Li-Ni composite oxide particles and non-aqueous electrolyte secondary battery

Abstract

The present invention provides a positive electrode active material particle powder of a lithium nickelate composite oxide having high energy density and excellent charge-discharge cycle characteristics when charged at high voltage, and a non-aqueous electrolyte secondary battery. The present invention provides a positive electrode active material particle powder, characterized in that the lithium nickelate composite oxide Li with a layered structure is 1+a Ni 1－b－c Co b M c O 2 (M is at least one of the elements Mn, Al, B, Mg, Ti, Sn, Zn, and Zr, -0.1≤a≤0.2, 0.05≤b≤0.5, 0.01≤c≤0.4) as the core particle X, and having a coating compound Y with an average film thickness of 0.2 to 5 nm containing at least one of the elements Al, Mg, Zr, Ti, and Si, and a layered rock salt structure containing Ni 2+ The ionic crystal phase exists between the core particle X and the coating compound Y as a layer.

Description

Technical Field

[0001] The present invention relates to positive electrode active material particles having high energy density and excellent charge-discharge cycle performance, and a non-aqueous electrolyte secondary battery using the same. Background Art

[0002] In recent years, the miniaturization and lightness of electronic devices such as mobile phones and personal computers have accelerated, and the demand for secondary batteries with high energy density as power sources for these devices has increased. Under such circumstances, batteries with large charge and discharge capacity per weight and volume and high charge and discharge cycle characteristics have attracted much attention.

[0003] At present, as a kind of positive electrode active material particle powder useful in high-energy lithium-ion secondary batteries, a layered structure of lithium nickel oxide LiNiO2 with a voltage of 4V is known. Compared with the lithium cobalt oxide LiCoO2 particle powder of the common positive electrode active material, the above-mentioned LiNiO2 particle powder is low-priced and has a high capacity, and has excellent output characteristics. Therefore, it is mainly used as the main power supply of electric tools. In recent years, it has also been used as a driving power supply for electric vehicles by utilizing its characteristics. However, due to Li + Segregation of substances other than ions from active material particles and incomplete reaction between raw material powders during synthesis cause problems such as reduced charge-discharge cycle characteristics. Therefore, further improvement of powder characteristics is required.

[0004] As is well known, in the NiO6 octahedron of the lithium nickelate crystal constituting the positive electrode active material particle powder, Ni 3+ The ion is in a low spin state at room temperature. 3+ The electron configuration of the ion's d orbital is t 2g 6 e g 1 , e g The electron in the Ni-O bond lengthens the distance between Ni and O, reducing the bonding strength. As a result, it is difficult to say that the stability of lithium nickelate crystals is high. 2+ Ions and Li + The ionic radius of the ions is close, which easily causes the structural defect of cation mixing during synthesis. That is, LiNiO2 particle powder represents Li 1－z Ni 1+z O2 (z>0) has a non-stoichiometric composition with Ni 2+ Ions exist in Li + In addition, when lithium nickelate is used as the positive electrode active material, the charged Ni 4+ ions are also in a metastable state, releasing oxygen at high temperatures, and developing thermal runaway of the battery. 3+Ions, Al 3+ Ion replacement of heterogeneous elements such as Ni 3+ ions to achieve improvement (Non-patent Reference 1).

[0005] On the other hand, when Ni is replaced by heterogeneous element ions 3+ The positive electrode active material particle powder of the lithium nickelate composite oxide with ions also contains lithium carbonate and lithium hydroxide in an amount greater than required as an impurity phase. The lithium compound in the impurity phase is the main factor in increasing the pH of the powder, causing gelation during the preparation of the electrode slurry, and further, as the secondary battery is charged and discharged, causing gas generation as a side reaction during high-temperature storage. In particular, the influence of lithium hydroxide is significant, so the unreacted products present on the surface of the particle powder are carbonated (patent references 1 and 2), or removed by washing with water and drying (non-patent reference 2). In addition, the side reaction is the generation of gas accompanying the charge and discharge of the secondary battery. + Electrochemical reactions or chemical reactions other than the change in the valence of transition metals in and out of the electrode active material. For example, there is the generation of hydrofluoric acid in the electrolyte caused by mixing or reaction between the generated water and the electrolyte LiPF6, and the reaction in which the electrode active material is destroyed by the hydrofluoric acid is a side reaction.

[0006] As a further improvement of the positive electrode active material particle powder of the nickelate lithium composite oxide, it is proposed to form the particle powder into a surface treatment of the core particle, and convert the unreacted lithium carbonate and lithium hydroxide into another lithium compound. The coating formed by the surface treatment acts as a protective film against hydrofluoric acid generated as a side reaction product during charging and discharging, thereby extending the life of the battery (Non-patent Reference 3).

[0007] As another further improvement of the positive electrode active material particle powder of the lithium nickel oxide composite oxide, a surface treatment using vapor phase growth to form the particle powder into a core particle was proposed, and a scheme of coating the inorganic compound with a very thin film was studied. The very thin film does not hinder the Li + The entry and exit of ions suppresses the collapse of the crystal structure near the surface of the particles accompanying charge and discharge, thereby extending the life of the battery (Non-Patent References 4 to 6).

[0008] Prior art literature

[0009] Non-patent literature

[0010] Non-patent document 1: C. Delmas et al., Electrochimica Acta, Vol. 45, 1999, pp. 243-253

[0011] Non-patent document 2: J. Kim et al., Electrochem. And Solid-State Lett., Vol. 9, 2006, pp. A19-A23

[0012] Non-patent document 3: M.-J. Lee et al., J. Mater. Chem. A, Vol. 3, 2015, pp. 13453-13460

[0013] Non-patent document 4: J.-S. Park et al., Chem. Mater., Vol. 26, 2014, pp. 3128-3134

[0014] Non-patent document 5: D. Mohanty et al., Scientific Reports, Vol. 6, 2016, pp. 26532-1-16

[0015] Non-patent document 6: Y.Cho et al., Nano Lett., Vol.13, 2013, pp.1145-1152

[0016] Patent Literature

[0017] Patent Document 1: Japanese Patent Application Laid-Open No. 10-302779

[0018] Patent Document 2: Japanese Patent Application Publication No. 2004-335345 Summary of the invention

[0019] Problems to be solved by the invention

[0020] Currently, positive electrode active material particles of lithium nickelate composite oxide for non-aqueous electrolyte secondary batteries that maintain high capacity during high voltage charging and exhibit excellent charge and discharge cycle characteristics are most in demand. However, positive electrode active material particles having sufficient characteristics have not yet been obtained.

[0021] That is, in the techniques described in Non-Patent Documents 1 and 2 and Patent Documents 1 and 2, even if the lithium hydroxide and / or lithium carbonate contained can be reduced, the side reactions generated at the positive electrode active material / electrolyte interface cannot be suppressed due to direct contact with the electrolyte, and it is difficult to say that they show excellent charge-discharge cycle characteristics. In addition, the cost of washing and drying the lithium nickelate composite oxide particles is relatively high, and it is difficult to say that it is a method suitable for mass production.

[0022] The technique described in non-patent document 3 is a method for treating the surface of lithium nickelate composite oxide particles with vanadium using a sol-gel method. However, vanadium has low safety and is an expensive method such as a sol-gel method, so it is difficult to say that it is a method suitable for mass production. In addition, the thickness of the obtained surface coating is 17 nm, which is too thick to suppress side reactions at the positive electrode active material / electrolyte interface.

[0023] The technology described in Non-Patent Document 4 is to use an atomic layer deposition method to deposit Ni 2+ A method for forming a very thin inorganic compound film on the surface of lithium nickelate composite oxide particles containing mainly nickel ions. However, it is difficult to say that only a very thin inorganic compound film can fully maintain direct contact between the positive electrode active material particles and the electrolyte, and it is difficult to say that the charge and discharge cycle characteristics of the battery are fully improved. In addition, compared with Ni 2+ Compared with lithium nickel oxide, which is mainly composed of Ni 3+ The surface of lithium nickelate particles, which are mainly ions, is highly alkaline. Therefore, it is difficult to say that each particle powder has the same problem regarding the surface state, and therefore the design concept of the particle powder is also different.

[0024] The technology described in Non-Patent Document 5 is to use an atomic layer deposition method to deposit Ni 3+ A method for forming a very thin film of an inorganic compound on the surface of a lithium nickelate composite oxide particle powder mainly composed of nickel ions. However, as mentioned above, it is difficult to say that only a very thin film of an inorganic compound can fully maintain direct contact between the positive electrode active material particles and the electrolyte, and it is difficult to say that the charge and discharge cycle characteristics of the battery are improved. In addition, it is difficult to say that the high alkalinity Ni 3+ The surface of the particles of lithium nickelate mainly composed of ions is fully surface treated.

[0025] In the technology described in Non-Patent Document 6, Ni 2+ Ion to Li + The site replacement of ions is used as a pillar effect. 2+ The crystalline phase of the layered rock salt structure of the ions covers the surface of the positive electrode active material particles to stabilize the surface of the particles. However, using only the above technology, the surface layer of the positive electrode active material particles is not sufficiently stabilized, and it is difficult to say that the charge and discharge cycle characteristics of the battery are fully improved.

[0026] Therefore, an object of the present invention is to provide positive electrode active material particles of lithium nickelate composite oxide which maintain high voltage and high capacity and have excellent charge and discharge cycle characteristics, and a secondary battery using the positive electrode active material particles.

[0027] Methods for solving problems

[0028] The above-mentioned technical problems can be achieved by the present invention described below.

[0029] That is, the present invention provides a positive electrode active material particle powder, characterized in that the layered structure of the lithium nickel oxide composite oxide Li 1+a Ni 1－b－c Co b M c O2 (M is at least one of the elements Mn, Al, B, Mg, Ti, Sn, Zn, and Zr, -0.1≤a≤0.2, 0.05≤b≤0.5, 0.01≤c≤0.4) as the core particle X, and having a coating compound Y with an average film thickness of 0.2 to 5 nm containing at least one of the elements Al, Mg, Zr, Ti, and Si, and a layered rock salt structure containing Ni 2+ The ionic crystal phase exists as a layer between the core particle X and the coating compound Y (Invention 1).

[0030] The present invention is also the positive electrode active material particles according to Invention 1, wherein the average valence of Ni is 2.80 to 3.10 (Invention 2).

[0031] In addition, the present invention is a positive electrode active material particle powder recorded in the present invention 1, wherein the content of lithium hydroxide LiOH is less than 0.50 weight%, the content of lithium carbonate Li2CO3 is less than 0.65 weight%, and the weight ratio of the lithium carbonate content to the lithium hydroxide content is greater than 0.9 (present invention 3).

[0032] The present invention is also a positive electrode active material particle powder according to the first embodiment of the present invention, wherein the BET specific surface area is 0.05 to 0.7 m 2 / g, median particle size of agglomerated particles D 50 The particle size is 1 to 30 μm, and the pH of the 2% powder is 11.6 or less (Present Invention 4).

[0033] The present invention also provides a non-aqueous electrolyte secondary battery, wherein the positive electrode active material particles described in Invention 1 are used as at least a part of the positive electrode active material (Invention 5).

[0034] Effects of the Invention

[0035] The positive electrode active material particles of the lithium nickelate composite oxide of the present invention have a coating compound Y in the lithium nickelate composite oxide core particles X. At the same time, the layered rock salt structure containing Ni 2+ The ionic crystal phase exists as a layer between the core particle X and the coating compound Y. Therefore, the direct contact between the electrolyte in the battery and the lithium nickelate composite oxide particles is prevented, the side reaction is suppressed, and the Li +As a result, the present invention is suitable as a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery which maintains a high capacity and has excellent charge and discharge cycle characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It uses the existing LiNi 0.80 Co 0.15 Al 0.05 X-ray diffraction pattern of powder with lattice constant of O2. DETAILED DESCRIPTION

[0037] The technical aspects of the present invention will be described in more detail as follows.

[0038] First, the lithium nickelate-based positive electrode active material particles of the present invention will be described.

[0039] The lithium nickelate LiNiO2 in the present invention adopts a trigonal layered structure of the space group R3-m. Here, the - of the space group should be written on 3, but it is recorded as such for convenience. The lithium nickelate LiNiO2 uses a cubic lattice as a unit cell, so the lattice constants that change are the a-axis and the c-axis. In addition, the lithium nickelate composite oxide of the same crystal structure in the present invention uses the lithium nickelate as a matrix and is composed of the chemical formula Li 1+a Ni 1－b－c Co b M c Here, M is at least one of the elements Mn, Al, B, Mg, Ti, Sn, Zn, and Zr, and -0.1≤a≤0.2, 0.05≤b≤0.5, and 0.01≤c≤0.4.

[0040] It is expected that the above M will be dissolved in lithium nickel oxide LiNiO2 due to the replacement of Ni 2+ Ion or Ni 3+ ions, therefore, the average valence of M is preferably close to 2 to 3. In addition, a, b and c preferably range from -0.05≤a≤0.1, 0.06≤b≤0.4, 0.02≤c≤0.38, and more preferably from -0.07≤a≤0.08, 0.07≤b≤0.35, 0.03≤c≤0.36.

[0041] In the nickelate lithium-based positive electrode active material particle powder of the present invention, the particle shown in the above chemical formula is used as the core particle X, and has a coating compound Y with an average film thickness of 0.2 to 5 nm containing at least one of the elements Al, Mg, Zr, Ti, and Si. If it is less than 0.2nm, it becomes a coating compound Y with a low coverage rate, which has no effect on the electrical properties. In addition, if it exceeds 5nm, it becomes an obstacle to the conduction of ions and electrons, high resistance and a bad effect on battery characteristics. Preferably, the above average film thickness is 0.21 to 2.0nm, and more preferably 0.22 to 1.0nm.

[0042] The coated compound Y of the lithium nickelate-based positive electrode active material particle powder of the present invention may be in an amorphous state or in a crystalline state. In the case of the crystalline state, epitaxial growth may also be performed with the core particle as the matrix. Here, epitaxial growth refers to the growth of the crystals of the coated compound Y along the crystal plane of the core particle X. Preferably, the crystalline structure of the coated compound Y is the same or similar crystalline structure as the parent lithium nickelate composite oxide, so that epitaxial growth can be performed. For example, the crystalline structure of the coated compound Y is preferably an oxide such as a layered structure, a layered rock salt structure, a rock salt structure, or a spinel structure. That is, it is preferred that oxygen forms a face-centered cubic lattice, or a deformed face-centered cubic lattice, and the anion layer formed by the oxygen cubic lattice contains at least one cation of the elements Al, Mg, Zr, Ti, and Si. More specifically, γ-Al2O3, α-LiAlO2, MgO, Li2ZrO3, Li2TiO3, etc. can be listed.

[0043] In the lithium nickelate-based positive electrode active material particles of the present invention, the layered rock salt structure containing Ni 2+ The crystalline phase of ions exists as a layer between the core particle X and the coating compound Y. That is, the core particle X is surrounded by the layered rock salt structure containing Ni 2+ The crystalline phase of the ions is covered and is also covered by the coating compound Y. The above Ni 2+ Ion intrusion into regular Li + Ion site, invading Ni 2+ The ions act as pillars to stabilize the interlayers of the layered rock salt structure. With this effect and the presence of the coating compound Y, the charge and discharge cycle characteristics of the battery using the positive electrode active material particles of the lithium nickel oxide composite oxide of the present invention can be further improved.

[0044] In the lithium nickelate-based positive electrode active material particles of the present invention, the core particles X have a layered rock salt structure containing Ni 2+ The mol% of the crystalline phase of the ions is preferably in the range of 0.1 mol% to 3.0 mol%. Here, the layered rock salt structure containing Ni 2+ The crystalline phase of ions exists between the core particle X and the coating compound Y. When the % is less than 0.1 mol, it is not expected that Ni 2+ The stabilization is caused by the pillar effect of ions. In addition, when the content exceeds 3.0 mol%, Li + The resistance to ion migration leads to a decrease in capacity. The more preferred range is 0.2 mol % to 2.5 mol %.

[0045] The average valence of Ni in the lithium nickelate-based positive electrode active material particles of the present invention is preferably 2.80 to 3.10. This is because when the average valence of Ni is within the above range, a high capacity of the battery can be expected. The average valence of Ni is more preferably 2.85 to 3.08, and the average valence of Ni is further preferably 2.90 to 3.05.

[0046] It is preferred that the coating compound Y of the lithium nickelate-based positive electrode active material particles of the present invention contain element Li. By containing Li, the Li in the coating compound Y + The movement of ions becomes easier, and as a result, the resistance of the battery is reduced.

[0047] The lithium nickelate-based positive electrode active material particles of the present invention are preferably positive electrode active material particles further coated with lithium carbonate. Lithium carbonate is one of the side reaction products during charge and discharge, and is one of the main reasons for reducing the charge and discharge cycle characteristics of the battery. By including lithium carbonate in the positive electrode active material before forming the battery, the formation of lithium carbonate, a side reaction product during charge and discharge, can be suppressed, so that the charge and discharge cycle characteristics of the battery are improved.

[0048] In the lithium nickelate-based positive electrode active material particle powder of the present invention, the content of lithium hydroxide LiOH is preferably less than 0.50 weight %, and the content of lithium carbonate Li2CO3 is less than 0.65 weight %. In particular, the lithium hydroxide content is preferably low, and the ratio of the lithium carbonate content to the lithium hydroxide content is preferably 0.9 or more. It is more preferred to reduce the impurity compounds that will become the above-mentioned alkali source as much as possible, the content of LiOH is less than 0.47 weight %, the content of Li2CO3 is less than 0.55 weight %, and the ratio of the lithium carbonate content to the lithium hydroxide content is more than 1.2. It is further preferred that the ratio of the lithium carbonate content to the lithium hydroxide content is 1.4 or more.

[0049] In the lithium nickelate-based positive electrode active material particles of the present invention, the BET specific surface area is preferably 0.05 to 0.7 m 2 / g. Below 0.05m 2 / g, the coarse particles become more, and in addition, when it exceeds 0.7m 2 / g, the particles become bulky and are unsuitable as positive electrode active material particles in either case. More preferably, the particle size is 0.1 to 0.5 m / g. 2 / g.

[0050] In the lithium nickelate-based positive electrode active material particles of the present invention, the median particle size D of the aggregated particles is preferably 50The particle size is 1 to 30 μm. When it is less than 1 μm, the particle powder becomes bulky, and when it exceeds 30 μm, the particles become more coarse, and in either case, it is not suitable as a positive electrode active material particle powder. It is more preferably 2 to 25 μm. It is further preferably 3 to 22 μm.

[0051] In the lithium nickelate-based positive electrode active material particles of the present invention, the 2% pH is preferably 11.6 or less, and more preferably 11.5 or less, from the viewpoint of gelation of the electrode slurry.

[0052] Next, a method for producing the core particle X of the lithium nickelate composite oxide of the present invention will be described.

[0053] In the manufacture of the core particle X of the lithium nickelate composite oxide of the present invention, nickel hydroxide particle powder is used as a precursor. The nickel element of the particle can also be replaced by cobalt element, element M (Mn, Al, B, Mg, Ti, Sn, Zn, Zr). The manufacturing method of the above-mentioned precursor is not particularly limited, and preferably a crystallization method of an ammonia coordination compound based on a wet reaction is used. The above-mentioned precursor is mixed with a lithium raw material and a desired additive, and the obtained mixture is fired. The lithium raw material is not particularly limited, and lithium carbonate, lithium hydroxide, and lithium hydroxide monohydrate can be used.

[0054] The core particle X of the lithium nickelate composite oxide in the present invention is made based on a solid phase reaction method in which a mixture of a precursor used in the aforementioned operation and each raw material is fired. Solid phase reaction is a method in which raw materials containing elements constituting the target particle powder are mixed and a chemical reaction between solid raw materials is promoted by high temperature heat treatment. In order to facilitate the diffusion of lithium in the solid phase reaction relative to the above-mentioned precursor, a lithium raw material with a fine particle size is desired. It is desired to mix the above-mentioned precursor and raw material by a dry method without using a solvent. As a mixing device for the raw material powder, a crusher, a ball mill, a Henschel mixer, a high-speed stirrer, etc. can be used.

[0055] As is well known, in the solid phase reaction synthesis of lithium nickelate, when fired at high temperature, a portion of the nickel is generated as Ni 2+ ions, replaced by Li in the crystal + ions, the battery capacity is reduced. In addition, it is known that during calcination at a higher temperature, as Li evaporates, NiO (Li 1－z Ni 1+z O2 z = 1). X-ray diffraction confirmed that the Ni 2+ Ion Li + Lithium ions are replaced by ions in the layered rock salt structure 1－z Ni 1+ zO2 (z>0) generation. In addition, through high-resolution transmission electron microscopy observation, it is known that Ni 2+ The layered rock salt structure of ions exists in greater quantities on the surface of active material particles (see J.Morales et al., Mat.Res.Bull., Vol.25, 1990, pp.623-630, H.Arai et al., Solid State Ionics, Vol.80, 1995, pp.261-269, and DPAbraham et al., J.Electrochem.Soc., Vol.80, 1995, pp.261-269)

[0056] The method for producing the core particles X of the lithium nickelate composite oxide of the present invention is characterized in that the mixture is fired at a temperature range of 600 to 930°C. When the firing temperature is lower than 600°C, the solid phase reaction cannot be sufficiently carried out, and the desired lithium nickelate composite oxide particle powder cannot be obtained. When the firing temperature exceeds 930°C, Li intrusion occurs as a structural defect. + Ionic sites of Ni 2+ The amount of ions increases, and the Li 1－z Ni 1+z O2 grows into a NiO impurity phase with a rock salt structure. The preferred temperature is 700-900°C.

[0057] In order to reduce Ni 2+ ion content, the core particles X of the lithium nickelate composite oxide in the present invention are preferably fired in an atmosphere with a high oxygen concentration. The holding time of the above-mentioned firing temperature is about 5 to 15 hours, and the heating and cooling rates are about 50 to 200°C / hour. As the firing furnace, a gas circulation box-type muffle furnace, a gas circulation rotary kiln, a roller kiln, etc. can be used.

[0058] In the core particle X of the lithium nickelate composite oxide of the present invention, when it is in the state of the core particle of the lithium nickelate composite oxide before becoming the core particle of the lithium nickelate composite oxide with the coating compound Y, or when it is in the state of the core particle of the lithium nickelate composite oxide with the coating compound Y, the change of the lattice constant and the crystallite size using the crystal information of X-ray diffraction is almost not observed, and the layered structure is maintained. It can be explained that the above results can be obtained because the coating compound Y is very thin. However, through the subsequent heat treatment described later, in the X-ray diffraction, the intensity ratio of the (003) plane of the lithium nickelate composite oxide to the (104) plane decreases, and as Ni 2+ The increase of ions, Li 1－z Ni 1+zThe O2 crystal phase increases. If explained with a simple model, it is speculated that a portion of the LiNiO2 in the surface layer of the core particle is separated into (1 / 2) Li2O and NiO, and changes into (1 / 4) O2 released into the atmosphere. That is, it is speculated that in the nickel oxide lithium positive electrode active material particle powder of the present invention, the layered rock salt structure containing Ni 2+ The crystalline phase of the ions forms a layer between the core particle X and the coating compound Y.

[0059] Next, a method for producing a coating compound Y having an average film thickness of 0.2 to 5 nm and containing at least one of the elements Al, Mg, Zr, Ti, and Si on the core particle X of the lithium nickelate composite oxide of the present invention will be described.

[0060] Preferably, the coating compound Y in the present invention is prepared by a vapor phase growth method. Examples of the vapor phase growth method include chemical vapor deposition (CVD), physical vapor phase growth (PVD), and atomic layer deposition (ALD). The atomic layer deposition method, which is one of the more preferred methods, is a method in which atoms are deposited layer by layer (approximately ) is a method of depositing atoms in a layer or granular form by repeating the following four steps. 1) Supplying raw gas A to the object to be processed, that is, raw gas A reacts on the surface of the object to be processed, 2) exhausting raw gas A, 3) supplying raw gas B that further reacts on the surface of the object to be processed, 4) exhausting raw gas B. Here, raw gas A and raw gas B must be gases of different compositions. (See X. Meng et al., Adv. Mater., Vol. 24, 2012, pp. 3589-3615, AW Weimer, PARTEC 2004, Particle Coating by Atomic Layer Deposition (ALD))

[0061] In the atomic layer deposition method of the manufacturing method of the coating compound Y in the present invention, the preferred combination of raw material gas A and raw material gas B is illustrated below. Raw material gas A / raw material gas B include Al2(CH3)6 / H2O; Mg(C2H5)2 / H2O; ZrCl4 / H2O; TiCl4 / H2O; SiCl4 / H2O, etc., and it is presumed that oxides, carbides, or hydroxides are formed by the same method.

[0062] In the atomic layer deposition method of the method for producing the coating compound Y of the present invention, the number of times of repeating step 1) to step 4) is 1 to 100 times, preferably 2 to 50 times, and more preferably 2 to 10 times.

[0063] In the atomic layer deposition method of the method for producing the coating compound Y in the present invention, the temperature at which the steps 1) to 4) are performed is any temperature within the range of 10 to 250°C.

[0064] In the method for producing the coating compound Y of the present invention, after the aforementioned vapor phase growth treatment, heat treatment can be performed in an air atmosphere at any temperature within the range of 150 to 500°C and the temperature holding time is 2.5 to 10 hours, and the heating and cooling rates are 50 to 200°C / hour. As a heat treatment furnace, a gas circulation box muffle furnace, a gas circulation rotary kiln, a roller kiln, etc. can be used. By performing the above-mentioned heat treatment, the layered rock salt structure containing Ni 2+ The crystalline phase of the ion is formed as a layer between the core particle X and the coating compound Y. The above-mentioned heat treatment can improve the epitaxial growth and crystallinity of the coating compound Y, and can also improve the reactivity of the coating compound Y with Li. Furthermore, the LiOH remaining in the particle powder after the above-mentioned film formation can also be converted into Li2CO3. The more preferred temperature range is 200-450°C, the more preferred temperature holding time is 3-8 hours, and the more preferred heating and cooling rates are 60-180°C / hour. In addition, as the temperature mode of the above-mentioned heat treatment, a mode other than the above-mentioned constant temperature rise and constant temperature drop rate ladder temperature mode can also be applied. That is, it can also be a multi-stage temperature mode such as temporarily keeping 100°C-2 hours at a constant temperature rise rate from room temperature, and further keeping 350°C-2 hours at a constant temperature. In addition to the air atmosphere, the above-mentioned heat treatment can also be carried out in an oxygen atmosphere, a nitrogen atmosphere, a high humidity atmosphere, or an atmosphere in which these atmospheres are compounded.

[0065] As described above, the coating compound Y in the present invention is formed into a film on the core particle X by a vapor phase growth method, and then a heat treatment is performed. Therefore, the coating compound Y is very thin, 0.2 to 5 nm, and is a uniform and highly crystalline thin film. As a particle surface analysis for identifying the crystalline structure of the coating compound Y, scanning transmission electron microscopy (STEM) observation, elemental analysis in the depth direction based on time-of-flight secondary ion mass spectrometry, and elemental analysis in the depth direction based on X-ray photoelectron spectroscopy can be listed. In addition, a method of estimating the concentration of elements dissolved by chemical etching of only the coating compound in a solvent can also be listed.

[0066] The observation of the coated compound Y in the present invention using STEM is carried out as described below. As a pretreatment for observing the sample, the particle powder of the present invention embedded in the resin is thinned into about 100nm by an ion slicer, and any 10 or so locations corresponding to the outermost surface of the agglomerated particles are observed by STEM. At this time, about 10 crystalline particles on the outermost surface are randomly selected, and the crystal band axis of the crystal of the layered structure of the lithium nickelate composite oxide is observed at the same time. The atomic column or atomic layer reflecting the electrostatic potential is observed in the bright field (BF) image to determine the crystal band axis. The position information of the heavy atoms is obtained from the high-angle scattering dark field (HAADF) image, and the influence of the interference fringes that may be generated in the BF image is removed to obtain information about the boundary surface of the core particle X and the coating compound Y. The inner side of the boundary surface becomes the core particle X, and the outer side becomes the coating compound Y. Therefore, the crystallization information of the coating compound Y is obtained from the BF image corresponding to the location. The distorted layer in the crystal of the lithium nickelate composite oxide related to the coating compound Y is confirmed from the low-angle scattering dark field (LAADF) image. The installed energy dispersive X-ray spectrometer (EDS) device identifies elements heavier than boron B and obtains the position information of the element. In addition, the installed electron energy loss spectroscopy (EELS) device identifies light elements such as lithium Li and obtains the position information of the element.

[0067] In the method for producing the coated compound Y of the present invention, the heat treatment after film formation by the aforementioned vapor phase growth method not only has excellent performance of the coated compound Y, but also modifies the surface of other positive electrode active material particles. That is, the aforementioned heat treatment is also accompanied by the effect of efficiently converting the lithium hydroxide LiOH remaining in the positive electrode active material particles into lithium carbonate Li2CO3. In particular, the following technical features can be set: by setting a low heating rate and maintaining the temperature, the moisture in the air is absorbed, and the residual lithium hydroxide LiOH is chemically converted into LiOH·H2O that is easily carbonated at low temperatures. It is also possible to slightly dissolve Li from the lithium nickelate composite oxide and chemically convert it into LiOH·H2O.

[0068] The precipitated lithium carbonate of the present invention is sometimes also in a granular or film-like state. As a particle surface analysis for identifying the structure of the above-mentioned lithium carbonate, STEM observation, high-resolution scanning electron microscope (SEM) observation, elemental analysis in the depth direction based on time-of-flight secondary ion mass spectrometry, elemental analysis in the depth direction based on X-ray photoelectron spectroscopy, etc. can be listed.

[0069] Next, a non-aqueous electrolyte secondary battery using the lithium nickelate-based positive electrode active material particles of the present invention will be described.

[0070] When the positive electrode sheet is manufactured using the positive electrode active material particles of the present invention, a conductive agent and a binder are added and mixed according to a conventional method. As the conductive agent, carbon black, graphite, etc. are preferred. As the binder, polytetrafluoroethylene, polyvinylidene fluoride, etc. are preferred. As a solvent, for example, N-methylpyrrolidone is preferably used. The slurry containing the positive electrode active material particles, the conductive agent and the binder is kneaded until it becomes honey-like using a scraper with a groove of 25μm to 500μm. The obtained positive electrode mixture slurry is applied to the collector at a coating speed of about 60cm / sec, and dried at 80 to 180°C to remove the solvent and soften the binder. An Al foil of about 20μm is used as the collector. The collector coated with the positive electrode mixture is subjected to a calendering roller treatment with a linear pressure of 0.1 to 3t / cm to obtain a positive electrode sheet.

[0071] As the negative electrode active material, lithium metal, lithium / aluminum alloy, lithium / tin alloy, graphite, etc. can be used, and the negative electrode sheet can be produced by the doctor blade method or metal rolling similar to the positive electrode.

[0072] As the solvent of the electrolyte solution, in addition to the combination of ethylene carbonate and diethyl carbonate, at least one organic solvent including carbonates such as propylene carbonate and dimethyl carbonate, and ethers such as dimethoxyethane can be used.

[0073] Furthermore, as the electrolyte, in addition to lithium hexafluorophosphate, at least one lithium salt such as lithium perchlorate or lithium tetrafluoroborate may be dissolved in the above-mentioned solvent and used.

[0074] The secondary battery with a counter electrode Li manufactured using the positive electrode active material particles of the present invention has an initial discharge capacity of 190 mAh / g or more at 25°C after charging at 4.4V to 3.0V. Generally, charging at 4.3V relative to the Li counter electrode is a high voltage, so the capacity is also high, and as a result, a secondary battery with a high energy density is obtained. In addition, within the same voltage range, when discharged at 0.5C for 20, 40, 60, ..., 140 cycles and discharged at 1C for other cycles, the capacity retention rate of 140 cycles is 85% or more relative to the initial discharge capacity at a rate of 1C. As a result, a secondary battery with excellent charge and discharge cycle characteristics when charged at a high voltage is obtained.

[0075] <Function>

[0076] The positive electrode active material particle powder of the lithium nickel oxide composite oxide of the present invention has a uniform and very thin coating compound Y obtained by a vapor phase growth method, and a layer containing Ni having a rock salt layer structure having a pillar effect exists as a layer between the core particle X and the coating compound Y. 2+The coated compound Y has a high coating rate, so when the secondary battery is repeatedly charged and discharged, it shows a high capacity and suppresses the side reactions generated. As a result, it is suitable as a positive electrode active material particle powder and a secondary battery with high energy density and excellent charge and discharge cycle characteristics.

[0077] Example

[0078] Specific examples of the present invention are illustrated below.

[0079] [Example 1]

[0080] Cobalt-containing nickel hydroxide as a precursor 0.84 Co 0.16 (OH)2 is obtained by crystallization of an ammonia coordination compound in an aqueous solvent over several days. The hydroxide, lithium hydroxide monohydrate LiOH·H2O and aluminum hydroxide Al(OH)3 are measured in a predetermined amount in a molar ratio of Li:Ni:Co:Al=1.02:0.81:0.15:0.04, mixed by a high-speed stirrer, and a lithium nickelate composite oxide capable of becoming a core particle X is obtained in a roller kiln at 770°C in an oxygen atmosphere.

[0081] The obtained particle powder that can become the core particle X is treated by atomic layer deposition. The raw material gas A of this method uses trimethylaluminum Al(CH3)3, and the raw material gas B uses H2O. The treatment is performed at 180°C for 4 cycles to obtain lithium nickelate composite oxide particle powder having a coating compound Y.

[0082] 300 g of the obtained lithium nickelate composite oxide with coating compound Y was heat treated at 350°C in the atmosphere for 3 hours at a heating and cooling rate of 150°C / hour from room temperature. It is believed that the LiOH remaining in the particle powder is converted into LiOH·H2O and further converted into Li2CO3 during the heat treatment. In addition, lithium nickelate composite oxide particles with coating compound Y having a high epitaxial growth degree are prepared by the above heat treatment. The obtained oxide particles are treated as positive electrode active material particles.

[0083] The powder evaluation and battery evaluation of the lithium nickelate-based positive electrode active material particles of the present invention were performed as follows. The obtained results are shown in Table 1.

[0084] In order to observe the surface and shape of the sample, a field emission scanning electron microscope (FE-SEM) S-4800 (Hitachi High-Technologies Corporation) was used.

[0085] The coating compound based on the ALD method is presumed to be Al2O3 according to the types of raw material gases. When quantifying, 5 g of the sample is dispersed in 100 cc of pure water. After boiling and cooling, it is calculated based on the amount of dissolved Al. In addition, based on the amount of Al obtained, assuming a true spherical shape with a median particle size D of the agglomerated particles described later, the film thickness of the coating compound is calculated. In addition, the coating rate of this coating compound is set to 100%. 50 The true spherical shape of 50

[0086] The average valence of nickel in the sample is quantified by iodometric titration. 0.100 g of the sample is accurately weighed, dissolved in hydrochloric acid, and mixed with potassium iodide solution. Through this mixing, the dissolved transition metal is reduced to divalent, and the iodide ions are converted into iodine molecules I2. The generated iodine molecules I2 are automatically titrated with a sodium thiosulfate solution of a reducing titration reagent, and thus, the average valence of nickel is obtained. Here, the average valence of cobalt is trivalent.

[0087] After drying and degassing the sample at 250 °C for 10 minutes under nitrogen, the BET specific surface area of the sample is measured using Macsorb [Quantachrome Instruments].

[0088] To identify the crystal phase of the sample and calculate the crystal structure parameters, measurement is performed using a powder X-ray diffractometer SmartLab 3 kW [(Rigaku Corporation)]. The X-ray diffraction pattern is measured through a monochromator under the conditions of Cu-Kα, 40 kV, and 44 mA, and measured at a step of 0.02° with 15 ≤ 2θ (deg.) ≤ 120 and at 3 deg. / min. To calculate the crystal information, the Rietveld method is used. Information on the cation mixing of Ni ions is obtained from the peak intensity ratio of the (003) plane and (104) plane of the layered rock salt structure shown in Figure 1 2+

[0089] The volume-based median particle size D of the agglomerated particles of the sample is measured using a laser diffraction scattering type particle size distribution analyzer SALD-2201 [(Shimadzu Corporation)]. 50

[0090] LiOH and Li2CO3 in the sample are determined by the Warder method calculated based on the hydrochloric acid titration curve of the solution suspended in water solvent at room temperature. Here, 10 g of the sample is suspended in 50 cc of water using a magnetic stirrer for 1 hour.

[0091] 2 g of the sample is suspended in 100 cc of pure water at room temperature, and the 2% pH of the sample is measured using a pH meter.

[0092] ​​​After the sample powder was completely dissolved in hydrochloric acid, the contents of lithium and nickel as main component elements and cobalt and aluminum as auxiliary components of the sample were measured by a calibration curve method using an ICP optical emission spectrometer (ICP-OES) ICPS-7510 [Shimadzu Corporation].

[0093] The secondary battery characteristics of a CR2032-type button battery produced by the following production method were evaluated using the obtained positive electrode active material particles.

[0094] The positive electrode active material, acetylene black as a conductive agent, graphite, and polyvinylidene fluoride as a binder were accurately weighed to a weight ratio of 90:3:3:4, dispersed in N-methyl-2-pyrrolidone, and fully mixed with a high-speed kneading device to prepare a positive electrode mixture slurry. Next, the mixture slurry was coated on the aluminum foil of the collector by a scraper PI-1210 film coater [Tester Sangyo Co., LTD], dried at 120°C, and pressed at 0.5t / cm to make a 1cm 2 A positive electrode sheet containing 9 mg of positive electrode active material particles was punched into Made into positive electrode.

[0095] As the negative electrode, use a punched of metallic lithium foil.

[0096] As the separator, CELGARD #2400 [Celgard, LLC] was used. A mixed solvent of ethylene carbonate and diethyl carbonate (1:1 volume ratio) in which 1 mol / L of LiPF6 was dissolved was used as the electrolyte. These components were assembled to make a CR2032 type button battery.

[0097] The battery was assembled in a glove box with an argon atmosphere whose dew point was controlled so that the electrolyte solution and metallic lithium would not be decomposed by the air.

[0098] The initial discharge capacity at 25°C was measured using the charge and discharge tester TOSCAT-3000 [TOYO system], and the test was performed at a constant current of 0.1C with the discharge voltage lower limit set to 3.0V and the charge upper limit voltage set to 4.4V. In addition, after charging to 4.4V at a constant current of 0.1C, the test was performed at 1C with the discharge voltage lower limit set to 3.0V, and the 1C discharge capacity ratio relative to the 0.1C discharge capacity was estimated. As a 140-cycle charge and discharge test at 25°C, the test was performed with the discharge voltage lower limit set to 3.0V and the charge upper limit voltage set to 4.4V. Discharge was performed at a constant current of 0.5C for the 20th, 40th, 60th, ..., 140th cycles and 1C for the others, and the 0.5C discharge capacity retention rate at the 140th cycle relative to the initial 1C discharge capacity, the so-called rate characteristic, was evaluated.

[0099] According to ICP composition analysis and XRD phase analysis, the lithium nickelate composite oxide particles that can become the core particles X obtained by the solid phase reaction are Li 1.02 Ni 0.81 Co 0.15 Al 0.04 O2. When the lattice constant is expressed by a hexagonal lattice, The lattice constant of the lithium nickelate-based positive electrode active material particles is substantially the same as that of the lithium nickelate composite oxide particles that can be the core particles X. Therefore, the core particles X of the positive electrode active material particles of the lithium nickelate composite oxide can be regarded as the layered structure of Li 1.02 Ni 0.81 Co 0.15 Al 0.04 O2.

[0100] However, the intensity ratio of the (003) / (104) plane of the X-ray diffraction pattern of the lithium nickelate composite oxide particles that can become the core particles X is 1.76, and the intensity ratio of the lithium nickelate positive electrode active material particles is 1.61. The above-mentioned heat treatment at 350°C for 3 hours in the atmosphere was observed to decrease. Therefore, it can be considered that the layered rock salt structure containing Ni 2+ The crystalline phase of ions forms a layer between the core particle X and the coating compound Y of the lithium nickelate-based positive electrode active material particles. The Ni 2+ / Ni 3+ In the case of lithium nickelate composite oxide particles that can be used as core particles X, it is 1.4 mol%, and in the case of lithium nickelate positive electrode active material particles, it is 1.9 mol%. The difference ΔNi 2+ / Ni 3+is 0.5 mol%. The difference ΔNi 2+ / Ni 3+ It can be considered that the lithium nickel oxide composite oxide particles contain Ni 2+ The mol% of the crystalline phase of the ions relative to the layered rock salt structure of the core particle X.

[0101] The obtained lithium nickelate positive electrode active material particles were observed by FE-SEM at a magnification of 50,000 times, and as a result, irregularities were observed on the particle surface. It is presumed that LiOH present on the particle surface was converted into Li2CO3.

[0102] The obtained lithium nickelate-based positive electrode active material particle powder is the same as other embodiments and comparative examples, and the powder properties and battery properties are shown in Table 1. The film thickness of the coated compound Y is extremely thin. The average valence of nickel is 2.99. The residual lithium hydroxide and lithium carbonate both show low contents, and their ratio is as high as 1.25, which is above 0.9. The initial capacity during 4.4V high voltage charging is also shown to be about 200mAh / g, and the 1C discharge capacity relative to the 0.1C discharge capacity is also as high as 90%. The capacity retention rate of 140 cycle characteristics at the same charging voltage is also as high as 85%.

[0103] [Example 2]

[0104] The same conditions as in Example 1 were used except that the heat treatment temperature after forming the coating compound Y by atomic layer deposition was changed from 350° C. to 400° C. The obtained oxide particles were evaluated as positive electrode active material particles.

[0105] [Comparative Example 1]

[0106] The layered lithium nickelate composite oxide Li obtained in Example 1 that can serve as the core particle X 1.02 Ni 0.81 Co 0.15 Al 0.04 O2 was used as positive electrode active material particles without surface treatment. As shown in Table 1, the amount of residual LiOH was high. The initial discharge capacity and rate characteristics of the battery were the same as those in the example, but the cycle characteristics were not good.

[0107] The obtained sample was observed by FE-SEM at a magnification of 50,000 times, and as a result, no irregularities were observed on the particle surface. This is different from Example 1, and it is presumed that the LiOH present on the particle surface still exists.

[0108] [Comparative Example 2]

[0109] As the positive electrode active material, a sample taken out from the middle of the production process of Example 1, that is, a sample processed by atomic layer deposition was used. As shown in Table 1, the amount of residual LiOH was high and the cycle characteristics of the battery were also poor.

[0110]

[0111] The lithium nickelate-based positive electrode active material particle powder of the present invention is characterized in that the core particle X is a layered lithium nickelate composite oxide and has a coating compound Y with an average film thickness of 0.2 to 5 nm, and the layered rock salt structure containing Ni 2+ The ionic crystal phase exists as a layer between the core particle X and the coating compound Y. The secondary battery obtained has high performance in that the battery capacity is high due to high voltage charging and the charge and discharge cycle characteristics are also high.

[0112] Industrial Applicability

[0113] The present invention comprises a very thin coating compound having an average film thickness of 0.2 to 5 nm in the positive electrode active material and containing Ni 2+ The crystalline phase of the layered rock salt structure of the ions forms a layer therebetween, providing a positive electrode active material particle powder of a lithium nickelate composite oxide having high energy density and excellent charge-discharge cycle characteristics when charged at a high voltage, and a non-aqueous electrolyte secondary battery. The lithium nickelate-based positive electrode active material particles have an extremely low content of lithium hydroxide as an impurity, and the obtained secondary battery has a long life shown by the charge-discharge cycle characteristics and a high energy density.

Claims

1. A positive electrode active material particle powder, Features: Lithium nickel oxide composite oxide with layered structure 1+a Ni 1－b－c Co b M c O 2 A core particle X having a coating compound Y having an average film thickness of 0.2 to 5 nm and containing at least one of the elements Al, Mg, Zr, Ti, and Si, Layered rock salt structure containing Ni 2+ The crystalline phase of ions exists as a layer between the core particle X and the coating compound Y, The layered rock salt structure contains Ni 2+ The mol% of the crystalline phase of the ions relative to the core particle X is in the range of 0.1 mol% to 3.0 mol%, The lithium nickelate composite oxide Li 1+a Ni 1－b－c Co b M c O 2 Here, M is at least one of the elements Mn, Al, B, Mg, Ti, Sn, Zn, and Zr, and -0.1≤a≤0.2, 0.05≤b≤0.5, and 0.01≤c≤0.

4.

2. The positive electrode active material particle powder according to claim 1, Features: The average valence of Ni is 2.80 to 3.

10.

3. The positive electrode active material particle powder according to claim 1, Features: The content of lithium hydroxide LiOH is less than 0.50 wt %, and the content of lithium carbonate Li 2 CO 3 The content is 0.65 wt % or less, and the weight ratio of the lithium carbonate content to the lithium hydroxide content is 0.9 or more.

4. The positive electrode active material particle powder according to claim 1, Features: BET specific surface area is 0.05~0.70m 2 / g, median particle size of agglomerated particles D 50 The particle size is 1 to 30 μm, and the pH value of 2% powder is below 11.

6.

5. A non-aqueous electrolyte secondary battery, Features: The positive electrode active material particles according to claim 1 are used as at least a part of the positive electrode active material.

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