JP2013051086A - Electrode material for secondary battery, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode material for a secondary battery arranged so that no irreversible capacity is produced.SOLUTION: The electrode material for a secondary battery comprises at least a layered lithium manganese-based complex oxide, a conductive material, and a binder. The complex oxide is characterized in (1) it is expressed by the general formula: xLi[LiMn]O(1-x)LiMeO, where Me represents one or more kinds of transition metals, x meets 0<x<1; (2) assuming that the material belongs to a space group R(-3)m, the lattice constant thereof falls in a range defined by 2.864 Å≤a≤2.878 Å and 14.27 Å≤c≤14.39 Å; and (3)the X-ray diffraction intensity ratio of (003)plane to (104)plane meets the condition I(003)/I(104)>1.

Description

  The present invention relates to an electrode material for a secondary battery and a method for producing the same.

In recent years, lithium secondary batteries (typically lithium ion batteries) have become increasingly important as vehicle-mounted power supplies or personal computers and portable terminals. In particular, a lithium ion secondary battery that is lightweight and has a high energy density is preferably used as a high-output power source for mounting on a vehicle.
In one typical configuration of this type of secondary battery, an electrode material (active material layer) containing an electrode active material capable of reversibly occluding and releasing lithium ions serving as charge carriers is formed by a conductive member (electrode current collector). The electrode material including the electrode active material has been studied since the electrode has a structure held in the body and can achieve higher energy density and higher output.

Examples of materials that have been widely used as positive electrode active materials include layered lithium nickel composite oxides and layered lithium cobalt composite oxides. Since these layered complex oxides have problems in terms of stability and cost, attention has recently been paid to the use of layered lithium manganese based complex oxides containing manganese. As this layered lithium manganese composite oxide, there is LiMn ₂ O ₄ having a spinel structure, but it does not have performance comparable to lithium nickel composite oxide or lithium cobalt composite oxide as a positive electrode active material. . Therefore, LiMnO ₂ has attracted attention as the most excellent material as a lithium manganese-based positive electrode active material.

On the other hand, the layered lithium manganese composite oxide includes monoclinic Li ₂ MnO ₃ having a high lithium content. A general layered rock salt type oxide has a structure in which a lithium layer, a transition metal layer, and an oxygen layer are laminated in a crystal structure, and lithium as a charge carrier exists mainly only in the lithium layer. However, in this Li ₂ MnO ₃ , in addition to the lithium layer, 1/3 of Mn of the transition metal layer is substituted with lithium, and thus lithium as a charge carrier can be contained excessively. However, since Li ₂ MnO ₃ is chemically stable and reaction-inactive, and has low charge / discharge characteristics, it has not received much attention as a positive electrode active material compared to other lithium manganese composite oxides. And when using as a positive electrode active material, it is common to use it by making it dissolve with other layered rock salt type oxides.

With regard to these layered lithium manganese composite oxides, for example, by limiting the ratio of atoms such as lithium, nickel, manganese, cobalt to a specific range, cost reduction, high voltage resistance and high safety, Cathode active material materials that are compatible with improved battery performance such as rate and output characteristics have been proposed (see, for example, Patent Documents 1 and 2).
In addition, in a lithium-manganese composite oxide having a layered structure, by limiting the valence of the metal element, the positive electrode active material is excellent in reversibility of charge / discharge, durability against charge / discharge cycles, and high energy density per volume Has been proposed (see, for example, Patent Document 3).

JP 2006-253119 A JP 2003-203633 A JP 2008-120679 A

Li ₂ MnO ₃ and the above-mentioned layered lithium manganese composite oxide, which is a solid solution thereof, have a lower capacity than conventional layered rock salt type oxides when used at less than 4.45 V with respect to the lithium electrode. There was a problem. Therefore, it is used as a high-capacity positive electrode active material by charging at 4.45 V or higher.
However, when used at 4.45 V or higher, the crystal structure is changed by doping with lithium ions to generate irreversible capacity. As a result, there is a problem that the cycle life due to repeated charge and discharge is short.

  The present invention was created to solve such conventional problems, and an object of the present invention is to provide an electrode material for a secondary battery that does not generate irreversible capacity resulting from a change in crystal structure. . Another object of the present invention is to provide a lithium secondary battery, a vehicle and other products provided with the electrode material for a secondary battery.

According to the present invention, an electrode material for a secondary battery having the following modes is provided.
Such an electrode material for a secondary battery includes a layered lithium manganese composite oxide (hereinafter sometimes simply referred to as a composite oxide) characterized by the following requirements (1) to (3), a conductive material, Includes binders.
(1) General formula:
xLi [Li _1/3 Mn _2/3 ] O _2. (1-x) LiMeO ₂
It is represented by Here, Me in the formula is one or more transition metals, and x satisfies 0 <x <1.
(2) The lattice constants when assigned to the space group R (−3) m are in the ranges of 2.864Å ≦ a ≦ 2.878Å and 14.27Å ≦ c ≦ 14.39Å.
(3) The X-ray diffraction intensity ratio between the (003) plane and the (104) plane is I (003) / I (104)> 1.

The composite oxide disclosed here is mainly composed of a lithium manganese based composite oxide in which LiMeO ₂ is dissolved in Li ₂ MnO ₃ . The electrode material has a manganese-based composite oxide having the above (1) to (3). For this reason, it has a crystal structure in which a lithium layer, a transition metal layer, and an oxygen layer are stacked in a uniaxial direction. As is clear from the above (1), lithium can be present in the transition metal layer (strictly speaking, a layer mainly composed of the transition metal). The transition metal layer is mainly composed of manganese (Mn), and up to 1/3 of the transition metal sites of the transition metal layer can be replaced with lithium (Li). As understood from these, the electrode material for a secondary battery disclosed here can be used as a high-capacity positive electrode active material.

  Such a composite oxide essentially has a strict crystal structure (in the case of the invention disclosed herein, a crystal), which is known in the art and is prepared by a conventional method consisting only of mixing and firing of raw materials. The grid dimensions are different. For example, as shown in the above (2) and (3), such a complex oxide has lattice constants a, c and (003) planes and (104) planes as compared with complex oxides prepared by a conventional method. Both X-ray diffraction intensity ratios are changed. Specifically, the lattice constant when such a complex oxide is assigned to the space group R (-3) m is larger than that of a complex oxide prepared by a conventional method, and (003) plane and The (104) plane X-ray diffraction intensity ratio is reduced. This change is due to the fact that slight changes in the crystal structure due to lithium desorption observed in complex oxides prepared by conventional methods accumulate due to repeated lithium insertion and desorption, and finally the change. Can be regarded as being equivalent to (or capable of absorbing) the state that has been completed (a state that does not change any more). That is, the composite oxide disclosed here has a stable structure in which the structural change accompanying the desorption of lithium ions from the transition metal layer has already been completed, and the lithium ions are desorbed from the transition metal layer by further charging. Even in this case, no further change in crystal structure is observed. That is, when this functions as a positive electrode active material, the problem of generation of irreversible capacity due to a change in crystal structure upon desorption of lithium ions is solved.

In addition, since such a complex oxide has an enlarged crystal lattice, movement of lithium ions having a large ionic radius becomes more free and a high reaction rate can be expected.
As for the space group notation R (−3) m by the Hermann-Morgan symbol above, “(−3)” should be represented by an overline in “3”, but in this specification, For simplicity, it is described as (-3).

In a preferred aspect of the secondary battery electrode material disclosed herein, the composite oxide includes at least Ni and Co as Me together with Mn,
Mn> Ni + Co
And the content molar ratio of Li, Mn, and said Me is the following formula:
1 <Li / (Mn + Me) ≦ 1.5
Meet. When such a composite oxide has such a composition, the electrode material for a secondary battery disclosed here can be used as a higher-capacity positive electrode active material.

In a preferred aspect of the secondary battery electrode material disclosed herein, the composite oxide is further characterized by the following requirements.
(4) The surface includes a cubic layer lacking lithium.
This can be said to be a characteristic configuration that accompanies the composite oxide as a result of the change in the crystal structure described above by the manufacturing method of the present invention described below.

  The present invention also provides a lithium secondary battery including a positive electrode in which a positive electrode active material layer is held on a positive electrode current collector, a negative electrode, and a non-aqueous electrolyte. In such a lithium secondary battery, the positive electrode active material layer includes at least one of the electrode materials for a secondary battery. Therefore, even when lithium ions are desorbed from the transition metal layer by charging, the above-mentioned composite oxide (that is, the positive electrode active material) does not change further in crystal structure, and the problem of reversible capacity is solved. A lithium secondary battery is realized. Therefore, it is considered that this lithium secondary battery has improved charge / discharge cycle characteristics.

Furthermore, the present invention provides a method for producing an electrode material for a secondary battery according to the following embodiment. That is, such a production method is a mixture of a layered lithium manganese composite oxide prepared by a conventional method (hereinafter sometimes simply referred to as a composite oxide prepared by a conventional method), a conductive material, and a binder. And subjecting the mixture to an electrochemical treatment comprising oxidation to an upper limit voltage of 4.5V to 5V and reduction to a lower limit voltage of 2.0V to 3V.
The composite oxide prepared by a conventional method has the general formula:
xLi [Li _1/3 Mn _2/3 ] O _2. (1-x) LiMeO ₂
It is represented by. Here, Me in the formula is one or more transition metals, and x satisfies 0 <x <1. Therefore, as described above, the composite oxide prepared by this conventional method can be a high-capacity positive electrode active material.
Further, by subjecting the mixture to electrochemical treatment by such a method, the crystal structure of the composite oxide prepared by a conventional method is changed. That is, the crystal structure of the composite oxide is changed to a state where the structural change accompanying the desorption of lithium ions from the transition metal layer is completely completed or to a stable structure capable of absorbing the state. Therefore, even when lithium ions are desorbed from the transition metal layer by charging, no further structural change occurs. Accordingly, a secondary battery material that is useful as a positive electrode active material and in which the problem of generation of irreversible capacity due to a change in crystal structure upon desorption of lithium ions is eliminated is provided.

In one preferable aspect of the production method disclosed herein, the composite oxide includes at least Ni and Co as Me together with Mn.
Mn> Ni + Co
And the content molar ratio of Li, Mn, and said Me is the following formula:
1 <Li / (Mn + Me) ≦ 1.5
It is characterized by satisfying. By using the composite oxide having such a composition, a higher-capacity electrode material for a secondary battery can be produced.

Moreover, the lithium secondary battery disclosed here does not have an irreversible capacity derived from the desorption of lithium ions as described above. Therefore, charge / discharge cycle characteristics are particularly required, and the battery has suitable performance as a battery used as a power source (power source) for driving a motor mounted on a vehicle. Therefore, the present invention provides a vehicle including the lithium secondary battery disclosed herein.
The lithium secondary battery disclosed herein can achieve higher capacity and improved cycle characteristics by the configuration as described above. For this reason, it is equipped with performance suitable as a battery mounted on a vehicle that requires high-rate charge / discharge. Therefore, according to the present invention, it is possible to provide a vehicle (for example, an automobile) including the lithium secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle).

It is a perspective view which shows typically the external shape of the lithium secondary battery which concerns on one Embodiment. It is a longitudinal cross-sectional view which follows the II-II line | wire in FIG. It is the figure which illustrated the XRD pattern of the material for secondary batteries which concerns on an Example. It is the figure which illustrated the transmission electron microscope (TEM) image of the material for secondary batteries concerning one embodiment of the present invention. It is the figure which illustrated the charging / discharging curve of the secondary battery which concerns on a comparative example. It is the figure which illustrated the charging / discharging curve of the secondary battery which concerns on an Example. It is a side view showing typically a vehicle provided with a lithium ion battery concerning one embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

In the present specification, the “lithium secondary battery” means a general battery that can be repeatedly charged using lithium ions as a charge carrier, and typically includes a lithium ion battery, a lithium polymer battery, a lithium capacitor, and the like.
In this specification, “active material” can reversibly occlude and release (typically insertion and removal) chemical species (for example, lithium ions in a lithium ion battery) that serve as charge carriers in a secondary battery. Refers to a substance.

<Electrode material for secondary battery>
An embodiment of the secondary battery electrode material disclosed herein and a method for producing the same will be described in detail below.
The electrode material for a secondary battery disclosed herein includes a layered lithium manganese composite oxide, a conductive material, and a binder. What is suitable as this complex oxide is
(1) General formula:
xLi [Li _1/3 Mn _2/3 ] O _2. (1-x) LiMeO ₂
It is the layered lithium manganese type complex oxide represented by these. Here, Me in the formula is one or more transition metals, and x satisfies 0 <x <1. As such a complex oxide, for example, 0.2 (Li ₂ MnO ₃ ) · 0.7 (LiFe _0.5 Mn _0.5 O ₂ ) <x = 0.3 >, 0.4 (Li ₂ MnO ₃ ) · 0.4 (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) <x = 0.6>. More preferably, the composite oxide includes at least both Ni and Co as Me. In this case, the content of Mn is set to be larger than the total content of Ni and Co. In addition, the molar ratio of Li to Mn and Me is represented by the following formula:
1 <Li / (Mn + Me) ≦ 1.5
Shall be satisfied. Thereby, it can become a composite oxidation part which contains lithium as a charge carrier stably and in large quantities. The composite oxide is further prepared to have the characteristics shown in the above (2) and (3).

Such adjustment can be performed by the manufacturing method disclosed herein. That is, by including the following steps (A) and (B), the crystal structure of the composite oxide as the high-capacity active material of (1) above is changed, and the features of (2) and (3) above It is converted into a new material that does not generate a disabling reverse capacity.
The manufacturing method disclosed here includes (A) a step of preparing a mixture of a layered lithium manganese composite oxide, a conductive material, and a binder.

The layered lithium manganese composite oxide as a starting material has a composition as shown in the above (1), and can be prepared by various known methods.
The conductive material is used to ensure the conductivity to the above complex oxide in the next electrochemical treatment step. Examples of the conductive material include carbon black (for example, acetylene black), carbon material such as graphite powder, or conductive metal powder such as nickel powder. These may be used individually by 1 type, and may be used in combination of 2 or more types. Although it does not specifically limit about the usage-amount of an electrically conductive material, For example, setting it as 1-20 mass parts (preferably 5-15 mass parts) with respect to 100 mass parts of positive electrode active materials is illustrated.

  The binding material is used to integrate the composite material and the conductive material. As the binder, various known binders can be used, and among them, a water-soluble polymer material that dissolves in water is preferable. For example, carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), hydroxypropylmethylcellulose phthalate (HPMCP), polyvinyl alcohol (PVA) and the like. In addition, a polymer material that is dispersed in water (water-dispersible) can be suitably used. For example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE) ), Etc., rubbers such as vinyl acetate copolymer, styrene butadiene block copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), and gum arabic. Although the usage-amount of a binder is not specifically limited, For example, it can be set as 0.5-10 mass parts with respect to 100 mass parts of positive electrode active materials as solid content weight.

These materials are mixed (including dissolution and dispersion) to prepare a mixture. The state of the mixture may be any form such as liquid, paste, kneaded or solid. In the case of a solid, the shape is not particularly limited.
Next, the invention disclosed herein performs (B) an electrochemical treatment consisting of oxidation with an upper limit voltage of 4.5 V to 5 V and reduction with a lower limit voltage of 2.0 V to 3 V on the mixture. Including that.
The upper limit voltage can be appropriately set in the range of 4.5V to 5V. For example, it can be set to 4.8V, or even 4.85V. If the upper limit voltage is less than 4.5 V, it is not preferable because an appropriate structural change as described above cannot be caused in the composite oxide. On the other hand, if it exceeds 5 V, the crystal structure of the composite oxide is destroyed, which is not preferable. The lower limit voltage can be appropriately set in the range of 2.0V to 3V. For example, it can be set to 2.5V. If the lower limit voltage is higher than 3V, problems occur in subsequent handling, which is not preferable. Moreover, since deterioration will be accelerated | stimulated when lower than 2.0V, it is unpreferable.

As a result of the electrochemical treatment, the composite oxide subjected to the electrochemical treatment as described above is changed into a crystal structure including the following features (2) to (4).
(2) The lattice constants when assigned to the space group R (−3) m are in the ranges of 2.864Å ≦ a ≦ 2.878Å and 14.27Å ≦ c ≦ 14.39Å.
By changing the crystal lattice in this way, no further change in the crystal structure is observed even when lithium ions are desorbed from the transition metal layer by further charging. Therefore, the irreversible capacity accompanying the change of the crystal structure does not occur. In addition, since the crystal lattice is expanded in this way, lithium having a relatively large ionic radius can easily move freely, and replacement of the transition metal with lithium is facilitated. Also by this, generation | occurrence | production of an irreversible capacity | capacitance is eliminated and the improvement of reaction rate can also be anticipated. Note that the lattice constant of the crystal lattice can be accurately obtained by performing Rietveld analysis or the like from the X-ray diffraction pattern, for example.

(3) The X-ray diffraction intensity ratio between the (003) plane and the (104) plane is I (003) / I (104)> 1.
The electrochemical treatment disclosed here reduces the X-ray diffraction intensity ratio between the (003) plane and the (104) plane. Here, the X-ray diffraction intensity ratio between the (003) plane and the (104) plane reflects the coordinate information of oxygen atoms in addition to the ratio of substitution between lithium and transition metal. It can be determined that the coordinate information of oxygen atoms does not change greatly and the smaller the value, the greater the substitution amount and the higher the tendency of the crystal structure to change. However, when the X-ray diffraction intensity ratio is 1 or less, the substitution amount is too large and the structure becomes unstable. Therefore, the X-ray diffraction intensity ratio is set to a value larger than 1. The upper limit of the X-ray diffraction intensity ratio is not particularly limited. A composite oxide showing a value of 2 or more has not been obtained.

(4) The surface includes a cubic layer lacking lithium.
By the electrochemical treatment disclosed here, lithium in the surface portion of the composite oxide is desorbed from the crystal structure, and a lithium-depleted cubic layer having a lattice constant of a = c is formed. This cubic crystal layer can be confirmed as a layer having a thickness of about 1 to 5 nm by, for example, observation with a transmission electron microscope. This layer is understood as a result of the electrochemical processing disclosed herein. As a result, although the lithium content of the composite oxide is reduced and the initial capacity is slightly reduced, this composite oxide has no irreversible capacity, and as a result, the capacity is changed to a composite oxide that generates irreversible capacity. It is maintained at a relatively high value.

  That is, the electrode material for secondary batteries disclosed here is suitably provided. This electrode material for a secondary battery is not particularly limited with respect to its form and shape, as in the case of the aforementioned mixture, and can take various forms. According to this secondary battery electrode material, as described above, it can be a high-capacity positive electrode active material, and there is no change in the crystal structure associated with the desorption of lithium ions. Therefore, a high-capacity positive electrode active material that eliminates the problem of irreversible capacity is provided.

<Lithium secondary battery>
The lithium secondary battery disclosed herein includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. As the positive electrode, a positive electrode having a form in which at least the electrode material for a secondary battery is attached to a current collector as an active material layer can be preferably used.

  As the positive electrode current collector, a rod-like body, a plate-like body, a foil-like body, a net-like body or the like mainly composed of aluminum, nickel, titanium, stainless steel, or the like can be used.

  On the other hand, as the negative electrode (typically, the negative electrode sheet) 76, an active material capable of reversibly occluding and releasing Li is collected as a negative electrode active material layer 74 together with a binder and a conductive material used as necessary. The thing attached to the body 72 can be preferably used.

As the negative electrode current collector 72, a rod-like body, a plate-like body, a foil-like body, a net-like body or the like mainly composed of copper, nickel, titanium, stainless steel, or the like can be used.
The binder is the same as that of the positive electrode, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR).
The conductive material and the binding material are not particularly limited, and can be the same as those used for the secondary battery electrode material disclosed herein, for example. As the conductive material, a carbon material such as carbon black can be preferably used.

  Examples of the negative electrode active material include various metal compounds (for example, metal oxides), specifically, Si, Ge, Sn, Pb, Al, Ga, In, As, Sb, Bi, and the like as constituent metal elements. It may be a metal compound (preferably a metal oxide). Moreover, for example, a granular negative electrode active material excellent in conductivity whose surface is sufficiently covered with a carbon coating can be suitably used. In this case, the conductive material is not contained in the negative electrode active material layer, or the content of the conductive material can be reduced as compared with the conventional case. Although the usage-amount of an electrically conductive material is not specifically limited, For example, about 1-30 mass parts (preferably about 2-20 mass parts, for example, 5-10 mass parts) with respect to 100 mass parts of negative electrode active materials to be used. Degree). A conductive material may be previously contained in the electrode active material supply material described above.

  Moreover, in the lithium secondary battery disclosed here, a separator can be interposed between the positive electrode and the negative electrode. As this separator, a porous sheet made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide, a nonwoven fabric, or the like can be used. Preferable examples include those composed of a porous polyolefin resin. For example, a porous separator sheet made of synthetic resin (for example, made of polyolefin such as polyethylene) can be suitably used. When a solid electrolyte or a gel electrolyte described later is used as the electrolyte, a separator may not be necessary (that is, in this case, the electrolyte itself can function as a separator).

  As the electrolyte, a liquid electrolyte containing a nonaqueous solvent and a lithium salt soluble in the solvent is preferably used. It may be a solid (gel) electrolyte in which a polymer is added to such a liquid electrolyte. As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used. For example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Generally lithium ion batteries such as 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone One kind or two or more kinds selected from non-aqueous solvents known as those that can be used in the electrolyte can be used.

Lithium salts include LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiClO _4, etc., one or more selected from various lithium salts known to be capable of functioning as a supporting electrolyte in the electrolyte of a lithium ion battery can be used. The concentration of the lithium salt is not particularly limited, and can be the same as, for example, the electrolyte used in a conventional lithium ion battery. Usually, a non-aqueous electrolyte containing a supporting electrolyte (lithium salt) at a concentration of about 0.1 mol / L to 5 mol / L (for example, about 0.8 mol / L to 1.5 mol / L) is preferably used. it can.

  When assembling the lithium secondary battery disclosed herein, the positive electrode and the negative electrode are accommodated in an appropriate container (a metal or resin casing, a bag made of a laminate film, etc.) together with the electrolyte, thereby providing a lithium secondary battery. Build a battery (lithium ion secondary battery). In a typical configuration of the lithium secondary battery disclosed herein, a separator is interposed between the positive electrode and the negative electrode. The shape (outer shape of the container) of the lithium secondary battery is not particularly limited, and may be, for example, a cylindrical shape, a square shape, a coin shape, or the like.

  The technology disclosed as described above is characterized in that the electrode material for a secondary battery of the present invention is subjected to electrochemical treatment, and the crystal structure is changed to a specific one. Therefore, the timing of this electrochemical treatment is not limited. For example, it may be performed before the assembly of the lithium secondary battery, or may be performed after the assembly, for example, as part of conditioning. In addition, as long as the object of the present invention can be realized, the material and shape of other battery components are not particularly limited, and the same aspects and modifications as those of conventional lithium secondary batteries (typically lithium ion batteries) Can be considered.

  Hereinafter, a lithium ion battery as a preferred embodiment of the lithium secondary battery disclosed herein will be described with reference to the drawings.

FIG. 1 is a perspective view schematically showing a lithium secondary battery according to this embodiment. 2 is a longitudinal sectional view taken along line II-II in FIG.
As shown in FIGS. 1 and 2, the lithium secondary battery 10 according to the present embodiment includes the above-described secondary battery electrode material and positive electrode current collector 62, separator 80, negative electrode active material, negative electrode current collector 72, and the like. A wound electrode body 50 and a square shape (typically a flat rectangular parallelepiped shape) that accommodates the wound electrode body 50 and a suitable non-aqueous electrolyte (not shown; typically an electrolyte) ) Battery case 15.

  The case 15 includes a box-shaped case main body 30 in which one of the narrow surfaces in the flat rectangular parallelepiped shape is an opening 20, and the opening 20 is attached (for example, welded) to the opening 20. And a lid 25 for closing. As a material constituting the case 15, the same material as that used in a general lithium secondary battery can be used as appropriate, and there is no particular limitation. For example, a metal (for example, aluminum, steel, etc.) container, a synthetic resin (for example, a polyolefin resin, a high melting point resin such as a polyamide resin, etc.), or the like can be preferably used. The case 15 according to the present embodiment is made of, for example, aluminum.

  The lid body 25 is formed in a rectangular shape that matches the shape of the opening 20 of the case body 30. Further, the lid body 25 is provided with a positive electrode terminal 60 and a negative electrode terminal 70 for external connection, respectively, and a part of these terminals 60, 70 protrudes from the lid body 25 toward the outside of the case 15. It is formed to do. Similarly to the case of the conventional lithium secondary battery, the lid 25 is provided with a safety valve (not shown) for discharging the gas generated inside the case 15 to the outside of the case 15 when the battery is abnormal. It has been. The safety valve can be used without any limitation as long as the safety valve is provided with a mechanism that opens when the pressure inside the case 15 exceeds a predetermined level and discharges the gas outside the case 15.

  As shown in FIG. 2, the lithium secondary battery 10 includes a wound electrode body 50 in the same manner as a normal lithium secondary battery. The electrode body 50 is accommodated in the case main body 30 in a posture in which the winding axis is laid down (that is, in the direction in which the opening 20 is positioned in the lateral direction with respect to the winding axis). The electrode body 50 includes a positive electrode sheet (positive electrode) 66 having a positive electrode active material layer 64 formed on the surface of a long sheet-like positive electrode current collector 62 and a long sheet-like negative electrode current collector (electrode current collector). A negative electrode sheet (negative electrode) 76 having a negative electrode active material layer (electrode active material layer) 74 formed on the surface of 72 is overlapped with two long separator sheets 80 and wound, and the resulting electrode body 50 is obtained. It is formed into a flat shape by crushing it from the side direction and causing it to be ablated.

  Further, in the wound positive electrode sheet 66, the positive electrode current collector 62 is exposed without forming the positive electrode active material layer 64 at one end portion along the longitudinal direction, while the negative electrode is wound. Also in the sheet 76, the negative electrode current collector 72 is exposed at one end portion along the longitudinal direction without forming the negative electrode active material layer 74. A positive electrode terminal 60 is joined to the exposed end of the positive electrode current collector 62, and is electrically connected to the positive electrode sheet 66 of the wound electrode body 50 formed in the flat shape. Similarly, the negative electrode terminal 70 is joined to the exposed end portion of the negative electrode current collector 72 and is electrically connected to the negative electrode sheet 76. The positive and negative electrode terminals 60 and 70 and the positive and negative electrode current collectors 62 and 72 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

  The materials and members themselves constituting the wound electrode body 50 having the above-described configuration are the conventional ones except that the secondary battery electrode material (here, the positive electrode active material layer 64) disclosed here is adopted as the positive electrode active material layer 64. It may be the same as the lithium secondary battery and is not particularly limited.

  The positive electrode sheet 66 can be produced by forming the above-described secondary battery electrode material in a layered manner on a long positive electrode current collector (for example, a long aluminum foil) 62. That is, a paste-like mixture prepared by dispersing a known layered lithium manganese composite material, a conductive material (for example, acetylene black) and a binder (for example, PVDF) in an organic solvent (for example, NMP) is prepared. The electrode material for a secondary battery is obtained by performing the electrochemical treatment disclosed in the above. The thus prepared secondary battery electrode material is applied to the negative electrode current collector 62, dried, and then compressed (pressed) to form the positive electrode active material layer 64. In addition, since the formation method itself of the positive electrode active material layer 64 may be the same as the conventional one and does not characterize the present invention, a detailed description thereof is omitted.

  The negative electrode sheet 76 is substantially the same as the positive electrode sheet 66 except that electrochemical treatment is performed, and a negative electrode active material layer 74 is formed on a long negative electrode current collector (for example, a long copper foil) 72. It is produced by doing. That is, a negative electrode active material layer forming paste is prepared by dispersing a negative electrode active material (for example, graphite) and a binder (for example, PVDF) in an organic solvent (for example, NMP). The prepared paste is applied to the negative electrode current collector 72, dried, and then compressed (pressed) to form the negative electrode active material layer 74. Note that the method of forming the negative electrode active material layer 74 may be the same as that of the conventional one, and does not characterize the present invention, and thus detailed description thereof is omitted.

The positive electrode sheet 66 and the negative electrode sheet 76 produced above are stacked and wound together with two separators (for example, porous polyolefin resin) 80, and the wound electrode body 50 obtained is rolled into the case body 30 with its winding shaft lying sideways. Non-aqueous electrolysis such as a mixed solvent of EC and DMC (for example, a mass ratio of 1: 1) containing an appropriate amount of a supporting salt (for example, a lithium salt such as LiPF ₆ ) (for example, a concentration of 1M). After injecting the liquid, the lithium secondary battery 10 of the present embodiment can be constructed by mounting the lid 25 on the opening 20 and sealing (for example, laser welding).

  In the embodiment described above, the electrode material for the secondary battery of the present invention is applied to the positive electrode active material of the lithium secondary battery. However, the present invention is not limited to this mode. For example, the positive electrode of the lithium polymer battery or the lithium ion capacitor The present invention can be applied to other electrodes.

  In the lithium secondary battery 10 having the above-described configuration, the lithium ions of the charge carrier are desorbed and inserted from the positive electrode active material 64 into the non-aqueous electrolyte as charging and discharging are repeated. When a conventional layered lithium manganese composite oxide was used as the positive electrode active material 64, the crystal structure of the composite oxide crystal lattice was changed little by little with the desorption of lithium ions, generating irreversible capacity. . However, the lithium ion battery 10 disclosed here uses the electrode material for a secondary battery of the present invention as a positive electrode active material, and even if lithium ions are repeatedly desorbed, such a change in crystal structure is observed. Absent. Therefore, the lithium ion battery 10 disclosed herein is excellent in charge / discharge cycle characteristics without generating irreversible capacity.

  Hereinafter, as specific examples, an electrode material for a secondary battery and a lithium secondary battery (sample battery) disclosed herein were constructed and their performance was evaluated.

<Sample 1>
[Preparation of positive electrode active material]
A layered lithium manganese composite oxide having a composition represented by the general formula: Li _1.2 Mn _0.54 Co _0.13 Ni _0.13 O ₂ was prepared. Namely, pure water is put into a beaker, lithium acetate dihydrate [Li (CH ₃ COO) · 2H ₂ O] as a lithium source, and manganese (II) acetate tetrahydrate as a manganese source [Mn (CH ₃ COO) ₂ .4H ₂ O], nickel acetate (II) tetrahydrate as a nickel source [Ni (CH ₃ COO) ₂ .4H ₂ O], and cobalt acetate (II ) Tetrahydrate [Co (CH ₃ COO) ₂ .4H ₂ O] and manganese acetate (II) tetrahydrate as a manganese source [Mn (CH ₃ COO) ₂ .4H ₂ O], and A predetermined amount of glycolic acid was added and dissolved and mixed. This was then adjusted to pH 1.8 with acetic acid and the water was evaporated overnight in an 80 ° C. oil bath. Then, after baking at 600 degreeC for 5 hours and grind | pulverizing in a mortar, it further baked at 900 degreeC for 5 hours.
<Sample 2>
[Preparation of secondary battery electrode material 1]
The layered lithium manganese composite oxide prepared in Sample 1, acetylene black, and polyvinylidene fluoride (PVDF) were mixed at a weight ratio of 85: 10: 5.
This mixture was applied to an Al foil and dried to prepare a positive electrode. 1 mol / L LiPF ₆ was added to a mixed solvent of 3: 3: 4 in a weight ratio of this positive electrode, lithium metal as the negative electrode, and ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as the electrolyte. Using the dissolved material, an electrochemical cell was assembled, and the positive electrode mixture was subjected to electrochemical treatment. The conditions for the electrochemical treatment were such that, at 25 ° C., the current density was 50 mA / g, oxidation to 4.8 V, and then reduction to 2.5 V.
<Sample 3>
[Preparation of secondary battery electrode material 2]
The electrochemical treatment was performed at 25 ° C. at a current density of 50 mA / g up to 4.8 V and then reduced to 2.5 V for 2 cycles.
<Sample 4>
[Preparation of secondary battery electrode material 3]
The conditions of the electrochemical treatment were the same as those of Sample 2 except that oxidation was performed to 4.8 V at a current density of 15 mA / g at 25 ° C. and then reduced to 2.5 V.

<Evaluation>
[X-ray diffraction analysis]
Samples 1 to 4 obtained above were subjected to X-ray diffraction analysis using Cu Kα rays. The obtained XRD pattern is shown in FIG. Table 1 shows the result of calculating the ratio of diffraction intensities from the (003) plane and the (104) plane as I (003) / I (104). In addition, about the pattern of the samples 2-4 of FIG. 3, the result of having decomposed | disassembled the electrochemical cell and taking out the positive electrode and having measured was shown. As is clear from Table 1, it was confirmed that the samples 2 to 4 subjected to the electrochemical treatment had a lower XRD intensity ratio of the (003) plane relative to the (104) plane than the untreated sample 1. . This indicates that a part of the transition metal has been rearranged in the Li layer.

[Transmission electron microscope (TEM) observation]
The layered lithium manganese composite oxide particles in Samples 1 to 4 obtained above were analyzed by TEM. For Samples 2 to 4, positive electrode mixture particles subjected to electrochemical treatment were taken out from the Al foil and used.
First, when the space group was analyzed from the electron diffraction patterns of the particles of Samples 1 to 4, it was confirmed that any of them could be attributed to R (-3) m. Next, the lattice constant of the crystal was examined from the electron beam diffraction images of the particles of Samples 1 to 4 and shown in Table 1. As is apparent from Table 1, it was confirmed that Samples 2 to 4 subjected to the electrochemical treatment had an increased lattice constant and an expanded crystal lattice as compared with the untreated Sample 1.
Further, the distribution of lithium elements in the particles was examined by a STEM-EELS spectral imaging method in which an electron beam energy loss spectrum (EELS) was measured using a scanning TEM (STEM). The results of the surface observation of the particles of Sample 2 are shown in FIG. As for the particles of sample 1, Li is distributed throughout the particles, whereas the particles of samples 2 to 4 subjected to electrochemical treatment have defects in the surface Li, and cubic layers are arranged. It was confirmed.

[ICP emission spectroscopy]
The particles of Samples 1 to 4 were subjected to elemental analysis for Li, Mn, Ni, and Co by ICP emission spectroscopy, and the Li amount relative to the transition metal (Mn, Ni, Co) was determined from the results, and (Li / (Mn + Me )) As shown in Table 1. Compared with sample 1, the particles of samples 2 to 4 have a smaller amount of Li, and reflect Li defects on the particle surface.

[Capacitance evaluation]
The materials of Samples 1 to 4 were evaluated for capacity characteristics using a coin battery. That is, for the composite oxide of Sample 1, as in Samples 2 to 4, acetylene black and polyvinylidene fluoride (PVDF) were mixed at a weight ratio of 85: 10: 5, and this mixture was applied to an Al foil. And dried to obtain a positive electrode. For Samples 2 to 4, positive electrodes after electrochemical treatment were used. The positive electrodes were pressed so as to have the same electrode density, and then punched into a circle having a diameter of 16 mm to produce an evaluation electrode.
A metal lithium foil having a diameter of 15 mm and a thickness of 0.15 mm was used as the counter electrode. As the separator, a porous polyolefin sheet having a diameter of 22 mm and a thickness of 0.02 mm was used. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as a lithium salt at a concentration of about 1 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7 was used. .
These constituent elements were incorporated into a stainless steel container to construct a coin cell for evaluation having a general shape with a thickness of 3.2 mm and a diameter of 20.0 mm (so-called 2032 type).

The coin cell produced as described above (hereinafter, the cell produced using the composite oxide of sample 1 is referred to as “cell of sample 1”, and the cell produced using the electrode material of sample 2 is referred to as “cell of sample 2”. In other words, at a constant current of 50 mA / g, an operation of charging until the voltage between the electrodes was 4.8 V and an operation of discharging until 2.5 V were performed. The charge / discharge curves of the sample 1 cell and the sample 2 cell are shown in FIGS. 5 and 6, respectively. Further, the charge capacity and the discharge capacity were measured for all the sample cells, and the coulomb efficiency (%) was obtained. Specifically, the coulomb efficiency (%) = (discharge capacity) / (charge capacity) × 100 was calculated, and the result is shown in Table 1.
As is apparent from the results of FIGS. 5 to 6 and Table 1, the cell of sample 1 has a coulomb efficiency of about 80%, which is the same as the conventional cell, whereas the cells of samples 2 to 4 subjected to electrochemical treatment are all. It was confirmed that the coulomb efficiency was 100% and no irreversible capacity was generated. As a result, it was confirmed that the cells of Samples 2 to 4 could ensure a higher capacity than Sample 1 even though the amount of lithium was small.

  In summary, the manufacturing method disclosed herein changes the crystal structure of the layered lithium manganese composite oxide contained in the secondary battery electrode material. As a result, the crystal structure of the positive electrode obtained when this secondary battery electrode material is used as the positive electrode active material layer forming material does not change even when lithium is desorbed from the positive electrode active material during charge and discharge. The occurrence of irreversible capacity resulting from this is considered to be eliminated.

As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.
Any of the lithium secondary batteries disclosed herein may have a performance suitable as a battery mounted on a vehicle, in particular, a high capacity maintenance ratio and an excellent durability. In addition, the capacity can be increased by using a metal oxide such as SiO _x as the negative electrode active material.
Therefore, according to the present invention, as shown in FIG. 7, there is provided a vehicle 100 including any lithium secondary battery 10 disclosed herein. In particular, a vehicle (for example, an automobile) including the lithium secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.

  According to the manufacturing method disclosed herein, an electrode material for a secondary battery having no irreversible capacity is provided. As a result, it is possible to provide a lithium secondary battery that is excellent in charge / discharge cycle characteristics, and thus in high-rate characteristics. Due to such features, the lithium secondary battery disclosed here is employed as an in-vehicle secondary battery (in particular, an in-vehicle lithium secondary battery), thereby providing a vehicle using, for example, a lithium secondary battery as a driving power source. can do.

DESCRIPTION OF SYMBOLS 10 Lithium secondary battery 15 Battery case 20 Opening part 25 Cover body 30 Case main body 50 Winding electrode body 60 Positive electrode terminal 62 Positive electrode current collector 64 Secondary battery electrode material (positive electrode active material layer)
66 Positive electrode sheet (positive electrode)
70 Negative electrode terminal 72 Negative electrode current collector 74 Negative electrode active material layer 76 Negative electrode sheet (negative electrode)
80 separator 100 vehicle

Claims (7)

Including a layered lithium manganese composite oxide, a conductive material, and a binder;
The composite oxide is
(1) General formula:
xLi [Li _1/3 Mn _2/3 ] O _2. (1-x) LiMeO ₂
(In the formula, Me is one or more transition metals, and x satisfies 0 <x <1.)
Represented by
(2) The lattice constant when attributed to the space group R (-3) m is in the range of 2.864Å ≦ a ≦ 2.878Å, 14.27Å ≦ c ≦ 14.39Å,
(3) An electrode material for a secondary battery, wherein the X-ray diffraction intensity ratio between the (003) plane and the (104) plane is I (003) / I (104)> 1. The composite oxide includes at least Ni and Co as the Me together with Mn,
Mn> Ni + Co
And, the molar ratio of Li to Mn and Me is represented by the following formula:
1 <Li / (Mn + Me) ≦ 1.5
The electrode material for a secondary battery according to claim 1, wherein The composite oxide further includes:
(4) including a cubic layer lacking lithium on the surface;
The electrode material for secondary batteries according to claim 1 or 2. A lithium secondary battery comprising a positive electrode in which a positive electrode active material layer is held on a positive electrode current collector, a negative electrode, and a nonaqueous electrolyte,
The said positive electrode active material layer is a lithium secondary battery containing the electrode material for secondary batteries in any one of Claims 1-3.   A vehicle comprising the lithium secondary battery according to claim 4. A method for producing an electrode material for a secondary battery,
Preparing a mixture of a layered lithium manganese composite oxide, a conductive material, and a binder;
Subjecting the mixture to an electrochemical treatment comprising oxidation to an upper limit voltage of 4.5 V to 5 V and reduction to a lower limit voltage of 2.0 V to 3 V;
Including
Here, the composite oxide has a general formula:
xLi [Li _1/3 Mn _2/3 ] O _2. (1-x) LiMeO ₂
(In the formula, Me is one or more transition metals, and x satisfies 0 <x <1.)
A manufacturing method represented by The composite oxide includes at least Ni and Co as the Me together with Mn,
Mn> Ni + Co
And, the molar ratio of Li to Mn and Me is represented by the following formula:
1 <Li / (Mn + Me) ≦ 1.5
The manufacturing method of Claim 6 which satisfy | fills.