyolefin resin, polyvinyl chloride resin, polystyrene resin, acrylic resin, phenol resin, polyphenylene resin, fluorine resin, or the like.

[0053] The shape of the exterior member, i.e., the battery shape, can be flat (thin), rectangular, cylindrical, coin, button, etc. The battery can be used in both small applications such as being mounted on portable electronic devices and large applications such as being mounted on two- to four-wheeled automobiles.

[0054] An example of a laminate film is a multi-layer film including a resin layer and a metal layer interposed between the resin layers. The metal layer is preferably an aluminum foil or an aluminum alloy foil for weight reduction. The resin layer may be made of a polymer material such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET). The laminate film can be molded into the shape of an exterior member by sealing it by heat fusion.

[0055] The metal container is made of aluminum or an aluminum alloy. The aluminum alloy is preferably an alloy containing elements such as magnesium, zinc, silicon, etc. When the alloy contains a transition metal such as iron, copper, nickel, or chromium, the amount of the transition metal is preferably 100 ppm or less.

[0056] Next, an example of a nonaqueous electrolyte battery according to a second embodiment will be described in more detail with reference to the drawings.

[0057] Fig. 2 is an exploded perspective view of an example of a nonaqueous electrolyte battery according to an embodiment. The battery shown in Fig. 2 is a sealed prismatic nonaqueous electrolyte battery. The nonaqueous electrolyte battery shown in Fig. 2 includes an outer can 1, a lid 2, a positive electrode external terminal 3, a negative electrode external terminal 4, and an electrode group 5. The outer can 1 and the lid 2 form an outer casing member. The outer can 1 has a bottomed rectangular cylindrical shape and is made of a metal such as aluminum, an aluminum alloy, iron, or stainless steel.

[0058] FIG. 3 is a partially developed perspective view of an electrode group used in the nonaqueous electrolyte battery shown in FIG. 2. As shown in FIG. 3, the flat electrode group 5 is formed by winding a positive electrode 6 and a negative electrode 7 in a flat shape with a separator 8 interposed therebetween. The positive electrode 6 includes a strip-shaped positive electrode collector made of, for example, a metal foil, a positive electrode current collector tab 6a having one end parallel to the long side of the positive electrode current collector, and a positive electrode material layer (positive electrode active material-containing layer) 6b formed on the positive electrode current collector except for at least the positive electrode current collector tab 6a. On the other hand, the negative electrode 7 includes a strip-shaped negative electrode collector made of, for example, a metal foil, a negative electrode current collector tab 7a having one end parallel to the long side of the negative electrode current collector, and a negative electrode material layer (negative electrode active material-containing layer) 7b formed on the negative electrode current collector except for at least the negative electrode current collector tab 7a.

[0059] The positive electrode 6, separator 8, and negative electrode 7 are wound with the positive electrode 6 and negative electrode 7 shifted in position so that the positive electrode current collector tab 6a protrudes from the separator 8 in the winding axis direction of the electrode group, and the negative electrode current collector tab 7a protrudes from the separator 8 in the opposite direction. With such winding, the electrode group 5 has the spirally wound positive electrode current collector tab 6a protruding from one end face, and the spirally wound negative electrode current collector tab 7a protruding from the other end face, as shown in Fig. 3. The electrode group 5 is impregnated with a nonaqueous electrolyte (not shown).

[0060] As shown in Fig. 2, the positive electrode current collector tab 6a and the negative electrode current collector tab 7a are each divided into two bundles with the vicinity of the winding center of the electrode group as the boundary. The conductive clamping member 9 has first and second clamping parts 9a and 9b having a substantially U-shape, and a connecting part 9c that electrically connects the first clamping part 9a and the second clamping part 9b. One bundle of the positive and negative electrode current collector tabs 6a and 7a is clamped by the first clamping part 9a, and the other bundle is clamped by the second clamping part 9b.

[0061] The positive electrode lead 10 has a substantially rectangular support plate 10a, a through hole 10b opened in the support plate 10a, and rectangular current collecting portions 10c and 10d branching into two from the support plate 10a and extending downward. On the other hand, the negative electrode lead 11 has a substantially rectangular support plate 11a, a through hole 11b opened in the support plate 11a, and rectangular current collecting portions 11c and 11d branching into two from the support plate 11a and extending downward.

[0062] The positive electrode lead 10 sandwiches the clamping member 9 between the current collecting portions 10c and 10d. The current collecting portion 10c is disposed in the first clamping portion 9a of the clamping member 9. The current collecting portion 10d is disposed in the second clamping portion 9b. The current collecting portions 10c and 10d, the first and second clamping portions 9a and 9b, and the positive electrode current collecting tab 6a are joined by, for example, ultrasonic welding. As a result, the positive electrode 6 of the electrode group 5 and the positive electrode lead 10 are electrically connected via the positive electrode current collecting tab 6a.

[0063] The negative electrode lead 11 sandwiches the clamping member 9 between the current collecting portions 11c and 11d. The current collecting portion 11c is disposed in the first clamping portion 9a of the clamping member 9. Meanwhile, the current collecting portion 11d is disposed in the second clamping portion 9b. The current collecting portions 11c and 11d, the first and second clamping portions 9a and 9b, and the negative electrode current collecting tab 7a are joined by, for example, ultrasonic welding. As a result, the negative electrode 7 of the electrode group 5 and the negative electrode lead 11 are electrically connected via the negative electrode current collecting tab 7a.

[0064] The materials of the positive and negative electrode leads 10, 11 and the clamping member 9 are not particularly specified, but are desirably the same as those of the positive and negative electrode external terminals 3, 4. For example, aluminum or an aluminum alloy is used for the positive electrode external terminal 3, and for example, aluminum, an aluminum alloy, copper, nickel, nickel-plated iron, or the like is used for the negative electrode external terminal 4. For example, when the material of the external terminal is aluminum or an aluminum alloy, it is preferable that the material of the lead is aluminum or an aluminum alloy. Also, when the external terminal is copper, it is preferable that the material of the lead is copper, or the like.

[0065] The rectangular plate-shaped lid 2 is seam-welded to the opening of the outer can 1, for example, by laser. The lid 2 is made of a metal such as aluminum, an aluminum alloy, iron, or stainless steel. It is preferable that the lid 2 and the outer can 1 are made of the same type of metal. The positive electrode external terminal 3 is electrically connected to the support plate 10a of the positive electrode lead 10, and the negative electrode external terminal 4 is electrically connected to the support plate 11a of the negative electrode lead 11. The insulating gasket 12 is disposed between the positive and negative electrode external terminals 3, 4 and the lid 2, and electrically insulates the positive and negative electrode external terminals 3, 4 from the lid 2. It is preferable that the insulating gasket 12 is a resin molded product.

[0066] The battery according to the second embodiment includes the electrode according to the first embodiment. Therefore, the battery according to the second embodiment can suppress increases in AC resistance and DC resistance even during cycling or calendaring at a high potential.

[0067] (Third embodiment) According to a third embodiment, there is provided a battery pack including a battery. The battery according to the second embodiment is used as the battery. The number of unit cells included in the battery pack can be one or more.

[0068] A plurality of batteries can be electrically connected in series, in parallel, or in a combination of series and parallel to form an assembled battery. A battery pack may include a plurality of assembled batteries.

[0069] The battery pack may further include a protection circuit. The protection circuit has a function of controlling charging and discharging of the battery. In addition, a circuit included in a device (e.g., electronic device, automobile, etc.) that uses the battery pack as a power source may be used as the protection circuit for the battery pack.

[0070] The battery pack may further include an external terminal for current flow. The external terminal for current flow is for outputting current from the battery to the outside and inputting current to the battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminal for current flow. When the battery pack is charged, a charging current (including regenerative energy of the vehicle's power) is supplied to the battery pack through the external terminal for current flow.

[0071] Next, an example of a battery pack according to a third embodiment will be described with reference to the drawings. Fig. 4 is a block diagram showing an example of an electric circuit of the battery pack according to the embodiment.

[0072] The battery pack shown in Fig. 4 includes a plurality of flat batteries 100 having the structure shown in Fig. 2 and Fig. 3. These cells 100 are electrically connected in series with each other as shown in Fig. 4.

[0073] As shown in FIG. 4, the printed wiring board is equipped with a thermistor 25, a protection circuit 26, and a terminal 27 for supplying electricity to an external device.

[0074] A positive electrode lead 28 is connected to a positive electrode external terminal of a cell 100 in the assembled battery, and the positive electrode lead 28 is electrically connected to a positive electrode connector 29 on the printed wiring board. A negative electrode lead 30 is connected to a negative electrode external terminal of another cell 100 in the assembled battery, and the negative electrode lead 30 is electrically connected to a negative electrode connector 31 on the printed wiring board. These connectors 29 and 31 are electrically connected to the protection circuit 26 by wiring 32 and 33 formed on the printed wiring board.

[0075] The thermistor 25 detects the temperature of each of the cells 100 and transmits the detection signal to the protection circuit 26. The protection circuit 26 can cut off the positive side wiring 34a and the negative side wiring 34b between the protection circuit 26 and the terminal 27 for supplying electricity to the external device under a predetermined condition. An example of the predetermined condition is when a signal is received from the thermistor 25 indicating that the temperature of the cell 100 is equal to or higher than a predetermined temperature. Another example of the predetermined condition is when overcharging, overdischarging, overcurrent, or the like of the cell 100 is detected. This detection of overcharging, or the like is performed for each cell 100 or for all the cells 100. When detecting each cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100. In the battery pack of FIG. 4, wiring 35 for voltage detection is connected to each cell 100, and a detection signal is transmitted to the protection circuit 26 through these wirings 35.

[0076] 4 has a configuration in which a plurality of unit cells 100 are connected in series, but the battery pack according to the third embodiment may have a plurality of unit cells 100 connected in parallel in order to increase the battery capacity. Alternatively, the battery pack according to the third embodiment may include a plurality of unit cells 100 connected in a combination of series and parallel connections. The assembled battery pack may be further connected in series or parallel.

[0077] Furthermore, although the battery pack shown in FIG. 4 includes a plurality of unit cells 100, the battery pack according to the third embodiment may include a single unit cell 100.

[0078] The battery pack may be modified depending on the application. The battery pack is preferably used for applications where cycle characteristics at high current characteristics are desired. Specifically, the battery pack may be used as a power source for digital cameras, or for in-vehicle applications such as two- to four-wheel hybrid electric vehicles, two- to four-wheel electric vehicles, and power-assisted bicycles. In particular, the battery pack is preferably used for in-vehicle applications.

[0079] In an automobile equipped with a battery pack according to this embodiment, the battery pack recovers, for example, regenerative energy for driving the automobile.

[0080] The battery pack of the third embodiment described above in detail includes the battery of the second embodiment. Therefore, the battery pack of the third embodiment can suppress increases in AC resistance and DC resistance even during cycling or calendaring at a high potential. EXAMPLES

[0081] <Preparation of non-aqueous electrolyte battery> Example 1 (Preparation of positive electrode) Lithium-containing nickel-cobalt-manganese composite oxide (LiNi) formed as a single particle as the active material 0.8 Co 0.1 Mn 0.1 O2 was prepared. The average particle size (D50) of the active material was 4 μm. Acetylene black was prepared as a conductive additive (conductive agent), and polyvinylidene fluoride was prepared as a binder. These active materials, conductive additive, and binder were dissolved and mixed in N-methylpyrrolidone (NMP) in a weight ratio of 93:5:2 to prepare a paste. The specific method for preparing the paste is described below. The active material and the conductive assistant were mixed using a Henschel mixer to form a composite material (compound) of the active material and the conductive assistant. The composite material and the binder obtained were dispersed in NMP and kneaded using a planetary mixer with a volume of 20 L. At this time, in order to avoid a sudden increase in viscosity, each material was added to the NMP little by little. The kneading was performed under a solid kneading condition with a solid content concentration (Non-Volatile content; NV) of 78.5%. Next, the kneaded material was transferred to a bead mill device with a volume of 2 L, and mixing was performed at a bead rotation speed of 800 rpm to prepare a paste. A paste-like dispersion liquid was used as a positive electrode coating liquid and uniformly applied to both sides of a current collector made of strip-shaped aluminum foil. The coating film of the positive electrode coating liquid was dried to form a positive electrode active material-containing layer. After drying, the strip was press-molded under the following conditions. A press roll made of a hard chrome-plated steel roll with a press roll diameter of Φ350 mm was used, and the press load was set to approximately 8 kN / cm. The rolled electrode was cut to a specified size. A current collecting tab was welded to the cut electrode to obtain a positive electrode. (Preparation of negative electrode) Li4Ti5O as the negative electrode active material 12 A spinel-type lithium titanium oxide represented by the formula (I), graphite as a conductive agent, and polyvinylidene fluoride as a binder were prepared. The negative electrode active material, conductive agent, and binder were dissolved and mixed in NMP in a weight ratio of 94:4:2 to prepare a paste. This paste was used as a negative electrode coating liquid and was uniformly applied to both sides of a negative electrode current collector made of a strip-shaped aluminum foil. The negative electrode coating liquid was dried to form a negative electrode active material-containing layer. The strip after drying was press-molded, and then cut to a predetermined size. The electrode thickness was adjusted to 130 μm. A current collecting tab was welded thereto to obtain a negative electrode. (Preparation of electrode groups) Two nonwoven separators made of cellulose were prepared. The thickness of each separator was 8 μm. Next, one separator, a positive electrode, the other separator, and a negative electrode were stacked in this order to form a wound body. This was performed continuously, and the thus obtained wound body was arranged so that the separator was located at the outermost periphery. Next, the coil of the obtained wound body was pressed while being heated. Thus, a wound electrode group was produced. (Preparation of non-aqueous electrolyte) As a non-aqueous solvent, a mixed solvent was prepared by mixing propylene carbonate and diethyl carbonate in a volume ratio of 1:2. LiPF6 was dissolved as an electrolyte salt in this mixed solvent to a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte. (Battery Assembly) Electrode terminals were attached to the positive and negative electrodes of the wound electrode group obtained as described above. The electrode group was placed in an aluminum rectangular container. The nonaqueous electrolyte was poured into the container, and the container was sealed to obtain a nonaqueous electrolyte battery. The nonaqueous electrolyte battery was designed to have a nominal capacity of 26 Ah. Example 2 A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the thickness of the separator was 6 μm. Example 3 A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the thickness of the separator was 10 μm. Comparative Example 1 A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the pressing load was changed to about 6 kN / cm and the positive electrode porosity was changed to 26.6%. Comparative Example 2 The active material is a lithium-containing nickel-cobalt-manganese composite oxide LiNi formed in polycrystals (secondary particles). 0.8 Co 0.1 Mn 0.1 O2 was prepared. The average particle diameter (D50) of the active material was 4.4 μm. A nonaqueous electrolyte battery was produced using the positive electrode active material formed from these secondary particles in the same manner as in Example 1, except that the load in Example 1 was used for pressing.

[0082] The obtained secondary battery was charged at 2C from SOC (state of charge) 0% to SOC 100% in a 45°C environment, and then discharged at 2C from SOC 100% to 0%, repeating this charge-discharge cycle for 1000 cycles, and the AC resistance increase rate after 1000 cycles and the DC resistance increase rate after 1000 cycles were measured, and the results are shown in Table 1. The resistance increase rate was calculated assuming that 0 cycle is 1.

[0083] In addition, the AC resistance increase rate and DC resistance increase rate of the secondary battery after storage for 28 days at SOC 100% in a 65°C environment were measured, and the results are shown in Table 1. The resistance increase rate was calculated assuming that it was 1 before storage. The above cycle test and calendar test were performed at a positive electrode potential of 4.2 V (relative to Li / Li) at SOC 100%. + ) higher than the value (4.25 vs Li / Li + ) was used.

[0084] Table 1 shows the average circularity at 25% cumulative distribution and the average circularity at 90% cumulative distribution. The method for measuring each average circularity is as described above. The cumulative distribution of the circularity of the positive electrode active material-containing layer of Example 1 is shown in FIG.

[0085] [Table 1]

[0086] As is clear from Table 1, Examples 1-3 showed low AC resistance and DC resistance in the 45°C-2C cycle from SOC 0% to SOC 100% compared to Comparative Examples 1 and 2. In addition, the AC resistance and DC resistance were similarly low in the 65°C-SOC 100% calendar. This shows that the batteries according to the embodiments of the present invention are superior in suppressing resistance increase compared to the other batteries. Example 4 LiNi with an average particle size (D50) of 3.5 μm 0.8 Co 0.1 Mn 0.1 A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that O2 single particles were used. Example 5 LiNi with an average particle size (D50) of 3.5 μm 0.85 Co 0.075 Mn 0.075 A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that O2 single particles were used and the press load was changed to about 9 kN / cm to change the positive electrode porosity to 22.9%. The obtained secondary battery was subjected to a cycle test and a calendar test under the conditions described above, and the results are shown in Table 3. In Table 3, the results of Examples 1 to 3 and Comparative Examples 1 and 2 are shown together. Table 2 also shows the particle type of the positive electrode active material, the positive electrode active material composition, the average particle size D50, the average circularity at 10% cumulative distribution, the average circularity at 25% cumulative distribution, the average circularity at 75% cumulative distribution, the average circularity at 90% cumulative distribution, and the porosity for Examples 4 and 5. Table 2 also shows the measurement results for Examples 1 to 3 and Comparative Examples 1 and 2. [Table 2] [Table 3] As is clear from Tables 2 and 3, in Examples 1 to 5, the AC resistance increase rate and DC resistance increase rate in the 45°C-2C cycle from SOC 0% to SOC 100%, and the average of the AC resistance increase rate and DC resistance increase rate in the 65°C-SOC 100% calendar are smaller than those of Comparative Examples 1 and 2. Thus, Examples 1 to 5 are excellent in the effect of suppressing the resistance increase during charge / discharge cycles and calendars (storage and preservation). The results of Comparative Example 1 show that the average resistance increase rate is large when the porosity is greater than 25%, even if the cumulative distribution of circularity is similar to that of Examples 1 to 3. The results of Comparative Example 2 show that even if the average circularity at 25% of the cumulative distribution of circularity is 0.05 to 0.60 and the average circularity at 90% of the cumulative distribution is 0.3 to 0.85, the average resistance increase rate is large when the active material is polycrystalline and the porosity is greater than 25%. Furthermore, by comparing Examples 1 to 5, it is found that Examples 1 to 4, which satisfy the average circularity at 25% of the cumulative distribution of circularity being 0.55 or less and the average circularity at 90% of the cumulative distribution being 0.81 or less, have a smaller average resistance increase rate than Example 5, and are excellent in the effect of suppressing resistance in both charge / discharge cycles and calendaring (storage, preservation). Examples 1 to 4 are examples which satisfy the average circularity at 10% of the cumulative distribution being 0.4 to 0.47, the average circularity at 25% of the cumulative distribution being 0.5 to 0.55, the average circularity at 75% of the cumulative distribution being 0.65 to 0.73, and the average circularity at 90% of the cumulative distribution being 0.75 to 0.81.

[0087] According to at least one of the embodiments and examples described above, an electrode is provided. The electrode includes an active material-containing layer. The active material-containing layer includes a single particle of an active material represented by the following formula (1). In a cumulative distribution of circularity, the average circularity at 25% of the cumulative distribution is 0.05 to 0.60, and the average circularity at 90% of the cumulative distribution is 0.3 to 0.85. The active material-containing layer has a porosity of 10% to 25% by mercury intrusion porosimetry. Li a Ni (1-b-c-d) Co b Mn c M d O2(1) Here, 1≦a≦1.2, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V.

[0088] The electrode can suppress increases in AC resistance and DC resistance even during cycling or calendaring at high potential.

[0089] 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, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. The invention as originally claimed in the present application is set forth below. [1] An electrode comprising a current collector and an active material-containing layer formed on the current collector, the active material-containing layer contains a single particle of an active material represented by the following formula (1), and in a cumulative distribution of circularity, the average circularity at 25% of the cumulative distribution is 0.05 or more and 0.60 or less, and the average circularity at 90% of the cumulative distribution is 0.3 or more and 0.85 or less, The active material-containing layer has a porosity of 10% or more and 25% or less, as measured by mercury intrusion porosimetry. Li a Ni (1-b-c-d) Co b Mn c M d O2(1) Here, 1≦a≦1.2, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V. [2] The electrode described in [1] is a positive electrode. [3] The electrode according to [1] or [2], wherein the cumulative distribution of circularity is a cumulative distribution of circularity for unit particles constituting the active material-containing layer. [4] The electrode according to [3], wherein the unit particle includes the single particle and a conductive agent. [5] A non-aqueous electrolyte battery comprising a positive electrode which is the electrode according to any one of [1] to [4], a negative electrode, and a non-aqueous electrolyte. [6] A battery pack comprising the nonaqueous electrolyte battery according to [5]. The following describes the embodiments of the invention. <1> An electrode comprising a current collector and an active material-containing layer formed on the current collector, the active material-containing layer contains a single particle of an active material represented by the following formula (1) and a conductive agent, and in a cumulative distribution of circularity for a unit particle containing the single particle and the conductive agent, the average circularity at 25% of the cumulative distribution is 0.05 or more and 0.60 or less, and the average circularity at 90% of the cumulative distribution is 0.3 or more and 0.85 or less, The active material-containing layer has a porosity of 10% or more and 25% or less, as measured by mercury intrusion porosimetry. Li a Ni (1-b-c-d) Co b Mn c M d O 2 (1) Here, 1≦a≦1.2, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V. <2> <1> The electrode described in is a positive electrode. <3> The average circularity at 25% of the cumulative distribution is 0.05 or more and 0.55 or less. <1> ~ <2> 13. The electrode according to any one of claims 1 to 12. <4> The average circularity at 25% of the cumulative distribution is 0.4 or more and 0.55 or less. <1> ~ <2> 13. The electrode according to any one of claims 1 to 12. <5> the average circularity at 25% of the cumulative distribution is 0.4 or more and 0.55 or less, and the average circularity at 90% of the cumulative distribution is 0.5 or more and 0.81 or less; <1> ~ <2> 13. The electrode according to any one of claims 1 to 12. <6> The average circularity at 10% of the cumulative distribution is 0.4 or more and 0.47 or less. <1> ~ <5> 13. The electrode according to any one of claims 1 to 12. <7> The average circularity at 75% of the cumulative distribution is 0.65 or more and 0.73 or less. <1> ~ <6> 13. The electrode according to any one of claims 1 to 12. <8> <1> ~ <7> A positive electrode which is the electrode according to any one of the above items; A negative electrode; Non-aqueous electrolyte A non-aqueous electrolyte battery comprising: <9> <8> A battery pack comprising the nonaqueous electrolyte battery according to claim 1.

Claims

1. An electrode comprising a current collector and an active material-containing layer formed on the current collector, the active material-containing layer comprises a single particle of an active material represented by the following formula (1) and a conductive agent, and each unit particle comprising the single particle and the conductive agent comprises a single particle of the active material and an aggregate in which the single particle of the active material is composited with the conductive agent, and in a cumulative distribution of circularity of the unit particle, an average circularity at 25% of the cumulative distribution is 0.05 or more and 0.60 or less and an average circularity at 90% of the cumulative distribution is 0.3 or more and 0.85 or less, The active material-containing layer has a porosity of 10% or more and 25% or less, as measured by mercury intrusion porosimetry. Li a Ni (1-b-c-d) Co b Mn c M d O 2 (1) Here, 1≦a≦1.2, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V.

2. The electrode according to claim 1 is a positive electrode.

3. The electrode according to any one of claims 1 to 2, wherein the average circularity at 25% of the cumulative distribution is 0.05 or more and 0.55 or less.

4. The electrode according to any one of claims 1 to 2, wherein the average circularity at 25% of the cumulative distribution is 0.4 or more and 0.55 or less.

5. 3. The electrode according to claim 1, wherein the average circularity at 25% of the cumulative distribution is 0.4 or more and 0.55 or less, and the average circularity at 90% of the cumulative distribution is 0.5 or more and 0.81 or less.

6. The electrode according to any one of claims 1 to 5, wherein the average circularity at 10% of the cumulative distribution is 0.4 to 0.

47.

7. The electrode according to any one of claims 1 to 6, wherein the average circularity at 75% of the cumulative distribution is 0.65 or more and 0.73 or less.

8. A positive electrode which is the electrode according to any one of claims 1 to 7; A negative electrode; Non-aqueous electrolyte A non-aqueous electrolyte battery comprising:

9. A battery pack comprising the nonaqueous electrolyte battery according to claim 8.

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