JP6400364B2 - Cathode active material for non-aqueous secondary battery and method for producing the same - Google Patents

Description

  The present invention relates to a positive electrode active material for a non-aqueous secondary battery and a method for producing the same.

  In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, development of small and lightweight secondary batteries having high energy density is strongly desired. In addition, development of a high output secondary battery is strongly desired as a battery for electric vehicles including hybrid vehicles.

  As a secondary battery satisfying such a requirement, there is a non-aqueous secondary battery represented by a lithium ion secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of desorbing and inserting lithium is used as an active material of the negative electrode and the positive electrode.

As a positive electrode active material of a lithium ion secondary battery, a lithium cobalt composite oxide (LiCoO ₂ ) having a layered structure that is relatively easy to synthesize is mainly put into practical use. In addition, a layered lithium nickel composite oxide (LiNiO ₂ ) using nickel, which is cheaper than cobalt, and a spinel lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese have been proposed. As a lithium transition metal composite oxide having a layered structure, a lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) using a plurality of transition metals has been proposed. When these lithium transition metal composite oxides are used as the positive electrode active material, a 4V class non-aqueous secondary battery can be realized.

  With respect to lithium transition metal composite oxides, techniques for increasing the ratio of lithium to transition metal elements according to the purpose have been proposed.

  For example, Patent Document 1 considers that by making the lithium ratio slightly higher than the stoichiometric ratio, disorder of the crystal structure is suppressed, lithium ion diffusion becomes smooth, and rate characteristics and output characteristics are improved. Has been. On the other hand, if the lithium ratio is too high, it is said that there is a risk of producing a heterogeneous phase or reducing battery performance.

Patent Document 2 discloses that in Li [Li _x (Ni _1/2 Mn _1/2 ) _1-x ] O ₂ , when lithium is excessive (x is greater than 0), the active material in an overcharged state On the other hand, it is described that when x is too large (x> 0.3), the electric capacity of the active material decreases.

  Furthermore, a technique related to a so-called solid solution system among lithium transition metal composite oxides having an increased lithium ratio has been proposed.

In Patent Document 3, LiMO ₂ (M is at least one kind of ion in which Ni is essential and its average oxidation number is +3) and Li ₂ M′O ₃ (M ′ is at least one kind of ion in which Mn is essential). A technique is disclosed in which the average oxidation number is +4) and the electrochemical stability of LiMO ₂ during charge and discharge is improved.

Patent Document 4 describes that a solid solution of LiMO ₂ (M is a transition metal element such as Co and Ni) and Li ₂ MnO ₃ can exhibit a discharge capacity of 200 mAh / g.

In Patent Document 5, three components of Li [Li _1/3 Mn _2/3 ] O ₂ , LiCoO ₂ and LiNi _1/2 Mn _1/2 O ₂ are solid-solved at a specific range ratio and a potential of 4.3 V or less. Technologies for increasing the discharge capacity in the region have been proposed.

JP 2007-214138 A International Publication No. 02/0708105 Pamphlet US Pat. No. 6,677,082 JP 2011-204563 A JP 2011-146392 A

Solid solution materials usually have a phase such as LiMO ₂ (hereinafter sometimes referred to as “112 phase”) and a phase such as Li ₂ MnO ₃ (hereinafter referred to as “213 phase”) in exchange of lithium ions. There is a solid solution. The 213 phase is electrochemically inactive by itself, but becomes active when dissolved with the 112 phase, resulting in an increase in capacity. Moreover, when the 213 phase is dissolved, the entire crystal structure is stabilized, and the crystal structure collapse accompanying the exchange of lithium ions is suppressed. As a result, the presence of the 213 phase contributes to the improvement of cycle characteristics. Therefore, in patent documents 3 to 5, the ratio of the 213 phase is set high. On the other hand, when the charging rate (State of Charge (SOC): the ratio of the capacity to the capacity at the time of full charge) becomes low during discharging (for example, SOC is 0.2 or less), the 213 phase contributes to the exchange of lithium ions. In the above prior art, the output characteristics at the time of low SOC have not been studied at all. However, since the 213 phase, which is inherently electrochemically inactive, is involved in the exchange of lithium-on, the movement of lithium ions is hindered and the secondary The internal resistance of the battery rises rapidly. As a result, the output of the secondary battery suddenly decreases in the low SOC region.

  This is a problem in applications such as an electric vehicle that always requires a certain output. Although it may be possible to avoid the use in the low SOC region, this will waste the capacity of the secondary battery, making it impossible to fully utilize the merit of using a high-capacity lithium-ion secondary battery. It is.

  In Patent Documents 1 to 5, as described above, there is nothing that has been considered for improving the output characteristics in the low SOC region, and there is nothing that can solve the above problems. Therefore, a lithium ion secondary battery (or a positive electrode active material therefor) capable of obtaining a certain level of output characteristics regardless of the SOC state has not yet been obtained.

  The present invention has been made in view of such circumstances, and an object thereof is to use a positive electrode active material capable of improving output characteristics not only in high capacity and high cycle characteristics but also in a low SOC region, and the use thereof. It is to provide a non-aqueous secondary battery.

As a result of diligent research in view of the above object, the present inventors have not only made the ratio of the 112 phase and the 213 phase a specific composition in the positive electrode active material made of a solid solution material, but also the primary particle size and 2 It has been found that by simultaneously controlling the secondary particle size, not only high capacity and high cycle characteristics but also output characteristics can be improved in a low SOC region. The present invention has been further researched and completed. That is, the present invention includes the following configurations.
Item 1. General formula (1);
_{xLi 2 MnO 3 · (1-} x) LiNi 1-s-t-u Co s Mn t M u O 2
[Wherein M is a metal element other than Li, Ni, Co and Mn; x is 0.32 to 0.48; s is 0 to 0.65; t is 0 to 0.5; s + t is 0.05. -0.75; u is 0-0.05. ]
And
The average primary particle size is 50-200 nm,
The central secondary particle size is 2.5-6 μm,
A positive electrode active material for a non-aqueous secondary battery comprising lithium transition metal composite oxide particles.
Item 7. A method for producing the positive electrode active material for a non-aqueous secondary battery,
General formula (2);
(Ni _{1-s′-t′-u ′} Co _{s ′} Mn _{t ′} M _{u ′} ) ₂ O ₃
[Wherein M is the same as above; s ′ is 0.17 to 0.23; t ′ is 0.55 to 0.75; u ′ is 0 to 0.05]
And a lithium transition metal composite oxide precursor particle having a central secondary particle diameter of 2.5 to 6 μm and a lithium compound, and then heating.
Item 10. A non-aqueous secondary battery using the positive electrode active material for a non-aqueous secondary battery or the positive electrode active material for a non-aqueous secondary battery obtained by the production method.

  According to the present invention, since the above characteristics are provided, not only a high capacity and a high cycle characteristic, but also a positive electrode active material capable of improving an output characteristic even in a low SOC region, and a non-aqueous two-phase system using the same. A secondary battery can be provided.

FIG. 1 is a graph showing the relationship between the average primary particle diameter and the output characteristics (R (0.1)) in the low SOC region of the lithium transition metal composite oxide particles of the present invention. FIG. 2 is a graph showing the relationship between the center secondary particle diameter and the load characteristics (Q ′ _id ) of the lithium transition metal composite oxide particles of the present invention.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to these specific embodiments and examples, and it goes without saying that various configurations of main types can be adopted.

1. Positive electrode active material for non-aqueous secondary battery The positive electrode active material for a non-aqueous secondary battery of the present invention has the general formula (1);
_{xLi 2 MnO 3 · (1-} x) LiNi 1-s-t-u Co s Mn t M u O 2
[Wherein M is a metal element other than Li, Ni, Co and Mn; x is 0.32 to 0.48; s is 0 to 0.65; t is 0 to 0.5; s + t is 0.05. -0.75; u is 0-0.05. ]
And a lithium transition metal composite oxide particle (hereinafter also referred to as “oxide particle of the present invention”).

  In the general formula (1), x, which is the content ratio of the 213 phase, is 0.32 to 0.48, preferably 0.35 to 0.45. In the prior art in which the output characteristics in the low SOC region have not been studied, the portion corresponding to x of the present invention is set to be large, but if it is too large, the lithium ions that are involved in charge and discharge are derived from the 213 phase. The ratio becomes high, and the benefits of improving the cycle characteristics cannot be obtained, and the cycle characteristics are relatively deteriorated. For the same reason, the output characteristics in the low SOC region, particularly in the region where the SOC is 0.2 or less, are degraded. In addition, if x is too small, the proportion of lithium ions in the 213 phase that are involved in charge / discharge increases, so that the benefits of improving the cycle characteristics cannot be obtained and the cycle characteristics are relatively deteriorated.

In the present invention, 112 phase (i.e., formula _{(LiNi 1-s-t-} u Co s Mn t M u O 2 in 1) of the present invention) in, as an essential nickel in terms of charge-discharge capacity, Further, cobalt and / or manganese, particularly cobalt and manganese are contained. Cobalt and manganese are particularly preferable because the crystal structure is stabilized. However, too much cobalt leads to an increase in cost and a decrease in capacity. On the other hand, if too much manganese is present, manganese ions are eluted into the electrolyte during charging and discharging, so adjustments must be made so as not to increase too much. Further, it is more preferable that the ratio of nickel, cobalt, and manganese is close to 1: 1: 1 because the balance of cost, stability during charge / discharge, charge / discharge capacity, etc. is more excellent. Furthermore, metallic elements other than lithium, nickel, cobalt, and manganese may be contained in the 112 phase in a small amount as long as the effects of the present invention are not impaired. From such a viewpoint, s is 0 to 0.65, preferably 0 to 0.45, and more preferably 0.28 to 0.38. t is 0 to 0.5, preferably 0.2 to 0.5, and more preferably 0.28 to 0.38. s + t is 0.05 to 0.75, preferably 0.62 to 0.72. u is 0 to 0.05, preferably 0 to 0.03.

  In the present invention, the other element M that may be included in the material constituting the 112 phase is not particularly limited as long as it is a metal element other than Li, Ni, Co, and Mn, but the crystal structure during charging and discharging is stable. In addition, Mg, Al, Ti, Zr, W, Mo, Nb, or a combination of these is preferable from the viewpoint that lithium ions can be smoothly desorbed or inserted during charging and discharging.

  On the other hand, the particle diameter of the oxide particles of the present invention is also important, and the smaller the average primary particle diameter, the better the output characteristics in the low SOC region. FIG. 1 is a graph showing the relationship between the average primary particle size and the output characteristics (R (0.1)) in the low SOC region when x = 0.4 and the center secondary particle size is about 4.2 μm. The same tendency is shown in other x and central secondary particle sizes. The average primary particle diameter is 200 nm or less, preferably 130 nm or less. From FIG. 1, when the average primary particle diameter is too large, the output characteristics in the low SOC region are deteriorated. This is because if the average primary particle size is too large, the distance required for lithium ions to be desorbed and inserted from the lithium transition metal composite oxide particles increases. On the other hand, lithium transition metal composite oxide particles having a small average primary particle size tend to be difficult to synthesize, which causes a deterioration in yield. In addition, the crystallinity of the obtained lithium transition metal composite oxide particles tends to decrease, and the movement of lithium ions inside the crystal tends to be hindered. As a result, the output characteristics in the low SOC region tend to deteriorate. From this viewpoint, in practice, it is usually 50 nm or more, preferably 60 nm or more.

  The center secondary particle diameter of the oxide particles of the present invention is 2.5 to 6 μm, preferably 3 to 5 μm. If the central secondary particle diameter of the oxide particles of the present invention is out of this range, the discharge capacity at the time of large current discharge is reduced. FIG. 2 is a graph showing the relationship between the central secondary particle size and the load characteristics (discharge rate 2.0 C) when x = 0.4 and the average primary particle size is about 100 nm. When the average primary particle size is small, this tendency appears more remarkably and the convex shape becomes larger. Although details are unknown, it is assumed that the ease of maintaining the shape of the secondary particles, the bond strength between the primary particles, the ease of contact between the particle surface and the electrolyte, and the like are influential. In the present invention, the central secondary particle size means a value (D50) at which the cumulative volume frequency is 50% in the particle size distribution curve.

  As described above, in the oxide particles of the present invention, by adjusting the average primary particle diameter and the central secondary particle diameter within the specific range, the contact condition between the electrolytic solution and the positive electrode active material of the present invention, lithium The ease of diffusion of ions into the positive electrode active material and the stability of the positive electrode active material particles during diffusion can be optimized to the extent that high output characteristics can be obtained regardless of the SOC region. In addition, it is more preferable that an average primary particle diameter shall be 60-130 nm, and a center secondary particle diameter shall be 3-5 micrometers.

The method for measuring the particle diameter of the oxide particles of the present invention is not particularly limited. For example, the average primary particle diameter can be obtained by, for example, observation with an electron microscope (SEM, TEM, etc.), and an average value of (major axis + minor axis) / 2 of an arbitrary number of primary particles can be set as the average primary particle diameter. . Further, the central secondary particle diameter can be obtained by, for example, obtaining a volume-based particle size distribution by a laser diffraction method and obtaining a value (D50) at which the cumulative frequency is 50% as the central secondary particle diameter.

2. Manufacturing method of positive electrode active material for non-aqueous secondary battery The manufacturing method of the positive electrode active material for non-aqueous secondary battery of the present invention is not particularly limited, has a specific composition, and has an average primary particle size and a center secondary. Although it is sufficient that the particle diameter can be controlled, the general formula (2);
(Ni _{1-s′-t′-u ′} Co _{s ′} Mn _{t ′} M _{u ′} ) ₂ O ₃
[Wherein M is the same as above; s ′ is 0.17 to 0.23; t ′ is 0.55 to 0.65; u ′ is 0 to 0.05]
Lithium transition metal composite oxide precursor particles (hereinafter sometimes referred to as “precursor particles”) having a central secondary particle diameter of 2.5 to 6 μm and a lithium compound are mixed, Next, it is preferable to obtain the oxide particles of the present invention by heating.

  When this method is employed, the composition is adjusted according to the ratio of the precursor particles to the lithium compound, and the central secondary particle diameter of the precursor particles represented by the general formula (2) used as a raw material is adjusted. The average primary particle size of the oxide particles of the present invention can be adjusted by adjusting the central secondary particle size of the oxide particles and adjusting the heating conditions.

When the ratio of nickel, cobalt, and manganese is close to 1: 1: 1 in LiNi _1- sttu Co _s Mn _t M _u O ₂ of the general formula (1), stability during charge / discharge, charge / discharge From the viewpoint that oxide particles having a better balance such as capacity can be obtained, and metal elements other than lithium, nickel, cobalt and manganese may be included in a range that does not impair the effects of the present invention in a small amount. s ′ is preferably 0.17 to 0.23, more preferably 0.18 to 0.22. t ′ is preferably 0.55 to 0.65, and more preferably 0.57 to 0.63. u ′ is preferably 0 to 0.05, and more preferably 0 to 0.03.

  Precursor particles having such a central secondary particle size are not particularly limited, but it is preferable that transition metals are dissolved in a solid solution by a so-called coprecipitation method, and the central secondary particle size is adjusted at this time. Thereby, since the kind of raw material compound can be reduced, control becomes easier.

  When the particle size of the precursor particles is controlled by the coprecipitation method, the average primary particle size of the precursor particles obtained can be controlled by the reaction field temperature, pH, stirring speed, and the like. Since the tendency changes depending on the shape of the container for storing the reaction field, the starting material, the input rate of the starting material to the reaction field, etc., it is preferable to adjust appropriately according to the actual conditions. The average primary particle diameter of the precursor particles thus obtained is preferably smaller than the average primary particle diameter of the oxide particles of the present invention to be obtained. Specifically, 2-100 nm is preferable and 5-50 nm is more preferable. In addition, when the aspect ratio of the primary particles of the precursor particles is extremely larger than 1 (acicular shape or the like), the short diameter of the primary particles of the precursor particles is regarded as the average primary particle diameter.

  In addition, the central secondary particle diameter of the precursor particles can be controlled by the aging time after the crystal precipitation of the precursor particles starts, the stirring speed, and the like. This tendency also varies depending on the shape of the reaction vessel and the like, so it is preferable to adjust appropriately according to actual conditions. Specifically, since the central secondary particle diameter of the oxide particles of the present invention is approximately the same as the central secondary particle diameter of the precursor particles, the central secondary particle diameter of the precursor particles is 2.5 to 6 micrometers is preferable and 3-5 micrometers is more preferable.

  The lithium compound is not particularly limited as long as the oxide particles of the present invention can be obtained, and examples thereof include lithium hydroxide, lithium carbonate, lithium oxide, lithium acetate, and the like. Ease of handling, ease of decomposition, etc. From this viewpoint, lithium hydroxide or lithium carbonate is preferable. These lithium compounds may be used alone or in combination of two or more.

  In the production method of the present invention, the mixing ratio of the precursor particles and the lithium compound can be adjusted as described above, and therefore may be set as appropriate according to the composition to be obtained. In particular, from the viewpoint of obtaining oxide particles with improved output characteristics in a region where the SOC is 0.2 or less, 2.64 to 2.96 mol of the lithium compound is preferable with respect to 1 mol of the precursor particles, 2.70-2.90 mol is more preferable.

  In the production method of the present invention, the precursor particles and the lithium compound are preferably fired by heating to obtain a target sintered body of the oxide particles of the present invention. As described above, the average primary particle diameter can be adjusted as the heating conditions (the higher the heating (firing) temperature, the larger the average primary particle diameter, and the lower the heating (firing) temperature, the average primary particle diameter. Therefore, it may be appropriately set according to the average primary particle diameter of the oxide particles to be obtained, but is preferably 750 to 1000 ° C, more preferably 800 to 950 ° C. If the heating (firing) temperature is too low, the crystal development is insufficient, and if it is too high, the sintering proceeds too much, or excessive growth of primary particles is caused. For the same reason, the heating (firing) time is preferably 2 to 20 hours, and more preferably 5 to 15 hours.

  In the production method described above, the transition metal composite oxide particles and the lithium compound are mixed and heated, but the method of the present invention is not limited thereto.

  As a result, the oxide particles of the present invention can be obtained. Thereafter, the oxide particles may be pulverized as necessary. Depending on the pulverization technique, the central secondary particle diameter of the oxide particles of the present invention can be adjusted at the pulverization stage while maintaining the electrochemical activity of the oxide particles of the present invention.

  Thereafter, post-treatment may be performed depending on purposes such as washing, classification, and additive mixing.

3. Non-aqueous secondary battery The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery using a positive electrode active material comprising the oxide particles of the present invention described above. The non-aqueous secondary battery of the present invention is suitably used as a non-aqueous secondary battery such as a lithium ion secondary battery or a lithium ion polymer secondary battery. The non-aqueous secondary battery of the present invention may be configured, for example, in a conventionally known non-aqueous electrolyte secondary battery using the above-described oxide particles of the present invention as at least a part of the positive electrode active material. The configuration of is not particularly limited. Specifically, the non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode, and a lithium ion conductive material (may further include a separator if necessary), and the positive electrode uses the oxide particles of the present invention. Containing the positive electrode active material. Hereinafter, a lithium ion secondary battery will be described as an example.

<Negative electrode>
The negative electrode has a negative electrode active material layer on the negative electrode current collector. At this time, the negative electrode active material layer may be formed only on one surface of the negative electrode current collector, or may be formed on both surfaces.

  The negative electrode active material layer includes a negative electrode active material. The negative electrode active material is not particularly limited. For example, carbonaceous materials such as graphite, graphite, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon); metallic lithium; Al, Alloy compounds of lithium, such as Si, Pb, Sn, Zn, and Cd; transition metal oxides such as tin oxide, titanium oxide, tungsten oxide, and molybdenum oxide; metal sulfides such as iron sulfide and titanium sulfide; lithium titanate Lithium composite oxide such as can be used.

  The negative electrode active material layer can contain a known conductive agent, binder, and the like. Examples of the conductive agent include acetylene black, carbon black, and graphite. Examples of the binder include polytetrafluoroethylene (PTFE), polyfucavinylidene (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, carboxymethyl cellulose (CMC), styrene-butadiene rubber, polyamide, poly Examples include acrylonitrile.

  The mixing ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode active material layer can be appropriately determined according to the required characteristics. In addition, since the shape of the negative electrode active material, the conductive agent, and the binder is usually in the form of particles or powder, when these are mixed to form a negative electrode active material layer forming king paste composition, an aqueous solvent such as water Alternatively, an organic solvent such as N-methyl-2-pyrrolidone (NMP) may be mixed to form a paste.

  The method for forming the negative electrode active material layer on the current collector is not particularly limited. For example, the negative electrode active material layer forming paste composition is applied and dried, and the density of the negative electrode active material layer is determined by a roll press or the like. The thickness can be adjusted. Known methods and conditions such as coating and drying can be employed.

  In addition to the above, the negative electrode active material can be molded into a sheet and used as a negative electrode as it is.

<Positive electrode>
The positive electrode has a positive electrode active material layer on the positive electrode current collector. At this time, the positive electrode active material layer may be formed only on one surface of the positive electrode current collector, or may be formed on both surfaces.

  As the positive electrode current collector, conventionally used aluminum, aluminum alloy, and the like can be used.

The positive electrode active material layer includes a positive electrode active material. The positive electrode active material is composed of the above-described oxide particles of the present invention. Moreover, as a positive electrode active material, the positive electrode active material conventionally used can also be used in the range which does not impair the effect of this invention not only the oxide particle | grains of said invention. Examples of such a positive electrode active material include various oxides, sulfides, and the like. For example, manganese dioxide (MnO ₂ ) iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (for example, Li _x Mn ₂ O ₄ , Li _x MnO ₂ etc.), lithium nickel composite oxide (eg Li _x NiO ₂ etc.), lithium cobalt composite oxide (eg Li _x CoO ₂ etc.), lithium nickel cobalt composite oxide (eg LiNi _1-y Co _y O) ₂ ), lithium nickel cobalt composite oxide (eg, LiNi _1-xy Co _x Mn _y O ₂ ), spinel type lithium manganese nickel composite oxide (eg, Li _x Mn _2-y Ni _y O ₄ ), lithium phosphates having an olivine structure (e.g., _{Li x FePO 4, Li x Fe} 1-y Mn y PO 4, L _x CoPO _4, etc.), iron sulfate _{(Fe 2 (SO 4)} 3), vanadium oxide (for example, _V 2 _{O 5,} etc.), and the like.

  In the present invention, 20 to 100% by weight, particularly 50 to 100% by weight of the positive electrode active material may be used as the oxide particles of the present invention.

  The positive electrode active material layer may contain a known conductive agent, binder, and the like. What was mentioned above can be used as a electrically conductive agent and a binder.

  The mixing ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode active material layer can be determined according to the required characteristics. In addition, since the shape of the positive electrode active material, the conductive agent, and the binder is usually in the form of particles or powder, when these are mixed to form a paste composition for forming a positive electrode active material layer, an aqueous solvent such as water Alternatively, an organic solvent such as N-methyl-2-pyrrolidone (NMP) may be mixed to form a paste.

  The method for forming the positive electrode active material layer on the positive electrode current collector is not particularly limited. For example, the positive electrode active material forming paste composition is applied and dried, and the density of the positive electrode active material layer is determined by a roll press or the like. The thickness can be adjusted. Known methods and conditions such as coating and drying can be employed.

<Lithium ion conductive material>
As the lithium ion conductive material in the non-aqueous secondary battery of the present invention, for example, a non-aqueous electrolyte solution obtained by dissolving an electrolyte salt in an organic solvent or a lithium ion conductive material other than the non-aqueous electrolyte solution can be used.

  As the nonaqueous electrolytic solution in the nonaqueous secondary battery of the present invention, an organic electrolytic solution in which an organic solvent and an electrolyte salt are combined can be used.

  Examples of the organic solvent in the organic electrolyte include low-viscosity chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; cyclic carbonates with high dielectric constant such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Cyclic esters such as γ-butyrolactone; chain ethers such as 1,2-dimethoxyethane and 1,2-diethoxyethane; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran and 1,3-dioxolane; methyl formate; Examples thereof include chain esters such as methyl acetate and methyl propionate; dimethylformamide; dimethyl sulfoxide; sulfolane; and mixed solvents thereof.

  Further, the electrolyte salt is not particularly limited as long as it is a compound that is not altered or decomposed by the operating voltage. For example, lithium iodide, lithium perchlorate, lithium tetrafluoroborate, lithium tetrafluorophosphate, Examples include lithium tetrachloroaluminate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium bis (trifluoromethanesulfonyl) imide, lithium bis (pentafluoroethanesulfonyl) imide, and mixtures thereof. .

  The non-aqueous electrolyte may be used as a gel by further adding a gelling agent or the like. Moreover, you may make it absorb and use a hygroscopic polymer.

  As the lithium ion conductive material other than the non-aqueous electrolyte, a solid electrolyte having conductivity of inorganic or organic lithium ions may be used.

<Separator>
As the separator, a microporous film made of an olefin resin such as polyethylene or polypropylene is used, and a material, a weight average molecular weight is formed by laminating a plurality of microporous films having different porosity, and various kinds of these microporous films are used. It may be one containing an appropriate amount of additives such as plasticizers, antioxidants, and flame retardants.

  As the shape of the power generation element, a wound oval shape, a circular shape, or the like can be used. Other battery components include a current collector, a terminal, an insulating plate, a battery case, and the like, but those components that have been conventionally used can be used as they are.

  The use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited.

  The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[Elemental analysis]
The elemental analysis of the positive electrode active materials of each Example and Comparative Example was performed by ICP-AES, and the composition of the lithium transition metal composite oxide was obtained.

[Average primary particle size]
A scanning electron microscope (SEM) photograph with a magnification of 20,000 times was taken, 50 primary particles in the photographing range were randomly selected, and the average value of (major axis + minor axis) / 2 was defined as the average primary particle diameter. .

[Central secondary particle size]
A volume-based particle size distribution was obtained by laser diffraction method, and a value (D50) at which the integration frequency was 50% was determined as the central secondary particle size.

Example 1
By the coprecipitation method, the general primary formula (Ni _0.197 Co _0.197 Mn _0.606 ) _{2 having} an average primary particle diameter of 20 nm (short diameter; the same in the following Examples and Comparative Examples) and a central secondary particle diameter of 4 μm Precursor particles represented by O ₃ were obtained.

Next, 9.8 × 10 ⁻¹ mol of the obtained precursor particles, 3.9 × 10 ⁻² mol of tungsten oxide (VI) and 2.8 mol of lithium hydroxide were mixed, and calcined at 900 ° C. for 12 hours in air. And the general formula;
Lithium transition metal composite oxide particles of Example 1 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 127 nm and a central secondary particle size of 4.6 μm.

Example 2
By coprecipitation, precursor particles represented by the general formula (Ni _0.214 Co _0.214 Mn _0.572 ) ₂ O ₃ having an average primary particle diameter of 20 nm and a central secondary particle diameter of 4 μm were obtained.

Next, 9.8 × 10 ⁻¹ mol of the obtained precursor particles, 3.9 × 10 ⁻² mol of tungsten oxide (VI) and 2.7 mol of lithium hydroxide were mixed, and calcined at 900 ° C. in air for 12 hours. And the general formula;
Lithium transition metal composite oxide particles of Example 2 represented by 0.35Li ₂ MnO ₃ .0.65LiNi _0.323 Co _0.323 Mn _0.323 W _0.030 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 145 nm and a central secondary particle size of 4.3 μm.

Example 3
By coprecipitation, precursor particles represented by the general formula (Ni _0.180 Co _0.180 Mn _0.640 ) ₂ O _{3 having} an average primary particle diameter of 20 nm and a central secondary particle diameter of 4 μm were obtained.

Next, 9.8 × 10 ⁻¹ mol of the obtained precursor particles, 3.9 × 10 ⁻² mol of tungsten (VI), and 2.9 mol of lithium hydroxide were mixed and baked at 900 ° C. in air for 12 hours. And the general formula;
Lithium transition metal composite oxide particles of Example 3 represented by 0.45Li ₂ MnO ₃ .0.55LiNi _0.321 Co _0,321 Mn _0.321 W _0.036 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 149 nm and a center secondary particle size of 4.2 μm.

Example 4
Similar to Example 1 except that the firing temperature was 950 ° C .;
The lithium transition metal composite oxide particles of Example 4 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 160 nm and a central secondary particle size of 4.3 μm.

Example 5
The general formula is similar to Example 1 except that the firing temperature is 1000 ° C .;
Lithium transition metal composite oxide particles of Example 5 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 200 nm and a central secondary particle size of 4.3 μm.

Example 6
Similar to Example 1 except that the firing temperature was 850 ° C .;
Lithium transition metal composite oxide particles of Example 6 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 111 nm and a central secondary particle size of 4.2 μm.

Example 7
Similar to Example 1, except that the firing temperature was 800 ° C.
Lithium transition metal composite oxide particles of Example 7 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 88 nm and a central secondary particle size of 4.2 μm.

Example 8
Except that the firing temperature was set to 750 ° C., the same general formula as in Example 1,
Lithium transition metal composite oxide particles of Example 8 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 73 nm and a central secondary particle size of 4.2 μm.

Example 9
Similar to Example 1, except that the firing temperature was 700 ° C .;
The lithium transition metal composite oxide particles of Example 9 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 56 nm and a central secondary particle size of 4.1 μm.

Example 10
Precursor particles represented by a general formula obtained by coprecipitation method and having an average primary particle diameter of 20 nm and a central secondary particle diameter of 3.2 μm; (Ni _0.197 Co _0.197 Mn _0.606 ) ₂ O ₃ In the same manner as in Example 1, except that
The lithium transition metal composite oxide particles of Example 10 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 126 nm and a central secondary particle size of 3.3 μm.

Example 11
Precursor particles represented by a general formula obtained by coprecipitation method having an average primary particle diameter of 20 nm and a central secondary particle diameter of 4.3 μm; (Ni _0.197 Co _0.197 Mn _0.606 ) ₂ O ₃ Except for the use of the general formula as in Example 1,
The lithium transition metal composite oxide particles of Example 11 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ are obtained.

  The resulting lithium transition metal composite oxide has an average primary particle size of 127 nm and a central secondary particle size of 4.9 μm.

Example 12
By coprecipitation, precursor particles represented by the general formula (Ni _0.2 Co _0.2 Mn _0.6 ) ₂ O ₃ having an average primary particle diameter of 20 nm and a central secondary particle diameter of 4 μm are obtained.

Next, 1.0 mol of the obtained precursor particles and 2.8 mol of lithium hydroxide are mixed and calcined at 900 ° C. for 12 hours in the air.
The lithium transition metal composite oxide particles of Example 12 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.333 Co _0.333 Mn _0.333 O ₂ are obtained.

  The resulting lithium transition metal composite oxide has an average primary particle size of 130 nm and a central secondary particle size of 4.2 μm.

Example 13
By coprecipitation, precursor particles represented by the general formula; (Ni _0.3 Mn _0.7 ) ₂ O ₃ having an average primary particle diameter of 20 nm and a central secondary particle diameter of 4 μm are obtained.

Next, 1.0 mol of the obtained precursor particles and 2.8 mol of lithium hydroxide are mixed and calcined at 900 ° C. for 12 hours in the air.
The lithium transition metal composite oxide particles of Example 13 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.5 Mn _0.5 O ₂ are obtained.

  The resulting lithium transition metal composite oxide has an average primary particle size of 135 nm and a central secondary particle size of 4.2 μm.

Example 14
By coprecipitation, precursor particles represented by the general formula; (Ni _0.30 Co _0.12 Mn _0.58 ) ₂ O ₃ having an average primary particle diameter of 20 nm and a central secondary particle diameter of 4 μm are obtained.

Next, 1.0 mol of the obtained precursor particles and 2.8 mol of lithium hydroxide are mixed and calcined at 900 ° C. for 12 hours in the air.
The lithium transition metal composite oxide particles of Example 14 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.5 Co _0.2 Mn _0.3 O ₂ are obtained.

  The resulting lithium transition metal composite oxide has an average primary particle size of 135 nm and a central secondary particle size of 4.2 μm.

Example 15
A general formula as in Example 1 except that 3.9 × 10 ⁻² mol of titanium oxide (IV) was used instead of 3.9 × 10 ⁻² mol of tungsten oxide (VI);
Lithium transition metal composite oxide particles of Example 15 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 Ti _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 127 nm and a central secondary particle size of 4.6 μm.

Example 16
By coprecipitation, precursor particles represented by the general formula; (Ni _0.234 Co _0.234 Mn _0.532 ) ₂ O ₃ having an average primary particle diameter of 20 nm and a central secondary particle diameter of 4 μm were obtained.

Next, 1.0 mol of the obtained precursor particles and 2.8 mol of lithium hydroxide are mixed and calcined at 900 ° C. for 12 hours in the air.
Lithium transition metal composite oxide particles of Example 16 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.39 Co _0.39 Mn _0.22 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 127 nm and a central secondary particle size of 4.2 μm.

Comparative Example 1
The coprecipitation method, an average primary particle size of 20 nm, the general formula of the central secondary particle diameter 4 [mu] _m; to obtain precursor particles represented by _{(Ni 0.231 Co 0.231 Mn 0.538)} 2 O 3.

Next, 9.8 × 10 ⁻¹ mol of the obtained precursor particles, 3.9 × 10 ⁻² mol of tungsten oxide (VI) and 2.6 mol of lithium hydroxide were mixed, and baked at 900 ° C. for 12 hours in the air. And the general formula;
Lithium transition metal composite oxide particles of Comparative Example 1 represented by 0.3Li ₂ MnO ₃ .0.7LiNi _0.324 Co _0.324 Mn _0.324 W _0.028 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 133 nm and a central secondary particle size of 4.4 μm.

Comparative Example 2
By coprecipitation, precursor particles represented by the general formula; (Ni _0.163 Co _0.163 Mn _0.674 ) ₂ O ₃ having an average primary particle diameter of 20 nm and a central secondary particle diameter of 4 μm were obtained.

Next, 1.0 mol of the obtained precursor particles, 3.9 × 10 ⁻² mol of tungsten oxide (VI), and 3.0 mol of lithium hydroxide were mixed, and calcined at 900 ° C. for 12 hours in the air.
Lithium transition metal composite oxide particles of Comparative Example 2 represented by 0.5Li ₂ MnO ₃ .0.5LiNi _0.320 Co _0.320 Mn _0.320 W _0.039 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 117 nm and a central secondary particle size of 4.4 μm.

Comparative Example 3
Precursor particles represented by a general formula (Ni _0.197 Co _0.197 Mn _0.606 ) ₂ O ₃ having an average primary particle diameter of 20 nm and a secondary particle diameter of 2.3 μm obtained by coprecipitation method are used. Except for the use of the general formula, as in Example 1,
Lithium transition metal composite oxide particles of Comparative Example 3 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 121 nm and a central secondary particle size of 2.4 μm.

Comparative Example 4
As in Example 1, except that the baking temperature was 1050 ° C., the general formula;
Lithium transition metal composite oxide particles of Comparative Example 4 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 245 nm and a central secondary particle size of 4.9 μm.

Comparative Example 5
As in Example 1, except that the firing temperature was 600 ° C., the general formula;
Lithium transition metal composite oxide particles of Comparative Example 5 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 48 nm and a central secondary particle size of 4.1 μm.

Comparative Example 6
Use of precursor particles represented by the general formula (Ni _0.118 Co _0.355 Mn _0.527 ) ₂ O ₃ having an average primary particle diameter of 20 nm and a central secondary particle diameter of 4 μm obtained by coprecipitation method Except for the general formula:
Lithium transition metal composite oxide particles of Comparative Example 6 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.194 Co _0.580 Mn _0.194 W _0.033 O ₂ are obtained.

  The resulting lithium transition metal composite oxide has an average primary particle size of 130 nm and a central secondary particle size of 4.2 μm.

Comparative Example 7
Precursor particles represented by the general formula (Ni _0.197 Co _0.197 Mn _0.606 ) ₂ O ₃ having an average primary particle diameter of 20 nm and a central secondary particle diameter of 6.2 μm obtained by coprecipitation method are used. Except for the use of the general formula, as in Example 1,
Lithium transition metal composite oxide particles of Comparative Example 7 represented by 0.4Li ₂ MnO ₃ .0.6LiNi _0.322 Co _0.322 Mn _0.322 W _0.033 O ₂ were obtained.

  The obtained lithium transition metal composite oxide had an average primary particle size of 100 nm and a central secondary particle size of 6.1 μm.

[Production of secondary battery for cycle characteristic evaluation]
A secondary battery for evaluation was produced in the following manner.

  90% by weight of the positive electrode active material of Examples 1 to 16 or Comparative Examples 1 to 7, 5% by weight of carbon powder as a conductive agent, and 5 parts by weight of PVDF (polyfucavinylidene) were added to NMP (N-methyl-2-pyrrolidone). The paste composition for forming a positive electrode active material layer was prepared by dispersing, dissolving or kneading. The obtained paste composition for forming a positive electrode active material layer was applied to a positive electrode current collector made of an aluminum foil and dried to obtain a positive electrode plate.

  A negative electrode active material layer forming paste composition is prepared by dispersing, dissolving or kneading 97.5% by weight of a carbon material as a negative electrode active material and 2.5% by weight of CMC (carboxymethyl cellulose) as a binder in pure water. did. The obtained paste composition for forming a negative electrode active material layer was applied to a negative electrode current collector made of copper foil and dried to obtain a negative electrode plate.

EC (ethylene carbonate) and MEC (methyl ethyl carbonate) were mixed at a volume ratio of 3: 7 to obtain a mixed solvent. In the obtained mixed solvent, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was dissolved so as to have a concentration of 1 mol / L to prepare a nonaqueous electrolytic solution.

  A porous polypropylene film was used as a separator.

  A lead electrode was attached to the produced positive electrode plate and negative electrode plate, and a positive electrode plate, a separator, and a negative electrode plate were stacked in this order. These were stored in a laminate pack, and the non-aqueous electrolyte prepared above was injected, and the laminate pack was sealed to obtain a laminate type secondary battery.

[Production of secondary battery for charge / discharge capacity and output characteristics evaluation]
A positive electrode plate was prepared in the same manner as the above-described secondary battery for cycle characteristic evaluation.

  While using metallic lithium as a negative electrode active material, it shape | molded to the thin sheet form and set it as the negative electrode plate.

  A nonaqueous electrolytic solution was prepared by dissolving lithium hexafluorophosphate as an electrolyte salt in DEC (diethyl carbonate) so as to have a concentration of 1 mol / L.

  A separator similar to the above secondary battery for evaluating cycle characteristics was used.

  A lead electrode was attached to the produced positive electrode plate, and the positive electrode plate, the separator, and the negative electrode plate were housed in this order. The bottom of the negative electrode was electrically connected to the bottom of the stainless steel container so that the bottom of the container became the negative electrode terminal. The separator was fixed by the side of the container made of Teflon (registered trademark). The tip of the positive lead electrode was led out of the container and used as a positive terminal. The positive and negative terminals were electrically insulated by the container side. After storing these in a container, the non-aqueous electrolyte prepared above was injected and sealed with a stainless steel container lid to obtain a sealed secondary battery.

[Test example: Evaluation of battery characteristics]
Using the secondary battery for evaluation described above, battery characteristics were evaluated for Examples 1 to 10 and 15 to 16 and Comparative Examples 1 to 5 and 7 in the following manner.

In an environment having a cycle characteristic of 25 ° C., constant current and constant voltage charging and constant current discharging were repeated 50 times at a full charge voltage of 4.5 V, a discharge voltage of 2.0 V, and a current density of 1.26 mA / cm ² with respect to the positive electrode. The ratio of the 50th discharge capacity to the first discharge capacity (50th discharge capacity / first discharge capacity) was _defined as a capacity retention rate _Ps50 . A high capacity retention rate indicates excellent cycle characteristics.

Under an environment with an initial charge capacity of 25 ° C., a full charge voltage of 4.6 V and a charge rate of 0.2 C (1 C: a current density at which discharge is completed in one hour from a fully charged state) are charged at a constant current and a constant voltage until the full charge voltage is reached. The capacity stored in was set as the initial charge capacity Q _ic .

After charging at constant current and constant voltage up to a full charge voltage of 4.6 V in an environment with an initial discharge capacity of 25 ° C., a discharge voltage of 2.0 V and a discharge rate of 0.05 C (1 C: current that finishes discharging in 1 hour from a fully charged state) A capacity discharged at a constant current at a density and discharged to a discharge voltage (2.0 V) was defined as an initial discharge capacity Q _id .

The load characteristic Q ′ _id was set in the same manner as the initial discharge capacity except that the load characteristic discharge rate was 2.0 C.

Capacitance SOC × Q at a discharge rate of 0.05 C (1 C: current density at which discharge is completed in 1 hour from a fully charged state) after charging at a constant current and constant voltage up to a full charge voltage of 4.6 V in an environment with an output characteristic of 25 ° C. _A constant current was discharged until _ic . After the discharge, the battery voltage V at discharge rates 0.05C, 0.1C, 0.5C and 1C was measured, and the current I and the battery voltage V were plotted. Battery resistance R (SOC) (battery resistance when SOC is a certain value) was determined from the slope of the approximate straight line of the plot. A lower R (SOC) indicates higher output characteristics at a certain SOC.

  About Examples 1-16 or Comparative Examples 1-7, the characteristic of a positive electrode active material is shown in Table 1, and a battery characteristic is shown in Table 2.

  From Tables 1 and 2, by using the positive electrode active material of the present invention in which the composition, average primary particle size and central secondary particle size were adjusted, not only high capacity and high cycle characteristics but also in the low SOC region It turns out that the positive electrode active material which can improve an output characteristic, and a non-aqueous-electrolyte secondary battery using the same can be provided. Further, as can be seen from the result of R (1.0), it can be seen that the significance of adjusting these simultaneously appears particularly in the low SOC region.

  The non-aqueous electrolyte secondary battery using the positive electrode active material of the present invention is excellent not only in high capacity and high cycle characteristics but also in output characteristics even in a low SOC region. It can be suitably used as a power source for required applications.

Claims (9)

General formula (1);
_{xLi 2 MnO 3 · (1-} x) LiNi 1-s-t-u Co s Mn t W u O 2
[Wherein x is 0.32 to 0.48; s is 0 to 0.65; t is 0 to 0.5; s + t is 0.05 to 0.75; 0 <u ≦ 0.05 . ]
And
The average primary particle size is 60-130 nm,
The central secondary particle size is 2.5-6 μm,
A positive electrode active material for a non-aqueous electrolyte secondary battery comprising lithium transition metal composite oxide particles.   The positive electrode active material for nonaqueous electrolyte secondary batteries according to claim 1, wherein s is 0 to 0.45 in the general formula (1).   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein x in the general formula (1) is 0.35 to 0.45.   4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide particles have an average primary particle diameter of 73 to 88 nm.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein a central secondary particle diameter of the lithium transition metal composite oxide particles is 3 to 5 µm. It is a manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries in any one of Claims 1-5,
General formula (2);
(Ni _{1-s′-t′-u ′} Co _{s ′} Mn _{t ′} W _{u ′} ) ₂ O ₃
[Wherein, s ′ is 0.17 to 0.23; t ′ is 0.55 to 0.75; 0 <u ′ ≦ 0.05 ]
And a lithium transition metal composite oxide precursor particle having a central secondary particle diameter of 2.5 to 6 μm and a lithium compound, and then heating.   The production method according to claim 6, wherein the lithium compound is lithium hydroxide and / or lithium carbonate.   The manufacturing method of Claim 6 or 7 whose heating temperature is 750-1000 degreeC.   A non-aqueous electrolyte secondary battery containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1.

Images