JP4770113B2 - Positive electrode active material for secondary battery, positive electrode for secondary battery, and secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material for a secondary battery, a positive electrode for a secondary battery, and a secondary battery.

  Lithium secondary batteries have the feature of being small and have a large capacity, and are widely used as power sources for mobile phones, notebook computers and the like. The lithium secondary battery described here is a battery that operates by moving lithium ions in the electrolyte solution, in which a positive electrode active material capable of occluding and releasing lithium exists in the positive electrode and the negative electrode, respectively. In addition to materials that occlude and release lithium ions, such as carbon materials, the materials include those that use metal materials that form alloys with Li, such as Li and Al.

There are several possible methods for increasing the energy density of a lithium secondary battery. Among them, increasing the operating potential of the battery is an effective means. Conventionally, lithium manganate is used in addition to lithium cobaltate as a positive electrode active material of a lithium secondary battery. In the lithium secondary battery using these compounds as the positive electrode active material, the operating potential is 4 V class (average operating potential = 3.6 to 3.8 V: lithium potential). This is because the expression potential is defined by the redox reaction of Co ions or Mn ions (Co ³⁺ ← → Co ⁴⁺ or Mn ³⁺ ← → Mn ⁴⁺ ).

Among lithium manganates, lithium manganese composite oxides having a spinel structure have been studied for their use because of their high voltage and high energy density. Here, in a battery using a 4V class spinel compound as a positive electrode active material, deterioration occurs with a charge / discharge cycle. As a cause of this deterioration, elution of Mn ³⁺ from the spinel compound into the electrolytic solution can be mentioned. Therefore, a method for suppressing this has been studied.

As a method of suppressing elution of Mn ³⁺ in a secondary battery using a 4V class spinel compound as a positive electrode active material, Patent Document 1 describes a technique of adding a metal oxide. As for positive electrode active materials other than spinel compounds, Patent Document 2 describes a technique of adding LiBiO ₂ (LBO) in a 4V class secondary battery using cobalt oxide. These methods are said to have a certain effect in improving the cycle characteristics of 4V class batteries.

On the other hand, in recent years, a 5V-class positive electrode active material having a higher energy density has also been developed. For example, it is known that an operating potential of 5 V class can be realized by using, as an active material, a spinel compound in which Mn of lithium manganate is substituted with Ni or the like. Specifically, a spinel compound such as LiNi _0.5 Mn _1.5 O ₄ has a potential plateau in a region of 4.5 V or more as a metallic lithium counter electrode potential (Patent Document 3).

In the 5V class spinel, unlike the case of the 4V class described above, Mn exists in a tetravalent state. Then, instead of oxidation reduction of Mn ³⁺ ← → Mn ⁴⁺ , the operating potential is defined by oxidation / reduction of Ni ²⁺ ← → Ni ⁴⁺ , for example. For this reason, in order to make maximum use of the oxidation and reduction of Ni ²⁺ ← → Ni ⁴⁺ , when LiNi _x Mn _2−x O ₄ is used, x = 0.5 is most preferable. If it is the range of 0.4 or more and 0.6 or less, a high energy density will be obtained.

Similarly, Li [CoMn] O ₄ , Li [FeMn] O ₄ , Li [CrMn] O ₄ , Li [Cu _x Mn _2−x ] O _{4, and the} like are 4.5 V or higher with respect to Li metal. It is known to charge and discharge with electric potential. In the case of Co, Fe, and Cr, the operating potential is defined by redox of M ³⁺ ← → M ⁴⁺ (M is Co, Fe or Cr) instead of redox of Mn ³⁺ ← → Mn ^4+. The Rukoto. The charge / discharge potential in the case of Co, Fe, and Cr is about 5V.

In these cases, theoretically, in the composition of LiM ³⁺ Mn ⁴⁺ O ₄ , redox of M ³⁺ ← → M ⁴⁺ (M is Co, Fe or Cr) is used to the maximum extent, High energy density can be obtained. In the case of LiM _x Mn _{2 -x} O ₄ , x = 1.0 is most preferable. Will be obtained. However, although the theoretical capacity is about 150 mAh / g, in practice, since it is difficult to produce spinel, the discharge capacity of 4.5 V or more is only about 100 mAh / g.
Japanese Patent Laid-Open No. 11-16666 JP-A-8-55624 JP-A-9-147867

In these 5V class spinels, since an element such as Ni is added, the amount of Mn ³⁺ generated by oxidation reduction of Mn ³⁺ ← → Mn ⁴⁺ decreases. For this reason, in a so-called 5 V class battery that charges and discharges at a potential of 4.5 V or higher, elution of Mn ^{3+ into} the electrolytic solution is suppressed, and excellent cycle characteristics are expected to be exhibited. However, even in the case of a 5V class battery, the cycle characteristics as expected were not actually obtained. Therefore, as a result of intensive studies on the cause of the 5V class battery, the following knowledge has been found.

First, in 5V spinel, since Ni etc. were added, it was confirmed that Ni elutes in electrolyte. In addition, it was confirmed that elution of Ti occurs in a compound to which Ti is added for the purpose of weight reduction. In addition to Mn ⁴⁺ , it was found that the cycle characteristics deteriorate due to the elution of these elements.

  In this way, in a 5V class battery that charges and discharges at a high potential, unlike in the case of a 4V class battery, element elution of a new mechanism that has not been known conventionally occurs, resulting in a decrease in cycle characteristics. I found something. In order to operate such a 5V class battery satisfactorily and improve the stability, it is necessary to design from a different viewpoint from the conventional 4V class battery.

  This invention is made | formed in view of the said situation, The objective is to provide the technique which improves the cycling characteristics of a 5V class secondary battery. Another object of the present invention is to provide a technique for improving the reliability of a 5V class secondary battery during high temperature operation.

  The present invention has been completed based on the new findings described above, and solves the problems peculiar to 5V class batteries.

According to the present invention comprises an oxide represented by the following general formula (1), and a oxide represented by one or more of the following general formula (2), oxides represented by the general formula (1) There is provided a positive electrode active material for a secondary battery, characterized in that the oxide represented by the general formula (2) is attached to the surface of the particle.
LiM ¹ _a M ² _2-a O ₄ (1)
(However, in the above general formula (1), M ¹ represents one or more transition elements selected from the group consisting of Ni, Cr, Fe, Co, and Cu. M ² is an essential element of Mn. (The above elements are shown. A part of Mn may be substituted by Ti or Si, and 0.4 <a <1.1.)
M ³ _b M ² _c O (2)
(However, in the above general formula (2), M ² represents one or more elements essential to Mn. A part of Mn may be substituted by Ti or Si. Further, M ³ represents Bi, One or two or more elements that require one or more elements selected from the group consisting of La, Nd, Sm, and Ta, provided that M ³ does not contain Li, and b> 0, c ≧ 0.)

The positive electrode active material according to the present invention includes an oxide represented by the general formula (1). For this reason, a high charge / discharge potential is realized. Moreover, since the oxide shown by the said General formula (2) is included, the oxide shown by the said General formula (1) at the time of charging / discharging the secondary battery using the positive electrode active material of this invention is comprised. Dissolution of the element into the electrolyte can be suppressed. For this reason, the fall of the cycling characteristics of a secondary battery can be suppressed, and a high output can be exhibited stably .

  According to this invention, the positive electrode for secondary batteries characterized by including the said positive electrode active material for secondary batteries is provided.

  According to the present invention, there is provided a secondary battery comprising at least a positive electrode and a negative electrode, wherein the positive electrode is the positive electrode for the secondary battery.

  Since the secondary battery using the positive electrode active material for secondary battery according to the present invention suppresses elution of the element constituting the oxide represented by the general formula (1) into the electrolytic solution, it has a high operating potential. Can be stably maintained.

In the positive electrode active material for a secondary battery of the present invention, the oxide represented by the general formula (2) may include at least an oxide represented by the following general formula (3).
M ³ _b O (3)
(However, in the above general formula (3), M ³ is one or two or more elements essentially including one or more elements selected from the group consisting of Bi, La, Nd, Sm and Ta. (However, M ³ does not contain Li, and b> 0.)

  By carrying out like this, melt | dissolution in the electrolyte solution of the element which comprises the oxide shown by the said General formula (1) can be suppressed further reliably.

In the positive electrode active material for a secondary battery of the present invention, the oxide represented by the general formula (2) may include at least a compound represented by the following general formula (4).
M ³ _b Mn _c O (4)
(However, in the above general formula (4), M ³ is one or two or more elements essentially including one or more elements selected from the group consisting of Bi, La, Nd, Sm and Ta. However, M ³ does not contain Li, and b> 0 and c> 0.)

  By carrying out like this, melt | dissolution in the electrolyte solution of the element which comprises the oxide shown by the said General formula (1) can be suppressed much more reliably.

In the positive electrode active material for a secondary battery of the present invention, that have adhered oxide represented on the surface of the oxide particles represented by the general formula (1) by the general formula (2). When the oxide particles represented by the general formula (1) are used, the discharge capacity of the secondary battery is increased, while elution of the constituent elements in the electrolytic solution is likely to occur. In the present invention, since the oxide represented by the general formula (2) is attached to the particle surface, the area in which the oxide represented by the general formula (1) is in direct contact with the electrolytic solution can be reduced. For this reason, dissolution of the element constituting the oxide represented by the general formula (1) into the electrolytic solution can be further reliably suppressed.

In the positive electrode active material for a secondary battery of the present invention, the oxide represented by the general formula (2) may adhere to the surface of the particles by firing. By doing so, the oxide represented by the general formula (2) can be firmly attached to the surface of the oxide particles represented by the general formula (1). For this reason, in the secondary battery using the positive electrode active material for a secondary battery of the present invention, the area where the oxide represented by the general formula (1) is in direct contact with the electrolytic solution can be more reliably reduced.

In the positive electrode active material for a secondary battery of the present invention, fine particles of the oxide represented by the general formula (2) may adhere to the surface of the particles. By doing so, the specific surface area of the oxide represented by the general formula (2) can be increased. Therefore, at least a part of the surface of the oxide particles represented by the general formula (1) can be reliably coated with a small addition amount.

In the positive electrode active material for a secondary battery of the present invention, the oxide layer represented by the general formula (2) may be formed on the surface of the particles. Thus, it is possible to further reliably cover at least a part of the surface of the particles of the oxide represented by the above general formula (1).

In the positive electrode active material for a secondary battery of the present invention, the element M ³ in the oxide represented by the general formula (2) penetrates into the spinel structure composed of the oxide represented by the general formula (1). May be. By carrying out like this, melt | dissolution in the electrolyte solution of the element which comprises the oxide shown by the said General formula (1) can be suppressed further reliably.

In the positive electrode active material for a secondary battery of the present invention, the crystal lattice constant of the oxide particles represented by the general formula (1) constituting the positive electrode active material is an oxide represented by the general formula (1). It may be larger than the intrinsic lattice constant of the crystal. If it carries out like this, the constituent element of the oxide shown by the said General formula (2) can be made into the state which penetrate | invaded into the spinel structure of the particle | grains of the oxide shown by the said General formula (1). For this reason, dissolution of the element constituting the oxide represented by the general formula (1) into the electrolytic solution can be further reliably suppressed.

  In the present invention, the oxide represented by the general formula (1) may contain Ni. By doing so, the battery can be stably operated.

  In the present invention, the oxide represented by the general formula (1) may contain Ti. By doing so, the weight of the battery can be reduced while maintaining the structure of the oxide represented by the general formula (1) stably.

  In this invention, the plateau area | region of the charging / discharging curve of a battery can be 4.5 V or more by a metal lithium counter electrode potential. By doing so, a high battery voltage and energy density can be obtained.

In the positive electrode active material for a secondary battery of the present invention, the M ¹ may be Ni, and the a may satisfy 0.4 <a <0.6. By doing so, the capacity of the secondary battery can be increased by setting M ¹ to Ni.

In the positive electrode active material for a secondary battery of the present invention, the M ² may be Mn and Ti, and the proportion of Ti in the entire M ² may be greater than 0 mol% and not greater than 20 mol%. By doing so, it is possible to reduce the weight of the positive electrode active material while maintaining a high energy density.

In the positive electrode for a lithium secondary battery of the present invention, the proportion of M ³ can be, for example, 0.01 mol% or more and 20 mol% or less with respect to the oxide represented by the general formula (1). By doing so, it is possible to reliably improve the cycle characteristics of the battery while ensuring a high capacity.

  Note that any combination of the above-described constituent elements, and those in which the constituent elements and expressions of the present invention are mutually replaced between methods and apparatuses are also effective as an aspect of the present invention. For example, according to the present invention, an electric device equipped with the secondary battery is provided. Examples of the electric device include a mobile phone, a notebook computer, a PDA (Personal Digital Assistant), various cameras, a navigation system, an automobile, a non-stop power supply, and a portable music device.

  As described above, according to the present invention, one or more elements selected from the group consisting of Bi, La, Nd, Sm and Ta are essential, and oxides of one or more elements excluding Li are added. By using the positive electrode active material that is included, the cycle characteristics of a 5V class secondary battery can be improved. In addition, according to the present invention, the reliability of a 5V class secondary battery during high temperature operation can be improved.

  Hereinafter, embodiments of the secondary battery of the present invention will be described. In the secondary battery of the present invention, the plateau region of the charge / discharge curve exists in the region of 4.5 V or more at the metal lithium counter electrode potential. The secondary battery of the present invention is mainly composed of a positive electrode using a lithium-containing metal composite oxide as a positive electrode active material and a negative electrode having a negative electrode active material capable of occluding and releasing lithium, and an electrical connection is made between the positive electrode and the negative electrode. A separator that does not occur is sandwiched, and the positive electrode and the negative electrode are immersed in a lithium ion conductive electrolyte solution, which is sealed in a battery case. When a voltage is applied to the positive electrode and the negative electrode, lithium ions are released from the positive electrode active material, and the lithium ions are occluded in the negative electrode active material, resulting in a charged state. In addition, by causing electrical contact between the positive electrode and the negative electrode outside the battery, lithium ions are released from the negative electrode active material, and lithium ions are occluded in the positive electrode active material, which is opposite to that during charging.

Here, the positive electrode includes a compound represented by the following general formula (1) as a main component and a compound represented by the following general formula (2) as a subcomponent.
LiM ¹ _a M ² _2-a O ₄ (1)
(However, in the general formula (1), M ¹ is one or more transition metals selected from the group consisting of Ni, Cr, Fe, Co, and Cu. Further, M ² is essential for Mn. Or a part of Mn may be substituted by Ti or Si, and 0.4 <a <1.1.)
M ³ _b M ² _c O (2)
(However, in the above general formula (2), M ² represents one or more elements essential to Mn. A part of Mn may be substituted by Ti or Si. Further, M ³ represents Bi, One or two or more elements that require one or more elements selected from the group consisting of La, Nd, Sm, and Ta, provided that M ³ does not contain Li, and b> 0, c ≧ 0.)

  The lithium-containing composite oxide represented by the general formula (1) is a 5V-class spinel compound having a plateau region at 4.5 V or higher at a metal lithium counter electrode potential. By using such a compound, a high voltage is realized.

In the general formula (1), M ¹ preferably includes Ni at least. By adopting a configuration containing Ni, cycle characteristics can be improved. In addition, when M ¹ is only Ni, the charge / discharge potential range is 4.5 V or more and 4.9 V or less, whereas when Co, Fe, Cr or Cu is included, the charge / discharge potential range is Is not less than 4.8V and not more than 5.2V, so that the decomposition of the electrolytic solution becomes remarkable. Moreover, it is preferable to make the value of b into a range in which the valence of Mn becomes +3.9 or more. For example, b> 0.4, preferably b> 0.45. By doing so, cycle characteristics can be stably improved. Also, b <0.6, preferably b <0.55. By doing so, the reliability of the battery can be improved.

In the compound represented by the general formula (1), M ² is an essential element as M ² . Further, Mn, which is an essential element in M ² , may be substituted with Ti or Si that is lighter than Mn. By doing so, the amount of discharge per weight increases, and the capacity of the battery can be increased.

For example, in the oxide represented by the general formula (1), M ² can have a composition in which Mn and Ti are essential. At this time, the proportion of Ti in the entire M ² may be, for example, greater than 0 mol%, and preferably 5 mol% or more. By doing so, the spinel compound can be reliably reduced in weight. Further, the proportion of Ti in the entire M ² can be set to, for example, 20 mol% or less, preferably 15 mol% or less. By doing so, a high energy density can be maintained.

  In the compound represented by the general formula (1), the oxygen site may be substituted with another anion. Other anions include Cl, F and the like.

  The compound represented by the general formula (2) is a subcomponent in the positive electrode active material. By including at least one oxide represented by the above general formula (2) in the positive electrode active material, elution of Mn and suppression of precipitation of the eluted Mn as an inert material on the negative electrode can be achieved. For this reason, the cycle characteristic of the battery using a spinel type 5V class positive electrode active material can be improved.

Examples of the oxide represented by the general formula (2) include an oxide represented by the following general formula (3). By including at least such a metal oxide, elution of components in the 5V class spinel can be reliably suppressed.
M ³ _b O (3)
(However, in the above general formula (3), M ³ is one or two or more elements essentially including one or more elements selected from the group consisting of Bi, La, Nd, Sm and Ta. (However, M ³ does not contain Li, and b> 0.)

Examples of the compound represented by the general formula (3) include bismuth oxide, lanthanum oxide, neodymium oxide, samarium oxide, and tantalum oxide. Specifically, for _{example, Bi 2 O 3, Nd 2} O 3, SmO, Sm 2 O 3, Ta 2 O 5, La 2 O 3 and the like.

Moreover, as an oxide shown by General formula (2), the compound shown by following General formula (4) is mentioned, for example.
M ³ _b Mn _c O (4)
(However, in the above general formula (4), M ³ is one or two or more elements essentially including one or more elements selected from the group consisting of Bi, La, Nd, Sm and Ta. However, M ³ does not contain Li, and b> 0 and c> 0.)

The compound represented by the general formula (4) is a composite oxide containing M ³ and Mn as essential components. Examples of the compound represented by the general formula (4) include bismuth manganese composite oxide, lanthanum manganese composite oxide, neodymium manganese composite oxide, samarium manganese composite oxide, and tantalum manganese composite oxide. Specifically, for example, a composite oxide of Mn and M ³ such as Bi ₂ Mn ₄ O ₁₀ , NdMnO ₃ , SmMnO ₃ , or LaMnO ₃ can be given.

Further, examples of the compounds represented by the general formula _{(2), BiNiO 3, NdNiO} 3, SmNiO 3, LaNiO 3, La 2 NiO 4, La 3 NiO 4, La 4 Ni 3 O 10 or Nd ₂ NiO _4,, etc. A composite oxide of Ni and an additive element, a composite oxide of Ti such as LaTiO ₃ , and the like may be included. In addition, these compounds are examples and can take various composition ratios.

  Since the positive electrode active material used in this embodiment includes the oxide represented by the general formula (1) as a main component, a high energy density is realized. And since the oxide shown by the said General formula (2) is made into a subcomponent, the elution of Mn in a high voltage area | region can be suppressed stably. Moreover, decomposition of the electrolyte solution in a high voltage region can be suppressed. For this reason, in the secondary battery of this Embodiment, a capacity | capacitance fall is suppressed also when it uses in a high voltage area | region at high temperature. Therefore, a secondary battery excellent in cycle characteristics at a high temperature can be stably obtained.

In this embodiment, the positive electrode active material contains a metal element contained in the oxide represented by the general formula (2) as a subcomponent in the crystal of the 5V class spinel compound represented by the general formula (1). It may further contain dissolved compounds. In the present embodiment, the positive electrode active material has a spinel structure of the compound represented by the general formula (1) as a main skeleton. When M ³ in the oxide represented by the general formula (2) partially penetrates into the spinel structure, the lattice constant of the spinel crystal is inherent to the inherent property of the compound represented by the general formula (1). It increases more than the lattice constant. By doing so, the cycle characteristics of the battery can be improved more reliably.

Moreover, the compound produced | generated by the metal element contained in the oxide shown by the said General formula (2) and the metal element contained in the oxide shown by the said General formula (1) may further be included as a subcomponent. This compound may form a crystal layer. Specifically, as such a compound, for example, a composite oxide of Li and a metal element contained in the oxide represented by the general formula (2), such as LiBiO ₂ , LiNdO ₂ , or LiSmO _2, etc. Can be mentioned.

  If the amount of the subcomponent oxide is small, the effect of improving the characteristics is not sufficient. If the amount is large, the capacity per mass of the positive electrode active material decreases, and the energy density of the battery decreases. For this reason, the amount of the oxide which is a subcomponent with respect to the whole positive electrode active material according to the present invention is preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more, It is 10 mass% or less.

When the amount of the subcomponent with respect to the 5V class spinel compound represented by the general formula (1) is converted into the number of moles, the additive element of the subcomponent with respect to the number of moles of the 5V class spinel compound, that is, the range of the number of moles of M ³ is, for example: It can be 0.01 mol% or more, preferably 0.1 mol% or more, more preferably 1 mol% or more. By doing so, the cycle characteristics of the battery can be reliably improved even when used at high temperatures. The proportion of M ³ with respect to the number of moles of the 5V class spinel compound can be, for example, 20 mol% or less, preferably 10 mol% or less, and more preferably 5 mol% or less. By doing so, the energy density of the battery can be improved. Further, the battery can be reduced in size or weight.

  In the present embodiment, the particle shape of the positive electrode active material is not particularly limited, such as a block shape, a spherical shape, a plate shape, or the like. In addition, the particle size and specific surface area of the positive electrode active material can be appropriately selected in consideration of the positive electrode film thickness, the electrode density of the positive electrode, the type of binder, and the like.

  In the present embodiment, in order to keep the energy density high, the particle shape, particle size distribution, average particle size, and the like so that the positive electrode density of the portion where the metal foil of the current collector is removed is 2.8 g / ml or more, The specific surface area and true density may be selected. In addition, among the positive electrode mixture composed of a positive electrode active material, a binder, a conductivity imparting agent, etc., the particle shape, particle size distribution, average particle diameter, and the like are such that the weight ratio occupied by the positive electrode active material is 85 w / w% or more. Specific surface area and true density are desirable.

  Moreover, it is preferable that the oxide shown by the said General formula (2) has adhered to the surface of the 5V class spinel compound shown by the said General formula (1). By doing so, it is possible to reduce the portion where the 5V class spinel compound and the electrolytic solution are in direct contact. For this reason, the elution to the electrolyte of the constituent element of a 5V class spinel compound can be suppressed reliably. Further, the decomposition of the electrolytic solution can be suppressed. For this reason, the fall of the cycling characteristics of the battery at high temperature can be suppressed, and the reliability of a battery can be improved reliably.

  The oxide represented by the general formula (2) preferably covers the surface of the 5V class spinel compound. By doing so, the reliability of the battery at high temperature can be further improved. Moreover, it is preferable that these subcomponents adhere and coat the surface of the 5V class spinel compound in a layered manner. Further, these subcomponents preferably adhere and coat the surface of the 5V class spinel compound uniformly, and more preferably cover the entire surface.

  Moreover, it is preferable that the oxide shown by the said General formula (2) is joined to the surface of 5V class spinel compound. By doing so, the reliability of the battery at high temperature can be further improved.

  Next, a method for manufacturing a secondary battery according to this embodiment will be described. First, a positive electrode active material and a method for manufacturing a positive electrode using the same will be described. The oxide represented by the general formula (1), which is the main component of the positive electrode active material, can be obtained by mixing and firing the raw materials containing the metal component constituting the compound.

Among the raw materials for producing the oxide represented by the general formula (1), Li ₂ CO ₃ , LiOH, Li ₂ O, Li ₂ SO _{4 and the} like can be used as the Li raw material. Among these, lithium salts such as Li ₂ CO ₃ and LiOH are highly reactive with the transition metal raw material, and the CO ₃ group and OH group are volatilized in the form of CO ₂ and H ₂ O during firing. It is preferably used because it does not adversely affect the active material. When performing F substitution, LiF can be used.

Of the M ¹ materials, NiO, Ni (OH) ₂ , NiSO ₄ , Ni (NO ₃ ) _2, etc. can be used as the Ni material. Further, as the Cr raw material, Cr oxides such as Cr ₂ O _3, Cr carbonates, Cr hydroxide, Cr sulfate, or the like can be used Cr nitrates. Moreover, Co oxides such as Co ₂ O ₃ , Co carbonate, Co hydroxide, Co sulfate, Co nitrate, and the like can be used as the Co raw material. Moreover, Cu oxides, such as CuO, Cu carbonate, Cu hydroxide, Cu sulfate, Cu nitrate etc. can be used as Cu raw material. As the Fe raw material, oxides such as Fe ₂ O ₃ and Fe ₃ O ₄ , Fe (OH) ₂ , FeCO ₃ , FeNO _{3 and the} like can be used.

Among M ² raw materials, various manganese oxides such as electrolytic manganese dioxide (EMD), Mn ₂ O ₃ , Mn ₃ O ₄ , chemical manganese dioxide (CMD), MnCO ₃ , MnSO _4, etc. are used as Mn raw materials. be able to. Further, as the Ti raw material, Ti ₂ O _3, Ti oxides such as TiO _2, Ti carbonates, Ti hydroxides, Ti sulfate, or the like can be used Ti nitrate. Further, SiO, SiO ₂ or the like can be used as the Si raw material.

  Moreover, when each positive electrode active material raw material is fired, element diffusion hardly occurs, and after firing the raw material, an oxide of each element may remain as a different phase. In such a case, it is possible to use, as a raw material, a mixture in which raw materials for each element are dissolved and mixed in an aqueous solution and then precipitated in the form of hydroxide, sulfate, carbonate, nitrate, or the like. It is also possible to use a mixed oxide obtained by firing such a mixture. When such a mixture is used as a raw material, each element can be diffused satisfactorily at the atomic level. For this reason, it is possible to easily produce a crystal with few different phases.

  The above-mentioned raw materials are weighed and mixed so as to have a target metal composition ratio. The mixing is performed by pulverizing and mixing with a ball mill or the like. And the obtained mixed powder is baked in the air or oxygen at the temperature of about 500-1200 degreeC, for example.

  The firing temperature is preferably high in order to diffuse each element. On the other hand, if the firing temperature is too high, oxygen deficiency occurs, which may inhibit the stability of battery characteristics. For these reasons, in the final firing process, the firing temperature is preferably about 500 to 900 ° C.

The lithium metal composite oxide represented by the general formula (1) is obtained by the above procedure. The BET specific surface area of the obtained lithium metal composite oxide represented by the general formula (1) can be, for example, 0.01 m ² / g or more, preferably 0.1 m ² / g or more. This is because if the specific surface area is too small, the ionic conductivity between the electrolytic solution and the positive electrode active material may decrease. The specific surface area of the lithium metal composite oxide represented by the general formula (1) can be, for example, 3 m ² / g or less, preferably 1 m ² / g or less. This is because the larger the specific surface area, the more binder is necessary, which is disadvantageous in terms of the capacity density of the positive electrode.

  Moreover, the average particle diameter of the lithium metal composite oxide represented by the general formula (1) can be, for example, 0.1 μm or more, preferably 1 μm or more. When the average particle size is small, the binding property of the formed positive electrode may be deteriorated. The average particle size can be, for example, 50 μm or less, preferably 20 μm or less. If the average particle size is large, uneven portions such as irregularities may occur in the positive electrode layer during the positive electrode film formation.

  The lithium metal composite oxide represented by the general formula (1) is mixed with a raw material that forms the oxide represented by the general formula (2) shown below to obtain the positive electrode active material of the present embodiment.

Among the raw materials for generating the oxide represented by the general formula (2), as the Bi raw material, specifically, for example, a solid phase such as Bi ₂ O ₃ , Bi (OH) ₃ or Bi (NO ₃ ) ₃ Raw materials can be used. Further, Bi (O-i-C 3 H 7) 3 or the like may be used a liquid-phase raw material is dissolved in an organic solvent.

Further, as the Nd raw material, specifically, for example, a solid phase raw material such as Nd ₂ O ₃ , Nd (NO ₃ ) ₃ , Nd ₂ (CO ₃ ) ₃ or Nd ₂ (SO ₄ ) ₃ can be used. . Alternatively, a liquid phase raw material in which Nd (Oi-C ₃ H ₇ ) ₃ or the like is dissolved in an organic solvent may be used.

As the Sm raw material, specifically, for example, a solid phase raw material such as Sm ₂ O ₃ , Sm (NO ₃ ) ₃ or Sm ₂ (SO ₄ ) ₃ can be used. Alternatively, a liquid phase raw material in which Sm (OiC ₃ H ₇ ) ₃ or the like is dissolved in an organic solvent may be used.

As the La raw material, specifically, a solid phase raw material such as La ₂ O ₃ , La (NO ₃ ) ₃ , La ₂ (CO ₃ ) ₃ or La ₂ (SO ₄ ) ₃ can be used. . Moreover, La (O-i-C 3 H 7) 3 or the like may be used a liquid-phase raw material is dissolved in an organic solvent.

Further, specifically, for example, a solid phase raw material such as Ta ₂ O ₅ can be used as the Ta raw material. In addition, organic metal raw materials such as Ta (OC ₂ H ₅ ) ₅ can also be used.

  When a solid phase raw material is used as a raw material for generating the oxide represented by the general formula (2), the raw material is pulverized so that the average particle size is, for example, 10 nm or more and 1 μm or less, and the general formula (1) It is preferable to mix with the oxide shown by these. When the thickness is smaller than 10 nm, it is difficult to handle the raw material during production, and when the thickness is larger than 1 μm, it is difficult to adhere to the surface of the positive electrode active material. Further, it is more preferable to grind so that the average particle diameter of the raw material is 50 nm or more and 500 μm or less.

Moreover, it is preferable that the oxide represented by the general formula (1) and the raw material for producing the oxide represented by the general formula (2) are mixed and then fired. By firing, the oxide represented by the general formula (2) can be reliably attached to the surface of the oxide particles represented by the general formula (1).

  Moreover, the positive electrode active material which concerns on this Embodiment can be produced as follows. That is, the oxide represented by the following general formula (1), one or more elements selected from the group consisting of Bi, La, Nd, Sm, and Ta and O are essential, and one or two or more excluding Li And a step of mechanically mixing a compound containing the element, and a step of firing the obtained mixture.

By firmly attaching the oxide represented by the above general formula (2) on the surface of the oxide particles represented by the above general formula (1), an oxide represented by the general formula, including Ni (1) In order to reliably suppress the elution of the constituent elements of the above, it is possible to appropriately select the firing conditions such as the temperature rising rate, the temperature falling rate, the holding time at high temperature, the firing temperature, etc. according to the material, not just firing. is important.

The firing method will be described later in Examples. For example, when Li [Ni _0.5 Mn _1.35 Ti _0.15 ] O ₄ and 1% by weight of Bi (OH) ₃ are used, the firing is performed at 600 ° C. for 6 hours to form a layer. This bismuth oxide can be fixed to the surface of the Li [Ni _0.5 Mn _1.35 Ti _0.15 ] O ₄ particle.

  In addition, when the raw material which produces | generates the oxide shown by the said General formula (2) is a liquid phase raw material, the oxide shown by the said General formula (2) and the oxide shown by the said General formula (2) After the raw materials are mixed, the mixture is baked and then further baked at a temperature of about 300 to 800 ° C. as in the case of using the solid phase raw material.

In addition to the oxide represented by the above general formula (2), a part of the elements contained in the oxide represented by the above general formula (2) is converted into an oxide represented by the above general formula (1) by firing. In some cases, a new crystal layer may be formed with the constituent elements. Specific examples of the crystal layer are as described above. In addition, by firing, an element contained in the oxide represented by the general formula (2) may diffuse into the spinel of the oxide represented by the general formula (1). For example, a composite oxide having a spinel structure represented by the following general formula (5) may be generated by diffusion.
Li [M ¹ _a M ² _2-ad M ³ _d ] O ₄ (5)
(However, in the general formula (5), M ¹ is one or more transition metals selected from the group consisting of Ni, Cr, Fe, Co, and Cu. Further, M ² is essential for Mn. One or more elements may be substituted, part of Mn may be substituted by Ti or Si, and 0.4 <a <1.1, and M ³ is Bi, La, Nd, Sm and Ta Or one or more elements selected from the group consisting of d> 0.)

  As described above, the interface between the 5V class spinel compound represented by the general formula (2) and the electrolytic solution is also in direct contact with the new crystal layer generated by firing and the presence of the spinel composite oxide in which the additive element is diffused. The part decreases. For this reason, suppression of decomposition | disassembly of electrolyte solution and suppression of the elution of the structural element of a 5V class spinel compound are achieved.

  Moreover, the complex oxide of the subcomponent adhering to the surface of the 5V class spinel compound may be granular or formed as a layered film on the surface. In the case of a granular form, the average particle size of the adhering subcomponent composite oxide is preferably 1 nm or more and 1 μm or less, and more preferably 10 nm or more and 300 nm or less. When the average particle size is large, a large amount of subcomponents are required to cover the surface of the oxide particles represented by the general formula (1), and the mass of the oxide represented by the general formula (1) in the positive electrode active material. Since the ratio decreases, the capacity per mass decreases. Moreover, when an average particle diameter is small, the effect which improves the reliability of a battery as a coating | cover is small.

  When the subcomponent composite oxide is formed on the surface of the active material in the form of a film, the film thickness is preferably 1 nm or more and 200 nm or less, and more preferably 5 nm or more and 100 nm or less. If the film thickness is thin, the effect of improving the battery characteristics by the film is small, and if the film thickness is thick, the electron conductivity and ion conductivity may be lowered.

  The positive electrode active material obtained by the above procedure is mixed with a conductivity-imparting material, formed on a current collector with a binder, and used as a positive electrode. Examples of the conductivity-imparting material include carbon materials such as acetylene black, carbon black, graphite, or fibrous carbon, metal substances such as Al, and conductive oxide powders. As the binder, polyvinylidene fluoride or the like is used. As the current collector, a metal thin film mainly composed of Al or the like is used.

  The addition amount of the conductivity-imparting material is preferably about 0.5 to 10% by mass with respect to the total amount of the positive electrode active material, the conductivity-imparting material and the binder. The amount of the binder added is preferably about 1 to 10% by mass with respect to the total amount of the positive electrode active material, the conductivity-imparting material, and the binder. When the ratio between the conductivity-imparting material and the binder is small, the electron conductivity may be inferior or electrode peeling may occur. Further, when the ratio between the conductivity-imparting material and the binder is large, the capacity per battery mass is small.

  The proportion of the positive electrode active material is preferably, for example, 70 to 99% by mass with respect to the total amount of the positive electrode active material, the conductivity-imparting material, and the binder. More preferably, it is 88-97 mass% with respect to the total amount of a positive electrode active material, a conductive provision material, and a binder. If the proportion of the positive electrode active material is too small, it is disadvantageous in terms of the energy density of the battery. On the other hand, when the proportion of the positive electrode active material is too large, the proportion per mass of the conductivity-imparting material and the binder becomes low, and the electronic conductivity tends to be inferior or the electrode tends to be peeled off.

  As the electrolytic solution solvent in the present embodiment, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), ethyl methyl carbonate ( EMC), chain carbonates such as diethyl carbonate (DEC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, and γ-lactones such as γ-butyrolactone, Chain ethers such as 1,2-ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, aceto Toamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl A mixture of one or more aprotic organic solvents such as 2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, and fluorinated carboxylic acid ester Can be used. Moreover, you may use what added the polymer etc. and solidified the electrolyte solution solvent in the gel form. Among these, it is suitable to use a mixture of a cyclic carbonate and a chain carbonate from the viewpoint of stability at a high voltage and the viscosity of the solvent. Specifically, for example, EC and DMC can be mixed and used.

Lithium salts are dissolved in these electrolyte solvents as electrolyte solution supporting salts. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO _{2) 2, LiN (C 2} F 5 SO 2) 2, lower aliphatic carboxylic acids, lithium carboxylate, chloroborane lithium, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, and the like. Further, the concentration of the electrolyte is, for example, not less than 0.5 mol / l and not more than 1.5 mol / l. If the concentration is higher than 1.5 mol / l, the density and viscosity increase. If the concentration is too low than 0.5 mol / l, the electrical conductivity may decrease.

  Next, a method for manufacturing a negative electrode according to this embodiment will be described. As the negative electrode active material, a material capable of occluding and releasing lithium is used, and a carbon material such as graphite or amorphous carbon, Li metal, Si, Sn, Al, SiO, SnO, or the like can be used alone or in combination. .

  A negative electrode can be formed on the negative electrode current collector by forming the negative electrode active material on the current collector with a conductivity-imparting material and a binder. As an example of the conductivity-imparting material, in addition to the carbon material, a conductive oxide powder or the like can be used. As the binder, polyvinylidene fluoride or the like can be used. As the current collector, a metal thin film mainly composed of Cu or the like can be used.

  The negative electrode and the positive electrode obtained by the above procedure are laminated via a separator in a dry air or inert gas atmosphere, or after being wound, the laminated one is accommodated in a battery can, or a synthetic resin and a metal foil The secondary battery according to this embodiment can be manufactured by sealing with a flexible film or the like made of the laminated body.

  The secondary battery according to the present embodiment has a structure as shown in FIG. FIG. 1 is a diagram schematically showing the configuration of a coin-type cell. A positive electrode active material layer 1 is formed on the positive electrode current collector 3 to constitute a positive electrode. Further, the negative electrode active material layer 2 is formed on the negative electrode current collector 4 to constitute a negative electrode. These positive electrode and negative electrode are arranged to face each other with a porous separator 5 in a state of being immersed in an electrolytic solution. A positive electrode outer can 6 that accommodates a positive electrode and a negative electrode outer can 7 that accommodates a negative electrode are joined via an insulating packing portion 8.

  Various shapes such as a square shape, a paper shape, a laminated shape, a cylindrical shape, and a coin shape can be adopted as the shape of the battery. The exterior material and other constituent members are not particularly limited, and may be selected according to the battery shape.

  The present invention has been described based on the embodiments. Those skilled in the art will understand that these embodiments are exemplifications, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. By the way.

  For example, the positive electrode of the secondary battery according to the present embodiment may include a positive electrode active material other than the positive electrode active material of the present invention.

  In this example, a coin-type lithium ion secondary battery having the configuration shown in FIG. 1 was fabricated and evaluated. Prior to the production of the battery, Samples 1 to 9 shown below were produced as the positive electrode active material. And the battery which uses these samples as a positive electrode active material was produced, and evaluation was performed.

(Preparation of positive electrode active material)
First, Sample 1 and Sample 2 shown below were produced as oxides represented by the general formula (1).
Li [Ni _0.5 Mn _1.5 ] O ₄ (Sample 1)
Li [Ni _0.5 Mn _1.35 Ti _0.15 ] O ₄ (Sample 2)

Li ₂ CO ₃ , MnO ₂ , NiO, TiO ₂ were used as raw materials. These raw materials were weighed so as to have a target metal composition ratio, and pulverized and mixed. The mixed powder was fired at 850 ° C. for 8 hours. According to the evaluation by X-ray diffraction, the crystal structures of Li [Ni _0.5 Mn _1.5 ] O ₄ (Sample 1) and Li [Ni _0.5 Mn _1.35 Ti _0.15 ] O ₄ (Sample 2) are almost single-phase spinel structures. It was confirmed. The lattice constants of Sample 1 and Sample 2 were 0.8170 nm and 0.8185 nm, respectively. Both the BET specific surface areas of Sample 1 and Sample 2 were about 0.5 m ² / g, and the average particle size was about 12 μm.

Next, the compound represented by the general formula (2), which is a subcomponent, was attached to the particle surface of Sample 1 or Sample 2, which is the main component. Bi (OH) ₃ , Nd ₂ (CO ₃ ) ₃ , Sm ₂ O ₃ , La ₂ O ₃ , and Ta ₂ O ₅ were used as subcomponent materials. At this time, in order to uniformly adhere to the particle surface of Sample 1 or Sample 2, the raw materials of these subcomponents were pulverized by a ball mill so that the average particle diameter was 1 μm or less.

Sample 1 and sample 2 which are the raw materials of the subcomponent and the positive electrode active material were mixed with the following composition to obtain sample 9 from sample 3. The mixed raw materials and their compositions are shown below. In the composition shown below,% represents mass%.
99% -Li [Ni _0.5 Mn _1.35 Ti _0.15 ] O ₄ + 1% -Bi (OH) ₃ (Sample 3)
98% -Li [Ni _0.5 Mn _1.35 Ti _0.15 ] O ₄ + 2% -Bi (OH) ₃ (Sample 4)
99% -Li [Ni _0.5 Mn _1.35 Ti _0.15 ] O ₄ + 1% -Nd ₂ (CO ₃ ) ₃ (Sample 5)
99% -Li [Ni _0.5 Mn _1.35 Ti _0.15 ] O ₄ + 1% -Sm ₂ O ₃ (Sample 6)
99% -Li [Ni _0.5 Mn _1.35 Ti _0.15 ] O ₄ + 1% -Ta ₂ O ₅ (Sample 7)
99% -Li [Ni _0.5 Mn _1.5 ] O ₄ + 1% -La ₂ O ₃ (Sample 8)
99% -Li [Ni _0.5 Mn _1.5 ] O ₄ + 1% -Bi (OH) ₃ (Sample 9)

  The positive electrode active material was obtained by baking the sample 3 to the sample 9 at 600 degreeC for 6 hours. As a result of analyzing the crystal structure of Sample 1 to Sample 9 by X-ray diffraction, the spinel structure phase, the oxide of the subcomponent element, and the crystal phase composed of the subcomponent element and the constituent element of the spinel compound are mixed. A phase was found to exist. Table 1 shows the lattice constants of the mixed raw material, the fired crystal phase confirmed by X-ray diffraction, and the spinel phase as the positive electrode active material. In Table 1, “%” regarding the composition represents “% by mass”.

As shown in Table 1, the positive electrode active materials of Sample 3 to Sample 9 subjected to the treatment of adding the subcomponent are composed of the spinel phase, the subcomponent element oxide, and the subcomponent element and the positive electrode active material. It was confirmed to be composed of complex oxides with elements. The lattice constant of the spinel phase increases in all cases when the cathode active material contains a minor component, compared to the inherent lattice constant of the crystal of the spinel compound of sample 1 or sample 2 when it does not contain it. did. From this result, it is considered that a part of the sub-component elements diffused into the spinel. Although not shown in Table 1, a complex oxide of Li and a constituent element of the oxide represented by the general formula (2) was slightly present. For example, in sample 3, it was confirmed that a small amount of LiBiO ₂ was present.

  Moreover, it was confirmed by scanning electron microscope-X-ray microanalyzer (SEM-EDX) observation that the added subcomponent element was present on the particle surface containing the spinel compound.

Furthermore, the transmission electron microscope (TEM) observation of the cross section of the obtained positive electrode active material was performed. FIG. 2 is a diagram showing a TEM image of the positive electrode active material of Sample 3. As shown in FIG. FIG. 2 shows the surface vicinity of 5V class spinel (LiNi _0.5 Mn _1.35 Ti _0.15 O ₄ : Sample 2) particles observed. A layered portion having a film thickness of about 20 nm was observed at the arrowed portion in the figure on the outermost surface of the particle, and as a result of EDX analysis, it was confirmed to be a phase containing Bi and oxygen.

  FIG. 3 is a diagram showing a TEM image of the positive electrode active material of Sample 5. From FIG. 3, unlike the case of adding Bi raw material, when Nd raw material is added, oxide fine particles are sparsely attached to the surface of 5V class spinel, and the surface of 5V class spinel particle It can be seen that the coverage of is lower than that of Bi. As a result of EDX analysis, it was confirmed that there was a phase containing Nd and oxygen in the arrowed portion on the outermost surface of the particle.

  Note that it was confirmed by TEM observation that the sample 6 to which the Sm raw material was added also adhered the fine particles of the Sm oxide as in the case of adding the Nd raw material. As a result of EDX analysis, it was confirmed that there was a phase containing Sm and oxygen.

(Preparation of positive electrode)
A positive electrode was produced using each of Sample 1 and Sample 9 as a positive electrode active material. A positive electrode active material and carbon as a conductivity-imparting material were mixed. The above mixture was dispersed in a solution in which polyvinylidene fluoride (PVDF) was dissolved in N-methylpyrrolidone (NMP) to form a slurry. The mass ratio of the positive electrode active material, the conductivity-imparting material, and the binder was 94: 3: 3. Carbon black was used as the conductivity imparting material.

The obtained slurry was applied on an Al current collector with a thickness of 25 μm. Then, it was dried in vacuum for 12 hours to obtain an electrode material. The electrode material was cut into a circle with a diameter of 12 mm. Then, it pressure-molded at 3 t / cm < ² >.

(Preparation of negative electrode)
A negative electrode in which a negative electrode current collector and a negative electrode active material layer are integrated by mixing graphite powder: PVdF = 90: 10 (% by weight), dispersing in NMP, coating on a 20 μm thick copper foil. A sheet was produced. The obtained negative electrode sheet was cut out into a circle having a diameter of 13 mm and used as the negative electrode of this example.

(Production of battery)
As the electrolytic solution, a solution obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at 40:60 (vol%) as an electrolytic solution solvent was used. Further, LiPF ₆ was used as the electrolyte supporting salt, and the supporting salt concentration was 1 mol / l.

  The positive electrode and the negative electrode were placed facing each other in a state where there was no electrical contact across the separator, placed in the coin cell, filled with the electrolyte and sealed. A polypropylene film was used as the separator. The secondary battery of this example was obtained by the above procedure. Hereinafter, the batteries obtained using Sample 1 to Sample 9 are referred to as Battery 1 to Battery 9, respectively.

(Evaluation of battery characteristics)
Each battery characteristic was evaluated about the battery 1-the battery 9 produced as mentioned above. The discharge capacity of the battery was about 2 mAh. Charging at the time of evaluation was carried out with a current of 2 mA with an upper limit voltage of 4.75 V, and after reaching 4.75 V, constant voltage charging was performed. The total charging time was 150 minutes. Discharging was performed at a constant current of 2 mA and the lower limit voltage was 2.5V.

  Charging / discharging was performed before storage, and the measured discharge capacity was defined as the discharge capacity before storage. After charging again, it was stored in a high-temperature bath at 60 ° C. for 1 week. Discharge was performed after storage, and the discharge capacity when the battery was charged and discharged again was taken as the recovery capacity. The ratio of the recovery capacity after storage to the discharge capacity before storage was defined as the recovery capacity ratio, and the cycle characteristics were evaluated based on the ratio. The evaluation results of the recovery capacity ratio are shown in Table 2. In Table 2, “%” regarding the composition represents “% by mass”.

  From Table 2, the batteries 3 to 9 including at least one oxide of Bi, La, Nd, Sm, and Ta or a composite oxide of these metals and Mn in the positive electrode do not contain oxide. It was confirmed that the recovery capacity ratio increased with respect to Sample 1 or Sample 2. Further, it is considered that the capacity recovery rate after high-temperature storage can be improved also by diffusing part of the sub-component elements into the spinel.

  Moreover, from Table 2, FIG. 2, and FIG. 3, the capacity | capacitance recovery rate of the battery was able to be improved by adhering the particulate or layered oxide on the surface of the 5V class spinel compound. Further, in the battery 3 and the battery 4 having Bi oxide, a further excellent capacity recovery rate could be obtained. This is thought to be because the surface of the 5V-class spinel compound was coated with oxide in a layered manner, and the particle surface coverage was high.

  Further, for the battery 2 and the battery 4, the elution amount of the spinel compound component was measured. Battery 2 and battery 4 after being stored at 60 ° C. for 1 week were disassembled, and the negative electrode was taken out. Then, composition analysis using ICP emission spectroscopy was performed, and the amounts of Mn, Ni, and Ti deposited on the negative electrode were measured.

  The obtained results are shown in Table 3. Table 3 shows the amount of precipitation of Mn, Ni, and Ti calculated as the amount per negative electrode area. From Table 3, in the battery 4 to which Bi was added, all of the amounts of Mn, Ni, and Ti deposited on the negative electrode decreased compared to the battery 2. Here, it can be considered that the amounts of Mn, Ni, and Ti deposited on the negative electrode are equivalent to the amounts of Mn, Ni, and Ti eluted from the positive electrode. Therefore, it is considered that by providing a Bi oxide layer on the surface of the spinel particles, elution of Mn, Ni, and Ti, which are constituent elements of the spinel compound, was suppressed. Further, in the 5V class battery of this example, since charging / discharging is performed by a change in the valence of Ni, suppression of deterioration of cycle characteristics is achieved by suppressing elution of Ni. Conceivable.

From the above results, at least one oxide of Bi, La, Nd, Sm and Ta on the particle surface of Li [Ni _0.5 Mn _1.35 Ti _0.15 ] O or Li [Ni _0.5 Mn _1.5 ] O ₄ , or By attaching a composite oxide of these metals and Mn, elution of Mn, Ni, and Ti in the lithium manganese composite oxide into the electrolytic solution could be suppressed. For this reason, the positive electrode active material of the present Example was able to suppress the capacity reduction when the battery was used at a high temperature and to improve the cycle characteristics. Thus, by using the positive electrode active material of this example, it is possible to improve the reliability of a 5V class battery. In addition, the oxide of the selected subcomponent element is considered to have an effect of suppressing the decomposition of the electrolytic solution in a 5V class battery.

It is sectional drawing which shows typically the secondary battery which concerns on this Embodiment. It is a figure which shows the TEM image of the positive electrode active material which concerns on an Example. It is a figure which shows the TEM image of the positive electrode active material which concerns on an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Positive electrode collector 4 Negative electrode collector 5 Porous separator 6 Positive electrode outer can 7 Negative electrode outer can 8 Insulation packing part

Claims (13)

An oxide represented by the following general formula (1) and one or more oxides represented by the following general formula (2), the surface of the oxide particles represented by the general formula (1) A positive electrode active material for a secondary battery, wherein an oxide represented by the formula (2) is attached.
LiM ¹ _a M ² _2-a O ₄ (1)
(However, in the above general formula (1), M ¹ represents one or more transition elements selected from the group consisting of Ni, Cr, Fe, Co, and Cu. M ² is an essential element of Mn. (The above elements are shown. A part of Mn may be substituted by Ti or Si, and 0.4 <a <1.1.)
M ³ _b M ² _c O (2)
(However, in the above general formula (2), M ² represents one or more elements essential to Mn. A part of Mn may be substituted by Ti or Si. Further, M ³ represents Bi, One or two or more elements that require one or more elements selected from the group consisting of La, Nd, Sm, and Ta, provided that M ³ does not contain Li, and b> 0, c ≧ 0.) 2. The secondary battery positive electrode active material according to claim 1, wherein the oxide represented by the general formula (2) includes at least an oxide represented by the following general formula (3). Positive electrode active material.
M ³ _b O (3)
(However, in the above general formula (3), M ³ is one or two or more elements essentially including one or more elements selected from the group consisting of Bi, La, Nd, Sm and Ta. (However, M ³ does not contain Li, and b> 0.) 3. The secondary battery positive electrode active material according to claim 1, wherein the oxide represented by the general formula (2) includes at least a compound represented by the following general formula (4). Positive electrode active material for batteries.
M ³ _b Mn _c O (4)
(However, in the above general formula (4), M ³ is one or two or more elements essentially including one or more elements selected from the group consisting of Bi, La, Nd, Sm and Ta. However, M ³ does not contain Li, and b> 0 and c> 0.) In the positive electrode active material for a secondary battery according to claims 1 to 3 any one, oxide represented by the general formula to the surface of the particles (2), characterized in that the attached by firing two Positive electrode active material for secondary battery. In the positive electrode active material for a secondary battery according to any one of claims 1 to 4, wherein the fine particles of the oxide represented by the general formula to the surface of the particles (2) are attached two Positive electrode active material for secondary battery. In the positive electrode active material for a secondary battery according to claims 1 to 4 any one, two, wherein the layer of oxide represented on the surface of the particle by formula (2) is formed next Positive electrode active material for batteries. The positive electrode active material for a secondary battery according to any one of claims 1 to 6, wherein the oxide represented by the general formula (2) is included in a spinel structure composed of the oxide represented by the general formula (1). A positive electrode active material for a secondary battery, wherein the element M ³ therein is invaded . The positive electrode active material for a secondary battery according to claim 7, wherein a lattice constant of a crystal of oxide particles represented by the general formula (1) constituting the positive electrode active material is represented by the general formula (1). A positive electrode active material for a secondary battery, wherein the positive electrode active material is larger than a specific lattice constant of an oxide crystal.   The positive electrode active material for a secondary battery according to claim 7 or 8, wherein the metal element contained in the oxide represented by the general formula (2) is solidified in the spinel compound crystal represented by the general formula (1). A positive electrode active material for a secondary battery, further comprising a dissolved compound. In the positive electrode active material for a secondary battery according to any one of claims 1 to 9, the amount of the oxide represented by the above general formula for the entire positive electrode active material for a secondary battery (2), 0.01 % To 20% by mass or less of a positive electrode active material for a secondary battery. In the positive electrode active material for a secondary battery according to any one of claims 1 to 10, moles of M ³ in the formula (2) to the number of moles of the spinel compound represented by the general formula (1) is, A positive electrode active material for a secondary battery, characterized by being 0.01 mol% or more and 20 mol% or less. A positive electrode for a secondary battery which comprises a positive electrode active material for a secondary battery according to any one of claims 1 to 11.   A secondary battery comprising at least a positive electrode and a negative electrode, wherein the positive electrode is a positive electrode for a secondary battery according to claim 12.

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