Electrode, battery, and battery pack

Abstract

According to an embodiment, there is provided an electrode possessing an active material-containing layer that contains an active material, a first conductive agent, and a second conductive agent. In the Raman chart, the ratio ID / IG of the integrated intensity ID of the D band to the integrated intensity IG of the G band for the first conductive agent is 0.5 < ID / IG < 2 and for the second conductive agent is 0 < ID / IG < 0.5. In a constituent material mapping image of the active material-containing layer by Raman spectroscopy, the occupied area S1 of the first conductive agent relative to the occupied area Sa of the active material satisfies 0.1 < S1 / Sa < 1.0; the occupied area S2 of the second conductive agent relative to the occupied area Sa of the active material satisfies 0.8 < S2 / Sa < 10; the distance R1 between the centroids of the first conductive agent relative to the distance Ra between the centroids of the active material satisfies 1.0 < R1 / Ra < 1.5; the distance R2 between the centroids of the second conductive agent relative to the distance Ra between the centroids of the active material satisfies 0.5 < R2 / Ra < 1.0; and R1, R2, and the distance R1-2 between the centroids between the first conductive agent and the second conductive agent satisfy R1 > R2 > R1-2.

Description

Electrodes, batteries, and battery packs

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

[0002] Secondary batteries, including non-aqueous electrolyte secondary batteries such as lithium-ion batteries, are widely used not only in electronic devices such as mobile phones but also in vehicles such as hybrid and electric vehicles. These applications require improvements in high capacity, long lifespan, and output performance.

[0003] Graphite is generally used as the negative electrode active material in non-aqueous electrolyte batteries. Graphite forms LiC6 through Li insertion and exhibits a theoretical capacity of 372 mAh / g. Furthermore, graphite has a Li reaction potential (the potential at which Li insertion-desorption reactions occur) of 0.1 V (vs. Li / Li). + Because it reacts at a potential of approximately 0.5 V (vs. Li / Li), using a graphite negative electrode can yield a high-power, high-energy-density battery. On the other hand, because the Li insertion reaction potential of graphite is close to the Li deposition potential, lithium dendrites easily precipitate due to overvoltage, etc. Since dendrites penetrate the separator, causing an internal short circuit, batteries using graphite negative electrodes have the disadvantage of low safety. In addition, in graphite, expansion and contraction occur in the c-axis direction during Li insertion and deinsertion, resulting in significant structural degradation of the graphite. Other negative electrode active materials for non-aqueous electrolyte batteries include those with a Li reaction potential of 0.5 V (vs. Li / Li). + Compounds that react at potentials higher than ) such as spinel-type lithium titanate (Li4Ti5O 12 Using this method can suppress the deposition of lithium dendrites. As a result, it is known that risks such as short circuits, self-discharge, and ignition can be avoided, making it possible to manufacture batteries with superior lifespan performance.

[0004] Lithium nickel-cobalt-manganate is an example of a positive electrode active material that excels in high-capacity performance. Conventional batteries using lithium nickel-cobalt-manganate as the positive electrode and lithium titanate as the negative electrode have advantages over batteries using graphite-based negative electrodes, such as superior rapid charge / discharge performance, long lifespan, and low-temperature performance. On the other hand, there is room for improvement in the positive electrode active material. In particular, there are problems with lifespan performance. During charge / discharge cycles, irreversible changes occur in the lithium nickel-cobalt-manganate particles of the positive electrode, such as particle fracture or degradation to a rock salt-type structure. This leads to a decrease in capacity and an increase in electrical resistance with each cycle. Conventional lithium nickel-cobalt-manganate is generally a polycrystalline system in which fine primary particles aggregate to form secondary particles. In the case of positive electrodes using such active materials, oxidation reactions between the positive electrode and electrolyte are likely to occur, especially during charge / discharge using high potential, resulting in problems such as significant gas generation and resistance increase.

[0005] Conversely, using an active material with a small specific surface area, such as a single crystal, as the positive electrode can reduce side reactions between the active material and the electrolyte. However, on the other hand, a smaller specific surface area reduces contact between the active material and the conductive agent, which raises concerns that the inside of the electrode may become divided into areas where current flows easily and areas where it does not, potentially leading to localized degradation of the active material.

[0006] Furthermore, conventional lithium secondary electrodes obtained using lithium-containing metal oxides as active materials have carbon or other conductive agents added to maintain conductive paths between the active materials in the electrodes. If the conductive agents are not properly dispersed between the active materials in the electrodes, they can aggregate and form conductive paths on their own. This can lead to problems such as uneven current distribution because current flows more easily through the aggregated conductive agents than through the active materials, reduced pressability during electrode fabrication, and weakened bonding force between the active material layer and the current collector.

[0007] International Publication No. 2016 / 068258, Japanese Patent Publication No. 2019-3946, International Publication No. 2023 / 131987

[0008] An object is to provide an electrode capable of realizing a battery with low electrical resistance and excellent life performance, a battery including this electrode, and a battery pack including this battery.

[0009] According to an embodiment, an electrode including an active material-containing layer containing an active material, a first conductive agent, and a second conductive agent is provided. In a Raman chart by Raman spectroscopy for the active material-containing layer, the integrated intensity I of the D band appearing at 1350 ± 10 cm for the first conductive agent -1 of, the integrated intensity I of the G band appearing at 1590 ± 10 cm D for, the ratio I -1 of, the integrated intensity I of the G band appearing at 1590 ± 10 cm G for, to I D / I G is in the range of 0.5 < I D / I G < 2. In the Raman chart, the ratio I D / I G for the second conductive agent is in the range of 0 < I D / I G < 0.5. In the constituent material mapping image by Raman spectroscopy for the active material-containing layer, the ratio S1 / Sa of the occupied area S1 of the first conductive agent to the occupied area Sa of the active material is in the range of 0.1 < S1 / Sa < 1.0. In the constituent material mapping image, the ratio S2 / Sa of the occupied area S2 of the second conductive agent to the occupied area Sa of the active material is in the range of 0.8 < S2 / Sa < 10. In the constituent material mapping image, the ratio R1 / Ra of the center-of-gravity distance R1 of the first conductive agent to the center-of-gravity distance Ra of the active material is in the range of 1.0 < R1 / Ra < 1.5. In the constituent material mapping image, the ratio R2 / Ra of the center-of-gravity distance R2 of the second conductive agent to the center-of-gravity distance Ra of the active material is in the range of 0.5 < R2 / Ra < 1.0. In the constituent material mapping image, the center-of-gravity distance R1 of the first conductive agent, the center-of-gravity distance R2 of the second conductive agent, and the center-of-gravity distance R1-2 between the first conductive agent and the second conductive agent satisfy the relationship R1 > R2 > R1-2.

[0010] According to another embodiment, a battery including the above electrode and an electrolyte is provided.

[0011] In yet another embodiment, a battery pack comprising the above-mentioned battery is provided.

[0012] Figure 1 is a schematic plan view showing an example electrode according to the embodiment. Figure 2 is a schematic cross-sectional view showing an example electrode according to the embodiment. Figure 3 is a conceptual diagram showing a constituent material mapping image of the active material-containing layer of an example electrode according to the embodiment, obtained by Raman spectroscopy. Figure 4 is a conceptual diagram showing a constituent material mapping image of the active material-containing layer of an example conventional electrode, obtained by Raman spectroscopy. Figure 5 is a conceptual diagram showing a method for calculating the centroid-to-centroid distance in a constituent material mapping image obtained by Raman spectroscopy. Figure 6 is a conceptual diagram showing a method for calculating the centroid-to-centroid distance in a constituent material mapping image obtained by Raman spectroscopy. Figure 7 is a conceptual diagram showing a method for calculating the centroid-to-centroid distance in a constituent material mapping image obtained by Raman spectroscopy. Figure 8 is a conceptual diagram showing a method for calculating the centroid-to-centroid distance in a constituent material mapping image obtained by Raman spectroscopy. Figure 9 is a graph showing the distribution of centroid-to-centroid distances for the active material-containing layer of an example conventional electrode. Figure 10 is a graph showing the distribution of centroid-to-centroid distances for the active material-containing layer of an example electrode according to the embodiment. Figure 11 is a cross-sectional view of an example battery according to the embodiment, cut in the thickness direction. Figure 12 is an enlarged cross-sectional view of part A in Figure 11. Figure 13 is a partially cutaway perspective view of a battery in another example according to the embodiment. Figure 14 is an exploded perspective view of a battery pack in one example according to the embodiment. Figure 15 is a block diagram showing the electrical circuit of the battery pack shown in Figure 14. Embodiment

[0013] One conventional method for improving lifespan is to increase the amount of conductive agent. If the amount of conductive agent is too low, it becomes difficult to maintain electrical contact between electrode components, including the active material, and the resistance of the electrodes increases. On the other hand, if the amount of conductive agent is increased too much, aggregation of the conductive agent is more likely to occur. As a result, current tends to flow only in low-resistance regions, causing localized degradation of the active material and leading to a decrease in lifespan.

[0014] In conventional lithium-containing metal composite compounds used as the positive electrode active material for lithium secondary batteries, active materials with a small specific surface area that are less prone to side reactions are sometimes used to improve the lifespan of the positive electrode. However, when using active materials with a small specific surface area, it is not only difficult to obtain electrical contact between the positive electrode active material and the conductive agent, but electrical contact is also easily lost due to the expansion and contraction of the positive electrode during battery charging and discharging. In such positive electrodes, current flows preferentially in the areas where good contact between the active material and the conductive agent is maintained, which can cause a localized increase in the positive electrode potential. Consequently, the positive electrode active material in the areas with increased positive electrode potential tends to deteriorate, leading to increased resistance and significant gas generation.

[0015] Therefore, particle shape control and coatings are applied to suppress the degradation of the active material. However, regardless of shape or surface condition, if the specific surface area of ​​the positive electrode is large, side reactions increase, leading to increased electrical resistance, and if the specific surface area is small, there is a concern that localized degradation as described above will occur. Consequently, these countermeasures do not fundamentally solve the degradation of the active material.

[0016] The embodiments will be described below with reference to the drawings. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted.

[0017] Furthermore, each figure is a schematic diagram intended to illustrate the embodiment and facilitate understanding of it. While the shape, dimensions, ratios, etc., may differ from those of the actual device, these can be appropriately modified in accordance with the following explanation and known technology.

[0018] (First Embodiment) According to the first embodiment, an electrode is provided. The electrode comprises an active material-containing layer containing an active material, a first conductive agent, and a second conductive agent. In a Raman chart obtained by measuring the active material-containing layer by Raman spectroscopy, both the first conductive agent and the second conductive agent are 1350 ± 10 cm². -1 The D band appears at 1590±10cm -1 It has a G band that appears there. The integrated intensity of the D band for the first conductive agent in the above Raman chart I DThe integrated intensity of the G band I G Ratio I D / I G 0.5 < I D / I G It is within the range of <2. Ratio I for the second conductive agent in the above Raman chart D / I G 0 < I D / I G It is within the range of <0.5. In the constituent material mapping image obtained by Raman spectroscopy of the active material-containing layer, the ratio S1 / Sa of the occupied area S1 of the first conductive agent to the occupied area Sa of the active material is within the range of 0.1 < S1 / Sa < 1.0. In the constituent material mapping image, the ratio S2 / Sa of the occupied area S2 of the second conductive agent to the occupied area Sa of the active material is within the range of 0.8 < S2 / Sa < 10. In the constituent material mapping image, the ratio R1 / Ra of the distance R1 between the centers of gravity of the first conductive agent to the distance Ra between the centers of gravity of the active material is within the range of 1.0 < R1 / Ra < 1.5. In the constituent material mapping image, the ratio R2 / Ra of the distance R2 between the centers of gravity of the second conductive agent to the distance Ra between the centers of gravity of the active material is within the range of 0.5 < R2 / Ra < 1.0. In the constituent material mapping image, the distance between the centroids R1 of the first conductive material, the distance between the centroids R2 of the second conductive material, and the distance between the centroids R1-2 between the first and second conductive materials satisfy the relationship R1 > R2 > R1-2.

[0019] The electrode according to the embodiment may be an electrode for a battery. Examples of batteries that may contain such an electrode include secondary batteries such as lithium-ion secondary batteries. Secondary batteries include non-aqueous electrolyte secondary batteries containing a non-aqueous electrolyte. The electrode may be, for example, a positive electrode for a battery.

[0020] An electrode that satisfies the above configuration is an electrode that uses multiple conductive agents with different physical properties along with the active material. Specifically, it is an electrode in which the conductive agents are uniformly dispersed by controlling the shape, amount added, and dispersion method of the conductive agents. In such an electrode, even if the active material has a large capacity but degrades greatly due to structural changes at high potentials, or has a large particle size and small specific surface area which is unfavorable for electrical contact but has few side reactions, the drawbacks of these active materials can be canceled out, and the battery life performance can be greatly improved.

[0021] For example, carbon black, such as acetylene black, which is commonly used as a conductive agent, exhibits conductivity based on percolation theory. Therefore, it is desirable for carbon black to have small particle size, a large specific surface area, and to form a well-developed agglomerate structure. However, in electrodes using active materials with a small specific surface area, a large amount of carbon black is required for electrical contact in order to form and maintain a conductive network between the active materials. In that case, aggregation of carbon black particles is more likely to occur, and the morphology of the carbon black changes from an agglomerate structure suitable for exhibiting conductivity to an aggregate structure. When aggregates are present, the region with lower resistance than the active material becomes larger, and current preferentially flows through that region. As a result, the charge-discharge reaction of the active material near the aggregate is promoted, the positive electrode potential rises, leading to localized degradation of the active material and consequently a decrease in lifespan performance.

[0022] Therefore, highly crystalline materials with large particle sizes and high orientation, such as flaky graphite which is considered to have little contribution to conductivity, are added and appropriately positioned between the carbon black and the active material. This allows for good formation and retention of the conductive network.

[0023] Carbon black has a large integrated intensity in the D band due to structural disorder, I D I G The ratio to is 0.5 < I D / I G<2.0 relationship is satisfied. That is, the first example of conductive agent mentioned above includes carbon black. Also, highly crystalline carbon has a large integrated intensity of the G band due to its layered structure, I D I G The ratio to is 0 < I D / I G The relationship <0.5 is satisfied. Such highly crystalline carbon is an example of a second conductive agent, and includes the flaky graphite mentioned above. Thus, the two can be distinguished by Raman spectroscopy. Furthermore, metal oxides such as lithium nickel cobalt manganese composite oxide do not have D-band or G-band. From this, it is possible to obtain a constituent material mapping image by binarizing these three phases in the Raman chart of the active material-containing layer and then superimposing them.

[0024] Furthermore, the occupied area of ​​each phase on the constituent material mapping image changes depending on the mixing ratio of the first and second conductive agents, which have different physical properties. Therefore, by analyzing the constituent material mapping image, it is possible to confirm whether the conductive agents are included in an appropriate mixing ratio from the ratio of the occupied areas of the active material, the first conductive agent, and the second conductive agent. Letting the occupied areas of the active material, the first conductive agent, and the second conductive agent be Sa, S1, and S2, respectively, the electrode according to the embodiment satisfies the relationships 0.1 < S1 / Sa < 1.0 and 0.8 < S2 / Sa < 10, thereby suppressing the formation of aggregates of the first conductive agent (carbon black, etc.) and ensuring good dispersion of the second conductive agent (highly crystalline carbon, etc.). As a result, the resistance of the electrode can be reduced and the battery life performance can be improved. Furthermore, by controlling the dispersion of conductive agents within the active material-containing layer, the first conductive agent maintains the good agglomerate structure of the carbon black mentioned above, while the second conductive agent (such as highly crystalline carbon) forms a conductive network throughout the electrode. As a result, the electrode can improve its lifespan by suppressing degradation due to charge-discharge cycles. Specifically, the centroidal distances Ra, R1, and R2 between the active materials, the centroidal distances R1-2 between the first and second conductive agents, and the centroidal distance R1-2 between the first and second conductive agents satisfy the relationships 1.0 < R1 / Ra < 1.5, 0.5 < R2 / Ra < 1.0, and R1 > R2 > R1-2, respectively, as these three phases are dispersed within the active material-containing layer. Therefore, the electrode can achieve the above effect.

[0025] In the electrodes in question, the ratio of the occupied area of ​​the active material-containing layer, as determined from the constituent material mapping image obtained from cross-sectional measurements by Raman spectroscopy, satisfies the relationships 0.1 < S1 / Sa < 1.0 and 0.8 < S2 / Sa < 10, respectively, thereby reducing electrical resistance and suppressing current unevenness. The occupied area of ​​the conductive agent in the cross-section of the active material-containing layer reflects the proportion of the conductive agent contributing to conductivity. That is, the ratio of the occupied area of ​​the conductive agent to the occupied area of ​​the active material serves as an indicator of electrical contact at the electrode. If 0.1 > S1 / Sa or S1 / Sa > 1.0, the first conductive agent, such as carbon black, may be present in insufficient or excessive amounts. In that case, sufficient conductivity may not be obtained, or current unevenness due to the formation of aggregates may become significant. Also, if 0.8 > S2 / Sa or S2 / Sa > 10, the second conductive agent (highly crystalline carbon) may be present in insufficient or excessive amounts. If the amount of highly crystalline carbon is insufficient, the desired conductive network cannot be formed, and the effects described above will not appear. Conversely, if the amount of highly crystalline carbon is excessive, the first conductive agent, which electrically connects individual particles, will not be able to perform its role adequately, leading to localized degradation of the active material. More preferably, it is desirable to satisfy the relationships S1 / Sa < 0.8 and 2.0 < S2 / Sa < 4.0, respectively. In electrodes having a preferred occupancy area ratio, in which the first conductive agent is reliably present between the active materials and the second conductive agent is present traversing them, the effect of improving lifetime performance is more pronounced.

[0026] Electrodes with superior lifetime performance can be obtained when the active material, the first conductive agent, and the second conductive agent are dispersed in relative positions such that the centroid-to-centroid distances, determined from the constituent material mapping image obtained from cross-sectional Raman spectroscopy measurements of the active material-containing layer, satisfy the relationships 1.0 < R1 / Ra < 1.5, 0.5 < R2 / Ra < 1.0, and R1 > R2 > R1-2, respectively. Simply considering only the occupied area may not lead to performance improvement if the dispersion is poor and uneven. When 1.0 > R1 / Ra or R1 / Ra > 1.5, the highly conductive first conductive agent may be present in insufficient or excessive amounts around the active material. If it is insufficient, the charge-discharge reaction will not occur sufficiently, and if it is excessive, current will flow more easily than in other active materials, leading to localized degradation. When 0.5 > R2 / Ra or R2 / Ra > 1.0, the second conductive agent may be present in insufficient or excessive amounts around the active material. If the amount is too low, the formation of a conductive network inside the electrode may be insufficient, and if it is too high, there may be a shortage of the first conductive agent necessary for interparticle conductivity, which may prevent the charge-discharge reaction from occurring sufficiently. If R1 < R2 or R1-2 < R2, an excess of the highly conductive first conductive agent may be present. In that case, current will flow more easily to nearby active materials than to other active materials, leading to localized degradation. If R2 < R1-2 or R1 < R1-2, the first conductive agent and the second conductive agent may exist in independent regions. In that case, the mutual or complementary effects of the conductive agents may not be obtained, and the effect of improving life performance may not be achieved.

[0027] The active material-containing layer contains Li as the active material. a Ni (1-b-c-d) Co b Mn c M d It is preferable that the mixture contains a lithium nickel cobalt manganese composite oxide represented by O2. Each subscript in the formula is within the ranges of 1 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, and 0 ≤ d ≤ 0.1. M includes at least one selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V.

[0028] The active material may have an average primary particle diameter of 2 μm to 7 μm. By setting the primary particle diameter of the active material particles in the active material-containing layer to 2 μm to 7 μm, the battery life performance can be improved. Setting the primary particle diameter to 2 μm or more reduces the specific surface area of ​​the electrodes, thereby reducing the influence of side reactions between the electrodes and the electrolyte on the life performance. Furthermore, setting the primary particle diameter to 7 μm or less allows for more uniform diffusion of lithium ions within the particles, suppressing localized structural degradation and improving life performance. More preferably, the primary particle diameter should be 3 μm to 4.5 μm. A more preferable range makes it easier to prevent aggregation and isolation of primary particles and to satisfy the above-mentioned distance between centers of gravity.

[0029] The specific surface area of ​​the active material, determined by nitrogen adsorption / desorption, is 0.5 m². 2 / g or more 1.0 m 2 It is preferable that the value is within the range of / g or less. The specific surface area is 0.5 m². 2 When the concentration is 1.0 m² or higher, the penetration of the electrolyte solution into the active material-containing layer is promoted, improving output performance and lifespan. 2 When the value is below / g, the contact between the active material and the conductive agent increases, further reducing electrical resistance and improving high-current output performance. Additionally, the mechanical stability of the electrodes increases.

[0030] The electrode may include a current collector. The current collector may, for example, be in the shape of a foil, strip, or plate. The active material-containing layer may be provided on the surface of at least one main surface of the current collector. That is, the current collector may have the active material-containing layer on one side or on both sides. The current collector may include portions on its surface that do not have the active material-containing layer. These portions may function as current-collecting tabs. Alternatively, the electrode may include current-collecting tabs separate from the current collector.

[0031] The active material-containing layer may include a binder in addition to the active material and conductive agent. The binder may be formulated to bind the dispersed active material and conductive agent together, and to bind the active material and conductive agent to the current collector.

[0032] Next, we will describe the materials that can be used in the active material-containing layer provided by the electrode according to the first embodiment and in the current collector that the electrode may include.

[0033] <Active material-containing layer> The density of the active material-containing layer is 2.0 g / cm³. 3 More than 4.0 g / cm 3 It is preferable that the density is less than 2.0 g / cm³. In electrodes having a density within the above range, the contact between the active material and the conductive agent is improved, allowing for the formation of a better conductive network and equalization of electrical resistance within the active material-containing layer. Therefore, batteries with excellent lifespan performance can be manufactured using such electrodes. 3 As a result, the contact between the active material, the first conductive agent, and the second conductive agent is improved, the electrical resistance within the active material-containing layer becomes uniform, and the battery life performance is improved. In addition, the mechanical stability of the electrodes is improved. Density: 4.0 g / cm³ 3 If the concentration is less than 3.20 g / cm³, the penetration of the electrolyte solution into the active material-containing layer is promoted, improving the lifespan performance. 3 More than 3.50 g / cm 3 A density of less than is desirable. In a more preferable range, the resistance equalization effect is greater and local degradation of the active material is reduced, making it possible to obtain a battery with an even longer lifespan.

[0034] As described above, the active material-containing layer may contain a binder in addition to the active material and conductive agent. The preferred blending ratio of the active material, conductive agent, and binder in the active material-containing layer is 63% to 99% by mass for the active material, 0.5% to 36% by mass for the conductive agent, and 0.5% to 17% by mass for the binder. The blending ratio of the conductive agent is the total blending ratio of the first conductive agent and the second conductive agent. It is preferable that the respective contents of the first conductive agent and the second conductive agent in the active material-containing layer are approximately the same. Specifically, the mass ratio of the first conductive agent and the second conductive agent to the mass of the active material-containing layer may be 0.0025 to 0.18, respectively.

[0035] <Active Material> As mentioned above, the active material in the active material-containing layer is lithium nickel cobalt manganese composite oxide (for example, Lia Ni (1-b-c-d) Co b Mn c M d O2; where 1 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, and 0 ≤ d ≤ 0.1; M may include at least one selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V. Other compounds can be used as active materials, but it is preferable to include at least the above-mentioned lithium nickel cobalt manganese composite oxide as an active material. Furthermore, it is more preferable to include an active material that contains the lithium nickel cobalt manganese composite oxide and has an average primary particle diameter of 2 μm or more and 7 μm or less. For example, the lithium nickel cobalt manganese composite oxide can be used as the first active material, and other second active materials can be further included in the active material-containing layer. Of course, the first active material may be used alone, or it may not contain the first active material but contain one or more second active materials.

[0036] The second active material can be various oxides, for example, lithium cobalt composite oxide (e.g., LiCoO ２ ), manganese dioxide, lithium manganese composite oxide (e.g., LiMn ２ O ４ LiMnO ２ ), lithium nickel composite oxide (for example, LiNiO ２ ), lithium nickel cobalt composite oxide (e.g., LiNi ０．８ Co ０．２ O ２ Examples include lithium-containing iron oxides, lithium-containing vanadium oxides, and chalcogen compounds such as titanium disulfide and molybdenum disulfide. The electrode may contain one of the above compounds as a second active material, or it may contain two or more of the above compounds as a second active material.

[0037] The proportion of the mass of the first active material to the total mass of the active material contained in the active material-containing layer is preferably 75% by mass or more and 100% by mass or less, and more preferably 80% by mass or more and 100% by mass or less.

[0038] The active material may, for example, have the shape of particles. That is, the active material-containing layer may contain particles of the active material. The active material particles may be primary particles, or a mixture of primary and secondary particles.

[0039] It is preferable for the proportion of primary particles and secondary particles in the active material to be high. Poor conductivity inside secondary particles (inside the hollow structure) eliminates the presence of primary particles contained therein, thereby improving contact between the active material particles and the conductive agent, and further reducing electrical resistance is possible.

[0040] From the above, it is desirable to dissolve the aggregation of secondary particles of the active material, while it is also desirable to maintain a particle size of 2 μm or larger without further crushing the primary particles of the active material. By not crushing the primary particles of the active material, an active material with a good crystal structure can be obtained, and good lifetime performance can be maintained. By making the average particle diameter of the active material 2 μm or larger, the specific surface area of ​​the electrode can be reduced, and the influence of side reactions between the electrode and electrolyte on lifetime performance can be reduced. On the other hand, by making the average particle diameter 7 μm or smaller, the diffusion of lithium ions within the solid can be made uniform within the particles, and lifetime performance can be further improved.

[0041] <Conductive Agent> As a conductive agent, it exhibits a conductivity of 1590 ± 10 cm² in the Raman chart obtained by Raman spectroscopy. -1 The integrated intensity I of the G band that appears G 1350±10cm -1 The integrated intensity of the D band that appears D Ratio I D / I G However, 0.5 < I D / I G <A first conductive agent which is a carbon material within the range of 2, and specific I D / I G 0 < I D / I G It includes at least a second conductive agent which is a carbon material within the range of <0.5. Roughly speaking, the first conductive agent is a carbon material with a low degree of graphitization, and the second conductive agent is a carbon material with high crystallinity and a high degree of graphitization.

[0042] Specific examples of the first conductive agent include carbon black such as acetylene black, Ketjen black, and furnace black. Specific examples of the second conductive agent include graphite, graphene, single-walled carbon nanotubes, and double-walled carbon nanotubes. Multi-walled carbon nanotubes have a specific ratio depending on the manufacturing method. D / I G The value can be 0.5 or less, or 0.5 or more. Furthermore, the role of carbon nanotubes within the active material-containing layer differs depending on their length. Short carbon nanotubes can exhibit conductivity based on percolation theory, similar to carbon black, and can construct agglomerate structures. Long carbon nanotubes can form conductive networks, similar to flake graphite. Additionally, as the second conductive agent, materials with high orientation, such as highly oriented graphite, are preferred. For example, graphite includes highly oriented flake graphite as well as spheroidal graphite, which has reduced orientation. Natural graphite is flake graphite. Spheroidal graphite is graphite obtained by spheroidization treatment. The active material-containing layer contains at least one of the first conductive agent and at least one of the second conductive agent. The active material-containing layer can contain conductive agents in combinations of one first conductive agent and two or more second conductive agents, or two or more first conductive agents and one first conductive agent. Furthermore, the active material-containing layer may contain two or more types of the first conductive agent and the second conductive agent.

[0043] The first conductive agent may, for example, have a particle shape. From the viewpoint of forming an agglomerate structure, it is desirable that the average particle size (primary particle diameter) of the first conductive agent is small. For this reason, it is desirable that the average particle size of the first conductive agent is 100 nm or less. For example, it is preferable to add acetylene black, which has excellent conductivity and whose average particle size is in the range of 20 nm to 100 nm, as the first conductive agent. A more preferable range for the average particle size of the first conductive agent is 30 nm to 70 nm.

[0044] The second conductive agent may have, for example, a flaky shape. The second conductive agent can form a conductive network by having a large particle size, but from the viewpoint of ensuring dispersibility that makes it easier to obtain the positional relationship with the active material and the first conductive agent mentioned above, it is desirable that the average particle size of the second conductive agent be 10 μm or less. It is more preferable that the average particle size of the second conductive agent be 1 μm or less.

[0045] As will be explained in more detail later, the particle size of the first and second conductive agents referred to here is the equivalent diameter of a circle, that is, the diameter of a sphere if the conductive agent particles were assumed to be spherical with the same volume or cross-sectional area.

[0046] It is preferable that the mass ratio of each of the first conductive agent and the second conductive agent to the active material is 0.18 or less. That is, it is preferable that the mixture contains 18 parts by mass or less of the first conductive agent and 18 parts by mass or less of the second conductive agent per 100 parts by mass of the active material.

[0047] <Binding Agents> As binding agents, materials containing fluorine atoms in their molecules are preferred because they have excellent oxidation resistance and improve lifespan. Examples of such binding agents include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorinated rubber. Other binding agents that can be used include, for example, styrene-butadiene rubber, acrylic resins and their copolymers, polyacrylic acid, and polyacrylonitrile. The active material-containing layer may contain one of the above binding agents, or two or more of the above binding agents.

[0048] <Current Collector> As the current collector, for example, metal foil or alloy foil can be used. Examples of metal foil include aluminum foil, stainless steel foil, and nickel foil. Examples of alloy foil include aluminum alloy, copper alloy, and nickel alloy.

[0049] Next, a specific example of the electrode according to the first embodiment will be described with reference to the drawings.

[0050] 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. Figure 2 is a schematic cross-sectional view schematically showing an example of the electrode.

[0051] The positive electrode 3 shown in Figures 1 and 2 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. In the illustrated example, the positive electrode active material containing layer 3b is provided on one main surface of the positive electrode current collector 3a, but the positive electrode active material containing layer 3b may be provided on both the front and back main surfaces of the positive electrode current collector 3a.

[0052] 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 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).

[0053] The positive electrode active material-containing layer 3b comprises at least a positive electrode active material 300, a first conductive agent 301, and a second conductive agent 302. Although not shown in the figures, the positive electrode active material-containing layer 3b may further contain a binder. The first conductive agent 301 is distributed in a way that fills the gaps between the particles of the positive electrode active material 300, forming conductive paths between the particles of the positive electrode active material 300. The first conductive agent 301, having a particle shape, is concentrated in some of the gaps between the positive electrode active material 300, thereby forming an agglomerate structure of the first conductive agent 301. The second conductive agent 302, having a scale shape, is dispersed so as to connect the agglomerate structures of the first conductive agent 301, thereby forming a conductive network within the positive electrode active material-containing layer 3b.

[0054] The electrode according to the first embodiment of the manufacturing method can be manufactured, for example, by the following method.

[0055] A mixture is obtained by adding the active material, the first conductive agent, the second conductive agent, and an optional binder to a suitable solvent. However, the first and second conductive agents are stirred separately in powder form, then added together and stirred again before being added to the solvent. This reduces the difference in the dispersion progress between the first and second conductive agents. Alternatively, the mixed powder of the first and second conductive agents obtained by stirring is added after other materials have been added to the solvent. At this time, an optional dispersant may be used to improve the dispersibility of each conductive agent and the dispersibility of the conductive agents themselves. The order in which the conductive agents are added may also be changed depending on the type of conductive agent used. By controlling the process, the distance between the centroids in the cross-section of the fabricated electrode can be controlled.

[0056] Next, the obtained mixture is placed in a stirrer. The mixture is stirred in this stirrer to obtain a slurry. During the stirring process, by reducing the rotation speed of the stirrer, a slurry that sufficiently maintains the conductive network of the conductive agent can be obtained. Conversely, by increasing the rotation speed of the stirrer, a slurry with good dispersion of the active material can be obtained. By using slurries obtained by reducing or increasing the stirring speed in this way, the occupied area of ​​each component in the cross-section and the distance between the centers of gravity of the fabricated electrode can be controlled. Furthermore, by increasing the rotation speed of the stirrer, it is possible to promote the disintegration of the active material and conductive agent particles, thereby improving the specific surface area of ​​the fabricated electrode. The stirring mechanism in the stirrer used may be changed depending on the type of conductive agent used.

[0057] The slurry thus obtained is applied to both sides or one side of the current collector. At this time, areas of the current collector may be left uncoated with slurry on either surface. Next, the coating is dried and pressed. By increasing the pressing load at this time, it is possible to improve the electrode density, and a higher electrode density tends to produce electrodes with better electrical contact and superior capacitance. Increasing the pressing load can change not only the electrode density but also the distance between the centers of gravity of each component in the cross-section of the manufactured electrode. For example, depending on the shape and strength of the active material, a large pressing load may cause pulverization or crushing, so the area Sa occupied by the active material in the cross-section increases or the distance Ra between the centers of gravity decreases. Also, because highly oriented, highly crystalline carbon materials have a large spread in the planar direction, the cross-sectional area of ​​the material when observed from the cross-section can be changed by changing the pressing load. For this reason, for a highly oriented, highly crystalline second conductive agent, a large pressing load tends to reduce the area S2 occupied in the cross-section.

[0058] Thus, electrodes can be fabricated.

[0059] The occupied area and centroidal distance in the mapping image of the active material-containing layer can be adjusted to the range described above by adjusting parameters such as the selection and mixing ratio of the types of active material, conductive agent, and binder, the particle size of the active material and conductive agent particles, the stirring (dispersion) conditions of the mixture, and the pressing conditions. For example, for the active material, the first conductive agent, and the second conductive agent, increasing the mixing ratio or increasing the particle size tends to increase the respective occupied areas Sa, S1, and S2. Also, for each component, increasing the mixing ratio or increasing the particle size tends to shorten the respective centroidal distances Ra, R1, and R2. However, the electrode according to the first embodiment cannot be manufactured without the idea of ​​adjusting the dispersion state of each component of the active material-containing layer, which contains the first and second conductive agents along with the active material, so that the above-mentioned ratio of occupied area 0.1 < S1 / Sa < 1.0 and 0.8 < S2 / Sa < 10, as well as the above-mentioned relationship of distance between centroids 1.0 < R1 / Ra < 1.5, 0.5 < R2 / Ra < 1.0, and R1 > R2 > R1-2, is satisfied in the constituent material mapping image obtained by Raman spectroscopy.

[0060] For example, in the mixing process, changing the order in which the active material and the first and second conductive agents are added to the solvent alters the dispersion state due to differences in solubility parameters between the dispersion solvent and the binder. Furthermore, as mentioned above, the stirring intensity in the stirring process affects the distance between the centers of gravity and the occupied area of ​​the active material and conductive agents in the resulting electrode. In addition, with respect to the pressing load, electrodes with extremely high or low density produced by excessive or insufficient pressing not only deviate from the preferred range described above, but the ratio of each occupied area and the ratio of the distance between the centers of gravity also tend to deviate from the aforementioned range. Thus, the above relationships cannot be satisfied unintentionally.

[0061] Specific examples of electrode fabrication will be explained in the examples below.

[0062] A preferred active material containing the aforementioned lithium nickel cobalt manganese composite oxide and having an average primary particle diameter of 2 μm to 7 μm can be obtained, for example, as follows: A precursor using nickel, cobalt, and manganese sources is calcined. Here, increasing the calcination temperature, increasing the calcination time, or increasing the amount of lithium-source precursors such as lithium carbonate promotes particle growth rather than nucleation. Therefore, by promoting particle growth by any method, a lithium nickel cobalt manganese composite oxide can be synthesized with an optimized chemical composition such that the primary particle diameter is 2 μm or more and the nickel content is above a predetermined level.

[0063] This section describes various measurement methods for electrodes. Specifically, it explains methods for measuring the composition of the active material, methods for measuring the particle size distribution and average particle size of the active material in the active material-containing layer using laser diffraction scattering, methods for measuring the specific surface area of ​​the active material using nitrogen adsorption / desorption, methods for measuring the density of the active material-containing layer, methods for obtaining a Raman chart using Raman spectroscopy, methods for image analysis of the Raman chart, and methods for measuring the average particle size of the conductive agent using electron microscopy. As for Raman chart image analysis methods, it explains methods for obtaining constituent material mapping by image analysis and methods for measuring occupied area and centroid distance by image analysis.

[0064] When analyzing electrodes incorporated into a battery, remove the electrodes using the following procedure.

[0065] First, prepare the battery to be measured. The battery to be measured must have a discharge capacity of 80% or more of its rated capacity. In other words, batteries that have deteriorated excessively will not be measured.

[0066] Next, discharge the prepared battery until the open-circuit voltage is between 2.0V and 2.2V. Then, transfer the discharged battery to a glove box filled with argon, where the dew point of the internal atmosphere is -70°C. Cut open the battery inside the glove box. Remove the electrode group from the opened battery. If the removed electrode group includes positive and negative leads, carefully cut the positive and negative leads, taking care not to short-circuit them.

[0067] Next, the electrode assembly is disassembled into a positive electrode, a negative electrode, and a separator. For example, the positive electrode is selected as the electrode to be measured. The resulting electrode is then washed using ethyl methyl carbonate as the solvent. In this washing process, the disassembled components are completely immersed in the ethyl methyl carbonate solvent and left in that state for 60 minutes.

[0068] After cleaning, the electrodes are subjected to vacuum drying. Vacuum drying is performed in a 25°C environment by reducing the pressure from atmospheric pressure to -97 kPa or higher and maintaining that state for 10 minutes. The electrodes thus removed after disassembly, cleaning, and vacuum drying are to be used for the following measurements.

[0069] <Measurement of Active Material Composition> The composition of the electrode active material can be determined by measuring the surface of the electrode using X-ray fluorescence (XRF).

[0070] <Measurement of particle size distribution by laser diffraction and scattering method> The particle size distribution of an electrode can be measured by the laser diffraction and scattering method described below.

[0071] After preparing the electrodes to be measured, the active material-containing layer is separated from the current collector using, for example, a spatula, to obtain a powdered electrode mixture sample containing the active material. Next, the powdered sample is added to a measurement cell filled with N-methylpyrrolidone (NMP) until the concentration reaches a measurable level. Note that the capacity of the measurement cell and the measurable concentration will vary depending on the particle size distribution analyzer.

[0072] A measurement cell containing NMP and an electrode mixture sample dissolved in it is irradiated with 40W ultrasonic waves for 5 minutes. Such ultrasonic irradiation can dissolve the aggregation between conductive agent particles and active material particles.

[0073] A measurement cell treated with ultrasound is inserted into a particle size distribution analyzer using laser diffraction / scattering to measure the particle size distribution. An example of such a particle size distribution analyzer is the Microtrac3100.

[0074] Thus, the particle size distribution of the active material-containing layer can be obtained.

[0075] Furthermore, by performing the above measurements using a sample of active material particles, the particle size distribution of the active material particles can be obtained. From the particle size distribution of the active material particles, the average primary particle size of the active material can be determined.

[0076] After dispersing and stirring the electrode mixture sample in NMP, the solvent is filtered and the resulting solid is calcined to remove the binder and conductive agent, thereby isolating the active material particles. The particle size at which the cumulative frequency from the smallest particle size side in the particle size distribution measured using the obtained active material particle sample reaches 50% (D 50 This corresponds to the average primary particle size of the active material.

[0077] <Measurement of Specific Surface Area of ​​Active Material by Nitrogen Adsorption-Desorption Method> The specific surface area of ​​the active material measured by nitrogen (N2) adsorption-desorption method corresponds to the BET specific surface area of ​​the active material particles. BET specific surface area is the specific surface area determined by the BET method and is calculated by the N2 gas adsorption-desorption method. The analysis is carried out, for example, by the following method.

[0078] As described above, the active material-containing layer is separated from the current collector to obtain a powdered electrode composite sample containing the active material from the electrode. The obtained powdered sample is heated briefly in air (about 1 hour at 500°C) to burn off unwanted parts such as binder components and carbon. The weight of the remaining active material sample is measured. Next, the sample is filled into the cell of the measuring device. The sample placed in the measuring cell for nitrogen adsorption / desorption measurement is dried at a temperature of 120°C or higher under N2 gas flow. After that, the specific surface area is measured using the BET single-point method or the BET multi-point method. An example of a measuring device that performs N2 gas adsorption / desorption measurement is the Quantasorb manufactured by QUANTACHROME.

[0079] <Measurement of the density of the active material-containing layer> The density of the active material-containing layer can be measured using the following procedure.

[0080] First, the thickness of the prepared electrode is measured using a thickness measuring device. Next, the electrode is punched out into 1 cm x 1 cm pieces using a cutting machine to obtain a 1 cm x 1 cm sample. The weight of this sample is then measured.

[0081] Next, the active material-containing layer is removed from the sample. For example, the active material-containing layer can be removed by immersing the sample in N-methylpyrrolidone. Any solvent can be used to remove the active material-containing layer without corroding the current collector. The thickness and weight of the remaining current collector sample are then measured.

[0082] Next, the thickness of the active material-containing layer is calculated by subtracting the thickness of the current collector from the thickness of the electrode. Also, the weight of the active material-containing layer in a 1cm x 1cm size is calculated by subtracting the weight of the current collector sample from the weight of the 1cm x 1cm sample. Then, the density of the active material-containing layer (unit: g / cm³) is calculated by dividing the weight of the 1cm x 1cm active material-containing layer by the thickness of the active material-containing layer. 3 It is possible to calculate this.

[0083] <Measurement by Raman Spectroscopy> Next, we will explain the procedure for obtaining a constituent material mapping image of the active material-containing layer using Raman spectroscopy.

[0084] (Acquisition of Raman Chart) Sampling is performed on the electrode extracted using the method described above. Sampling is performed at any 10 points on the electrode to be measured. At this time, it is preferable to sample from 10 different locations rather than dividing a sample taken from a specific location within the electrode into 10 points. Furthermore, it is preferable to perform sampling on an electrode portion having a thickness such that the entire measurement field of view in the Raman spectroscopy measurement described later becomes a cross-sectional image of the electrode, particularly a cross-sectional image of the active material-containing layer.

[0085] For each electrode sample obtained by sampling using the method described above, the sample is fixed so that the cross-section of the active material-containing layer faces the direction from which the Raman laser is emitted. As a specific example of the fixing method, the sample can be prepared as follows: The sample is placed in a container so that the cross-section faces directly upwards, and the sample is fixed to the bottom of the container with a metal fitting. A curable resin is poured into the container and left to stand until the resin has hardened, so that the electrode cross-section can be fixed in a desired direction. After that, a new cross-section can be exposed by mechanically cutting along a plane parallel to the bottom surface, and a measurement sample can be prepared so that the cross-section can be observed. At this time, graphitization may occur depending on the carbon material used, so the energy used for cutting must be reduced to a level that does not affect the measurement.

[0086] The sample is fixed to the sample stage and loaded into the Raman spectrometer. Surface Raman spectroscopy is performed on the loaded sample in a 50 μm × 50 μm field of view to obtain a Raman chart. When obtaining the Raman chart, measurements are taken at 10,000 points, which are obtained by dividing the 50 μm × 50 μm field of view into 100 vertical and 100 horizontal points. An example of a measurement device for Raman spectroscopy is the WITec α300 confocal microspectroscopy analyzer. The measurement conditions are as follows, for example. However, if the sample is significantly affected by heat, it is necessary to shorten the exposure time and increase the number of integrations, or to lower the laser power. Conversely, if the acquired spectrum becomes unclear, it is necessary to lengthen the exposure time or increase the number of integrations. Exposure time: 10 s or 20 s Number of integrations: 1 Lens magnification: 50x Measurement range: 50 μm × 50 μm Laser power: 5%.

[0087] (Creation of constituent material mapping image) Next, using a Raman chart with 10,000 points, spectra are extracted from 10 arbitrary points in each high-concentration region to obtain an average spectrum. Multivariate analysis is performed on this average spectrum to separate significant spectral components. For each separated component spectrum, the crystallinity of the active material, the first conductive agent, and the second conductive agent is determined from the peak position, intensity, and intensity ratio. Using the obtained spectra of each constituent material and the Raman chart with 10,000 points, mapping of the abundance of each constituent material is performed. Note that the first conductive agent and the second conductive agent have D and G bands at close positions in the Raman chart, but by calculating the degree of overlap using the individual spectra of each agent through fitting, the presence of the first conductive agent and the second conductive agent at that point can be distinguished. The abundance of each constituent material can be represented, for example, by different shades of color for each constituent material.

[0088] Examples of constituent material mapping images created from Raman charts are shown in the conceptual diagrams in Figures 3 and 4. Figure 3 shows a mapping image of the active material-containing layer of an example electrode according to the embodiment, and Figure 4 shows a mapping image of the active material-containing layer of an example of a conventional electrode. Each figure corresponds to a schematic diagram of a constituent material mapping image in which the active material 310 is shown as a white area, the first conductive agent 311 as a green area, the second conductive agent 312 as a red area, and the remainder as a yellow area. The blank horizontal bands seen at the top and bottom of each figure correspond to the space above and below the cross-section of the active material-containing layer in the thickness direction.

[0089] In the mapping image of the electrode example according to the embodiment shown in Figure 3, the active material 310, the first conductive agent 311, and the second conductive agent 312 are evenly distributed within the field of view. In particular, the presence of the second conductive agent 312 throughout the entire area and adjacent to the active material 310 forms a conductive network. Furthermore, the presence of the first conductive agent 311 everywhere improves the conductivity throughout the active material-containing layer. Therefore, in the sample shown in Figure 3, charging and discharging occur uniformly within the electrode.

[0090] In contrast, in the mapping image of a conventional electrode example shown in Figure 4, the first conductive agent 311 occupies most of the field of view, and although the second conductive agent 312 is adjacent to the active material 310 in some areas, the second conductive agent 312 is distributed locally and does not form a conductive network. Due to the uneven distribution of the conductive agent, the distribution of the charge-discharge reaction is also uneven, and localized degradation progresses in the electrode.

[0091] (Measurement of occupied area and distance between centroids) The occupied areas Sa, S1, S2 of the active material, the first conductive agent, and the second conductive agent in the above mapping image, as well as their ratios S1 / Sa and S2 / Sa, and the distances Ra, R1, R2 between the centroids of the active material, the first conductive agent, and the second conductive agent, as well as their ratios R1 / Ra and R2 / Ra, can be obtained by numerical analysis of the mapping data of the constituent materials obtained as described above. The distance between the centroids of the first conductive agent and the second conductive agent R1-2 cannot be directly measured from the mapping data, but it can be obtained by calculation using the distance between the centroids of all conductive agents combined (all first and second conductive agents), the distance between the centroids of the first conductive agents R1, and the distance between the centroids of the second conductive agents R2. Note that the centroid distances Ra, R1, R2, and R1-2 obtained by measurement represent the arithmetic mean of each centroid distance in the mapping image.

[0092] In this case, the constituent material mapping image used for image analysis is such that the area occupied by the active material, the first conductive agent, or the second conductive agent is at least 1 μm. ２ The selection is made so as described above. The occupied area of ​​at least one of the constituent materials, either the active material, the first conductive agent, or the second conductive agent, is 1 μm. ２ The following conditions are unsuitable for measuring the occupied area and the distance between the centers of gravity: More preferably, the occupied area of ​​the positive electrode active material is 10 μm². ２ It would be good to have more than that.

[0093] The method for determining the centroidal distance R1-2 between the first and second conductive materials will be explained with reference to the drawings. Figures 5 to 8 conceptually represent the method for determining the centroidal distance between the first and second conductive materials in the mapping image. In these figures, only the first and second conductive materials are conceptually shown to facilitate understanding, and the active material is omitted. Numerical analysis of the mapping data makes it possible to directly measure the centroidal distances R211, R212, and R213 between the first conductive materials 210 as shown in Figure 5, and the centroidal distances R221, R222, and R223 between the second conductive materials 220 as shown in Figure 6. However, the centroidal distances R231 to R239 between the first conductive material 210 and the second conductive material 220, as shown in Figure 7, cannot be directly measured by numerical analysis of the mapping data. However, if we consider the first conductive agent 210 and the second conductive agent 220 to belong to the same group without distinction, it is possible to directly measure the distance between the centroids of all first conductive agents 210s, all second conductive agents 220s, and between the first conductive agent 210 and the second conductive agent 220, as shown in Figure 8. Therefore, by measuring the distance between the centroids of all conductive agents as shown in Figure 8 and subtracting the distances between the centroids of only the first conductive agent 210 and only the second conductive agent 220 (R211, R12, R13, R221, R222, R223) shown in Figures 5 and 6 respectively, the distances between the centroids of the first conductive agent 210 and the second conductive agent 220 (R231 to R239) shown in Figure 7 can be calculated.

[0094] An example of measurement results for the distance between centroids is shown. First, Figures 9 and 10 show graphs representing the distribution of the centroid distances obtained for the mapping images shown in Figures 3 and 4, showing the frequency for each centroid distance. Figure 9 is a graph of the centroid distance obtained for the example of a conventional electrode shown in Figure 4. Figure 10 is a graph of the centroid distance obtained for the example of an electrode of the embodiment shown in Figure 3. In both graphs, the dotted line Da represents the frequency distribution (histogram) of the centroid distances of the active materials, and the integral area under this curve is equal to the average value Ra of the centroid distances between the active materials in each mapping image. The integral area under the dashed line D1 corresponding to the first conductive agent is equal to the average value R1 of the centroid distances between the first conductive agents in the mapping image. The integral area under the solid line D2 corresponding to the second conductive agent is equal to the average value R2 of the centroid distances between the second conductive agents in the mapping image. The integrated area under the dashed line D12, which represents the frequency distribution of the centroidal distance between the first and second conductive materials, is equal to the average value R12 of the centroidal distance between the first and second conductive materials in the mapping image.

[0095] The data for the distance between centroids corresponding to the distribution shown in Figure 10 are summarized in Table 1 below.

[0096]

[0097] (Verification of Measurement and Analysis Results) Through the above measurements and analyses, Raman charts, average spectra, multivariate analysis results, constituent material mapping images, and the occupied area and centroid distance of each constituent material can be obtained for 10 measurement samples. If the values ​​for 3 or more of the 10 measurement samples are within the above range and satisfy the above relationship, then the electrode in question is effective in improving the battery life performance as described above. More preferably, there should be 6 or more samples, in which case a high effect can be obtained.

[0098] Furthermore, if the measurement or analysis results do not allow for the differentiation of the active material, the first conductive agent, and the second conductive agent, or if the measurement sample does not contain any of the active material, the first conductive agent, or the second conductive agent, it will be determined that the measurement and analysis were not effective and will not be included in the 10 samples.

[0099] <Measurement of Average Particle Size of Conductive Agent>The average particle size of each conductive agent can be determined, for example, by observing the cross-section observed during the above-described Raman spectroscopic measurement with a transmission electron microscope (TEM). Alternatively, the active material-containing layer may be peeled off from the taken-out electrode, sampled by dispersing it in a solvent such as ethanol, and then observed by TEM. Also, since the observed shape and the value of the interplanar spacing d of the graphene plane ((002) plane) of the conductive agent are different, different types of conductive agents can be distinguished by electron microscope observation. For example, the higher the graphitic property, the closer the value of the interplanar spacing d is to 0.335 nm. By comparing the constituent material mapping image obtained by Raman spectroscopic measurement with the TEM image, it is also possible to confirm the correspondence to each of the first conductive agent and the second conductive agent in the TEM image. 002 Since the values of 002 are different, different types of conductive agents can be distinguished by electron microscope observation. For example, the higher the graphitic property, the closer the value of the interplanar spacing d 002 is to a value close to 0.335 nm. By comparing the constituent material mapping image obtained by Raman spectroscopic measurement with the TEM image, it is also possible to confirm the correspondence to each of the first conductive agent and the second conductive agent in the TEM image.

[0100] For each type of conductive agent, as the particle sizes of 30 randomly selected particles, for example, the equivalent circle diameter is calculated by image analysis using the image analysis software "Particle Analysis" ver. 3.5 manufactured by Nippon Steel & Sumitomo Metal Corporation, and the average value of the obtained equivalent circle diameters is taken as the average particle size. The average particle size is typically the diameter of the sphere assuming that the particle has the same volume or the same cross-sectional area as the sphere. However, in image analysis, care should be taken so that the equivalent circle diameter of aggregates such as aggregates and agglomerates is not calculated.

[0101] The electrode according to the first embodiment includes an active material-containing layer containing at least an active material, a first conductive agent, and a second conductive agent. The first conductive agent is a material in which the ratio I D of the integrated intensity I of the D band to the integrated intensity I G of the G band obtained by Raman spectroscopy is in the range of 0.5 < I D / I G < 2. For the second conductive agent, the ratio I D / I G is such that 0 < I D / I G < 0.5 D / I GThe material is within the range of <0.5. In a Raman spectroscopy mapping image of the active material-containing layer, the occupied area Sa and centroidal distance Ra of the active material, the occupied area S1 and centroidal distance R1 of the first conductive agent, the occupied area S2 and centroidal distance R2 of the second conductive agent, and the centroidal distance R1-2 between the first and second conductive agents satisfy the relationships 0.1 < S1 / Sa < 1.0, 0.8 < S2 / Sa < 10, 1.0 < R1 / Ra < 1.5, 0.5 < R2 / Ra < 1.0, and R1 > R2 > R1-2. This electrode can realize a battery with low electrical resistance, excellent capacity retention rate, and suppressed resistance increase, resulting in superior lifespan performance.

[0102] (Second Embodiment) According to the second embodiment, a battery is provided. The battery comprises the electrode and electrolyte according to the first embodiment. As described above, the electrode according to the first embodiment can realize a battery with excellent lifespan performance. Therefore, the battery according to the second embodiment can have excellent lifespan performance.

[0103] The battery may comprise a positive electrode and a negative electrode. The battery may include the electrode according to the first embodiment as the positive electrode.

[0104] The battery may further include a separator positioned between the positive and negative electrodes. The positive electrode, negative electrode, and separator can constitute an electrode group. The electrolyte can be held within the electrode group.

[0105] Furthermore, such a battery may further comprise an outer casing that houses the electrode group and the electrolyte.

[0106] 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.

[0107] The battery in question may be, for example, a lithium-ion secondary battery. The battery may also include, for example, a non-aqueous electrolyte battery containing a non-aqueous electrolyte as the electrolyte.

[0108] The positive electrode, negative electrode, electrolyte, separator, outer casing, positive electrode terminal, and negative electrode terminal will be described in detail below.

[0109] (1) The positive electrode comprises a positive electrode current collector and a positive electrode active material-containing layer (positive electrode composite layer) supported on one side or both sides of the positive electrode current collector, which includes a positive electrode active material, a conductive agent, and a binder.

[0110] The positive electrode may be the electrode according to the first embodiment. In the embodiment as a positive electrode, the positive electrode current collector, positive electrode active material, and positive electrode active material containing layer correspond to the current collector, active material, and active material containing layer of the electrode according to the first embodiment, respectively. The electrode according to the first embodiment has been described in detail above, so the description of the positive electrode here will be omitted.

[0111] (2) The negative electrode comprises a negative electrode current collector and a negative electrode active material-containing layer (negative electrode composite layer) supported on one side or both sides of the negative electrode current collector. The negative electrode active material-containing layer contains negative electrode active material. In addition to the negative electrode active material, the negative electrode active material-containing layer may further contain a conductive agent and a binder. The conductive agent may be added to enhance current collection performance and to suppress contact resistance between the negative electrode active material and the negative electrode current collector. The binder may be added to bind the dispersed negative electrode active material together and to bind the negative electrode active material to the negative electrode current collector.

[0112] Materials The following describes materials that can be used in the negative electrode active material-containing layer and the negative electrode current collector.

[0113] <Negative Electrode Active Material Containing Layer> The blending ratio of the negative electrode active material, conductive agent, and binder in the negative electrode active material containing layer is preferably within the range of 70% to 96% by mass for the negative electrode active material, 2% to 28% by mass for the conductive agent, and 2% to 28% by mass for the binder. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the negative electrode active material containing layer is improved, and excellent high-current performance and low-temperature performance can be expected. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient bonding between the negative electrode active material containing layer and the current collector is achieved, and excellent cycle performance can be expected.

[0114] On the other hand, from the viewpoint of increasing capacity, it is preferable that the conductive agent and the binder each be 28% by mass or less.

[0115] <Negative electrode active material> The negative electrode preferably contains a negative electrode active material capable of inserting and extracting lithium ions at a potential of 0.4 V (vs. Li / Li + ). In the battery according to the second embodiment including such a negative electrode, precipitation of lithium due to charge and discharge can be suppressed. Therefore, such a battery is excellent in rapid charge and discharge performance.

[0116] As the negative electrode active material capable of inserting and extracting lithium ions at a potential of 0.4 V (vs. Li / Li + ), for example, lithium titanate having a spinel-type crystal structure represented by Li 4+x Ti5O 12 (x changes in the range of -1 ≤ x ≤ 3 due to charge and discharge reaction), lithium having a lamusdelite-type crystal structure 2+x Ti3O7 (x changes in the range of -1 ≤ x ≤ 3 due to charge and discharge reaction), metal composite oxides containing at least one selected from the group consisting of Ti and at least one of P, V, Sn, Cu, Ni, and Fe, etc. can be mentioned. Examples of the metal composite oxide containing at least one selected from the group consisting of Ti and at least one of P, V, Sn, Cu, Ni, and Fe include, for example, TiO2 - P2O5, TiO2 - V2O5, TiO2 - P2O5 - SnO2, TiO2 - P2O5 - MeO (Me is at least one element selected from the group consisting of Cu, Ni, and Fe). These metal composite oxides change into lithium titanium composite oxides when lithium is inserted by charging. Among the lithium titanium composite oxides, spinel-type lithium titanate is excellent in cycle performance and is preferable.

[0117] The negative electrode may contain other active materials, and examples thereof include carbonaceous substances and metal compounds.

[0118] Examples of the carbonaceous substances include natural graphite, artificial graphite, coke, vapor-grown carbon fiber, mesophase pitch-based carbon fiber, spherical carbon, and resin-fired carbon. More preferable carbonaceous substances include vapor-grown carbon fiber, mesophase pitch-based carbon fiber, and spherical carbon. The carbonaceous substances preferably have an interplanar spacing d002 of the (002) plane by X-ray diffraction of 0.34 nm or less.

[0119] As metal compounds, metal sulfides and metal nitrides can be used. Examples of metal sulfides include titanium sulfide such as TiS2, molybdenum sulfide such as MoS2, and FeS, FeS2, Li x Iron sulfides such as FeS2 (0 ≤ x ≤ 2) can be used. As for metal nitrides, for example, lithium cobalt nitride (e.g., Li x Co y N (0 < x < 4, 0 < y < 0.5) can be used.

[0120] In addition to the lithium titanium composite oxides mentioned above, the negative electrode active material may also contain other lithium titanium composite oxides such as monoclinic niobium titanium oxide and orthorhombic titanium-containing composite oxides.

[0121] As an example of the monoclinic type niobium titanium oxide mentioned above, Li a Ti 1-x M1 x Nb 2-y M2 y O 7+δ Examples of compounds represented by are: Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0 ≤ a ≤ 5, 0 ≤ x < 1, 0 ≤ y < 2, -0.3 ≤ δ ≤ 0.3. A specific example of monoclinic titanium niobium oxide is Li a One example is Nb2TiO7 (0 ≤ a ≤ 5).

[0122] Another example of monoclinic titanium niobium oxide is Li a Ti 1-x M3 x+y Nb 2-y O 7-δ A compound represented by the formula is shown below. Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the empirical formula are 0 ≤ a ≤ 5, 0 ≤ x < 1, 0 ≤ y < 2, and -0.3 ≤ δ ≤ 0.3.

[0123] As an example of an orthorhombic titanium-containing composite oxide, Li 2+a M4 2-x Ti6-y M5 z O 14+σ A compound represented by the formula is shown below. Here, M4 is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. M5 is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦a≦6, 0≦x<2, 0≦y<6, 0≦z<6, -0.5≦σ≦0.5. A specific example of an orthorhombic titanium-containing composite oxide is Li 2+a Na2Ti6O 14 (0 ≤ a ≤ 6) is one example.

[0124] Of the above active materials, one may be included in the negative electrode as the negative electrode active material, or two or more may be included in the negative electrode as the negative electrode active material.

[0125] <Conductive Agents> 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.

[0126] <Binding Agents> Examples of binding agents include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, and styrene-butadiene rubber (SBR). Other binding agents that can be used include carboxymethyl cellulose (CMC), polyimide, and polyamide. These binding agents may be used individually or in combination.

[0127] <Negative Electrode Current Collector> As the negative electrode current collector, a material that is electrochemically stable at the potential in which the lithium ion insertion-desorption reaction of the negative electrode active material occurs can be used. The negative electrode current collector is preferably a metal foil consisting of at least one selected from copper, nickel, stainless steel, and aluminum, or an aluminum alloy foil containing at least one selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si.

[0128] The shape of the negative electrode current collector can be varied depending on the application of the battery using the negative electrode.

[0129] The negative electrode current collector may include portions on its surface that do not support the negative electrode active material-containing layer. These portions can function as negative electrode current collecting tabs. Alternatively, the negative electrode may include current collecting tabs separate from the negative electrode current collector.

[0130] <Manufacturing Method> The negative electrode can be manufactured, for example, by the following method.

[0131] First, a slurry for producing a negative electrode is prepared by suspending the negative electrode active material, binder, and optionally a conductive agent in a suitable solvent. As the solvent, a commonly used solvent such as N-methylpyrrolidone is used. The obtained slurry is applied onto a negative electrode current collector. By drying the applied slurry and applying a press, a negative electrode can be obtained that includes a negative electrode current collector and a negative electrode active material-containing layer formed on the negative electrode current collector. Alternatively, the negative electrode active material, binder, and optionally a conductive agent may be formed into pellets and used as the negative electrode active material-containing layer.

[0132] (3) Separator A material having electrical insulating properties is used as the separator. It is not particularly limited as long as it has insulating properties, but for example, porous films or nonwoven fabrics made of polymers such as polyolefin, cellulose, polyethylene terephthalate, and vinylon can be used as separators. The separator material may be one type or two or more types may be used in combination.

[0133] (4) Examples of electrolytes include liquid nonaqueous electrolytes prepared by dissolving an electrolyte salt (solute) in a nonaqueous solvent, and gel-like nonaqueous electrolytes obtained by compounding a liquid nonaqueous electrolyte with a polymer material.

[0134] Examples of electrolyte salts include lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium hexalithium antimonate (LiSbF6), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (LiCF3SO3; commonly known as LiTFS), and lithium bistrifluoromethanesulfonylamide {Li(CF3SO2)2N}. Examples of lithium salts include {LiTFSI}, bispentafluoroethanesulfonylamide lithium {Li(C2F5SO2)2N; commonly known as LiBETI}, bisoxalatoborate lithium {LiB(C2O4)2; commonly known as LiBOB}, and difluoro(trifluoro-2-oxide-2-trifluoro-methylpropionato(2-)-0,0)borate lithium {LiBF2OCOC(CF3)2; commonly known as LiBF2(HHIB)}. These electrolyte salts may be used individually or in combination of two or more. Among these, LiPF6 and LiBF4 are particularly preferred.

[0135] It is preferable to dissolve the electrolyte salt in a non-aqueous solvent at a concentration of 1 mol / L to 3 mol / L. Within this electrolyte salt concentration range, it is possible to further improve performance when high load currents are applied while suppressing the effect of viscosity increase due to increasing electrolyte salt concentration.

[0136] Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC); linear carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC); cyclic ethers such as tetrahydrofuran (THF) and 2-methyl tetrahydrofuran (2-MeTHF); and 1,2-dimethoxyethane. Examples of organic solvents include linear ethers such as ethane (DME); cyclic esters such as γ-butyrolactone (BL); linear esters such as methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate; and organic solvents such as 1,3-dioxolane; acetonitrile (AN); and sulfolane (SL). These organic solvents can be used individually or as a mixture of two or more. It is preferable to use a non-aqueous solvent containing cyclic carbonates and / or linear carbonates.

[0137] Examples of polymer materials used in gel-like non-aqueous electrolytes include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0138] (5) Exterior components The exterior components may be formed from laminate film or made of a metal container. Alternatively, resin containers made of polyolefin resin, polyvinyl chloride resin, polystyrene resin, acrylic resin, phenolic resin, polyphenylene resin, fluororesin, etc. may be used as exterior components. When a metal container is used, the lid may be integrated with the container or be a separate component. The wall thickness of the metal container is preferably 3 mm or less, and more preferably 0.5 mm or less.

[0139] Examples of exterior component shapes include flat (thin), rectangular, cylindrical, coin-shaped, button-shaped, sheet-shaped, and laminated types. These exterior components can be used for small batteries mounted in portable electronic devices, as well as for large batteries mounted in two-wheeled or four-wheeled vehicles.

[0140] The thickness of the laminate film exterior component is preferably 0.5 mm or less. Examples of laminate films include multilayer films containing a resin layer and a metal layer placed between the resin layers. For weight reduction, the metal layer is preferably aluminum foil or aluminum alloy foil. For the resin layer, a film made of polymer materials such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET) can be used. The laminate film can be sealed by heat fusion and molded into the shape of the exterior component.

[0141] Metal containers are made from aluminum or aluminum alloys. Aluminum alloys containing elements such as magnesium, zinc, and silicon are preferred. When aluminum or aluminum alloys contain transition metals such as iron, copper, nickel, and chromium, their content is preferably 100 ppm or less.

[0142] An example of such a battery will be described with reference to Figures 11 and 12. The flat-type battery shown in Figure 11 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 12, 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.

[0143] 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.

[0144] As shown in Figure 11, 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.

[0145] The battery in question is not limited to the configurations shown in Figures 11 and 12, but can also have a configuration like the one shown in Figure 13.

[0146] In the rectangular battery shown in Figure 13, 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 the wound electrode group 1 described with reference to Figures 11 and 12, for example.

[0147] The negative electrode current collector 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 current collector 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.

[0148] The negative electrode current collector 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 current collector 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.

[0149] The positive electrode current collector 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 current collector 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.

[0150] Although the illustrated battery uses a wound-type electrode group in which a separator is wound together with the positive and negative electrodes, a stack-type electrode group in which the positive and negative electrodes are alternately stacked with a separator in between may also be used. Alternatively, the electrode group may have other structures.

[0151] The battery according to the second embodiment includes the electrodes according to the first embodiment. Therefore, this battery has excellent capacity retention and suppressed resistance increase, resulting in excellent lifespan performance.

[0152] (Third Embodiment) According to the third embodiment, a battery pack is provided. This battery pack comprises the battery according to the second embodiment.

[0153] 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.

[0154] Next, an example of a battery pack according to the third embodiment will be described with reference to the drawings.

[0155] Figure 14 is an exploded perspective view of an example battery pack according to the second embodiment. Figure 15 is a block diagram showing the electrical circuit of the battery pack in Figure 14.

[0156] The battery pack 20 shown in Figures 14 and 15 comprises a plurality of single cells 21. Each single cell 21 may be a flat-type battery, an example of the second embodiment described with reference to Figure 13.

[0157] 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 15.

[0158] 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 15, 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.

[0159] 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.

[0160] 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 14 and 15, 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] Figures 14 and 15 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.

[0165] 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.

[0166] The battery pack according to the third embodiment comprises the battery according to the second embodiment. Therefore, this battery pack has excellent capacity retention and suppressed resistance increase, resulting in excellent lifespan performance.

[0167] The present invention will be further explained with the following examples, but the present invention is not limited to the embodiments listed below unless it exceeds the spirit of the invention.

[0168] (Example 1) <Fabrication of the positive electrode> Lithium nickel cobalt manganese composite oxide LiNi with an average primary particle diameter of 3.7 μm was used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2, acetylene black as the first conductive agent, graphite as the second conductive agent, and polyvinylidene fluoride (PVdF) as a binder were prepared. Of the prepared materials, the first and second conductive agents were each stirred in powder form using a mixer capable of rotation and revolution, then added together and stirred again. The remaining materials were added to N-methylpyrrolidone (NMP), and then the stirred conductive agents were added. By mixing the prepared materials with the NMP solution in this way, a slurry for cathode preparation was obtained in which the materials were suspended in NMP. Furthermore, the slurry for cathode preparation was dispersed. Zirconia beads with a diameter of 2 mm were added to the slurry and the material was uniformly dispersed by stirring with a mixer capable of rotation and revolution.

[0169] The mass ratios of the positive electrode active material, the first conductive agent, the second conductive agent, and the binder introduced into the NMP were 100 parts by mass, 5 parts by mass, 5 parts by mass, and 5 parts by mass, respectively.

[0170] The obtained slurry was applied to both sides of a strip-shaped aluminum foil (current collector) with a thickness of 12 μm and dried. A pressing process was then carried out to produce a current collector and a positive electrode having active material-containing layers on both sides.

[0171] <Fabrication of the negative electrode> Lithium titanate (Li4Ti5O) of the spinel type is used as the negative electrode active material. 12 Graphite was prepared as a conductive agent and PVdF as a binder. The prepared materials were suspended in N-methylpyrrolidone to obtain a slurry for negative electrode fabrication. The mass ratios of the negative electrode active material, conductive agent, and binder added to the N-methylpyrrolidone were 95% by mass, 2.5% by mass, and 2.5% by mass, respectively. The prepared slurry for negative electrode fabrication was applied to both sides of a strip-shaped aluminum foil (current collector) with a thickness of 12 μm and dried, and then the negative electrode was fabricated through a pressing process.

[0172] <Fabrication of Electrode Group> The positive and negative electrodes fabricated as described above were stacked with a separator in between. A cellulose separator with a thickness of 14 μm and a width of 85 mm was used as the separator. The resulting laminate was wound around an axis extending in the direction of the short side of the positive and negative electrode current collectors. The wound positive electrode, negative electrode, and separator were subjected to a heat press at 80°C and fixed with insulating tape. Thus, a wound electrode group comprising a positive electrode, a negative electrode, and a separator positioned between the positive and negative electrodes was obtained.

[0173] <Preparation of Non-Aqueous Electrolyte> A non-aqueous solvent was prepared by mixing propylene carbonate (PC) and diethyl carbonate (DEC) in a 1:1 volume ratio. Lithium hexafluoride phosphate (LiPF6) was dissolved in the obtained non-aqueous solvent at a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[0174] <Battery Assembly> The flattened electrode group obtained as described above was inserted into a metal can made of 0.5 mm thick aluminum plate. The opening of the metal can was sealed with a sealing plate, and the electrode group was housed inside the metal can, which served as the outer casing. The non-aqueous electrolyte prepared as described above was injected into the container through the electrolyte inlet provided in the sealing plate. Next, a sealing lid was welded to the periphery of the electrolyte inlet to fabricate a flattened non-aqueous electrolyte battery.

[0175] (Examples 2-3, Comparative Examples 1-6) In Examples 2-3 and Comparative Examples 1-6, batteries were manufactured in the same manner as in Example 1, except that the average particle sizes of the positive electrode active material, the first conductive agent, and the second conductive agent were changed from Example 1 as shown in Table 2, and the design of the positive electrode active material-containing layer was changed to those shown in Tables 2 and 3 by adjusting the mass portion of each conductive agent, the dispersion conditions of the slurry for positive electrode manufacturing, and the press load of the active material-containing layer. For the design of the positive electrode active material-containing layer, as shown in Tables 2 and 3, the specific surface area and electrode density obtained by nitrogen adsorption-desorption (BET) method, as well as the occupied areas S1 and S2 of the first and second conductive agents, the occupied area Sa of the positive electrode active material, the distances between the centroids R1 and R2 of the first and second conductive agents, the distances between the centroids R1-2 between each conductive agent, and the distance Ra between the centroids of the positive electrode active material were adjusted.

[0176] Table 2 below summarizes the design of the positive electrode active material-containing layer in each example and comparative example. The design of the active material-containing layer includes the average primary particle diameter of the positive electrode active material particles, the specific surface area measured by the nitrogen adsorption / desorption method (BET method) described above, the average particle size of the first conductive agent and its mass ratio to the positive electrode active material, the average particle size of the second conductive agent and its mass ratio to the positive electrode active material, and the density measured by the method described above.

[0177] Table 3 below summarizes the analysis results of the constituent material mapping images obtained by Raman spectroscopy for the positive electrode active material-containing layer in each example and comparative example. The image analysis results show the occupied areas S1 and S2 of the first and second conductive agents, the occupied area Sa of the positive electrode active material, the ratio of occupied areas S1 / Sa and S2 / Sa, the distances between the centroids of the first and second conductive agents R1 and R2, the distance between the centroids of each conductive agent R1-2, the distance between the centroids of the positive electrode active material Ra, and the ratios of the centroid distances R1 / Ra and R2 / Ra.

[0178]

[0179]

[0180] <Measurement of Volume Resistivity of Active Material Layer> The volume resistivity (unit: Ω・cm) of the active material layer of the positive electrode was measured as follows. The electrodes were removed from the battery using the method described in the section on <Method of Electrode Measurement>, and samples were taken from the removed electrodes.

[0181] Sampling was performed by selecting a 10 cm x 10 cm sample from the smoothest possible surface of the active material-containing layer. The cut electrode sample was placed in an electrode resistance measuring device without bending, and the volume resistivity of the active material-containing layer was measured by pressing the electrode probe against it. A HIOKI RM2610 electrode resistance measuring system was used as the electrode resistance measuring device. The measurement was performed in potential measurement + calculation mode, with the resistance range set to Auto range and the number of calculation iterations set to 30. In the above mode, a simulation was performed using a virtual model to obtain the potential, and the resistance value used in the virtual model was changed and iterative calculations were performed until the difference between the potential obtained and the potential distribution obtained when a constant current was passed through the surface of the electrode to be measured (i.e., the measured potential) became small. The volume resistivity was determined from the resistance value when the difference between the model and the measurement became sufficiently small.

[0182] <Cycle Testing> Cycle testing was performed on each of the manufactured batteries as follows.

[0183] First, the battery was charged in a 25°C environment and adjusted to a State of Charge (SOC) of 50%. Then, it was left idle for one hour, and the Open Circuit Voltage (OCV) at that time was recorded. After that, it was discharged at a current of 10C, and the voltage drop at that time was measured. The discharge resistance value (in mΩ) of this battery was obtained by subtracting the OCV value from the voltage drop value at 10C discharge and dividing the resulting value by the current value of 10C.

[0184] Next, the battery was charged at a 3C rate to 100% State of Charge (SOC) and discharged at a 3C rate to 0% SOC in a 65°C environment for 700 charge-discharge cycles. The discharge capacity was measured during the discharge at both the 1st and 700th cycles.

[0185] After performing the 700th discharge cycle, the battery's discharge resistance was measured again.

[0186] The capacity retention rate was calculated from the discharge capacities of the first and 700th cycles using the following formula: Capacity retention rate (unit: %) = [Discharge capacity at 700th cycle / Discharge capacity at 1st cycle] × 100%. In addition, the resistance increase rate was calculated from the discharge resistance values ​​before and after performing 700 charge-discharge cycles using the following formula: Resistance increase rate (unit: %) = [Discharge resistance value after cycle / Discharge resistance value before cycle] × 100%. The calculated results are shown in Table 4 below.

[0187]

[0188] Table 4 shows that the batteries prepared in Examples 1-3 exhibit low electrode resistivity and achieve excellent capacity retention. On the other hand, Comparative Example 1-6 shows that the positive electrode volume resistivity, battery capacity retention, and resistance rise suppression are all inferior to those of Examples 1-3. In Examples 1-3, the compositional mapping images obtained using Raman spectroscopy showed that the ratios of the occupied areas S1 and S2 of the first and second conductive agents to the occupied area Sa of the active material were 0.1 < S1 / Sa < 1.0 and 0.8 < S2 / Sa < 10, respectively, and the ratios of the distances between the centroids R1 and R2 of the first and second conductive agents to the distance between the centroids Ra of the active material were 1.0 < R1 / Ra < 1.5 and 0.5 < R2 / Ra < 1.0, respectively, and furthermore, the distances between the centroids R1 and R2 of the first and second conductive agents were such that the relationship R1 > R2 > R1-2 was satisfied with the distance between the centroids R1 and R2 between the centroids R1 and R2 of the first and second conductive agents, and a positive electrode active material-containing layer was obtained, in which the ratio and positional relationship of each conductive agent and the active material were appropriately controlled so that the conductive network between particles in the positive electrode active material-containing layer and the conductive network of the entire positive electrode active material-containing layer was good.

[0189] On the other hand, the batteries of Comparative Examples 1-6 did not satisfy at least one of the above conditions in the positive electrode active material-containing layer, and the volume resistivity of the positive electrode active material-containing layer, as well as the battery's capacity retention rate and resistance increase suppression, were all inferior to those of Examples 1-3. In other words, because a conductive path could not be formed throughout the positive electrode active material-containing layer, the electrode resistivity could not be kept low, and local degradation of the active material could not be suppressed, resulting in a failure to achieve both excellent capacity retention rate and resistance increase suppression.

[0190] Specifically, in Comparative Example 1, the occupied area of ​​each conductive agent was within the range described above, but the distance between the centers of gravity was outside the range described above, with R1 / Ra being small and R2 / Ra being large. Also, R2 was at a longer distance than R1. In Comparative Example 1, the volume resistivity of the positive electrode was high, resulting in a lower battery capacity retention rate and a higher resistance increase rate than in Examples 1-3. Although the ratio of conductive agents in the active material-containing layer was appropriate, the positional relationship was not appropriate, and the formation of a conductive network within the positive electrode and the maintenance of conductivity between particles were not achieved. As a result, the electrical resistance of the positive electrode alone was high, and it can be seen that the resistance increase worsened with charge-discharge cycles due to the non-uniform distribution of the reaction. In detail, it can be seen that the first conductive agent, which has high conductivity, was excessively present around the active material from the small R1 / Ra, resulting in a small volume resistivity of the electrode, which made current unevenness more likely, and localized degradation of the active material progressed. Furthermore, the large R2 / Ra ratio indicates that there was little of the second conductive agent near the active material and the first conductive agent, preventing the formation of conductive paths throughout the active material-containing layer and thus failing to suppress local degradation of the active material.

[0191] In Comparative Example 2, the occupied area was within the range, but the distance between the centers of gravity showed that R1 / Ra was smaller, and R2 was longer than R1. In Comparative Example 2, although the volume resistivity of the positive electrode and the increase in battery resistance were relatively low, the battery's capacity retention rate was even lower than in Comparative Example 1. That is, the ratio of the conductive agent in the active material-containing layer was appropriate, but the positional relationship of the first conductive agent was not appropriate. From the R2 / Ra within the above range, it can be seen that the conductive path by the second conductive agent was well formed. However, from the small R1 / Ra, it can be seen that the highly conductive first conductive agent was excessively present around the active material. As a result, the utilization rate locally increased in the active material near the first conductive agent, worsening the local degradation of the positive electrode and the decrease in capacity retention rate due to the uneven utilization rate associated with the charge-discharge cycle.

[0192] In Comparative Example 3, the occupied area was outside the range due to a large S1 / Sa ratio. Similar to Comparative Example 1, the distance between the centers of gravity was small, R1 / Ra was large, and R2 was longer than R1. In Comparative Example 3, the positive electrode volume resistivity was even higher than in Comparative Example 1, and the battery capacity retention rate was even lower and the resistance increase suppression was even higher compared to Comparative Example 1. In Comparative Example 3, as indicated by the large S1 / Sa ratio, the amount of the first conductive agent was excessive, leading to the formation of aggregates, and as indicated by the small R1 / Ra ratio, these aggregates were located near the active material. Also, as indicated by the large R2 / Ra ratio, a conductive path was not formed by the second conductive agent. As a result, the conductivity of the active material-containing layer as a whole was not improved, and rather, current unevenness became pronounced due to the excessive concentration of the first conductive agent near the active material, indicating that localized degradation of the active material progressed.

[0193] In Comparative Example 4, the S1 / Sa ratio for the occupied area was small and outside the range. Regarding the distance between the centers of gravity, both R1 / Ra and R2 / Ra were large and outside the range. In Comparative Example 4, the positive electrode had a high volume resistivity, the battery had a low capacity retention rate, and the resistance increase rate was remarkably high. The small S1 / Sa indicates that the proportion of the highly conductive first conductive agent was small, and the large R1 / Ra and R2 / Ra indicate that each conductive agent was not present near the active material. Therefore, not only was a conductive path not formed throughout the active material-containing layer, but local conductivity could not be increased either. As a result, there was current unevenness, and even in areas where relatively high current flowed, the electrical resistance was not particularly low, leading to localized degradation of the active material.

[0194] In Comparative Example 5, the occupied area S2 / Sa was large and outside the range. Regarding the distance between the centers of gravity, both R1 / Ra and R2 / Ra were large, with R1-2 being a longer distance than R2. In Comparative Example 5, the positive electrode volume resistivity was high, the battery capacity retention rate was low, and the resistance increase rate was considerably high. The large S2 / Sa indicates that the proportion of the second conductive agent was excessive, and the large R1 / Ra and R2 / Ra indicate that each conductive agent was insufficient in the vicinity of the active material. Therefore, it can be concluded that this led to localized degradation of the active material within the active material-containing layer.

[0195] In Comparative Example 6, the occupied area was within the range, but R1 / Ra was large and outside the range. In Comparative Example 6, the volume resistivity of the positive electrode was remarkably high, the battery capacity retention rate was low, and the resistance increase rate was even higher than in Comparative Example 4. The large R1 / Ra indicates that there was little of the first conductive agent in the active material or in the vicinity of the first conductive agent. Therefore, it can be seen that the current necessary for the charge-discharge reaction could not be transmitted to the active material, the electrical resistance increased, and the degradation of the active material progressed.

[0196] According to the one or more embodiments and examples described above, an electrode is provided. The electrode comprises an active material and the integrated intensity I of the G band in a Raman chart. G Integrated intensity I of the D band D Ratio I D / I G 0.5 < I D / I G A first conductive agent where < 2 and 0 < I D / I GThe device comprises an active material-containing layer containing a second conductive agent having a coefficient of <0.5. In a constituent material mapping image of the active material-containing layer obtained by Raman spectroscopy, the occupied area S1 of the first conductive agent, the occupied area S2 of the second conductive agent, and the occupied area Sa of the active material satisfy the relationships 0.1 < S1 / Sa < 1.0 and 0.8 < S2 / Sa < 10. In the constituent material mapping image, the distance between the centroids R1 of the first conductive agent, the distance between the centroids R2 of the second conductive agent, the distance between the centroids Ra of the active material, and the distance between the centroids R1-2 between the first and second conductive agents satisfy the relationships 1.0 < R1 / Ra < 1.5, 0.5 < R2 / Ra < 1.0, and R1 > R2 > R1-2. The above electrode can provide a battery and battery pack with low electrical resistance and excellent lifespan performance.

[0197] 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.

[0198] Several embodiments of the present invention are described below. [1] A device comprising an active material-containing layer containing an active material, a first conductive agent, and a second conductive agent, wherein the Raman chart obtained by Raman spectroscopy of the active material-containing layer shows a value of 1350 ± 10 cm for the first conductive agent. -1 The integrated intensity of the D band that appears D 1590±10cm -1 The integrated intensity I of the G band that appears G Ratio I D / I G 0.5 < I D / I G < 2, and ratio I of the second conductive agent D / I G 0 < I D / I GThe ratio S1 / Sa of the occupied area S1 of the first conductive agent to the occupied area Sa of the active material is within the range of <0.5, and in the constituent material mapping image obtained by Raman spectroscopy of the active material-containing layer, the ratio S1 / Sa of the occupied area S1 of the first conductive agent to the occupied area Sa of the active material is within the range of 0.1 < S1 / Sa < 1.0, and the ratio S2 / Sa of the occupied area S2 of the second conductive agent to the occupied area Sa of the active material is within the range of 0.8 < S2 / Sa < 10. In the constituent material mapping image, the ratio R1 / Ra of the distance between the centroids of the first conductive agent to the distance Ra between the centroids of the active material is within the range of 1.0 < R1 / Ra < 1.5, the ratio R2 / Ra of the distance R2 between the centroids of the second conductive agent to the distance Ra between the centroids of the active material is within the range of 0.5 < R2 / Ra < 1.0, and the electrode satisfies the relationship R1 > R2 > R1-2 between the distance R1 between the centroids of the first conductive agent, the distance R2 between the centroids of the second conductive agent, and the distance R1-2 between the centroids of the first conductive agent and the second conductive agent. [2] The active material is Li a Ni (1-b-c-d) Co b Mn c M d The electrode according to [1], represented by O2, where 1 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, and 0 ≤ d ≤ 0.1, and M comprises a compound selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V, and has an average primary particle diameter of 2 μm or more and 7 μm or less. [3] The specific surface area of ​​the active material obtained by nitrogen adsorption / desorption is 0.5 m². 2 / g or more 1.0 m 2 An electrode according to [1] or [2], wherein the density of the active material is 0.18 / g or less. [4] An electrode according to any one of [1] to [3], wherein the average particle size of the first conductive agent is 100 nm or less, the average particle size of the second conductive agent is 10 μm or less, and the mass ratio of the first conductive agent and the second conductive agent to the active material is 0.18 or less. [5] The density of the active material-containing layer is 2.0 g / cm³ 3 More than 4.0 g / cm 3An electrode according to any one of [1] to [4], which is less than [6]. A battery comprising the electrode according to [1] to [5] and an electrolyte. A battery pack comprising the battery according to [6].

[0199] 1...Electrode group, 2...Outer casing, 3...Positive electrode, 3a...Positive electrode current collector, 3b...Positive electrode active material layer, 4...Negative electrode, 4a...Negative electrode current collector, 4b...Negative electrode active material layer, 5...Separator, 6...Negative electrode terminal, 7...Positive electrode terminal, 11...Electrode group, 12...Container, 13...Rectangular lid, 14...Negative electrode current collector tab, 16...Glass material, 17...Positive electrode current collector tab, 18...Positive electrode terminal, 20...Battery pack, 21...Single cell, 22...Adhesive tape, 23...Battery pack, 24...Printed circuit board 1. Board, 25. Thermistor, 26. Protection circuit, 27. Terminal for supplying power to external equipment, 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, 300. Positive active material, 301. First conductive agent, 302. Second conductive agent.

Claims

1. An electrode comprising an active material-containing layer containing an active material, a first conductive agent, and a second conductive agent, wherein in a Raman chart obtained by Raman spectroscopy of the active material-containing layer, the integrated intensity I of the D band appearing at 1350 ± 10 cm G , D for the first conductive agent is such that the ratio I D of the integrated intensity I of the G band appearing at 1590 ± 10 cm -1 for the first conductive agent is within the range of 0.5 < I G / I D / I G < 2, and the ratio I D / I G for the second conductive agent is within the range of 0 < I D / I G < 0.

5. In a constituent material mapping image obtained by Raman spectroscopy of the active material-containing layer, the ratio S1 / Sa of the occupied area S1 of the first conductive agent to the occupied area Sa of the active material is within the range of 0.1 < S1 / Sa < 1.0, and the ratio S2 / Sa of the occupied area S2 of the second conductive agent to the occupied area Sa of the active material is within the range of 0.8 < S2 / Sa < 10. In the constituent material mapping image, the ratio R1 / Ra of the center-of-gravity distance R1 of the first conductive agent to the center-of-gravity distance Ra of the active material is within the range of 1.0 < R1 / Ra < 1.5, and the ratio R2 / Ra of the center-of-gravity distance R2 of the second conductive agent to the center-of-gravity distance Ra of the active material is within the range of 0.5 < R2 / Ra < 1.

0. The center-of-gravity distance R1 of the first conductive agent, the center-of-gravity distance R2 of the second conductive agent, and the center-of-gravity distance R1-2 between the first conductive agent and the second conductive agent satisfy the relationship R1 > R2 > R1-2.​​​​ 2. The active material is Li a Ni (1-b-c-d) Co b Mn c M d The electrode according to claim 1, which is represented by O2, where 1 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, and 0 ≤ d ≤ 0.1, and M comprises a compound containing at least one selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V, and has an average primary particle diameter of 2 μm or more and 7 μm or less.

3. The specific surface area of ​​the active material obtained by nitrogen adsorption / desorption is 0.5 m². 2 / g or more 1.0 m 2 The electrode according to claim 1 or 2, wherein the amount is less than or equal to / g.

4. The electrode according to claim 1 or 2, wherein the average particle size of the first conductive agent is 100 nm or less, the average particle size of the second conductive agent is 10 μm or less, and the mass ratio of the first conductive agent and the second conductive agent to the active material is 0.18 or less, each.

5. The density of the active material-containing layer is 2.0 g / cm³. 3 More than 4.0 g / cm 3 The electrode according to claim 1 or 2, wherein the electrode is less than [amount missing].

6. A battery comprising the electrode described in claim 1 or 2 and an electrolyte.

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

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