JP2007188699A - Nonaqueous electrolyte secondary battery and method of manufacturing positive active material for nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having higher charge/discharge characteristics (load characteristics) than a conventional nonaqueous electrolyte secondary battery, and to provide the method of manufacturing a positive active material for the nonaqueous electrolyte secondary battery. <P>SOLUTION: The nonaqueous secondary battery is equipped with at least a positive electrode containing positive active material particles covered with a low valence oxide of a transition metal element; a negative electrode; and a nonaqueous electrolyte containing a lithium salt. The positive active material for the nonaqueous electrolyte secondary battery is manufactured in such a way that the low valence oxide particles of the transition metal element and positive active material particles are dispersed in a solvent to prepare slurry, the solvent is removed from the slurry, and then residual particles are dried to obtain the positive active material particles covered with the low valence oxide particles of the transition metal element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery (lithium secondary battery) having excellent load characteristics, and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

In the automobile industry, EV drive batteries are being actively developed in order to promote the introduction of electric vehicles (EV) and hybrid electric vehicles (HEV) instead of vehicles using fossil fuels such as gasoline vehicles.
As a battery for EV, researches on a storage battery, a nickel-cadmium battery, a nickel-hydrogen battery, and the like have been conducted, but a lithium secondary battery is considered promising in terms of weight and energy density.

The lithium secondary battery currently on the market is based on cobalt, which is a rare metal, as the positive electrode material, and there is a concern about resource when it becomes a large battery for EVs and the cost may increase. There is. Therefore, research on spinel-type LiMn ₂ O ₄ has been actively conducted as an alternative positive electrode material. However, spinel-type LiMn ₂ O ₄ cannot solve the cycle deterioration at high temperatures, and compared with other positive-electrode materials. Because of its low capacity, it has not yet been put into practical use, such as a shift to Ni.
In addition, the positive electrode material made of Ni—Co—Mn ternary composite oxide has higher capacity and thermal stability than spinel type LiMn ₂ O ₄ , and the process cost is lower than that of Ni type positive electrode material. It is characterized by being inexpensive.

However, since EV requires a large amount of energy when starting and accelerating, and a large amount of energy generated when decelerating must be efficiently regenerated, a lithium secondary battery used as an EV power source has high output characteristics and input characteristics. Required.
Since the lithium secondary battery is a mechanism that converts it into electric energy by diffusion of Li ⁺ ions having an ionic radius larger than that of H ⁺ ions, there is a drawback that quick charge / discharge cannot be performed, and Ni—Co—Mn ternary system as a positive electrode material Even in a lithium secondary battery using a composite oxide, further excellent charge / discharge characteristics (load characteristics) are required to mount it on an EV.

  Therefore, as a positive electrode material for a non-aqueous electrolyte secondary battery such as a lithium secondary battery, it is coated with a metal oxide or metal sulfide having electrical conductivity such as titanium (Ti) or tin (Sn) or lithium ion conductivity. A proposal using a positive electrode material made of Li-Ni composite oxide on the surface of a positive electrode active material (see Patent Document 1), a specific amount of titanium and / or lithium titanate on a part of the surface of lithium cobalt oxide particles Non-aqueous electrolyte secondary battery using a positive electrode active material coated with Pt (Patent Document 2), and around the positive electrode active material from Ti, Al, Sn, Bi, Cu, Si, Ga, W, Zr, B, Mo Batteries using a metal containing at least one selected metal and / or an intermetallic compound obtained by combining a plurality of these and / or an oxide as a positive electrode (Patent Document 3), etc., and lithium Development of new electrode materials of the following cell, a number of proposals have been made for the surface treatment of the said workpiece. However, development of a non-aqueous decomposition secondary battery having even better charge / discharge characteristics (load characteristics) is desired in the market.

JP 2003-173775 A JP 2002-151078 A Japanese Patent Laid-Open No. 11-16666

  The present invention has been made in view of the above circumstances, and a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery having charge / discharge characteristics (load characteristics) further superior to those of conventional nonaqueous electrolyte secondary batteries. An object of the present invention is to provide a method for producing a positive electrode active material.

  The present inventors performed various surface treatments on the positive electrode active material particles employed as the positive electrode of non-aqueous electrolyte secondary batteries such as lithium secondary batteries, and used these as positive electrodes of non-aqueous electrolyte secondary batteries. As a result of intensive studies on the effects on the charge / discharge characteristics (load characteristics) of the non-aqueous electrolyte secondary battery, it is a specific transition metal oxide, and the transition metal element in the same transition metal oxide Non-aqueous electrolyte secondary with excellent charge / discharge characteristics (load characteristics) by using positive electrode active material particles coated with oxides with low oxygen number (low valence oxide) bonded to the surface A battery was obtained, and the present invention was obtained with the knowledge that the object of the present invention was achieved.

That is, the nonaqueous electrolyte secondary battery of the present invention has the following configuration.
(1) A non-aqueous electrolyte comprising a positive electrode including positive electrode active material particles whose surface is coated with a low-valent oxide of a transition metal element, a negative electrode, and a non-aqueous electrolyte containing a lithium salt Secondary battery.
(2) The low-valent oxide of the transition metal element is at least one of titanium (Ti), tin (Sn), vanadium (V), niobium (Nb), molybdenum (Mo), and tungsten (W). The nonaqueous electrolyte secondary battery according to (1) above, which is a low-valent oxide of an element.
(3) The coating amount of the low-valent oxide of the transition metal element is 0.1 to 10.0% by weight, more preferably 0.3 to 3.0% by weight with respect to the positive electrode active material particles. The nonaqueous electrolyte secondary battery according to (1) or (2), wherein

(4) The non-aqueous solution according to any one of (1) to (3), wherein the positive electrode active material is a Ni—Co—Mn ternary composite oxide or a lithium-transition metal composite oxide. Electrolyte secondary battery.
(5) The lithium-containing oxide is one of lithium cobaltate (LiCoO ₂ ), spinel type lithium manganate (LiMn ₂ O ₄ ), and lithium nickelate (LiNiO ₂ ). 4) A nonaqueous electrolyte secondary battery.
(6) The nonaqueous electrolyte secondary battery according to any one of (1) to (5), wherein the low-valent oxide of the transition metal element is titanium monoxide.

(7) The transition is made to the surface of the positive electrode active material particles by removing the solvent from a slurry obtained by dispersing low-valent oxide particles of transition metal elements and positive electrode active material particles in a solvent and drying the slurry. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising attaching low-valent oxide particles of a metal element.

  According to the present invention, since positive electrode active material particles coated with a low-valent oxide of a transition element having many oxygen vacancies on the surface and excellent in electronic conductivity are used as a positive electrode, it is superior to conventional ones. Thus, a non-hydrolytic secondary battery having charge / discharge characteristics (load characteristics) can be obtained.

The present invention will be described in detail below.
The nonaqueous electrolyte secondary battery of the present invention comprises a nonaqueous electrolyte containing a positive electrode, a negative electrode, a separator, and a lithium salt as essential components. The positive electrode is obtained by applying a positive electrode mixture containing a positive electrode active material, a conductive agent and a binder on a positive electrode plate (for example, a positive electrode current collector made of an aluminum plate or the like).
The non-aqueous electrolyte secondary battery of the present invention is a conventional non-aqueous electrolyte secondary battery except that the positive electrode active material constituting the positive electrode includes positive electrode active material particles coated with a low-valent oxide of a transition element on the surface. It consists of the same composition.
The method for producing a non-aqueous electrolyte secondary battery of the present invention is characterized in that a low-valent oxide of a transition element is used as a starting material for a coating material that covers the surface of a positive electrode active material that is a positive electrode of the battery. And

The positive electrode active material of the non-aqueous electrolyte secondary battery according to the present invention is, for example, dispersed in a solution in which a predetermined amount of transition metal element low oxide particles are dispersed in a volatile solvent such as ethanol. The mixture is sufficiently stirred to form a slurry, and then the solvent is evaporated and dried to coat the surface of the positive electrode active material particles with low oxide particles of transition metal.
Moreover, the surface of the positive electrode active material particles can be obtained by a method of mixing the positive electrode active material and a predetermined amount of transition metal element low oxide particles using a ball mill or various blenders, a chemical vapor deposition (CVD) method, or a powder coating apparatus. It can also be produced by a dry coating method, such as attaching a predetermined amount of transition metal element low oxide particles.

  Among transition metal element low-oxides covering the surface of the positive electrode active material particles in the present invention, titanium (Ti), tin (Sn), vanadium (V), niobium (Nb), molybdenum (Mo), and tungsten The low oxide particles of at least one transition metal element in (W), titanium monoxide, tin monoxide, vanadium monoxide, niobium monoxide, molybdenum dioxide, tungsten dioxide, etc. are preferably used. In particular, it is more preferable to coat titanium monoxide which is a low atomized oxide of Ti.

  The amount of the transition metal element low-valence oxide coated on the surface of the positive electrode active material particles is preferably 0.1 to 10.0% by weight, more preferably, the positive electrode active material particles. It is good to set it as 0.3 to 3.0 weight%. If the coating amount of the transition metal element oxide is less than 0.1% by weight of the positive electrode active material particles, the coating area covering the active material surface is reduced, and the effect of coating with a low oxidation state oxide (low valence oxide) Since it does not appear, it is not preferable, and when it is more than 10.0% by weight, the capacity per unit weight is decreased, which is not preferable.

In the present invention, a “low-valent oxide” of a transition metal element is an oxidation in which the number of oxygen atoms bonded to the transition metal element is not the maximum among the oxides of each specific transition metal element. Say things. For example, when the transition metal element is Ti, titanium dioxide and titanium monoxide are known as Ti oxides, but in the present invention, the low atom of the transition metal coated on the surface of the positive electrode active material particles Examples of the valent oxide include titanium monoxide instead of titanium dioxide, and examples of the Mo and W oxide include molybdenum dioxide and tungsten dioxide instead of molybdenum trioxide and tungsten trioxide.
These low-valent oxides of transition metal elements are oxides containing a large amount of oxygen vacancies, and are excellent in electron conductivity, so that the rate characteristics are further improved.

As the positive electrode active material particles coated with the low-valent oxide of the transition metal element, Ni—Co—Mn ternary composite oxide or lithium-transition metal composite oxide is used. Lithium-containing oxides, particularly lithium cobaltate (LiCoO ₂ ), spinel type lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ), magnesium oxide (MgO), titanium oxide (TiO ₂ ) or zirconium oxide A lithium cobaltate composite compound in which (ZrO ₂ ) and LiCoO ₂ are mixed is preferably used.

  The positive electrode mixture applied on the positive electrode plate may contain a conductive agent, a binder, a filler, and the like in addition to the positive electrode active material. As the conductive agent, for example, a conductive material selected from the group consisting of natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, carbon fiber, metal powder such as nickel powder, and the like. One type or two or more types of sexual materials can be used. Among the above, it is preferable to use graphite and acetylene black as a conductive agent. In addition, the compounding quantity of the electrically conductive agent to a positive mix is 1 to 50 weight%, Preferably it exists in the range of 2 to 30 weight%.

  Examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl pyrrolidone, ethylene-propylene-diene turbolimer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber, One or more of polysaccharides such as polyethylene oxide, thermoplastic resins, and polymers having rubber elasticity can be used. The blending amount of the binder to the positive electrode mixture is preferably in the range of 2 to 30% by weight.

  Furthermore, any filler can be used as long as it is a fibrous material that does not cause a chemical change in the nonaqueous electrolyte secondary battery. Usually, an olefin polymer such as polypropylene or polyethylene, glass fiber, or carbon fiber is used. Such fibers are used. The blending amount of the filler in the positive electrode mixture is not particularly limited, but is preferably in the range of 0 to 30% by weight. In addition, the compounding quantity to the positive mix of the positive electrode active material of this invention is although it does not specifically limit, Preferably it is 60 to 95 weight%, Especially preferably, it exists in the range of 70 to 94 weight%.

Next, non-aqueous electrolytes used in non-aqueous electrolyte secondary batteries are, for example, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyl lactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl oxalate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl 2-Oxazodinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, at least one kind of aprotic organic solvent such as 1,3-propane sultone And solvent combined, lithium salts such as LiClO ₄ is dissolved in the _{solvent, LiBF 4, LiPF 6, LiCF} 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, LiAlCl 4, chloroborane lithium, It is composed of one or more lithium salts such as lower aliphatic lithium carboxylate and lithium tetraphenylborate.

  In addition to the non-aqueous electrolyte, an organic solid electrolyte can also be used. Examples thereof include a polyethylene derivative or a polymer containing the same, a polypropylene oxide derivative or a polymer containing the same, and a phosphate ester polymer.

  A desired amount of the above compounds can be mixed to constitute a non-aqueous electrolyte secondary battery. The current collector of the electrode is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the constructed nonaqueous electrolyte secondary battery.For example, stainless steel, nickel, aluminum, titanium, calcined carbon, The surface of aluminum or stainless steel is treated with carbon, nickel, copper, titanium or silver. The negative electrode is made of stainless steel, nickel, copper, titanium, aluminum, calcined carbon, etc. A surface treated with carbon, nickel, titanium, silver, or the like, or an Al—Cd alloy is used.

EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, this is merely an example and does not limit the present invention.
[Example 1]
(Preparation of positive electrode active material)
Titanium monoxide powder of 0.5 mol% with respect to the metal of the Li (Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ (positive electrode active material) powder used (High Purity Chemical Laboratory Co., Ltd.) Manufactured and having a purity of 99% up) was added to ethanol, and this was subjected to a dispersion treatment using an ultrasonic cleaner for 1 hour to obtain an ethanol dispersion of titanium monoxide powder.
Next, Li (Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ (positive electrode active material) powder is charged into this dispersion and stirred to prepare a mixed slurry of titanium monoxide and the positive electrode active material. Prepared.
Next, ethanol was completely stripped from the mixed slurry of Li (Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ (positive electrode active material) and titanium monoxide by an evaporator, and 0.5 A positive electrode active material of Example 1 coated with mol% titanium monoxide was prepared.

(Production of coin-type non-aqueous electrolyte secondary battery)
90% by weight of the positive electrode active material of Example 1 obtained as described above, 7% by weight of acetylene black, and 3% by weight of PTFE were mixed to obtain a positive electrode material, which was formed by extending the thickness of 70 to 80 μm. It was punched into a disk shape of 11 mm, pressed into an aluminum mesh and dried to obtain a positive electrode.
Using this positive electrode plate, a non-aqueous electrolyte secondary battery was manufactured using each member such as a separator, a negative electrode, a current collector plate, and an electrolytic solution. Among these, the coin cell of Example 1 of CR2016 type using a metal lithium foil for the negative electrode and 1: 1 vol% LiPF ₆ / PC (propylene carbonate) + DMC (dimethyl carbonate) for the non-aqueous electrolyte (non-aqueous electrolyte) A water electrolyte secondary battery) was produced.

(Battery load characteristics test)
The coin-type non-aqueous electrolyte secondary battery of Example 1 manufactured as described above was operated at 20 ° C., the initial discharge capacity was confirmed at 0.2 mA · cm ⁻² , and then 0.2 C at 20 ° C. The load characteristics were evaluated at 10C.
The charge / discharge test was performed for 2 cycles at 0.2C, 1C, 2C, 3C, 6C, and 10C, and the discharge capacity at the second cycle was defined as the discharge capacity at each rate. These discharge capacity and the discharge capacity of the initial discharge capacity ratio of the discharge capacity divided by (0.2 mA · cm ^over discharge capacity at ²⁾ (0.2 C discharge capacity /0.2mA · cm ^{over 2,} 1C discharge capacity /0.2 mA · cm ⁻² discharge capacity, 2C discharge capacity / 0.2 mA · cm ⁻² discharge capacity, 3C discharge capacity / 0.2 mA · cm ⁻² discharge capacity, 6C discharge capacity / 0 discharge capacity .2mA · ^cm-2, and were evaluated load characteristics from discharge capacity) of the discharge capacity /0.2mA · cm ^-2 of 10C (that is towards the discharge capacity ratio is large load characteristic is good means). The obtained results are shown in Table 1.

[Example 2]
In the same manner as the positive electrode active material of Example 1, except that 2.5 mol% titanium monoxide was used instead of 0.5 mol% titanium monoxide, 2.5 mol% of titanium monoxide was formed on the surface. The positive electrode active material of Example 2 coated with titanium oxide was prepared, and the coin cell (nonaqueous electrolyte secondary battery of Example 1) was used except that the positive electrode active material of Example 2 was used instead of the positive electrode active material of Example 1. ), A coin cell (nonaqueous electrolyte secondary battery) of Example 2 was produced.
Next, the load characteristics of the obtained coin cell (nonaqueous electrolyte secondary battery) of Example 2 were evaluated in the same manner as in Example 1. The obtained results are shown in Table 1.

Example 3
In the same manner as the positive electrode active material of Example 1 except that 5.0 mol% titanium monoxide was used instead of 0.5 mol% titanium monoxide, 5.0 mol% The positive electrode active material of Example 3 coated with titanium oxide was prepared, and the coin cell (nonaqueous electrolyte secondary battery of Example 1) was used except that the positive electrode active material of Example 3 was used instead of the positive electrode active material of Example 1. ) To produce a coin cell (nonaqueous electrolyte secondary battery) of Example 3.
Next, for the obtained coin cell (non-aqueous electrolyte secondary battery) of Example 3, the load characteristics of this battery were evaluated in the same manner as in Example 1. The obtained results are shown in Table 1.

[Comparative Example 1]
90 parts by weight of Li (Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ (positive electrode active material) powder, 7 parts by weight of acetylene black (AB) and polytetrafluoroethylene (PTFE) used in Example 1 A positive electrode active material of Comparative Example 1 was prepared by mixing 3 parts by weight with a mortar.
Next, the coin cell of Comparative Example 1 (non-aqueous electrolyte secondary battery) was used in the same manner as the coin cell (non-aqueous electrolyte secondary battery) of Example 1 except that the positive electrode active material of Comparative Example 1 was used instead of the positive electrode active material of Example 1. A water electrolyte secondary battery) was produced.
Next, the load characteristics of the obtained coin cell (nonaqueous electrolyte secondary battery) of Comparative Example 1 were evaluated in the same manner as in Example 1. The obtained results are shown in Table 1.

[Comparative Example 2]
A positive electrode active material of Comparative Example 2 was produced in the same manner as the positive electrode active material of Example 1 except that 2.5 mol% of titanium dioxide was used instead of 0.5 mol% of titanium monoxide. Next, the coin cell (non-aqueous electrolyte) of Comparative Example 2 was used in the same manner as the coin cell (non-aqueous electrolyte secondary battery) of Example 1 except that the positive electrode active material of Comparative Example 2 was used instead of the positive electrode active material of Example 1. An electrolyte secondary battery) was produced.
Next, the load characteristics of the obtained coin cell (nonaqueous electrolyte secondary battery) of Comparative Example 2 were evaluated in the same manner as in Example 1. The obtained results are shown in Table 1.

As can be seen from Table 1, the non-aqueous electrolyte secondary batteries (Examples 1 to 3) of the present invention have a discharge capacity retention rate of 3C or more, in particular, higher than that of the conventional ones (Comparative Examples 1 and 2).
Moreover, as can be seen from the comparison between Examples 1 to 3 (particularly Example 2) and Comparative Example 2, Li (Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ (positive electrode active material) powder particles The non-aqueous electrolyte secondary battery of the present invention using the positive electrode active material formed by coating titanium monoxide on the surface of the conventional non-aqueous electrolyte using the positive electrode active material formed by coating the same positive electrode active material with titanium dioxide. Compared to the electrolyte secondary battery (Comparative Example 2), the discharge capacity retention rate is particularly large and the load characteristics are good at 3C or more.

  The non-aqueous electrolyte secondary battery of the present invention is particularly excellent in load characteristics, and has various shapes such as coins, buttons, sheets, cylinders, and corners, for example, notebook computers, laptop computers, pocket word processors, cellular phones, cordless. The present invention can be applied to electronic devices such as telephones, portable CDs, and radios, and consumer electronic devices such as automobiles, electric vehicles, and game machines.

Claims (7)

  A non-aqueous material comprising at least a positive electrode including positive electrode active material particles coated with a low-valent oxide of a transition metal element, a negative electrode, and a non-aqueous electrolyte containing a lithium salt Electrolyte secondary battery.   The low-valent oxide of the transition metal element includes at least one element selected from titanium (Ti), tin (Sn), vanadium (V), niobium (Nb), molybdenum (Mo), and tungsten (W). The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is a low valence oxide.   3. The non-aqueous electrolyte 2 according to claim 1, wherein a coating amount of the low-valent oxide of the transition metal element is 0.1 to 10.0% by weight with respect to the positive electrode active material particles. Next battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is a Ni—Co—Mn ternary composite oxide or a lithium-transition metal composite oxide. . The lithium-containing oxide is one of lithium cobaltate (LiCoO ₂ ), spinel-type lithium manganate (LiMn ₂ O ₄ ), and lithium nickelate (LiNiO ₂ ). Non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the low-valent oxide of the transition metal element is titanium monoxide.   By removing the solvent from the slurry obtained by dispersing the low-valent oxide particles of the transition metal element and the positive electrode active material particles in a solvent and drying, the transition metal element is deposited on the surface of the positive electrode active material particles. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising attaching low-valent oxide particles.