Positive electrode and method for producing same, and non-aqueous electrolyte secondary battery comprising positive electrode and method for producing same

Abstract

The positive electrode has an active material layer. The active material layer includes an active material including at least a first active material, and a binder. The surfaces of first secondary particles in which first primary particles of the first active material are aggregated are covered with a boron compound. The first secondary particles are a lithium transition metal composite oxide that contains a titanium compound at the grain boundaries of the first primary particles, and contains 75 mol% or more of Ni relative to the total number of moles of metal elements that do not include Li. The binding material covers the first active material.

Description

Technical Field The present invention relates to a positive electrode and a method for producing the same, and a nonaqueous electrolyte secondary battery including the positive electrode and a method for producing the same. Background Art Japanese Patent Application Laid-Open No. 2007-273259 discloses that in order to improve the storage characteristics and cycle characteristics of non-aqueous electrolyte secondary batteries (hereinafter also referred to as "secondary batteries") such as lithium ion batteries, a positive electrode plate is heat treated within a specific temperature range in order to suppress expansion of the secondary battery. Summary of the invention In recent years, the capacity of vehicle-mounted secondary batteries has been increased to have a high energy density. In a high-capacity secondary battery, if the charge and discharge cycle is repeated, it is easy to expand further, and the constraint pressure (constraint pressure) used to give a reaction force to the expansion also increases. Therefore, a method for further suppressing the increase of the constraint pressure in the high-capacity secondary battery is needed. An object of the present disclosure is to provide a positive electrode capable of suppressing an increase in reaction force associated with repeated charge and discharge cycles of a nonaqueous electrolyte secondary battery, a method for producing the same, and a nonaqueous electrolyte secondary battery including the positive electrode and a method for producing the same.

[0001] The positive electrode is a positive electrode having an active material layer. The active material layer includes: an active material including at least a first active material, and a binding material. The surfaces of the first secondary particles formed by agglomeration of the first primary particles of the first active material are coated with a boron compound. The first secondary particles are lithium transition metal composite oxides having a titanium compound at grain boundaries of the first primary particles and containing 75 mol % or more of Ni based on the total molar number of metal elements excluding Li, and the binder covers the first active material.

[0002] The positive electrode according to [1], wherein the binder covers 60% or more of the surface of the first active material.

[0003] The positive electrode according to [1] or [2], wherein the boron compound contains Li.

[0004] The positive electrode according to any one of [1] to [3], wherein the content of B in the first active material is 0.5 to 3 mol % relative to the total number of moles of metal elements excluding Li.

[0005] The positive electrode according to any one of [1] to [4], wherein Ti is further dissolved in the first secondary particles.

[0006] The positive electrode according to any one of [1] to [5], wherein the first secondary particles contain 1 to 5 mol % of Ti based on the total number of moles of metal elements excluding Li.

[0007] The positive electrode according to any one of [1] to [6], wherein the binder is polyvinylidene fluoride. The content of the polyvinylidene fluoride in the active material layer is 0.3 to 2 wt % based on the weight of the active material layer.

[0008] The positive electrode according to any one of [1] to [7], wherein the first secondary particle contains a lithium-transition metal composite oxide represented by the following formula (I). Li x (Ni (1-y-z) Co y Me z )O2(I) [In formula (I), 1.0≤x≤1.2, 0.02≤y≤0.15, and 0.02≤z≤0.18, Me includes Ti and may include one or more selected from Mn, Al, Mg, Mo, Nb, and Zr.]

[0009] The positive electrode according to any one of [1] to [8], wherein the residual alkali content of the first active material is 0.03 to 0.3 wt %.

[0010] The positive electrode according to any one of [1] to [9], wherein the active material further includes a second active material. The first secondary particles are formed by agglomeration of more than 100 first primary particles. The second active material is a single particle or a second secondary particle formed by aggregation of 100 or less second primary particles. The average particle size (D50) of the second active material is 1 / 3 or less of the average particle size (D50) of the first active material.

[0011] The positive electrode according to

[10] , wherein the second active material includes single crystal particles.

[0012] The positive electrode according to any one of [1] to

[11] , wherein the positive electrode has an elastic modulus of 3 to 12 GPa.

[0013] A nonaqueous electrolyte secondary battery comprising the positive electrode according to any one of [1] to

[12] .

[0014] A method for manufacturing a positive electrode is a method for manufacturing a positive electrode having an active material layer, comprising: The step of applying the mixture onto the positive electrode current collector, drying and compressing to form a mixture layer; and The step of heat treating the mixture layer at a temperature ranging from the melting point to the thermal decomposition temperature of the binder material, The mixture comprises: an active material including at least a first active material, and the binding material. The surfaces of the first secondary particles formed by agglomeration of the first primary particles of the first active material are coated with a boron compound. The first secondary particles are lithium transition metal composite oxides having a titanium compound at grain boundaries of the first primary particles and containing 75 mol % or more of Ni based on the total molar number of metal elements excluding Li.

[0015] The method for manufacturing a positive electrode according to

[14] , wherein the content of B in the first active material is 0.5 to 3 mol%. The first secondary particles contain 1 to 5 mol % of Ti based on the total molar number of metal elements excluding Li.

[0016] The method for producing a positive electrode according to

[14] or

[15] , wherein the binder is polyvinylidene fluoride, The content of the polyvinylidene fluoride in the active material layer is 0.3 to 2 wt % based on the weight of the active material layer.

[0017] A method for producing a non-aqueous electrolyte secondary battery, comprising: producing a positive electrode by the method for producing a positive electrode described in any one of

[14] to

[16] . The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is an explanatory diagram schematically showing a first active material contained in an active material layer of a positive electrode according to an embodiment. Figure 2 It is a flowchart which shows the manufacturing method of the positive electrode which concerns on embodiment. DETAILED DESCRIPTION In this specification, as for the numerical range such as "x to y", unless otherwise specified, it includes the upper limit and the lower limit. That is, "x to y" means a numerical range of "above x and below y". A numerical value arbitrarily selected from the numerical range can be set as a new upper limit or lower limit. For example, a new numerical range can be set by arbitrarily combining a numerical value within the numerical range with a numerical value recorded in another part, table, or figure in this specification. (positive electrode) Figure 1 It is an explanatory diagram schematically showing a first active material contained in an active material layer of a positive electrode according to an embodiment. The positive electrode of the present embodiment (hereinafter also referred to as the "present positive electrode") is used, for example, in non-aqueous electrolyte secondary batteries such as lithium-ion batteries (hereinafter also referred to as "secondary batteries"). The present positive electrode has an active material layer, and the active material layer includes: an active material including at least a first active material 10, and a binding material 5. The surface of the first secondary particle 2 formed by the aggregation of the first primary particles 1 of the first active material 10 is coated with a boron compound (hereinafter also referred to as the "B compound") 4. The first secondary particle 2 is a lithium transition metal composite oxide having a titanium compound (hereinafter also referred to as the "Ti compound") 3 at the grain boundary of the first primary particle 1 and containing 75 mol% or more of Ni relative to the total molar number of metal elements excluding Li. The binding material 5 covers the first active material 10. In this way, the active material layer includes a coated particle 11, which is a first active material 10 formed by further coating the surface of the first secondary particle 2 with the B compound 4 with the binding material 5 ( Figure 1 ). The elastic modulus of the positive electrode is preferably 3 to 12 GPa, 5 to 10 GPa, 5 to 9 GPa, or 6 to 8 GPa. By having the elastic modulus within the above range, the positive electrode can have moderate flexibility, and thus it is easy to suppress the increase in the reaction force associated with the repeated charge and discharge cycles of the secondary battery. The elastic modulus of the positive electrode can be adjusted by the type of the first active material contained in the active material layer, the content of the Ti compound 3 and the B compound 4 in the first active material, etc., so as to be within the above range. The elastic modulus can be measured by the method described in the embodiments described later, and for a laminate formed by stacking the positive electrodes, it is calculated based on the change in thickness of the laminate when a compressive force is applied in the stacking direction. The positive electrode may have an active material layer on the positive electrode collector. The active material layer may be formed only on one side of the positive electrode collector or on both sides. The positive electrode collector is, for example, a metal foil made of aluminum materials such as aluminum and aluminum alloys, as long as it is a metal foil that is stable in the potential range of the positive electrode. The active material layer is preferably formed on one side or both sides of the surface of the positive electrode collector excluding the portion connected to the positive electrode lead. The active material at least includes a first active material 10. The first active material 10 is in particle form. The first active material 10 is a first secondary particle 2 formed by agglomerating first primary particles 1, and the surface is coated with a B compound 4. The first secondary particle 2 is preferably formed by agglomerating more than 100 first primary particles 1, and the number of agglomerated first primary particles may be 500 or more, 1000 or more, or 10000 or more, and is usually 5000000 or less. The first secondary particle 2 contains the Ti compound 3 at the grain boundary of the first primary particle 1. The presence of the Ti compound 3 at the grain boundary of the first primary particle 1 makes it easy to obtain the coated particle 11 in a good coating state by the binder 5. As a result, the flexibility of the positive electrode can be improved, so it is easy to obtain a positive electrode that can suppress the increase of the reaction force associated with the repetition of the charge and discharge cycle of the secondary battery. As for the Ti compound 3 contained in the grain boundary of the first primary particle 1, when the first secondary particle 2 is synthesized (described later), metal elements other than Ti and undissolved Ti may precipitate as a compound. The Ti compound 3 may exist on the surface of the first primary particle 1, or on the surface of the first secondary particle 2. As for the Ti compound 3 existing on the surface of the first primary particle 1, it is preferred that when looking at the first secondary particle 2 as a whole, it is not present in a partial manner, but exists throughout the entirety. In the case where the Ti compound 3 exists on the surface of the first secondary particle 2, it may exist in a manner covering the entire surface of the first secondary particle 2, or it may be dispersed on the surface of the first secondary particle 2. In the case where the Ti compound 3 is in a particulate form, the particle size of the particulate Ti compound 3 is preferably smaller than the particle size of the first primary particle 1. In the first secondary particle 2, a Ti compound 3 is included at the grain boundary of the first primary particle 1, and a portion of Ti may exist inside the first primary particle 1 or may be dissolved. For example, Ti may form a solid solution with other metal elements such as other transition metal elements other than Ti contained in the first primary particle 1. The Ti compound 3 may be any compound as long as it contains Ti. For example, it may be composed of Li p Ti q O r [wherein, 1≤p≤4, 1≤q≤5, 1≤r≤12] represents a lithium-containing titanium compound. The lithium-containing titanium compound may be a titanium source such as titanium oxide used for synthesizing the first secondary particle 2, which is generated by reacting with Li during calcination during the synthesis of the first secondary particle 2. The first secondary particle 2 preferably contains 1 to 5 mol% of Ti relative to the total molar number of metal elements excluding Li. The content of Ti in the first active material 10 may be 1 to 4 mol%, preferably 1 to 3 mol%, 1.5 to 3 mol%, or 2 to 3 mol% relative to the total molar number of metal elements excluding Li. When the content of Ti in the first secondary particle 2 is within the above range, it is easy to obtain the coated particle 11, and it is easy to obtain: a positive electrode capable of suppressing the increase of the reaction force associated with the repeated charge and discharge cycles of the secondary battery. As for the Ti compound 3 and the solid-dissolved Ti existing on the surface of the first primary particle 1 or the first secondary particle 2, it can be confirmed by, for example, SEM (scanning transmission electron microscope), and can be quantified by ICP (high frequency inductively coupled plasma) luminescence analysis, XPS (X-ray photoelectron spectroscopy). As for the Ti solid-dissolved in the first primary particle 1 or the first secondary particle 2, it can be quantified by, for example, EDS (energy dispersive X-ray spectroscopy). As for the Ti compound existing on the surface of the first primary particle 1 or the first secondary particle 2 in the state of a titanium compound containing lithium, it can also be confirmed by Li mapping analysis (Li mapping analysis) using EPMA (electron probe microanalyzer), EELS (electron energy loss spectroscopy), TOF-SIMS (time-of-flight secondary ion mass spectrometry), XPS (X-ray photoelectron spectroscopy), XRD (X-ray diffraction), and XAFS (X-ray absorption microstructure). In this specification, the Ti compound and solid-soluted Ti present in the grain boundary of the first primary particle 1 are confirmed by SEM and EPMA, the Ti content is determined by ICP emission analysis, and the presence of the Ti compound as a titanium compound containing lithium is confirmed by EPMA and TOF-SIMS analysis. The first secondary particle 2 is a lithium transition metal composite oxide, and the content of Ni relative to the total molar number of metal elements excluding Li (hereinafter also referred to as "Ni content") is 75 mol% or more. The Ni content may be 78 mol% or more, 80 mol% or more, 82 mol% or more, 75 to 98 mol%, 80 to 95 mol%, or 82 to 90 mol%. By having the Ni content of the first secondary particle 2 within the above range, a secondary battery with a high energy density can be obtained. The first secondary particle 2 contains Li, Ni and Ti, but may contain metal elements other than these. As the metal element, one or more metal elements selected from Co, Mn, Al, Zr, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, and Si can be listed. The first secondary particles 2 preferably include a lithium-transition metal composite oxide represented by the following formula (I). Li x (Ni (1-y-z) Co y Me z )O2(I) [In formula (I), 1.0≤x≤1.2, 0.02≤y≤0.15, and 0.02≤z≤0.18, Me includes Ti, and may include one or more selected from Mn, Al, Mg, Mo, Nb, and Zr.] In formula (I), x may be 1.01≤x≤1.09, 1.03≤x≤1.08, or 1.05≤x≤1.07. In formula (I), y may be 0.03≤y≤0.12, 0.05≤y≤0.10, or 0.06≤y≤0.09. In formula (I), Me preferably includes Ti, and includes one or more selected from Mn and Al, and more preferably includes Ti and Mn. In formula (I), z may be 0.05≤z≤0.17, 0.1≤z≤0.16, or 0.12≤z≤0.16. The first secondary particles 2 may be, for example, a lithium transition metal composite oxide represented by the following formula (II). Li a Ni b Co c Mn d Ti e O f (II) [In formula (II), 0.8≤a≤1.2, b≥0.70, c≤0.10, 0.03≤d≤0.12, 0.01≤e≤0.05, 1≤f≤2, b+c+d+e=1.] The composition of the first secondary particles 2 can be determined by ICP (inductively coupled plasma) emission analysis. The first secondary particle 2 can be synthesized, for example, by the following steps. First, a Li source such as lithium hydroxide (LiOH) is added to a nickel compound containing at least Ni and the mixture is calcined to obtain a lithium nickel composite oxide. The nickel compound is, for example, a composite oxide or a composite hydroxide containing Ni, Co and Mn. Next, a Ti source such as titanium dioxide (TiO2) is added to the lithium nickel composite oxide and the mixture is calcined to obtain a lithium transition metal composite oxide, thereby obtaining the first secondary particle 2. A Li source such as lithium hydroxide may be added together with the addition of the Ti source. The temperature for calcination by adding the Ti source is, for example, 550 to 850°C. As a method for allowing a Ti compound to exist at the grain boundary of the first primary particle 1 of the first secondary particle 2, a method of adjusting the amount of the Ti source added during the synthesis of the first secondary particle 2 and the like can be cited. The surface of the first secondary particle 2 of the first active material 10 is coated with the B compound 4. The presence of the B compound 4 on the surface of the first secondary particle 2 makes it easy to obtain coated particles 11 in a good coating state by the binder 5. As a result, the flexibility of the positive electrode can be improved, so it is easy to obtain a positive electrode that can suppress the increase of the reaction force associated with the repetition of the charge and discharge cycle of the secondary battery. As for the B compound 4, it may preferably cover the entire surface of the first secondary particle 2, and may be dispersed on the surface of the first secondary particle. As for the B compound 4 existing on the surface of the first secondary particle 2, it is preferred that it is not present in a partial manner but exists throughout the entire first secondary particle 2 when looking at the first secondary particle 2 as a whole. However, the B compound 4 preferably does not completely cover the entire surface of the first secondary particle 2, and preferably there is an area on the surface of the first secondary particle 2 where the B compound 4 is not attached. As for the proportion of the B compound 4 covering the first secondary particle, it is preferably less than 99%, may be less than 90%, may be less than 70%, and is usually more than 50%. The B compound 4 only needs to contain B, and may contain Li, for example. The B compound 4 containing Li may be generated by reacting a boron source such as boric acid, boron oxide, and lithium borate used in the synthesis of the first active material 10 with Li during calcination performed during the synthesis of the first active material 10. The content of B (boron) in the first active material 10 may be 0.2 to 3 mol%, preferably 0.5 to 3 mol%, 0.7 to 2.5 mol%, or 0.8 to 2.3 mol%. When the content of B is within the above range, it is easy to obtain coated particles 11 with good coating state by the binder 5. As a result, it is easy to obtain a positive electrode that can suppress the increase of the reaction force associated with the repetition of the charge and discharge cycle of the secondary battery. As for the B compound in the first active material 10, it can be confirmed by, for example, SEM (scanning electron microscope), and can be quantified by ICP emission analysis, EPMA, XPS, etc. The ratio of the area covered by the B compound 4 in the total surface area of ​​the above-mentioned first secondary particle can be measured by EPMA or XPS. In EPMA, the ratio of the peak area of ​​B (boron) to the total peak area of ​​the metal element excluding Li can be calculated. In XPS, the molar fraction of B relative to the total number of moles of the metal element excluding Li can be calculated. As for the B compound containing Li, it can be confirmed by Li mapping analysis in the analysis of EELS and TOF-SIMS. In this specification, as for the B compound covering the first secondary particle, it is confirmed by SEM, the content of B is obtained by ICP emission analysis, and as for the B compound containing Li, it is confirmed by TOF-SIMS. The first active material 10 can be synthesized, for example, by washing the synthesized first secondary particle 2 with water, adding a B source (boron source) and firing. Examples of the B source include boric acid (H3BO3), boron oxide (B2O3), and boric acid lithium compounds (LiBO2, Li2B4O7). A Li source such as lithium hydroxide can be added together with the B source. The firing temperature for firing with the addition of the B source is, for example, 200 to 500°C. The residual alkali content of the first active material 10 is preferably 0.03 to 0.3 wt %, 0.05 to 0.25 wt %, or 0.1 to 0.2 wt %. When the residual alkali content of the first active material 10 is within the above range, the expansion and degradation of the secondary battery caused by the gas generated by the residual alkali can be suppressed. The residual alkali content of the first active material 10 is determined by measuring the pH of a suspension in which the first active material 10 is suspended in water, as described in the examples described later. As for the active material, in addition to the first active material 10, a second active material may also be included. The second active material is a single particle, or a second secondary particle formed by agglomeration of less than 100 second primary particles. When the second active material is a second secondary particle, the number of second primary particles contained in the second active material is preferably less than the number of first primary particles 1 contained in the first active material 10, and may be 2 to 50, 2 to 30, 2 to 10, or 2 to 5. The average particle size (D50) of the second active material may preferably be less than 1 / 3 of the average particle size (D50) of the first active material, may be less than 1 / 4, or may be less than 1 / 5. The average particle size (D50) in this specification is the particle size at which the accumulation of the frequency from the smaller particle size in the volume-based particle size distribution becomes 50%. As for the volume-based particle size distribution, it can be measured by a laser diffraction particle size distribution measuring device. As described later, the active material layer is formed by applying a mixture containing an active material and a binding material on the positive electrode collector, drying and compressing. The active material sometimes cracks during this compression. Sometimes the active material cracks with the charge and discharge cycle of the secondary battery. If the active material cracks, the specific surface area of ​​the active material increases, so it is sometimes easy to react with the electrolyte to produce gas, or sometimes it is easy to expand with the charge and discharge of the secondary battery. As for the second active material, it is not easy to crack compared with the first active material 10, so by including the second active material in the active material layer, the generation of the above-mentioned gas and the expansion of the secondary battery can be suppressed. From this point of view, the single particles and the second primary particles constituting the second active material are preferably single crystal particles. The second active material is preferably a lithium transition metal composite oxide. The surface of the second active material may be coated with the B compound or may not be coated. As the second secondary particle constituting the second active material, the first secondary particle 2 described in the first active material 10 can be listed. However, the second secondary particle may or may not have a Ti compound at the grain boundary of the second primary particle. The lithium transition metal composite oxide constituting the second active material may be the same as or different from the lithium transition metal composite oxide constituting the first active material 10. As for the active material, other active materials other than the first active material 10 and the second active material may be included within the scope that does not impair the purpose of the present disclosure. As other active materials, lithium transition metal composite oxides or compounds other than lithium transition metal composite oxides whose Ni content is outside the range of the first secondary particle 2 can be listed. These other active materials may be primary particles or secondary particles. The active material layer includes a binding material 5. The binding material 5 covers the first active material 10. If the charge and discharge cycle of the secondary battery is repeated, the active material expands and contracts, so sometimes the active material cracks and cracks are generated. If the binding material enters the crack and accumulates, the active material layer becomes hard, the softness of the positive electrode is lost, and the elastic modulus of the positive electrode becomes larger. The positive electrode with a large elastic modulus is difficult to absorb the expansion and contraction of the active material, and it becomes difficult to suppress the increase in the reaction force. In contrast, the first active material 10 is covered with a binding material 5, so the elastic modulus of the positive electrode is difficult to increase. In particular, in the first active material 10, there is a Ti compound 3 at the grain boundary of the first primary particle 1, and the surface of the first secondary particle 2 is covered with a B compound 4, so the wettability of the first active material 10 and the binding material 5 is improved, and it is easy to obtain a coated particle 11 with a good coating state produced by the binding material 5. Therefore, it is easy to further suppress the increase in the reaction force associated with the repetition of the charge and discharge cycle of the secondary battery. The binding material 5 preferably covers more than 60% of the surface of the first active material 10. As for the proportion of the surface of the first active material 10 covered by the binding material 5, it can be more than 70%, more than 80%, more than 85%, and, for example, less than 98%, less than 95%. By being within the range of the above ratio, the flexibility of the positive electrode is improved, and the increase in the reaction force associated with the repetition of the charge and discharge cycle of the secondary battery is easily suppressed. As for the proportion of the first active material 10 covered by the binding material 5, as described in the embodiments described later, the image obtained by binarizing the SEM image of the active material layer and the mapping image of the binding material corresponding to the SEM image are overlapped, and the distribution of the binding material is analyzed and calculated thereby. Examples of the binder 5 include polyvinylidene fluoride (hereinafter also referred to as "PVdF"), polytetrafluoroethylene (PTFE) and other fluororesins, polyacrylonitrile (PAN), polyimide, acrylic resins, polyolefins, cellulose resins such as carboxymethyl cellulose (CMC), polyethylene oxide (POE), etc. The binder 5 is preferably PVdF. When the binder 5 is PVdF, the content of PVdF in the active material layer can be 0.3-2wt%, 0.5-1.8wt%, or 0.7-1.5wt% relative to the weight of the active material. Even if the content of PVdF in the active material layer is within the above range, the coated particles 11 with good coating state produced by PVdF can be obtained, so the increase of the reaction force accompanied by the repetition of the charge and discharge cycle of the secondary battery can be effectively suppressed. As for the active material layer, in addition to the active material and the binding material 5, a conductive material may be included. As the conductive material, for example, a carbon material may be listed. For example, the carbon material may be listed as one or more selected from fibrous carbon, carbon black (acetylene black, Ketjen black, etc.), coke and activated carbon. As fibrous carbon, carbon nanotubes (CNT) may be listed. CNT may be a single-layer carbon nanotube (SWCNT) or a multilayer carbon nanotube such as a two-layer carbon nanotube (DWCNT). (Manufacturing method of positive electrode) Figure 2 The flowchart of the manufacturing method of the positive electrode of the embodiment is shown. The manufacturing method of the positive electrode of the present embodiment can manufacture the positive electrode for the secondary battery, and can also manufacture the present positive electrode. The manufacturing method of the positive electrode includes: the steps of applying the mixture on the positive electrode collector, drying and compressing, thereby forming a mixture layer; and the step of heat-treating the mixture layer at a temperature within the range of the melting point to the thermal decomposition temperature of the binding material. The mixture includes: an active material including at least a first active material, and a binding material. In the first active material, the surface of the first secondary particle formed by agglomeration of the first primary particles is coated with the B compound. The first secondary particle is a lithium transition metal composite oxide having a Ti compound at the grain boundary of the first primary particle and containing 75 mol% or more of Ni relative to the total molar number of metal elements excluding Li. The binder covers the first active material. As the positive electrode collector, the metal foil described above can be listed. As the first active material, the first active material 10 described above can be listed, and as the first primary particle and the first secondary particle, the first primary particle 1 and the first secondary particle 2 described above can be listed. As the B compound and the Ti compound, the B compound 4 and the Ti compound 3 described above can be listed. The Ni content and the Ti content of the first secondary particle and the content of the B compound in the first active material can also be set to the range described above. As the binding material, the binding material 5 described above can be listed, preferably PVdF. The content of PVdF in the active material layer can be set to the range described above. The mixture can be prepared by adding a solvent such as N-methyl-2-pyrrolidone (NMP) to an active material including a first active material, a binder, and materials forming an active material layer such as a conductive material used as needed, and kneading them. In the step of forming the material mixture layer, the material mixture may be applied to only one side of the positive electrode current collector or to both sides. The material mixture applied to the positive electrode current collector is dried and compressed to obtain the material mixture layer. In the process of heat treatment, the mixture layer formed on the positive electrode collector is heat treated at a temperature within the range of the melting point to the thermal decomposition temperature of the binding material. The heat treatment temperature may be the melting point to the melting point + 100 ° C, or the melting point + 30 ° C to the melting point + 60 ° C. As for the melting point and thermal decomposition temperature of the binding material, the melting point and thermal decomposition temperature of the binding material with the largest content (weight) in the binding material contained in the mixture are set. By heat treating the mixture layer in the above-mentioned temperature range, the first active material can be well coated with the binding material. As for the first active material, since the B compound exists on the surface of the first secondary particle having the Ti compound at the grain boundary of the first primary particle, the wettability of the binding material and the first active material is improved. Thus, by performing the heat treatment process, the binding material can well cover the first active material, so it is easy to suppress the increase of the reaction force associated with the repeated charge and discharge cycles of the secondary battery. As for the melting point of the binding material, it can be measured by, for example, differential scanning calorimetry (DSC). The thermal decomposition temperature of the binder can be measured, for example, by a thermogravimetric differential thermal analyzer (TG-DTA). (Non-aqueous electrolyte secondary battery) The non-aqueous electrolyte secondary battery of the present embodiment (hereinafter also referred to as "the present battery") comprises the present positive electrode, and generally comprises: an electrode body comprising the present positive electrode and a non-aqueous electrolyte. The present battery may comprise: a battery case for accommodating the electrode body and the non-aqueous electrolyte. The battery case may comprise: an outer casing having an opening, and a sealing plate for sealing the opening. The outer casing and the sealing plate are preferably made of metal, and can be formed using aluminum, aluminum alloy, iron, or iron alloy, for example, can be formed using an aluminum laminate film. A resin sheet serving as an electrode holder may be arranged between the electrode body and the outer casing. The electrode body may include the positive electrode, the negative electrode and the separator. In the electrode body, the active material layer of the positive electrode and the negative electrode active material layer of the negative electrode are opposite to each other via the separator. The electrode body may be a stacked type in which the positive electrode, the negative electrode and the separator are stacked, or a wound type in which a stacked body formed by stacking the positive electrode, the negative electrode and the separator is wound. The negative electrode generally has a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector is, for example, a metal foil made of a copper material such as copper or a copper alloy. The negative electrode active material layer contains a negative electrode active material and may further contain a conductive material and a binder. As the negative electrode active material, for example, carbon-based active material particles and metal-based active material particles can be listed. As carbon-based active material particles, one or more particles selected from carbon materials such as graphite such as natural graphite and artificial graphite, hard carbon, soft carbon and amorphous coated graphite can be listed. As metal-based active material particles, particles of metal elements such as metal elements or metal oxides containing elements selected from silicon (Si), tin (Sn), antimony (Sb), bismuth (Bi), titanium (Ti), and germanium (Ge) can be listed. Metal-based active material particles preferably include one or more particles selected from Si, SiOx (x = 0.5 to 1.5), a composite of Si and C (hereinafter also referred to as "SiC composite"), and Sn. As the conductive material, there can be listed carbon materials such as fibrous carbon (CNT (SWCNT, DWCNT)), carbon black (e.g., acetylene black, Ketjen black), coke, activated carbon, etc. As the binder, there can be listed cellulose resins such as carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose, polyacrylic acid, SBR, etc. The spacer has a substrate, and may have a functional layer on at least one side of the substrate. The substrate may be a porous sheet such as a film or non-woven fabric composed of a resin such as polyethylene and polypropylene, polyester, cellulose, polyamide, etc. The substrate may have a single-layer structure or a multi-layer structure. The functional layer may include, for example, an adhesive layer and a heat-resistant layer, and may have one or both of these. The adhesive layer may be formed, for example, by an adhesive. The heat-resistant layer may include, for example, a filler and a binder. The non-aqueous electrolyte is preferably a product containing a supporting salt in a non-aqueous solvent such as an organic solvent. As supporting salts, LiPF6, LiBF4, LiClO4, LiFSO3, LiBOB (lithium bis(oxalate)borate) etc. can be listed. The non-aqueous electrolyte can include one or more supporting salts of these. As non-aqueous solvents, for example, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), butylene carbonate (BC) and diethyl carbonate (DEC) etc. can be listed. The non-aqueous electrolyte can include one or more non-aqueous solvents of these. The non-aqueous electrolyte can further include additives such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate. (Method for producing non-aqueous electrolyte secondary battery) The manufacturing method of the battery includes the step of manufacturing a positive electrode by the manufacturing method of the positive electrode. The manufacturing method of the battery may further include: the step of obtaining an electrode body using the positive electrode, the negative electrode and the separator; and the step of accommodating the electrode body and the non-aqueous electrolyte in a battery case. Example Hereinafter, the present disclosure will be described in more detail with reference to Examples and Comparative Examples. [Example 1] (Synthesis of the First Active Material) Nickel·cobalt·manganese hydroxide, lithium hydroxide and titanium dioxide were mixed and calcined at 770°C for 10 hours in an oxygen atmosphere to obtain a lithium transition metal composite oxide. The lithium transition metal composite oxide was crushed, washed with water, mixed with boric acid, and calcined at 300°C for 1 hour to obtain a first active material. The addition amounts of titanium dioxide and boric acid were adjusted so that the amounts of Ti and B contained in the first active material were the amounts shown in Table 1. (Production of positive electrode) The first active material, acetylene black and polyvinylidene fluoride (PVdF, melting point 175°C, thermal decomposition temperature 420°C) as a binding material are mixed at 97.5:1.5:1.0 (weight ratio of solid components), and an appropriate amount of N-methyl-2-pyrrolidone (NMP) is added and kneaded to obtain a mixture. The mixture is applied to both sides of an aluminum foil as a positive electrode collector, dried, and a coating film is formed. The coating film is rolled using a roller to form an active material layer, and after heat treatment at 230°C for 3 minutes, it is cut into an electrode size, thereby obtaining a positive electrode having an active material layer formed on both sides of the positive electrode collector. The melting point of PVdF is measured by differential scanning calorimetry (DSC), and the thermal decomposition temperature of PVdF is measured by a thermogravimetric differential thermal analyzer (TG-DTA). (Production of negative electrode) Natural graphite as a negative electrode active material, sodium carboxymethyl cellulose (CMC-Na) as a binder, and styrene butadiene rubber (SBR) are mixed in water at a ratio of 100:1:1 (weight ratio of solid content) to obtain a negative electrode mixture. The negative electrode mixture is applied to both sides of a copper foil as a negative electrode collector and dried to obtain a coating film. The coating film is rolled using a roller to form a negative electrode active material layer, and cut into an electrode size, thereby obtaining a negative electrode having a negative electrode active material layer formed on both sides of the negative electrode collector. (Fabrication of non-aqueous electrolyte secondary battery) An aluminum lead as a positive electrode lead is welded to the exposed portion of the positive electrode collector where no active material layer is formed in the positive electrode collector. A nickel lead as a negative electrode lead is welded to the exposed portion of the negative electrode collector where no negative electrode active material layer is formed in the negative electrode collector. The positive electrode with the positive electrode lead installed is stacked with the negative electrode with the negative electrode lead installed via a polyolefin separator, and after being wound into a spiral shape, they are radially pressed to obtain a flat wound electrode body. In an outer casing composed of an aluminum laminate, the wound electrode body is accommodated, a non-aqueous electrolyte is injected, and the opening of the outer casing is sealed to obtain a secondary battery with a designed capacity of 650 mAh. The non-aqueous electrolyte uses a product containing the following mixed solvent, supporting salt and additive. As a mixed solvent, a product in which ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed in a volume ratio of EC:EMC:DMC=3:3:4 is used. As a supporting salt, lithium hexafluorophosphate (LiPF6) is used, and it is dissolved in a concentration of 1.0 mol / L relative to the above-mentioned mixed solvent. As an additive, vinylene carbonate (VC) is used, and it is dissolved in a concentration of 2.0 weight % relative to the above-mentioned mixed solvent. [Examples 2 to 5, Comparative Examples 1 to 4] The first active material and the positive electrode were obtained according to the procedure of Example 1, and a nonaqueous electrolyte secondary battery was prepared except that the addition amounts of titanium dioxide and boric acid were adjusted so that the Ti and B contained in the first active material became the amounts shown in Tables 1 and 2. [Observation of the first active material and the binder] (Confirmation of Ti) The first active material was observed using a scanning transmission electron microscope (SEM, JEOL "JSM-7800F"), and an EPMA (electron probe microanalyzer) element mapping image corresponding to a 50,000-fold SEM image was obtained to confirm whether a Ti compound existed at the grain boundary of the first primary particle, and to confirm Ti dissolved in the first secondary particle. The results are shown in Tables 1 and 2. EPMA and TOF-SIMS were used to confirm the Ti compound existing at the grain boundary of the first primary particle, and the results showed that they were all titanium compounds containing lithium. The first active material was observed using the SEM, and a 10,000-fold SEM image was obtained under a low acceleration state of 1 kV. The presence of B was inferred from the presence of the black area, and the coating state of the first secondary particles generated by the B compound was confirmed. The results are shown in Tables 1 and 2. The B compound coating the first secondary particles was confirmed by TOF-SIMS, and the results showed that all contained Li. For the positive electrode obtained in Example 2 and Comparative Example 4, the first active material was observed using the above-mentioned SEM to confirm the coating state of the first active material generated by the binding material (PVdF). As for the coating ratio of the first active material generated by the fluorine element, a mapping image of the fluorine (F) element of the first active material coated with the binding material was obtained, and it was overlapped with the binarized SEM image, and the fluorine distribution on the surface of the first active material was analyzed by image analysis, thereby calculating. [Composition of the first active material] The composition of the first active material was analyzed by ICP emission analysis to determine the content of Ni, B, and Ti relative to the total molar number of metal elements excluding Li. The results are shown in Tables 1 and 2. The first secondary particles of Examples 1 to 5 and Comparative Examples 1 to 4 are all lithium transition metal composite oxides represented by the above formula (I). The composition of the first secondary particles obtained in Examples 1 to 5 is Li 1.04 Ni 0.82 Co 0.05 Mn 0.13 Ti 0.03 O2. [Measurement of the Residual Alkali Amount of the First Active Material] A predetermined amount of the first active material was dispersed in pure water at 25°C to obtain a dispersion. The amount of alkali required for titration was calculated from the titration curve obtained by dropping hydrochloric acid into the dispersion and performing neutralization titration, and this was taken as the residual alkali amount. The results are shown in Tables 1 and 2. [Measurement of Elastic Modulus of Positive Electrode] Insert 8 sheets of positive electrode stacked in a size of 30×40 mm into a laminated bag (laminate bag), inject 1 g of electrolyte, and vacuum seal the laminated bag. As for the electrolyte, 1 mol / L of LiPF6 was dissolved in a mixed solvent of EC:EMC:DMC=3:4:3 (volume ratio) to prepare. Using Autograph AGX-10kNV2D (manufactured by Shimadzu Corporation), the elastic modulus [GPa] was determined from the thickness change when a compressive force was applied in the stacking direction of the laminated body in the vacuum-sealed laminated bag. Specifically, for the laminate, a compressive force of 0.5 kN was applied every 1 h, and the elastic modulus [GPa] was determined based on the strain change when the compressive force was applied 4 h later (when a compressive force of 2 kN was applied). The results are shown in Tables 1 and 2. [Measurement of the rate of increase of the reaction force of the secondary battery] A secondary battery was placed in the fixture of Autograph AGX-10kNV2D (manufactured by Shimadzu Corporation), and the battery was repeatedly charged and discharged at a current value of 1 / 3C rate under a restraining pressure of 1MPa to obtain an SS curve (stress-strain curve). The load at this time was divided by the cross-sectional area of ​​the secondary battery (battery) to calculate the stress value. The ratio of the stress value during charging after 200 cycles of repeated charge and discharge to the stress value during the initial charge of the secondary battery was calculated and used as the increase rate [%] of the reaction force of the secondary battery. The results are shown in Tables 1 and 2.

Table 1

Table 2

Claims

1. The positive electrode is the positive electrode with an active material layer. The active material layer includes: an active material including at least a first active material, and a binding material, The surfaces of the first secondary particles formed by agglomeration of the first primary particles of the first active material are coated with the boron compound. The first secondary particle is a lithium transition metal composite oxide having a titanium compound at a grain boundary of the first primary particle and containing 75 mol % or more of Ni based on the total molar number of metal elements excluding Li, The binding material covers the first active material.

2. The positive electrode according to claim 1, wherein The bonding material covers more than 60% of the surface of the first active material.

3. The positive electrode according to claim 1, wherein The boron compound includes Li.

4. The positive electrode according to claim 1, wherein The content of B in the first active material is 0.5 to 3 mol % based on the total number of moles of metal elements excluding Li.

5. The positive electrode according to claim 1, wherein Ti is further solid-solved in the first secondary particles.

6. The positive electrode according to claim 1, wherein The first secondary particles contain 1 to 5 mol % of Ti based on the total moles of metal elements excluding Li.

7. The positive electrode according to claim 1, wherein The bonding material is polyvinylidene fluoride, The content of the polyvinylidene fluoride in the active material layer is 0.3 to 2 wt % relative to the weight of the active material layer.

8. The positive electrode according to claim 1, wherein The first secondary particle includes a lithium transition metal composite oxide represented by the following formula (I): Li x (Ni (1-y-z) Co y Along with z )O2(I) In formula (I), 1.0≤x≤1.2, 0.02≤y≤0.15, and 0.02≤z≤0.18, Me includes Ti, and may include one or more selected from the group consisting of Mn, Al, Mg, Mo, Nb, and Zr.

9. The positive electrode according to claim 1, wherein The residual alkali content of the first active material is 0.03-0.3 wt %.

10. The positive electrode according to claim 1, wherein The active substance further comprises a second active substance, The first secondary particles are formed by agglomeration of more than 100 first primary particles. The second active material is a single particle or a second secondary particle formed by aggregation of 100 or less second primary particles. The average particle size (D50) of the second active material is 1 / 3 or less of the average particle size (D50) of the first active material.

11. The positive electrode according to claim 10, wherein The second active material includes single-crystalline particles.

12. The positive electrode according to claim 1, wherein The elastic modulus of the positive electrode is 3 to 12 GPa. 13 . A nonaqueous electrolyte secondary battery comprising the positive electrode according to claim 1 .

14. A method for manufacturing a positive electrode, which is a method for manufacturing a positive electrode having an active material layer, comprising: A step of applying a mixture onto a positive electrode current collector, drying and compressing to form a mixture layer; and The step of heat treating the mixture layer at a temperature ranging from the melting point to the thermal decomposition temperature of the binder material, The mixture comprises: an active material including at least a first active material, and the binding material, The surfaces of the first secondary particles formed by agglomeration of the first primary particles of the first active material are coated with the boron compound. The first secondary particles are lithium transition metal composite oxides having a titanium compound at the grain boundaries of the first primary particles and containing 75 mol % or more of Ni based on the total molar number of metal elements excluding Li.

15. The method for manufacturing a positive electrode according to claim 14, wherein: The content of B in the first active material is 0.5 to 3 mol%. The first secondary particles contain 1 to 5 mol % of Ti based on the total moles of metal elements excluding Li.

16. The method for manufacturing a positive electrode according to claim 14, wherein: The bonding material is polyvinylidene fluoride, The content of the polyvinylidene fluoride in the active material layer is 0.3 to 2 wt % relative to the weight of the active material layer.

17. A method for manufacturing a non-aqueous electrolyte secondary battery, comprising: A step of manufacturing a positive electrode by the method for manufacturing a positive electrode according to any one of claims 14 to 16.

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