Electrode, battery, and battery pack

Abstract

According to an embodiment, there is provided an electrode including an active material-containing layer containing active material particles. The active material particles include an oxide represented by the general formula: LidNi1-a-bCoaMnbO2, where 0.9≤d≤1.25, 1.1≤a / b≤1.8, and 0.65≤a / (1-a-b)≤0.9. The electrode satisfies formula (1).　(1): 2.0≤X / Y≤ 3.0, where X is a BET specific surface area (m2 / g) of the active material-containing layer, and Y is a pore specific surface area (m2 / g) of the active material-containing layer as obtained by a mercury penetration method.

Description

Electrode, Battery, and Battery Pack

[0001] An embodiment relates to an electrode, a battery, and a battery pack.

[0002] For example, in a non-aqueous electrolyte battery or the like, a lithium-containing transition metal compound is used as a positive electrode active material. The positive electrode can be produced, for example, by dispersing positive electrode active material particles, a conductive agent, and a binder in a dispersion medium to prepare a slurry, and applying this slurry to a current collector. As the specific surface area of the positive electrode active material-containing layer of this positive electrode increases, the chemical reaction field contributing to charge and discharge becomes larger. By increasing the chemical reaction field, improvement in high-current performance or low-temperature performance can be expected. On the other hand, when the specific surface area increases, side reactions with the electrolytic solution tend to occur more easily. When side reactions occur, life performance such as cycle performance and high-temperature storage performance tends to deteriorate.

[0003] International Publication No. 2023 / 131987

[0004] An object is to provide an electrode capable of realizing a battery having excellent low-temperature performance and suppressed resistance increase, a battery including this electrode, and a battery pack including this battery.

[0005] According to an embodiment, an electrode including an active material-containing layer containing active material particles is provided. The active material particles are represented by the general formula: Li a Ni 1-a-b Co a Mn b O2, 0.9 ≤ d ≤ 1.25, 1.1 ≤ a / b ≤ 1.8, 0.65 ≤ a / (1 - a - b) ≤ 0.9, and contain an oxide represented by. The electrode satisfies the following formula (1). <00,00098> 2.0 ≤ X / Y ≤ 2 3.0 (1) However, X is the BET specific surface area (m 2 / g) of the active material-containing layer, and Y is the pore specific surface area (m 2 / g) of the active material-containing layer by mercury intrusion porosimetry.

[0007] Further, according to an embodiment, a battery including the electrode of the embodiment is provided.

[0008] According to another embodiment, a battery pack including the battery of the embodiment is provided.

[0009] FIG. 1 is a plan view schematically showing an example of an electrode according to an embodiment. FIG. 2 is a cross-sectional view of an example of a battery according to the embodiment cut in the thickness direction. FIG. 3 is an enlarged cross-sectional view of part A in FIG. 2. FIG. 4 is a partially cutaway perspective view of another example of a battery according to the embodiment. FIG. 5 is an exploded perspective view of an example of a battery pack according to the embodiment. FIG. 6 is a block diagram showing the electrical circuit of the battery pack shown in FIG. 5. Embodiment

[0010] Hereinafter, embodiments will be described with reference to the drawings. In the embodiments, the same reference numerals are given to common configurations, and redundant explanations are omitted. Also, each figure is a schematic diagram for facilitating the explanation and understanding of the embodiments, and there are parts where the shape, dimensions, ratio, etc. are different from those of the actual device, but these can be appropriately designed and changed in consideration of the following explanations and known techniques.

[0011] (First Embodiment) The electrode of the first embodiment has a general formula: Li d Ni 1-a-b Co a Mn b O2, 0.9 ≤ d ≤ 1.25, 1.1 ≤ a / b ≤ 1.8, 0.65 ≤ a / (1 - a - b) ≤ 0.9, and includes an active material-containing layer containing active material particles containing an oxide represented by the formula. The electrode satisfies the following formula (1).

[0012] 2.0 ≤ X / Y ≤ 3.0 (1) However, X is the BET specific surface area (m 2 / g) of the active material-containing layer, and Y is the pore specific surface area (m 2 / g) of the active material-containing layer by mercury intrusion porosimetry.

[0013] The electrode can be at least one of a positive electrode or a negative electrode. It is desirable that the electrode is a positive electrode.

[0014] For example, in a secondary battery, ions and electrons move between the positive and negative electrodes. In batteries such as secondary batteries, the larger the specific surface area of ​​the active material-containing layer (electrode composite layer), the larger the chemical reaction field that contributes to charging and discharging, and the better the output performance at low temperatures tend to be. On the other hand, a larger specific surface area makes side reactions with the electrolyte (e.g., electrolyte solution) more likely to occur. Side reactions affect lifespan performance, such as cycle performance and high-temperature storage performance. Therefore, it is difficult to realize a battery with both excellent low-temperature output performance and lifespan performance simply by changing the composition of the active material-containing layer (electrode composite layer).

[0015] The electrode of this embodiment provides a battery with excellent low-temperature output performance and long-life performance. The active material particles containing the oxide represented by the above general formula have an a / b ratio of 1.1 to 1.8, which suppresses cation mixing in the oxide, and also facilitates reactions involving Li ion insertion and deinsertion at the electrolyte (e.g., electrolyte) interface. Therefore, the active material particles can contribute to reducing initial low-temperature resistance. The oxide represented by the above general formula has an a / (1-a-b) ratio of 0.65 to 0.9, which contributes to suppressing resistance increase. Because the active material particles containing this oxide have high thermal stability, they can suppress side reactions with the electrolyte, which contributes to improving long-life performance.

[0016] The active material particles are preferably in the form of secondary particles. Secondary particles are aggregates of primary particles, in other words, aggregates of primary particles. The active material particles may consist only of secondary particles, or they may contain individual primary particles.

[0017] In electrodes containing active material particles and secondary particles, if a large force is applied that could damage the active material, partial disintegration of the secondary particles is more likely to occur than cracking of the primary particles. When secondary particles are partially disintegrated, primary particles separate from them. The separated primary particles can enter the gaps between particles in the active material-containing layer, thereby reducing the macroscopic pores within the active material-containing layer. When the macroscopic pores are reduced, the pore specific surface area Y (m²) of the active material-containing layer obtained by mercury intrusion method decreases. 2The BET specific surface area (m²) of the active material-containing layer tends to decrease. Furthermore, suppressing the cracking of primary particles reduces the number of microscopic pores within the active material-containing layer. The reduction in microscopic pores leads to a decrease in the BET specific surface area (m²) of the active material-containing layer. 2 The increase in X ( / g) tends to be suppressed. When X / Y is less than 2.0, side reactions with the electrolyte (electrolyte solution) increase, making it difficult to suppress the increase in resistance. This is presumed to be because many of the secondary particles have been broken down. On the other hand, when X / Y is greater than 3.0, in addition to side reactions with the electrolyte (electrolyte solution), uneven reactions are more likely to occur during charging and discharging. As a result, both the initial low-temperature resistance and the rate of resistance increase increase. This is presumed to be because the aggregation of secondary particles has loosened and the primary particles have separated, as well as because the primary particles have also broken. By setting X / Y between 2.0 and 3.0, it is possible to partially break down the secondary particles while suppressing damage such as the breaking of primary particles. As a result, side reactions with the electrolyte (electrolyte solution) can be suppressed, and uneven reactions during charging and discharging can be reduced.

[0018] Therefore, by specifying the composition of the active material particles and the X / Y value as described above, we have discovered for the first time that it is possible to reduce the initial low-temperature resistance and suppress the increase in resistance during calendering and charge-discharge cycles. A more preferable range for X / Y is 2.2 to 2.6.

[0019] The electrodes of the embodiment will be described with reference to the drawings.

[0020] Figure 1 is a partially cutaway plan view schematically showing an example of an electrode according to the embodiment. Here, an example of a positive electrode is shown.

[0021] The positive electrode 3 shown in Figure 1 comprises a positive electrode current collector 3a and a positive electrode active material containing layer 3b provided on the surface of the positive electrode current collector 3a. The positive electrode active material containing layer 3b is supported on the main surface of the positive electrode current collector 3a.

[0022] Furthermore, the positive electrode current collector 3a includes a portion on its surface where the positive electrode active material-containing layer 3b is not provided. This portion functions, for example, as a positive electrode current collector tab 3c. In the illustrated example, the positive electrode current collector tab 3c is a narrow portion that is narrower than the positive electrode active material-containing layer b. The width of the positive electrode current collector tab 3c may be narrower than the width of the positive electrode active material-containing layer 3b, or it may be the same width as the positive electrode active material-containing layer 3b. Instead of the positive electrode current collector tab 3c, which is part of the positive electrode current collector 3a, a separate conductive member may be electrically connected to the positive electrode 3 and used as an electrode current collector tab (positive electrode current collector tab).

[0023] The electrode according to this embodiment comprises a current collector and an active material-containing layer (electrode composite layer) formed on the current collector.

[0024] As the current collector, for example, a sheet containing a highly electrically conductive material can be used. For example, aluminum foil or aluminum alloy foil can be used as the current collector. When using aluminum foil or aluminum alloy foil, its thickness is, for example, 20 μm or less, preferably 15 μm or less.

[0025] The current collector has an active material-containing layer formed on at least one surface. That is, the active material-containing layer may be supported on one surface of the current collector, or on both surfaces. Preferably, the surface of the current collector on which the active material-containing layer is supported is the main surface of the current collector. The current collector may also include portions that do not support the active material-containing layer. Such portions can be used, for example, as electrode tabs.

[0026] The active material-containing layer contains an active material that includes an oxide represented by the above general formula. As the oxide, for example, one or more of the above-mentioned types can be used. The active material may also contain an active material other than the oxide represented by the above general formula.

[0027] The oxide Li represented by the above general formula d Ni 1-a-b Co a Mn b It is desirable that the O2 has a rock salt layered structure.

[0028] The oxide Li represented by the above general formula d Ni 1-a-b Co a Mn b In O2, it is desirable that a satisfies the condition 0.25 ≤ a ≤ 0.5.

[0029] The active material particles have a BET specific surface area of ​​0.4 (m²). 2 / g) or more 0.8(m 2 It is desirable that the amount is less than or equal to ( / g). Furthermore, it is desirable that the active material particles have a secondary particle diameter D50 of 5 μm or more and 7 μm or less as the average secondary particle diameter. By specifying the BET specific surface area and average secondary particle diameter of the active material particles within the above range, the effect of suppressing side reactions between the electrode and electrolyte can be enhanced. The secondary particle diameter D50 is the particle diameter at which the cumulative frequency from the small particle diameter side accounts for 50% in the particle size distribution (particle diameter distribution) of the active material particles.

[0030] BET specific surface area X (m²) of the active material-containing layer 2 / g) is 7 (m 2 / g) ≤ X ≤ 8 (m 2 It is preferable that it be ( / g), and more preferably in the range of 7.0 (m 2 / g) ≤ X ≤ 8.0 (m 2 It is ( / g). Also, the pore specific surface area Y (m²) of the active material-containing layer obtained by mercury intrusion method. 2 / g) is 2.5 (m 2 / g) ≤ Y ≤ 3.5 (m 2 It is desirable that X be 7 (m 2 ( / g) or more, and Y to 2.5 (m 2 By increasing the concentration to 8 (m / g) or more, the penetration of the electrolyte (electrolyte solution) into the electrode can be promoted, thereby allowing the electrolyte to be uniformly retained on the electrode. Also, by setting X to 8 (m 2 Keep it below / g and set Y to 3.5 (m 2 By keeping it below 7 ( / g), good contact between the active material particles and the conductive agent can be maintained. Therefore, 7 (m 2 / g) ≤ X ≤ 8 (m 2 / g) and 2.5 (m 2 / g) ≤ Y ≤ 3.5 (m 2Satisfying the condition ( / g) contributes to both suppressing the increase in initial resistance (especially initial low-temperature resistance) and suppressing the increase in resistance during charge-discharge cycles.

[0031] The active material-containing layer may further include a conductive agent and a binder as auxiliary components. The conductive agent may be added as needed to enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include acetylene black, carbon black, and graphite. There may be one or more types of conductive agents. The binder can bond the active material and the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber (SBR), polypropylene (PP), polyethylene (PE), and carboxymethylcellulose (CMC). There may be one or more types of binders.

[0032] The active material-containing layer may consist, for example, of an active material, a conductive agent, and a binder.

[0033] From the viewpoint of energy density, it is desirable that the content of auxiliary components in the active material-containing layer be 25% by weight or less. For example, when preparing a slurry for producing an active material-containing layer, it is preferable that the proportions of the active material, conductive agent, and binder added to the dispersion medium be 75-97% by weight, 2-20% by weight, and 1-5% by weight, respectively.

[0034] The electrode according to this embodiment can be manufactured, for example, by the method described below.

[0035] A slurry is prepared to create an active material-containing layer. The slurry can be prepared, for example, as follows:

[0036] Secondary oxide particles represented by the above general formula, a conductive agent, and a binder are added to a dispersion medium and stirred. An example of the dispersion medium is NMP (N-methyl-2-pyrrolidone). Stirring can be performed, for example, using a bead mill. Since the active material is secondary particles, strong dispersion by the bead mill, for example by increasing the disk rotation speed and decreasing the flow rate, can suppress damage to the active material and break up the active material secondary particles without exposing new surfaces due to cracking of the active material particles. As an example, in the bead mill apparatus used in the example, when using φ2 mm zirconia beads and a packing rate of 80%, it is desirable to set the rotation speed to 1400 to 2000 rpm and the flow rate to 30 to 60 cc / min. As a result, an excessive increase in the BET specific surface area X of the active material-containing layer is suppressed, while the pore specific surface area Y of the active material-containing layer by the mercury intrusion method is reduced, so that X / Y can be kept within the range of 2.0 to 3.0.

[0037] Next, the slurry prepared as described above is applied to the surface of the current collector. At this time, it is also possible to leave uncoated areas on the current collector. After application, the coating is dried to obtain an active material-containing layer.

[0038] Next, the electrode can be obtained by pressing the active material-containing layer together with the current collector. A cutting process can also be included after drying or after pressing.

[0039] Next, we will explain the method for measuring the pore specific surface area Y of the active material-containing layer, the BET specific surface area X of the active material-containing layer, the composition of the active material, and the secondary particle diameter D50 as the average secondary particle diameter of the active material particles, using the mercury intrusion method.

[0040] (1) Preparation of the electrode to be measured First, prepare the electrode to be measured. If the electrode to be measured is one that is built into a battery, remove the electrode from the battery using the following procedure.

[0041] First, the battery is discharged. For example, in the case of a non-aqueous electrolyte battery containing lithium titanium oxide (e.g., lithium titanate) as the negative electrode active material, it is discharged from any charge state to 1.5V at a reference current value. The reference current value for this battery is determined as follows: The battery is charged with a constant current to 2.7V at a sufficiently small current value in an environment of 25°C. Next, the battery is charged at a constant voltage of 2.7V for 3 hours. The discharge capacity of this battery, which can be continuously discharged at a constant current until the voltage reaches 1.5V, is measured at a sufficiently small current value, and this is taken as the provisional reference capacity. The current value that can be supplied at a constant current over 1 hour to this provisional reference capacity is taken as the provisional reference current value. After measuring the provisional reference capacity, the battery is charged with a constant current to 2.7V at the provisional reference current value determined in this way in an environment of 25°C. Next, this battery is charged at a constant voltage of 2.7V for 3 hours. From this state, measure the discharge capacity that can be discharged at a constant current until the voltage reaches 1.5V, using a provisional reference current value. If the discharge capacity obtained here is not within ±10% of the previously determined provisional reference capacity, this discharge capacity is set as the new provisional reference capacity, and the current value that can supply constant current to this new provisional reference capacity over one hour is set as the new provisional reference current value, and the discharge capacity measurement is repeated in the same manner. On the other hand, if the measured discharge capacity is within ±10% of the previously determined provisional reference capacity, the previously determined provisional reference capacity is set as the battery's reference capacity. The discharge capacity measurement to determine the battery's reference capacity should be limited to three times or less. The current value that can supply constant current to the reference capacity over one hour is set as the reference current value. The reference current value obtained in the above manner can also be expressed as 1C.

[0042] Next, the battery, which has been discharged as described above, is placed in an inert atmosphere such as a glove box filled with argon. Inside this atmosphere, the outer casing of the battery is cut open using scissors or wire cutters and the electrode group is removed. By disassembling the removed electrode group, the electrode to be measured can be taken out. During this series of disassembly operations, electrical insulation between the positive electrode and the negative electrode should be maintained. (2) Sample preparation Next, the prepared electrode is cut into appropriate sizes using scissors or the like in an inert atmosphere to obtain a sample. An appropriate size is, for example, a strip of 12 mm x 25 mm. Next, the surface of the sample is washed with ethyl methyl carbonate (EMC), which is an organic solvent. The size of the sample may be adjusted after washing. After washing, the sample is subjected to vacuum drying. Alternatively, it may be subjected to natural drying under an argon atmosphere. (3) Measurement For mercury intrusion measurement of the sample, for example, a Shimadzu Autopore 9520 can be used. The 16 samples prepared as described above were folded and placed in a measurement cell, and measurements were taken under initial pressure of 20 kPa (equivalent to a pore diameter of approximately 60 μm) and termination pressure of approximately 400 MPa (equivalent to a pore diameter of approximately 3 nm). The pore specific surface area was calculated assuming the pore shape was cylindrical.

[0043] From the measurement results obtained using the mercury intrusion method described above, the specific surface area Y of the pores in the active material-containing layer of the electrode in the measurement sample can be determined.

[0044] Next, we will explain the method for measuring the BET specific surface area X of the active material-containing layer.

[0045] BET specific surface area refers to the specific surface area determined by the BET method, and is calculated using the N2 gas adsorption method. The analysis is carried out, for example, by the following method.

[0046] (2) Cut out several strip-shaped measurement samples with a planar shape and dimensions of 0.5 cm × 2.0 cm from the electrode prepared in the sample preparation. Measure the weight of the cut measurement samples. Next, load 24 measurement samples into the cell of the measuring device. Place these measurement samples into the measuring cell for nitrogen adsorption / desorption measurement, and N ２ Dry at a temperature of 120°C or higher under gas flow. Then, measure the specific surface area using the BET single-point method or the BET multi-point method.２ An example of a measuring device used for gas adsorption measurements is the Quantasorb manufactured by QUANTACHROME.

[0047] Next, we will explain the method for analyzing the composition of the active material.

[0048] (2) The composition of the active material can be determined by measuring the surface of the electrode prepared in the sample preparation using X-ray fluorescence (XRF).

[0049] The method for measuring the secondary particle diameter D50, which is the average secondary particle diameter of the active material particles, is described below.

[0050] (2) Scanning electron microscope (SEM) observation is performed on the electrodes prepared in the sample preparation. Five SEM images are acquired, and 10 secondary particles of the active material are randomly selected from each field of view. An aggregate of primary particles is considered a secondary particle. The particle size of each of the selected active material secondary particles, i.e., a total of 50 active material secondary particles, is measured, and the average value is calculated from the obtained measurements.

[0051] According to the electrode of the first embodiment described above, the general formula is Li d Ni 1-a-b Co a Mn b The device comprises an active material-containing layer containing active material particles that include an oxide represented by O2, 0.9 ≤ d ≤ 1.25, 1.1 ≤ a / b ≤ 1.8, and 0.65 ≤ a / (1-a-b) ≤ 0.9. The electrode satisfies the following equation (1).

[0052] 2.0 ≤ X / Y ≤ 3.0 (1) where X is the BET specific surface area (m²) of the active material-containing layer. 2 Y is the specific surface area of ​​the pores of the active material-containing layer by the mercury intrusion method (m²). 2 It is / g).

[0053] According to the electrodes of this embodiment, initial low-temperature resistance can be reduced, and resistance increases during calendar storage and charge-discharge cycles can be suppressed. Therefore, a battery with excellent low-temperature performance and lifespan can be provided.

[0054] (Second Embodiment) According to the second embodiment, a battery comprising the electrodes of the first embodiment is provided. The battery may be a primary battery or a secondary battery. An example of the battery is a non-aqueous electrolyte battery. An example of a non-aqueous electrolyte battery is a lithium battery (including a lithium-ion battery). When the battery is a non-aqueous electrolyte secondary battery, the battery includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. Such a battery may further comprise a separator disposed between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the separator can constitute an electrode group. The non-aqueous electrolyte can be held in the electrode group. The electrode group can have a structure such as, for example, a laminated structure with a separator interposed between the positive electrode and the negative electrode, or a wound structure in which the positive electrode and the negative electrode are wound in a spiral or flat spiral shape with a separator interposed between them.

[0055] Furthermore, such a battery may further comprise an outer casing that houses the electrode group and the non-aqueous electrolyte.

[0056] 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. Each electrode terminal may be connected, for example, to a current-collecting tab of the electrode in question. At least a portion of the positive terminal and at least a portion of the negative terminal may extend outside the housing member.

[0057] The positive electrode and negative electrode, separator, non-aqueous electrolyte, positive electrode terminal, negative electrode terminal, and outer casing members according to the embodiment will be described in more detail below. An example in which the electrode of the first embodiment is used as the positive electrode will be described below. <Negative Electrode> The negative electrode comprises a negative electrode current collector and a negative electrode active material containing layer (negative electrode composite layer) formed on the negative electrode current collector. The negative electrode active material containing layer may contain a negative electrode active material, a conductive agent, and a binder.

[0058] As the negative electrode active material, for example, a material that can be used in combination with active material particles contained in the positive electrode to perform a charge-discharge reaction can be used.

[0059] As the negative electrode active material, it is preferable to use a material that allows lithium insertion and deinsertion reactions to proceed at a potential 1V or more higher than the oxidation-reduction potential of lithium. Using a negative electrode active material containing such a material can suppress the deposition of lithium dendrites associated with charge-discharge cycles, thereby suppressing the decrease in lithium ions within the non-aqueous electrolyte battery system. As a result, such a non-aqueous electrolyte battery can suppress the decrease in lithium ion diffusivity associated with charge-discharge cycles, and consequently exhibit a better capacity retention rate.

[0060] An example of a substance in which lithium insertion and removal reactions can proceed at a potential 1V or more higher than the oxidation-reduction potential of lithium is a titanium-containing oxide. Examples of titanium-containing oxides include lithium titanium-containing oxide, titanium oxide, and niobium titanium-containing oxide. A single type of titanium-containing oxide may be used, or a mixture of two or more types of titanium-containing oxides may be used. Titanium-containing oxides having a spinel structure are desirable. A negative electrode active material containing a titanium-containing oxide having a spinel structure can further improve the low-temperature performance and lifespan of the battery.

[0061] Examples of lithium titanium-containing oxides include lithium titanate (e.g., Li) which has a spinel-type crystal structure. 4+x Ti5O 12 (x changes between 0 and 3 depending on the charge / discharge state) and lithium titanate having a ramsdellite-type crystal structure (for example, Li 2+x It contains Ti3O7 (where x varies between 0 and 2 depending on the charge / discharge state).

[0062] The lithium ion storage potential of lithium titanium-containing oxides is 1 V (relative to Li / Li + Preferably, it is 1 V (relative to Li / Li) + It exhibits lithium-ion storage potentials of the above.

[0063] An example of a titanium oxide is monoclinic β-type titanium dioxide TiO2(B). TiO2(B) is 1V (relative to Li / Li +At potentials above 1 / 2, the intercalation and release reactions of lithium can proceed. In addition, titanium oxide may retain some Li after charging and discharging.

[0064] An example of a niobium-titanium composite oxide is Nb₂TiO₃. Alternatively, the negative electrode active material can be an active material other than a titanium-containing oxide, such as a carbon material.

[0065] The negative electrode active material may be in any of the following forms: individual primary particles, secondary particles formed by aggregation of primary particles, or a mixture of primary and secondary particles.

[0066] The average secondary particle diameter (μm) of the negative electrode active material particles is A N (μm), when the average secondary particle diameter of the positive electrode active material (μm) is Ap (μm), the average secondary particle diameter of the negative electrode active material particles A N The ratio A of the average secondary particle diameter Ap of the positive electrode active material particles to the ratio A is preferably satisfied by the following equation (2).

[0067] 5 ≤ A(Ap / A) N ) ≤ 10 (2) The average secondary particle diameter of the negative electrode active material can be measured in the same way as described in the electrode of the first embodiment.

[0068] By setting A to 10 or less, the difference between the self-discharge rate of the positive electrode and the self-discharge rate of the negative electrode during calendar storage and charge-discharge cycles becomes smaller, thereby suppressing the rise in positive electrode potential. As a result, the degradation of the positive electrode can be suppressed. To reduce A, one can either reduce the average secondary particle diameter of the positive electrode active material or increase the average secondary particle diameter of the negative electrode active material. Reducing the average secondary particle diameter of the positive electrode active material tends to increase side reactions during charge-discharge cycles. On the other hand, increasing the average secondary particle diameter of the negative electrode active material tends to decrease the Li ion diffusivity of the negative electrode active material particles, leading to a decrease in input / output performance at low temperatures. By setting A to 5 or more and 10 or less, it is possible to ensure initial low-temperature resistance, suppress side reactions during charge-discharge cycles, and suppress the degradation of the positive electrode caused by the rise in positive electrode potential.

[0069] It is desirable to keep the ratio of the BET specific surface area of ​​the negative electrode active material particles to the BET specific surface area of ​​the positive electrode active material particles (specific surface area of ​​negative electrode active material particles / specific surface area of ​​positive electrode active material particles) to 25 or less. This brings the self-discharge rate of the negative electrode and the self-discharge rate of the positive electrode closer together, thereby suppressing the rise in the positive electrode potential. As a result, the degradation of the positive electrode can be suppressed.

[0070] Conductive agents can be added as needed to enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents in the negative electrode include carbon materials. Carbon materials are preferably those with high alkali metal absorption and conductivity. Examples of carbon materials include acetylene black, carbon black, and graphite. The number of conductive agents can be one or more.

[0071] A binder can bond the active material to the current collector. Examples of binders used in the negative electrode include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber (SBR), polypropylene (PP), polyethylene (PE), and carboxymethylcellulose (CMC). One or more types of binders can be used.

[0072] A negative electrode active material-containing layer is formed on at least one surface of the negative electrode current collector. That is, the negative electrode active material-containing layer may be supported on one surface of the negative electrode current collector, or on both surfaces. The surface of the negative electrode current collector on which the negative electrode active material-containing layer is supported is preferably the main surface of the negative electrode current collector. The negative electrode current collector may also include portions that do not support the negative electrode active material-containing layer. Such portions can be used, for example, as negative electrode tabs.

[0073] As the negative electrode current collector, for example, a sheet containing a material with high electrical conductivity can be used. For example, copper foil, aluminum foil, or aluminum alloy foil can be used as the negative electrode current collector. Its thickness is, for example, 20 μm or less, preferably 15 μm or less. The aluminum alloy foil may contain magnesium, zinc, silicon, etc. Furthermore, it is preferable that the content of transition metals such as iron, copper, nickel, and chromium in the aluminum alloy foil is 1% or less.

[0074] The negative electrode can be fabricated, for example, by the following procedure.

[0075] First, the negative electrode active material, conductive agent, and binder are prepared. These are then added to a suitable solvent to prepare the negative electrode slurry. In this process, it is preferable that the weight percentages of the negative electrode active material, negative electrode conductive agent, and negative electrode binder added to the solvent be 70-98% by weight, 0-20% by weight, and 0.5-10% by weight, respectively.

[0076] The slurry thus obtained is applied to the surface of the negative electrode current collector, dried, and pressed. Cutting may be performed as needed. Thus, a negative electrode can be obtained comprising a negative electrode current collector and a negative electrode active material-containing layer supported on the negative electrode current collector. <Separator> The separator may be made of an insulating material and can prevent electrical contact between the positive electrode and the negative electrode. Preferably, the separator is made of a material through which the electrolyte can pass, or has a shape through which the electrolyte can pass. Examples of separators include synthetic resin nonwoven fabrics, polyethylene porous films, polypropylene porous films, and cellulose-based separators. <Non-aqueous electrolyte> The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte. It is desirable that the electrolyte is dissolved in the non-aqueous solvent.

[0077] The electrolyte is, for example, an alkali salt, preferably a lithium salt. Examples of lithium salts include lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoride arsenate (LiAsF6), lithium perchlorate (LiClO4), and lithium trifluoromethanesulfonate (LiCF3SO3). Preferably, the electrolyte is at least one of lithium hexafluoride phosphate (LiPF6) or lithium tetrafluoroborate (LiBF4). The concentration of the electrolyte in the non-aqueous electrolyte is preferably 0.5 to 3.0 M (mol / L).

[0078] The non-aqueous solvent may be any known non-aqueous solvent used in lithium-ion batteries. Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), γ-butyrolactone (GBL), acetonitrile (AN), and dimethoxyethane (DME). The non-aqueous solvent may be a single substance or a mixture.

[0079] Furthermore, additives may be added to this non-aqueous electrolyte. Examples of substances that can be used as additives include organic compounds such as vinylene carbonate (VC) and Li salts such as lithium bisoxalate borate (LiBOB), but are not particularly limited. The amount of additive added is preferably 0.1 to 3.0% by weight relative to the non-aqueous electrolyte. <Positive and Negative Terminals> The positive and negative terminals are preferably made of a material with high electrical conductivity. When these terminals are connected to the current collector, it is preferable that these terminals be made of the same material as the current collector in order to reduce contact resistance. <Exterior Member> As the exterior member, for example, a laminate film with a thickness of 0.5 mm or less or a metal container with a thickness of 1 mm or less can be used. The thickness of the laminate film is more preferably 0.2 mm or less. The metal container is more preferably 0.5 mm or less in thickness, and even more preferably 0.2 mm or less in thickness.

[0080] The shapes of the exterior components include flat (thin), rectangular, cylindrical, coin-shaped, and button-shaped types. Depending on the battery size, the exterior components can include, for example, exterior components for small batteries installed in portable electronic devices, and exterior components for large batteries installed in two-wheeled or four-wheeled automobiles.

[0081] As the laminate film, a multilayer film in which a metal layer is arranged between resin layers can be used. For weight reduction, aluminum foil or aluminum alloy foil is preferred for the metal layer. For the resin layer, polymer materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used. The laminate film can be sealed by heat fusion and molded into the shape of the exterior component.

[0082] Metal containers can be made from aluminum or aluminum alloys. Aluminum alloys containing elements such as magnesium, zinc, and silicon are preferred. If the alloy contains transition metals such as iron, copper, nickel, and chromium, their content is preferably 1% by weight or less. This dramatically improves long-term reliability and heat dissipation in high-temperature environments.

[0083] Next, a specific example of a non-aqueous electrolyte battery according to the second embodiment will be described with reference to the drawings.

[0084] An example of such a battery will be described with reference to Figures 2 and 3. The flat-type battery shown in Figure 2 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 3, 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.

[0085] 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.

[0086] As shown in Figure 2, 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.

[0087] The battery in question is not limited to the configurations shown in Figures 2 and 3, but can also have a configuration like the one shown in Figure 4.

[0088] In the rectangular battery shown in Figure 4, 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 2 and 3, for example.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] The illustrated battery uses a wound electrode group in which a separator is wound together with the positive and negative electrodes. However, a stacked electrode group in which the positive and negative electrodes are alternately stacked with separators in between may also be used. In the case of a stacked structure such as a stacked type, separate separators may be placed between the positive and negative electrodes, or a zigzag-folded separator may be used. Alternatively, the electrode group may have other structures.

[0093] (Third Embodiment) According to the third embodiment, a battery pack is provided. This battery pack comprises the battery according to the second embodiment.

[0094] 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.

[0095] Next, an example of a battery pack according to the third embodiment will be described with reference to the drawings.

[0096] Figure 5 is an exploded perspective view of an example battery pack according to the second embodiment. Figure 6 is a block diagram showing the electrical circuit of the battery pack in Figure 5.

[0097] The battery pack 20 shown in Figures 5 and 6 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 4.

[0098] 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 6.

[0099] 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 6, 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.

[0100] 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.

[0101] 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 shut off 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 5 and 6, 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.

[0102] Protective sheets 36 made of rubber or resin are placed on three sides of the battery pack 23, excluding the side from which the positive terminal 61 and negative terminal 51 protrude.

[0103] 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.

[0104] 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.

[0105] Figures 5 and 6 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.

[0106] 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.

[0107] The battery pack according to the third embodiment comprises the battery according to the second embodiment. Therefore, this battery pack can reduce initial low-temperature resistance and further suppress resistance increases during calendar storage and charge-discharge cycles. As a result, it is possible to provide a battery pack with excellent low-temperature performance and lifespan performance.

[0108] Examples are described below, but the present invention is not limited to the examples described below, unless it exceeds the spirit of the present invention.

[0109] (Example 1) In Example 1, the electrode for Example 1 was prepared by following the procedure below.

[0110] (1) As the active material for preparing the slurry, a rock salt layered lithium nickel cobalt manganese composite oxide LiNi has an average particle size of 6.0 μm for the secondary particles. 0.45 Co 0.35 Mn 0.20 O2 powder was prepared. The atomic ratio of Co to Mn (a / b) and the atomic ratio of Co to Ni (a / 1-a-b) were determined, and the BET specific surface area SSA (m²) of lithium nickel cobalt manganese composite oxide particles were determined. 2 Table 1 shows the values ​​(per g). 82% by weight of this active material powder, 9% by weight of acetylene black (average particle size 35 nm) as a conductive agent, 4.5% by weight of graphite (average particle size 3.4 μm) as a conductive agent, and 4.5% by weight of polyvinylidene fluoride (PVdF) as a binder were added to N-methylpyrrolidone (NMP) and mixed by stirring.

[0111] The resulting mixture was then subjected to bead dispersion. For bead dispersion, an AIMEX Co., Ltd. bead mill RMH-03 was used. Zirconia beads with a diameter of φ2 mm were used, with a packing density of 80%. As dispersion conditions, the rotation speed was set to 1400 rpm and the flow rate to 30 cc / min in order to promote the disintegration of secondary particles of the active material.

[0112] (2) A current collector made of aluminum foil with a thickness of 12 μm was prepared. The slurry prepared earlier was applied to both sides of this current collector. During application, areas of the current collector were left uncoated with slurry. Next, the coating was dried. Then, the dried coating was pressed together with the current collector. By pressing as described above, the electrode of Example 1 was obtained, comprising a current collector and an active material-containing layer (electrode composite layer) supported on both sides thereof. The BET specific surface area X (m²) of the active material-containing layer in the electrode of Example 1 2 / g), pore specific surface area Y (m²) of the active material-containing layer by mercury intrusion method. 2Table 1 shows the values ​​of ( / g) and X / Y. [Fabrication of Non-Aqueous Electrolyte Battery] (1) Connection of Positive Electrode Terminal The electrode from Example 1 was prepared as the positive electrode. A strip-shaped positive electrode terminal was electrically connected to the portion of the current collector of the electrode from Example 1 that was not coated with slurry by ultrasonic bonding. (2) Fabrication of Negative Electrode A spinel-structured lithium titanium composite oxide (Li4Ti5O) was used as the negative electrode active material. 12 A powder of lithium titanium composite oxide was prepared. The average secondary particle size of the lithium titanium composite oxide particles was 0.75 μm. The BET specific surface area SSA of the lithium titanium composite oxide particles is shown in Table 1. 94.3 wt% of this active material powder, 3.8 wt% of graphite as a conductive agent, and 1.9 wt% of PVdF as a binder were added to NMP and mixed to prepare a slurry.

[0113] On the other hand, a negative electrode current collector made of aluminum foil with a thickness of 12 μm was prepared. The slurry prepared earlier was applied to both sides of this negative electrode current collector. During application, areas of the negative electrode current collector were left uncoated with slurry. Next, the coating was dried and pressed. Thus, the negative electrode current collector and the slurry with a density of 2.2 g / cm³ were formed. 3 A negative electrode was fabricated comprising a negative electrode active material-containing layer.

[0114] Next, a strip-shaped negative electrode terminal was electrically connected to the portion of the negative electrode current collector that had not been coated with slurry by ultrasonic bonding. (3) Fabrication of electrode group The positive electrode prepared as described above, a separator made of cellulose with a thickness of 10 μm, the negative electrode fabricated as described above, and another separator were stacked in this order to obtain a laminate. Next, this laminate was wound in a spiral shape so that the negative electrode was located on the outermost circumference to fabricate an electrode group. Next, the core was removed from the electrode group, and then the electrode group was pressed while being heated at 90°C. Thus, a flattened electrode group having dimensions of 58 mm in width, 95 mm in height, and 3.0 mm in thickness was fabricated.

[0115] (4) The electrode group obtained from the battery was housed in a bag-shaped outer casing made of a laminate film with a thickness of 0.1 mm, which consists of an aluminum foil with a thickness of 40 μm and polypropylene layers formed on both sides of the aluminum foil. At this time, one end of the positive electrode terminal and the negative electrode terminal extended out from the outer casing. Next, the electrode group housed in the outer casing was vacuum dried at 95°C for 12 hours. Then, with one end of the positive electrode terminal and the negative electrode terminal extending out from the outer casing and a partial opening remaining, the peripheral edge of the outer casing was heat-sealed.

[0116] (5) Preparation of non-aqueous electrolyte A mixed solvent was prepared by mixing propylene carbonate (PC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2. Lithium hexafluoride phosphate (LiPF6) was dissolved in this mixed solvent at a concentration of 1.0 M. Thus, a non-aqueous electrolyte was prepared. (6) Battery fabrication The non-aqueous electrolyte prepared earlier was injected into the outer casing through the opening left open during heat sealing, and then the opening was closed. Thus, the non-aqueous electrolyte secondary battery of Example 1 was fabricated.

[0117] In the battery of Example 1, the average secondary particle diameter A of the negative electrode active material particles N Table 2 shows the ratio A of the average secondary particle diameter Ap of the positive electrode active material particles to .

[0118] (Example 2) The electrode was manufactured in the same manner as in Example 1, except that the BET specific surface area of ​​the positive electrode active material particles was changed as shown in Table 1 below, and the rotation speed during dispersion using a bead mill was changed to 1400 rpm and the flow rate to 30 cc / min.

[0119] A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that the manufactured electrode was used as the positive electrode.

[0120] (Example 3) As the active material, a rock salt layered lithium nickel cobalt manganese composite oxide LiNi with an average particle size of 6.0 μm of secondary particles was used. 0.45 Co 0.3 Mn 0.25O2 powder was prepared. The atomic ratio of Co to Mn (a / b) and the atomic ratio of Ni (a / 1-a-b) were determined, and the BET specific surface area (m²) of the lithium nickel cobalt manganese composite oxide particles was determined. 2 The values ​​(per g) are shown in Table 1.

[0121] An electrode was manufactured in the same manner as in Example 1, except that the above-mentioned positive electrode active material particles were used, and the rotation speed during dispersion using a bead mill was changed to 1400 rpm and the flow rate to 30 cc / min.

[0122] A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that the manufactured electrode was used as the positive electrode.

[0123] (Example 4) The negative electrode was prepared in the same manner as in Example 1, except that the average secondary particle diameter of the negative electrode active material particles was changed to 0.58 μm and the BET specific surface area was changed to the values ​​shown in Table 1 below. A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that this negative electrode was used.

[0124] (Comparative Example 1) Lithium nickel cobalt manganese composite oxide LiNi with a rock salt layered structure and an average particle diameter of 6.0 μm of secondary particles as the active material. 0.5 Co 0.2 Mn 0.3 O2 powder was prepared. The atomic ratio of Co to Mn (a / b) and the atomic ratio of Ni (a / 1-a-b) were determined, and the BET specific surface area (m²) of the lithium nickel cobalt manganese composite oxide particles was determined. 2 The values ​​(per g) are shown in Table 1.

[0125] An electrode was manufactured in the same manner as in Example 1, except that the above-mentioned positive electrode active material particles were used, and the rotation speed during dispersion using a bead mill was changed to 1900 rpm and the flow rate to 30 cc / min.

[0126] A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that the manufactured electrode was used as the positive electrode.

[0127] (Comparative Example 2) An electrode was manufactured in the same manner as in Example 1, except that the rotation speed during dispersion using a bead mill was set to 1900 rpm and the flow rate was changed to 60 cc / min.

[0128] A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that the manufactured electrode was used as the positive electrode.

[0129] (Comparative Example 3) An electrode was prepared in the same manner as in Example 1, except that the average particle diameter and BET specific surface area of ​​the positive electrode active material secondary particles were changed as shown in Table 1.

[0130] (Comparative Example 4) Lithium nickel cobalt manganese composite oxide LiNi with a rock salt layered structure and an average particle diameter of 4.0 μm of secondary particles as the active material. 0.45 Co 0.3 Mn 0.25 O2 powder was prepared. The atomic ratio of Co to Mn (a / b) and the atomic ratio of Ni (a / 1-a-b) were determined, and the BET specific surface area (m²) of the lithium nickel cobalt manganese composite oxide particles was determined. 2 The values ​​(per g) are shown in Table 1.

[0131] An electrode was manufactured in the same manner as in Example 1, except that the above-mentioned positive electrode active material particles were used, and the rotation speed during dispersion using a bead mill was changed to 1400 rpm and the flow rate to 30 cc / min.

[0132] A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that the manufactured electrode was used as the positive electrode.

[0133] In the examples and comparative examples, the composition of the positive electrode active material particles, atomic ratio a (a / b), atomic ratio a (a / 1-a-b), average particle diameter, BET specific surface area, and BET specific surface area X (m²) of the positive electrode active material-containing layer are specified. 2 / g), pore specific surface area Y (m²) of the positive electrode active material-containing layer by mercury intrusion method. 2 Table 1 shows the ratio ( / g), X / Y, composition of the negative electrode active material particles, and BET specific surface area. Table 2 shows the ratio A and the ratio of the BET specific surface area of ​​the negative electrode active material particles to the BET specific surface area of ​​the positive electrode active material particles. Each variable was measured using the method described above.

[0134] Furthermore, the initial low-temperature resistance: HPPC discharge resistance (-20°C, 1C, 10s) and the low-temperature resistance increase: the rate of increase in low-temperature resistance during a cycle test (55°C, 3C / 3C, 2000 cycles) were measured in the examples and comparative examples. The initial low-temperature resistance was determined from the voltage drop when discharged at -20°C and 1C for 10 seconds. Next, the method for measuring the rate of increase in low-temperature resistance will be explained. After performing a charge-discharge cycle of 3C charging followed by 3C discharge for 2000 cycles at 55°C, the low-temperature resistance after 2000 cycles was measured from the voltage drop when discharged at -20°C and 1C for 10 seconds. The rate of increase in low-temperature resistance was calculated from the ratio of the low-temperature resistance after 2000 cycles to the initial low-temperature resistance (low-temperature resistance after 2000 cycles / initial low-temperature resistance). The initial low-temperature resistance and the rate of increase in low-temperature resistance for the other examples are shown in Table 2, with the initial low-temperature resistance and the rate of increase in low-temperature resistance for Example 1 set to 100.

[0135]

[0136]

[0137] As is clear from Tables 1 and 2, the electrodes of Examples 1 to 4 have low initial low-temperature resistance and small resistance increase with charge-discharge cycles.

[0138] In contrast, the electrode of Comparative Example 1 has a positive electrode active material composition that falls outside the range of the general formula, and the dispersion using a bead mill was performed at a higher rotation speed than in Example 1, resulting in an X / Y ratio greater than 3. Therefore, the electrode of Comparative Example 1 had a higher initial low-temperature resistance than Examples 1-4, and the rate of resistance increase with charge-discharge cycles was also greater than in Examples 1-4.

[0139] The electrode in Comparative Example 2 used the same positive electrode active material as in Example 1, but the dispersion using a bead mill was performed at a higher rotation speed and for a shorter time than in Example 1, resulting in an X / Y ratio less than 2. Although the initial low-temperature resistance of the electrode in Comparative Example 2 was equivalent to that of Example 4, the rate of resistance increase associated with the charge-discharge cycle was greater than that of Examples 1-4.

[0140] Although the electrodes of Comparative Examples 3 and 4 were subjected to the same dispersion conditions as in Example 1, the average particle size and BET specific surface area of ​​the active material secondary particles were not appropriate, resulting in X / Y being less than 2. Therefore, although the initial low-temperature resistance of the electrodes of Comparative Examples 3 and 4 was lower than that of Examples 1-4, the rate of resistance increase associated with the charge-discharge cycle was greater than that of Examples 1-4.

[0141] According to the electrodes of at least one embodiment and example described above, the general formula is Li d Ni 1-a-b Co a Mn b It contains an oxide represented by O2, 0.9 ≤ d ≤ 1.25, 1.1 ≤ a / b ≤ 1.8, and 0.65 ≤ a / (1-a-b) ≤ 0.9. Furthermore, the electrode satisfies the following equation (1).

[0142] 2.0 ≤ X / Y ≤ 3.0 (1) where X is the BET specific surface area (m²) of the active material-containing layer. 2 Y is the specific surface area of ​​the pores of the active material-containing layer by the mercury intrusion method (m²). 2 It is / g).

[0143] Such electrodes can reduce initial low-temperature resistance and further suppress resistance increases during calendar storage and charge-discharge cycles. Therefore, it is possible to provide batteries and battery packs with excellent low-temperature performance and lifespan.

[0144] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0145] 1...Electrode group, 2...Outer casing, 3...Positive electrode, 3a...Positive electrode current collector, 3b...Positive electrode active material containing layer, 3c...Positive electrode current collector tab, 4...Negative electrode, 4a...Negative electrode current collector, 4b...Negative electrode active material containing layer, 5...Separator, 6...Negative electrode terminal, 7...Positive electrode terminal, 11...Electrode group, 12...Container, 13...Rectangular lid, 14...Negative electrode tab, 15...Negative electrode terminal, 16...Insulating material, 17...Positive electrode tab, 18...Positive electrode terminal, 20...Battery pack, 21...Single cell, 22... 23...Adhesive tape, 24...Battery pack, 25...Printed circuit board, 26...Thermistor, 27...Protection circuit, 28...Terminal for supplying power to external devices, 29...Positive lead, 30...Positive connector, 31...Negative lead, 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. General formula: Li d Ni 1-a-b Co a Mn b An electrode comprising an active material-containing layer containing active material particles comprising an oxide represented by O2, 0.9 ≤ d ≤ 1.25, 1.1 ≤ a / b ≤ 1.8, and 0.65 ≤ a / (1-a-b) ≤ 0.9, and satisfying the following equation (1): 2.0 ≤ X / Y ≤ 3.0 (1) where X is the BET specific surface area (m²) of the active material-containing layer. 2 Y is the pore specific surface area (m²) of the active material-containing layer by the mercury intrusion method. 2 It is / g).

2. The Li d Ni 1-a-b Co a Mn b The electrode according to claim 1, wherein a in O₂ satisfies 0.25 ≤ a ≤ 0.

5.

3. The active material particles have a BET specific surface area of ​​0.4 (m²). 2 / g) or more 0.8(m 2 The electrode according to claim 1, wherein the amount is less than or equal to ( / g) and the average secondary particle diameter is 5 μm or more and 7 μm or less.

4. The above X is 7 (m 2 / g) ≤ X ≤ 8 (m 2 / g) and Y is 2.5 (m 2 / g) ≤ Y ≤ 3.5 (m 2 The electrode according to claim 1, wherein the value is / g.

5. A battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is the electrode described in any one of claims 1 to 4.

6. The battery according to claim 5, wherein the negative electrode comprises negative electrode active material particles containing a titanium-containing oxide having a spinel structure.

7. The battery according to claim 6, satisfying the following equation (2): 5 ≤ A ≤ 10 (2) where A is the ratio of the average secondary particle diameter of the positive electrode active material particles to the average secondary particle diameter of the negative electrode active material particles.

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

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