Positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery

Abstract

The present invention relates to a positive electrode active material for a lithium ion secondary battery, which contains a lithium-nickel composite oxide having a hexagonal layered structure, and which is characterized in that the lithium-nickel composite oxide has a mass ratio of Li: Ni: M = a: b: c (0.90 < = a < 1.00, 0.80 < = b < 1.00, 0.00 < c < = 0.20, and b + c = 1), and in that the mass ratio of Li: Ni: M = a: b: c (0.90 < = a < 1.00, 0.80 < = b < 1.00, 0.00 < c < = 0.20, and b + c = 1); the element M is at least one element selected from the group consisting of Mn, Co, Al, Ti, Zr, W, Fe, Si, Nb, Mg, Ca, B, Na, K, Mo, Cu, V, P, and Ba), the occupancy of nickel present in the lithium site obtained by a powder neutron diffraction pattern is 2.5%-10.0%, and the half-value width of the diffraction peak of the (003) plane in a powder X-ray diffraction pattern is 0.054 DEG or more and less than 0.074 DEG.

Description

Technical Field

[0001] This disclosure relates to positive electrode active materials for lithium-ion secondary batteries and lithium-ion secondary batteries. Background Technology

[0002] In recent years, with the widespread adoption of portable electronic devices such as handheld telephones and laptop computers, there is a strong demand for the development of small, lightweight, and non-aqueous electrolyte secondary batteries with high energy density and durability. Furthermore, there is a strong demand for high-output secondary batteries used in electric vehicles, such as power tools and hybrid vehicles.

[0003] As a secondary battery that meets these requirements, there are non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries. Lithium-ion secondary batteries using lithium metal composite oxides with layered or spinel-type crystal structures as the positive electrode active material have achieved high voltages in the 4V range, and their practical application as high-energy-density batteries is underway.

[0004] As lithium metal composite oxides, lithium-cobalt composite oxide (LiCoO2), which is relatively easy to synthesize, lithium-nickel composite oxide (LiNiO2), which uses nickel, which is cheaper than cobalt, and lithium-nickel-cobalt-manganese composite oxide (LiNiO2) were proposed. 1 / 3 Co 1 / 3 Mn 1 / 3 O2), using manganese-based lithium manganese composite oxide (LiMn2O4), lithium nickel manganese composite oxide (LiNi 0.5 Mn 0.5 O2), etc.

[0005] In recent years, there has been a growing demand for improved performance in lithium-ion secondary batteries, leading to various research studies.

[0006] For example, Patent Documents 1 to 5 disclose improved cycle characteristics, such as capacity retention rate, for lithium-ion secondary batteries using lithium composite oxides by controlling the particle characteristics of the lithium composite oxides.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2001-243949 Patent Document 2: Japanese Patent Application Publication No. 2004-355824 Patent Document 3: Japanese Patent Application Publication No. 2017-188444 Patent Document 4: Japanese Patent Application Publication No. 2017-188445 Patent Document 5: International Publication No. 2017 / 169129 Summary of the Invention The problem that the invention aims to solve However, as lithium-ion secondary batteries are used for various applications as described above, further performance improvements are required. Therefore, for the positive electrode active material used in lithium-ion secondary batteries, there is a need to improve its performance, such as cycle characteristics, using methods different from the past.

[0008] Therefore, in view of the problems of the prior art, one aspect of the present invention is to provide a positive electrode active material for lithium-ion secondary batteries that has excellent cycle characteristics when used in lithium-ion secondary batteries.

[0009] Methods for solving problems To solve the above-mentioned problems, according to one aspect of the present invention, A positive electrode active material for lithium-ion secondary batteries is provided, which is a lithium-nickel composite oxide containing a hexagonal crystal layered structure. The aforementioned lithium-nickel composite oxide contains lithium (Li), nickel (Ni), and element M in a molar ratio of Li:Ni:M = a:b:c (where 0.90≤a<1.00, 0.80≤b<1.00, 0.00<c≤0.20, b+c=1, and element M is selected from at least one element chosen from the group consisting of Mn, Co, Al, Ti, Zr, W, Fe, Si, Nb, Mg, Ca, B, Na, K, Mo, Cu, V, P, and Ba). The lithium-nickel composite oxide powder neutron diffraction pattern was analyzed using the Rietveld method, revealing that the nickel content at the lithium sites (3b sites) was between 2.5% and 10.0%. The half-width of the diffraction peaks on the (003) plane of the powder X-ray diffraction pattern of the aforementioned lithium-nickel composite oxide, measured using Cu-Kα rays as an X-ray source, is greater than 0.054° and less than 0.074°.

[0010] The effects of the invention According to one aspect of the present invention, it is possible to provide a positive electrode active material for lithium-ion secondary batteries that exhibits excellent cycle characteristics when used in lithium-ion secondary batteries. Attached Figure Description

[0011] Figure 1 This describes the process for manufacturing the positive electrode active material.

[0012] Figure 2 A schematic diagram illustrating the coin-shaped battery used for battery evaluation.

[0013] Figure 3A schematic diagram illustrating the laminated battery used for battery evaluation.

[0014] Figure 4 The image shows the powder neutron diffraction pattern of the lithium-nickel composite oxide obtained in Example 1, and the simulated pattern resolved using Rietveld. Detailed Implementation

[0015] Hereinafter, specific embodiments will be described with reference to the accompanying drawings. The present invention is not limited to the following embodiments, and various modifications and substitutions can be applied to the following embodiments without departing from the scope of the present invention.

[0016] [Positive electrode active material for lithium-ion secondary batteries] The positive electrode active material (hereinafter also referred to as "positive electrode active material") for lithium-ion secondary batteries according to this embodiment will be described below.

[0017] (1) For lithium-nickel composite oxides The positive electrode active material of this embodiment contains lithium-nickel composite oxide. The positive electrode active material of this embodiment may consist solely of lithium-nickel composite oxide, and even in this case, it is possible that it contains unavoidable impurities introduced during the manufacturing process.

[0018] Lithium-nickel composite oxides can have a hexagonal layered structure.

[0019] (1-1) Regarding the shape of particles The morphology of the particles in lithium nickel composite oxides is not particularly limited. For example, it can contain at least one of a single primary particle and a secondary particle formed by the aggregation of multiple primary particles. Therefore, lithium nickel composite oxides can contain both a single primary particle and the aforementioned secondary particles. Furthermore, lithium nickel composite oxides can be composed of only a single primary particle or only secondary particles.

[0020] The lithium-nickel composite oxide preferably contains individual primary particles, and preferably has a high number ratio. This is because, by including individual primary particles in the lithium-nickel composite oxide and increasing its number ratio, the cycle characteristics as capacity retention during repeated charge-discharge are particularly improved when the positive electrode active material of this embodiment is used in a secondary battery. This is believed to be because, by including individual primary particles in the lithium-nickel composite oxide and increasing its number ratio, particle collapse during repeated charge-discharge is suppressed, and a large number of particles conducive to charge-discharge are maintained.

[0021] Preferably, the proportion of individual primary particles relative to the total number of particles in the lithium nickel composite oxide is 30% or more, more preferably 50% or more. The proportion of individual primary particles in the lithium nickel composite oxide is 100%, meaning it can consist solely of individual primary particles.

[0022] Furthermore, when the lithium nickel composite oxide contains secondary particles, it is preferable that the number of primary particles constituting the secondary particles is small. Specifically, the number of primary particles constituting the secondary particles is preferably 15 or less, more preferably 10 or less. By keeping the number of primary particles constituting the secondary particles in the lithium nickel composite oxide small, when the positive electrode active material of this embodiment is used in a lithium-ion secondary battery (hereinafter also referred to as "secondary battery"), the cycle characteristics as capacity retention during repeated charge and discharge are particularly improved.

[0023] When determining whether the particles of lithium-nickel composite oxide are primary particles, secondary particles, or both, a general situation can be confirmed by observing the images (hereinafter also referred to as "SEM images") of the particles using a scanning electron microscope (SEM). However, this method is sometimes inaccurate. In the positive electrode active material involved in this embodiment, it is preferable to process the particles into a cross-section and use the SEM image to determine the presence or absence of primary and secondary particles.

[0024] Specifically, for example, lithium-nickel composite oxide is preferably embedded in resin and processed using a cross-sectional polishing (CP) machine to achieve a state where the particles can be observed in cross-section. Then, SEM images are observed to determine the presence or absence of primary and secondary particles. Preferably, the above evaluation is performed on 50 or more particles. There is no particular upper limit to the number of particles evaluated; however, considering the productivity of the evaluation, it is preferable to evaluate particles of 200 or fewer. Furthermore, the aforementioned ratio of primary particle numbers can be calculated from the evaluation results.

[0025] Furthermore, when using a focused ion beam (FIB) processing apparatus for band contrast and cross-section processing in electron beam backscatter diffraction (hereinafter also referred to as "EBSD"), the aforementioned particle cross-section can be confirmed by observing images using an attached scanning ion microscope (SIM).

[0026] (1-2) Constituent elements The lithium-nickel composite oxide comprises lithium (Li), nickel (Ni), and element M (M). Furthermore, element M may be at least one element selected from the group consisting of Mn, Co, Al, Ti, Zr, W, Fe, Si, Nb, Mg, Ca, B, Na, K, Mo, Cu, V, P, and Ba. Additionally, a small amount of elements other than those listed above may be included.

[0027] Lithium-nickel composite oxides can contain lithium (Li), nickel (Ni), and element M (M) except for oxygen in a molar ratio of Li:Ni:M = a:b:c.

[0028] The above a, b, c satisfy 0.90≤a<1.00, 0.80≤b<1.00, 0.00<c≤0.20, and b+c=1.

[0029] In addition, lithium-nickel composite oxides can use Li a Ni b M c O 2＋α Statement: α preferably satisfies -0.2 ≤ α ≤ 0.2. Since a, b, c, and element M have already been described, their explanation is omitted.

[0030] The following explains each element.

[0031] (lithium) In the above molar ratios, the value of 'a' representing the molar ratio of Li corresponds to the molar ratio of lithium (Li) to the molar ratio of elements other than lithium and oxygen (Me) (Li / Me ratio). Elements other than lithium and oxygen (Me) are equivalent to Ni and element M. In the above molar ratios, 'a' ranges from 0.90 to 1.00. That is, lithium is preferably deficient compared to the case where the stoichiometric ratio of lithium-nickel composite oxide is 'a' = 1.00.

[0032] By setting the value of 'a' to 0.90 or higher, the reaction resistance is suppressed, thereby increasing the battery output. By setting the value of 'a' to less than 1.00, the amount of lithium compounds, i.e., the alkali content, adhering to the particle surface of the positive electrode active material of this embodiment can be suppressed. Therefore, when the positive electrode active material of this embodiment is applied to a secondary battery, gas generation during the battery reaction can be suppressed.

[0033] The preferred value for 'a' is 0.92 ≤ a < 0.99.

[0034] (nickel) In the above-mentioned mass ratios, the range of b, which represents the mass ratio of Ni, is 0.80 ≤ b < 1.00. When the value of b is within the above range, the positive electrode active material of this embodiment can be applied to a secondary battery to achieve a high battery capacity.

[0035] (Element M) In the above-mentioned mass ratio, the range of c, representing the mass ratio of element M, is 0.00 < c ≤ 0.20, preferably 0.02 ≤ c ≤ 0.20, and more preferably 0.05 ≤ c ≤ 0.20. Furthermore, the lithium-nickel composite oxide may contain multiple types of element M. In this case, the total mass ratio of element M contained in the lithium-nickel composite oxide preferably satisfies the above-mentioned range. Since candidate elements of element M have already been described, their details are omitted here. The types of element M contained in the lithium-nickel composite oxide can be appropriately selected according to the required battery characteristics, etc.

[0036] For example, element M may contain Co. When the mass ratio of Co contained in the above-mentioned mass ratio c is c1, the range of c1 is preferably 0 < c1 ≤ 0.20, more preferably 0.02 ≤ c1 ≤ 0.18, and even more preferably 0.03 ≤ c1 ≤ 0.15. When the value of c1 is within the above range, when the positive electrode active material of this embodiment is applied to a secondary battery, high thermal stability and output characteristics can be achieved. In addition, when element M contains only Co, c = c1. Furthermore, as described above, the total mass of element M preferably satisfies the range of c described above. Therefore, for example, the total of c1 + c2 + c3 with c2 and c3 described below preferably satisfies the suitable range of c described above.

[0037] Furthermore, element M may include Mn. When the molar ratio of Mn contained in c is c2, the range of c2 is preferably 0 < c2 ≤ 0.20, more preferably 0.02 ≤ c2 ≤ 0.20, and even more preferably 0.05 ≤ c2 ≤ 0.20. When c2 is within the above range, thermal stability can be improved when the positive electrode active material of this embodiment is applied to a secondary battery. Additionally, when element M contains only Mn, c = c2.

[0038] Element M may include Al. When the mass ratio of Al contained in c in the above-mentioned mass ratio is c3, the range of c3 is preferably 0 < c3 ≤ 0.10, more preferably 0.01 ≤ c3 ≤ 0.08, and even more preferably 0.01 ≤ c3 ≤ 0.06. When c3 is within the above range, the thermal stability can be improved when the positive electrode active material of this embodiment is applied to a secondary battery. Furthermore, when element M contains only Al, c = c3.

[0039] In addition, the composition of lithium-nickel composite oxides can be determined by quantitative analysis using inductively coupled plasma (ICP) luminescence analysis.

[0040] (1-3) Nickel occupancy at lithium sites (3b sites) The lithium-nickel composite oxide contained in the positive electrode active material of this embodiment has a nickel (Ni) occupancy rate of lithium sites (3b sites) obtained by resolving the powder neutron diffraction pattern determined by powder neutron diffraction using the Rietveld method. This occupancy rate is preferably 2.5% or more and 10.0% or less, more preferably 2.6% or more and 8.0% or less, and even more preferably 2.7% or more and 7.0% or less.

[0041] Furthermore, the nickel occupancy of lithium sites (3b sites) obtained from the above powder neutron diffraction pattern is hereinafter referred to as "Ni(Li(3b))".

[0042] Under repeated charge-discharge cycles of the secondary battery, lithium is repeatedly inserted into and removed from the interlayers of the lithium-nickel composite oxide. However, during repeated charge-discharge cycles, the interlayers repeatedly expand and contract due to lithium insertion and removal, resulting in changes in the crystal structure of the lithium-nickel composite oxide, which does not contribute to lithium generation during charge-discharge. Therefore, the cycle performance is considered to be reduced.

[0043] In contrast, in the lithium-nickel composite oxide contained in the positive electrode active material of this embodiment, nickel occupies a portion of the lithium sites. Therefore, even when lithium is detached from the interlayer of the lithium-nickel composite oxide, nickel remains in that interlayer. That is, this nickel is considered to act as a pillar in that interlayer, suppressing changes in the interlayer distance during repeated charging and discharging of the secondary battery. Therefore, even during repeated charging and discharging of the secondary battery, changes in the crystal structure of the lithium-nickel composite oxide can be suppressed, and the generation of lithium that does not contribute to charging and discharging can be suppressed. Therefore, according to the positive electrode active material of this embodiment, by controlling the occupancy rate of nickel occupied by lithium sites that were not previously used, the cycle characteristics in the case of a secondary battery can be improved.

[0044] Specifically, it is believed that by making the Ni(Li(3b)) content 2.5% or higher, the function of nickel as an interlayer pillar can be fully utilized, stabilizing the crystal structure during charge and discharge, and particularly improving cycle characteristics. Furthermore, by making the Ni(Li(3b)) content 10.0% or lower, the reduction in the completeness of the crystallization of the lithium-nickel composite oxide can be suppressed. Therefore, sufficient lithium content is ensured to facilitate charge and discharge, suppressing reaction resistance and significantly improving battery capacity and output.

[0045] Furthermore, when calculating the aforementioned Ni(Li(3b)), the Rietveld analysis was performed using X-ray diffraction patterns. However, the lithium-nickel composite oxide contained in the positive electrode active material of this embodiment may contain elements other than nickel, such as cobalt and manganese, which are difficult to identify using X-rays. In addition, lithium, hydrogen, and oxygen, which are light elements, are difficult to evaluate accurately using X-rays. Therefore, when using X-ray diffraction patterns, it is generally difficult to calculate the accurate value of Ni(Li(3b)).

[0046] In contrast, by using neutron lines, the elements contained in lithium-nickel composite oxides can be evaluated more accurately compared to the case using X-ray diffraction patterns. Therefore, powder neutron diffraction patterns are required when calculating the aforementioned Ni(Li(3b)).

[0047] The half-width of the peak on the (1-4)(003) surface The lithium-nickel composite oxide contained in the positive electrode active material of this embodiment has diffraction peaks belonging to the (003) plane in the powder X-ray diffraction pattern measured by powder X-ray diffraction (hereinafter also referred to as "XRD") using Cu-Kα rays as an X-ray source. Preferably, the lithium-nickel composite oxide contained in the positive electrode active material of this embodiment has a half-width at half-maximum (WWHM) of the diffraction peaks in the (003) plane of the aforementioned X-ray diffraction pattern of 0.054° or more and less than 0.074°. The WWHM of the diffraction peaks in the (003) plane refers to the width of the spectrum in the intensity value of half the intensity of the diffraction peaks belonging to the (003) plane.

[0048] The half-width at half-maximum (WWHM) of the diffraction peaks on the (003) plane is an indicator of the crystallinity of the lithium-nickel composite oxide. Furthermore, by making the WWHM of the diffraction peaks on the (003) plane less than 0.074°, a lithium-nickel composite oxide with particularly excellent crystallinity can be produced. Therefore, when the positive electrode active material of this embodiment containing this lithium-nickel composite oxide is applied to a secondary battery, the battery capacity can be increased, and a secondary battery with excellent battery capacity and cycle characteristics can be produced. However, even if the WWHM of the diffraction peaks on the (003) plane is made excessively small, the effect of increasing the battery capacity will saturate; therefore, the WWHM of the diffraction peaks on the (003) plane is preferably 0.054° or more.

[0049] In addition, the above-mentioned X-ray diffraction pattern is preferably measured using an XRD diffraction apparatus equipped with the Bragg Brentano optical system and using a flat sample holder.

[0050] (1-5) Median particle size (D50) The median particle size (D50) of the particle size distribution of the positive electrode active material obtained by laser diffraction / scattering method is preferably 0.5 μm or more and 20 μm or less, more preferably 1.0 μm or more and 10 μm or less, even more preferably 2.0 μm or less and 8.0 μm or less, and particularly preferably 2.0 μm or more and 7.0 μm or less.

[0051] By making the median particle size of the positive electrode active material of this embodiment less than 20 μm, the contact area with the electrolyte when used in secondary batteries can be sufficiently increased, thereby increasing battery capacity. Furthermore, by making the median particle size of the positive electrode active material of this embodiment greater than 0.5 μm, the operability during electrode fabrication is improved.

[0052] The median particle size (D50) can be determined, for example, from the cumulative volume value measured by a laser diffraction scattering particle size analyzer.

[0053] (1-6) Average primary particle size The average primary particle size of the lithium nickel composite oxide is preferably greater than 0.5 μm and less than 6.0 μm. By making the average primary particle size of the lithium nickel composite oxide greater than 0.5 μm, it means that the size of the primary particles and the microcrystals constituting the primary particles can be sufficiently increased, and the crystallinity of the lithium nickel composite oxide can be improved. Therefore, when the positive electrode active material of this embodiment containing this lithium nickel composite oxide is applied to a secondary battery, the battery capacity can also be improved, and a secondary battery with excellent battery capacity and cycle characteristics can be produced.

[0054] However, even if the average primary particle size of the lithium nickel composite oxide is excessively increased, the effect of improving the battery capacity will saturate. Therefore, the average primary particle size of the lithium nickel composite oxide is preferably 6.0 μm or less.

[0055] The average primary particle size of the lithium-nickel composite oxide is determined by averaging the primary particles observed using a scanning electron microscope (SEM) to measure their major axis length. There is no particular limitation on the number of primary particles evaluated when calculating the average primary particle size.

[0056] For example, in the case where the lithium nickel composite oxide contains secondary particles, it is preferable that for 10 to 20 secondary particles, a total of 20 to 30 primary particles are selected from each secondary particle, and the major axis length of the selected primary particles is measured.

[0057] Furthermore, when the lithium nickel composite oxide contains primary particles that do not constitute secondary particles, it is preferable to evaluate at least 5 primary particles. There is no particular upper limit to the number of primary particles evaluated in this way; for example, it is preferable to evaluate 20 or fewer.

[0058] When the lithium-nickel composite oxide contains only secondary particles or only primary particles of monomers, the aforementioned number of primary particles can be selected for each type of primary particle. Furthermore, the length of the major axis of the selected primary particles can be measured, and their average value can be used as the average primary particle size of the lithium-nickel composite oxide.

[0059] In the case where the lithium-nickel composite oxide comprises both secondary particles and monomeric primary particles, the number of primary particles selected for each of the secondary particles and monomeric primary particles can be chosen. Furthermore, the length of the major axis of all selected primary particles can be measured, and their average value can be set as the average primary particle size of the lithium-nickel composite oxide.

[0060] For the positive electrode active material, the median particle size (D50) is within the range described above, and for the contained lithium nickel composite oxide, the average primary particle size is within the range described above. Thus, when the positive electrode active material is applied to a secondary battery, the battery capacity and cycle characteristics can be particularly improved, thus achieving both.

[0061] (1-7) Lithium dissolution From the viewpoint of suppressing gas generation in secondary batteries, in the positive electrode active material of this embodiment, the amount of lithium dissolved in water when the positive electrode active material is immersed in water (hereinafter also referred to as "dissolved lithium amount") is preferably 0.15% by mass or less, and more preferably 0.10% by mass or less, relative to the total positive electrode active material.

[0062] By keeping the amount of dissolved lithium within the above range, it is possible to suppress the generation of gas in the secondary battery.

[0063] The lower limit of the amount of lithium dissolved from the positive electrode active material in this embodiment is not particularly limited, but is preferably 0.05% by mass or more.

[0064] In order to specifically suppress the amount of lithium dissolved from the positive electrode active material, the lithium-nickel composite oxide preferably contains Zr as element M. Furthermore, by performing a water washing treatment on the positive electrode active material, the amount of lithium dissolved can be suppressed.

[0065] [Manufacturing method of positive electrode active material for lithium-ion secondary batteries] The method for manufacturing the positive electrode active material for lithium-ion secondary batteries described above is not particularly limited if a positive electrode active material with the aforementioned characteristics is obtained. Hereinafter, an example of the method for manufacturing the positive electrode active material according to this embodiment will be described.

[0066] Furthermore, as described above, the positive electrode active material manufacturing method of this embodiment can manufacture the described positive electrode active material, therefore, some of the already described matters are omitted from the description.

[0067] The method for manufacturing the positive electrode active material in this embodiment can be based on, for example... Figure 1 The process 10 shown is implemented. That is, the method for manufacturing the positive electrode active material in this embodiment can include a mixing step (S1) and a calcination step (S2).

[0068] In the mixing process (S1), nickel composite compounds and lithium compounds can be mixed to obtain a raw material mixture.

[0069] In the calcination process (S2), the above-mentioned raw material mixture can be calcined to generate lithium-nickel composite oxide.

[0070] In addition, in the mixing process (S1), element M, unlike the nickel composite compound mentioned above, can be added as a compound containing element M, or a nickel composite compound containing element M can be used.

[0071] The following is an example of the composition of each process.

[0072] (1) Mixing process (S1) In the mixing step (S1), as described above, the nickel composite compound and the lithium compound can be mixed to obtain a raw material mixture. Furthermore, in the mixing step, a compound containing element M can be added as needed, and then mixed.

[0073] Nickel compounds, lithium compounds, and compounds containing element M as needed can be added and mixed, for example, in powder (solid phase). The following describes the materials supplied to the mixing process.

[0074] (1-1) For raw materials (Nickel complex) The nickel composite compound used in the mixing process (S1) can be obtained by known methods. The content ratio (composition ratio) of element Ni and element M (such as Co) in the nickel composite compound is essentially maintained even in lithium nickel composite oxide particles. Therefore, the content ratio of each element is preferably within the same range as that in the lithium nickel composite oxide described above. Therefore, the nickel composite compound preferably contains nickel (Ni) and element M (M) in a mass ratio of Ni:M = b:c. b, c, and element M have been described in the lithium nickel composite oxide, and their description is omitted here.

[0075] In addition, the nickel composite compound used in this embodiment may contain a small amount of the above-mentioned elements (elements M such as Ni and Co) and elements other than oxygen, without hindering the effects of the present invention.

[0076] Nickel complex compounds can be hydroxides or oxides. Furthermore, they can be mixtures of hydroxides and oxides. Methods for manufacturing nickel complex hydroxides include, for example, neutralization crystallization using an aqueous solution of a metal salt and an alkaline solution. Additionally, by heat treatment of the nickel complex hydroxide, or by removing moisture from the nickel complex hydroxide, some or all of the nickel complex hydroxide can be converted into nickel complex oxides.

[0077] Furthermore, when the nickel complex compound is a nickel complex hydroxide, Ni is preferred. b M c (OH) 2＋β Furthermore, when the nickel complex compound is a nickel complex oxide, Ni is preferred. b M c O 1＋γ For elements b, c, and M, which are described in the lithium-nickel composite oxide, the description is omitted. β and γ preferably satisfy -0.2 ≤ β ≤ 0.2 and -0.2 ≤ γ ≤ 0.2, respectively.

[0078] (Lithium compounds) The lithium compound is not particularly limited, and any known compound containing lithium can be used, such as one or more selected from lithium carbonate, lithium hydroxide, and lithium nitrate. Alternatively, the lithium compound can be a mixture of two or more compounds selected from the above-mentioned compounds.

[0079] From the viewpoint of minimizing the impact of residual impurities and allowing for dissolution at the firing temperature, lithium compounds are more preferably selected from one or more of lithium carbonate and lithium hydroxide. Furthermore, from the viewpoint of obtaining lithium-nickel composite oxides with particularly high crystallinity, lithium hydroxide is more preferably selected as the lithium compound.

[0080] (Compounds of element M) As described above, during the mixing process, a compound of element M can be added as needed and mixed. The type of compound of element M is not particularly limited, but it is preferred to use one or more selected from hydroxides, oxides, chlorides, nitrates, sulfates, carbonates, etc.

[0081] (1-2) Mixing method There are no particular limitations on the method of mixing the nickel complex, lithium compound, and compound containing element M as needed. It is preferable to mix the particles thoroughly without disrupting their framework.

[0082] The mixing of raw materials such as nickel composite compounds can be carried out using, for example, a general mixer, such as a vibratory mixer, laser mixer, Julia mixer, V stirrer, etc. Insufficient mixing can sometimes lead to deviations in the mass ratio (Li / Me) of lithium (Li) and elements other than lithium and oxygen (Me) among the individual particles of the positive electrode active material, resulting in problems such as insufficient battery characteristics. Therefore, thorough mixing is preferable. As mentioned above, elements other than lithium and oxygen (Me) are equivalent to Ni and element M.

[0083] (1-3) Mixing ratio The lithium compound is preferably mixed such that the Li / Me ratio in the mixture obtained by the mixing process is 0.90 or higher and less than 1.00. That is, the Li / Me ratio in the raw material mixture is preferably mixed in the same way as the Li / Me ratio in the resulting calcined product. This is because the molar ratios of each element, Li, nickel, and element M, do not change before and after the calcination process (S2), so the Li / Me ratio of the raw material mixture in the mixing process (S1) is equal to that of the calcined product. In addition, the content (ratio) of elements in the raw material mixture is essentially maintained even in lithium-nickel composite oxides.

[0084] (2) Firing process (S2) The firing process (S2) is a process of firing the raw material mixture obtained from the mixing process (S1) to obtain a calcined product containing lithium-nickel composite oxide. When the raw material mixture is fired, lithium from the lithium compound diffuses into the nickel composite compound, forming a lithium-nickel composite oxide. The lithium compound melts at the firing temperature and penetrates into the nickel composite compound, forming a calcined product of lithium-nickel composite oxide.

[0085] The firing conditions in the firing process (S2) are not particularly limited. For a lithium-nickel composite oxide composition as the target, the conditions can be selected in a way that makes the characteristics such as the nickel content at the lithium site (3b site) within the desired range. Hereinafter, examples of suitable firing conditions will be described.

[0086] (atmosphere) The firing atmosphere is preferably an oxidizing atmosphere. This oxidizing atmosphere preferably has an oxygen concentration of 80% by volume or more, more preferably 85% by volume or more. Alternatively, the oxidizing atmosphere can also be an oxygen atmosphere, and therefore the oxygen concentration can be 100% by volume or less.

[0087] (Firing temperature) The firing process is preferably carried out in two stages. That is, the temperature is preferably raised to the firing temperature of the first stage, held (first firing step), then raised to the firing temperature of the second stage, held (second firing step), and then cooled.

[0088] For example, the first firing temperature, which is the firing temperature of the first stage, is preferably 400°C or higher and 600°C or lower, and the holding time at the first firing temperature is preferably 5 hours or higher.

[0089] The second firing temperature, which is the firing temperature for the second stage, is preferably higher than 770°C and lower than 950°C, and the holding time at the second firing temperature is preferably 10 hours or more.

[0090] When firing using the above-described temperature pattern, even with Li deficiency compared to the stoichiometric ratio, the crystallinity of the lithium-nickel composite oxide increases, resulting in a high-capacity positive electrode active material. Furthermore, the nickel content at the lithium sites (3b sites) can be easily set within the range described above. Moreover, the crystallinity of the resulting lithium-nickel composite oxide is particularly improved. Additionally, depending on the lithium and nickel content ratio in the desired composition of the lithium-nickel composite oxide, firing conditions such as suitable firing temperature can vary by ensuring the nickel content at the lithium sites (3b sites) is within a desired range. Therefore, it is preferable to select the optimal firing temperature, heating rate, holding time, and other temperature conditions within the above-described temperature range based on the desired composition.

[0091] In the case of a two-stage firing process, in the first firing process at the first firing temperature of the first stage, the lithium compound can be melted and fully diffused in the nickel composite compound, allowing the lithium to react with the nickel composite compound. Furthermore, in the second firing process at the second firing temperature of the second stage, crystal growth can be promoted.

[0092] The method for manufacturing the positive electrode active material in this embodiment can include any process other than the mixing process and the firing process described above.

[0093] (3) Crushing process The calcined material obtained from the calcination process (S2) can be the positive electrode active material of this embodiment. However, although sintering between particles in the calcined material obtained after the calcination process (S2) is suppressed, coarse particles are sometimes formed due to weak sintering and agglomeration. In such cases, the method for manufacturing the positive electrode active material of this embodiment can include a pulverizing process for pulverizing the calcined material. By pulverizing the calcined material, the aforementioned sintering and agglomeration can be eliminated to adjust the particle size distribution.

[0094] (4) Crushing process The method for manufacturing the positive electrode active material in this embodiment can include a pulverization step of pulverizing the calcined material or the pulverized powder after the calcination step (S2) or after the pulverization step described above.

[0095] The method for manufacturing the positive electrode active material in this embodiment includes a pulverization step, which enables secondary particles to be converted into primary particles, thereby allowing the primary particles to obtain the main lithium-nickel composite oxide.

[0096] The primary particles obtained after the pulverization process can be used alone or mixed with aggregated particles.

[0097] In addition, after the crushing process, screening can be performed to select particles of the desired particle size.

[0098] (5) Water washing process The method for manufacturing the positive electrode active material in this embodiment can include a water washing process for washing the calcined material obtained from the calcination process (S2).

[0099] By implementing a water washing process, residual lithium remaining on the surface of lithium-nickel composite oxide particles can be removed.

[0100] In the water washing process, the fired material can be mixed with water and used as a slurry for water washing (slurrying process).

[0101] There are no particular limitations on the water used for slurrying in the washing process. For example, it is preferable to use water with a conductivity of less than 10 μS / cm, and more preferably water with a conductivity of less than 1 μS / cm.

[0102] In addition, during the washing process, it is preferable to use a slurry prepared by stirring.

[0103] In the washing process, after slurry formation, the slurry can be separated into solid and liquid components, namely filtered and dewatered, to obtain washed powder (solid-liquid separation process). There are no particular limitations on the equipment used for filtration and dewatering; for example, centrifugal separators and filter presses can be used for solid-liquid separation.

[0104] In the washing process, the water-containing washed powder obtained after solid-liquid separation is preferably dried (drying process). There are no particular limitations on the drying conditions, but it is preferred to carry out the drying at a temperature of 100°C to 350°C in an oxidizing atmosphere or a vacuum atmosphere.

[0105] Furthermore, by washing the calcined lithium-nickel composite oxide produced during the mixing process under conditions where the Li / Me ratio is 1.00 or higher as described above, a lithium-nickel composite oxide with a Li / Me ratio of 0.90 or higher and less than 1.00 can be obtained. However, under the above conditions, according to the inventors' research based on the present invention, the positive electrode active material that meets the requirements of the positive electrode active material of this embodiment cannot be obtained regarding the nickel occupancy at the lithium site (3b site), and the effect of the positive electrode active material of this embodiment cannot be obtained.

[0106] [Lithium-ion secondary battery] The lithium-ion secondary battery of this embodiment has at least a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode may contain the positive electrode active material for lithium-ion secondary batteries described above.

[0107] Hereinafter, for one configuration example of the secondary battery of this embodiment, each component will be described. The secondary battery of this embodiment, for example, includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is constructed using the same components as a general lithium-ion secondary battery. Furthermore, the embodiments described below are merely illustrative, and the lithium-ion secondary battery of this embodiment can be implemented with various modifications and improvements based on the knowledge of those skilled in the art, as exemplified by the following embodiments. Moreover, the application of the secondary battery is not particularly limited.

[0108] (positive electrode) The positive electrode of the secondary battery in this embodiment can contain the positive electrode active material described above.

[0109] The following is an example of a method for manufacturing the positive electrode. First, the aforementioned positive electrode active material (powder), conductive material, and binder (adhesive) can be mixed to form a positive electrode composite material. Then, solvents for purposes such as activated carbon and viscosity adjustment are added as needed, and the mixture is kneaded to produce a positive electrode composite material paste.

[0110] The mixing ratio of the various materials in the cathode composite becomes a key factor determining the performance of the lithium-ion secondary battery, and therefore can be adjusted according to the application. The mixing ratio of the materials can be the same as that of the cathode of a known lithium-ion secondary battery. For example, when the total mass of the solid components of the cathode composite excluding the solvent is set to 100% by mass, it can contain the following proportions: cathode active material of 60% to 95% by mass, conductive material of 1% to 20% by mass, and binder of 1% to 20% by mass.

[0111] The obtained positive electrode paste is coated, for example, onto the surface of an aluminum foil current collector, and dried to allow the solvent to disperse, thus producing a sheet-like positive electrode. If necessary, to increase the electrode density, pressure can be applied using methods such as roller pressing. The sheet-like positive electrode obtained in this way can be cut to appropriate sizes according to the desired battery and supplied for battery manufacturing.

[0112] As conductive materials, for example, carbon black materials such as graphite (natural graphite, artificial graphite, and expanded graphite), acetylene black, and Ketjen black (registered trademark) can be used.

[0113] As a binder (adhesive), it plays a role in retaining the particles of active substances. For example, it is possible to use one or more of the following: poly(1,1-difluoroethylene) (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene monomer (EPDM), styrene butadiene, cellulose resins, and polyacrylic acid.

[0114] The cathode active material and conductive material can be dispersed as needed, and a solvent for dissolving the binder can be added to the cathode composite. Specifically, organic solvents such as N-methyl-2-pyrrolidone can be used as the solvent. Furthermore, activated carbon can be added to the cathode composite to increase the double-layer capacity.

[0115] The method for manufacturing the positive electrode is not limited to the methods exemplified above; other methods can be used. For example, the positive electrode composite material can be pressed into shape and then dried under a vacuum atmosphere.

[0116] (negative electrode) The negative electrode can be made of metallic lithium, lithium alloys, etc. Alternatively, the negative electrode can be formed by mixing a binder with a negative electrode active material capable of absorbing and releasing lithium ions, coating the paste-like negative electrode material (with the addition of a suitable solvent) onto the surface of a metal foil current collector such as copper, drying it, and then compressing it as needed to increase the electrode density.

[0117] As the negative electrode active material, for example, sintered organic compounds such as natural graphite, artificial graphite, and phenolic resins, and powdered carbonaceous materials such as coke can be used. In this case, as the negative electrode binder, fluorinated resins such as PVDF can be used, similar to those used for the positive electrode, and organic solvents such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing these active materials and binders.

[0118] (partition) It can be configured to sandwich a separator between the positive and negative electrodes as needed. The separator is a separator that separates the positive and negative electrodes and retains the electrolyte. Known separators can be used, for example, thin films of polyethylene, polypropylene, etc., and membranes with a large number of tiny pores.

[0119] (Non-aqueous electrolyte) As a non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used.

[0120] As a non-aqueous electrolyte, a non-aqueous electrolyte in which lithium salt, as a supporting salt, is dissolved in an organic solvent can be used. Furthermore, a non-aqueous electrolyte in which lithium salt is dissolved in an ionic liquid can be used. Additionally, an ionic liquid refers to a salt composed of cations and anions other than lithium ions, which is liquid at room temperature.

[0121] As an organic solvent, one of the following can be used alone, or two or more can be used in combination: cyclic carbonates such as ethylene carbonate, propylene carbonate, butyl carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butane sulcolone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate.

[0122] As supporting salts, LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, and their complex salts can be used. Furthermore, the non-aqueous electrolyte can contain free radical scavengers, surfactants, and flame retardants.

[0123] Furthermore, solid electrolytes can be used as non-aqueous electrolytes. Solid electrolytes possess the property of being able to withstand high voltages. Examples of solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

[0124] Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0125] There are no particular limitations on the oxide-based solid electrolyte; for example, an oxide-based solid electrolyte containing oxygen (O) and possessing lithium-ion conductivity and electronic insulation properties can be used. Examples of oxide-based solid electrolytes include lithium phosphate (Li3PO4) and Li3PO4N... X LiBO2N X , LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1＋X Al X Ti 2-X (PO4)3 (0≤X≤1), Li 1＋X Al X Ge 2-X (PO4)3(0≤X≤1), LiTi2(PO4)3, Li 3X La 2 / 3-X TiO3(0≤X≤2 / 3), Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O 12 Li 3.6 Si 0.6 P 0.4 One or more of the following: O4, etc.

[0126] There are no particular limitations on the sulfide-based solid electrolyte; for example, a sulfide-based solid electrolyte containing sulfur (S) and possessing lithium-ion conductivity and electronic insulation properties can be used. For example, one or more of the following can be used as a sulfide-based solid electrolyte: Li₂S-P₂S₅, Li₂S-SiS₂, LiI-Li₂S-SiS₂, LiI-Li₂S-P₂S₅, LiI-Li₂S-B₂S₃, Li₃PO₄-Li₂S-Si₂S, Li₃PO₄-Li₂S-SiS₂, LiPO₄-Li₂S-SiS, LiI-Li₂S-P₂O₅, and LiI-Li₃PO₄-P₂S₅.

[0127] In addition, other inorganic solid electrolytes besides those mentioned above can be used as inorganic solid electrolytes, such as Li3N, LiI, Li3N-LiI-LiOH, etc.

[0128] As an organic solid electrolyte, there are no particular limitations if it is a polymeric compound exhibiting ionic conductivity; for example, copolymers such as polyethylene oxide and polypropylene oxide can be used. Furthermore, the organic solid electrolyte may contain a supporting salt (lithium salt).

[0129] (The shape and structure of a secondary battery) As described above, the lithium-ion secondary battery of this embodiment can be in various shapes such as cylindrical or stacked. Even when any shape is used, if a non-aqueous electrolyte is used as the electrolyte in the secondary battery of this embodiment, the positive and negative electrodes can be stacked together by means of a separator to form an electrode body. The resulting electrode body is impregnated with a non-aqueous electrolyte, and the positive current collector is connected to the positive terminal that extends to the outside, and the negative current collector is connected to the negative terminal that extends to the outside, using current-collecting leads or the like, to form a structure that is sealed within the battery casing.

[0130] Furthermore, as described above, the secondary battery of this embodiment is not limited to the form in which a non-aqueous electrolyte is used as a non-aqueous electrolyte. For example, a secondary battery using a solid non-aqueous electrolyte, i.e., an all-solid-state battery, can be manufactured. In the case of manufacturing an all-solid-state battery, the composition other than the positive electrode active material can be changed as needed.

[0131] The secondary battery of this embodiment can be used for various applications. It can be manufactured as a high-capacity, high-output secondary battery, and is therefore generally suitable for power supplies in small portable electronic devices requiring high capacity (laptop personal computers, mobile phone terminals, etc.) and for power supplies in electric vehicles requiring high output.

[0132] Furthermore, the secondary battery of this embodiment can be miniaturized and has a high output, making it suitable as a power source for electric vehicles where installation space is limited. In addition, the secondary battery of this embodiment can be used not only as a power source for purely electrically driven electric vehicles, but also as a power source for so-called hybrid vehicles that use combustion mechanisms in conjunction with gasoline engines, diesel engines, etc.

[0133] Example The present invention will be further described in detail below through embodiments, but the present invention is not limited to these embodiments in any way.

[0134] Here, we will first explain the positive electrode active material and the evaluation method of the secondary battery obtained from the following examples and comparative examples.

[0135] (Evaluation of positive electrode active material) The obtained positive electrode active material was evaluated as follows.

[0136] (a) Evaluation of the composition For the positive electrode active material, the composition was analyzed by ICP-luminescence analysis. The evaluation results are shown in the "Composition" column of Table 1.

[0137] (b) Nickel occupancy at lithium site (3b) Approximately 2g of the positive electrode active material prepared according to the following examples and comparative examples was filled into a vanadium tube and then completely sealed. Furthermore, neutron diffraction measurements were performed using the BL20 (iMATERIA) of the Japan Proton Accelerator Research Complex (J-PARC) at an intensity of over 10,000 cps in two-frame mode.

[0138] The neutron diffraction pattern obtained from the back-side detector array was analyzed using the Z-Code software using Rietveld. The space group was set to R-3m, and lithium at site 3b and nickel mixed in (nickel at lithium sites) were seeded with nickel and element M at site 3a. After refining the size factor, lattice constant, and global parameters, the seat occupancy and atomic coordinates were also refined. Furthermore, for atomic displacement parameters, lithium was set to 0.9–1.0 Å. 2 Nickel and element M: 0.3–0.5 Å 2 Oxygen: 0.6–0.8 Å 2The range was fixed. After refining the seat occupancy and atomic coordinates, it was assumed that the S-value of the reliability parameter converged below 3.0. The nickel seat occupancy of the lithium site (3b site) was calculated, and the results are shown in the "Ni Occupancy at 3b Sites" column of Table 1. In addition, the S-value used as a reliability parameter during Rietveld analysis is shown in the "S-value" column of Table 1.

[0139] In addition, powder neutron diffraction measurements can be performed using HRPD (High Resolution Powder Diffractometer) at the JRR-3 reactor of the Japan Atomic Energy Agency and SuperHRPD at J-PARC.

[0140] (c)(003) Half-width of surface peak X-ray diffraction patterns were measured using Cu-Kα rays as the X-ray source in an XRD diffraction apparatus (PANalytical, X'Pert PRO). The half-width of the spectrum, representing half the maximum intensity, was calculated from the diffraction peaks of the (003) plane of the hexagonal layered structure obtained from the obtained X-ray diffraction pattern. The sample was filled into the groove of a circular glass holder (flat sample holder, inner diameter 24 mm φ, groove depth 0.5 mm, PANalytical part number 9200 540 12391) with an outer diameter of 32 mm φ, and fixed to a predetermined sample holder (PANalytical part number 9430018 13321) for measurement. Furthermore, the XRD diffraction apparatus used was equipped with a Bragg Brentano optical system.

[0141] The evaluation results are displayed in the “(003) Half-value Width” column of Table 1.

[0142] Furthermore, the obtained X-ray diffraction pattern confirms that the positive electrode active material prepared by the following examples and comparative examples contains lithium nickel composite oxide, which has a hexagonal layered structure.

[0143] (d) Average primary particle size In the SEM images of lithium-nickel composite oxide particles, 15 secondary particles that could be observed as a whole through image analysis were selected, and primary particles were then selected from each of the selected secondary particles. At this point, primary particles were selected in total, totaling 30.

[0144] Furthermore, in cases where lithium-nickel composite oxide particles contain primary particles that do not constitute secondary particles, 10 primary particles that can be observed as a whole are selected in the aforementioned SEM observation images.

[0145] Furthermore, the major axis length of the selected primary particles was measured, and the average value was set as the average primary particle size. The evaluation results are shown in the "Average Primary Particle Size" column of Table 1.

[0146] In addition, when the lithium nickel composite oxide particles contain only secondary particles, the major axis length of 30 primary particles selected from the secondary particles is measured, and the average of the major axis lengths of all 30 primary particles is set as the average primary particle size of the lithium nickel composite oxide particles.

[0147] Furthermore, when the lithium-nickel composite oxide particles contain primary particles other than secondary particles, the major axis lengths of 30 primary particles selected from the secondary particles and 10 primary particles selected from the primary particles are measured. The average major axis length of all 40 measured primary particles is then set as the average primary particle size of the lithium-nickel composite oxide particle.

[0148] (e) Median particle size (D50) The particle size distribution of a volume reference is determined using a laser diffraction scattering particle size analyzer (manufactured by Nikkiso Corporation, micro-track HRA), and the median particle size is obtained from this particle size distribution.

[0149] The evaluation results are shown in the "D50" column of Table 1.

[0150] (f) The ratio of the number of individual primary particles After embedding lithium-nickel composite oxide particles in thermosetting resin, they were polished using a cross-section polisher (Nippon Electron Ltd., SM-09010). The resulting particle cross-sections were observed using a Schottky field emission scanning electron microscope (Carl Zeiss Ltd., Ultra 55), and the number ratio of individual primary particles was evaluated using 100 particles.

[0151] (Making and evaluating a secondary battery) (a) Evaluation of charging capacity, discharging capacity, and coulombic efficiency (a-1) Making a coin-shaped battery Using the positive electrode active material prepared by the following examples and comparative examples, a process was carried out to produce... Figure 2 The coin-shaped battery shown.

[0152] Figure 2 As shown, the coin-shaped battery CBA consists of a housing CA and electrodes housed within the housing CA.

[0153] The housing CA has a hollow positive electrode container PC with an opening at one end, and a negative electrode container NC disposed at the opening of the positive electrode container PC. If the negative electrode container NC is disposed at the opening of the positive electrode container PC, it is configured such that a space for accommodating electrodes is formed between the negative electrode container NC and the positive electrode container PC.

[0154] The electrode comprises a positive electrode PE, a separator SE1, and a negative electrode NE, which are arranged and stacked in sequence. The positive electrode PE is in contact with the inner surface of the positive electrode container PC, and the negative electrode NE is housed in the housing CA through a wave-shaped gasket WW, in contact with the inner surface of the negative electrode container NC.

[0155] In addition, the housing CA is equipped with a gasket GA, which maintains a non-contact state between the positive electrode tank PC and the negative electrode tank NC, i.e., an electrically insulating state, thereby controlling their relative movement and fixing them in place. Furthermore, the gasket GA seals the gap between the positive electrode tank PC and the negative electrode tank NC, and has the function of completely blocking the airtight and liquid-tight connection between the inside and outside of the housing CA.

[0156] The coin-shaped battery CBA is manufactured as follows. First, 52.5 mg of the positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene (PTFE) resin obtained from the various examples and comparative examples are mixed. The resulting mixture is then thinned into a film with a diameter of 11 mm and a weight of approximately 75 mg to form the positive electrode PE. This film is then dried in a vacuum dryer at 100°C for 12 hours.

[0157] Using the prepared positive electrode PE, negative electrode NE, separator SE1, and electrolyte, the coin-shaped battery CBA was fabricated in a glove box under an Ar atmosphere where the dew point was managed to be -60°C.

[0158] The negative electrode (NE) uses lithium metal that has been stamped into a disc shape with a diameter of 13mm.

[0159] The separator SE1 uses a 25 μm thick porous polyethylene membrane. The electrolyte is a 1:1 mixture (manufactured by Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1M LiClO4 as the supporting electrolyte.

[0160] (a-2) Evaluation of charging capacity, discharging capacity, and efficiency After fabricating the coin-shaped battery CBA, let it sit for about 12 hours until the open circuit voltage (OCV) stabilizes, then set the current density relative to the positive terminal to 0.1 mA / cm². 2The capacity at which charging continues until the cutoff voltage of 4.3V is defined as the charging capacity. Furthermore, after charging is stopped for one hour, the capacity at which discharging continues until the cutoff voltage of 2.5V is defined as the discharging capacity. Finally, the coulombic efficiency, which is the ratio of the discharging capacity to the charging capacity, is calculated.

[0161] (b) Cyclic characteristics (b-1) Fabrication of laminated batteries Using the positive electrode active material prepared by the following examples and comparative examples, a process was carried out to produce... Figure 3 The laminated battery shown.

[0162] Figure 3 As shown, the laminated battery LBA has a structure in which the product obtained by impregnating the positive electrode film PS, separator SE2, and negative electrode film NS with electrolyte is sealed by the laminate LA. In addition, the positive electrode film PS is connected to a positive electrode fin PT, the negative electrode film NS is connected to a negative electrode fin NT, and the positive electrode fin PT and the negative electrode fin NT are exposed outside the laminate LA.

[0163] The laminated battery (LBA) is fabricated as follows: 20.0 g of the obtained positive electrode active material, 2.35 g of acetylene black, and 1.18 g of poly(1,1-difluoroethylene) are dispersed in a slurry of N-methyl-2-pyrrolidone (NMP) on an Al foil at a density of 1 cm. 2 The positive electrode active material was coated with a paste containing 7.0 mg of positive electrode active material. Next, the product obtained by coating the Al foil with the paste containing the positive electrode active material was dried in the atmosphere at 120°C for 30 minutes to remove NMP. The Al foil coated with the positive electrode active material was cut into strips with a width of 66 mm and rolled under a load of 1.2 t to produce a positive electrode film. Furthermore, the positive electrode film was cut into rectangles of 50 mm × 30 mm and dried in a vacuum dryer at 120°C for 12 hours to obtain the positive electrode film PS for a laminated battery (LBA).

[0164] In addition, a negative electrode paste, consisting of a mixture of graphite powder with an average particle size of approximately 20 μm and poly(1,1-difluoroethylene), was prepared and coated onto the negative electrode membrane NS of copper foil. The separator SE2 used a porous polyethylene membrane with a thickness of 20 μm, and the electrolyte was a 3:7 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1M LiPF6 as the supporting electrolyte (manufactured by Ube Industries, Ltd.).

[0165] In a dry chamber where the dew point is controlled at -60°C, an electrolyte is impregnated in the above-mentioned stack of positive electrode film PS, separator SE2 and negative electrode film NS, and sealed by stacking LA to produce a laminated battery LBA.

[0166] (b-2) Cyclic characteristics Cyclic characteristics were evaluated by measuring the capacity retention after 500 charge-discharge cycles. Specifically, firstly, the laminated battery LBA was placed in a thermostatic bath maintained at 25°C with a current density of 0.3 mA / cm². 2 The circuit is charged until the cutoff voltage reaches 4.2V, then stopped after 10 minutes. This process is repeated five times, alternating between charging and discharging until the cutoff voltage reaches 2.5V. Next, the circuit is maintained in a constant temperature bath at 45°C with a current density of 2.0 mA / cm². 2 The circuit was charged until the cutoff voltage of 4.2V, then stopped after 10 minutes. This process was repeated 500 times until the cutoff voltage of 2.5V was reached. Furthermore, the capacity retention rate, calculated as the ratio of the adjusted discharge capacity of the 500th cycle to the discharge capacity of the first cycle, was evaluated. The discharge capacity of the first cycle and the capacity retention rate are displayed in the "Initial Discharge Capacity" and "Capacity Retention Rate" columns of "Cycle Characteristics" in Table 1.

[0167] (Manufacturing conditions for positive electrode active materials) [Example 1] Nickel composite oxide (D50 particle size: 5.2 μm) with a nickel:co molar ratio of Ni:Co = 95.0:5.0, obtained using a known method, is mixed with lithium hydroxide to prepare a raw material mixture (mixing process).

[0168] In the mixing process, a vibratory mixer (Willi A Bachofen (WAB) type: TURBULA Type T2C) is used to thoroughly mix the nickel composite oxide with lithium hydroxide to prepare the raw material mixture.

[0169] In the mixing process, each raw material was weighed and mixed such that the mass ratio of lithium (Li) in the raw material mixture to nickel and cobalt (Me), which are metals other than lithium, was 0.92. Furthermore, the nickel composite oxide was obtained by heat treatment of a nickel composite hydroxide obtained using a crystallization method.

[0170] The raw material mixture is fired in an oxygen-containing atmosphere with an oxygen concentration of 90% by volume and the remainder being nitrogen (firing process). The oxygen concentration in the oxygen-containing atmosphere during the firing process is shown in the "Oxygen Concentration" column of Table 1. In the first firing process, the temperature is raised to 500°C, the first firing temperature, and held at 500°C for 7 hours. After the first firing process, a second firing process is performed. In the second firing process, the temperature is raised to 780°C, the second firing temperature, and held at 780°C for 12 hours, thus completing the firing.

[0171] The pulverized and calcined lithium-nickel composite oxide (pulverization process) yields a positive electrode active material containing lithium-nickel composite oxide particles.

[0172] The obtained positive electrode active material was observed using SEM, and the results confirmed that the average primary particle size of the lithium nickel composite oxide particles was 1.2 μm, consisting of secondary particles containing these primary particles. That is, the ratio of individual primary particles was 0. This was also true in Examples 2 and 4 below.

[0173] Other evaluation results are shown in Table 1.

[0174] Figure 4 The powder neutron diffraction pattern of the lithium-nickel composite oxide, as determined in Example 1, is shown (Observed). Figure 4 The diagram also displays the simulated pattern obtained by Rietveld analysis, the difference between the measured powder neutron diffraction pattern and the simulated pattern, and the Bragg positions. Figure 4 In region 40, during the measurement of this region, a peak was generated in the neutron line of the cut wavelength due to a problem with the device, which was not cut during the normal measurement, and therefore it was excluded from the objects analyzed by Rietveld.

[0175] Furthermore, using the obtained positive electrode active material, the described coin-shaped battery and laminated battery were fabricated and evaluated. The evaluation results are shown in Table 1.

[0176] [Example 2] In the mixing process, the mixing ratio of lithium hydroxide and nickel composite oxide was varied so that the Li / Me ratio of the raw material mixture was as shown in the "Li / Me Ratio Added" column of Table 1. Furthermore, the holding time at the first firing temperature in the first firing process was set to the conditions shown in Table 1. Apart from the above points, positive electrode active materials, coin-type batteries, and laminated batteries were fabricated under the same conditions as in Example 1 and evaluated. The evaluation results are shown in Table 1.

[0177] [Example 3] The holding time at the first firing temperature in the first firing process, the holding time at the second firing temperature in the second firing process, and the oxygen concentration in the oxygen-containing atmosphere of the firing process were set to the conditions shown in Table 1. Furthermore, the lithium-nickel composite oxide after the pulverization process was pulverized using a ball mill (pulverization process) to obtain a positive electrode active material containing lithium-nickel composite oxide particles.

[0178] In addition to the points mentioned above, positive electrode active materials, coin-shaped batteries, and laminated batteries were fabricated under the same conditions as in Example 2 and evaluated. The evaluation results are shown in Table 1.

[0179] The obtained positive electrode active material was observed by SEM, and the results confirmed that the lithium nickel composite oxide particles contained individual primary particles as well as secondary particles formed by the aggregation of multiple primary particles.

[0180] The ratio of the number of particles in a single event was calculated to be 91.3%.

[0181] [Example 4] In the mixing process, a nickel composite oxide with a nickel:Mn:Co mass ratio of Ni:Mn:Co = 85.0:10.0:5.0 is used as the nickel composite oxide. Furthermore, the mixing ratio of lithium hydroxide to the nickel composite oxide is selected such that the Li / Me ratio for the raw material mixture is the value shown in the "Li / Me Ratio Added" column of Table 1.

[0182] In the firing process, the holding time at the first firing temperature in the first firing process and the second firing temperature in the second firing process were set to the conditions shown in Table 1. Except for the points mentioned above, positive electrode active materials, coin-type batteries, and laminated batteries were fabricated under the same conditions as in Example 1 and evaluated. The evaluation results are shown in Table 1.

[0183] [Example 5] The holding time at the first firing temperature in the first firing process, the holding time at the second firing temperature in the second firing process, and the oxygen concentration in the oxygen-containing atmosphere of the firing process were set to the conditions shown in Table 1. Furthermore, the lithium-nickel composite oxide after the pulverization process was pulverized using a ball mill (pulverization process) to obtain a positive electrode active material containing lithium-nickel composite oxide particles.

[0184] In addition to the points mentioned above, positive electrode active materials, coin-shaped batteries, and laminated batteries were fabricated under the same conditions as in Example 4 and evaluated. The evaluation results are shown in Table 1.

[0185] The obtained positive electrode active material was observed by SEM, and the results confirmed that the lithium nickel composite oxide particles contained individual primary particles as well as secondary particles formed by the aggregation of multiple primary particles.

[0186] The ratio of the number of particles in a single event was calculated to be 97.5%.

[0187] [Comparative Example 1] The mixing ratio of lithium hydroxide to nickel composite oxide was varied in the mixing process to achieve the Li / Me ratio of the raw material mixture as shown in the "Li / Me Ratio Added" column of Table 1. Apart from the points mentioned above, positive electrode active materials, coin-type batteries, and laminated batteries were fabricated and evaluated under the same conditions as in Example 2. The evaluation results are shown in Table 1.

[0188] [Comparative Example 2] Pure water at 20°C was added to the positive electrode active material obtained from Comparative Example 1 to prepare a slurry containing 1250g of positive electrode active material per 1L of water (slurry preparation process). Next, the slurry was stirred for 20 minutes and then passed through a filter press for dehydration to produce a washed filter cake (solid-liquid separation process). Water with a conductivity of 1μS / cm or less was used as the pure water.

[0189] The obtained washed filter cake was dried at 190°C for 10 hours under vacuum to obtain the positive electrode active material of Comparative Example 2 (drying process).

[0190] The obtained positive electrode active material was evaluated as described above. The evaluation results are shown in Table 1. Furthermore, using the obtained positive electrode active material, except for the procedures described in Example 1, coin-type batteries and laminated batteries were fabricated and evaluated. The evaluation results are shown in Table 1.

[0191] [Comparative Example 3] In the mixing process, the mixing ratio of lithium hydroxide and nickel composite oxide was varied so that the Li / Me ratio of the raw material mixture was the value shown in the "Li / Me Ratio Added" column of Table 1. Apart from the points mentioned above, positive electrode active materials, coin-type batteries, and laminated batteries were prepared under the same conditions as in Example 4 and evaluated. The evaluation results are shown in Table 1.

[0192] [Table 1] (Evaluation Results) Based on the results shown in Table 1, it can be confirmed that the positive electrode active materials of Examples 1 to 3, which contain lithium sites (3b sites) and have a nickel content of 2.5% to 10.0%, can improve cycle characteristics compared with Comparative Examples 1 and 2, which have the same nickel and element M content ratios.

[0193] Furthermore, a comparison of Examples 4 and 5 with Comparative Example 3 confirms that they are identical.

[0194] This application claims priority based on Japan Patent Application No. 2023-123249, filed on July 28, 2023, the entire contents of which are incorporated herein by reference.

[0195] Explanation of symbols CBA coin-type battery PE positive electrode NE negative electrode SE1 partition GA washers WW wave washers CA casing PC Positive Electrode Can NC negative electrode container LBA laminated cells PS positive electrode film NS negative electrode film SE2 partition LA lamination PT positive electrode fin NT negative electrode fin

Claims

1. A positive electrode active material for lithium-ion secondary batteries, comprising a lithium-nickel composite oxide with a hexagonal crystal system layered structure. The lithium-nickel composite oxide contains lithium (Li), nickel (Ni), and element M (M) in a mass ratio of Li:Ni:M = a:b:c. 0.90≤a<1.00, 0.80≤b<1.00, 0.00<c≤0.20, b+c=1, wherein the element M is at least one element selected from the group consisting of Mn, Co, Al, Ti, Zr, W, Fe, Si, Nb, Mg, Ca, B, Na, K, Mo, Cu, V, P, and Ba. The lithium-nickel composite oxide powder neutron diffraction pattern was analyzed using the Rietveld method, revealing that the nickel occupancy at the lithium site (3b site) was between 2.5% and 10.0%. The half-width of the diffraction peaks on the (003) plane of the powder X-ray diffraction pattern of the lithium-nickel composite oxide, measured using Cu-Kα rays as an X-ray source, is greater than 0.054° and less than 0.074°.

2. The positive electrode active material for lithium-ion secondary batteries according to claim 1, The average primary particle size of the lithium-nickel composite oxide is greater than 0.5 μm and less than 6.0 μm.

3. The positive electrode active material for lithium-ion secondary batteries according to claim 1 or 2, The median particle size in the volumetric reference particle size distribution obtained by laser diffraction / scattering method is between 0.5 μm and 20 μm.

4. A lithium-ion secondary battery, comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises the positive electrode active material for lithium-ion secondary batteries as described in any one of claims 1 to 3.

Images