Electrodes, batteries, and battery packs

Abstract

According to an embodiment, an electrode is provided, comprising a current collector and an active material layer located on the current collector. The active material layer contains an active material and a conductive agent. The active material comprises a lithium nickel cobalt manganese composite oxide. The specific surface area S of the active material layer obtained by nitrogen adsorption is... BET The specific surface area S of the micropores containing the active material layer obtained by mercury intrusion porosimetry Hg Satisfying 0.8 BET / S Hg The relationship is <2.0. The volume resistivity R of the layer containing the active material is... V The interfacial resistance R at the interface between the current collector and the layer containing the active material is below 10 Ω·cm. I 0.5Ω·cm 2 Below. Volume resistivity R V With interface resistance R I The ratio of R V / R I 3cm ‑1 Above and 20cm ‑1 the following.​

Description

Technical Field

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

[0002] Secondary batteries, including non-aqueous electrolyte secondary batteries such as lithium-ion batteries, are not only used in electronic devices such as mobile phones, but in recent years they have also been expected to be used in hybrid electric vehicles, electric vehicles, and large systems such as electric aircraft and energy storage. Therefore, secondary batteries require improved performance in terms of high capacity, high current output, and long lifespan.

[0003] Graphite is commonly used as the negative electrode active material in non-aqueous electrolyte batteries. Using a graphite negative electrode can result in batteries with high output and high energy density. However, it is known that lithium dendrites can easily precipitate in graphite negative electrodes due to overvoltage or other factors. These dendrites can penetrate the separator, causing internal short circuits. Furthermore, graphite undergoes stretching and contraction along the c-axis during Li insertion-extraction, leading to significant structural degradation.

[0004] Other negative electrode active materials used in non-aqueous electrolyte batteries include known spinel-type lithium titanate (Li4Ti5O4). 12 If lithium titanate is used, the precipitation of lithium dendrites can be suppressed, thus avoiding dangers such as short circuits, self-discharge and fire, and enabling the production of batteries with excellent high current output performance and lifespan.

[0005] As positive electrode active materials for non-aqueous electrolyte batteries, lithium nickel cobalt manganese oxide (LCA) offers high capacity and excellent performance. Compared to batteries using graphite-based negative electrodes, conventional batteries using LCA as the positive electrode and lithium titanate as the negative electrode exhibit superior characteristics such as rapid charge / discharge performance, long lifespan, and low-temperature performance. However, there is room for improvement in the positive electrode active material, particularly regarding lifespan performance.

[0006] In batteries using secondary particles of lithium nickel cobalt manganese oxide as the positive electrode active material, the specific surface area increases due to the expansion and contraction of the positive electrode active material caused by repeated charging and discharging during pressurization to increase the electrode density of the positive electrode, resulting in particle breakage. Furthermore, lithium nickel cobalt manganese oxide typically uses a polycrystalline system that forms secondary particles composed of finely shaped primary particles. However, compared to primary particles, the polycrystalline system has a larger surface roughness and specific surface area. For positive electrodes using such active materials, there is a problem of significant performance degradation due to easy oxidation reactions between the positive electrode and the electrolyte during high-potential charging and discharging and storage.

[0007] As a countermeasure to this problem, it is known that using single-crystal active materials with high destructive strength and low surface roughness can improve charge-discharge cycle life and rolling life. However, corresponding to the reduction in surface roughness, there is a tendency for the contact points between the active material and the conductive agent to decrease. Therefore, the contact between the active material and the conductive agent is easily broken due to the expansion and contraction of the active material during charge-discharge cycles. Within the electrode, on the one hand, current is difficult to flow in the parts where the contact between the active material and the conductive agent is broken, and on the other hand, current preferentially flows in the parts where the contact is maintained. As a result, the positive electrode potential locally increases, and the degradation of the active material easily develops into a problem.

[0008] Existing technical documents Patent documents Patent Document 1: International Publication No. 2023 / 026482 Patent Document 2: International Publication No. 2023 / 131987 Summary of the Invention

[0009] The problem that the invention aims to solve The object of the present invention is to provide an electrode for a battery that achieves excellent lifespan performance, a battery having the electrode, and a battery pack having the battery.

[0010] Methods for solving problems According to an embodiment, an electrode is provided, comprising a current collector and an active material layer located on the current collector. The active material layer contains an active material and a conductive agent. The active material comprises a lithium nickel cobalt manganese composite oxide. The specific surface area S of the active material layer obtained by nitrogen adsorption is... BET The specific surface area S of the micropores containing the active material layer obtained by mercury intrusion porosimetry Hg Satisfying 0.8 BET / S Hg The relationship is <2.0. The volume resistivity R of the layer containing the active material is... V The interfacial resistance R at the interface between the current collector and the layer containing the active material is below 10 Ω·cm. I 0.5Ω·cm 2 The following is the volume resistivity R. V With interface resistance R I The ratio of R V / R I 3cm -1 Above and 20cm -1 the following.

[0011] According to another embodiment, a battery is provided which includes the electrodes and electrolyte.

[0012] According to yet another embodiment, a battery pack is provided which includes the battery. Attached Figure Description​

[0013] Figure 1 This is a top view of an electrode that schematically illustrates one example of an embodiment.

[0014] Figure 2 This is a cross-sectional view of a battery cut along the thickness direction, representing one example of an implementation.

[0015] Figure 3 yes Figure 2 An enlarged sectional view of part A.

[0016] Figure 4 This is a partial cross-sectional perspective view of the battery, which is another example of the implementation method.

[0017] Figure 5 This is an exploded perspective view of a battery pack, representing one example of an implementation method.

[0018] Figure 6 It is shown Figure 5 The diagram shows a block diagram of the battery pack circuit. Detailed Implementation

[0019] In lithium-ion secondary battery cathodes using conventional lithium-metal composite compounds as positive electrode active materials, active materials with low surface roughness are sometimes used to improve cathode lifespan performance, thus reducing the likelihood of side reactions. However, when using active materials such as single crystals with low surface roughness, not only are there fewer contact points with the conductive agent and current collector, but electrical contact is also easily lost due to the expansion and contraction of the cathode during battery charging and discharging. In such cathodes, current preferentially flows through the areas where the contact between the active material and the conductive agent remains good, potentially causing a localized rise in cathode potential. Therefore, there is a tendency for increased resistance and significant gas generation to occur due to the degradation of the positive electrode active material in the areas with higher cathode potentials.

[0020] Furthermore, if the interfacial resistance between the layer containing the active material and the current collector is high, current will have difficulty flowing through the active material within the active material layer, accelerating battery degradation. Typically, the active material and the current collector are bonded together with an adhesive, and the conductive agent is distributed at this bonded area or directly contacts the current collector, thereby ensuring conductivity. Even when using active materials with low surface roughness, such as single-crystal active materials, the number of contact points with the conductive agent and current collector remains relatively small, leading to increased interfacial resistance.

[0021] On the other hand, as a countermeasure to the aforementioned problem, one approach is to increase the amount of conductive agent. In particular, it is known that adding large amounts of carbon black and carbon nanotubes, which have small particle sizes and are easily distributed in the fine gaps at the current collector / active material layer interface, can reduce interfacial resistance. However, even with aggressive reduction of interfacial resistance, if the interfacial resistance is significantly lower than the volume resistivity of the active material layer itself, current can easily flow near the interface, while in other parts of the active material layer, current flow becomes difficult. Therefore, especially during high-rate cycling, large currents easily flow through the active material near the interface, leading to a localized increase in the positive electrode potential and a tendency for the active material to deteriorate.

[0022] The issues can be summarized as follows. From a lifetime performance perspective, lithium nickel cobalt manganese oxide (LiCO) is preferably a single-crystal cathode active material with excellent high-capacity performance. However, due to its low surface roughness, contact with conductive agents can easily cause problems. Furthermore, the contact between the single-crystal active material and the current collector is also prone to breakage, easily leading to an increase in interfacial resistance. On the other hand, even if a large amount of carbon black, carbon nanotubes, or other conductive agents are added to reduce the interfacial resistance, a difference between the resistance of the active material layer and the interfacial resistance can easily occur, resulting in a deterioration in lifetime performance.

[0023] Hereinafter, embodiments will be described with reference to the accompanying drawings. Furthermore, common structures will be labeled with the same reference numerals in the embodiments, and repeated descriptions will be omitted.

[0024] In addition, the figures are schematic diagrams used to facilitate the explanation and understanding of the embodiments. Their shapes, sizes, proportions, etc. may differ from the actual devices, but they can be appropriately modified with reference to the following description and known techniques.

[0025] (First Implementation) According to a first embodiment, an electrode is provided. The electrode includes a current collector and an active material layer thereon. The active material 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 layer is determined by nitrogen adsorption. BET The specific surface area of ​​the pores, S, determined by mercury intrusion porosimetry Hg Satisfying 0.8 BET / S Hg The relationship is <2.0. The volume resistivity R of the layer containing the active material is... V The interfacial resistance R at the interface between the current collector and the layer containing the active material is below 10 Ω·cm. I 0.5Ω·cm 2 The following is the volume resistivity R. V With interface resistance R I The ratio of R V / R I 3cm​-1 Above and 20cm -1 the following.

[0026] The electrode in this embodiment can be a battery electrode. Examples of batteries that may include this electrode include secondary batteries such as lithium-ion batteries. Secondary batteries include those containing a non-aqueous electrolyte. This electrode can be, for example, a positive electrode for a battery.

[0027] The electrode conforming to the aforementioned configuration is an electrode using a single-crystal lithium nickel cobalt manganese composite oxide (NCM). Compared to cathodes using secondary particle NCMs with varying surface structures and surface areas due to differences in the aggregation mode of primary particles, this electrode exhibits fewer micropores and a more uniform surface condition. Therefore, the specific surface area obtained by nitrogen adsorption and mercury infiltration methods is comparable. Furthermore, when comparing the pore volume obtained by mercury infiltration between single-crystal and secondary particle types, the value is smaller for the single-crystal type, which has fewer pores. The specific surface area S obtained by nitrogen adsorption (as described later, based on the BET (Brunauer, Emmett, Teller) method) is... BET Compared with the pore specific surface area S obtained by mercury intrusion porosimetry Hg The ratio of S BET / S Hg The closer the specified value is to 1.0 for single-crystal NCM, the better its lifetime performance. Compared to secondary particle NCM, single-crystal NCM has fewer micropores and a more uniform surface, therefore, it exhibits S... BET / S Hg The value tends to be close to 1.0. By controlling the electrode density using single-crystal NCM, whose specific surface area remains constant regardless of the measurement method, the contact area with the electrolyte can be controlled, thereby improving battery performance.

[0028] For a layer containing active substances, if the specific surface area S measured by nitrogen adsorption method is... BET Compared with the pore specific surface area S determined by mercury intrusion porosimetry Hg The ratio of S BET / S Hg At 0.8 BET / S Hg Within the range of <2.0, the effective surface area conducive to electrode reaction can be accurately controlled, and resistance can be reduced while gas generation is suppressed. That is, by satisfying the above relationship, the specific surface area of ​​the active material can be reduced, and in particular, the oxidation reaction between the electrode and electrolyte, which is a significant problem during high-potential charge-discharge cycles and storage, can be suppressed, resulting in an electrode with good lifespan performance.

[0029] The specific surface area S, measured by nitrogen adsorption method, is for the layer containing active substances. BET ​In this process, the specific surface area of ​​micropores and mesopores with diameters ranging from approximately 0.1 nm to 100 nm within the electrode is primarily reflected. In contrast, the specific surface area of ​​fine pores, S, measured by mercury intrusion porosimetry, is... Hg This mainly reflects the specific surface area of ​​mesopores and macropores with diameters of approximately 1 nm to 1 mm within the pores of the active material layer. That is, the ratio S between the two is... BET / S Hg This becomes an indicator of the ratio of micropores to macropores in an electrode. 0.8>S BET / S Hg or S BET / S Hg When the specific surface area is greater than 2.0, micropores or macropores can exist in large quantities. In this case, it is difficult to control the effective surface area that facilitates side reactions between the active material and the electrolyte (liquid electrolyte), and the reaction area increases, thus increasing the resistance. A more preferable specific surface area is S0. BET Compared with the specific surface area S of fine pores Hg The ratio satisfies 0.85 BET / S Hg The relationship is <1.15. For electrodes with a specific surface area difference of less than 15%, the electrode reaction area is further controlled, which can more significantly reduce the resistance.

[0030] The specific surface area S containing the active material layer, as determined by nitrogen adsorption. BET Preferably at 1.0m 2 / g≤S BET ≤5.0m 2 Within the range of / g. If the specific surface area S BET 1.0m 2 A specific surface area of ​​S > 1 g promotes electrolyte penetration and improves output and lifespan performance. BET It is 5.0m 2 Below a certain value (e.g.), the increased contact between active material particles and between the active material and the conductive agent further reduces resistance and improves high-current output performance. Additionally, the mechanical stability of the electrode increases. The specific surface area S obtained by the nitrogen adsorption method... BET Electrodes meeting the aforementioned range can improve the contact between the active material and the conductive agent and reduce resistance, enabling the fabrication of batteries with excellent input / output performance. Furthermore, it is preferable that the active material layer also has a content exceeding 3.0 g / cm³. 3 And less than 3.6 g / cm 3 The preferred density. More preferably, the specific surface area S obtained by nitrogen adsorption method containing a positive electrode active material layer. BET At 2.5m 2 / g≤S BET ≤3.0m 2 ​Within the range of / g. In a more preferred range, the active material, conductive agent, and binder are well dispersed, and the electrode density can be easily and appropriately controlled, enabling the fabrication of batteries with low resistance and high input / output performance.

[0031] The electrode comprises a current collector and an active material layer (electrode mixture layer). The current collector may be, for example, in the shape of a foil, a strip, or a plate. The active material layer may be disposed on at least one main surface of the current collector. That is, the current collector may have the active material layer on one side or both the front and back sides. The current collector may include a portion of its surface that does not have the active material layer. This portion may function as a current collector tab. Alternatively, the electrode may also include a current collector tab disposed separately from the current collector.

[0032] The active material layer contains active material and conductive agent. In addition to active material and conductive agent, the active material layer may also contain binder. The binder can be incorporated to bind the dispersed active materials together and to bind the active materials to the current collector.

[0033] For this electrode, the volume resistivity R of the active material layer is... V The interfacial resistance R at the interface between the current collector and the layer containing the active material is below 10 Ω·cm. I 0.5Ω·cm 2 The following describes the electrode. Although a single-crystal active material with low surface roughness is used, the contact between the active material and the conductive agent is good, and contact interruption due to expansion and contraction during charge-discharge cycles is less likely. Therefore, an electrode with good lifespan performance can be obtained.

[0034] Furthermore, regarding this electrode, the volume resistivity R of the active material layer is... V The interfacial resistance R between the current collector and the layer containing the active material I The ratio of R V / R I Meets 3cm -1 ≤R V / R I ≤20cm -1 The relationship. For electrodes that satisfy this relationship, the volume resistivity R... V With interface resistance R I The balance is good, and the following current bias is unlikely to occur: during battery charging and discharging, current flows more easily in the active material near the current collector / active material layer interface than in the active material in other locations. Therefore, by satisfying this relationship, localized degradation of the active material near the interface can be suppressed, thus obtaining an electrode exhibiting good cycle performance.

[0035] The thickness of the active material layer is preferably 10 μm or more and 60 μm or less. Electrodes containing an active material layer with a thickness of 10 μm or more can have high capacity. For active material layers with a thickness of 60 μm or less, the aforementioned volume resistivity R is easily achieved. V With interface resistance R I Achieving a well-balanced distribution of conductive agents.

[0036] The active material layer may contain Li a Ni (1-b-c-d) Co b Mn c M d O2 represents a lithium nickel cobalt manganese composite oxide as the active material. The subscripts in the formula are in the ranges of 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.

[0037] The active material can have an average primary particle size of 2 μm or more and 7 μm or less. In the active material layer, by setting the primary particle size of the active material particles to 2 μm or more and 7 μm or less, the battery's lifespan performance can be improved. By setting the primary particle size to 2 μm or more, the specific surface area of ​​the electrode is reduced, which can decrease the impact of side reactions between the electrode and the electrolyte on lifespan performance. Furthermore, by setting the primary particle size to 7 μm or less, the diffusion of lithium ions within the solid state of the particles becomes more uniform, further suppressing localized structural degradation and improving lifespan performance. More preferably, the primary particle size is set to 3 μm or more and 4.5 μm or less. Within a more preferred range, by preventing the aggregation or isolation of primary particles, lifespan performance can be further improved.

[0038] In addition, the specific surface area of ​​the active material is preferably 0.5 m². 2 / g or more and 2.0m 2 / g or less. The specific surface area of ​​the active material mentioned here refers to the specific surface area measured by nitrogen adsorption method for the individual, unlayered active material particles. If the specific surface area of ​​the active material is 0.5m²... 2 When the specific surface area of ​​the active material is above a certain value (e.g., g), the contact area between the active material and the conductive agent increases, thus improving output performance. If the specific surface area of ​​the active material is 2.0 m², this is beneficial. 2 When the specific surface area of ​​the active material is below a certain value (e.g., g / g), the contact area between the active material and the electrolyte is limited to a suitable size, side reactions are suppressed, and therefore the resistance is less likely to increase. Therefore, by setting the specific surface area of ​​the active material particles to 0.5 m² / g... 2 / g or more and 2.0m 2A specific surface area of ​​less than 0.5 m² / g allows for an appropriate contact area between the active material and the electrolyte, enabling the fabrication of electrodes and batteries with low resistance and excellent lifespan. More preferably, the specific surface area of ​​the active material is 0.5 m² / g. 2 / g or more and 1.0m 2 / g or less. Within a more preferred range, the contact area between the active material and the electrolyte can be easily controlled, making it easy to obtain electrodes with low resistance and excellent lifespan performance.

[0039] Material Next, the active material layer and the materials that can be used in the current collector of the electrode in the first embodiment will be described.

[0040] <Contains active substance layer> As described above, the active material layer may contain a binder in addition to the active material and the conductive agent. The preferred proportions of the active material, conductive agent, and binder in the active material layer are: active material 80% to 95% by mass, conductive agent 0.5% to 18% by mass, and binder 0.5% to 17% by mass.

[0041] <Active Substances> The active material layer contains a lithium nickel cobalt manganese composite oxide as the active material. Preferably, the lithium nickel cobalt manganese composite oxide contains the aforementioned Li... a Ni (1-b-c-d) Co b Mn c M d O2. Furthermore, an active material comprising the lithium nickel cobalt manganese composite oxide and having an average primary particle size of 2 μm or more and 7 μm or less is more preferred. Alternatively, the lithium nickel cobalt manganese composite oxide may be used as the first active material, and a second active material may be further included in the active material layer. Of course, the first active material may be used alone, or it may be used without the first active material but containing one or more second active materials.

[0042] As secondary active materials, various oxides can be cited, such as lithium cobalt composite oxides (e.g., LiCoO2), manganese dioxide, lithium manganese composite oxides (e.g., LiMn2O4, LiMnO2), lithium nickel composite oxides (e.g., LiNiO2), and lithium nickel cobalt composite oxides (e.g., LiNi). 0.8 Co 0.2 O2), lithium iron oxides, lithium vanadium oxides, titanium disulfide, molybdenum disulfide, and other chalcogenides, etc. The electrode may contain one of these compounds as a second active material, or it may contain two or more of these compounds as a second active material.

[0043] The proportion of the first active substance in the total mass of the active substance contained in the active substance layer is preferably 75% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less.

[0044] The active substance can, for example, have a particle shape. That is, the active substance layer can contain particles of the active substance. The active substance particles can be primary particles, or a mixture of primary and secondary particles.

[0045] In the active material particles, it is preferable to have a higher proportion of primary particles and a lower proportion of secondary particles. The internal conductivity of secondary particles (within the hollow structure) is poor, and by eliminating the presence of primary particles within them, the resistance can be further reduced.

[0046] As described above, it is preferable to break down the agglomeration of secondary particles of the active material. On the other hand, it is preferable not to further pulverize the primary particles of the active material, but to maintain the particle size at 2 μm or more. By not breaking the primary particles of the active material, an active material with a good crystal structure can be obtained, thus maintaining good lifetime performance. In addition, by making the average particle size of the active material 2 μm or more, the specific surface area of ​​the electrode can be reduced, thereby reducing the impact of side reactions between the electrode and the electrolyte on lifetime performance. On the other hand, by making the average particle size 7 μm or less, lithium ions can diffuse uniformly within the solid state of the particles, further improving lifetime performance.

[0047] <Conductive agent> The conductive agent preferably comprises 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 layer may contain one conductive agent or two or more conductive agents.

[0048] For example, it is preferable to include a conductive agent, such as carbon black or carbon nanotubes, which can be distributed in a way that fills the gaps between active materials, and a conductive agent, such as flake graphite, which, due to its relatively large particle size, can serve as a wide conductive pathway connecting multiple active material particles. The former, for example, is distributed in a way that fills the gaps between active materials during the pressing process in electrode fabrication, thus functioning as a conductive pathway between active materials. Therefore, since it can be distributed throughout the entire electrode, increasing the content of the former conductive agent can simultaneously reduce the volume resistivity R. V and interface resistance R I The latter has difficulty entering tiny gaps such as the interface between the current collector and the active material layer, and is easily distributed in the active material layer. For example, by increasing the content of flake graphite, the volume resistivity R can be preferentially reduced. VIt can suppress the breakage of the conductive pathway of single-crystal active material and reduce the volume resistivity R V With interface resistance R I The deviation from the target material causes localized degradation of the active material. Therefore, the content of flake graphite in the active material layer is preferably 3% by mass or more relative to the mass of the active material layer.

[0049] Regarding graphite, besides highly oriented flake graphite, there is also spheroidal graphite with reduced orientation. Natural graphite is flake graphite. Spheroidal graphite is obtained through spheroidization treatment.

[0050] <Adhesive> Materials containing fluorine atoms in their molecules are preferred as binders due to their excellent oxidation resistance and improved lifespan. Examples of such binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluoropolymers. Other binders include styrene-butadiene rubber, acrylic resins and their copolymers, polyacrylic acid, and polyacrylonitrile. Additionally, binders incorporating modified groups can also be used. The active material layer may contain one or more of these binders.

[0051] <Current collector> As a current collector, metal foil or alloy foil can be used, for example. Examples of metal foils include aluminum foil, stainless steel foil, and nickel foil. Examples of alloy foils include aluminum alloys, copper alloys, and nickel alloys.

[0052] Next, specific examples of the electrodes of the first embodiment will be described with reference to the accompanying drawings.

[0053] Figure 1 This is a partial cross-sectional top view schematically illustrating an example of an electrode according to an embodiment. Here, as an example of an electrode, an example positive electrode is illustrated.

[0054] Figure 1 The positive electrode 3 shown includes a positive electrode current collector 3a and a layer 3b containing positive electrode active material disposed on the surface of the positive electrode current collector 3a. The layer 3b containing positive electrode active material is supported on the main surface of the positive electrode current collector 3a.

[0055] Additionally, the positive current collector 3a includes a portion of its surface where the layer containing the positive active material 3b is not disposed. This portion functions, for example, as a positive current collector tab 3c. In the illustrated example, the positive current collector tab 3c is a narrow portion with a width narrower than the layer containing the positive active material 3b. The width of the positive current collector tab 3c can be narrower than the width of the layer containing the positive active material 3b, or it can be the same as the width of the layer containing the positive active material 3b. Alternatively, instead of using the positive current collector tab 3c as part of the positive current collector 3a, a separately disposed conductive component can be electrically connected to the positive electrode 3 and used as an electrode current collector tab (positive current collector tab).

[0056] Production method The electrodes of the first embodiment can be manufactured, for example, by the following method.

[0057] First, a primary active material (first active material) is prepared. At least one lithium nickel cobalt manganese composite oxide is used as the first active material. For example, a preferred active material comprising the lithium nickel cobalt manganese composite oxide and having an average primary particle size of 2 μm or more and 7 μm or less can be obtained as described below. A precursor using nickel, cobalt, and manganese sources is calcined. Here, if the calcination temperature is increased, the calcination time is increased, or the amount of a lithium source, represented by lithium carbonate, is increased, particle growth is promoted compared to nucleation. Therefore, it is possible to synthesize a lithium nickel cobalt manganese composite oxide with an optimized chemical composition, having a primary particle size of 2 μm or more and a nickel content ratio of at least a specified level, in a manner that promotes particle growth through optional methods.

[0058] 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 are added to a suitable dispersion medium to obtain a mixture. For example, NMP (N-methyl-2-pyrrolidone) can be used as a dispersion medium. The amounts of each material added are preferably set within the range corresponding to the previously described proportions.

[0059] Next, the resulting mixture is fed into a mixer. In this mixer, the mixture is stirred to obtain a slurry. During the stirring process, by increasing the rotational speed of the mixer, the active material and conductive agent particles can be pulverized, thereby increasing the specific surface area S of the fabricated electrode. BET The value of [value missing]. Further processing of the obtained slurry, such as by subjecting it to a pulverizer, can further disperse the active substances and conductive agents in the slurry more finely. Additionally, an optional dispersant can be used to improve the dispersibility of the conductive agent.

[0060] The resulting slurry is applied to both sides or one side of the current collector. At this point, any uncoated portions of the current collector may remain. The coating is then allowed to dry. The drying rate varies depending on the type of adhesive and appropriate conditions. For example, when using an adhesive with modified groups, these groups can trap the conductive agent. Therefore, even among adhesives with the same molecular weight, the adhesive with modified groups is more prone to causing the conductive agent to detach from the interface between the coating and the current collector due to migration within the coating. Therefore, when using an adhesive with modified groups, it is preferable to slow down the drying rate.

[0061] Next, the dried coating is pressed. At this point, by increasing the pressing load, the electrode density can be increased; for example, the penetration of carbon black between active material particles can be adjusted. Furthermore, increasing the pressing load further reduces the pore size and pore surface area S within the electrode, which can be measured by mercury porosimetry. Hg The value can be adjusted to a range that provides excellent performance. This allows for the fabrication of electrodes.

[0062] The pore distribution in the active material layer can be adjusted to the range described earlier by adjusting parameters such as the selection and proportion of the active material, conductive agent, and binder, the particle size of the active material and conductive agent, the stirring (dispersion) conditions of the mixture, and the pressing conditions. Furthermore, in the stirring process, reducing the rotation of the mixer can yield a slurry that adequately maintains the conductive network of the conductive agent. Conversely, increasing the rotation of the mixer can yield a slurry with good dispersion of the active material. Electrodes fabricated using slurries obtained by reducing or increasing stirring in this way can increase the pore specific surface area S. BET The value of . Furthermore, as mentioned above, increasing the pressing load can increase the electrode density, but further increasing the electrode density tends to result in electrodes with good electrical contact and excellent capacity. Conversely, decreasing the pressing load can increase the pore size and pore specific surface area S inside the electrode, which can be measured by mercury intrusion porosimetry. Hg To produce excellent electrodes with low input resistance.

[0063] Specific examples of electrode fabrication are described in the embodiments in the later section.

[0064] Electrode Measurement Various measurement methods for electrodes are described. Specifically, methods for determining the composition of active materials, methods for determining the average primary particle size of active material particles, and methods for determining the pore surface area S by nitrogen adsorption are explained. BET Methods for determining the specific surface area S of fine pores by mercury infiltration method Hg Methods for determining the volume resistivity R of the layer containing active materialV Methods for determining the interfacial resistance R at the interface between the current collector and the layer containing the active material. I Methods for determining the content of conductive agents in layers containing active materials.

[0065] When analyzing the electrodes assembled in the battery, the electrodes are removed in the following order.

[0066] First, prepare the battery to be tested. The battery to be tested must have a discharge capacity of 100% or more of its rated capacity. That is, batteries that have deteriorated significantly are not considered for testing. Next, set the prepared battery to a discharge state. 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 an optional charging state to a current value equal to the reference current value until the battery voltage reaches 1.5V.

[0067] Next, the discharged battery is transferred to an argon-filled glove box with an internal dew point of -70°C. The battery is then cut open inside the glove box. The electrode assembly is removed from the cut battery. Throughout this series of disassembly operations, care must be taken to maintain electrical insulation between the positive and negative electrodes.

[0068] Next, the electrode assembly is disassembled into a positive electrode, a negative electrode, and a diaphragm. For example, the positive electrode is selected as the electrode to be measured. The electrode thus obtained is cleaned using methyl ethyl carbonate as a solvent. For this cleaning, the disassembled components are completely immersed in methyl ethyl carbonate solvent and left in this state for 60 minutes.

[0069] After cleaning, the electrode was subjected to vacuum drying. Vacuum drying was performed at 25°C, with the pressure reduced from atmospheric pressure to above -97 kPa, and maintained at this state for 10 minutes. The electrode, after undergoing this decomposition, cleaning, and vacuum drying process, was used for the following measurements.

[0070] <Determination of the composition of active substances> By using X-ray fluorescence (XRF) to measure the surface of the electrode, the composition of the active material of the electrode can be determined.

[0071] <Determination of the average primary particle size of active material particles> The average primary particle size of the active material particles can be determined by the laser diffraction-scattering method described below.

[0072] After preparing the electrode to be measured, the active material layer is separated from the current collector using a scraper or similar tool, thereby obtaining a powdered electrode mixture sample containing the active material. Next, the binder and conductive agent are removed by sintering the powdered sample, separating the active material particles. The resulting sample of active material particles is then placed into a measuring unit filled with N-methylpyrrolidone (NMP) until a measurable concentration is reached. Furthermore, the capacity of the measuring unit and the measurable concentration will vary depending on the particle size distribution measuring device.

[0073] The measuring unit containing NMP and dissolved active material samples was irradiated with 40W ultrasound for 5 minutes. This ultrasonic irradiation broke up the aggregation of active material particles.

[0074] The ultrasonically treated measuring unit is inserted into a particle size distribution measuring device based on laser diffraction / scattering to measure the particle size distribution. An example of such a device is the Microtrac 3100. Based on the particle size distribution of the active material, the average primary particle size of the active material can be determined. The particle size distribution measured shows the particle size at which the cumulative frequency (D) from the smallest particle size side is considered to be 50%. 50 This corresponds to the average primary particle size of the active material.

[0075] <Determination of pore specific surface area obtained by nitrogen adsorption method> The specific surface area S of the micropores obtained by nitrogen (N2) adsorption method for the active material layer BET This corresponds to the BET specific surface area of ​​the electrode. The BET specific surface area refers to the specific surface area determined by the BET method, calculated by the nitrogen adsorption method. Analysis is carried out, for example, by the following methods.

[0076] Multiple strips of planar material, each measuring 5 mm × 20 mm, are cut from the electrode. The weight of the cut sample is measured. Next, 24 sample pieces are loaded into the unit of the measuring apparatus. These samples are placed in the measuring unit for nitrogen adsorption-desorption measurement and dried at a temperature above 120°C under a nitrogen flow. The specific surface area is then measured using the BET single-point method or the BET multi-point method. An example of a measuring apparatus for nitrogen adsorption measurement is the Quantasorb, manufactured by QUANTACHROME.

[0077] <Determination of Specific Surface Area of ​​Fine Pores Obtained by Mercury Intrusion Porosimetry> The following explains the specific surface area S of the micropores containing the active material layer obtained by mercury intrusion porosimetry. Hg The determination method.

[0078] Multiple planar strips measuring 12 mm × 25 mm were cut from the electrodes as test samples. The weight of the cut test samples was measured. Next, 16 folded test samples were loaded into the unit of the measuring device. These test samples were measured under an initial pressure of 20 kPa (equivalent to a pore diameter of approximately 60 μm) and a final pressure of 400 MPa (pore diameter of approximately 3 nm).

[0079] Next, from other test samples cut from the same electrode, the active material layer is peeled off using a scraper, for example, to obtain a current collector sheet. The weight of this current collector sheet is measured. The weight of the active material layer contained in the test sample is determined by subtracting the weight of the current collector sheet from the weight of the previously measured test sample. In addition, the pore distribution after removing the weight of the current collector is recalculated for a specific range (0.003 μm to 2 μm).

[0080] Based on the pore distribution obtained as described above and the weight of the active substance layer contained in the sample, the specific surface area of ​​the pores containing the active substance layer (unit: m²) can be calculated. 2 / g).

[0081] Specific surface area of ​​fine pores (specific surface area of ​​fine pores S) Hg The shape of the fine hole is calculated as a cylindrical shape.

[0082] In addition, the analytical principle of mercury porosimetry is based on the following Washburn equation (1).

[0083] D=-4γcosθ / P (1) Here, D is the pore diameter, and γ is the surface tension of mercury (480 dyne·cm). -1 ), θ is the contact angle between mercury and the wall of the pore (140°), and P is the applied pressure. γ and θ are constants, so the relationship between the applied pressure P and the pore diameter D can be obtained according to Washburn's equation (1). By measuring the mercury intrusion volume at this time, the pore diameter and its volume distribution can be derived.

[0084] As an example of a measuring device for measuring pore size distribution, the Autopore 9520 pore size distribution measuring device manufactured by Micromeritics can be cited.

[0085] <Determination of volume resistivity of the active material layer and interfacial resistance between the current collector and the active material layer> Multiple strips of planar material, each measuring 50 mm × 50 mm, were cut from the electrode as the test sample. After separately measuring the thickness of the active material layer, the thickness of the current collector, and the volume resistivity of the current collector, and confirming that the sample was fully dried, the electrode resistance was measured.

[0086] Here, the volume resistivity of the active material layer and the interfacial resistance between the current collector and the active material layer are calculated by modeling the electrode sheet as a hypothetical electrode sheet with two layers plus one interfacial layer. A constant current flows through the surface of the electrode sheet, and the potential distribution generated on the surface is measured at multiple points. Then, the resistance of each layer is used as a variable, and a calculated potential consistent with the measured potential is calculated through iterative calculations (curve regression). If the measured potential and the calculated potential are consistent, the volume resistivity of the active material layer and the interfacial resistance between the current collector and the active material layer can be calculated separately. In this calculation, information on the thickness of the active material layer, the thickness of the current collector, and the volume resistivity of the current collector needs to be prepared separately. For example, this information can be measured in advance using a portion of multiple cut 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 composed of Al or Cu, its general physical property value can be used, and the measurement can be omitted.

[0087] As an example of a measuring apparatus for measuring the volume resistivity of the active material layer and the interfacial resistance between the current collector and the active material layer, the RM2610 electrode resistance measuring system manufactured by HIOKI Electric Co., Ltd. is cited. The cut sample is placed upright in the electrode resistance measuring apparatus without bending, and the volume resistivity of the active material layer is measured by pressing the electrode probe. The measurement is performed in potentiometric measurement + calculation mode, with the resistance range set to Auto and the number of repetitions set to 30.

[0088] <Determination of the content of conductive agent in the active material layer> In determining the content of conductive agents in the active material layer, one method that can be used is the detection of the constituent material mapping image using Raman spectroscopy. The determination procedure is shown below.

[0089] The electrode obtained by the method described above is fixed with its cross-section containing the active material layer facing the direction of the laser emitted for Raman measurement. As a specific example of the fixing method, the sample can be prepared as follows: The sample is placed in a container with its cross-section facing directly upwards, and the sample is fixed to the bottom of the container using a metal component. By allowing curable resin to flow into the container and allowing it to stand until the resin has completely cured, the electrode cross-section can be fixed in any orientation. Then, by mechanically cutting along a plane parallel to the bottom surface to expose a new cross-section, the measurement sample can be prepared in a way that allows observation of its cross-section. At this time, depending on the carbon material used, graphitization may sometimes be intensified; therefore, it is necessary to reduce the energy during cutting to a level that does not affect the measurement.

[0090] The sample is fixed on the sample stage and placed into the Raman spectroscopy apparatus. For the placed sample, surface Raman spectroscopy is performed with a field of view of 50 μm × 50 μm to obtain the Raman spectrum. When obtaining the Raman spectrum, 10,000 points are measured within the 50 μm × 50 μm field of view, divided into 100 points vertically and 100 points horizontally. An example of a measuring apparatus for Raman spectroscopy measurement is the WITec α300 confocal microspectrophotometer. Measurement conditions are as follows. However, in cases where the thermal effect on the sample is significant, it is necessary to shorten the exposure time, increase the number of accumulations, or reduce the laser power. Conversely, if the obtained spectrum becomes unclear, it is preferable to extend the exposure time or increase the number of accumulations. Exposure time: 10s or 20s Total number of times: 1 Lens magnification: 50x Measurement range: 50μm × 50μm Laser power: 5%.

[0091] (The creation of material mapping images) Next, using Raman spectra at 10,000 points, spectra were extracted from 10 randomly selected points in each high-concentration region to obtain average spectra. Multivariate analysis was performed on these average spectra to distinguish significant spectral components. For each distinguished component spectrum, the crystallinity of the active material and conductive agent was determined based on peak position, intensity, and intensity ratio. The presence ratio of each component was mapped using the obtained spectra of each constituent material and the 10,000-point Raman spectra.

[0092] Here, depending on the type of carbon material, the value in the Raman spectrum is at 1350±10 cm⁻¹. -1 The integrated intensity of the D-band appearing at 1590±10cm is similar to that at 1590±10cm. -1 The ratio of the integrated intensities of the G-bands appearing at different locations is different. For example, in carbon black, the integrated intensity of the D-band, generated by structural disorder, is large, while the integrated intensity of the D-band is I... D Integral intensity I of G-band G The ratio satisfies 0.5 D / I G The relationship is <2.0. For highly crystalline carbon such as flake graphite, the integrated intensity of the G-band generated by the layered structure is large, therefore I D with I G The ratio satisfies 0 D / I G The relationship is <0.5. Carbon nanotubes (CNTs) have a structure in which one or more layers of graphene are rolled into a cylindrical shape, but depending on the number of layers and the manufacturing method, I D / I G ​​The differences are not apparent. These examples exhibit D-bands and G-bands at close positions, but even when two or more carbon materials as described above are present as conductive agents, the presence of various conductive agents at that point can be distinguished by calculating the degree of overlap through fitting the spectra of each monomer. The proportion of each constituent material can be represented, for example, by the different shades of color for each constituent material.

[0093] From the above, it can be seen that the ratio of active material to conductive agent within the active material layer can be determined from the obtained mapping image. This value can be further analyzed by multiplying it by the individual densities (g / cm³) of the active material, flake graphite, and other materials. 3 (Unit), which can include the content of conductive agent, to calculate the content of each component in the electrode.

[0094] The electrode of the first embodiment includes a current collector and an active material layer containing at least a lithium nickel cobalt manganese composite oxide as the active material. Regarding the active material layer, the specific surface area S, measured by nitrogen adsorption, is... BET Compared with the pore specific surface area S determined by mercury intrusion porosimetry Hg Satisfying 0.8 BET / S Hg The relationship is <2.0. The volume resistivity R of the layer containing the active material is... V The interfacial resistance R at the interface between the current collector and the layer containing the active material is below 10 Ω·cm. I 0.5Ω·cm 2 Below. Furthermore, the volume resistivity R V With interface resistance R I The ratio of R V / R I 3cm -1 Above and 20cm -1 The following describes how this electrode enables batteries with excellent capacity retention and suppressed resistance rise, resulting in superior lifetime performance.

[0095] (Second Implementation) According to a second embodiment, a battery is provided. The battery includes the electrodes and electrolyte of the first embodiment. As described above, the electrodes of the first embodiment enable a battery with excellent lifespan performance. Therefore, the battery of the second embodiment can have excellent lifespan performance.

[0096] The battery can have a positive electrode and a negative electrode. The battery can include the electrode of the first embodiment as the positive electrode.

[0097] The battery can also be further equipped with a separator disposed between the positive and negative electrodes. The positive electrode, negative electrode, and separator can constitute an electrode assembly. The electrolyte can be retained in the electrode assembly.

[0098] ​In addition, the battery can be further equipped with an outer packaging component that houses the electrode assembly and electrolyte.

[0099] Furthermore, the battery may further include 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 collector tab of the target electrode. At least a portion of the positive terminal and at least a portion of the negative terminal may extend outward from the outer packaging component.

[0100] The battery can be, for example, a lithium-ion secondary battery. Alternatively, the battery may include a non-aqueous electrolyte battery containing a non-aqueous electrolyte as the electrolyte.

[0101] The following provides a detailed description of the positive electrode, negative electrode, electrolyte, separator, outer packaging components, positive terminal, and negative terminal.

[0102] (1) Positive electrode The positive electrode includes a positive current collector and a layer containing positive active material (positive electrode binder layer) supported on one side or both sides of the positive current collector. The layer containing positive active material includes positive active material, conductive agent and binder.

[0103] The positive electrode can be the electrode of the first embodiment. Regarding the form of the positive electrode, the positive current collector, the positive active material, and the layer containing the positive active material are respectively equivalent to the current collector, the active material, and the layer containing the active material of the electrode of the first embodiment. The electrode of the first embodiment has been described in detail above, therefore the description of the positive electrode here is omitted.

[0104] (2) Negative electrode The negative electrode comprises a negative electrode current collector and a layer containing negative electrode active material (negative electrode binder layer) supported on one side or both sides of the negative electrode current collector. The layer containing negative electrode active material contains negative electrode active material. In addition to the negative electrode active material, the layer may also contain a conductive agent and a binder. A conductive agent may be incorporated to improve current collection performance and suppress the contact resistance between the negative electrode active material and the negative electrode current collector. A binder may be incorporated to bond the dispersed negative electrode active material to each other and to bond the negative electrode active material to the negative electrode current collector.

[0105] Material The following describes materials that can be used in the negative electrode active material layer and the negative electrode current collector.

[0106] <Contains a layer of negative electrode active material> The preferred proportions of the negative electrode active material, conductive agent, and binder in the negative electrode active material layer are within the following ranges: negative electrode active material 70% by mass or more and 96% by mass or less, conductive agent 2% by mass or more and 28% by mass or less, and binder 2% by mass or more and 28% by mass or less. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the negative electrode active material layer can be improved, and excellent high-current performance and low-temperature performance are expected. In addition, by setting the amount of binder to 2% by mass or more, the adhesion between the negative electrode active material layer and the current collector becomes sufficient, and excellent cycle performance is expected.

[0107] On the other hand, from the viewpoint of high capacity, the conductive agent and the binder are preferably 28% by mass or less.

[0108] <Negative Electrode Active Material> The negative electrode preferably contains components capable of operating at 0.4V (vs. Li / Li). + A negative electrode active material that allows lithium ion insertion and extraction at potentials above a certain threshold. In the second embodiment of the battery, the deposition of lithium caused by charging and discharging can be suppressed. Therefore, such a battery exhibits superior fast charge / discharge performance.

[0109] As capable of operating at 0.4V (vs. Li / Li + Anode active materials that allow lithium-ion insertion and extraction at potentials above a certain level include, for example, Li. 4+x Ti5O 12 Lithium titanate with a spinel-type crystal structure (x varies within the range of -1 ≤ x ≤ 3 through charge-discharge reactions) and Lithium titanate with an orthorhombic manganese oxide-type crystal structure are represented by (x varies within the range of -1 ≤ x ≤ 3) 2+x Ti3O7 (where x varies within the range of -1 ≤ x ≤ 3 through charge-discharge reactions), and metal composite oxides containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe, are examples. Examples of metal composite oxides containing Ti and at least one element 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 transform into lithium-titanium composite oxides through lithium intercalation during charging. Among lithium-titanium composite oxides, spinel-type lithium titanate exhibits excellent cycle performance and is preferred.

[0110] The negative electrode can contain other active materials, such as carbonaceous materials and metal compounds.

[0111] Examples of carbonaceous materials include natural graphite, synthetic graphite, coke, vapor-grown carbon fibers, mesophase pitch-based carbon fibers, spherical carbon, and resin-fired carbon. More preferred carbonaceous materials include vapor-grown carbon fibers, mesophase pitch-based carbon fibers, and spherical carbon. Preferably, the carbonaceous material has a surface spacing d002 of 0.34 nm or less for the (002) planes as measured by X-ray diffraction.

[0112] As metal compounds, metal sulfides, metal nitrides, etc., can be used. As metal sulfides, examples include titanium sulfide such as TiS2, molybdenum sulfide such as MoS2, and FeS, FeS2, and Li. x Iron sulfides such as FeS2 (0≤x≤2) can be used. As metal nitrides, lithium cobalt nitrides (e.g., Li) can be used. x Co y N; 0 <x<4、0<y<0.5)。

[0113] In addition to the lithium-titanium composite oxides mentioned above, other lithium-titanium composite oxides, such as monoclinic niobium titanium oxides and orthorhombic titanium-containing composite oxides, may also be included as negative electrode active materials.

[0114] As an example of the monoclinic niobium titanium oxide, Li can be cited as an example. a Ti 1-x M1 x Nb 2-y M2 y O 7+δ The compound is represented by M1, which is selected from at least one of the group consisting of Zr, Si, and Sn. M2 is selected from at least one of the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0 ≤ a ≤ 5, 0 ≤ x < 1, 0 ≤ y < 2, and -0.3 ≤ δ ≤ 0.3. As a specific example of a monoclinic niobium titanium oxide, Li can be cited. a Nb2TiO7 (0≤a≤5).

[0115] Other examples of monoclinic niobium titanium oxides include those made from Li a Ti 1-x M3 x+y Nb 2-y O 7-δ The compound is indicated by M3. Here, M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0 ≤ a ≤ 5, 0 ≤ x < 1, 0 ≤ y < 2, and -0.3 ≤ δ ≤ 0.3.

[0116] As an example of orthorhombic titanium-containing composite oxides, one could cite Li... 2+a M4 2-x Ti6-y M5 z O 14+σ The compound is indicated by M4. 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 compositional formula are 0 ≤ a ≤ 6, 0 ≤ x < 2, 0 ≤ y < 6, 0 ≤ z < 6, and -0.5 ≤ σ ≤ 0.5. As a specific example of an orthorhombic titanium-containing composite oxide, Li can be cited. 2+a Na2Ti6O 14 (0≤a≤6).

[0117] One of the active substances can be included in the negative electrode as a negative electrode active substance, or two or more of the active substances can be included in the negative electrode as negative electrode active substances.

[0118] <Conductive agent> Examples of conductive agents include carbonaceous materials such as acetylene black, carbon black, graphite, carbon nanofibers, and carbon nanotubes. These carbonaceous materials can be used alone or in combination.

[0119] <Adhesive> Examples of adhesives include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluoropolymers, and styrene-butadiene rubber (SBR). Additionally, carboxymethyl cellulose (CMC), polyimide, and polyamide can also be used as adhesives. These adhesives can be used alone or in combination.

[0120] <Negative Electrode Current Collector> As the negative electrode current collector, an electrochemically stable material can be used at the potential where the lithium-ion insertion-deintercalation reaction of the negative electrode active material occurs. The negative electrode current collector is preferably a metal foil composed 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.

[0121] The shape of the negative electrode current collector can vary depending on the intended use of the battery.

[0122] The negative electrode current collector may consist of a portion of its surface that does not support a layer containing the negative electrode active material. This portion can function as a negative electrode current collector tab. Alternatively, the negative electrode may also include current collector tabs that are separate from the negative electrode current collector.

[0123] <Production Method> The negative electrode can be made, for example, by the following method.

[0124] First, a slurry for making a negative electrode is prepared by suspending the negative electrode active material, binder, and optionally conductive agent in a suitable solvent. A common solvent, such as N-methylpyrrolidone, is used as the solvent. The resulting slurry is coated onto a negative electrode current collector. By drying the coated slurry and pressing it, a negative electrode containing a negative electrode current collector and a layer of negative electrode active material formed on the current collector can be obtained. Alternatively, the negative electrode active material, binder, and optionally conductive agent can be formed into granules and used as the layer of negative electrode active material.

[0125] (3) Diaphragm As a diaphragm, an electrically insulating material is used. There are no particular limitations as long as it is insulating, but for the diaphragm, for example, porous membranes or nonwoven fabrics made of polymers such as polyolefins, cellulose, polyethylene terephthalate, and vinylon can be used. The diaphragm material can be one type, or two or more types can be used in combination.

[0126] (4) Electrolytes Examples of electrolytes include liquid non-aqueous electrolytes prepared by dissolving electrolyte salts (solutes) in non-aqueous solvents, and gel-like non-aqueous electrolytes formed by combining liquid non-aqueous electrolytes with polymer materials.

[0127] Examples of lithium salts that can be cited as electrolyte salts include lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexalithium antimonyate (LiSbF6), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (LiCF3SO3; commonly known as LiTFS), lithium bis(trifluoromethanesulfonamide) {Li(CF3SO2)2N; commonly known as LiTFSI}, lithium bis(pentafluoroethanesulfonamide) {Li(C2F5SO2)2N; commonly known as LiBETI}, lithium bis(oxalateborate) {LiB(C2O4)2; commonly known as LiBOB}, and lithium difluoro(trifluoro-2-oxide-2-trifluoro-methylpropionate(2-)-O,O)borate {LiBF2OCOOC(CF3)2; commonly known as LiBF2(HHIB)}. These electrolyte salts can be used alone or in combination of two or more. Among them, LiPF6 and LiBF4 are particularly preferred.

[0128] The electrolyte salt is preferably dissolved in a non-aqueous solvent at a concentration between 1 mol / L and 3 mol / L. Electrolyte salt concentrations within this range can suppress the increase in viscosity caused by rising electrolyte salt concentrations and further improve performance under high load currents.

[0129] Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC); chain 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. Chain ethers such as ethane (DME); cyclic esters such as γ-butyrolactone (BL); chain esters such as methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate; 1,3-dioxolane; acetonitrile (AN); sulfolane (SL); and other organic solvents. These organic solvents can be used alone or in mixtures of two or more. Non-aqueous solvents containing cyclic carbonates and / or chain carbonates are preferred.

[0130] Examples of polymeric materials used in gel-like non-aqueous electrolytes include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0131] (5) Outer packaging components The outer packaging component can be formed from a laminated film or made of a metal container. Alternatively, resin containers made from polyolefin resins, polyvinyl chloride resins, polystyrene resins, acrylic resins, phenolic resins, polyphenylene resins, fluoropolymer resins, etc., can also be used for the outer packaging component. When using a metal container, the lid can be an integral part of the container or a separate component. The wall thickness of the metal container is preferably 3 mm or less, more preferably 0.5 mm or less.

[0132] Examples of shapes for outer packaging components include flat (thin), square, cylindrical, coin-shaped, button-shaped, sheet-shaped, and stacked types. These outer packaging components can be used for small batteries in portable electronic devices, as well as for large batteries in two-wheeled or four-wheeled automobiles.

[0133] The wall thickness of the laminated film outer packaging component is preferably 0.5 mm or less. Examples of laminated films include multilayer films comprising a resin layer and a metal layer disposed between the resin layers. For weight reduction, the metal layer is preferably aluminum foil or aluminum alloy foil. The resin layer can be, for example, a film made of polymer materials such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET). The laminated film can be sealed by heat welding to form the shape of the outer packaging component.

[0134] The metal container is made of aluminum or an aluminum alloy. Preferably, the aluminum alloy contains elements such as magnesium, zinc, and silicon. In the case of aluminum or aluminum alloy containing transition metals such as iron, copper, nickel, and chromium, the content of these metals is preferably less than 100 ppm.

[0135] Reference Figure 2 and Figure 3 Here is an example illustrating the battery. Figure 2 The flat battery shown comprises a flat, wound electrode assembly 1, an outer packaging component 2, a positive terminal 7, a negative terminal 6, and an electrolyte (not shown). The outer packaging component 2 is a pouch-shaped outer packaging component made of laminated film. The wound electrode assembly 1 is housed within the outer packaging component 2. Figure 3 As shown, the wound electrode assembly 1 includes a positive electrode 3, a negative electrode 4, and a diaphragm 5. It is formed by winding a stack of materials stacked in the order of negative electrode 4, diaphragm 5, positive electrode 3, and diaphragm 5 from the outside into a vortex shape and then pressing it into shape.

[0136] The positive electrode 3 includes a positive current collector 3a and a layer 3b containing positive active material. The layer 3b contains positive active material. The layer 3b is formed on both sides of the positive current collector 3a. The negative electrode 4 includes a negative current collector 4a and a layer 4b containing negative active material. The layer 4b contains negative active material. In the outermost portion of the negative electrode 4, the layer 4b is formed only on one side of the inner surface of the negative current collector 4a. In other portions of the negative electrode 4, the layer 4b is formed on both sides of the negative current collector 4a.

[0137] like Figure 2As shown, near the outer periphery of the wound electrode assembly 1, the positive terminal 7 is connected to the positive electrode 3. Additionally, the negative terminal 6 is connected to the outermost negative electrode 4. Both the positive terminal 7 and the negative terminal 6 extend outwards through the opening in the outer packaging component 2.

[0138] The battery is not limited to the aforementioned. Figure 2 and Figure 3 The structure shown, for example, can be set as Figure 4 The structure shown.

[0139] exist Figure 4 In the square battery shown, the wound electrode assembly 11 is housed within a bottomed rectangular cylindrical metal container 12, which serves as the outer packaging component. A rectangular cap 13 is welded to the opening of the container 12. The flat wound electrode assembly 11 may, for example, have the same shape as the referenced... Figure 2 and Figure 3 The winding electrode assembly 1 described herein has the same configuration.

[0140] One end of the negative current collector tab 14 is electrically connected to the negative current collector, and the other end is electrically connected to the negative terminal 15. The negative terminal 15 is fixed to the rectangular cover 13 by an airtight seal with glass material 16 sandwiched between it. One end of the positive current collector tab 17 is electrically connected to the positive current collector, and the other end is electrically connected to the positive terminal 18 fixed to the rectangular cover 13.

[0141] The negative current collector tab 14 is made of materials such as aluminum or aluminum alloys containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. To reduce the contact resistance with the negative current collector, the negative current collector tab 14 is preferably made of the same material as the negative current collector.

[0142] The positive current collector tab 17 is made of materials such as aluminum or aluminum alloys containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. To reduce the contact resistance with the positive current collector, the positive current collector tab 17 is preferably made of the same material as the positive current collector.

[0143] It should be noted that the battery illustrated uses a wound electrode assembly, which is formed by winding the separator together with the positive and negative electrodes. However, a stacked electrode assembly, in which the positive and negative electrodes are alternately layered with the separator in between, can also be used. Alternatively, the electrode assembly can have other structures.

[0144] The battery of the second embodiment includes the electrodes of the first embodiment. Therefore, the battery has excellent capacity retention, suppressed resistance rise, and excellent lifespan performance.

[0145] (Third Implementation) According to a third embodiment, a battery pack is provided. This battery pack includes the battery of the second embodiment.

[0146] The battery pack of the third embodiment may include one or more batteries (single cells) as described in the second embodiment previously. Multiple batteries in such a battery pack may also be connected in series or parallel to form a battery array. Such a battery pack may include multiple battery arrays.

[0147] Next, an example of a battery pack according to the third embodiment will be described with reference to the accompanying drawings.

[0148] Figure 5 This is an exploded perspective view of a battery pack, which is an example of a second embodiment. Figure 6 It is shown Figure 5 A block diagram of the battery pack circuit.

[0149] Figure 5 and Figure 6 The battery pack 20 shown includes multiple individual cells 21. Each individual cell 21 can be a reference cell. Figure 4 A flat battery is an example of one of the second embodiments described.

[0150] Multiple individual cells 21 are stacked such that their outwardly extending negative terminals 51 and positive terminals 61 are aligned in the same direction and secured with adhesive tape 22, thereby forming a battery pack 23. Figure 6 As shown, these individual cells 21 are electrically connected in series with each other.

[0151] The printed wiring substrate 24 is arranged side-by-side with the negative terminal 51 and positive terminal 61 of the single cell 21. For example... Figure 6 As shown, a thermistor 25, a protection circuit 26, and a terminal 27 for powering external devices are mounted on the printed circuit board 24. Additionally, an insulating plate (not shown) is mounted on the surface of the printed circuit board 24 opposite to the battery pack 23 to prevent unnecessary connections with the wiring of the battery pack 23.

[0152] The positive terminal lead 28 is connected to the bottom positive terminal 61 of the battery pack 23, and its front end is inserted into the positive terminal connector 29 of the printed circuit board 24 for electrical connection. The negative terminal lead 30 is connected to the top negative terminal 51 of the battery pack 23, and its front end is inserted into the negative terminal connector 31 of the printed circuit board 24 for electrical connection. These connectors 29 and 31 are connected to the protection circuit 26 through wirings 32 and 33 formed on the printed circuit board 24.

[0153] Thermistor 25 detects the temperature of the individual cell 21, and this detection signal is sent to protection circuit 26. Protection circuit 26 can, under specified conditions, block the positive-side wiring 34a and negative-side wiring 34b between protection circuit 26 and terminal 27 for powering external devices. An example of the specified conditions is, for example, when the detected temperature of thermistor 25 reaches or exceeds a specified temperature. Other examples of the specified conditions include detecting overcharging, over-discharging, or overcurrent of the individual cell 21. This overcharging detection is performed on each individual cell 21 or the entire battery pack 23. When detecting each individual cell 21, the battery voltage, positive electrode potential, or negative electrode potential can be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each individual cell 21. Figure 5 as well as Figure 6 In the case of battery pack 20, each individual battery 21 is connected to wiring 35 for voltage detection. Detection signals are sent to protection circuit 26 through these wirings 35.

[0154] Protective sheets 36 made of rubber or resin are provided on the three sides of the battery pack 23, excluding the protruding sides of the positive terminal 61 and the negative terminal 51.

[0155] The battery pack 23, along with each protective sheet 36 and the printed circuit board 24, is housed within a storage container 37. Specifically, protective sheets 36 are disposed on the two inner sides along the long side and the inner side along the short side of the storage container 37, and the printed circuit board 24 is disposed on the inner side opposite to the short side. The battery pack 23 is located within the space enclosed by the protective sheets 36 and the printed circuit board 24. A cover 38 is attached to the upper surface of the storage container 37.

[0156] Alternatively, heat shrinkable tape can be used instead of adhesive tape 22 to secure the battery pack 23. In this case, protective tabs are placed on both sides of the battery pack, and the heat shrinkable tape is wrapped around it to heat shrink and secure the battery pack.

[0157] exist Figure 5 and Figure 6 The diagram shows a method of connecting individual cells 21 in series, but they can also be connected in parallel to increase battery capacity. Furthermore, assembled battery packs can also be connected in series and / or in parallel.

[0158] Furthermore, the form of such a battery pack can be appropriately modified depending on the application. The preferred application is one where good cycle performance is desired when drawing high current. Specific applications include powering digital cameras, two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, and electric bicycles. This type of battery pack is particularly suitable for automotive applications.

[0159] The battery pack of the third embodiment includes the battery of the second embodiment. Therefore, such a battery pack has excellent capacity retention, suppressed resistance rise, and excellent lifespan performance.

[0160] Example The following examples illustrate the invention in more detail, but the invention is not limited to the embodiments described below, as long as they do not exceed the spirit of the invention.

[0161] (Example 1) <The Making of the Positive Electrode> A lithium nickel cobalt manganese composite oxide (LiNi) with an average primary particle size of 5.0 μm was prepared 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 polyvinylidene fluoride (PVdF) with modified groups as a binder were mixed in N-methylpyrrolidone to obtain a slurry for positive electrode fabrication. The mass ratios of the positive electrode active material, the first conductive agent, the second conductive agent, and the binder added to N-methylpyrrolidone were set to 89 parts by mass, 3.3 parts by mass, 3.7 parts by mass, and 4 parts by mass, respectively. The resulting slurry was coated at a rate of 80 g / m². 2 The coating was applied to both sides of a 12 μm thick aluminum foil (current collector) with a strip shape, and then dried. During coating, an uncoated portion remained on a portion of the aluminum foil, serving as current collector tabs. Drying was performed using a 10 m long dryer, conveyed at a speed of 10 m / min. The resulting coating, along with the current collector, was pressed to obtain an active material layer with a thickness of 25 μm on each side. This is how the positive electrode was fabricated.

[0162] <Making the Negative Electrode> Prepare spinel-type lithium titanate Li4Ti5O 12 The negative electrode active material, flake graphite as a conductive agent, and PVdF as a binder were used. 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 N-methylpyrrolidone were set to 95% by mass, 2.5% by mass, and 2.5% by mass, respectively. The prepared negative electrode slurry was coated at a rate of 100 g / m². 2 The coating was applied to both sides of a 12 μm thick aluminum foil (current collector) with a strip shape, and then dried. During coating, an uncoated portion remained on a portion of the aluminum foil, serving as current collector tabs. The resulting coating, along with the current collector, was pressed to obtain a density of 2.5 g / cm³. 3 The layer contains active material. This is how the negative electrode was made.

[0163] <Electrode Assembly Fabrication> The positive and negative electrodes, fabricated as described above, are overlapped with a 10 μm thick separator sandwiched between them. The resulting laminate is wound with the negative electrode on the outermost periphery. The resulting electrode assembly is heated to 80°C and pressed, then fixed with insulating tape. In this way, a flat, wound electrode assembly is obtained, comprising a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes.

[0164] <Preparation of Non-Aqueous Electrolytes> A non-aqueous solvent was prepared by mixing propylene carbonate (PC) and diethyl carbonate (DEC) in a 1:1 volume ratio. A non-aqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) in the obtained non-aqueous solvent at a concentration of 1.0 mol / L.

[0165] <Battery Assembly> The electrode assembly, shaped into a flat form as described above, is inserted into a bottomed rectangular cylindrical container made of aluminum with a plate thickness of 0.3 mm. The opening of the container is sealed with a sealing plate, and the electrode assembly is housed inside the container, which serves as the outer packaging component. The non-aqueous electrolyte prepared as described above is injected into the container through an electrolyte inlet provided on the sealing plate. Next, a flat non-aqueous electrolyte secondary battery is fabricated by welding a sealing cap around the periphery of the electrolyte inlet.

[0166] (Examples 2-4) In Examples 2-4, based on Example 1, the proportions 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. Otherwise, the battery was fabricated using the same method as in Example 1. By changing the proportions of the conductive agents, the pressability of the coating film of the positive electrode fabrication slurry changed, and the thickness of the positive electrode active material layer on each side of the current collector was as shown in Table 2.

[0167] (Example 5) In Example 5, based on Example 1, 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 positive electrode fabrication and the pressing load of the active material layer were adjusted. The design of the positive electrode active material layer was changed to the design shown in Tables 1 and 2. Otherwise, the battery was fabricated using the same method as in Example 1. As for the design of the positive electrode active material layer, as shown in Tables 1 and 2, the pore specific surface area S obtained by mercury intrusion porosimetry was adjusted. Hg The specific surface area S obtained by nitrogen adsorption method (BET method) BET And the thickness of the positive electrode active material layer on one side of each current collector.

[0168] (Examples 6 and 7) In Examples 6 and 7, based on Example 1, the amount of the slurry used for making the positive electrode was changed in the coating of the current collector; otherwise, the battery was fabricated using the same method as in Example 1. By changing the amount of the slurry used for making the positive electrode, a layer containing positive electrode active material with a thickness on each side of the current collector as shown in Table 2 was obtained.

[0169] (Comparative Example 1) In Comparative Example 1, based on Example 1, 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 making the positive electrode and the pressing load containing the active material layer were adjusted. The design containing the positive electrode active material layer was changed to the design shown in Tables 1 and 2. Otherwise, the battery was made using the same method as in Example 1.

[0170] (Comparative Example 2) In Comparative Example 2, based on Example 1, the battery was fabricated using the same method 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.

[0171] (Comparative Example 3) In Comparative Example 3, the amount of positive electrode slurry coated onto the current collector was significantly increased compared to Example 1. Otherwise, the battery was fabricated using the same method as in Example 1. By changing the amount of positive electrode slurry coated, a layer containing positive electrode active material with a thickness on each side of the current collector as shown in Table 2 was obtained.

[0172] (Compare Examples 4 and 5) In Comparative Examples 4 and 5, based on Example 1, the proportions of AB and FG used for the positive electrode were changed as shown in Table 2. Otherwise, the batteries were manufactured using the same method as in Example 1.

[0173] Tables 1 and 2 below summarize the designs of the positive electrode active material layer in each embodiment and comparative example. As for the design of the active material layer, the specific surface area S, measured by the nitrogen adsorption method (BET method), is used. BET The specific surface area S of the pores determined by the mercury intrusion porosimetry method. Hg and their ratio S BET / S Hg Table 1 shows the results. Table 2 shows the mass fractions of the first and second conductive agents used in the positive electrode active material layer, and the volume resistivity R of the positive electrode active material layer as determined by the method described above. V The interfacial resistivity R between the positive electrode active material layer and the positive electrode current collector, as measured by the method described above. I Their ratio R V / R IAnd the thickness of the positive electrode active material layer on one side of the current collector.

[0174] Table 1

[0175] Table 2

[0176] <Cyclic Test> For each battery manufactured, a cycle test was performed as described below.

[0177] First, charge the battery at 1C at 25°C until it reaches 100% State of Charge (SOC). Then, discharge the battery to 0% SOC at 0.2C and measure the discharge capacity. Next, charge the battery to 50% SOC at 1C and measure the charging resistance (in mΩ).

[0178] Next, the battery was charged at 3C rate to 100% State of Charge (SOC) and discharged at 3C rate to 0% SOC for 2000 cycles at 25°C. After the 2000th discharge cycle, the discharge capacity and charging resistance were measured again after 2000 cycles, following the same procedure as before the charge-discharge cycle measurements.

[0179] Based on the discharge capacity before and after 2000 charge-discharge cycles, the capacity retention rate is calculated using the following formula: Capacity retention rate (unit: %) = [Discharge capacity after cycle / Discharge capacity before cycle] × 100%. Additionally, based on the discharge resistance value before and after 2000 charge-discharge cycles, the resistance rise rate is calculated using the following formula: Resistance rise rate (unit: %) = [Charging resistance value after cycle / Charging resistance value before cycle] × 100%. The calculated results are shown in Table 3 below.

[0180] Table 3

[0181] As shown in Table 3, the batteries fabricated in Examples 1-7 achieved a good balance between capacity retention and resistance rise suppression. On the other hand, it can be seen that, for Comparative Examples 1-5, either or both of capacity retention and resistance rise suppression were worse than in Examples 1-7. For Examples 1-7, in the layer containing the positive electrode active material, the ratio of the pore specific surface area to the pore volume using the single-crystal nickel-cobalt-manganese composite oxide was 0.8. BET / S Hg ​In a layer containing a positive electrode active material with a resistance R < 2.0, the volume resistivity R of the active material layer itself can be achieved. V The interfacial resistance R between the active material layer and the current collector I The ratio is 3cm -1 ≤R V / R I ≤20cm -1 Such uniform resistance allows for appropriate control of electrolyte permeability into the layer containing the positive electrode active material and the electrode reaction area, while also suppressing localized degradation of the layer containing the positive electrode active material.

[0182] On the other hand, the batteries of Comparative Examples 1 to 5 showed the following results: in the positive electrode active material layer, none of the conditions were met, and either or both of the capacity retention rate and the resistance rise suppression were worse than those of Examples 1 to 7.

[0183] Specifically, in Comparative Example 1, S BET With S Hg The ratio is 2.1. Therefore, it can be seen that the positive electrode active material obtained in Comparative Example 1 has more micropores, and secondary particles are formed from polycrystalline material. In Comparative Example 1, the capacity retention rate is quite low. It is confirmed that the large specific surface area of ​​the polycrystalline positive electrode active material leads to accelerated performance degradation through side reactions between the positive electrode and the electrolyte.

[0184] In Comparative Example 2, carbon nanotubes (CNTs) were used instead of flake graphite as the second conductive agent in the positive electrode. Because of their fibrous shape, CNTs, like flake graphite, can connect active material particles within the active material layer to form wide conductive pathways, thereby increasing the volume resistivity R of the active material layer. V Reduced. However, at the same time, CNTs, like acetylene black, can penetrate into the tiny gaps between active materials, thus reducing the interfacial resistance R between the active material layer and the current collector. I It also decreased significantly, R V / R I The current increases significantly. As a result, the current in the layer containing the positive electrode active material is biased towards the interface with the current collector, resulting in uneven charging and discharging within the active material layer, thereby reducing the capacity retention rate.

[0185] In Comparative Example 3, the coating amount of the slurry used to form a thick layer containing the positive electrode active material was large, resulting in a stronger effect from the migration of the binder during slurry drying. This indicates that the interfacial resistance R between the active material layer and the current collector is high. I A significant increase. Specifically, acetylene black does not remain near the interface, and the interface resistance R... IIncreased. Due to the high interface resistance, current has difficulty flowing from the current collector to the layer containing the positive electrode active material, and the degradation of the active material layer is aggravated during charging and discharging. Therefore, this is an undesirable result from the perspectives of both capacity retention and resistance rise rate.

[0186] In Comparative Example 4, due to the small amount of acetylene black applied to the positive electrode, the interfacial resistance R was reduced. I Increase, R V / R I Less than 3cm -1 Therefore, in Comparative Example 4, the current also has difficulty flowing from the current collector to the layer containing the positive electrode active material. During charging and discharging, the deterioration of the active material layer is aggravated, resulting in poor capacity retention and resistance rise rate.

[0187] In Comparative Example 5, due to the small amount of flake graphite applied to the positive electrode, the volume resistivity R of the active material layer was low. V Increase, R V / R I More than 20cm -1 Therefore, it is difficult for current to flow in the layer containing the positive electrode active material. The current concentrates near the interface with the current collector, resulting in localized deterioration of the electrode components near the interface, and consequently, an increase in the rate of increase in resistance.

[0188] An electrode is provided according to one or more embodiments and examples described above. The electrode comprises: an active material layer containing a lithium nickel cobalt manganese composite oxide as the active material; and a current collector. The specific surface area S in the active material layer, measured by nitrogen adsorption, is... BET Compared with the pore specific surface area S determined by mercury intrusion porosimetry Hg Satisfying 0.8 BET / S Hg The volume resistivity R of the active material layer is less than 2.0 and below 10 Ω·cm. V Relative to 0.5Ω·cm 2 The following are the interfacial resistance R between the current collector and the interface containing the active material layer. I Meets 3cm -1 ≤R V / R I ≤20cm -1 The electrodes provide batteries and battery packs with excellent lifespan performance.

[0189] ​Several embodiments of the present invention have been described, but these embodiments are provided by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, 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 or spirit of the invention, and are also included in the scope of the invention as described in the claims and its equivalents.

[0190] Several embodiments of the present invention are described below.

[0191] [1] An electrode comprising a current collector and an active material layer, the active material layer being located on the current collector and containing an active material and a conductive agent. The active material comprises a lithium-nickel-cobalt-manganese composite oxide, and the specific surface area S of the active material layer is obtained by nitrogen adsorption. BET The specific surface area S of the pores in the active material layer obtained by mercury intrusion porosimetry Hg Satisfying 0.8 BET / S Hg <2.0 relationship, The volume resistivity R of the active material layer V The interfacial resistance R at the interface between the current collector and the layer containing the active material is below 10 Ω·cm. I 0.5Ω·cm 2 Hereinafter, the volume resistivity R V With the interface resistance R I The ratio of R V / R I 3cm -1 Above and 20cm -1 the following.

[0192] [2] According to the electrode of [1], wherein the conductive agent comprises at least flake graphite, and the content of the flake graphite in the active material layer is more than 3% by mass relative to the mass of the active material layer.

[0193] [3] The electrode according to [1] or [2], wherein the thickness of the aforementioned active material layer is 10 μm or more and 60 μm or less.

[0194] [4] The electrode according to any one of [1] to [3], wherein the lithium nickel cobalt manganese composite oxide is made of Li a Ni (1-b-c-d) Co b Mn c M d ​O2 represents 1≤a≤1.2, 0≤b≤0.4, 0≤c≤0.4 and 0≤d≤0.1, and M contains a compound having 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.

[0195] [5] A battery comprising any one of [1] to [4] electrodes and an electrolyte.

[0196] [6] A battery pack comprising the battery described in [5].

[0197] [Explanation of reference numerals in the attached figures] 1 Electrode assembly; 2 Outer packaging component; 3 Positive electrode; 3a Positive electrode current collector; 3b Layer containing positive electrode active material; 4 Negative electrode; 4a Negative electrode current collector; 4b Layer containing negative electrode active material; 5 Separator; 6 Negative terminal; 7 Positive terminal; 11 Electrode assembly; 12 Container; 13 Rectangular cover; 14 Negative electrode current collector tab; 16 Glass material; 17 Positive electrode current collector tab; 18 Positive terminal; 20 Battery pack; 21 Single cell; 22 Adhesive tape; 23 Battery assembly; 24 Printed circuit board; 25 Thermistor; 26 Protection circuit; 27 Terminal for powering external devices; 28 Positive side lead; 29 Positive side connector; 30 Negative side lead; 31 Negative side connector; 32 Wiring; 33 Wiring; 34a Positive side wiring; 34b Negative side wiring; 35 Wiring; 36 Protective plate; 37 Storage container; 38 Lid; 51 Negative terminal; 61 Positive terminal.

Claims

1. An electrode comprising a current collector and an active material layer, the active material layer being located on the current collector and containing an active material and a conductive agent. The active material comprises a lithium nickel cobalt manganese composite oxide. The specific surface area S of the active material layer obtained by nitrogen adsorption method BET The specific surface area S of the pores in the active material layer obtained by mercury intrusion porosimetry Hg Satisfying 0.8 BET / S Hg <2.0 relationship,​ The volume resistivity R of the active material layer V The interfacial resistance R at the interface between the current collector and the layer containing the active material is below 10 Ω·cm. I 0.5Ω·cm 2 Hereinafter, the volume resistivity R V With the interface resistance R I The ratio of R V / R I 3cm -1 Above and 20cm -1 the following.

2. The electrode according to claim 1, wherein, The conductive agent contains at least flake graphite, and the content of the flake graphite in the active material layer is more than 3% by mass relative to the mass of the active material layer.

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

4. The electrode according to claim 1 or 2, wherein, The lithium-nickel-cobalt-manganese composite oxide is made of Li a Ni (1-b-c-d) Co b Mn c M d O2 represents 1≤a≤1.2, 0≤b≤0.4, 0≤c≤0.4 and 0≤d≤0.1, and M contains a compound having 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 electrodes and electrolyte as described in claim 1 or 2.

6. A battery pack comprising the battery of claim 5.

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