Electrode, secondary battery, and battery pack

Abstract

According to an embodiment, there is provided an electrode comprising an active material that contains an oxide represented by the general formula: LixNi1-a-b-cCoaMnbMcO2 (in the formula, x, a, b, and c are 0.9 ≤ x ≤ 1.25, 0.05 ≤ a ≤ 0.5, 0.03 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.2, and M includes one or more metal elements other than Ni, Co, and Mn). The electrode satisfies formula (1).　Formula (1) 0.001 < B / (A + B) ≤ 0.09. In formula (1), A is the pore volume (mL / g) in the pore diameter range from at least 0.01 μm to not greater than 0.3 μm in the pore diameter distribution according to mercury porosimetry of the electrode, and B is the pore volume (mL / g) in the pore diameter range from greater than 0.3 μm to and not greater than 1 μm in the pore diameter distribution according to mercury porosimetry of the electrode.

Description

Electrode, Secondary Battery, and Battery Pack

[0001] Embodiments of the present invention relate to an electrode, a secondary battery, and a battery pack.

[0002] With the recent increase in the capacity of lithium-ion batteries, improvement in energy density has been demanded. As the positive electrode active material of a lithium-ion battery, nickel cobalt manganese composite oxide, lithium iron phosphate, lithium manganate, etc. are known. As one method of further increasing the capacity of a battery using a nickel cobalt manganese composite oxide as the positive electrode, it is known to increase the nickel ratio in the nickel cobalt manganese composite oxide.

[0003] In a battery provided with a positive electrode containing a nickel cobalt manganese composite oxide as an active material, when charge-discharge cycles are performed under conditions over a wide range of states of charge (SOC), the amount of gas generated due to deterioration of the active material is large. In particular, when a nickel cobalt manganese composite oxide having a high nickel ratio is used, the amount of gas generated significantly increases, and thus there is a problem of achieving both an increase in the capacity of the battery and suppression of gas generation.

[0004] International Publication WO2011 - 108106, Japanese Patent Application Laid-Open No. 2012 - 54135, Japanese Patent Application Laid-Open No. 10 - 255763

[0005] An object is to provide an electrode capable of suppressing gas generation while increasing the capacity of a battery, a secondary battery provided with this electrode, and a battery pack.

[0006] According to an embodiment, an oxide represented by the general formula Li x Ni 1-a-b-c Co a Mn b M c O2 (where x, a, b, and c are 0.9 ≤ x ≤ 1.25, 0.05 ≤ a ≤ 0.5, 0.03 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.2, and M contains one or more metal elements other than Ni, Co, and Mn) is provided. The electrode satisfies the following formula (1).

[0007] 0.001 < B / (A + B) ≤ 0.09 (1) However, in formula (1), A is the pore volume (mL / g) in the pore diameter range of 0.01 μm or more and 0.3 μm or less in the pore size distribution by the mercury intrusion method of the electrode, and B is the pore volume (mL / g) in the pore diameter range larger than 0.3 μm and 1 μm or less in the pore size distribution by the mercury intrusion method of the electrode.

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

[0009] According to another embodiment, a battery pack is provided. The battery pack includes the secondary battery.

[0010] FIG. 1 is a plan view schematically showing an example of an electrode. FIG. 2 is a cross section obtained by cutting an example of a battery according to the embodiment in the thickness direction. FIG. 3 is an enlarged cross-sectional view of part E in FIG. 2. FIG. 4 is a partially cut-away 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 an electrical circuit of the battery pack shown in FIG. 5. FIG. 7 is a diagram showing an example of the pore size distribution by the mercury intrusion method of the electrodes of the examples and comparative examples. Embodiment

[0011] Hereinafter, embodiments will be described with reference to the drawings. In the embodiments, the same reference numerals are given to common configurations, and duplicate descriptions are omitted.

[0012] Also, each figure is a schematic diagram for facilitating the explanation and understanding of the embodiment, 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 explanation and known techniques. (First Embodiment) The first embodiment relates to an electrode. The electrode has the general formula Li x Ni 1-a-b-c Co a Mn b M cThe active material contains an oxide represented by O2. In the general formula, x, a, b, and c are 0.9 ≤ x ≤ 1.25, 0.05 ≤ a ≤ 0.5, 0.03 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.2. M contains one or more metallic elements other than Ni, Co, and Mn. The electrode satisfies the following equation (1): 0.001 < B / (A + B) ≤ 0.09 (1) where, in equation (1), A is the pore volume (mL / g) in the range of pore diameters of 0.01 μm to 0.3 μm in the pore diameter distribution of the electrode by mercury intrusion method, and B is the pore volume (mL / g) in the range of pore diameters greater than 0.3 μm and 1 μm or less in the pore diameter distribution of the electrode by mercury intrusion method. Here, the pore size distribution obtained by the mercury intrusion method has the pore size (μm) on the horizontal axis and the log differential pore volume (mL / g) on ​​the vertical axis. The method for measuring the pore size distribution by the mercury intrusion method will be described later.

[0013] According to the electrode of this embodiment, gas generation can be reduced even during charge-discharge cycles. Although the mechanism by which the gas generation suppression effect is obtained is not clear, it is presumed to be as described below.

[0014] The electrodes of the embodiment can be used, for example, in non-aqueous electrolyte secondary batteries such as lithium secondary batteries. An example of a secondary battery is one which comprises an electrolyte containing a solvent. In this electrolyte, Li ions (Li + Li ions can diffuse accompanied by a shell (also called a solvation structure) with a Stokes radius larger than that of the solvent molecule. Pores with a diameter greater than 0.3 μm and less than or equal to 1 μm can promote the diffusion of solvated Li ions within the electrode. On the other hand, electrodes with pores in the range of 0.01 μm to 0.3 μm are easier to increase in density. Therefore, pores in the range of 0.01 μm to 0.3 μm can contribute to increasing the capacity of the electrode.

[0015] By making the value expressed as B / (A+B) greater than 0.001, it is possible to promote the entry of solvated Li ions into the pores and the diffusion of Li ions. On the other hand, an increase in the value expressed as B / (A+B) may hinder contact between the active material and the conductive agent. If the contact between the active material and the conductive agent is insufficient, current concentration is more likely to occur. By making the value expressed as B / (A+B) greater than 0.001 and less than or equal to 0.09, it is possible to ensure contact between the active material and the conductive agent while promoting the entry of solvated Li ions into the pores and the diffusion of Li ions. As a result, the electrodes can react almost uniformly and without unevenness during charging and discharging, so gas generation during the charge-discharge cycle can be suppressed. Therefore, the charge-discharge cycle life can be improved.

[0016] Therefore, by making the value expressed as B / (A+B) greater than 0.001 and less than or equal to 0.09, a high-capacity electrode with low gas generation can be realized. The value expressed as B / (A+B) can be made greater than 0.001 and less than or equal to 0.025. Within this range, the amount of gas generated can be further reduced. Thus, the charge-discharge cycle life can be improved.

[0017] The electrodes will be described in detail below.

[0018] The electrode has pores with a pore diameter in the range of 0.01 μm to 1 μm. The electrode may have only pores with a pore diameter in the range of 0.01 μm to 1 μm, but it may also have pores of a size outside this range. For example, the electrode may have a ratio of pore volume (mL / g) represented by (A + B) in equation (1) above to pore volume (mL / g) (hereinafter referred to as pore volume C) for pore diameters of 0.01 μm to 60 μm in the pore diameter distribution by the mercury intrusion method of 80% or more. In an electrode where the ratio of pore volume (A + B) to pore volume C is 80% or more, a large portion of the pores with a pore diameter of 0.01 μm to 60 μm are pores with a pore diameter in the range of 0.01 μm to 1 μm, making it easier to obtain the gas generation suppression effect by specifying equation (1). Furthermore, the pore diameter of the pores in electrodes with a 100% proportion is in the range of 0.01 μm to 1 μm. The proportion can be in the range of 80% to 100%, but it is desirable to set the upper limit of the proportion to 90%. By setting the proportion to 80% to 90%, the ratio of pores with a diameter in the range of 0.01 μm to 1 μm and pores with a diameter exceeding 1 μm can be appropriately adjusted. As a result, the diffusivity of Li ions is further improved, increasing the uniformity of the charge-discharge reaction in the electrode, and thus reducing the amount of gas generated during the charge-discharge cycle.

[0019] The electrode may have at least one peak in the pore size distribution obtained by the mercury intrusion method, in the range of pore sizes from 0.1 μm to 0.3 μm. It is desirable that at least one peak includes the peak with the maximum height. Here, the peak is defined as having a pore volume exceeding the minimum pore volume (mL / g) in the range of pore sizes from 0.003 μm to 0.005 μm. The peak with the maximum height is the peak whose peak top is the maximum value of the log differential pore volume in the range of pore sizes from 0.01 μm to 1 μm.

[0020] The presence of a peak with maximum height in the pore diameter range of 0.1 μm to 0.3 μm allows for a greater number of pores with a pore diameter in this range than pores with pore diameters outside this range. As a result, the gas generation suppression effect of equation (1) can be further enhanced.

[0021] The electrode may comprise, for example, a current collector and an electrode composite layer (an active material-containing layer). The electrode may be either a positive or negative electrode.

[0022] The current collector may have, for example, a first surface and a second surface which is the back surface of the first surface. The current collector may have, for example, a strip shape or a sheet shape.

[0023] The current collector is preferably an aluminum foil, or an aluminum alloy foil containing aluminum and one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si.

[0024] The active material-containing layer may be formed, for example, on both the first and second surfaces of the current collector. Alternatively, the active material-containing layer may be formed on either the first or second surface of the current collector. The current collector may include portions on neither the first nor the second surface that do not support the active material-containing layer. These portions can function, for example, as electrode tabs or electrode leads.

[0025] The active material-containing layer may contain an active material. The active material has the general formula Li x Ni 1-a-b-c Co a Mn b M cIt contains an oxide represented by O2 (hereinafter referred to as the first oxide). The first oxide can also be called a lithium nickel cobalt manganese-containing oxide or a lithium nickel cobalt manganese composite oxide. The lithium nickel cobalt manganese-containing oxide may have a layered structure. In the general formula, x, a, b, and c are 0.9 ≤ x ≤ 1.25, 0.05 ≤ a ≤ 0.5, 0.03 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.2. M contains one or more metallic elements other than Ni, Co, and Mn. The reason for limiting x, a, b, and c to the above ranges is explained below.

[0026] The value of x can vary within the range of 0.9 to 1.25. Setting x to 0.9 or higher allows the active material to maintain a stable crystal structure. Setting x to 1.25 or lower increases the discharge capacity. Setting the value represented by (1-a-b-c) to 0.49 or higher results in a high-capacity active material, thereby increasing the energy density of the battery. Setting the value of (1-a-b-c) to 0.9 or lower prevents a decrease in the structural and thermal stability of the active material, thus improving the safety and lifespan characteristics of the battery. Setting a to 0.05 or higher or 0.5 allows for practical battery performance. Setting b to 0.03 or higher or 0.5 allows for practical battery performance. M may contain one or more metallic elements other than Ni, Co, and Mn. For example, M may contain one or more elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Sr, Zr, Nb, Mo, and W. As explained above, the first oxide makes it possible to realize batteries with excellent energy density, lifespan, and safety. On the other hand, the first oxide has a problem with gas generation during charging and discharging. By satisfying equation (1) in an electrode containing the first oxide as an active material, gas generation during charging and discharging can be suppressed, thus obtaining a battery with excellent energy density, lifespan, and safety. In the first oxide, the preferred range for (1-a-b-c) is 0.6 ≤ (1-a-b-c) ≤ 0.9. By specifying the value of (1-a-b-c) within this range, the energy density of the active material can be increased, and thus the energy density of the electrode can be improved, but gas generation becomes more likely during the charge-discharge cycle. The pore size distribution that satisfies equation (1) is highly effective in suppressing gas generation when the molar ratio of Ni (1-a-b-c) is between 0.6 and 0.9. Therefore, by setting the molar ratio of Ni in the first oxide (1-a-b-c) to 0.6 or higher and 0.9 or lower, it is possible to achieve a high energy density while reducing the amount of gas generated during the charge-discharge cycle.

[0027] The first oxide can have a particle form. The particles of the first oxide may be, for example, single crystal particles, aggregates of single crystal particles, or aggregates of polycrystalline particles. The particles of the first oxide may also be a mixture of single crystal particles and aggregates of single crystal particles. Single crystal particles are also called primary particles. Aggregates of single crystal particles are also called secondary particles. Examples of aggregates of single crystal particles include simply aggregates of single crystal particles, aggregates of particles bonded together by sintering, and aggregates of particles fused together. Aggregates of single crystal particles may or may not have boundaries between particles. It is desirable that the particles of the first oxide include aggregates of single crystal particles. By including aggregates of single crystal particles in the particles of the first oxide, it is possible to suppress the cracking of the particles and the creation of new pores in the electrode when the particles of the first oxide repeatedly undergo the intercalation and deintercalation reaction of Li ions during the charge-discharge cycle. As a result, the pore size distribution that satisfies equation (1) can be maintained even after repeated charge-discharge cycles, thus suppressing gas generation over long cycles.

[0028] The shape of the particles of the first oxide can be, for example, granular, fibrous, or flaky.

[0029] The active material may include other active materials besides the first oxide. The proportion of the first oxide in the active material can be, for example, 70% by mass or more and 100% by mass or less. Examples of other active materials include, for example, manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (e.g., Li x Mn2O4 or Li x MnO2; 0 < x ≤ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≤ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-yO2; 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), lithium phosphate oxide having an olivine structure (e.g., Li x FePO4; 0<x≦1, Li x Fe 1-y Mn y PO4; 0<x≦1, 0<y≦1, Li x This includes CoPO4 (0 < x ≤ 1), iron sulfate (Fe2(SO4)3), and vanadium oxide (e.g., V2O5).

[0030] As the active material, one of the compounds listed above may be used alone. Alternatively, a mixture of two or more of the compounds listed above may be used as the active material.

[0031] The average particle size of the active material particles can be, for example, between 1 μm and 10 μm.

[0032] The active material-containing layer may further contain a conductive agent and a binder, if necessary. The conductive agent that the electrode may contain can enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as acetylene black, carbon black, graphite, carbon nanofibers, and carbon nanotubes. One of these carbonaceous materials may be used alone, or a combination of carbonaceous materials may be used.

[0033] A binder can have the effect of binding the active material, conductive agent, and current collector together. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, acrylic resin or copolymer thereof, polyacrylic acid, and polyacrylonitrile.

[0034] The proportion of active material in the electrode composite layer (active material-containing layer) can be, for example, 80% by mass or more and 95% by mass or less. The proportion of conductive agent in the electrode composite layer (active material-containing layer) can be, for example, 3% by mass or more and 18% by mass or less. The conductive agent can exert the effects described above by being in an amount of 3% by mass or more. By being in an amount of 18% by mass or less, the decomposition of the electrolyte on the surface of the conductive agent under high-temperature storage can be reduced. The proportion of binder in the electrode composite layer (active material-containing layer) can be, for example, 2% by mass or more and 17% by mass or less. Sufficient electrode strength can be obtained by being in an amount of 2% by mass or more. By being in an amount of 17% by mass or less, the amount of binder, which is an insulating material in the electrode, can be reduced, and the internal resistance can be reduced.

[0035] Electrodes can be manufactured, for example, by the following method. First, the active material, conductive agent, binder, and a portion of the solvent are placed in a stirrer and then stirred with a stirring blade. This step is called the first stirring step. In the first stirring step, the slurry (mixture) is stirred while the solid content ratio is high, so the viscosity of the slurry increases, and the stirring torque value increases as stirring progresses. The maximum value of the stirring torque value is denoted as T1. If stirring continues further, the added materials are broken down, and the stirring torque value decreases. This stirring torque value is denoted as T2. At this stage, the remaining solvent is placed in the stirrer and stirred further with the stirring blade. This step is called the second stirring step. When the viscosity of the slurry reaches a predetermined value, the second stirring step is terminated. The ratio (%) of the stirring torque value T2 to the maximum stirring torque value T1 is defined as the stirring torque decrease rate (%). By keeping the stirring torque decrease rate at 85% or less, the stirring in the first stirring step is sufficient, and the active material, conductive agent, and binder can be uniformly dispersed. As a result, an active material-containing layer satisfying equation (1) can be formed. The lower limit of the reduction rate of the stirring torque can be, for example, 75%.

[0036] The slurry obtained in the second stirring step is applied to one or both surfaces of the current collector, and the coating is dried. Then, the dried coating is subjected to pressing. Thus, an electrode can be obtained that comprises a current collector and an electrode composite layer (active material-containing layer) formed on one or both sides of the current collector, and that satisfies equation (1). The value expressed as B / (A+B) can be brought into a predetermined range by adjusting, for example, the electrode material such as the active material, the solid content ratio of the slurry in the first stirring step, and the rate of reduction of the stirring torque. On the other hand, the ratio of the pore volume (A+B) to the pore volume C can be brought into a predetermined range by adjusting, for example, the solid content ratio of the slurry in the second stirring step. If the solid content ratio of the slurry in the second stirring step is high, the viscosity of the slurry will be high. If the viscosity of the slurry is high, the shape of the irregularities on the surface of the slurry layer applied to the current collector will not be easily broken down, and the surface of the slurry layer will dry in a rougher state. As a result, the surface of the electrode composite layer becomes more irregular, which reduces the ratio of pore volume (A + B) to pore volume C. On the other hand, if the solid content ratio of the slurry in the second stirring step is low, the viscosity of the slurry decreases. When the viscosity of the slurry is low, the shape of the irregularities on the surface of the slurry layer on the current collector breaks down, and the surface of the slurry layer becomes smoother before drying. As a result, the surface irregularities of the electrode composite layer are reduced, which increases the ratio of pore volume (A + B) to pore volume C.

[0037] 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.

[0038] 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. The positive electrode current collector 3a also 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 3b. 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).

[0039] The methods for measuring pore size distribution and active material composition are described below. <Electrode Removal> If the electrode to be measured is incorporated into a battery, remove the electrode from the battery as a measurement sample as follows: Discharge the battery and disassemble it in a glove box under an argon atmosphere to remove the electrode. Wash the electrode with diethyl carbonate and then vacuum dry it. This is how the measurement sample is obtained. <Method for Measuring Pore Volume Distribution in Active Material-Containing Layer by Mercury Intrusion Method> The electrode obtained by the above method can be used as a sample. For pore size distribution measurement, use the Autopore 9520 model manufactured by Shimadzu Corporation. For measurement, cut one of the samples to a size of approximately 25 mm in width, fold it, place it in a standard cell, and insert it into the measurement chamber. The measurement is performed under initial pressure of 20 kPa (approximately 3 psia, equivalent to a pore diameter of approximately 60 μm) and termination pressure of 414,000 kPa (approximately 60,000 psia, equivalent to a pore diameter of approximately 0.003 μm). Note that the pore size distribution obtained by the mercury intrusion method includes not only the pore size of the active material-containing layer but also the pore size of the electrode current collector. However, the pore size of the current collector is significantly smaller and present in smaller proportions than the pore size of the active material-containing layer, so it can be ignored. The pore volume is calculated based on the obtained pore size distribution graph. An example of a pore size distribution graph is shown in Figure 7. <Confirmation of lithium nickel cobalt manganese-containing oxide> The active material contained in the electrode can be identified as follows, and the presence or absence of lithium nickel cobalt manganese-containing oxide can be confirmed.

[0040] As described above, after cleaning and drying the electrodes removed from the battery, the obtained electrodes are attached to a glass sample plate. At this time, care should be taken to prevent the electrodes from peeling off or lifting by using double-sided tape or similar. If necessary, the electrodes may be cut to an appropriate size for attachment to the glass sample plate. In addition, a Si standard sample may be added to the electrodes to correct the peak position.

[0041] Next, the glass plate with the electrodes attached is placed in a powder X-ray diffraction (XRD) apparatus, and a diffraction pattern is acquired using Cu-Kα rays. Using Cu-Kα rays as the source, the X-ray diffraction pattern can be obtained by performing measurements while varying 2θ within the measurement range of 5 to 90°.

[0042] For powder X-ray diffraction measurements, for example, a SmartLab manufactured by Rigaku is used. The measurement conditions are as follows: X-ray source: Cu target output: 45kV, 200mA Solar slit: 5° for both incident and receiving Step width: 0.02deg Scan rate: 20deg / min Semiconductor detector: D / teX Ultra 250 Sample plate holder: Flat glass sample plate holder (thickness 0.5mm) Measurement range: 5°≦2θ≦90°.

[0043] If other equipment is used, measurements should be performed using standard Si powder for powder X-ray diffraction to obtain measurement results equivalent to those described above. The conditions under which the peak intensity and peak top position match those obtained with the above equipment should be found, and the sample should be measured under those conditions.

[0044] If the active material being measured contains a lithium nickel cobalt manganese-containing oxide, it can be confirmed by X-ray diffraction measurement that an X-ray diffraction pattern belonging to space group R3-m can be obtained.

[0045] Next, the sample containing the active material is observed using a scanning electron microscope (SEM). For SEM observation, it is desirable to handle the sample removed from the battery in an inert atmosphere such as argon or nitrogen to prevent it from coming into contact with the atmosphere.

[0046] Using a 3000x SEM observation image, several particles with primary or secondary particle morphology are selected within the field of view. The selection is made to ensure the particle size distribution is as broad as possible. Energy dispersive X-ray spectroscopy (EDX) is used to identify the types and composition of the active material elements in the observed active material particles. This allows for the identification of the types and amounts of elements other than Li contained in each selected particle. The same procedure is performed for each of the multiple active material particles to determine their mixing state.

[0047] Next, the composite layer (active material-containing layer) is separated from the current collector using, for example, a spatula, to obtain a powdered electrode composite sample containing the active material. The collected powdered sample is washed with acetone and dried. The obtained powder is dissolved in hydrochloric acid, the conductive agent is filtered out, and then diluted with deionized water to prepare the measurement sample. The metal content ratio in the measurement sample is calculated by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0048] If there are multiple types of active materials, their mass ratios are estimated from the elemental content ratios specific to each active material. The ratio of the specific elements to the mass of the active material is determined from the composition of the constituent elements, which is obtained by energy-dispersive X-ray spectroscopy.

[0049] Thus, the active material contained in the electrode can be identified. <Method for confirming single crystal particles> Whether the active material is a single crystal particle can be confirmed, for example, by analyzing the electron diffraction pattern using a transmission electron microscope (TEM). According to the electrode of the first embodiment described above, the general formula Li x Ni 1-a-b-c Co a Mn b M cThe active material contains an oxide represented by O2 (wherein x, a, b, and c are 0.9 ≤ x ≤ 1.25, 0.05 ≤ a ≤ 0.5, 0.03 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.2. M includes one or more metallic elements other than Ni, Co, and Mn). The electrode also satisfies equation (1).

[0050] 0.001 < B / (A + B) ≤ 0.09 (1) The above electrode can improve capacity and reduce gas generation during charge-discharge cycles. Therefore, the charge-discharge cycle life can be improved. (Second Embodiment) According to the second embodiment, a battery is provided which includes a positive electrode, a negative electrode, and an electrolyte. At least one of the positive electrode or the negative electrode is the electrode of the embodiment.

[0051] Examples of batteries according to this embodiment include secondary batteries such as lithium-ion secondary batteries. Secondary batteries include non-aqueous electrolyte secondary batteries containing a non-aqueous electrolyte. The battery may include a separator, an outer casing, or both. The positive electrode, negative electrode, and separator can constitute an electrode group. The electrolyte can be held in the electrode group. The battery may further comprise an outer casing that houses the electrode group and the electrolyte. Furthermore, the battery may further comprise a positive electrode terminal electrically connected to the positive electrode and a negative electrode terminal electrically connected to the negative electrode. At least a portion of the positive electrode terminal and at least a portion of the negative electrode terminal may extend outside the outer casing. (Positive electrode) The positive electrode may comprise, for example, a positive electrode current collector and a positive electrode composite layer (positive electrode active material containing layer). The electrode of the first embodiment can be used for the positive electrode. (Negative electrode) The negative electrode may include a negative electrode current collector and a negative electrode composite layer (negative electrode active material containing layer). The negative electrode composite layer (negative electrode active material-containing layer) can be formed, for example, on one side or both sides of the current collector. The current collector may have, for example, a strip shape or a sheet shape. The negative electrode composite layer (negative electrode active material-containing layer) may contain the negative electrode active material and optionally a conductive agent and a binder.

[0052] Examples of negative electrode active materials include metal oxides, carbonaceous materials, and metal compounds. The negative electrode active material can consist of one or more types.

[0053] Examples of carbonaceous materials include natural graphite, artificial graphite, coke, vapor-grown carbon fibers, mesophase-pitch carbon fibers, spherical carbon, and resin-fired carbon. More preferred carbonaceous materials include vapor-grown carbon fibers, mesophase-pitch carbon fibers, and spherical carbon. The interplanar spacing d of the (002) plane of the carbonaceous material is determined by X-ray diffraction. ００２ It is preferable that the wavelength is 0.34 nm or less.

[0054] As metal compounds, metal sulfides and metal nitrides can be used. For example, TiS ２ Titanium sulfide such as MoS ２ Molybdenum sulfide such as FeS, for example, FeS ２ Li ｘ FeS ２ Iron sulfide such as the above can be used. As for metal nitrides, for example lithium cobalt nitride (e.g. Li ｓ Co ｔ N, 0 < s < 4, 0 < t < 0.5) can be used.

[0055] Examples of metal oxides include titanium-containing oxides. Examples of titanium-containing oxides include lithium titanium-containing oxides (lithium titanium composite oxides) and niobium titanium-containing oxides (niobium titanium composite oxides). It is preferable that the titanium-containing oxides include lithium titanium composite oxides. Electrodes containing titanium-containing oxides such as lithium titanium composite oxides have a redox potential of 0.4 V (vs. Li / Li) relative to the oxidation-reduction potential of lithium. + Since it can exhibit a Li storage potential of ) or higher, it is possible to prevent the deposition of metallic lithium on the electrode surface when high current input and output are repeated. The titanium-containing oxide is particularly preferably a lithium titanium composite oxide having a spinel-type crystal structure. As a specific example of such a spinel-type lithium titanium composite oxide, Li ４＋ａ Ti ５ O １２ Examples include lithium titanate having a spinel structure, where the subscript a changes with charge and discharge within the range of 0 ≤ a ≤ 3, and represented as .

[0056] Examples of niobium-titanium-containing oxides include monoclinic niobium-titanium-containing oxides. Examples of monoclinic niobium-titanium-containing oxides include Nb2TiO7, Nb2Ti2O9, and Nb 10 Ti2O 29 Nb 14 TiO 37 Nb 24 TiO 62 It includes.

[0057] The active material can take the form of, for example, particles or fibers. The active material particles may be primary particles, secondary particles, or a mixture of primary and secondary particles. An example of secondary particles is an aggregate of primary particles.

[0058] The active material may contain further active materials other than the titanium-containing oxide mentioned above. For convenience, the active material containing the titanium-containing oxide mentioned above will be referred to as the "first active material," and the other further active materials will be referred to as the "second active material." If the second active material is further included in addition to the first active material, the second active material will be 0.4V (vs. Li / Li + It is desirable to use an active material that can exhibit a Li storage potential of ) or higher. If a second active material is included, the mass ratio of the second active material to the first active material is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less.

[0059] Conductive agents can enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as acetylene black, carbon black, graphite, carbon nanofibers, and carbon nanotubes. These carbonaceous materials may be used individually or in combination.

[0060] A binder can have the effect of binding the active material, conductive agent, and current collector together. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, acrylic resin and its copolymers, polyacrylic acid, and polyacrylonitrile.

[0061] The proportion of negative electrode active material in the negative electrode composite layer (negative electrode active material-containing layer) can be, for example, 70% by mass or more and 97.5% by mass or less. The proportion of conductive agent in the negative electrode composite layer (negative electrode active material-containing layer) can be, for example, 2% by mass or more and 20% by mass or less. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the composite layer (active material-containing layer) can be improved, and excellent high-current performance and low-temperature performance can be expected. On the other hand, from the viewpoint of increasing capacity, it is preferable that the amount of conductive agent be 20% by mass or less. The proportion of binder in the negative electrode composite layer (negative electrode active material-containing layer) can be, for example, 0.5% by mass or more and 10% by mass or less. By setting the amount of binder to 0.5% by mass or more, sufficient bonding between the composite layer (active material-containing layer) and the current collector can be achieved, and excellent high-temperature storage performance can be expected. On the other hand, from the viewpoint of increasing capacity, it is preferable that the amount of binder be 10% by mass or less. A current collector suitable for the type of negative electrode active material can be used. The negative electrode current collector may contain at least one element from among copper, nickel, and aluminum. Examples of negative electrode current collector forms include foil and porous materials. When the negative electrode active material contains titanium-containing oxide, the negative electrode current collector is preferably formed from aluminum foil or aluminum alloy foil containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 20 μm or less, and more preferably 15 μm or less. (Separator) A separator can be placed, for example, between the positive electrode and the negative electrode. The separator may include a portion that is in contact with or facing only one of the electrodes, either the positive or the negative electrode.

[0062] The separator is not particularly limited, and for example, a microporous membrane, woven fabric, or nonwoven fabric, or a laminate of the same or different materials can be used. Examples of materials for forming the separator include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene copolymer, and cellulose. (Non-aqueous electrolytes) Examples of electrolytes include non-aqueous electrolytes. For example, liquid non-aqueous electrolytes or gel-like non-aqueous electrolytes can be used.

[0063] Liquid non-aqueous electrolytes can be prepared by dissolving an electrolyte in an organic solvent. The electrolyte concentration is preferably in the range of 0.5 to 3 mol / l. Gel-like non-aqueous electrolytes are prepared by compounding a liquid electrolyte with a polymer material.

[0064] Examples of electrolytes include lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoride arsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium salts such as bistrifluoromethylsulfonyliimide lithium [LiN(CF3SO2)2]. One of these electrolytes may be used alone, or two or more electrolytes may be used in combination. The electrolyte preferably contains LiPF6.

[0065] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate; linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); acetonitrile (AN), γ-butyllactone (GBL), and sulfolane (SL). One of these solvents may be used alone, or two or more solvents may be used in combination.

[0066] Examples of more preferred organic solvents include mixed solvents obtained by mixing two or more selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC). By using such mixed solvents, a non-aqueous electrolyte battery with excellent charge-discharge cycle characteristics can be obtained. Additives can also be added to the non-aqueous electrolyte. (Outer packaging) As outer packaging, for example, a bag-shaped container made of laminate film or a metal container can be used.

[0067] While not particularly limited in shape, examples include flat, rectangular, cylindrical, coin-shaped, button-shaped, sheet-shaped, and laminated types. Of course, this includes not only small batteries used in portable electronic devices, but also large batteries used in two-wheeled or four-wheeled vehicles.

[0068] As a laminating film, for example, a multilayer film can be used in which a metal layer is sandwiched between resin films. Alternatively, a multilayer film consisting of a metal layer and a resin layer covering the metal layer can also be used.

[0069] For the metal layer, it is preferable to use aluminum foil or aluminum alloy foil for weight reduction. For the resin film, 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 formed into the shape of the exterior component. The laminate film preferably has a thickness of 0.2 mm or less.

[0070] The metal container can be made of aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. On the other hand, the content of transition metals such as iron, copper, nickel, and chromium is preferably 100 ppm or less. This makes it possible to dramatically improve long-term reliability and heat dissipation in high-temperature environments. The metal container preferably has a wall thickness of 0.5 mm or less, and more preferably 0.2 mm or less. The metal container can also function as either a positive or negative electrode terminal. (Positive electrode terminal) The positive electrode terminal is preferably made of a material that is electrically stable and conductive in the range of 3.0 V to 4.5 V relative to the oxidation-reduction potential of lithium. The positive electrode terminal is preferably made of aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably made of the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector. Furthermore, the positive electrode terminal and the positive electrode current collector, for example, the positive electrode lead, can also be connected via a positive electrode current collector tab. The positive electrode current collector tab is preferably made of the same material as the positive electrode terminal and the positive electrode current collector. (Negative electrode terminal) The negative electrode terminal is preferably made of a material that is electrically stable and conductive in the range of 0.8V to 3.0V relative to the oxidation-reduction potential of lithium. The negative electrode terminal is preferably made of aluminum, or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector. Furthermore, the negative electrode terminal and the negative electrode current collector, for example, the negative electrode lead, can also be connected via a negative electrode current collector tab. The negative electrode current collector tab is preferably made of the same material as the negative electrode terminal and the negative electrode current collector.

[0071] An example of a battery according to the embodiment 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.

[0072] 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.

[0073] As shown in Figure 3, near the outer peripheral end 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.

[0074] The battery is not limited to the configurations shown in Figures 2 and 3, but can also be configured as shown in Figure 4, for example.

[0075] 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.

[0076] 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.

[0077] The negative electrode tab 14 is manufactured from a material such as copper, nickel, aluminum, or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, or Si. Preferably, the negative electrode tab 14 is made of the same material as the negative electrode current collector to reduce contact resistance with the negative electrode current collector.

[0078] 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.

[0079] The battery shown in the illustration uses a wound electrode group in which the separator is wound together with the positive and negative electrodes, but the structure of the electrode group is not particularly limited. For example, a stacked electrode group in which the separator is folded in a zigzag pattern and the positive and negative electrodes are alternately arranged at the folded parts, or a stacked electrode group in which the positive and negative electrodes are alternately arranged with a separator in between, may be used.

[0080] The battery according to the first embodiment includes the electrode of the first embodiment as at least one of the positive or negative electrodes. Therefore, the battery capacity can be improved and the amount of gas generated during the charge-discharge cycle can be reduced.

[0081] (Third Embodiment) According to the third embodiment, a battery pack is provided. This battery pack comprises a battery according to the embodiment.

[0082] The battery pack according to the embodiment may comprise one or more of the batteries (single cells) 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.

[0083] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0084] Figure 5 is an exploded perspective view of an example battery pack according to the embodiment. Figure 6 is a block diagram showing the electrical circuit of the battery pack in Figure 5.

[0085] 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, as described in the embodiment with reference to Figure 2.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] The battery pack according to the second embodiment comprises the battery according to the first embodiment. Therefore, the battery pack can improve capacity and reduce the amount of gas generated during charge-discharge cycles.

[0096] [Examples] Examples are described below, but the present invention is not limited to the examples listed below unless it exceeds the spirit of the present invention.

[0097] (Example 1) In Example 1, the non-aqueous electrolyte battery of Example 1 was prepared by following the procedure below. <Method for preparing the positive electrode> As the positive electrode active material, Li of the general formula x Ni 1-a-b-c Co a Mn b M c An aggregate of single crystal grains of lithium nickel cobalt manganese composite oxide was prepared, represented by the formula (where x is 0.98, 1-a-b-c is 0.80, a is 0.10, b is 0.10, and c is 0).

[0098] A mixture of positive electrode active material, polyvinylidene fluoride as a binder, and acetylene black as a conductive agent was prepared in a mixing ratio of 100 parts by mass (93% by mass): 2 parts by mass (2% by mass): 5 parts by mass (5% by mass). The positive electrode active material, binder, conductive agent, and N-methylpyrrolidone (NMP) were added to a planetary mixer. The solid content ratio of the total materials added is shown in Table 2. All the added materials were stirred using the planetary mixer to perform the first stirring step. During stirring, the operating current of the impeller was monitored as the stirring torque. After the operating current of the impeller rose from the start of stirring and reached the maximum current value (5.9 A), stirring was continued for another 50 minutes to obtain an intermediate slurry. The operating current value of the impeller at this time (4.9 A) was defined as the stirring torque value T2. The percentage decrease in stirring torque (%) was calculated from the ratio (%) of the stirring torque value T2 to the maximum stirring torque value T1 (maximum current value), and it was found to be 83%.

[0099] Next, N-methylpyrrolidone (NMP) was added to the intermediate slurry to set the solid content ratio of the total material (referred to as the second stirred solid content ratio) to 64% by mass. These were then stirred using a planetary mixer to perform the second stirring step and obtain a slurry.

[0100] The slurry was applied to both sides of a current collector made of aluminum foil, and the coating was dried. Furthermore, the dried coating was subjected to a roll press treatment. Thus, the current collector and the electrode density (excluding the current collector) formed on both sides of the current collector was 3.3 g / cm³. 3 A positive electrode was fabricated comprising a positive electrode active material-containing layer. <Method for fabricating the negative electrode> Li was used as the negative electrode active material. ４ Ti ５ O １２ A lithium titanate with a spinel structure represented by [formula] was prepared. A slurry was prepared by mixing the negative electrode active material with polyvinylidene fluoride as a binder, graphite as a conductive agent, and N-methylpyrrolidone (NMP) as a solvent. The mixing ratio of the negative electrode active material, binder, and conductive agent was 100 parts by mass (94% by mass): 2 parts by mass (2% by mass): 4 parts by mass (4% by mass). The obtained slurry was applied to aluminum foil as a current collector, dried, and then the electrode density (excluding the current collector) was 2.2 g / cm³. 3The electrodes were press-molded to obtain the negative electrode. <Fabrication of the electrode group> The positive electrode and negative electrode prepared as described above were stacked with a cellulose separator in between to obtain a stacked electrode group. The positive electrode terminal and the negative electrode terminal were connected to this electrode group. <Preparation of liquid non-aqueous electrolyte> A mixed solvent of propylene carbonate and diethyl carbonate (volume ratio 1:2) was prepared as a mixed solvent. Lithium hexafluoride phosphate (LiPF6) was dissolved in this solvent at a concentration of 13.3% by mass. Thus, a liquid non-aqueous electrolyte was prepared. <Assembly> The electrode group and liquid non-aqueous electrolyte prepared as described above were placed in a metal container, and the container was sealed to obtain a non-aqueous electrolyte secondary battery.

[0101] (Examples 2-8 and Comparative Examples 1 and 2) Non-aqueous electrolyte secondary batteries were manufactured in the same manner as in Example 1, except that the solid content ratio of the intermediate slurry in the first stirring step, the rate of decrease of the stirring torque in the first stirring step, and the second stirring solid content ratio were set as shown in Table 2 below. (Example 9) As the positive electrode active material, Li of the general formula x Ni 1-a-b-c Co a Mn b M c An aggregate of polycrystalline particles of lithium nickel cobalt manganese composite oxide was prepared, represented by the formula (wherein x is 0.98, 1-a-b-c is 0.80, a is 0.10, b is 0.10, and c is 0). The solid content ratio of the intermediate slurry in the first stirring step, the rate of decrease in stirring torque in the first stirring step, and the solid content ratio in the second stirring step were set as shown in Table 2 below. Except for these, a non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.

[0102] The pore size distribution of the positive electrode of the examples and comparative examples was measured by the mercury intrusion method using the method described above. For the obtained pore size distribution, Table 1 shows the pore volume A (mL / g) in the range of pore size 0.01 μm to 0.3 μm, the pore volume B (mL / g) in the range of pore size greater than 0.3 μm and 1 μm or less, B / (A+B), the ratio (%) of pore volume (A+B) (mL / g) to pore volume C (mL / g) in the range of pore size 0.01 μm to 60 μm, and the pore size of the peak top of the maximum peak (μm). Each non-aqueous electrolyte secondary battery prepared in each example and comparative example was evaluated using the following procedure. <Measurement of 1C discharge capacity> The 1C discharge capacity of the secondary battery was confirmed using the following procedure. First, the secondary battery was charged with a constant current (CC) at 1C until the battery voltage reached 2.75V, and then charged with a constant voltage (CV) at 2.75V for 2 hours. To confirm the 1C discharge capacity, the secondary battery in this state was discharged with a constant current of 1C until the battery voltage reached 1.5V, and the discharge capacity at this discharge was defined as the 1C discharge capacity. <Cycle Test> The secondary battery whose 1C discharge capacity was measured using the above procedure was charged and discharged at a 3C current value in a constant temperature bath at 75°C. After 600 cycles, the battery was removed, and the capacity was confirmed at 25°C, and the amount of gas generated was calculated as shown in Table 1.

[0103]

[0104]

[0105] As is clear from Tables 1 and 2, the electrodes of Examples 1 to 9 generate less gas during charge-discharge cycles compared to the electrodes of Comparative Examples 1 and 2. When comparing Examples 2, 7, and 8, which have the same B / (A+B) value, the electrode of Example 2, where the ratio of pore volume (A+B) to pore volume C is 80% or more and 90% or less, generated less gas during charge-discharge cycles than the electrodes of Examples 7 and 8, where the ratio is less than 80% or greater than 90%. By comparing Example 2 and Example 9, which have the same lithium nickel cobalt manganese composite oxide composition and pore volumes A, B, and C, it can be seen that the electrode of Example 2, which uses an aggregate of single crystal particles of lithium nickel cobalt manganese composite oxide, generates less gas during charge-discharge cycles than the electrode of Example 9, which uses an aggregate of polycrystalline particles of lithium nickel cobalt manganese composite oxide.

[0106] Figure 7 shows the pore size distribution of the electrodes (positive electrodes) of Examples 1-3 and Comparative Examples 1 and 2. In the pore size distribution shown in Figure 7, the horizontal axis is pore size diameter (μm) and the vertical axis is log differential intrusion (mL / g). Figure 7 also shows the pore size distribution of the electrode (positive electrode) of the reference example. The positive electrode of the reference example has the same composition as the positive electrode of Example 1. In addition, the pore volume A of the positive electrode of the reference example was 0.0645 (mL / g), the pore volume B was 0.0145 (mL / g), B / (A+B) was 0.184, the ratio (%) of pore volume (A+B) (mL / g) to pore volume C (mL / g) was 89, and the pore size at the peak top of the maximum peak was 0.25 (μm). The electrodes of Comparative Examples 1-2 and the Reference Example have a peak in the pore diameter range of 0.1 μm to 0.3 μm, similar to Examples 1-6. Comparing the pore diameter distribution of the Reference Example electrode with that of Comparative Example 2, it can be seen that the pore volume in the range of pore diameter 0.3 μm to 1 μm or less is larger in the Reference Example electrode than in Comparative Example 2, and the B / (A+B) value of the Reference Example electrode is larger than that of Comparative Example 2. (Example 10) As the positive electrode active material, the general formula Li x Ni 1-a-b-c Co a Mn b M cAn aggregate of single-crystal particles of lithium nickel cobalt manganese composite oxide represented by the formula (wherein x is 0.98, 1-a-b-c is 0.50, a is 0.20, b is 0.30, and c is 0) was prepared. The positive electrode was fabricated in the same manner as in Example 2, except that this positive electrode active material was used. A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the obtained positive electrode was used. (Comparative Example 3) The positive electrode was fabricated in the same manner as in Comparative Example 1, except that an aggregate of single-crystal particles of lithium nickel cobalt manganese composite oxide with the same composition as in Example 10 was used as the positive electrode active material. A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the obtained positive electrode was used. The 1C discharge capacity and cycle tests described above were performed on the secondary batteries of Example 10 and Comparative Example 3, and the amount of gas generated was measured. The amount of gas generated in the secondary battery of Example 10 is expressed with the amount of gas generated in the secondary battery of Comparative Example 3 set to 100%, and the results are shown in Table 3. Furthermore, the gas generation amount of the secondary battery in Example 2 is represented with the gas generation amount of the secondary battery in Comparative Example 1 set to 100%, and the results are shown in Table 3. Table 3 shows the following: The electrodes of Example 2 and Comparative Example 1 satisfy the molar ratio of Ni oxide (1-a-b-c) of 0.6 ≤ (1-a-b-c) ≤ 0.9. A comparison of Example 2 and Comparative Example 1 shows that the gas generation amount of the electrode in Example 2, where B / (A+B) is greater than 0.001 and ≤ 0.09, is 40% less than the gas generation amount of the electrode in Comparative Example 1, where B / (A+B) is outside the range. On the other hand, the electrodes of Example 10 and Comparative Example 3 have a molar ratio of Ni oxide (1-a-b-c) of 0.5. As is clear from the comparison of Example 10 and Comparative Example 3, the gas generation amount of the electrode in Example 10, where B / (A+B) is greater than 0.001 and ≤ 0.09, is less than that of the electrode in Comparative Example 3, where B / (A+B) is outside the range, but the rate of reduction in gas generation was greater in Example 2.

[0107] According to the one or more embodiments and examples described above, the general formula Li x Ni 1-a-b-c Co a Mn b M cThe active material contains an oxide represented by O2 (wherein x, a, b, and c are 0.9 ≤ x ≤ 1.25, 0.05 ≤ a ≤ 0.5, 0.03 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.2. M includes one or more metallic elements other than Ni, Co, and Mn). The electrode also satisfies equation (1). This electrode allows for improved capacity and reduced gas generation during charge-discharge cycles. Therefore, the charge-discharge cycle life can be improved.

[0108] 0.001 < B / (A + B) ≤ 0.09 (1) where, in equation (1), A is the pore volume (mL / g) in the range of pore diameters of 0.01 μm or more and 0.3 μm or less in the pore diameter distribution obtained by the mercury intrusion method of electrodes, and B is the pore volume (mL / g) in the range of pore diameters greater than 0.3 μm and 1 μm or less in the pore diameter distribution obtained by the mercury intrusion method of electrodes.

[0109] The invention of embodiments is described below. <1> General formula Li x Ni 1-a-b-c Co a Mn b M c An electrode comprising an active material containing an oxide represented by O2 (wherein x, a, b, and c are 0.9 ≤ x ≤ 1.25, 0.05 ≤ a ≤ 0.5, 0.03 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.2, and M includes one or more metallic elements other than Ni, Co, and Mn), and satisfying the following equation (1).

[0110] 0.001 < B / (A + B) ≤ 0.09 (1) However, in equation (1), A is the pore volume (mL / g) in the range of pore diameters of 0.01 μm or more and 0.3 μm or less of the pore diameter distribution of the electrode by the mercury intrusion method, and B is the pore volume (mL / g) in the range of pore diameters greater than 0.3 μm and 1 μm or less of the pore diameter distribution. <2> The electrode according to <1>, wherein the active material includes an aggregate of single crystal particles of the oxide. <3> The electrode according to <1> or <2>, wherein the value of (1-a-b-c) in the general formula of the oxide is 0.6 ≤ (1-a-b-c) ≤ 0.9. <4> An electrode according to any one of <1> to <3>, wherein the ratio of the pore volume (mL / g) represented by (A + B) in formula (1) above to the pore volume (mL / g) in the range of pore diameter 0.01 μm to 60 μm is 80% or more. <5> An electrode according to any one of <1> to <4> that is a positive electrode for a lithium secondary battery. <6> A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is an electrode according to any one of <1> to <5>. <7> The secondary battery according to <6>, wherein the negative electrode contains a lithium titanium-containing oxide. <8> A battery pack comprising the secondary battery according to <6> or <7>.

[0111] 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.

[0112] 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, 16...Glass material, 17...Positive electrode tab, 18...Positive electrode terminal, 20...Battery pack, 21...Single cell, 22...Adhesive tape P, 23...Battery pack, 24...Printed circuit board, 25...Thermistor, 26...Protection circuit, 27...Terminal for supplying power to external devices, 28...Positive lead, 29...Positive connector, 30...Negative lead, 31...Negative connector, 32...Wiring, 33...Wiring, 34a...Positive wiring, 34b...Negative wiring, 35...Wiring, 36...Protective sheet, 37...Storage container, 38...Lid, 51...Negative terminal, 61...Positive terminal.

Claims

1. General formula Li x Ni 1-a-b-c Co a Mn b M c An electrode comprising an active material containing an oxide represented by O2 (wherein x, a, b, and c are 0.9 ≤ x ≤ 1.25, 0.05 ≤ a ≤ 0.5, 0.03 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.2, and M includes one or more metallic elements other than Ni, Co, and Mn), and satisfying the following equation (1): 0.001 < B / (A + B) ≤ 0.09 (1) However, in equation (1), A is the pore volume (mL / g) in the range of pore diameters of 0.01 μm to 0.3 μm in the pore diameter distribution of the electrode by the mercury intrusion method, and B is the pore volume (mL / g) in the range of pore diameters greater than 0.3 μm and 1 μm or less in the pore diameter distribution.

2. The electrode according to claim 1, wherein the active material comprises an aggregate of single crystal particles of the oxide.

3. The electrode according to claim 1, wherein the value of (1-a-b-c) in the general formula of the oxide is 0.6 ≤ (1-a-b-c) ≤ 0.

9.

4. The electrode according to claim 1, wherein the ratio of the pore volume (mL / g) represented by (A + B) in formula (1) above to the pore volume (mL / g) in the range of pore diameters of 0.01 μm or more and 60 μm or less is 80% or more.

5. The electrode according to claim 1, which is a positive electrode for a lithium secondary battery.

6. A secondary 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 5.

7. The secondary battery according to claim 6, wherein the negative electrode contains a lithium titanium-containing oxide.

8. A battery pack comprising the secondary battery described in claim 6.

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