JP2011028999A - Cathode material for lithium ion battery and lithium ion battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cathode material having stable battery characteristics (especially, high capacity and cycle characteristics) irrespective of a composition method and composition conditions. <P>SOLUTION: The cathode material for a lithium ion battery is expressed in general formula (1) (in the formula, 0<x<1, M<SP>1</SP>is one or more kinds of transition metal wherein an average oxidation state is 4+, and M<SP>2</SP>is one or more kinds of transition metal wherein an average oxidation state is 3+) with a ratio (c/a) of a c-axis length to an a-axis length of the lattice constant in case of defining a crystal structure as a rock salt type hexagonal crystal satisfying 4.983≤c/a≤4.995. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a positive electrode material for a lithium ion battery and a lithium ion battery using the same. More specifically, the present invention relates to an improvement for increasing the battery capacity and improving the cycle durability.

  In recent years, in order to cope with global warming, reduction of the amount of carbon dioxide is eagerly desired. In the automobile industry, there is a great expectation for the reduction of carbon dioxide emissions by the introduction of electric vehicles and hybrid electric vehicles, and motor drive batteries that hold the key to commercialization of these are actively being developed.

  As a battery for driving a motor, a lithium ion battery having a relatively high theoretical energy is attracting attention, and is currently being developed rapidly. In general, a lithium ion battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of the negative electrode current collector using a binder. It is connected via an electrolyte layer and is configured to be stored in a battery case.

  In order for electric vehicles equipped with such a lithium ion battery to be widely spread, it is necessary to make the lithium ion battery high performance and cheaper. Particularly for electric vehicles, the travel distance per charge needs to be close to the travel distance per refueling of a gasoline engine vehicle, and a battery with higher energy density is desired. In order to make the battery have a high energy density, it is necessary to increase the electric capacity per unit mass of the positive electrode and the negative electrode.

A lithium manganese composite oxide having a layered structure has been proposed as a positive electrode material that can meet this demand. Among them, the solid solution of the electrochemically inactive layered Li ₂ MnO ₃ and the electrochemically active layered LiMO ₂ (where M is a transition metal such as Co or Ni) exceeds 200 mAh / g. It is expected as a candidate for a high-capacity positive electrode material that can exhibit a large electric capacity (for example, see Patent Document 1).

Special table 2004-528691 gazette

  However, such solid solution positive electrode materials have battery characteristics that vary greatly depending on the synthesis method and the synthesis conditions such as the amount of charged lithium, and it has been difficult to obtain a positive electrode material having stable battery characteristics.

  Then, an object of this invention is to provide the positive electrode material which has the stable battery characteristic (especially cycling characteristics) irrespective of a synthesis method and synthesis conditions.

  The present inventors have intensively studied to solve the above problems. As a result, in the positive electrode solid solution material, it has been found that the above problem can be solved by controlling the composition of the positive electrode solid solution material and the ratio (c / a) between the c-axis length and the a-axis length of the lattice constant. Completed the invention.

  That is, the positive electrode material for a lithium ion battery of the present invention has the general formula (1):

(Where 0 <x <1, M ¹ is one or more transition metals having an average oxidation state of 4+, and M ² is one or more transition metals having an average oxidation state of 3+. is there.)
It is represented by The ratio (c / a) between the c-axis length and the a-axis length of the lattice constant when the crystal structure is defined as a rock salt type hexagonal crystal satisfies 4.983 ≦ c / a ≦ 4.995.

  The charge / discharge cycle characteristics of the positive electrode material for lithium ion batteries of the present invention are greatly improved regardless of the synthesis method and synthesis conditions.

1 is a schematic diagram showing a basic configuration of a flat (stacked) non-bipolar lithium ion secondary battery, which is a representative embodiment of the present invention. xLi is a schematic diagram showing a ^{_{[Li 1/3 M 1 2/3 O 2}} ] · (1-x) LiM 2 O 2 crystal structure of the rock salt type hexagonal. FIG. 3A is a drawing showing electron diffraction simulation results, and FIG. 3A is a drawing showing electron diffraction simulation results of a model structure of a Li ₂ M ¹ O ₃ —LiM ² O ₂ solid solution, and FIG. 3B is a model of LiM ² O ₂ . It is drawing which shows the electron diffraction simulation result of a structure. Li is a _{[Li 1/3 Mn 2/3 O 2]} -LiNi 1/2 Mn 1/2 O 2 -LiNi 1/3 Mn 1/3 Co 1/3 basic composition diagram of _{O 2} system. 1 is a perspective view schematically showing the appearance of a stacked battery which is an embodiment of the present invention. FIG. 6A is an external view of an assembled battery according to an embodiment of the present invention, FIG. 6A is a plan view of the assembled battery, FIG. 6B is a front view of the assembled battery, and FIG. 6C is a side view of the assembled battery. It is a conceptual diagram of the vehicle carrying the assembled battery which concerns on one Embodiment of this invention. 4 is an electron beam diffraction pattern of a sample obtained in Example 2. FIG. It is a graph which shows the relationship between the lattice constant ratio (c / a) of the crystal structure of the sample obtained by the Example and the comparative example, and discharge capacity.

  One exemplary embodiment of the present invention is represented by the general formula (1):

(Where 0 <x <1, M ¹ is one or more transition metals having an average oxidation state of 4+, and M ² is one or more transition metals having an average oxidation state of 3+. is there.)
It is the positive electrode material for lithium ion batteries represented by these. The ratio (c / a) between the c-axis length and the a-axis length of the lattice constant when the crystal structure is defined as a rock salt type hexagonal crystal satisfies 4.983 ≦ c / a ≦ 4.995.

A so-called solid solution positive electrode material represented by the general formula: xLi [Li _1/3 M ¹ _2/3 O ₂ ]. (1-x) LiM ² O ₂ is expected as a high-capacity material. . However, such solid solution positive electrode materials have greatly different battery characteristics depending on the synthesis method and the synthesis conditions such as the amount of charged lithium, and the relationship between the battery characteristics and the crystal structure has been unclear. In addition, although this solid solution positive electrode has a large discharge capacity, there is a problem that if the charge / discharge potential is increased, the cycle characteristics are poor and the battery is easily deteriorated by repeated charge / discharge. As described above, it is difficult to obtain a positive electrode material having stable battery characteristics with a solid solution positive electrode.

  On the other hand, in the present invention, when the ratio (c / a) between the c-axis length and the a-axis length of the lattice constant of the crystal structure is within a predetermined range, the above problem is improved, and the synthesis method In addition, a high-capacity positive electrode material having excellent cycle durability can be provided regardless of the synthesis conditions. Furthermore, in the lithium ion battery of the present invention, a battery having high energy density and good cycle durability can be obtained by using the positive electrode material for lithium ion batteries of the present invention as the main active material of the positive electrode.

The details of the mechanism for increasing the capacity and improving the cycle durability by controlling the ratio (c / a) of the c-axis length to the a-axis length of the lattice constant of the crystal structure are unknown. It is estimated that it is caused by such changes. Assuming that the crystal structure of xLi [Li _1/3 M ¹ _2/3 O ₂ ]. (1-x) LiM ² O ₂ is a cubic NaCl structure that shares the apex of the hexagonal rock salt crystal structure, The lattice constant ratio of the crystal structure is calculated to be about 4.9. However, a repulsive force acts between oxygen and oxygen in the hexagonal rock salt type crystal structure, so that a strain that extends in the c-axis direction is generated, and the ratio between the c-axis length and the a-axis length of the actual crystal structure ( c / a) is greater than 4.9. This change in c-axis length affects the diffusion distance of Li and the stability of the crystal structure, and as a result, a high-capacity positive electrode material having excellent cycle durability is considered to be obtained. However, these are merely mechanism estimations, and the scope of the present invention is not limited to the form in which the capacity characteristics and cycle durability are improved by such mechanisms.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited only to the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. The dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from actual ratios.

  First, a basic configuration of a lithium battery to which the positive electrode material of the present embodiment can be applied will be described with reference to the drawings.

[Battery overall structure]
In this invention, a lithium ion battery should just be formed using the positive electrode material for lithium ion batteries of this embodiment, and it does not restrict | limit in particular regarding other structural requirements.

  For example, when the lithium ion battery is distinguished by its form / structure, it can be applied to any conventionally known form / structure, such as a stacked (flat) battery or a wound (cylindrical) battery. is there. By adopting a stacked (flat) battery structure, long-term reliability can be secured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

  Moreover, when viewed in terms of electrical connection form (electrode structure) in a lithium ion battery, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. is there.

  In the following description, as a representative embodiment, a case of a non-bipolar (internal parallel connection type) lithium ion secondary battery using a positive electrode material for a lithium ion battery will be described as an example. However, the technical scope of the present invention is not limited to the following forms.

  FIG. 1 is a schematic diagram showing a basic configuration of a flat (stacked) non-bipolar lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) according to an embodiment of the present invention. As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior body. . Here, in the power generation element 21, the negative electrode in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11, the electrolyte layer 17, and the positive electrode active material layer 15 are disposed on both surfaces of the positive electrode current collector 12. It has a configuration in which a positive electrode is laminated. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are stacked in this order so that one negative electrode active material layer 13 and the positive electrode active material layer 15 adjacent thereto face each other with the electrolyte layer 17 therebetween. .

  Thereby, the adjacent negative electrode, electrolyte layer, and positive electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 of the present embodiment has a configuration in which a plurality of the single battery layers 19 are stacked and electrically connected in parallel. In addition, although the negative electrode active material layer 13 is arrange | positioned only in the single side | surface at all the outermost layer negative electrode collectors located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost positive electrode current collector is positioned in both outermost layers of the power generation element 21, and the outermost positive electrode current collector is arranged on one or both surfaces A positive electrode active material layer may be disposed.

  The negative electrode current collector 11 and the positive electrode current collector 12 are attached to a negative electrode current collector plate 25 and a positive electrode current collector plate 27 that are electrically connected to the respective electrodes (negative electrode and positive electrode), and are sandwiched between end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The negative electrode current collector plate 25 and the positive electrode current collector plate 27 are ultrasonically welded to the negative electrode current collector 11 and the positive electrode current collector 12 of each electrode via a negative electrode lead and a positive electrode lead (not shown), respectively, as necessary. Or resistance welding or the like.

  Hereinafter, members constituting the battery of this embodiment will be described in detail.

(Positive electrode material for lithium ion battery)
In the present invention, the main active material of the positive electrode (positive electrode active material layer) is represented by the general formula: xLi [Li _1/3 M ¹ _2/3 O ₂ ] · (1-x) LiM ² O _2. It is a so-called solid solution positive electrode material. Since Li [Li _1/3 M ¹ _2/3 O ₂ ] can also be expressed as Li ₂ M ¹ O ₃ , in this specification, the general formula: xLi [Li _1/3 M ¹ _2/3 O ₂ ] · a solid solution represented by _{^{(1-x) LiM 2 O}} 2, also referred to as ^{_{Li 2 M 1 O 3 -LiM 2}} O 2 based solid solution.

FIG. 2 is a schematic diagram showing the crystal structure of xLi [Li _1/3 M ¹ _2/3 O ₂ ]. (1-x) LiM ² O ₂ rock salt type hexagonal crystal. As shown in FIG. 2, the solid solution includes a metal layer composed of transition metals (M ¹ , M ² ) and lithium (Li), an oxygen layer 1 composed of oxygen (O), a lithium layer 1 composed of lithium (Li), oxygen An oxygen layer 2 made of (O) and a lithium layer 2 made of lithium (Li). Here, in the Li ₂ M ¹ O ₃ —LiM ² O ₂ solid solution having a rock salt type hexagonal crystal structure, lithium is regularly arranged in every three in the a-axis direction and the b-axis direction in the two-dimensional plane in the metal layer. Is forming.

The lithium (Li) regularly arranged in the metal layer is caused by Li _1/3 of [Li _1/3 M ¹ _2/3 O ₂ ]. Such a periodic arrangement structure of lithium can be confirmed from electron beam diffraction data. FIG. 3A shows an electron diffraction simulation result of a model structure of a Li ₂ M ¹ O ₃ —LiM ² O ₂ solid solution. As shown in FIG. _3A, in the solid solution of Li ² M 1 _{O 3} and ^LiM 2 _{O 2,} diffraction spots appear due to 3-fold cycle of the lithium in the metal layer to the electron-ray diffraction data.

On the other hand, in the case of a normal LiM ² O ₂ solid solution, lithium is irregularly arranged in the metal layer. FIG. 3B shows an electron diffraction simulation result of the model structure of LiM ² O ₂ . As shown in FIG. 3B, diffraction spots associated with the triple period of lithium in the metal layer do not appear in the electron diffraction data.

  X in the general formula (1) may be any number that satisfies 0 <x <1. From the viewpoint of further improving battery characteristics (cycle characteristics, high capacity), preferably 0.4 ≦ x <1, more preferably 0.5 ≦ x ≦ 0.8, and still more preferably 0.6. ≦ x ≦ 0.75.

Electrochemically inactive Li [Li _{1 in the} solid solution represented by the above general formula (1): xLi [Li _1/3 M ¹ _2/3 O ₂ ]. (1-x) LiM ² O ₂ the ^{M 1} of ^{_{/ 3 M 1 2/3 O 2]}} , may be a one or more transition metals average oxidation state is 4+, not particularly limited. M ¹ in the above formula may be at least one transition metal element selected from the group consisting of Mn, Zr, and Ti, and is preferably Mn. By using these transition metals, an electrochemically inactive layered Li ₂ M ¹ O ₃ crystal structure of the solid solution positive electrode material represented by the general formula (1) can be taken. In particular, when M ¹ is Mn, it has a large capacity at a potential (3 to 5 V) convenient for the positive electrode material, which is advantageous in increasing the discharge capacity. In addition, in the form in which Ti and Zr are added in appropriate amounts to Mn, Ti and Zr are inferior in capacity characteristics compared to Mn, but contribute to the stabilization of the crystal structure, so a part of the high capacity of Mn (in the present invention) It can be effectively used in applications where stabilization is required even at the expense of the range that does not impair the effect of increasing the discharge capacity.

Electrochemically active LiM ² O ₂ in the solid solution represented by the general formula (1): xLi [Li _1/3 M ¹ _2/3 O ₂ ] · (1-x) LiM ² O ₂ As M ² , there is no particular limitation as long as it is one or more transition metals having an average oxidation state of 3+. M ² in the above formula may be at least one transition metal element selected from the group consisting of Ni, Co, Cr, Al, Mn, Zr, Ti, Fe, Mg, and Zn, preferably Is preferably one or more elements selected from Mn, Ni, and Co. When these transition metals are used, a positive electrode material having a high capacity and good cycle durability can be produced.

The “average oxidation state” indicates the average oxidation state of the metal constituting M ¹ or M ² and is calculated from the molar amount and valence of the constituent metal. For example, when M ² is composed of 50% Ni ²⁺ and 50% Mn ^{4+ on} a molar basis, the average oxidation state of M ² is (0.5) · (+2) + (0.5 ) · (+4) = + 3 However, the average oxidation state of M ¹ or M ² may deviate slightly from 4+ or 3+ due to crystal defects or the like, respectively, but such a solid solution of the positive electrode material is also included in the scope of the present invention.

  In a preferred embodiment, the positive electrode material for a lithium ion battery has the general formula (2):

It is represented by That is, in the general formula (1): xLi [Li _1/3 M ¹ _2/3 O ₂ ] · (1-x) LiM ² O ₂ , M ¹ is Mn, and LiM ² O ₂ is LiNi _{1. / 2} Mn _1/2 O ₂ and LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . In such a positive electrode material, cycle characteristics and capacity characteristics are further improved. FIG. 4 shows a basic composition diagram of the Li [Li _1/3 Mn _2/3 O ₂ ] —LiNi _1/2 Mn _1/2 O ₂ —LiNi _1/3 Mn _1/3 Co _1/3 O ₂ system. The positive electrode material of the present embodiment preferably has a composition belonging to the shaded portion in FIG.

  That is, it is preferable that x in the general formula (2) is a number satisfying 0.4 ≦ x <1. However, from the viewpoint of further improving battery characteristics (cycle characteristics, high capacity) and reducing the content of expensive transition metals such as Ni and Co, preferably 0.5 ≦ x ≦ 0.8, More preferably, 0.6 ≦ x ≦ 0.75.

  Y in the general formula (2) may be any number satisfying 0 ≦ y ≦ 1. However, from the viewpoint of further improving the battery characteristics (cycle characteristics, high capacity) and reducing the content of expensive cobalt, preferably 0.25 ≦ y ≦ 1.0, more preferably 0.8. 5 ≦ y <1.0.

  In the positive electrode material of the present invention, the ratio (c / a) between the c-axis length and the a-axis length of the lattice constant when the crystal structure is defined as a rock salt type hexagonal crystal is 4.983 ≦ c / a ≦ 4.995. Meet. In such a case, a positive electrode material with improved cycle characteristics and capacity characteristics can be obtained. In order to further improve the cycle characteristics, 4.983 ≦ c / a ≦ 4.987 is preferable, and 4.984 ≦ c / a ≦ 4.986 is more preferable.

Next, as a method for producing the solid solution (positive electrode material) represented by the general formula (1): xLi [Li _1/3 M ¹ _2/3 O ₂ ] · (1-x) LiM ² O ₂ , The method is not limited, and a conventionally known production method can be used as appropriate. For example, as shown in the Example mentioned later, it can carry out as follows using a composite carbonate method.

First, as starting materials, metal sulfates and nitrates of transition metal elements corresponding to M ¹ and M ² in the above general formula (1) (for example, nickel sulfate, cobalt sulfate, manganese sulfate, etc.) Quantitatively weigh and prepare these mixed solutions. Aqueous ammonia was added dropwise until pH 7 was reached, and a Na ₂ CO ₃ solution was further added dropwise to form a complex carbonate of M ¹ -M ² (however, the M ¹ and M ^{2 in} the above formulas were used to determine the M -N metal complex carbonates are different types). Then, after suction filtration, it is washed with water and dried at a predetermined temperature for a predetermined time (for example, 120 ° C. for 5 hours). The obtained dried product is calcined at a predetermined temperature for a predetermined time (for example, at 500 ° C. for 5 hours). A small excess of LiOH.H ₂ O is added thereto and mixed in an automatic mortar for a predetermined time (for example, 30 minutes). Here, the ratio (c / a) between the c-axis length and the a-axis length of the lattice constant of the crystal structure can be controlled to a desired value by adjusting the addition amount of LiOH.H ₂ O. Then, by carrying out main firing at a predetermined temperature for a predetermined time (for example, at 900 ° C. for 12 hours), the above general formula (1): xLi [Li _1/3 M ¹ _2/3 O ₂ ] · ( 1-x) A solid solution represented by LiM ² O ₂ can be produced. After the main calcination, quenching with liquid nitrogen or the like is preferable because the reactivity and cycle stability are improved and a very beautiful solid solution state can be obtained.

In addition, the identification of the solid solution represented by the general formula (1): xLi [Li _1/3 M ¹ _2/3 O ₂ ]. (1-x) LiM ² O ₂ is performed by electron diffraction, X-ray diffraction ( XRD), inductively coupled plasma (ICP) elemental analysis can be used.

The positive electrode material for a lithium ion battery is preferably subjected to an oxidation treatment. The method for the oxidation treatment is not particularly limited. For example,
(1) Charging or charging / discharging in a predetermined potential range, specifically charging or charging / discharging in a low potential region that does not cause a significant change in the solid solution positive electrode crystal structure from the beginning;
(2) Oxidation with an oxidizing agent (for example, halogen such as bromine or chlorine) corresponding to charging;
(3) Oxidation treatment using a redox mediator;

  Here, the oxidation treatment method (1) is not particularly limited, but in a state where the battery is configured, or in an electrode or an electrode-corresponding configuration so as not to exceed a predetermined maximum potential, Charging or charging / discharging (= charging / discharging pretreatment with regulated potential) is effective. This is because a positive electrode material for a lithium ion battery having high capacity and good cycle durability, and thus a high energy density battery using the positive electrode material can be manufactured.

  As the charge / discharge pretreatment method with regulated potential, the highest potential in the predetermined potential range with respect to the lithium metal counter electrode (the upper limit potential of charge / discharge converted to lithium metal or lithium metal) is preferably 3.9 V or more and less than 4.6 V, More preferably, it is desirable to perform charging and discharging for 1 to 30 cycles under the condition of 4.4V or more and less than 4.6V. By performing oxidation treatment by charging / discharging within the above range, a positive electrode for a lithium ion battery having high capacity and good cycle durability, and thus a battery having a high energy density can be produced. In particular, when charging or charging / discharging at a maximum potential of about 4.8 V in order to obtain a high capacity after the oxidation treatment (pre-charge / discharge pretreatment with regulated potential), particularly remarkable effects such as cycle durability can be obtained. It can be expressed effectively. Further, in this case, it is preferable from the viewpoint of improving durability that the upper limit potential is gradually increased (stepwise) after the initial charge / discharge at the predetermined upper limit potential. Note that the potential converted to lithium metal or lithium metal corresponds to a potential based on the potential exhibited by the lithium metal in the electrolytic solution in which 1 mol of lithium ion is dissolved.

  In addition, it is desirable to further increase the maximum potential in the predetermined potential range for charging and discharging stepwise after 1 to 30 cycles of charging and discharging in the predetermined potential range with respect to the lithium metal counter electrode. In particular, 4.7V, 4.8Vvs. When using up to the high potential capacity of Li (use of high capacity), the maximum potential of the charge / discharge potential in the oxidation process is increased step by step for a short period of oxidation treatment (pre-charge / discharge pretreatment) However, the durability of the electrode can be improved.

  The number of cycles required for charging and discharging at each stage when raising the maximum potential (upper limit potential) in a predetermined potential range of charging and discharging is not particularly limited, but a range of 1 to 10 is effective. . In addition, the total number of charge / discharge cycles in the oxidation process when increasing the maximum potential (upper limit potential) in the predetermined potential range of charge / discharge (the total number of cycles required for charge / discharge in each stage) ) Is not particularly limited, but a range of 4 to 20 times is effective.

  There is no particular limitation on the range of increase (increase) in potential when increasing the maximum potential (upper limit potential) in a predetermined potential range of charge and discharge in stages, but 0.05V to 0.1V is effective. is there.

  It is effective that the final maximum potential (end maximum potential) when increasing the maximum potential (upper limit potential) in a predetermined potential range of charge / discharge stepwise is 4.6V to 4.9V. . However, the present invention is not limited to the above range, and oxidation treatment (charge / discharge pretreatment with regulated potential) may be performed up to a higher termination maximum potential as long as the above effects can be achieved.

  However, it is only necessary to perform charging in the predetermined potential range described above. The maximum potential in the predetermined potential range at this time is also charged under the condition of 3.9 V or more and less than 4.6 V, more preferably 4.4 V or more and less than 4.6 V with respect to the lithium metal counter electrode as described above. It is desirable to do.

  The minimum potential in the predetermined potential range is not particularly limited, and is 2 V or more and less than 3.5 V, more preferably 2 V or more and less than 3 V with respect to the lithium metal counter electrode. By performing oxidation treatment (charging / discharging pretreatment with regulated potential) by charging or charging / discharging within the above range, a positive electrode for a lithium ion battery having a high capacity and good cycle durability and a battery having a high energy density can be produced. The charge / discharge potential (V) refers to a potential per unit cell (unit cell).

  The temperature of the electrode (material) to be charged / discharged as the oxidation treatment (pre-charge / discharge pretreatment with regulated potential) can be arbitrarily set as long as it does not impair the effects of the present invention. From the economical point of view, it is desirable to carry out at room temperature that does not require special heating and cooling. On the other hand, it is desirable to carry out at a temperature higher than room temperature from the viewpoint that a larger capacity can be expressed and the cycle durability can be improved by a short charge / discharge treatment.

  The step (time) for applying the oxidation treatment (pre-charge / discharge pretreatment with regulated potential) method is not particularly limited. For example, as described above, the oxidation treatment can be performed in a state where a battery is configured, or in a configuration corresponding to an electrode or an electrode. That is, any of application in the state of positive electrode active material powder, application by constituting an electrode, and application after assembling a battery together with the negative electrode may be used. Application to a battery can be carried out by applying an oxidation treatment condition (condition for pre-charge / discharge with regulated potential) in consideration of the potential profile of the capacitance of the negative electrode to be combined. Here, in the case where the battery is configured, it is superior in that the oxidation treatment of a large number of electrodes can be performed at a time, rather than the individual electrodes or the respective configurations corresponding to the electrodes. On the other hand, when it is performed for each individual electrode or each electrode-corresponding configuration, it is easier to control conditions such as the oxidation potential than the state in which the battery is configured, and variations in the degree of oxidation to individual electrodes occur. It is excellent in a difficult point.

  The oxidizing agent used in the oxidation method (2) is not particularly limited, and for example, halogen such as bromine and chlorine can be used. These oxidizing agents may be used alone or in combination. Oxidation with an oxidizing agent can be gradually oxidized by, for example, dispersing solid solution fine particles in a solvent in which the solid solution positive electrode material does not dissolve, and blowing and dissolving the oxidizing agent into the dispersion solution.

  As the redox mediator (electron transfer agent) used in the oxidation treatment method of (3) above, a compound that has an appropriate redox potential and electron mobility, forms a radical, or accepts or donates an electron. Any active compound can be used. As the redox mediator, for example, a series of derivatives in which the para-position of triphenylamine is blocked and stabilized can be used. Among them, those in which hydrogen at the para-position and / or meta-position is substituted with a halogen such as bromine can be preferably used. These can be preferably used because the oxidation-reduction potential can be finely controlled by the position, type and number of substituents. In addition, various transition metal complexes that are stable with an appropriate redox potential can also be preferably used. An example of this is a complex of 2,2'-bipyridine and its derivatives such as ruthenium and osmium. In addition, what can be used as a redox shuttle for preventing overcharge of a so-called lithium ion battery, and those having an appropriate oxidation-reduction potential can be suitably used. These redox mediators may be used alone or in combination. It may be used step by step from a low oxidation-reduction potential to a high stepwise one. Furthermore, it is also effective to oxidize stepwise while using a high oxidation-reduction potential and controlling the reaction amount with certainty. It is also preferable to carry out reduction by using this in reverse to incorporate a process corresponding to the discharge of the battery electrode, or to repeat the process corresponding to charge (oxidation) and discharge (reduction). Oxidation using a redox mediator can be performed, for example, using a platinum net as a working electrode, a counter electrode separated by an ion conductive diaphragm, and a reference electrode as necessary, as follows. That is, the solid solution is dispersed in the electrolyte solution in which the redox mediator is dissolved, and the redox mediator is oxidized while controlling the potential of the working electrode with respect to the reference electrode, and the solid solution positive electrode material is oxidized using the redox mediator. Can be made.

  The above is the description regarding the characteristic configuration requirements of the lithium ion battery of the present embodiment, and the other configuration requirements are not particularly limited. Therefore, in the following, other structural requirements other than the characteristic structural requirements of the lithium ion battery of the present invention will be described below with a focus on the respective structural requirements of the stacked battery 10 described above. However, it goes without saying that the constituent elements of batteries other than the stacked battery, for example, bipolar batteries, can be configured by appropriately using the same constituent elements.

[Current collector]
As the current collector (the negative electrode current collector 11, the positive electrode current collector 12; the current collector 14), any member conventionally used as a current collector material for a battery can be appropriately employed. As an example, examples of the positive electrode current collector and the negative electrode current collector include aluminum, nickel, iron, stainless steel (SUS), titanium, and copper. Among these, from the viewpoints of electron conductivity and battery operating potential, aluminum is preferable as the positive electrode current collector, and copper is preferable as the negative electrode current collector. A typical thickness of the current collector is 10 to 20 μm. However, a current collector having a thickness outside this range may be used. The current collector plate can also be formed of the same material as the current collector.

[Active material layer]
The active material layers (the negative electrode active material layer 13 and the positive electrode active material layer 15) are configured to include an active material (negative electrode active material, positive electrode active material, reference electrode active material). In addition, these active material layers include a binder, a conductive agent for increasing electric conductivity, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and an electrolyte supporting salt for increasing ionic conductivity as necessary. (Lithium salt) and the like.

(A) Active material The material (material) of the positive electrode active material and the negative electrode active material is not particularly limited as long as it has the characteristic constituent features of the lithium ion battery of the present invention. What is necessary is just to select suitably according to the kind of.

Specifically, as the positive electrode active material, the positive electrode material for a lithium ion battery of the present invention represented by the general formula (1): xLi ₂ M ¹ O _3. (1-x) LiM ² O ₂ is used as the positive electrode. Used as the main active material. As the positive electrode active material, a positive electrode material represented by the above general formula (1): xLi ₂ M ¹ O _3. (1-x) LiM ² O ₂ may be used alone, and further as necessary. Other conventionally known positive electrode active materials may be used in combination. In order to exert the effect of the present invention remarkably, the positive electrode material represented by the general formula (1): xLi ₂ M ¹ O _3. (1-x) LiM ² O ₂ is preferably contained in the active material. It is contained by mass% or more, more preferably 80 mass% or more, still more preferably 90 mass% or more.

The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium, and any conventionally known negative electrode active material can be used. For example, high crystalline carbon graphite (natural graphite, artificial graphite, etc.), low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen black, acetylene black, channel black, lamp black, oil furnace black, Carbon materials such as thermal black), fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon fibril; Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, and the like, and simple elements of these elements alloyed with lithium oxide containing (silicon monoxide (SiO), SiO _x 0 <x <2), tin _{(SnO 2} dioxide), SnO x (0 <x <2), etc. SnSiO ₃₎ and carbides (such as silicon carbide (SiC)) or the like; a metal material of a lithium metal or the like; lithium - titanium Lithium-transition metal composite oxides such as composite oxides (lithium titanate: Li ₄ Ti ₅ O ₁₂ ); and other conventionally known negative electrode active materials can be used. The negative electrode active material may be used alone or in the form of a mixture of two or more.

  The average particle diameter of each active material contained in each active material layer (13, 15) is not particularly limited, but is usually about 0.1 to 100 μm from the viewpoint of high capacity, reactivity, and cycle durability. The thickness is preferably 1 to 20 μm.

The compounding ratio of the components contained in each active material layer (13, 15) is not particularly limited, and can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries or lithium ion batteries. Moreover, there is no restriction | limiting in particular also about the thickness of an active material layer, The conventionally well-known knowledge about a lithium ion secondary battery or a lithium ion battery can be referred suitably. For example, the thickness of the active material layer is about 2 to 100 μm. (B) Binder A binder is added to maintain the electrode structure by binding the active materials or the active material and the current collector. Is done.

  As such a binder, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polymethyl acrylate (PMA), Thermosetting resins such as polymethyl methacrylate (PMMA), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP) and polyacrylonitrile (PAN), epoxy resins, polyurethane resins, and urea resins And rubber-based materials such as styrene butadiene rubber (SBR).

(C) Conductive agent A conductive agent means the conductive additive mix | blended in order to improve electroconductivity. The conductive agent that can be used in the present embodiment is not particularly limited, and a conventionally known one can be used. Examples thereof include carbon materials such as carbon black such as acetylene black, graphite, and carbon fiber. When the conductive agent is included, an electronic network inside the active material layer is effectively formed, which can contribute to improvement in reliability by improving output characteristics of the battery and improving liquid retention of the electrolyte.

(D) Electrolyte As the electrolyte, a liquid electrolyte, a gel polymer electrolyte, and an intrinsic polymer electrolyte described in the section of [Electrolyte layer] described later can be used without particular limitation. Specific forms of the liquid electrolyte, the gel polymer electrolyte, and the intrinsic polymer electrolyte will be described later in the section of (electrolyte layer), and the details are omitted here. These electrolytes may be used alone or in combination of two or more. Moreover, an electrolyte different from the electrolyte used for the electrolyte layer described later may be used, or the same electrolyte may be used.

[Electrolyte layer]
The electrolyte layer is a layer containing a non-aqueous electrolyte. A nonaqueous electrolyte (specifically, a lithium salt) contained in the electrolyte layer has a function as a carrier of lithium ions that moves between the positive and negative electrodes during charge and discharge. The nonaqueous electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a polymer electrolyte may be used.

The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent that can be used as the plasticizer include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). As the supporting salt (lithium _{salt), Li (CF 3 SO 2} ) 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 Compounds that can be added to the electrode mixture layer, such as SO _3, can be employed as well.

  On the other hand, the polymer electrolyte is classified into a gel polymer electrolyte containing an electrolytic solution (gel electrolyte) and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel polymer electrolyte has a configuration in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. Using a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block the ion conductivity between the layers. The ion conductive polymer used as the matrix polymer (host polymer) is not particularly limited. For example, polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVDF-HFP), polyethylene glycol (PEG), polyacrylonitrile (PAN), Examples thereof include polymethyl methacrylate (PMMA) and copolymers thereof. Here, the ion conductive polymer may be the same as or different from the ion conductive polymer used as the electrolyte in the active material layer, but is preferably the same. The type of the electrolytic solution (electrolyte salt and plasticizer) is not particularly limited, and an electrolyte salt such as the lithium salt exemplified above and a plasticizer such as carbonates may be used.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, by using an intrinsic polymer electrolyte as the electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

  The matrix polymer of gel polymer electrolyte or intrinsic polymer electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

  The non-aqueous electrolyte contained in these electrolyte layers may be one kind alone, or two or more kinds.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel polymer electrolyte, a separator is used for the electrolyte layer. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene.

  It can be said that the thinner the electrolyte layer, the better to reduce the internal resistance. The thickness of the electrolyte layer is usually 1 to 100 μm, preferably 5 to 50 μm.

[Exterior body]
In a lithium ion secondary battery, it is desirable to accommodate the entire power generating element in an exterior body in order to prevent external impact and environmental degradation during use. As the exterior body, a conventionally known metal can case can be used, and a bag-like case that can cover a power generation element using a laminate film containing aluminum can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto.

[Battery appearance]
FIG. 5 is a perspective view schematically showing the appearance of a stacked battery according to an embodiment of the present invention. As shown in FIG. 5, the stacked battery 10 has a rectangular flat shape, and a negative electrode current collector plate 25 and a positive electrode current collector plate 27 for taking out electric power are drawn out from both sides thereof. Yes. The power generation element 21 is encased in an outer package 29 of the battery 10 and the periphery thereof is heat-sealed. The power generation element 21 is sealed with the negative electrode current collector plate 25 and the positive electrode current collector plate 27 drawn out. Here, the power generation element 21 corresponds to the power generation element 21 of the stacked battery 10 shown in FIG. 1, and is composed of a negative electrode (negative electrode active material layer) 13, an electrolyte layer 17, and a positive electrode (positive electrode active material layer) 15. A plurality of battery layers (single cells) 19 are stacked.

  The lithium ion battery of the present invention is not limited to a flat shape (stacked type) as shown in FIG. For example, the wound type lithium ion battery may have a cylindrical shape, or may have a shape that is a flattened rectangular shape by deforming such a cylindrical shape. . In the cylindrical shape, a laminate sheet or a conventional cylindrical can (metal can) may be used as the exterior material, and there is no particular limitation.

  Further, the removal of the current collector plates 25 and 27 shown in FIG. 5 is not particularly limited, and the negative electrode current collector plate 25 and the positive electrode current collector plate 27 may be pulled out from the same side or the negative electrode current collector plate 25. The positive electrode current collector plate 27 may be divided into a plurality of pieces and taken out from each side. Further, in a wound bipolar secondary battery, a terminal may be formed using, for example, a cylindrical can (metal can) instead of the current collector plate.

  According to this embodiment, a lithium ion battery having a high capacity and excellent charge / discharge cycle can be provided. The lithium ion battery of this embodiment is a power source for driving a vehicle or an auxiliary power source that requires high volume energy density and high volume output density as a large capacity power source for an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, a hybrid fuel cell vehicle, etc. Can be suitably used.

[Battery]
A plurality of the batteries of this embodiment may be connected in parallel and / or in series to form an assembled battery. FIG. 6 is an external view of an assembled battery according to an embodiment of the present invention. 6A is a plan view of the assembled battery, FIG. 6B is a front view of the assembled battery, and FIG. 6C is a side view of the assembled battery.

  In the form shown in FIG. 6, a small assembled battery 35 that can be attached and detached by connecting a plurality of the stacked batteries 10 of the above embodiment in series and / or in parallel is formed. A plurality of small assembled batteries 35 that can be attached and detached are connected in series and / or in parallel to form an assembled battery 37. As a result, the assembled battery 37 is an assembled battery 37 having a large capacity and a large output suitable for a vehicle driving power source and an auxiliary power source that require high volume energy density and high volume output density. The small assembled batteries 35 that can be attached and detached are connected to each other using an electrical connection means such as a bus bar, and the assembled batteries 35 are stacked in a plurality of stages using a connection jig 39. How many non-bipolar lithium ion secondary batteries are connected to produce the assembled battery 35, and how many assembled batteries 35 are laminated to produce the assembled battery 37 are determined by the vehicle mounted ( It may be determined according to the battery capacity and output of the electric vehicle. According to this embodiment, an assembled battery having a high capacity and excellent charge / discharge cycle can be provided.

[vehicle]
The stacked battery 10 or the assembled battery 37 can be used as a power source for driving the vehicle. The stacked battery 10 or the assembled battery 37 may be, for example, a hybrid vehicle, a fuel cell vehicle, an electric vehicle (all are automobiles (commercial vehicles such as passenger cars, trucks, buses, etc.), motorcycles, etc.) Motorcycles) and tricycles). Thereby, the motor vehicle excellent in the charge / discharge cycle can be provided. However, the application is not limited to automobiles. For example, if it is another vehicle, it can be applied to various power sources for moving bodies such as trains, and it can be used for mounting uninterruptible power supplies and the like. It can also be used as a power source.

  FIG. 7 is a conceptual diagram of a vehicle equipped with the assembled battery 37 of the present invention. As shown in FIG. 7, in order to mount the assembled battery 37 in a vehicle such as the automobile 40, the assembled battery 37 is mounted under the seat in the center of the vehicle body of the automobile 40. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 37 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or may be mounted in an engine room in front of the vehicle. The automobile 40 using the assembled battery 37 as described above has excellent durability and can provide a sufficient output even when used for a long period of time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and driving performance.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

1. Synthesis of Solid Solution Cathode Material A sample was synthesized as follows using a composite carbonate method. Nickel sulfate, cobalt sulfate, and manganese sulfate are weighed in predetermined amounts to prepare a mixed solution thereof. Ammonia water is added dropwise until pH 7 is reached, and a Na ₂ CO ₃ solution is further added dropwise to add Ni—Co—. A complex carbonate of Mn was precipitated. While the Na ₂ CO ₃ solution was dropped, pH 7 was maintained with aqueous ammonia. Then, it filtered by suction, washed with water, and dried at 120 degreeC for 5 hours. This was calcined at 500 ° C. for 5 hours. A small excess of LiOH.H ₂ O was added thereto and mixed for 30 minutes in an automatic mortar. The addition amount of LiOH.H ₂ O was 1.2 to 1.4 when the transition metal amount (total molar amount of Ni, Co, and Mn) was 0.8.

Then, after baking at 900 degreeC for 12 hours, it cooled rapidly using liquid nitrogen. Thus, solid solution positive electrode materials of Examples 1 to 13 and Comparative Examples 1 to 4 shown in Table 1 below were synthesized. In addition, the values of x and y in Table 1 are represented by the general formula (2): xLi [Li _1/3 Mn _2/3 O ₂ ]. (1-x) [yLiNi _1/2 Mn _1/2 O _2. (1-y) corresponds to x and y in LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ].

2. Analysis of synthetic sample (1) X-ray diffraction (XRD): X-ray diffraction measurement was performed on the obtained sample. All the synthesized samples could be assigned to the following space groups, and diffraction lines showing a superlattice structure appeared at 20 to 23 °.

  (2) Electron diffraction: Electron diffraction measurement was performed on the obtained sample. In the electron beam diffraction patterns of all the samples of the examples, diffraction spots derived from the periodic arrangement structure of lithium in the metal layer appeared. FIG. 8 shows an electron diffraction pattern of the sample obtained in Example 2. From FIG. 8, diffraction spots (arrows in FIG. 8) derived from the periodic arrangement structure of lithium in the metal layer can be confirmed.

  (3) Elemental analysis: The obtained sample was subjected to inductively coupled plasma (ICP) elemental analysis to confirm that the obtained sample had the composition shown in Table 1.

3. Evaluation of Positive Electrode Material (1) Preparation of Electrode and Evaluation Cell An evaluation cell was prepared by the following procedure using the positive electrode active material shown in Table 1 above. First, a positive electrode active material: conductive binder (TAB-2) = 66: 34 (mass ratio) was formed into a pellet having a diameter of 16 mm by using a kneading method, and 2 pieces were formed on a stainless mesh (current collector) having the same diameter. The sample was positively bonded at a pressure of tons and dried by heating at 120 ° C. for 4 hours under vacuum to obtain a sample positive electrode. The amount of active material per unit area was set to 10 mg.

Metallic lithium was used as the negative electrode. The sample positive electrode and negative electrode obtained above were opposed to each other through two 25 μm-thick polypropylene porous membranes as separators and placed on the bottom of the coin cell. Subsequently, after mounting a gasket for maintaining insulation between the positive electrode and the negative electrode, an electrolyte was injected using a syringe, and a spring and a spacer were laminated. Then, the upper part of the coin cell was overlapped and caulked to obtain an evaluation cell. In addition, as electrolyte solution, electrolyte solution of ethylene carbonate (EC): diethyl carbonate (DMC) = 1: 2 (volume ratio) of 1M LiPF ₆ was used.

(2) Charge / discharge test (pre-charge / discharge treatment)
Each evaluation cell produced by the above method was charged at a constant current of 0.4 mA until the potential difference reached 4.5V, and then discharged until the potential difference reached 2.0V. This operation was repeated twice. Further, in the same manner, charging / discharging in the range of 4.6V to 2.0V, charging / discharging in the range of 4.7V to 2.0V, and charging / discharging in the range of 4.8V to 2.0V were performed twice. It was.

(Evaluation)
The evaluation cell after the above charge / discharge pretreatment was charged at a constant current of 0.4 mA until 4.8 V (= maximum potential), and then discharged until 2.0 V (= minimum potential). . This charge / discharge process was defined as one cycle, a charge / discharge cycle test of 30 cycles was performed, and the discharge capacity at the 30th cycle was measured. The results are shown in FIG. FIG. 9 is a graph showing the relationship between the lattice constant ratio (c / a) of the crystal structures of the samples obtained in Examples and Comparative Examples and the discharge capacity.

  From Table 1 and FIG. 9, the ratio (c / a) between the c-axis length and the a-axis length of the lattice constant when the crystal structure is defined as a rock salt type hexagonal crystal is in the range of 4.984 to 4.995. It was found that the cells using the positive electrode active material of Examples 1 to 10 maintained a high discharge capacity even after 30 cycles of charge and discharge. In particular, the cells of Examples 1 to 10 using the positive electrode active material having a ratio (c / a) of the c-axis length to the a-axis length of the lattice constant in the range of 4.983 to 4.987 are 30 cycles. The later discharge capacity was large. On the other hand, the cell of the comparative example in which the ratio (c / a) between the c-axis length and the a-axis length of the lattice constant is not in the desired range is the 30th cycle discharge compared to the cells of Examples 1-10. It was confirmed that the capacity was small.

  From the above, when the positive electrode active material of the present invention in which the ratio of c-axis length to a-axis length (c / a) is in a desired range, a battery with improved cycle characteristics and capacity characteristics is obtained. It was confirmed.

10 stacked battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer (negative electrode),
15 positive electrode active material layer (positive electrode),
17 electrolyte layer,
19 Single battery layer (single cell),
21 power generation elements,
25 negative current collector,
27 positive current collector,
29 exterior body (laminate sheet),
35 A small assembled battery that can be attached and detached,
37 battery pack,
39 Connecting jig,
40 cars.

Claims (8)

General formula (1):
(Where 0 <x <1, M ¹ is one or more transition metals having an average oxidation state of 4+, and M ² is one or more transition metals having an average oxidation state of 3+. is there.)
Represented by
When the crystal structure is defined as a rock salt type hexagonal crystal, the ratio (c / a) between the c-axis length and the a-axis length of the lattice constant satisfies 4.983 ≦ c / a ≦ 4.995. Positive electrode material. 2. The positive electrode material for a lithium ion battery according to claim 1, wherein M ¹ is at least one transition metal element selected from the group consisting of Mn, Zr, and Ti. ^3. The lithium according to claim 1, wherein M ² is at least one transition metal element selected from the group consisting of Ni, Co, Cr, Al, Mn, Zr, Ti, Fe, Mg, and Zn. Positive electrode material for ion batteries. General formula (2):
(In the formula, 0.4 ≦ x <1.0 and 0 ≦ y ≦ 1.)
The positive electrode material for a lithium ion battery according to any one of claims 1 to 3, represented by:   5. The lithium ion according to claim 1, wherein a ratio (c / a) between the c-axis length and the a-axis length of the lattice constant satisfies 4.983 ≦ c / a ≦ 4.987. Positive electrode material for batteries.   The lithium ion battery which uses the positive electrode material for lithium ion batteries of any one of Claims 1-5 as a positive electrode active material.   An assembled battery using the lithium ion battery according to claim 6.   A vehicle equipped with the lithium ion battery according to claim 6 or the assembled battery according to claim 7 as a driving power source.