Electrode, battery, and battery pack

Abstract

According to an embodiment of the present invention, there is provided an electrode comprising a current collector and an active material–containing layer on the current collector. The active material-containing layer contains an active material and a conductive agent. The active material contains a lithium nickel cobalt manganese composite oxide. The specific surface area SBET of the active material–containing layer as measured by the nitrogen gas adsorption method and the pore specific surface area SHg of the active material–containing layer as measured by mercury porosimetry satisfy the relation 0.8 < SBET / SHg < 2.0. The volume resistivity RV of the material-containing layer is 10 Ω·cm or less. The interface resistance RI of the interface between the current collector and the active material–containing layer is 0.5 Ω·cm2 or less. The ratio RV / RI of the volume resistivity RV to the interface resistance RI is between 3 cm-1 and 20-1, inclusive.

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 expected to be applied not only to electronic devices such as mobile phones, but also to vehicles such as hybrid electric vehicles and electric vehicles, as well as to large-scale systems such as electric aircraft and power storage. Therefore, secondary batteries are required to have improved capacity, high current output, and long lifespan.

[0003] Graphite is generally used as the negative electrode active material in non-aqueous electrolyte batteries. High-power, high-energy-density batteries can be obtained by using a graphite negative electrode. However, it is known that lithium dendrites can easily precipitate in graphite negative electrodes due to overvoltage, etc. Internal short circuits can occur when dendrites penetrate the separator. In addition, graphite undergoes expansion and contraction in the c-axis direction due to lithium insertion and deinsertion, resulting in significant structural degradation of the graphite.

[0004] Other negative electrode active materials for non-aqueous electrolyte batteries include, for example, spinel-type lithium titanate (Li4Ti5O 12 ) is known. By using lithium titanate, the deposition of lithium dendrites can be suppressed, thus avoiding risks such as short circuits, self-discharge, and ignition, and making it possible to manufacture batteries with excellent high-current output performance and lifespan.

[0005] Lithium nickel-cobalt manganese oxide is an example of a positive electrode active material for non-aqueous electrolyte batteries, offering excellent high-capacity performance. Conventional batteries using lithium nickel-cobalt manganese oxide as the positive electrode and lithium titanate as the negative electrode have advantages over batteries using graphite-based negative electrodes, including superior rapid charge / discharge performance, long lifespan, and low-temperature performance. However, there is room for improvement in the positive electrode active material. In particular, there are problems with lifespan performance.

[0006] In batteries using lithium nickel-cobalt-manganate secondary particles as the positive electrode active material, when pressure is applied to increase the electrode density of the positive electrode, or when the positive electrode active material expands and contracts due to repeated charging and discharging, particle cracking occurs in the active material, increasing the specific surface area. Furthermore, lithium nickel-cobalt-manganate is generally used in a polycrystalline form, where fine primary particles aggregate to form secondary particles. Polycrystalline forms have greater surface roughness and a larger specific surface area compared to primary particles. Positive electrodes using such active materials have the problem that oxidation reactions between the positive electrode and electrolyte are more likely to occur during charging and discharging using high potential or during storage under high potential conditions, leading to significant performance degradation.

[0007] To address this issue, it is known that using single-crystal active materials with high fracture strength and low surface roughness improves charge-discharge cycle life and calendar life. However, reducing surface roughness tends to decrease the number of contact points between the active material and the conductive agent. Consequently, the expansion and contraction of the active material during charge-discharge cycles can easily break contact between the active material and the conductive agent. Within the electrode, current flow is poor in areas where contact between the active material and the conductive agent is broken, while current preferentially flows to areas where contact is maintained. As a result, the positive electrode potential increases locally, leading to accelerated degradation of the active material, which is a problem.

[0008] International Publication No. 2023 / 026482, International Publication No. 2023 / 131987

[0009] The objective is to provide an electrode that can realize a battery with excellent lifespan performance, a battery equipped with this electrode, and a battery pack equipped with this battery.

[0010] According to the embodiment, an electrode is provided comprising a current collector and an active material-containing layer on the current collector. The active material-containing layer contains an active material and a conductive agent. The active material includes a lithium nickel cobalt manganese composite oxide. The specific surface area S of the active material-containing layer by nitrogen gas adsorption method. BET and the pore specific surface area S of the active material-containing layer by the mercury intrusion method. Hg is 0.8 < S BET / S HgSatisfies the relationship of <2.0. The volume resistivity R of the active material-containing layer V is 10 Ω·cm or less. The interfacial resistance R at the interface between the current collector and the active material-containing layer I is 0.5 Ω·cm ２ or less. The ratio R of the volume resistivity R I to the interfacial resistance R V is V R I 3 cm －１ or more and 20 cm －１ or less.

[0011] According to another embodiment, a battery including the above electrode and electrolyte is provided.

[0012] According to still another embodiment, a battery pack including the above battery is provided.

[0013] FIG. 1 is a plan view schematically showing an example of an electrode according to an embodiment. FIG. 2 is a cross-sectional view of an example of a battery according to the embodiment cut in the thickness direction. FIG. 3 is an enlarged cross-sectional view of part A in FIG. 2. FIG. 4 is a partially cutaway perspective view of another example of a battery according to the embodiment. FIG. 5 is an exploded perspective view of an example of a battery pack according to the embodiment. FIG. 6 is a block diagram showing an electrical circuit of the battery pack shown in FIG. 5. Embodiment

[0014] In a lithium secondary battery positive electrode obtained by using a conventional lithium-containing metal composite compound as a positive electrode active material, in order to improve the life performance of the positive electrode, an active material with a small surface roughness that is less likely to cause side reactions may be used. However, when using an active material such as a single crystal with a small surface roughness, not only are there few contact points with the conductive agent and the current collector, but electrical contact is likely to be lost due to the expansion and contraction of the positive electrode accompanying charge and discharge of the battery. In such a positive electrode, current preferentially flows in a portion where the contact between the active material and the conductive agent is well maintained, and thus the positive electrode potential may locally increase. Therefore, there is a tendency for resistance increase and significant gas generation to occur due to deterioration of the positive electrode active material in the portion where the positive electrode potential has increased.

[0015] Furthermore, if the interfacial resistance between the active material layer and the current collector is high, current will not flow easily to the active material within the active material layer, accelerating battery degradation. Generally, the active material and the current collector are bonded together by a binder, and conductivity is ensured by the distribution of a conductive agent at the bonding site or by direct contact with the current collector. When using active materials such as single crystals with low surface roughness, the number of contact points with the conductive agent and current collector is reduced, leading to increased interfacial resistance.

[0016] On the one hand, one way to address the above issues is to increase the amount of conductive agent. In particular, it is known that interfacial resistance can be reduced by adding a large amount of carbon black or carbon nanotubes, which have small particle sizes and are easily distributed in fine gaps such as the interface between the current collector and the active material-containing layer. On the other hand, even if interfacial resistance is actively reduced, if the interfacial resistance is significantly lower than the volume resistivity of the active material-containing layer itself, current will flow easily near the interface, while current will not flow easily in other parts of the active material-containing layer. Therefore, especially during high-rate cycling, a large current tends to flow through the active material near the interface, leading to a localized increase in the positive electrode potential and accelerating degradation of the active material.

[0017] The above issues can be summarized as follows: For lithium nickel-cobalt-manganate, a positive electrode active material with excellent high-capacity performance, it is desirable to use a single-crystal system from the viewpoint of longevity performance. However, due to its low surface roughness, contact with the conductive agent is prone to problems. Furthermore, contact between the single-crystal active material and the current collector is easily broken, which tends to increase interfacial resistance. On the other hand, even if interfacial resistance is reduced by adding a large amount of conductive agents such as carbon black or carbon nanotubes, a difference between the resistance of the active material-containing layer and the interfacial resistance tends to occur, resulting in a deterioration of longevity performance.

[0018] 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.

[0019] 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.

[0020] (First Embodiment) According to the first embodiment, an electrode is provided. The electrode comprises a current collector and an active material-containing layer thereon. The active material-containing layer contains an active material comprising a lithium nickel cobalt manganese composite oxide and a conductive agent. The specific surface area S of the active material-containing layer is determined by the nitrogen gas adsorption method. BET The specific surface area of ​​the pores S, determined by the mercury intrusion method. Hg This means 0.8 < S BET / S Hg The relationship <2.0 is satisfied. Volume resistivity R of the active material-containing layer. V The interfacial resistance R of the interface between the current collector and the active material-containing layer is 10 Ω·cm or less. I 0.5Ω·cm ２ The following is the interfacial resistance R. I Volume resistivity R V Ratio R V / R I 3cm －１ 20cm or more －１ The following applies:

[0021] 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.

[0022] The electrode that satisfies the above configuration is an electrode using single-crystal type lithium nickel cobalt manganese composite oxide (NCM). Compared to a positive electrode using secondary particle type NCM, where the surface structure and surface area differ depending on the aggregation method of primary particles, this electrode has fewer micropores and a more uniform surface condition. Therefore, the specific surface area is approximately the same for both the nitrogen gas adsorption method and the mercury intrusion method. Furthermore, when comparing the pore volume obtained by the mercury intrusion method between the single-crystal type and the secondary particle type, the single-crystal type, with fewer pores, has a smaller value. The specific surface area S obtained by the nitrogen gas adsorption method (based on the BET (Brunauer, Emmett, Teller) method, as described later) BET and the pore specific surface area S obtained by the mercury intrusion method Hg Ratio S BET / S Hg The closer the value specified by is to 1.0, the better the lifetime performance of the single-crystal type NCM. Compared to secondary particle type NCM, single-crystal type NCM has fewer micropores and a more uniform surface state, so S BET / S Hg The value tends to be close to 1.0. By using single-crystal NCM, whose specific surface area value is constant regardless of the measurement method, as the active material and controlling the electrode density, it is possible to control the contact area with the electrolyte and improve battery performance.

[0023] The specific surface area S of the active material-containing layer was measured by the N2 gas adsorption method. BET and the pore specific surface area S measured by the mercury intrusion method Hg The ratio S BET / S Hg 0.8 < S BET / S Hg Within the range of <2.0, the effective area contributing to the electrode reaction can be precisely controlled, reducing electrical resistance and suppressing gas generation. In other words, by satisfying the above relationship, the specific surface area of ​​the active material can be reduced, suppressing oxidation reactions between the electrode and electrolyte, which are particularly problematic in charge-discharge cycles using high potentials and in storage, and resulting in electrodes with good lifespan performance.

[0024] Specific surface area S measured by nitrogen gas adsorption method on the active material-containing layer BETThis mainly reflects the specific surface area of ​​micropores and mesopores within the electrode, which have pore diameters ranging from approximately 0.1 nm to 100 nm. In contrast, the pore specific surface area S measured by the mercury intrusion method... Hg This mainly reflects the specific surface area of ​​mesopores and macropores within the active material-containing layer, which have pore diameters ranging from approximately 1 nm to 1 mm. That is, the ratio S of the two. BET / S Hg This is an indicator representing the ratio of micropores to macropores in the electrode. 0.8 > S BET / S Hg Or S BET / S Hg If the specific surface area is >2.0, there may be a large number of either micropores or macropores. In that case, it is difficult to control the effective area that contributes to the side reaction between the active material and the electrolyte (liquid electrolyte), and the reaction area becomes larger, resulting in a greater increase in electrical resistance. More preferably, the specific surface area S BET and pore specific surface area S Hg The ratio to is 0.85 < S BET / S Hg It is desirable to satisfy the relationship <1.15. In electrodes where the difference in specific surface area is narrower than 15%, the electrode reaction area is more controlled as described above, and the effect of reducing electrical resistance is more pronounced.

[0025] Specific surface area S of the active material-containing layer measured by nitrogen gas adsorption method BET 1.0 m 2 / g≦S BET ≤5.0 m 2 It is preferable to keep it within the range of / g. Specific surface area S BET 1.0 m 2 Increasing the specific surface area (S) above 1g promotes electrolyte penetration, improving output performance and lifespan. BET 5.0 m 2 When the value is reduced to below / g, contact between active material particles and 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. Specific surface area S by nitrogen gas adsorption method. BETIn electrodes that satisfy the above range, the contact between the active material and the conductive agent can be improved, reducing electrical resistance and enabling the creation of batteries with excellent input / output performance. In addition, if the active material-containing layer is 3.0 g / cm³ as described above... 3 Exceeding 3.6 g / cm³ 3 It is even more desirable to have a preferred density of less than . More preferably, the specific surface area S of the positive electrode active material-containing layer by nitrogen gas adsorption method. BET 2.5 m 2 / g≦S BET ≤3.0 m 2 It is desirable that the value be within the range of / g. In a more preferable range, the dispersion of the active material, conductive agent, and binder is good, and it is easier to properly control the electrode density, making it possible to manufacture batteries with lower resistance and higher input / output performance.

[0026] The electrode comprises a current collector and an active material-containing layer (electrode composite layer). 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 can 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 can function as current-collecting tabs. Alternatively, the electrode may include current-collecting tabs separate from the current collector.

[0027] The active material-containing layer contains an active material and a conductive agent. In addition to the active material and conductive agent, the active material-containing layer may also contain a binder. The binder may be added to bind the dispersed active material together and to bind the active material to the current collector.

[0028] In the electrode in question, the volume resistivity R of the active material-containing layer V The interfacial resistance R between the current collector and the active material-containing layer is 10 Ω·cm or less. I 0.5Ω·cm ２ The following is the result: Although the electrode uses a single-crystal active material with low surface roughness, the contact between the active material and the conductive agent is good, and contact breakage due to expansion and contraction during charge-discharge cycles is less likely to occur. Therefore, an electrode with good lifespan performance can be obtained.

[0029] Furthermore, in such electrodes, the interfacial resistance R between the current collector and the active material-containing layer is I Volume resistivity R of the active material-containing layer V Ratio R V / R I However, 3 cm -1 ≤R V / R I ≤20 cm -1 The following relationship is satisfied. For electrodes that satisfy this relationship, the volume resistivity R V and interfacial resistance R I This provides a good balance, preventing current bias during battery charging and discharging, where current flows more easily to the active material near the current collector / active material layer interface than to other parts of the active material. Therefore, by satisfying the above relationship, localized degradation of the active material near the interface can be suppressed, resulting in electrodes that exhibit good cycle performance.

[0030] It is desirable that the thickness of the active material-containing layer be between 10 μm and 60 μm. Electrodes containing an active material-containing layer with a thickness of 10 μm or more can have high capacitance. For an active material-containing layer with a thickness of 60 μm or less, the above volume resistivity R V and interfacial resistance R I It is easier to achieve a distribution of conductive agent that strikes a good balance with the other properties.

[0031] The active material-containing layer contains Li as the active material. a Ni (1-b-c-d) Co b Mn c M d It may contain a lithium nickel cobalt manganese composite oxide represented by O2. Each subscript in the formula is within the ranges 1 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, and 0 ≤ d ≤ 0.1, respectively. 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.

[0032] The active material may have an average primary particle diameter of 2 μm or more and 7 μm or less. In the active material-containing layer, by setting the primary particle diameter of the active material particles to 2 μm or more and 7 μm or less, the life performance of the battery can be improved. By making the primary particle diameter 2 μm or more, the specific surface area of the electrode becomes smaller, and the influence of the side reaction between the electrode and the electrolyte on the life performance can be reduced. Further, by making the primary particle diameter 7 μm or less, the solid-state diffusion of lithium ions within the particles becomes uniform, local structural deterioration is further suppressed, and the life performance is improved. More preferably, the primary particle diameter is preferably 3 μm or more and 4.5 μm or less. In a more preferable range, by preventing aggregation and isolation of the primary particles, the life performance can be further improved.

[0033] Further, the specific surface area of the active material is preferably 0.5 m 2 / g or more and 2.0 m 2 / g or less. The specific surface area of the active material referred to here means the specific surface area measured by the nitrogen gas adsorption method for the state of the active material particles alone without forming a layer. When the specific surface area of the active material is 0.5 m 2 / g or more, the contact area between the active material and the conductive agent increases, and the output performance can be improved. When the specific surface area of the active material is 2.0 m 2 / g or less, the contact area between the active material and the electrolyte solution is kept at an appropriate size and side reactions are suppressed, so the electrical resistance is less likely to increase. Therefore, by setting the specific surface area of the active material particles to 0.5 m 2 / g or more and 2.0 m 2 / g or less, the contact area between the active material and the electrolyte solution can be made appropriate, and an electrode and a battery with low resistance and excellent life performance can be manufactured. More preferably, the specific surface area of the active material is preferably 0.5 m 2 / g or more and 1.0 m 2 / g or less. In a more preferable range, it is easy to control the contact area between the active material and the electrolyte solution, and it is easy to obtain an electrode with low resistance and excellent life performance.

[0034] Next, materials that can be used for the active material-containing layer and the current collector included in the electrode according to the first embodiment will be described.

[0035] <Active Material Containing Layer>As described above, the active material containing layer can include a binder in addition to the active material and the conductive agent. The mixing ratios of the active material, the conductive agent, and the binder in the active material containing layer are preferably such that the active material is 80% by mass or more and 95% by mass or less, the conductive agent is 0.5% by mass or more and 18% by mass or less, and the binder is 0.5% by mass or more and 17% by mass or less.

[0036] <Active Material>The active material containing layer includes a lithium nickel cobalt manganese composite oxide as the active material. As the lithium nickel cobalt manganese composite oxide, Li as described above a Ni (1-b-c-d) Co b Mn c M d O2 is preferably included. Further, 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. The lithium nickel cobalt manganese composite oxide can be used as the first active material, and the active material containing layer can further include another second active material. Of course, the first active material can be used alone, or one or more second active materials can be included without including the first active material.

[0037] As the second active material, various oxides can be used, for example, lithium cobalt composite oxides (for example, LiCoO ２ ), manganese dioxide, lithium manganese composite oxides (for example, LiMn ２ O ４ , LiMnO ２ ), lithium nickel composite oxides (for example, LiNiO ２ ), lithium nickel cobalt composite oxides (for example, LiNi ０．８ Co ０．２ O ２ ), lithium-containing iron oxides, vanadium oxides containing lithium, and chalcogen compounds such as titanium disulfide and molybdenum disulfide. The electrode may include one of the above compounds as the second active material, or may include two or more of the above compounds as the second active material.

[0038] 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.

[0039] 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.

[0040] It is preferable for the proportion of primary particles and secondary particles in the active material to be high. The conductivity inside the secondary particles (inside the hollow structure) is poor, and by eliminating the presence of primary particles contained therein, it is possible to further reduce electrical resistance.

[0041] 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. In addition, 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.

[0042] <Conductive Agent> The conductive agent preferably contains a carbon material. Examples of carbon materials include carbon black such as acetylene black, Ketjen black, and furnace black, as well as graphite and carbon nanotubes. The active material-containing layer may contain one conductive agent or two or more conductive agents.

[0043] For example, it is desirable to include a conductive agent that can be distributed to fill the gaps between active materials, such as carbon black or carbon nanotubes, and at the same time, a conductive agent that has a relatively large particle size, such as flake graphite, and can act as a broad conductive path connecting multiple active material particles. The former, for example, is distributed to fill the gaps between active materials when a pressing process is performed during electrode fabrication, and acts as a conductive path between active materials. Therefore, since it can be distributed throughout the electrode, increasing the content of the former conductive agent increases the volume resistivity R V and interfacial resistance R I It has the effect of reducing both of the following. The latter does not easily penetrate into fine gaps such as the interface between the current collector and the active material-containing layer, and is more likely to be distributed in the bulk of the active material-containing layer. For example, by increasing the content of flake graphite, the volume resistivity R V This allows for the preferential reduction of conductive path breaks in single-crystal active materials and volume resistivity R. V and interfacial resistance R I This suppresses localized degradation of the active material due to discrepancies with the other components. Therefore, it is preferable that the amount of flake graphite in the active material-containing layer be 3% by mass or more relative to the mass of the active material-containing layer.

[0044] Graphite exists in two forms: flaky graphite, which has high orientation, and spheroidal graphite, which has lower orientation. Natural graphite is flaky graphite. Spheroidal graphite is obtained by spheroidization treatment.

[0045] <Binding Agents> As binding agents, materials containing fluorine atoms in their molecules are preferred because they exhibit 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. Furthermore, binding agents in which a modified group has been introduced into the above binding agents can also be used. The active material-containing layer may contain one of the above binding agents, or two or more of the above binding agents.

[0046] <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.

[0047] Next, a specific example of the electrode according to the first embodiment will be described with reference to the drawings.

[0048] 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.

[0049] The positive electrode 3 shown in Figure 1 comprises a positive electrode current collector 3a and a positive electrode active material containing layer 3b provided on the surface of the positive electrode current collector 3a. The positive electrode active material containing layer 3b is supported on the main surface of the positive electrode current collector 3a.

[0050] Furthermore, the positive electrode current collector 3a includes a portion on its surface where the positive electrode active material-containing layer 3b is not provided. This portion functions, for example, as a positive electrode current collector tab 3c. In the illustrated example, the positive electrode current collector tab 3c is a narrow portion that is narrower than the positive electrode active material-containing layer b. The width of the positive electrode current collector tab 3c may be narrower than the width of the positive electrode active material-containing layer 3b, or it may be the same width as the positive electrode active material-containing layer 3b. Instead of the positive electrode current collector tab 3c, which is part of the positive electrode current collector 3a, a separate conductive member may be electrically connected to the positive electrode 3 and used as an electrode current collector tab (positive electrode current collector tab).

[0051] The electrode according to the first embodiment of the manufacturing method can be manufactured, for example, by the following method.

[0052] First, the main active material (first active material) is prepared. As the first active material, at least one type of lithium nickel cobalt manganese composite oxide is used. For example, a preferred active material containing the above-mentioned lithium nickel cobalt manganese composite oxide and having an average primary particle size of 2 μm to 7 μm can be obtained 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, a lithium nickel cobalt manganese composite oxide can be synthesized in which the chemical composition is optimized so that the primary particle size, achieved by any method of promoting particle growth, is 2 μm or more and the nickel content ratio is above a predetermined level.

[0053] A mixture is obtained by adding a lithium nickel cobalt manganese composite oxide prepared as the first active material, an optional second active material, a conductive agent, and an optional binder to a suitable dispersion medium. Examples of dispersion media include NMP (N-methyl-2-pyrrolidone). The amount of each material added is preferably within the range corresponding to the mixing ratio described above.

[0054] Next, the obtained mixture is placed into a stirrer. The mixture is stirred in this stirrer to obtain a slurry. During the stirring process, increasing the rotational speed of the stirrer makes it possible to further break down the active material and conductive agent particles, and the specific surface area S of the electrode after fabrication is increased. BET The value can be improved. By further processing the obtained slurry, such as by grinding it, the active material and conductive agent in the slurry can be dispersed more finely. In addition, any dispersant may be used to improve the dispersibility of the conductive agent.

[0055] The slurry thus obtained is applied to both sides or one side of the current collector. At this time, areas on the current collector may be left without the slurry applied to either surface. Next, the coating is dried. The appropriate drying conditions differ depending on the type of binder. For example, when a binder with a modifying group is used, the modifying group can capture the conductive agent. Therefore, even among binders with similar molecular weights, a binder with a modifying group is more prone to the detachment of the conductive agent from the interface between the coating and the current collector due to migration within the coating compared to a binder without a modifying group. Accordingly, when using a binder with a modifying group, it is preferable to dry it at a slower drying rate.

[0056] Next, the dried coating is pressed. By increasing the pressing load at this time, it is possible to improve the electrode density, and for example, the degree to which carbon black penetrates between active material particles can be adjusted. In addition, increasing the pressing load allows for the measurement of the pore diameter and pore specific surface area S inside the electrode by the mercury intrusion method. Hg It is possible to reduce this value and adjust it to a value within the above range that provides superior performance. Thus, electrodes can be fabricated.

[0057] The pore distribution in 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. Furthermore, by reducing the rotation of the stirrer during the stirring process, a slurry that sufficiently maintains the conductive network of the conductive agent can be obtained. Conversely, by increasing the rotation of the stirrer, a slurry with good dispersion of the active material can be obtained. In electrodes fabricated using slurries obtained by reducing or increasing the stirring in this way, the pore specific surface area S BET The value of can be improved. In addition, as mentioned above, the electrode density can be improved by increasing the press load, and it tends to be easier to produce electrodes with better electrical contact and superior capacitance when the electrode density is higher. Conversely, by decreasing the press load, the pore diameter and pore specific surface area S inside the electrode, which can be measured by the mercury intrusion method, can be improved.Hg By increasing the value, it is possible to create excellent electrodes with low input resistance.

[0058] Specific examples of electrode fabrication will be explained in the examples below.

[0059] This section describes various measurement methods for electrodes. Specifically, it covers methods for measuring the composition of the active material, methods for measuring the average primary particle size of the active material particles, and methods for determining the pore specific surface area S by nitrogen gas adsorption. BET Method for measuring the pore specific surface area S by mercury intrusion method Hg Method for measuring the volume resistivity R of the active material-containing layer. V Method for measuring the interfacial resistance R of the interface between the current collector and the active material-containing layer. I The methods for measuring the content of the conductive agent in the active material-containing layer will be explained.

[0060] When analyzing electrodes incorporated into a battery, remove the electrodes using the following procedure.

[0061] First, prepare the battery to be measured. The battery to be measured must have a discharge capacity of 100% or more of its rated capacity. In other words, batteries that have deteriorated will not be measured. Next, discharge the prepared battery. For example, in the case of a non-aqueous electrolyte battery containing lithium nickel cobalt manganese composite oxide as the positive electrode active material and lithium titanate as the negative electrode active material, discharge it from any charge state to a battery voltage of 1.5V with a current value equal to the reference current value.

[0062] Next, the discharged battery is moved into a glove box filled with argon, where the dew point of the internal atmosphere is -70°C. Inside this glove box, the battery is cut open. The electrode group is removed from the opened battery. Care is taken to maintain electrical insulation between the positive and negative electrodes during this series of disassembly operations.

[0063] 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.

[0064] 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.

[0065] <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).

[0066] <Measurement of the average primary particle diameter of active material particles> The average primary particle diameter of active material particles can be measured by the laser diffraction / scattering method described below.

[0067] 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 calcined to remove the binder and conductive agent, and the active material particles are isolated. The obtained active material particle sample is then placed into a measurement cell filled with N-methylpyrrolidone (NMP) until a measurable concentration is reached. Note that the capacity of the measurement cell and the measurable concentration will vary depending on the particle size distribution analyzer.

[0068] A measurement cell containing NMP and a sample of active material dissolved in it is irradiated with 40W ultrasonic waves for 5 minutes. Such ultrasonic irradiation can dissolve the aggregation of active material particles.

[0069] 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 a particle size distribution analyzer is the Microtrac3100. The average primary particle size of the active material can be determined from the particle size distribution of the active material particles. The particle size at which the cumulative frequency from the smallest particle size side in the measured particle size distribution reaches 50% (D 50 This corresponds to the average primary particle size of the active material.

[0070] <Measurement of pore specific surface area by nitrogen gas adsorption method> Pore specific surface area S of the active material-containing layer by nitrogen (N2) gas adsorption method BETThis corresponds to the BET specific surface area of ​​the electrode. The BET specific surface area is the specific surface area determined by the BET method and is calculated using the nitrogen gas adsorption method. The analysis is performed, for example, by the following method.

[0071] Multiple strip-shaped measurement samples with a planar shape and dimensions of 5 mm × 20 mm are cut from the electrode. The weight of the cut measurement samples is measured. Next, 24 measurement samples are placed into the cell of the measuring device. These measurement samples are placed in a measuring cell for nitrogen adsorption and desorption measurement and dried at a temperature of 120°C or higher under a nitrogen 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 for nitrogen gas adsorption measurement is the Quantasorb manufactured by QUANTACHROME.

[0072] <Measurement of pore specific surface area by mercury intrusion method> Pore specific surface area S of the active material-containing layer by mercury intrusion method Hg The measurement method is described below.

[0073] Multiple strip-shaped measurement samples with a planar shape and dimensions of 12 mm × 25 mm are cut from the electrode. The weight of the cut measurement samples is measured. Next, 16 folded measurement samples are loaded into the cell of the measuring device. These measurement samples are measured under conditions of an initial pressure of 20 kPa (equivalent to a pore diameter of approximately 60 μm) and a termination pressure of 400 MPa (equivalent to a pore diameter of approximately 3 nm).

[0074] Next, from another measurement sample cut from the same electrode, the active material-containing layer is peeled off, for example, using a spatula, to obtain a current collector piece. The weight of this current collector piece is measured. By subtracting the weight of the current collector piece from the weight of the measurement sample measured earlier, the weight of the active material-containing layer contained in the measurement sample can be determined. In addition, the pore distribution, excluding the weight of the current collector, is recalculated for a specific range (0.003 μm to 2 μm).

[0075] From the pore distribution obtained as described above and the weight of the active material-containing layer contained in the measurement sample, the specific surface area of ​​the pores of the active material-containing layer (unit: m²) can be calculated. 2 You can calculate ( / g).

[0076] Pore ​​specific surface area (Pore specific surface area S) Hg ) calculates the shape of the pores as cylindrical.

[0077] The analytical principle of the mercury intrusion method is based on Washburn's equation (1) below.

[0078] D = -4γcosθ / P (1) where D is the pore diameter and γ is the surface tension of mercury (480 dyne·cm) －１ γ and θ are the contact angle between mercury and the pore wall (140°), and P is the applied pressure. Since γ and θ are constants, the relationship between the applied pressure P and the pore diameter D can be determined from Washburn's equation (1), and by measuring the volume of mercury intrusion at that time, the pore diameter and its volume distribution can be derived.

[0079] One example of a measuring device for pore size distribution measurement is the Autopore 9520 pore size distribution analyzer manufactured by Micromeristics.

[0080] <Measurement of volume resistivity of the active material-containing layer and interface resistance between the current collector and the active material-containing layer> Cut out several strip-shaped measurement samples with a planar shape of 50 mm x 50 mm from the electrode. After separately measuring the thickness of the active material-containing layer, the thickness of the current collector, and the volume resistivity of the current collector, confirm that the samples are sufficiently dry and then measure the electrode resistance.

[0081] Here, the volume resistivity of the active material-containing layer and the interfacial resistance between the current collector and the active material-containing layer are calculated by modeling the electrode sheet as a virtual electrode sheet consisting of two layers plus one interface layer. A constant current is passed through the surface of the electrode sheet, and the potential distribution generated on the surface is measured at multiple points. Next, using the resistance of each layer as a variable, a calculated potential that matches the measured potential is calculated by iterative calculation (curve regression). When the measured potential and the calculated potential match, the volume resistivity of the active material-containing layer and the interfacial resistance between the current collector and the active material-containing layer can be calculated, respectively. This calculation requires the separate preparation of information such as the thickness of the active material-containing layer, the thickness of the current collector, and the volume resistivity of the current collector. For example, this information can be measured in advance using a portion of several cut-out samples. However, regarding the volume resistivity of the current collector, if the constituent material of the current collector can be identified, for example, if the current collector is made of Al or Cu, its general physical properties can be used, and measurement can be omitted.

[0082] An example of a measuring device for measuring the volume resistivity of the active material-containing layer and the interfacial resistance between the current collector and the active material-containing layer is the RM2610 electrode resistance measurement system manufactured by HIOKI E.E. CORPORATION. The cut-out sample is placed on the electrode resistance measurement device without bending, and the volume resistance of the active material-containing layer is measured by pressing the electrode probe against it. The measurement is performed in potential measurement + calculation mode, with the resistance range set to Auto range and the number of calculation iterations set to 30.

[0083] <Measurement of conductive agent content in the active material-containing layer> One method for measuring the conductive agent content in the active material-containing layer is to use Raman spectroscopy to detect constituent material mapping images. The measurement procedure is shown below.

[0084] The electrode extracted using the method described above is fixed in a position where 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 position facing the desired direction. After that, a new cross-section is 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.

[0085] 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. Also, if the acquired spectrum becomes unclear, conversely, the exposure time should be increased or the number of integrations should be increased: Exposure time: 10 s or 20 s Number of integrations: 1 Lens magnification: 50x Measurement range: 50 μm × 50 μm Laser power: 5%.

[0086] (Creation of constituent material mapping images) Next, using a Raman chart with 10,000 points, spectra are extracted from any 10 points in each high-concentration region to obtain the 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 and 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, the abundance ratio of each constituent material is mapped.

[0087] Here, depending on the type of carbon material, the Raman chart shows 1350 ± 10 cm². -1 The integrated intensity of the D band appearing at 1590±10cm² -1 The ratio to the integrated intensity of the G band that appears is different. For example, carbon black has a large integrated intensity of the D band due to structural disorder, and the integrated intensity of the D band is different. D The integrated intensity of the G band I G The ratio to is 0.5 < I D / I G <2.0 relationship is satisfied. For highly crystalline carbon such as flaky graphite, the integrated intensity of the G band due to the layered structure is large, I D I G The ratio to is 0 < I D / I G The relationship <0.5 is satisfied. Carbon nanotubes (CNTs) have a structure in which one or more layers of graphene are rolled into a tube, but depending on the number of layers and manufacturing method, I D / I G The ratios are different. These examples have D and G bands in close proximity, but even when two or more such carbon materials are included as conductive agents, the presence of each conductive agent at that point can be distinguished by calculating the degree of overlap using the individual spectra and fitting them together. The relative abundance of each constituent material can be represented, for example, by different shades of color for each constituent material.

[0088] From the above, the obtained mapping image reveals the relative abundance of active material and conductive agent within the active material-containing layer. This value is then combined with the density (g / cm³) of each material, such as the active material and flaky graphite. 3 By multiplying by the unit, the content of each component within the electrode, including the content of the conductive agent, can be determined.

[0089] The electrode according to the first embodiment comprises a current collector and an active material-containing layer containing at least lithium nickel cobalt manganese composite oxide as an active material. In the active material-containing layer, the specific surface area S is measured by the N2 gas adsorption method. BET And the pore specific surface area S measured by the mercury intrusion method. Hg This means 0.8 < S BET / S Hg The relationship <2.0 is satisfied. Volume resistivity R of the active material-containing layer. V However, it is 10 Ω·cm or less, and the interfacial resistance R at the interface between the current collector and the active material-containing layer I However, 0.5Ω·cm ２ The following applies. And the interfacial resistance R I Volume resistivity R V Ratio R V / R I However, 3 cm －１ 20cm or more －１ The following is true: This electrode enables the creation of a battery with excellent lifespan performance, exhibiting superior capacity retention and suppressed resistance increase.

[0090] (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.

[0091] 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.

[0092] 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.

[0093] Furthermore, such a battery may further comprise an outer casing that houses the electrode group and the electrolyte.

[0094] 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.

[0095] 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.

[0096] The positive electrode, negative electrode, electrolyte, separator, outer casing, positive electrode terminal, and negative electrode terminal will be described in detail below.

[0097] (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.

[0098] 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.

[0099] (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.

[0100] Materials The following describes materials that can be used in the negative electrode active material-containing layer and the negative electrode current collector.

[0101] <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.

[0102] 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.

[0103] <Negative electrode active material> The negative electrode is 0.4 V (vs. Li / Li + It is preferable to include a negative electrode active material that allows for the insertion and removal of lithium ions at a potential of ) or higher. In the battery according to the second embodiment, which is equipped with such a negative electrode, the deposition of lithium due to charging and discharging can be suppressed. Therefore, such a battery has superior rapid charge and discharge performance.

[0104] 0.4 V (vs. Li / Li + For example, Li 4+x Ti5O 12 Lithium titanate having a spinel-type crystal structure (where x changes in the range of -1 ≤ x ≤ 3 due to charge-discharge reactions), and Li having a ramsdellite-type crystal structure 2+xExamples include Ti3O7 (where x changes in the range of -1 ≤ x ≤ 3 due to charge-discharge reactions), and metal composite oxides containing Ti and at least one selected from the group consisting of P, V, Sn, Cu, Ni, and Fe. Examples of metal composite oxides containing Ti and at least one selected from the group consisting of P, V, Sn, Cu, Ni, and Fe include TiO2-P2O5, TiO2-V2O5, TiO2-P2O5-SnO2, and TiO2-P2O5-MeO (where Me is at least one element selected from the group consisting of Cu, Ni, and Fe). These metal composite oxides are transformed into lithium titanium composite oxides by the insertion of lithium during charging. Among lithium titanium composite oxides, spinel-type lithium titanate is preferred due to its excellent cycle performance.

[0105] The negative electrode may also contain other active materials, such as carbonaceous materials and metallic compounds.

[0106] Examples of carbonaceous materials include natural graphite, artificial graphite, coke, vapor-grown carbon fibers, mesophase-pitch carbon fibers, spherical carbon, and resin-fired carbon. More preferred carbonaceous materials include vapor-grown carbon fibers, mesophase-pitch carbon fibers, and spherical carbon. Preferably, the carbonaceous material has a (002) plane interplanar spacing d002 of 0.34 nm or less, as determined by X-ray diffraction.

[0107] 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.

[0108] 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.

[0109] 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).

[0110] 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.

[0111] As an example of an orthorhombic titanium-containing composite oxide, Li 2+a M4 2-x Ti 6-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.

[0112] 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.

[0113] <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.

[0114] <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.

[0115] <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.

[0116] The shape of the negative electrode current collector can be varied depending on the application of the battery using the negative electrode.

[0117] 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.

[0118] <Manufacturing Method> The negative electrode can be manufactured, for example, by the following method.

[0119] 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.

[0120] (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.

[0121] (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.

[0122] 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.

[0123] 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.

[0124] Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC); linear carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 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.

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

[0126] (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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] An example of such a battery will be described with reference to Figures 2 and 3. The flat-type battery shown in Figure 2 comprises a flat-shaped wound electrode group 1, an outer casing member 2, a positive electrode terminal 7, a negative electrode terminal 6, and an electrolyte (not shown). The outer casing member 2 is a bag-shaped outer casing member made of laminate film. The wound electrode group 1 is housed in the outer casing member 2. As shown in Figure 3, the wound electrode group 1 includes a positive electrode 3, a negative electrode 4, and a separator 5, and is formed by spirally winding a laminate made by stacking the negative electrode 4, separator 5, positive electrode 3, and separator 5 from the outside in that order, and then press molding it.

[0131] 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.

[0132] As shown in Figure 2, near the outer edge of the wound electrode group 1, the positive electrode terminal 7 is connected to the positive electrode 3. The negative electrode terminal 6 is connected to the negative electrode 4 in the outermost layer. Both the positive electrode terminal 7 and the negative electrode terminal 6 extend to the outside through an opening in the outer casing member 2.

[0133] The battery in question is not limited to the configurations shown in Figures 2 and 3, but can also have a configuration like the one shown in Figure 4.

[0134] In the rectangular battery shown in Figure 4, the wound electrode group 11 is housed in a bottomed rectangular cylindrical metal container 12, which serves as the outer casing. A rectangular lid 13 is welded to the opening of the container 12. The flattened wound electrode group 11 may have a configuration similar to that of the wound electrode group 1 described with reference to Figures 2 and 3, for example.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] (Third Embodiment) According to the third embodiment, a battery pack is provided. This battery pack comprises the battery according to the second embodiment.

[0141] 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.

[0142] Next, an example of a battery pack according to the third embodiment will be described with reference to the drawings.

[0143] Figure 5 is an exploded perspective view of an example battery pack according to the second embodiment. Figure 6 is a block diagram showing the electrical circuit of the battery pack in Figure 5.

[0144] The battery pack 20 shown in Figures 5 and 6 comprises a plurality of individual cells 21. Each individual cell 21 may be a flat-type battery, an example of the second embodiment described with reference to Figure 4.

[0145] Multiple individual cells 21 are stacked so that their outwardly extending negative terminals 51 and positive terminals 61 are aligned in the same direction, and then fastened together with adhesive tape 22 to form a battery pack 23. These individual cells 21 are electrically connected in series with each other, as shown in Figure 6.

[0146] The printed circuit board 24 is positioned opposite the side from which the negative terminal 51 and positive terminal 61 of the single cell 21 extend. As shown in Figure 6, the printed circuit board 24 is equipped with a thermistor 25, a protection circuit 26, and terminals 27 for supplying power to external devices. An insulating plate (not shown) is attached to the side of the printed circuit board 24 that faces the battery pack 23 to avoid unnecessary connections with the wiring of the battery pack 23.

[0147] 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.

[0148] The thermistor 25 detects the temperature of the individual cell 21, and the detection signal is transmitted to the protection circuit 26. The protection circuit 26 can shut off the positive side wiring 34a and the negative side wiring 34b between the protection circuit 26 and the terminal 27 for supplying power to external devices under predetermined conditions. An example of a predetermined condition is when the temperature detected by the thermistor 25 exceeds a predetermined temperature. Another example of a predetermined condition is when overcharging, over-discharging, overcurrent, etc., of the individual cell 21 is detected. This detection of overcharging, etc., is performed for individual cell 21 or for the entire battery pack 23. When detecting individual cell 21, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each individual cell 21. In the battery pack 20 of Figures 5 and 6, wiring 35 for voltage detection is connected to each individual cell 21. Detection signals are transmitted to the protection circuit 26 through these wirings 35.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] Figures 5 and 6 show a configuration in which the single cells 21 are connected in series, but they may be connected in parallel to increase the battery capacity. Furthermore, assembled battery packs can also be connected in series and / or in parallel.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] (Example 1) <Fabrication of the positive electrode> Lithium nickel cobalt manganese composite oxide LiNi with an average primary particle diameter of 5.0 μm was used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2, acetylene black (AB) as the first conductive agent, flake graphite (FG) as the second conductive agent, and polymeric polyvinylidene fluoride (PVdF) with a modified group as a binder were prepared. The prepared materials were mixed in N-methylpyrrolidone to obtain a slurry for cathode fabrication. The mass ratios of the cathode active material, first conductive agent, second conductive agent, and binder added to the N-methylpyrrolidone were 89 parts by mass, 3.3 parts by mass, 3.7 parts by mass, and 4 parts by mass, respectively. The obtained slurry was applied to both sides of a strip-shaped aluminum foil (current collector) with a thickness of 12 μm, at a rate of 80 g / m² per unit area. 2 The material was applied and dried. During application, an uncoated portion was left on the aluminum foil to serve as a current-collecting tab. A 10 m long dryer was used for drying, and the material was transported at a speed of 10 m / min. The resulting coating was pressed together with the current collector to obtain an active material-containing layer with a thickness of 25 μm per side. Thus, the positive electrode was fabricated.

[0157] <Fabrication of the negative electrode> Lithium titanate (Li4Ti5O) of the spinel type is used as the negative electrode active material. 12 Scale-like graphite was prepared as a conductive agent, and PVdF as a binder. The prepared materials were mixed 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, at a rate of 100 g / m² per unit area. 2 The coating was applied and dried. During application, an uncoated portion was left on the aluminum foil to serve as a current-collecting tab. The resulting coating film had a density of 2.5 g / cm³. ３ The current collector was pressed together to obtain the active material-containing layer. Thus, the negative electrode was fabricated.

[0158] <Fabrication of Electrode Group> The positive and negative electrodes fabricated as described above were stacked with a 10 μm thick separator in between. The resulting laminate was wound up so that the negative electrode was located on the outermost periphery. The electrode group obtained by winding was pressed while being heated to 80°C and fixed with insulating tape. Thus, a flat-shaped wound electrode group comprising a positive electrode, a negative electrode, and a separator positioned between the positive and negative electrodes was obtained.

[0159] <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.

[0160] <Battery Assembly> The flattened electrode group obtained as described above was inserted into a bottomed rectangular cylindrical can made of 0.3 mm thick aluminum. The opening of the can was sealed with a sealing plate, and the electrode group was housed inside the 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 secondary battery.

[0161] (Examples 2 to 4) In Examples 2 to 4, batteries were manufactured in the same manner as in Example 1, except that the amounts of acetylene black (AB) and flake graphite (FG) used in the first and second conductive agents of the positive electrode were changed as shown in Table 2. The change in the amount of conductive agent altered the pressability of the coating film of the slurry for manufacturing the positive electrode, and the thickness of the positive electrode active material-containing layer per side of the current collector became the values ​​shown in Table 2.

[0162] (Example 5) In Example 5, the battery was manufactured in the same manner as in Example 1, except that the proportions of AB and FG used in the positive electrode were changed as shown in Table 2, and the dispersion conditions of the slurry for manufacturing the positive electrode and the press load of the active material-containing layer were adjusted to change the design of the positive electrode active material-containing layer to those shown in Tables 1 and 2. The design of the positive electrode active material-containing layer was as shown in Tables 1 and 2, with a pore specific surface area S determined by the mercury intrusion method. Hg , specific surface area S by nitrogen gas adsorption method (BET method) BET The thickness of the positive electrode active material-containing layer per side of the current collector was adjusted.

[0163] (Examples 6 and 7) In Examples 6 and 7, batteries were manufactured in the same manner as in Example 1, except that the amount of slurry for positive electrode production applied to the current collector was changed. By changing the amount of slurry for positive electrode production applied, a positive electrode active material-containing layer with a thickness per side of the current collector was obtained, as shown in Table 2.

[0164] (Comparative Example 1) In Comparative Example 1, a battery was manufactured in the same manner as in Example 1, except that the proportions of AB and FG used in the positive electrode were changed as shown in Table 2, and the dispersion conditions of the slurry for manufacturing the positive electrode and the press load of the active material-containing layer were adjusted to change the design of the positive electrode active material-containing layer to those shown in Tables 1 and 2.

[0165] (Comparative Example 2) In Comparative Example 2, a battery was prepared in the same manner as in Example 1, except that carbon nanotubes (CNTs) were used instead of FG as the conductive agent for the positive electrode, and the amounts of CNTs and AB were changed as shown in Table 2.

[0166] (Comparative Example 3) In Comparative Example 3, a battery was manufactured in the same manner as in Example 1, except that the amount of slurry for positive electrode production applied to the current collector was significantly increased compared to Example 1. By changing the amount of slurry for positive electrode production applied, a positive electrode active material-containing layer with a thickness per side of the current collector was obtained, as shown in Table 2.

[0167] (Comparative Examples 4 and 5) In Examples 4 and 5, batteries were prepared in the same manner as in Example 1, except that the proportions of AB and FG used in the positive electrode were changed as shown in Table 2.

[0168] Tables 1 and 2 below summarize the design of the positive electrode active material-containing layer in each example and comparative example. The design of the active material-containing layer is based on the specific surface area S measured by the nitrogen gas adsorption method (BET method) described above. BET , the pore specific surface area S measured by the mercury intrusion method described above Hg , and their ratio S BET / S Hg This is shown in Table 1. Table 2 shows the mass parts of the first and second conductive agents used in the positive electrode active material-containing layer, and the volume resistivity R of the positive electrode active material-containing layer measured by the method described above. V The interfacial resistivity R between the positive electrode active material-containing layer and the positive electrode current collector, as measured by the method described above. I , their ratio R V / R I This also shows the thickness of the positive electrode active material-containing layer per side of the current collector.

[0169]

[0170]

[0171] <Cycle Testing> Cycle testing was performed on each of the manufactured batteries as follows.

[0172] First, the battery was charged at a current of 1C in a 25°C environment until its State of Charge (SOC) reached 100%. Then, the battery was discharged at a current of 0.2C until its SOC reached 0%, and the discharge capacity was measured. Subsequently, the battery was charged at a current of 1C until its SOC reached 50%, and the charging resistance (in mΩ) was measured.

[0173] 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 25°C environment for 2000 charge-discharge cycles. After the 2000th discharge cycle, the discharge capacity and charging resistance were measured again using the same procedure as before the charge-discharge cycle.

[0174] The capacity retention rate was calculated from the discharge capacity before and after 2000 charge-discharge cycles using the following formula: Capacity retention rate (unit: %) = [Discharge capacity after cycle / Discharge capacity before cycle] × 100%. In addition, the resistance increase rate was calculated from the discharge resistance values ​​before and after 2000 charge-discharge cycles using the following formula: Resistance increase rate (unit: %) = [Charging resistance value after cycle / Charging resistance value before cycle] × 100%. The calculated results are shown in Table 3 below.

[0175]

[0176] Table 3 shows that the batteries fabricated in Examples 1 to 7 achieve both excellent capacity retention and suppression of resistance increase. On the other hand, Comparative Examples 1 to 5 show that either capacity retention, resistance increase suppression, or both are inferior compared to Examples 1 to 7. In Examples 1 to 7, the ratio of pore specific surface area to pore volume using the single-crystal nickel-cobalt-manganese composite oxide in the positive electrode active material layer is 0.8 < S. BET / S Hg In a positive electrode active material-containing layer satisfying <2.0, the interfacial resistance R between the active material-containing layer and the current collector I The volume resistivity R of the active material-containing layer itself V The ratio is 3 cm -1 ≤R V / R I ≤20 cm -1 We were able to achieve a uniform electrical resistance that satisfies the following conditions. By doing so, we were able to appropriately control the penetration of the electrolyte into the positive electrode active material-containing layer and the electrode reaction area, while suppressing localized degradation of the positive electrode active material-containing layer.

[0177] On the other hand, the batteries of Comparative Examples 1 to 5 did not satisfy any of the above conditions in the positive electrode active material-containing layer, and either the capacity retention rate or the suppression of resistance increase, or both, were inferior compared to Examples 1 to 7.

[0178] Specifically, in Comparative Example 1, S Hg S for BET The ratio was 2.1. Therefore, it can be seen that the positive electrode active material obtained in Comparative Example 1 had many micropores and secondary particles were formed due to polycrystalline structure. In Comparative Example 1, the capacity retention rate was considerably low. It was confirmed that the large specific surface area of ​​the polycrystalline positive electrode active material led to performance degradation due to side reactions between the positive electrode and the electrolyte.

[0179] In Comparative Example 2, carbon nanotubes (CNTs) were used instead of flake graphite as the second conductive agent for the positive electrode. Because CNTs have a fibrous shape, they can connect active material particles within the active material-containing layer to form wide conductive paths, similar to flake graphite, thereby increasing the volume resistivity R of the active material-containing layer. V The interfacial resistance R between the active material layer and the current collector is decreasing. However, at the same time, CNTs can penetrate into the fine gaps between the active material, just like acetylene black, so the interfacial resistance R between the active material layer and the current collector is decreasing. I R has also decreased significantly. V / R I The ratio had increased significantly. As a result, the current within the positive electrode active material layer was biased towards the interface with the current collector, and the non-uniform charging and discharging within the active material layer led to a decrease in capacity retention.

[0180] In Comparative Example 3, a large amount of slurry was applied to form a thick positive electrode active material layer, which resulted in a strong influence from the migration of the binder during slurry drying, thus affecting the interfacial resistance R between the active material layer and the current collector. I This is reflected in a significant increase in the interfacial resistance R. Specifically, acetylene black does not remain near the interface, and the interfacial resistance R I The resistance increased. Due to the high interfacial resistance, current did not flow easily from the current collector to the positive electrode active material layer, and the active material layer deteriorated during charging and discharging, resulting in unfavorable results in terms of both capacity retention rate and resistance increase rate.

[0181] In Comparative Example 4, the amount of acetylene black added to the positive electrode was small, resulting in a low interfacial resistance R. I R increases V / R I The ratio is 3 cm -1 It fell below that level. Therefore, in Comparative Example 4 as well, current did not flow easily from the current collector to the positive electrode active material-containing layer, and the active material-containing layer deteriorated during charging and discharging, resulting in unsatisfactory capacity retention and resistance increase rates.

[0182] In Comparative Example 5, the amount of flake graphite added to the positive electrode was small, resulting in a low volume resistivity R of the active material-containing layer. V As R increases, V / R I The ratio is 20 cm -1 This exceeded the limit. Consequently, current flowed poorly through the positive electrode active material-containing layer, and the current concentrated near the interface with the current collector. This resulted in localized degradation of the electrode material near the interface, leading to an increase in the resistance increase rate.

[0183] According to the one or more embodiments and examples described above, an electrode is provided. The electrode comprises an active material-containing layer containing lithium nickel cobalt manganese composite oxide as the active material and a current collector. In the active material-containing layer, the specific surface area S measured by the N2 gas adsorption method BET and the pore specific surface area S measured by the mercury intrusion method Hg toga 0.8 < S BET / S Hg The volume resistivity R of the active material-containing layer satisfies the relationship <2.0 and is 10 Ω·cm or less. V And, 0.5Ω·cm ２ The interfacial resistance R at the interface between the current collector and the active material-containing layer is as follows: I And, 3 cm －１ Above ≤ R V / R I ≤20cm －１ The following relationship is satisfied. The above electrodes can provide batteries and battery packs with excellent lifespan performance.

[0184] 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.

[0185] Several embodiments of the present invention are described below. [1] A current collector and an active material containing an active material and a conductive agent located on the current collector, wherein the active material contains a lithium nickel cobalt manganese composite oxide, and the specific surface area S of the active material containing layer is determined by nitrogen gas adsorption. BET and the specific surface area S of the pores of the active material-containing layer by the mercury intrusion method. Hg 0.8 < S BET / S Hg The relationship <2.0 is satisfied, and the volume resistivity R of the active material-containing layer V The interfacial resistance R of the interface between the current collector and the active material-containing layer is 10 Ω·cm or less. I 0.5Ω·cm ２ The following is the interfacial resistance R I The volume resistivity R V Ratio R V / R I 3cm －１ 20cm or more －１ The electrodes are as follows: [2] The conductive agent contains at least flake graphite, and the content of the flake graphite in the active material-containing layer is 3% by mass or more relative to the mass of the active material-containing layer, as described in [1]. [3] The electrode according to [1] or [2], wherein the thickness of the active material-containing layer is 10 μm or more and 60 μm or less. [4] The lithium nickel cobalt manganese composite oxide is Li a Ni (1-b-c-d) Co b Mn c M dAn electrode according to any one of [1] to [3], 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. [5] A battery comprising the electrode according to any one of [1] to [4] and an electrolyte. [6] A battery pack comprising the battery according to [5].

[0186] 1...Electrode group, 2...Outer casing, 3...Positive electrode, 3a...Positive electrode current collector, 3b...Positive electrode active material containing layer, 4...Negative electrode, 4a...Negative electrode current collector, 4b...Negative electrode active material containing layer, 5...Separator, 6...Negative electrode terminal, 7...Positive electrode terminal, 11...Electrode group, 12...Container, 13...Rectangular lid, 14...Negative electrode 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, 2 3...Battery pack, 24...Printed circuit board, 25...Thermistor, 26...Protection circuit, 27...Terminal for supplying power to external devices, 28...Positive lead, 29...Positive connector, 30...Negative lead, 31...Negative connector, 32...Wiring, 33...Wiring, 34a...Positive wiring, 34b...Negative wiring, 35...Wiring, 36...Protective sheet, 37...Storage container, 38...Lid, 51...Negative terminal, 61...Positive terminal.

Claims

1. A collector and a active material-containing layer provided on the collector and containing an active material and a conductive agent, the active material includes a lithium nickel cobalt manganese composite oxide, and the specific surface area S of the active material-containing layer by the nitrogen gas adsorption method BET and the pore specific surface area S of the active material-containing layer by the mercury intrusion method Hg satisfy the relationship of 0.8 < S BET / S Hg < 2.0, and the volume resistivity R of the active material-containing layer V is 10 Ω·cm or less, and the interfacial resistance R at the interface between the collector and the active material-containing layer I is 0.5 Ω·cm ２ or less, and the ratio R of the volume resistivity R to the interfacial resistance R I V is V R I / R －１ is 3 cm －１ or more and 20 cm or less.​ 2. The electrode according to claim 1, wherein the conductive agent comprises at least flake graphite, and the content of the flake graphite in the active material-containing layer is 3% by mass or more relative to the mass of the active material-containing layer.

3. The electrode according to claim 1 or 2, wherein the thickness of the active material-containing layer is 10 μm or more and 60 μm or less.

4. The lithium nickel cobalt manganese composite oxide is Li a Ni (1-b-c-d) Co b Mn c M d The electrode according to claim 1 or 2, 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.

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

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

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