JP2010177042A - Positive electrode for nonaqueous electrolyte battery, method of manufacturing the same, and nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode for a nonaqueous electrolyte battery which has small moving resistance of a lithium ion between positive electrode particles and hardly generates cracks during a charge and discharge cycle, and the nonaqueous electrolyte battery which is superior in charge and discharge cycle characteristics. <P>SOLUTION: In the positive electrode for the nonaqueous electrolyte battery wherein a positive electrode active material sintered compact becomes principal, the positive electrode active material sintered compact is a sintered compact of powder of the positive electrode wherein a coated layer is formed on at least a part of the surface of the powder itself in which lithium composite oxide is principal, and the coated layer is made from amorphous lithium transition metal oxide including one or more of elements selected from a group of Mn, Fe, Co, and Ni. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a positive electrode for a nonaqueous electrolyte battery, a method for producing the same, and a nonaqueous electrolyte battery, and more particularly, a positive electrode for a nonaqueous electrolyte mainly comprising a sintered body of positive electrode powder provided with a coating layer made of an amorphous lithium transition metal oxide. The present invention also relates to a non-aqueous electrolyte battery using the non-aqueous electrolyte positive electrode.

  Non-aqueous electrolyte batteries using non-aqueous electrolytes such as non-aqueous electrolytes and solid electrolytes, such as lithium and lithium alloys, are used as negative electrodes. Among them, non-aqueous electrolyte secondary batteries are mobiles such as mobile phones and laptop computers. Widely used as a power source for electronic devices. Recently, application to a large-capacity power source such as an electric vehicle battery is also planned. And since the packing density of an active material can be made high as a positive electrode for nonaqueous electrolyte secondary batteries used for these power supplies, the sintered positive electrode attracts attention. However, conventional non-aqueous electrolyte secondary batteries, particularly non-aqueous electrolyte secondary batteries using a sintered positive electrode, have a characteristic that discharge capacity does not decrease even after repeated charge and discharge, which has become increasingly severe in recent years, so-called It cannot be said that the requirements for the charge / discharge cycle characteristics are sufficiently satisfied.

For this reason, various studies have been made with the aim of further improving the performance of nonaqueous electrolyte batteries. As one of the research results, for example, as a means for improving load characteristics and charge / discharge cycle characteristics of a non-aqueous electrolyte lithium battery, the surface of a positive electrode active material powder (powder body) made of LiCoO ₂ , LiNiO ₂ or the like is formed on LiTiO _2. An invention relating to a positive electrode coated with the above powder is disclosed (Patent Document 1). In the present invention, the surface resistance of the positive electrode active material powder (powder body) is covered with LiTiO ₂ powder, thereby reducing the interfacial resistance between the positive electrode active material powders (powder body), thereby improving the charge / discharge cycle characteristics. It is an improvement.

Japanese Patent No. 3687665

  However, although the invention is effective in the presence of a non-aqueous electrolyte, there is little risk of ignition, liquid leakage, etc., and all the solid electrolytes that are considered to be mainstream as power sources for mobile devices and electric vehicles are used. The solid-type nonaqueous electrolyte battery does not exhibit the effect because there is no nonaqueous electrolyte. Further, it cannot be said that a satisfactory effect is exhibited even in a non-aqueous electrolyte battery using a sintered positive electrode.

  For this reason, development of the technique which improves a charge / discharge cycle characteristic was desired also in the all-solid-state nonaqueous electrolyte battery and the nonaqueous electrolyte battery using a sintered positive electrode.

  As a result of intensive studies aimed at solving the above-mentioned problems, the present inventors have determined that when a positive electrode material powder is sintered to produce a positive electrode, the powder body is an amorphous lithium transition metal containing a predetermined substance. By coating with an oxide, good sintering was achieved, and as a result, it was found that the charge / discharge cycle characteristics of the nonaqueous electrolyte battery were improved, and the present invention was completed. The invention of each claim will be described below.

(A) The positive electrode for a non-aqueous electrolyte battery of the present invention is
A positive electrode for a non-aqueous electrolyte battery mainly comprising a positive electrode active material sintered body,
The positive electrode active material sintered body is a sintered body of positive electrode powder in which a coating layer is formed on at least a part of the surface of a powder body mainly composed of a lithium composite oxide,
The coating layer is an amorphous lithium transition metal oxide containing one or more elements selected from the group consisting of Mn, Fe, Co, and Ni.

  In the present invention, a coating layer made of an amorphous lithium transition metal oxide containing at least one element selected from the group consisting of Mn, Fe, Co and Ni is formed on at least a part of the surface of the powder body. Therefore, a sintered body with a strong bond between the positive electrode powders, a small lithium ion migration resistance between the positive electrode powders, and a sintered non-aqueous electrolyte battery positive electrode that is difficult to crack during charge / discharge cycles. Obtainable. And by using such a positive electrode for nonaqueous electrolyte batteries, since the deterioration of the characteristics of the positive electrode is suppressed even if the charge / discharge cycle is repeated, the charge / discharge cycle characteristics of the nonaqueous electrolyte battery can be greatly improved. .

  That is, in the case of the positive electrode powder in which the coating layer made of the amorphous lithium transition metal oxide is formed, the atoms contained in the coating layer are easily diffused between the positive electrode powders due to thermal motion, and the sintering easily proceeds. The positive electrode powder without a layer is firmly bonded to each other even at a firing temperature at which sintering is difficult to proceed. For this reason, a lithium ion migration resistance between the positive electrode powders is small, and a sintered positive electrode for a non-aqueous electrolyte battery that hardly causes cracks in the charge / discharge cycle is obtained.

  Here, “at least part of the coating layer is formed” means that the powder body is not coated with an amorphous layer at all or only part of the powder body due to the property of forming a coating layer on the powder surface. This means that there may be some that are not coated, and it is preferable that 30% or more of the total surface area of the powder body is coated.

The lithium composite oxide includes a general formula LiMO ₂ or LiM ₂ O ₄ (where M is one or more of Co, Mn, Ni, and Al, and includes Co, Mn, Ni, and Al in M). A lithium composite oxide represented by a ratio of 50 at% or more can be preferably used. As such a lithium composite oxide, for example, LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiMn ₂ O ₄ , LiMn _1.9 Co _0.1 O _{4 and the} like. LiFePO ₄ can also be used.

  Moreover, it is preferable that the powder main body which has lithium complex oxide as a main body, and the coating layer coating layer which consists of an amorphous lithium transition metal oxide are the same compositions from the surface which sinters positive electrode powder more firmly.

In addition, the negative electrode layer can be formed at a temperature at which a lithium composite oxide as an active material, for example, LiCoO ₂ is difficult to be decomposed, and in order to meet the recent demand for small size and light weight for nonaqueous electrolyte batteries, Since it is necessary to form thinly and uniformly, it is preferable to form by a vapor phase method.

(B) The nonaqueous electrolyte battery of the present invention is
The positive electrode for nonaqueous electrolyte batteries described in the invention of (A) is used.

  In the present invention, since the positive electrode for a non-aqueous electrolyte battery described in the invention of (A) is used, a non-aqueous electrolyte battery having excellent charge / discharge cycle characteristics can be provided.

(C) The nonaqueous electrolyte battery of the present invention is
The nonaqueous electrolyte battery described in the invention of (B) is characterized in that a lithium ion conductive solid electrolyte is used.

  In the present invention, the non-aqueous electrolyte battery described in the invention of (B), that is, the positive electrode for a non-aqueous electrolyte battery described in the invention of (A) is used. Can be obtained. Furthermore, since the positive electrode for a non-aqueous electrolyte battery is a positive electrode mainly composed of a lithium composite oxide, and a lithium ion conductive solid electrolyte is used, the all-solid-type battery has less risk of ignition and liquid leakage. It is possible to provide a nonaqueous electrolyte battery having sufficiently satisfactory charge / discharge cycle characteristics while taking advantage of the features of the nonaqueous electrolyte battery.

As the lithium ion conductive solid electrolyte, a sulfide-based solid electrolyte containing Li ₂ S and P ₂ S ₅ having excellent lithium ion conductivity of about 10 ⁻⁴ S / cm, for example, is preferably used.

In order to prevent the positive electrode and the sulfide-based solid electrolyte from reacting with each other, an interface layer (also referred to as a buffer layer) is preferably provided at the interface between the positive electrode and the solid electrolyte. Specifically, Li _X La _{(2-X) / 3} TiO ₃ (X = 0.1 to 0.5), Li ₄ Ti _{5 is} difficult to form a high resistance layer at the interface between the positive electrode and the sulfide solid electrolyte. O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ , Li _1.3 Al _0.3 T _1.7 (PO ₄ ) ₃ , Li _1.8 Cr _0.8 Ti _1.2 (PO It is preferable to form an interface layer composed of at least one of ₄ ) ₃ , Li _1.4 In _0.4 Ti _1.6 (PO ₄ ) ₃ , LiTaO ₃ and LiNbO ₃ .

(D) The method for producing the positive electrode for a non-aqueous electrolyte battery of the present invention comprises:
A method for producing a positive electrode for a non-aqueous electrolyte battery mainly comprising a positive electrode active material sintered body,
A coating comprising an amorphous lithium transition metal oxide containing at least one element selected from the group consisting of Mn, Fe, Co and Ni on at least a part of the surface of the powder body mainly composed of lithium composite oxide A positive electrode powder production process for producing a positive electrode powder having a layer formed thereon;
A positive electrode active material sintered body manufacturing process for sintering the positive electrode powder;
It is characterized by having.

  Each of the above steps can be easily carried out, and the positive electrode for a nonaqueous electrolyte battery described in the invention of (A) can be produced with a small number of steps. That is, in the present invention, a positive electrode for a non-aqueous electrolyte battery with greatly improved charge / discharge cycle characteristics can be easily produced.

  According to the present invention, it is possible to provide a positive electrode for a non-aqueous electrolyte battery that has a low lithium ion transfer resistance between positive electrode powders and is less likely to crack during a charge / discharge cycle. It can be greatly improved.

It is a figure which shows notionally the side surface of the laminated body of the all-solid-state nonaqueous electrolyte secondary battery which concerns on one embodiment of this invention.

  Hereinafter, the present invention will be described based on the best mode. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

(Example)
1. Preparation of positive electrode a. Formation of coating layer on powder body Using a sputtering method, a coating layer made of amorphous LiCoO ₂ with an average thickness of 0.1 μm is formed on the surface of LiCoO ₂ powder (powder body) with an average particle diameter of 1 μm, An active material powder for positive electrode (positive electrode powder) was obtained. Specifically, the powder main body is placed on a sample stage having a vibration mechanism arranged directly under a target made of LiCoO ₂ in a sputtering apparatus, and sputtering is performed while vibrating the powder main body in an atmosphere of Ar and oxygen. It was.

The LiCoO ₂ powder body having an average particle diameter of 1 μm was prepared by firing powder powder of lithium carbonate and cobalt oxide and then pulverizing them. The target used for sputtering was prepared by press-molding lithium carbonate and cobalt oxide powders and firing them.

  Moreover, the electron beam diffraction method was used for crystallinity evaluation. Specifically, the coating layer region of the sample cross section was analyzed by electron beam diffraction, and it was confirmed that the powder body was coated with an amorphous layer.

B. Pressure Molding and Sintering A predetermined amount of this positive electrode powder was put into a mold and pressure molded at 40 MPa to obtain a molded body. Furthermore, this molded body was sintered at 900 ° C. in the atmosphere using a firing furnace, and a positive electrode made of LiCoO _{2 having} a diameter of 20 mm and a thickness of 100 μm was obtained. The reason why the sintering temperature is set to 900 ° C. is to prevent decomposition of LiCoO ₂ as an active material during sintering.

  Since the coating layer made of amorphous lithium transition metal oxide is formed on the positive electrode powder, the positive electrode powder easily diffuses between the positive electrode powders, and the sintering easily proceeds. Even at a relatively low temperature of 900 ° C. A sintered body in which the positive electrode powders are firmly bonded can be obtained.

C. Production of an all-solid-state non-aqueous electrolyte secondary battery On one surface (upper surface) of the positive electrode, an interface layer (also referred to as a buffer layer) having a thickness of 0.02 μm made of LiNbO ₃ is formed by laser deposition, and then by laser deposition. A solid electrolyte layer having a thickness of 5 μm composed of Li ₂ S and P ₂ S ₅ is formed, and finally a negative electrode active material layer having a thickness of 1 μm composed of Li and Si is sequentially formed by a vacuum evaporation method. A water electrolyte secondary battery was produced.

  Specifically, the laminated body in which the positive electrode, the interface layer, the solid electrolyte layer, and the negative electrode active material layer are formed in this order is further subjected to a treatment such as storing in a case, so that the all-solid-type nonaqueous electrolyte secondary The battery is complete.

  The side surface of the laminate is conceptually shown in FIG. In FIG. 1, 10 is a positive electrode, 20 is an interface layer, 30 is a solid electrolyte layer, and 40 is a negative electrode active material layer. Reference numerals 11 and 12 schematically represent the enlarged powder body and coating layer of the positive electrode powder included in the positive electrode 10, respectively.

(Comparative example)
As a comparative example, an all-solid-state nonaqueous electrolyte secondary battery was manufactured in the same manner as in the example except that the coating layer made of amorphous LiCoO ₂ was not formed on the powder body.

(performance test)
The charge-discharge cycle test of the produced solid-state nonaqueous electrolyte secondary batteries of Examples and Comparative Examples was performed at room temperature at a current density of 0.1 mA / cm ² and a voltage range of 4.2 V to 3.0 V. Carried out. Table 1 shows the capacity retention rate after 10 cycles of charge / discharge of each battery (discharge capacity at 10 cycles / maximum discharge capacity during the cycle).

As is apparent from Table 1, the capacity retention rate after 10 cycles of the example is 90%, whereas the comparative example is only 10%. Thus, when a LiCoO ₂ powder (powder body) is sintered to produce a positive electrode, after 10 cycles after forming a coating layer made of amorphous LiCoO ₂ in advance on the powder body prior to sintering. It can be seen that the effect of improving the capacity retention rate is extremely large.

  Next, the batteries of Examples and Comparative Examples in which the capacity retention rate test after 10 cycles of charge / discharge was completed were disassembled, and the state of the positive electrode was observed with a scanning electron microscope. In the observation, many cracks of about 5 μm were observed on the positive electrode of the nonaqueous electrolyte secondary battery of the comparative example, whereas no cracks were observed on the positive electrode of the nonaqueous electrolyte secondary battery of the example.

The reason why no cracks occurred in the positive electrode of the example seems to be that the coating body made of amorphous LiCoO ₂ was formed on the powder body, so that the positive electrode powder was firmly bonded and firmly sintered. For this reason, the movement of lithium ions is also good, and it seems that good results were obtained in the performance test.

That is, the charge / discharge characteristics were greatly improved, and from the viewpoint of preventing damage due to charge / discharge of the positive electrode, the effect of forming a coating layer made of amorphous LiCoO ₂ in advance on the powder body prior to sintering was supported. .

  As described above, the present invention has been described by taking an example of an all-solid-type non-aqueous electrolyte secondary battery that is a secondary battery using a solid electrolyte as an electrolyte. However, the present invention is not limited to an all-solid-type non-aqueous electrolyte battery or a non-aqueous electrolyte battery. The present invention is not limited to a water electrolyte secondary battery, and can be applied to all nonaqueous electrolyte batteries in which a sintered positive electrode is used.

DESCRIPTION OF SYMBOLS 10 Positive electrode 11 Powder main body 12 Coating layer 20 Interface layer 30 Solid electrolyte layer 40 Negative electrode active material layer

Claims (4)

A positive electrode for a non-aqueous electrolyte battery mainly comprising a positive electrode active material sintered body,
The positive electrode active material sintered body is a sintered body of positive electrode powder in which a coating layer is formed on at least a part of the surface of a powder body mainly composed of a lithium composite oxide,
The positive electrode for a nonaqueous electrolyte battery, wherein the coating layer is an amorphous lithium transition metal oxide containing one or more elements selected from the group consisting of Mn, Fe, Co, and Ni.   A nonaqueous electrolyte battery comprising the positive electrode for a nonaqueous electrolyte battery according to claim 1.   The nonaqueous electrolyte battery according to claim 2, wherein a lithium ion conductive solid electrolyte is used. A method for producing a positive electrode for a non-aqueous electrolyte battery mainly comprising a positive electrode active material sintered body,
A coating comprising an amorphous lithium transition metal oxide containing at least one element selected from the group consisting of Mn, Fe, Co and Ni on at least a part of the surface of the powder body mainly composed of lithium composite oxide A positive electrode powder production process for producing a positive electrode powder having a layer formed thereon;
A positive electrode active material sintered body manufacturing process for sintering the positive electrode powder;
The manufacturing method of the positive electrode for nonaqueous electrolyte batteries characterized by having.

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