JP6136849B2 - Positive electrode containing surface-modified active material and high-resistance metal compound - Google Patents

Description

  The present invention relates to a positive electrode including a surface modifying active material and a high resistance metal compound.

The active material of the secondary battery has been known that various materials are used, of which layered rock-salt of the general _{formula: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 1 .2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V A material represented by at least one element selected from Mo, Nb, W, La, 1.7 ≦ f ≦ 2.1) is widely used as an active material for lithium ion secondary batteries.

  However, when the material represented by the above general formula is used as an active material of a high-capacity secondary battery driven at a high voltage required for an in-vehicle secondary battery, for example, the resistance of the material to the high voltage Therefore, the capacity maintenance rate of the secondary battery could not be maintained at a level satisfying.

For this reason, in recent years, various studies for improving the resistance to high voltages of various materials used as active materials have been conducted. In this examination, the following three methods are generally proposed.
1) Doping the active material with a different element 2) Forming a protective film on the active material surface 3) Changing the composition of the active material surface layer

  The method 1) will be described in detail. The active material, such as Al or Zr, that is not present in the active material is doped with the active material, thereby suppressing deterioration of the active material associated with charge / discharge, that is, absorption / release of Li. can do.

  The method 2) will be described in detail. As disclosed in Patent Document 1 below, a protective film is formed on the surface of the active material with a phosphate to prevent direct contact between the electrolyte and the active material. The deterioration of the active material due mainly to contact with the electrolytic solution can be suppressed.

  The above method 3) will be described in detail. Patent Document 2 listed below discloses an active material obtained by coating the surface of an active material with an Al compound and heat-treating it, and increasing the Al composition of the active material surface layer. Is disclosed.

  Each of the above three methods has the following drawbacks and has not necessarily resulted in a satisfactory active material.

  The disadvantage of the above method 1) is that doping with a different element that is not electrochemically driven effectively reduces the amount of Li that can be absorbed and released in the active material. The capacity of the ion secondary battery itself is reduced.

  The disadvantage of the above method 2) is that the protective film formed on the surface of the active material becomes an electric resistance and current does not flow easily. In order to overcome this drawback, the protective film may be an extremely thin film, but it is very difficult to establish such a technique at the industrial level.

  The above method 3) is theoretically desirable because it does not easily cause the capacity reduction, which is the disadvantage of 1), and does not form the electrical resistance protective film, which is the disadvantage of 2). In this technique, the active material surface layer is substantially doped with Al, and not only the same defects as in 1) are observed, but the active material surface layer has an increased Al composition by the treatment method described in the same document. Even if the material and the active material not subjected to the treatment are compared, no particularly advantageous effect is observed.

  That is, in the technology for modifying these active materials, it cannot always be said that a sufficient level of active materials can be obtained.

  From the viewpoint of safety of the lithium ion secondary battery, it is important to ensure safety when the lithium ion secondary battery is internally short-circuited. As a method for confirming safety at the time of an internal short circuit of a battery, a nail penetration test for observing the behavior of the battery when a nail is penetrated through the battery is known. Actually, Patent Document 3 describes a lithium ion secondary battery that did not ignite as a result of a nail penetration test. Here, the lithium ion secondary battery disclosed in Patent Document 3 is obtained by dividing an electrode into sheets having a specific shape. The technique disclosed in Patent Document 3 defines the area and shape of a sheet obtained by dividing an electrode and the distance between a positive electrode current collector and a negative electrode current collector with a certain relational expression. Several restrictions were placed on the battery components. Since lithium ion secondary batteries are sometimes used in aircraft and automobiles, the level of safety required for lithium ion secondary batteries is higher.

JP 2006-127932 A JP 2001-196063 A JP 2003-157854 A

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a lithium ion secondary battery excellent in safety even under high voltage driving.

  As a result of intensive studies by the present inventors, it has been found that when a specific treatment is performed on a material that can be an active material, the surface layer of the material is modified. And when the material whose surface layer is modified is used as an active material for a lithium ion secondary battery, the capacity of the secondary battery is preferably maintained, especially when the secondary battery is driven at a high voltage around 4.5V. Even so, it has been found that an excellent capacity retention rate is exhibited. Furthermore, the present inventor has found that a lithium ion secondary battery including a positive electrode containing a surface-modifying active material and a specific metal compound is excellent in safety even during an internal short circuit, and completes the present invention. It came to.

  The first positive electrode of the present invention includes a positive electrode active material surface-modified with a phosphate ion-containing solution and a high-resistance metal compound having a higher resistance than the positive electrode active material.

The second positive electrode of the present invention has a general formula of a layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D Is at least one selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La Element, 1.7 ≦ f ≦ 2.1), and three consecutive high-angle scattering annular dark-field scanning transmission electrons obtained by observing the same 3b site of the layered rock salt structure from the <1-100> orientation When seven sets of intensity ratios obtained by dividing the minimum value of the integrated intensities of the microscopic image by the maximum value are calculated, the first superlattice structure portion in which the average value n of the seven sets of intensity ratios is less than 0.9 A positive electrode active material having a surface layer, and a high resistance metal compound having a higher resistance than the positive electrode active material. And butterflies.

The third positive electrode of the present invention has a general formula of a layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D Is at least one selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La Element, 1.7 ≦ f ≦ 2.1), and arbitrary three consecutive high-angle scattering annular dark field scans obtained by observing the same 3b site of the layered rock salt structure from the <1-100> orientation The integral intensities of the transmission electron microscope images are p1, p2, and q (0.9 × p1 ≦ p2 ≦ 1.1 × p1, q is p <0.9 × p2 when p1 ≦ p2, and p2 ≦ p1) A positive electrode active material having a second superlattice structure portion represented by q <0.9 × p1) in the surface layer, and the positive electrode active material A high-resistance metal compound having a higher resistance than the quality is included.

The fourth positive electrode of the present invention has a general formula of a layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D Is at least one selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La Positive electrode having a third superlattice structure portion, which is represented by the element 1.7 ≦ f ≦ 2.1) and satisfies both the conditions of the first superlattice structure portion and the conditions of the second superlattice structure portion in the surface layer It includes an active material and a high-resistance metal compound having a higher resistance than the positive electrode active material.

The fifth positive electrode of the present invention has a general formula of a layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D Is at least one selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La Element, 1.7 ≦ f ≦ 2.1), including at least Ni, Co, and Mn, and the composition ratio of Ni, Co, and Mn is Ni: Co: Mn = b2: c2: d2 (where b2 + c2 + d2 = A positive electrode active material having a high manganese portion represented by 1, 0 <b2 <1, 0 <c2 <c, d <d2 <1) on a surface layer, and a high-resistance metal compound having a higher resistance than the positive electrode active material It is characterized by including.

  The secondary battery using the positive electrode of the present invention is excellent in safety even when it is internally short-circuited under high voltage drive.

It is a schematic diagram of a normal superlattice surface of Ni _1/3 Co _1/3 Mn _1/3 in which a surface composed of a layered rock salt structure 3b site is expressed by a [√3 × √3] R30 ° type. It is an image applicable to the layered rock salt structure 3b site surface comprised by the 1st-3rd superlattice structure part observed by the high angle scattering cyclic | annular dark field scanning transmission electron microscope. Layered rock salt structure 3b site surface with normal superlattice surface measured for commercially available layered rock salt type LiNi _1/3 Co _1/3 Mn _1/3 O ₂ observed by high angle scattering annular dark field scanning transmission electron microscopy It is a statue of. It is an image of the vicinity of the boundary between the first to third superlattice structures and the normal superlattice surface observed by high-angle scattering annular dark field scanning transmission electron microscopy. It is the integrated intensity data of the image shown in FIG. It is a schematic diagram which shows the one aspect | mode of the lithium ion secondary battery provided with the positive electrode of this invention.

  The best mode for carrying out the present invention will be described below. Unless otherwise specified, the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

  The first positive electrode of the present invention includes a positive electrode active material surface-modified with a phosphate ion-containing solution and a high-resistance metal compound having a higher resistance than the positive electrode active material. By using the surface-modified cathode active material, the capacity of the secondary battery can be suitably maintained. In addition, a battery including a high-resistance metal compound having a higher resistance than that of the positive electrode active material in the positive electrode can suppress the generation of significant current due to the presence of the high-resistance metal compound even during an internal short circuit.

  “Positive electrode active material surface-modified with a phosphate ion-containing solution” means a positive electrode active material whose surface state has been changed by performing a specific treatment using a phosphate ion-containing solution on the positive electrode active material. Means.

  A specific treatment using a phosphate ion-containing solution (hereinafter, also referred to as “specific treatment of the present invention”) will be described. The specific processing of the present invention may be either the following processing 1 or processing 2.

  Treatment 1: A magnesium nitrate aqueous solution is prepared, and a material as a positive electrode active material is added and stirred. Next, an aqueous diammonium hydrogen phosphate solution is added to the aqueous solution and stirred. After the material is isolated by filtration, it is fired.

  Treatment 2: An aqueous solution containing magnesium nitrate and diammonium hydrogen phosphate is prepared, and a material as a positive electrode active material is added and stirred. After the material is isolated by filtration, it is fired.

  The concentration of the magnesium nitrate aqueous solution, the diammonium hydrogen phosphate aqueous solution, and the aqueous solution containing magnesium nitrate and diammonium hydrogen phosphate used in the treatment 1 or the treatment 2 are not particularly limited. The thing in the range of -2 mass% is preferable. What is necessary is just to set the stirring time in the process 1 or the process 2 suitably.

Firing is a process for adjusting the crystallinity of the active material, and it may be performed within a range of 500 to 1000 ° C. for about 1 to 10 hours. You may grind | pulverize after a baking process and you may make it a desired particle size. Moreover, you may dry between the filtration process in a process 1 or the process 2, and a baking process. Drying is a process for removing moisture adhering to the material, and it may be performed for about 1 to 10 hours within a range of 100 to 150 ° C., and is also effective under reduced pressure conditions. Since this treatment modifies only the surface of the positive electrode active material, the composition and resistance of the positive electrode active material itself are not substantially changed before and after the specific treatment of the present invention, or only slight changes. Does not occur.

  The positive electrode active material may be any material that is generally used as a material capable of inserting and extracting lithium ions.

As the positive electrode active material, the layered compound Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, At least one element selected from Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 2.1) and Li ₂ MnO ₃ . In addition, you may employ | adopt any of the positive electrode active material described in detail with the following 2nd-5th positive electrode as a positive electrode active material surface-modified with the phosphate ion containing solution.

The high resistance metal compound may be a material having a higher resistance than the positive electrode active material. For example, as a positive electrode active material, a layered compound Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, at least one element, 1.7 ≦ When f ≦ 2.1) or Li ₂ MnO ₃ is employed, a silicate transition metal lithium salt and / or a phosphate transition metal lithium salt may be employed as the high resistance metal compound.

Examples of the silicate transition metal lithium salt include compounds represented by Li ₂ MSiO ₄ (M is one or more elements selected from transition elements). Specific examples of the lithium silicate transition metal lithium salt include, for example, Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , Li ₂ NiSiO ₄ , Li ₂ CoSiO ₄ , Li ₂ Fe _0.9 Co _0.1 SiO ₄ , Li ₂ Fe _{0. .75} Co _0.25 SiO ₄ , Li ₂ Fe _0.5 Co _0.5 SiO ₄ , and Li ₂ Fe _0.25 Co _0.75 SiO ₄ .

Examples of the phosphate transition metal lithium salt include compounds represented by LiMPO ₄ (M is one or more elements selected from transition elements). Specific examples of the transition metal phosphate lithium salt, for example, LiFePO ₄ having an olivine _{structure, LiMnPO 4, LiNiPO 4, LiCoPO} 4, LiVPO 4, LiMn 0.8 Fe 0.2 PO 4, LiMn 0.1 Fe 0. ₉ PO ₄ can be mentioned.

Although the lithium silicate transition metal lithium salt and the lithium phosphate transition metal lithium have lithium, the general formula of the layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb Compared with a lithium-containing composite oxide represented by at least one element selected from W, La and 1.7 ≦ f ≦ 2.1), the charge / discharge potential of lithium ions is low. Therefore, when both coexist on the positive electrode of a lithium ion secondary battery, the lithium silicate transition metal lithium salt and the phosphate transition metal lithium salt do not substantially function as an active material capable of occluding lithium ions and exist as high resistance compounds. It will be. Here, when an internal short circuit occurs in the lithium ion secondary battery, since a lithium silicate transition metal lithium salt and a phosphate transition metal lithium salt function as a high resistance compound, a significant current is generated between the positive electrode and the negative electrode. Can be suppressed.

  Note that the high resistance metal compound itself may act as the positive electrode active material.

The second positive electrode of the present invention has a general formula of a layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D Is at least one selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La Element, 1.7 ≦ f ≦ 2.1), and three consecutive high-angle scattering annular dark-field scanning transmission electrons obtained by observing the same 3b site of the layered rock salt structure from the <1-100> orientation When seven sets of intensity ratios obtained by dividing the minimum value of the integrated intensities of the microscopic image by the maximum value are calculated, the first superlattice structure portion in which the average value n of the seven sets of intensity ratios is less than 0.9 A positive electrode active material having a surface layer, and a high resistance metal compound having a higher resistance than the positive electrode active material. And butterflies.

The third positive electrode of the present invention has a general formula of a layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D Is at least one selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La Element, 1.7 ≦ f ≦ 2.1), and arbitrary three consecutive high-angle scattering annular dark field scans obtained by observing the same 3b site of the layered rock salt structure from the <1-100> orientation The integral intensities of the transmission electron microscope images are p1, p2, and q (0.9 × p1 ≦ p2 ≦ 1.1 × p1, q is p <0.9 × p2 when p1 ≦ p2, and p2 ≦ p1) A positive electrode active material having a second superlattice structure portion represented by q <0.9 × p1) in the surface layer, and the positive electrode active material A high-resistance metal compound having a higher resistance than the quality is included.

The fourth positive electrode of the present invention has a general formula of a layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D Is at least one selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La Positive electrode having a third superlattice structure portion, which is represented by the element 1.7 ≦ f ≦ 2.1) and satisfies both the conditions of the first superlattice structure portion and the conditions of the second superlattice structure portion in the surface layer It includes an active material and a high-resistance metal compound having a higher resistance than the positive electrode active material.

  Here, the said 1st superlattice structure part, 2nd superlattice structure part, and 3rd superlattice structure part which exist in a positive electrode active material surface layer are excellent in charging / discharging deterioration tolerance compared with the inside of an active material. Specifically, the first to third superlattice structures are structural stability when Li is extracted from the active material during charging of the lithium ion secondary battery, and corrosion resistance to the electrolyte for the lithium ion secondary battery. Excellent in properties. As a result, the stability of the active material surface layer directly in contact with the electrolyte in which Li enters and exits is relatively improved, and as a result, the deterioration of the active material is suppressed.

  In the general formulas of the positive electrode active materials in the second to fourth positive electrodes of the present invention, those satisfying 0 <b <1, 0 <c <1, 0 <d <1 are preferable, and at least any of b, c, and d It is preferable that one of the ranges is 0 <b <70/100, 0 <c <50/100, 10/100 <d <1, and 1/3 ≦ b ≦ 50/100, 20/100 ≦ c ≦ More preferably, the range is 1/3, 1/3 ≦ d <1, and b = 1/3, c = 1/3, d = 1/3, or b = 50/100, c = 20 / 100 and d = 30/100 are particularly preferred. About a, e, and f, what is necessary is just a numerical value within the range prescribed | regulated by a general formula, and a = 1, e = 0, and f = 2 can be illustrated.

The layered rock salt structure will be described.
General _{formula: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1,0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, At least one element selected from Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, and La (1.7 ≦ f ≦ 2.1) The crystal structure of the composite metal oxide represented is a rhombohedral system and has a three-fold axis and mirror surface with inversion symmetry, and is represented by a space group R-3m. In “R-3m”, “−3” represents 3 with an overline. Then, the layered rock salt structure of the composite metal oxide of the general formula has the 3a _{sites, Ni b Co c Mn d D} 3b site, _{O f} layers with _e (face) of the layer (surface) having a Li _a The 6c site of the layer (surface) is repeated in the order of 6c site, 3b site, 6c site, and 3a site. Here, the 3a site, 3b site, and 6c site are descriptions expressed in accordance with the Wyckoff symbol.

The first to third superlattice structures will be described.
The first superlattice structure portion includes the integrated intensity of three consecutive high-angle scattering annular dark-field scanning transmission electron microscope images obtained by observing the same 3b site of the layered rock salt structure from the <1-100> orientation. When seven sets of intensity ratios obtained by dividing the minimum value by the maximum value are calculated, this means a structure in which the average value n of the seven sets of intensity ratios is less than 0.9. In <1-100>, “−1” represents 1 with an overline. The <1-100> orientation is one of the overall representations of equivalent vectors among the vectors in which the direction in the crystal is represented by the Miller index. Here, specifically, in the 3b site surface of the layered rock salt structure One of the <1-100> orientations is an orientation inclined 30 ° to the right from the straight line connecting nickel, cobalt, and manganese in order from the bottom to the top in the crystal plane of the 3b site in FIG. . The average value n is not particularly limited as long as it is less than 0.9, but is preferably less than 0.86, more preferably less than 0.82, and still more preferably less than 0.80.

  The second superlattice structure unit is an integrated intensity of any continuous three high-angle scattering annular dark field scanning transmission electron microscope images obtained by observing the same 3b site of the layered rock salt structure from the <1-100> orientation. Are sequentially p1, p2, q (0.9 × p1 ≦ p2 ≦ 1.1 × p1, q is q <0.9 × p2 when p1 ≦ p2, and q <0. When p2 ≦ p1. It means the structure represented by 9 × p1). The p1, p2, and q are not particularly limited as long as they are within the above ranges. However, when p1 ≦ p2, q <0.85 × p2 is preferable, q <0.80 × p2 is more preferable, and q <0.75 Xp2 is more preferable. Similarly, when p2 ≦ p1, q <0.85 × p1 is preferable, q <0.80 × p1 is more preferable, and q <0.75 × p1 is more preferable.

Journal of The Electrochemical Society, 151 (10) A1545-A1551 (2004) describes a crystal plane Ni _1/3 composed of a 3b site of a layered rock salt structure in LiNi _1/3 Co _1/3 Mn _1/3 O ₂ . A Co _1/3 Mn _1/3 superlattice surface is disclosed. The superlattice surface of Ni _1/3 Co _1/3 Mn _1/3 can be expressed as [√3 × √3] R30 ° type in Wood's notation. FIG. 1 shows a schematic diagram of a superlattice plane of Ni _1/3 Co _1/3 Mn _1/3 expressed in the [√3 × √3] R30 ° type.

  In the following description, a superlattice surface that may exist before a specific treatment of the present invention is referred to as a “normal superlattice surface”.

  High angle scattering annular dark field scanning transmission electron microscopy is the so-called HAADF-STEM, where a thinly focused electron beam is applied to the sample while scanning, and the scattered electrons scattered at a high angle are detected by an annular detector. A method of displaying the integrated intensity of detected electrons.

  In the present invention, the crystal plane of the active material measured by high-angle scattering annular dark field scanning transmission electron microscopy is a metal layer containing Ni, Co, and Mn, and is a plane corresponding to the superlattice plane of the above document. .

[√3 × √3] R30 ° -type Ni _1/3 Co _1/3 Mn _1/3 normal superlattice surface in LiNi _1/3 Co _1/3 Mn _1/3 O ₂ with high angle scattering annular dark field The minimum of the integrated intensities of three consecutive high-angle scattering annular dark-field scanning transmission electron microscope images observed from the <1-100> orientation by scanning transmission electron microscopy and obtained from the same 3b site surface of the layered rock salt structure When seven sets of intensity ratios obtained by dividing the value by the maximum value are calculated, the average value n of the seven sets becomes 0.9 or more and less than 1. In addition, the normal superlattice surface is observed from the <1-100> orientation by high-angle scattering annular dark field scanning transmission electron microscopy, and any three consecutive high angles obtained from the same 3b site surface of the layered rock salt structure The integrated intensities of the scattered annular dark field scanning transmission electron microscope images are p1, p2, and p3 (0.9 × p1 ≦ p2 ≦ 1.1 × p1, 0.9 × p1 ≦ p3 ≦ 1.1 × p1,. 9 × p2 ≦ p3 ≦ 1.1 × p2). That is, in the normal superlattice plane of [√3 × √3] R30 ° type Ni _1/3 Co _1/3 Mn _1/3 in LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , layered rock salt There is no particular difference in the integrated intensity observed on the same 3b site surface of the structure. Therefore, the normal superlattice layer is clearly distinguished from the first to third superlattice structures of the present invention. In the first to third superlattice structures of the active material of the present invention, the intensity of the rear one of the three consecutive integrated intensities is smaller than the intensity of the previous two. In other words, the first to third superlattice structures of the active material of the present invention regularly disrupt the integrated intensity pattern obtained from the normal superlattice plane represented by the [√3 × √3] R30 ° type. It can be said that.

  “Having first to third superlattice structures in the active material surface layer” means that the first to third superlattice structures are present in the surface layer regardless of the amount. As long as the first to third superlattice structures are present in the surface layer of the active material, the stability of the active material inside is maintained more than the location where the first to third superlattice structures are present. The effect of maintaining is demonstrated. The first to third superlattice structures are preferably present in the entire surface layer of the active material from the viewpoint of maintaining capacity.

  The surface layer means a layer including the surface of the active material. The surface layer is preferably thicker from the viewpoint of the stability of the active material of the present invention, but there is no practical problem as long as the thickness is sufficient to prevent contact between the electrolyte and the active material. Considering the ease of progress of the Li charge / discharge reaction, it is preferable that the thickness of the surface layer is thin. The surface layer thickness t (nm) is, for example, 0 <t <20, preferably 0.01 <t <10, more preferably 0.1 <t <5, still more preferably 1 <t <3. 5 <t <2.5 is most preferred.

  The first to third superlattice structure portions may be scattered on the surface layer, or may exist as a layer of the first to third superlattice structure portions. The thickness s (nm) of the first to third superlattice structure portions is, for example, 0 <s <20, preferably 0.01 <s <10, more preferably 0.1 <s <5, and 1 < s <3 is more preferable, and 1.5 <s <2.5 is most preferable.

  The shape of the positive electrode active material in the second to fourth positive electrodes is not particularly limited, but is preferably 100 μm or less, more preferably 1 μm or more and 50 μm or less in terms of the average particle size of the secondary aggregate. When the thickness is less than 1 μm, there may be a problem that, when an electrode is manufactured using an active material, the adhesion to the current collector is easily impaired. If it exceeds 100 μm, the size of the electrode may be affected, or the separator constituting the secondary battery may be damaged. The average particle diameter may be measured with a general particle size distribution meter, or may be measured and calculated with a microscope.

The inside of the positive electrode active material in the second to fourth positive electrodes has a general formula: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1 , D is at least selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La There is no limitation as long as it is represented by 1 element, 1.7 ≦ f ≦ 2.1). The interior preferably has a normal superlattice surface of [√3 × √3] R30 ° type.

  The positive electrode active material in the 2nd-4th positive electrode of this invention can be manufactured through the process 1 or the process 2 demonstrated in the 1st positive electrode.

Considering the difference in the integrated intensity pattern observed between the first to third superlattice structures and the conventional normal superlattice surface, and the specific contents of the processing 1 or processing 2, the processing 1 or processing 2 will be described. It can be considered that a part of the metal in the [√3 × √3] R30 ° normal superlattice plane of the 3b site of the layered rock salt structure is specifically removed. For example, if it is considered that only Co is removed specifically in the NiCoMn at the 3b site in LiNi _1/3 Co _1/3 Mn _1/3 O _{2 having} a layered rock salt structure, the regular first to _third orders of the present invention are exceeded. Explain the integrated intensity of the lattice structure. It will be easier to understand if only Co is specifically removed in the schematic diagram of FIG. That is, by treatment with an aqueous solution of treatment 1 or process 2, layered rock-salt of the general _{formula: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1,0 ≦ e <1, D is selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La It is estimated that the specific metal was specifically removed from the surface layer of the material represented by at least one element, 1.7 ≦ f ≦ 2.1). Here, it is presumed that the crystal of the material is distorted by the removal of the specific metal. Next, it is presumed that the first to third superlattice structures having a stable crystal structure were generated by the interaction between the high temperature state and the stress on the surface layer caused by the crystal distortion in the firing step to be performed.

  The 3b site of the layered rock salt structure of the above general formula is advantageously composed of [√3 × √3] R30 ° type.

  Hereinafter, the [√3 × √3] R30 ° type of the 3b site of the layered rock salt structure of the general formula, the metal defect of the 3b site by the above specific treatment, and the relationship with the first to third superlattice structures of the present invention Discuss about. In order to facilitate understanding, it is assumed that the 3b site is composed of NiCoMn3 element.

As described in the above-mentioned document, when the 3b site of the layered rock salt structure is composed of Ni _1/3 Co _1/3 Mn _1/3 , the normal superlattice plane can be expressed as [√3 × √3] R30 ° type. It is as follows. Here, paying attention to the valence of Ni, Co, and Mn, these metals are present at the 3b site with stable valences of Ni ²⁺ , Co ³⁺ , and Mn ⁴⁺ , respectively. Each metal takes a regular [√3 × √3] R30 ° type corresponding to the valence in order to avoid localization of positive charges.

Next, the case where the 3b site of the layered rock salt structure is composed of Ni _5/10 Co _2/10 Mn _3/10 will be considered. Since the average valence of the 3b site needs to be “3 ⁺ ”, Ni, Co, and Mn cannot exist only with stable valences of Ni ²⁺ , Co ³⁺ , and Mn ⁴⁺ . Compared with Ni _1/3 Co _1/3 Mn _1/3 , Ni _5/10 Co _2/10 Mn _3/10 is Ni rich and Co poor, so part of Ni instead of the lack of Co ³⁺ Exists as Ni ³⁺ . In the schematic diagram of FIG. 1, it will be easier to understand if a part of Co is replaced with Ni. Therefore, even when the 3b site is composed of Ni _5/10 Co _2/10 Mn _3/10 , each metal has a regular [√3 × √ according to the valence in order to avoid localization of positive charges. 3] It can be said that it is advantageous to adopt the R30 ° type.

Similarly, for example, when the 3b site of the layered rock salt structure is Ni poor and Co rich compared to Ni _1/3 Co _1/3 Mn _1/3 , Co instead of Ni 2 ⁺ is insufficient. A part of it exists as Co ²⁺ . Further, for example, 3b site of the layered rock-salt _structure, compared with Ni _1/3 Co 1/3 _{Mn 1/3,} of Mn instead of ^{Ni 2+} to be insufficient when it becomes is Mn rich in Ni-poor one Part will be present as Mn ²⁺ . Therefore, even if the composition of the 3b site composed of the layered rock salt structure NiCoMn3 element is different from that of Ni _1/3 Co _1/3 Mn _1/3 , each metal of the 3b site is localized in a positive charge. In order to avoid this, it is considered advantageous to adopt a regular [√3 × √3] R30 ° type according to the valence.

  Then, since the specific metal at the 3b site is selectively removed by the treatment 1 or the treatment 2, regular metal defects are generated at the 3b site. The first to third superlattice structures of the present invention represent regular metal defects from the 3b site of the normal superlattice surface. In the specific treatment of the present invention, among NiCoMn3 elements, Co is most easily removed and Mn is hardly removed.

According to the above consideration, the general formula of the layered rock salt type subjected to the treatment 1 or the treatment 2: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La In the surface layer of the material represented by at least one element selected from: 1.7 ≦ f ≦ 2.1), the 3b site is b = 1/3, c = 1/3, d = 1/3, e = It is considered that the first to third superlattice structures of the present invention can be produced not only in the case of being composed of 0 Ni _1/3 Co _1/3 Mn _1/3 but also in other cases.

  According to the above mechanism, the surface of the material before treatment 1 or treatment 2 preferably has a [√3 × √3] R30 ° type normal superlattice surface. However, even if the surface of the material before treatment 1 or treatment 2 does not usually have a superlattice surface, distortion of the crystal of the material and stress concentration near the surface of the material due to treatment 1 or treatment 2, and It can be presumed that exposure of the material under high temperature conditions can cause rearrangement of metal elements on the surface of the material, resulting in the first to third superlattice structures having a stable crystal structure. It can also be estimated that a [√3 × √3] R30 ° -type normal superlattice surface may be formed in the vicinity of the first to third superlattice structures thus generated.

The first to third superlattice structures are present on the surface layer of the positive electrode active material of the second to fourth positive electrodes. Even if the first to third superlattice structures are generated by removing the specific metal as described above, that is, the specific metal is removed, the surface layer of the second to fourth positive electrodes has a surface layer relative to the entire volume of the positive electrode active material. since the volume occupied by a slight, composition change occurring in the first to third superlattice structure has the general _{formula: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, The composition of at least one element selected from La, 1.7 ≦ f ≦ 2.1) is not substantially affected.

  The high resistance metal compounds in the second to fourth positive electrodes of the present invention are the same as those described for the first positive electrode.

The fifth positive electrode of the present invention has a general formula of a layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D Is at least one selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La Element, 1.7 ≦ f ≦ 2.1), including at least Ni, Co, and Mn, and the composition ratio of Ni, Co, and Mn is Ni: Co: Mn = b2: c2: d2 (where b2 + c2 + d2 = A positive electrode active material having a high manganese portion represented by 1, 0 <b2 <1, 0 <c2 <c, d <d2 <1) on a surface layer, and a high-resistance metal compound having a higher resistance than the positive electrode active material It is characterized by including.

  The following reason is presumed that the lithium ion secondary battery using the fifth positive electrode of the present invention exhibits an excellent capacity retention rate.

General formula of layered rock salt type: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, At least one element selected from Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 2 When the material represented by .1) is used as an active material for a lithium ion secondary battery, the transition metals Ni, Co, and Mn of the general formula are considered to have the following roles.

  It is most active during Ni: Li charge / discharge reaction. The capacity increases as the Ni content in the active material increases. On the other hand, the active material tends to deteriorate as the Ni content in the active material increases.

  Mn: Most inactive during Li charge / discharge reaction. The capacity decreases as the Mn content increases in the active material. On the other hand, the crystal structure of the active material is more stable as the Mn content increases in the active material.

  The activity during the Co: Li charge / discharge reaction is intermediate between Ni and Mn. The capacity and the degree of stability with respect to the content in the active material are also intermediate between Ni and Mn.

  Then, if the Mn composition ratio of the active material surface layer is higher than the Mn composition ratio inside the active material, the stability of the active material surface layer in direct contact with the electrolyte in which Li enters and exits is relatively improved. As a result, the deterioration of the active material is suppressed. In addition, since the change in the composition ratio of the active material surface layer is negligible when viewed as a whole of the active material, the decrease in activity during the Li charge / discharge reaction due to the increase in the Mn composition ratio of the active material surface layer is minimized. It can be.

  In the general formula of the positive electrode active material in the fifth positive electrode of the present invention, those satisfying 0 <b <1, 0 <c <1, 0 <d <1 are preferable, and at least one of b, c and d is It is preferable that the ranges are 0 <b <80/100, 0 <c <50/100, 10/100 <d <1, 1/3 ≦ b ≦ 50/100, 20/100 ≦ c ≦ 1/3. 1/3 ≦ d <1 is more preferable, and b = 1/3, c = 1/3, d = 1/3, or b = 50/100, c = 20/100, d. = 30/100 is particularly preferred. About a, e, and f, what is necessary is just a numerical value within the range of a general formula, and a = 1, e = 0, and f = 2 can be illustrated.

  The high manganese part will be described. The high manganese portion is a metal oxide containing at least Ni, Co, and Mn, and the composition ratio of Ni, Co, and Mn is Ni: Co: Mn = b2: c2: d2 (where b2 + c2 + d2 = 1, 0 <b2 <1, 0 <c2 <c, d <d2 <1).

  The values of b2, c2, and d2 are not limited as long as the above conditions are satisfied.

  b2 is more preferably in the range of 20/100 <b2 <70/100, and more preferably in the range of 25/100 <b2 <45/100. Further, b2 is preferably in the range of 0.5 × b <b2 <2 × b, more preferably in the range of 0.8 × b <b2 <1.4 × b, and 0.9 × b <b2 <1.1. The range of xb is more preferable.

  c2 is more preferably in the range of 5/100 <c2 <c, and more preferably in the range of 10/100 <c2 <25/100. Further, c2 is preferably in the range of 0.2 × c <c2 <0.9 × c, more preferably in the range of 0.5 × c <c2 <0.8 × c, and 0.6 × c <c2 <. A range of 0.7 × c is more preferable.

  d2 is more preferably in the range of 35/100 <d2 <85/100, and further preferably in the range of 45/100 <d2 <75/100. D2 is preferably in the range of 1.1 × d <d2 <85/100, more preferably in the range of 1.2 × d <d2 <75/100, and 1.3 × d <d2 <65/100. A range is more preferred.

  “Having a high manganese part in the surface layer” means that the high manganese part exists in the surface layer regardless of the amount. As long as the high manganese portion exists in the surface layer of the active material, the stability of the active material inside is maintained at least as compared with the location where the high manganese portion exists, and as a result, the effect of maintaining the capacity is exhibited. The high manganese part is preferably present in the entire surface layer of the active material from the viewpoint of maintaining the capacity.

  The surface layer means a layer including the surface of the positive electrode active material. The surface layer is preferably thicker from the viewpoint of the stability of the positive electrode active material, but there is no practical problem as long as the thickness is sufficient to prevent contact between the electrolyte and the active material. Considering the ease of progress of the Li charge / discharge reaction, it is preferable that the thickness of the surface layer is thin. The surface layer thickness t (nm) is, for example, 0 <t <20, preferably 0.01 <t <10, more preferably 0.1 <t <5, still more preferably 1 <t <3. 5 <t <2.5 is most preferred.

  The high manganese part may be scattered on the surface layer or may exist as a layer of the high manganese part. The thickness s (nm) of the layer of the high manganese portion is, for example, 0 <s <20, preferably 0.01 <s <10, more preferably 0.1 <s <5, and further 1 <s <3. Preferably, 1.5 <s <2.5 is most preferable.

  Moreover, it is preferable that the high manganese part exists in the active material center direction from the surface of a positive electrode active material, and exists in the range of at least 2 nm.

The high manganese part exists in the surface layer of the positive electrode active material. Then, as compared with the overall volume of the active material of the present invention, the volume occupied by the surface layer slightly, the composition of the high manganese portions general _{formula: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge , V, Mo, Nb, W, La at least one element, 1.7 ≦ f ≦ 2.1) is not substantially affected.

  The shape of the positive electrode active material in the fifth positive electrode is not particularly limited, but is preferably 100 μm or less, and more preferably 1 μm or more and 50 μm or less in terms of the average particle size of the secondary aggregate. When the thickness is less than 1 μm, there may be a problem that, when an electrode is manufactured using an active material, the adhesion to the current collector is easily impaired. If it exceeds 100 μm, the size of the electrode may be affected, or the separator constituting the secondary battery may be damaged. The average particle diameter may be measured with a general particle size distribution meter, or may be measured and calculated with a microscope.

  The positive electrode active material in the fifth positive electrode of the present invention can be produced by the following treatment 3 or treatment 4.

Process 3: Prepare the aqueous solution of magnesium nitrate, layered rock-salt of the general _{formula: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1,0 ≦ e <1, D is at least one selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, and La And the material represented by 1.7 ≦ f ≦ 2.1) is added and stirred. Next, an aqueous diammonium hydrogen phosphate solution is added to the aqueous solution and stirred. The active material whose surface layer composition ratio is modified to be rich in Mn is isolated by filtration.

Process 4: An aqueous solution containing diammonium hydrogen phosphate or an aqueous solution containing magnesium nitrate and diammonium hydrogen phosphate is prepared, and a layered rock salt type general formula: Li _a Ni _b Co _c Mn _{d De} O _f ( 0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, At least one element selected from P, Ga, Ge, V, Mo, Nb, W, and La, and a material represented by 1.7 ≦ f ≦ 2.1) are added and stirred. The active material whose surface layer composition ratio is modified to be rich in Mn is isolated by filtration.

  The concentration of the magnesium nitrate aqueous solution, the diammonium hydrogen phosphate aqueous solution, and the aqueous solution containing magnesium nitrate and diammonium hydrogen phosphate used in the treatment 3 or the treatment 4 are not particularly limited. The thing in the range of -2 mass% is preferable. What is necessary is just to set the stirring time in the process 3 or the process 4 suitably.

  After the treatment 3 or the treatment 4, the active material in which the composition ratio of the surface layer is modified to be rich in Mn may be dried and / or fired. Drying is a process for removing water adhering to the active material, and it may be performed within a range of 100 to 150 ° C. for about 1 to 10 hours, and it is also effective to perform under reduced pressure conditions. Firing is a process for adjusting the crystallinity of the active material, and it may be performed within a range of 500 to 1000 ° C. for about 1 to 10 hours. You may grind | pulverize after a baking process and you may make it a desired particle size. Note that the drying step and the firing step do not particularly affect the composition ratio of the active material.

  The formation of the high manganese part can be confirmed by measuring the surface of the treated positive electrode active material by X-ray photoelectron spectroscopy and performing composition analysis. The thickness of the surface layer containing the high manganese part is determined by, for example, observing the cut surface obtained by cutting the active material with a transmission electron microscope, or TEM-EDX combining a transmission electron microscope and a dispersion X-ray analyzer. It can be confirmed by measuring with and analyzing the composition. Moreover, composition ratios other than the surface layer in an active material can be confirmed by measuring the cut surface which cut | disconnected the active material, for example with TEM-EDX which combined the transmission electron microscope and the dispersion | distribution X-ray analyzer.

  As is clear from treatment 3 or treatment 4, the composition ratio of the active material surface layer is modified to be Mn rich in the positive electrode active material, although Mn is not added in the above treatment. Therefore, the technique of the present invention is completely different from the technique of simply adding Mn or a Mn-containing compound to the active material and adhering it to or near the active material surface.

By performing the treatment 3 or the treatment 4, the Mn composition ratio of the surface layer of the positive electrode active material is increased, but the Co composition ratio is lowered. The Ni composition ratio may be high or low. And in view of the fact that the Mn composition ratio of the active material surface layer is high and the Co composition ratio is low, despite the fact that Mn is not added in the treatment 3 or the treatment 4, the above treatment gives the general formula: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S , Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, and La, represented by 1.7 ≦ f ≦ 2.1) It can be estimated that Co on the surface layer of the material was eluted in the aqueous solution (in some cases Ni was also eluted in the aqueous solution), and as a result, a change in the surface layer composition ratio occurred. The elution with respect to the aqueous solution seems to be in the order of Co, Ni, and Mn.

If so, high manganese unit has the general _{formula: Li a3 Ni b3 Co c3 Mn} d3 D e3 O f3 (0.2 ≦ a3 ≦ 1.2,0 <b3 + c3 + d3 + e3 <1,0 <b3 ≦ b, 0 <c3 <c, 0 <d3 ≦ d, 0 ≦ e3 <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, It can also be represented by at least one element selected from Ga, Ge, V, Mo, Nb, W, and La (1.7 ≦ f3 ≦ 2.1).

  The high resistance metal compound in the fifth positive electrode of the present invention is the same as that described for the first positive electrode.

  The first to fifth positive electrodes of the present invention include each positive electrode active material and a high resistance metal compound having higher resistance than the positive electrode active material. The compounding ratio of each positive electrode active material and the high resistance metal compound in the first to fifth positive electrodes of the present invention is not particularly limited. A preferable blending ratio of each positive electrode active material and the high resistance metal compound is preferably 0.1: 1 to 10: 1, more preferably 0.5: 1 to 5: 1, and more preferably 1: 1 to 3: 1. 1 is particularly preferred. During normal operation of the secondary battery, the high-resistance metal compound simply becomes a high-resistance compound, and therefore it is not preferable to exist in an excessive amount in the positive electrode. Moreover, when there is too little quantity of a high resistance metal compound, since resistance of a positive electrode will become low and it cannot suppress that an excessive electric current arises at the time of an internal short circuit of a battery, it is unpreferable.

  Here, it is known that a difference occurs between the initial charge capacity and the initial discharge capacity in the secondary battery, and this difference in capacity is generally called the irreversible capacity of the negative electrode active material. For example, in the case of a lithium ion secondary battery, lithium ions contained in the positive electrode active material of the positive electrode are irreversibly incorporated into the negative electrode active material, and the lithium ions incorporated irreversibly function as a charge carrier. It means not. In consideration of this, each positive electrode of the present invention has a high resistance metal compound such that the total amount of metal ions such as lithium contained in the high resistance metal compound corresponds to the irreversible capacity of the negative electrode active material. It is preferable to mix | blend. Note that the irreversible capacity of the negative electrode active material is a capacity calculated by subtracting the initial discharge capacity from the initial charge capacity of the secondary battery, so that those skilled in the art can easily calculate by a simple experiment. .

  Moreover, in the 1st-5th positive electrode of this invention, each positive electrode active material and a high resistance metal compound may exist in the same layer, and may exist in a separate layer. Hereinafter, a layer including each positive electrode active material is referred to as a positive electrode active material layer, a layer including a high resistance metal compound is referred to as a high resistance metal compound layer, and a layer including each positive electrode active material and the high resistance metal compound is referred to as a composite layer. There is a case.

  The positive electrode usually comprises a current collector, which is a chemically inert electronic high conductor for keeping current flowing through the electrode during discharge or charging of the secondary battery.

  The current collector of the positive electrode is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. For example, silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, Examples thereof include at least one selected from tin, indium, titanium, ruthenium, tantalum, chromium, and molybdenum, and metal materials such as stainless steel. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

  You may add a binder and / or a conductive support agent to a positive electrode active material layer, a high resistance metal compound layer, or a composite material layer as needed.

  The binder serves to bind the active material, the high-resistance metal compound, and the conductive additive to the surface of the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. be able to.

  Moreover, you may employ | adopt the polymer which has a hydrophilic group as a binder. Examples of the hydrophilic group of the polymer having a hydrophilic group include a phosphate group such as a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group, and a phosphate group. Among them, a polymer containing a carboxyl group in the molecule such as polyacrylic acid, carboxymethyl cellulose, and polymethacrylic acid, or a polymer containing a sulfo group such as poly (p-styrenesulfonic acid) is preferable. A polymer containing many carboxyl groups and / or sulfo groups such as polyacrylic acid or a copolymer of acrylic acid and vinyl sulfonic acid becomes water-soluble. Therefore, the polymer having a hydrophilic group is preferably a water-soluble polymer, and a polymer containing a plurality of carboxyl groups and / or sulfo groups in one molecule is preferable.

  A polymer containing a carboxyl group in the molecule can be produced by, for example, a method of polymerizing an acid monomer or adding a carboxyl group to the polymer. Acid monomers include acrylic acid, methacrylic acid, vinyl benzoic acid, crotonic acid, pentenoic acid, angelic acid, tiglic acid, etc., acid monomers having one carboxyl group in the molecule, itaconic acid, mesaconic acid, citraconic acid, fumaric acid Examples include maleic acid, 2-pentenedioic acid, methylene succinic acid, allyl malonic acid, isopropylidene succinic acid, 2,4-hexadiene diacid, acetylenedicarboxylic acid, and other acid monomers having two or more carboxyl groups in the molecule. Is done. A copolymer obtained by polymerizing two or more kinds of monomers selected from these may be used.

  For example, it is made of a copolymer of acrylic acid and itaconic acid, as described in JP2013-065493A, and contains an acid anhydride group formed by condensation of carboxyl groups in the molecule. It is also preferable to use a polymer as a binder. The structure derived from a highly acidic monomer having two or more carboxyl groups in one molecule is considered to facilitate trapping of lithium ions and the like before the electrolytic solution decomposition reaction occurs during charging. Furthermore, the acidity is not excessively increased because there are more carboxyl groups and the acidity is higher than polyacrylic acid and polymethacrylic acid, and a predetermined amount of the carboxyl groups are changed to acid anhydride groups.

  The blending ratio of the binder in the positive electrode active material layer is preferably a mass ratio of active material: binder = 1: 0.005 to 1: 0.3. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered. The blending ratio of the binder of the high resistance metal compound layer is preferably a mass ratio of high resistance metal compound: binder = 1: 0.005 to 1: 0.3. The blending ratio of the binder in the composite layer is preferably (active material + high resistance metal compound): binder = 1: 0.005 to 1: 0.3 in mass ratio.

  The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (Vapor Grown Carbon). Fiber: VGCF) and various metal particles are exemplified. These conductive assistants can be added to the active material layer alone or in combination of two or more.

  The blending ratio of the conductive additive in the positive electrode active material layer is preferably a mass ratio of active material: conductive additive = 1: 0.01 to 1: 0.5. This is because if the amount of the conductive auxiliary is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary is too large, the moldability of the active material layer is deteriorated and the energy density of the electrode is lowered. The blending ratio of the conductive assistant in the high resistance metal compound layer is preferably a mass ratio of high resistance metal compound: conductive assistant = 1: 0.01 to 1: 0.5. The blending ratio of the conductive assistant in the composite layer is preferably (active material + high resistance metal compound): conductive assistant = 1: 0.01 to 1: 0.5 in terms of mass ratio.

  In order to form each layer on the surface of the current collector, a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used. An active material or the like may be applied to the surface. Specifically, a composition for forming a layer containing a positive electrode active material and / or a high-resistance metal compound and, if necessary, a binder and a conductive additive is prepared, and an appropriate solvent is added to the composition to form a paste. Then, after applying to the surface of the current collector, it is dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.

  In the first to fifth positive electrodes of the present invention, a positive electrode active material layer may be formed on a current collector, and a high resistance metal compound layer may be formed thereon, or a high resistance metal may be formed on the current collector. A compound layer may be formed, and a positive electrode active material layer may be formed thereon, or a mixture layer may be formed on a current collector. In addition, the first to fifth positive electrodes of the present invention may be formed by appropriately stacking a positive electrode active material layer, a high resistance metal compound layer, or a composite material layer.

  In addition, you may add a well-known active material to the positive electrode active material layer or a composite material layer within the range which does not deviate from the meaning of this invention.

  A lithium ion secondary battery can be manufactured using the first to fifth positive electrodes of the present invention. The lithium ion secondary battery includes a negative electrode and an electrolyte in addition to each positive electrode of the present invention as a battery component.

  The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. The current collector described in the positive electrode may be adopted.

As the negative electrode active material, a material capable of inserting and extracting lithium ions can be used. Accordingly, there is no particular limitation as long as it is a simple substance, alloy, or compound that can occlude and release lithium ions. For example, as a negative electrode active material, Li, group 14 elements such as carbon, silicon, germanium and tin, group 13 elements such as aluminum and indium, group 12 elements such as zinc and cadmium, group 15 elements such as antimony and bismuth, magnesium , Alkaline earth metals such as calcium, and group 11 elements such as silver and gold may be employed alone. When silicon or the like is used for the negative electrode active material, a silicon atom reacts with a plurality of lithiums, so that it becomes a high-capacity active material. However, there is a problem that volume expansion and contraction due to insertion and extraction of lithium becomes significant. In order to reduce the fear, it is also preferable to employ an alloy or compound in which another element such as a transition metal is combined with a simple substance such as silicon as the negative electrode active material. Specific examples of the alloy or compound include tin-based materials such as Ag-Sn alloy, Cu-Sn alloy, Co-Sn alloy, carbon-based materials such as various graphites, SiO _x (disproportionated to silicon simple substance and silicon dioxide). Examples thereof include silicon-based materials such as 0.3 ≦ x ≦ 1.6), silicon alone, or composites obtained by combining silicon-based materials and carbon-based materials. Further, the anode active _{material, Li 2 Ti 3 O 7,} Li 4 Ti 5 lithium titanate, such as _{O 12, Nb 2 O 5,} TiO 2, WO 2, MoO 2, Fe 2 O 3, SnB 0.4 An oxide such as P _0.6 O _3.1 and SnSiO ₃ or a nitride represented by Li _3−x M _x N (M═Co, Ni, Cu) may be employed. One or more of these materials can be employed as the negative electrode active material.

  The negative electrode active material layer includes a negative electrode active material and, if necessary, a binder and / or a conductive aid. What is necessary is just to use a binder and a conductive support agent with the mixing | blending similar to what was demonstrated with the positive electrode what was demonstrated with the positive electrode.

  In order to form the negative electrode active material layer on the surface of the current collector, a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used. Each active material may be applied to the surface of the electric body. Specifically, an active material layer-forming composition containing an active material and, if necessary, a binder and a conductive aid is prepared, and an appropriate solvent is added to the composition to make a paste, and then the collection is performed. After applying to the surface of the electric body, it is dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.

  The electrolytic solution includes a solvent and an electrolyte dissolved in the solvent.

  Examples of the solvent used in the electrolytic solution include non-aqueous solvents such as cyclic esters, chain esters, ethers, and fluorine-containing cyclic esters. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. Fluorine-containing cyclic esters are those in which a part of hydrogen constituting the cyclic ester is substituted with fluorine, and fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, trifluoropropylene carbonate Can be illustrated. A plurality of the above-described solvents may be used in combination as the solvent for the electrolytic solution. In particular, it is preferable to use three types of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate in combination.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , (CF ₃ SO ₂ ) ₂ NLi, and (FSO ₂ ) ₂ NLi. The concentration of the electrolyte in the electrolytic solution is preferably in the range of 0.5 to 1.7 mol / L.

  A separator is used in the lithium ion secondary battery as necessary. The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes. As separators, natural resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polymer), polyester, polyacrylonitrile and other polysaccharides, cellulose, amylose and other polysaccharides, fibroin, keratin, lignin and suberin Examples thereof include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as polymers and ceramics. The separator may have a multilayer structure.

  The thickness of the separator is not particularly limited, but is preferably in the range of 5 μm to 100 μm, more preferably in the range of 10 μm to 50 μm, and particularly preferably in the range of 15 μm to 30 μm.

  An example of the manufacturing method of a lithium ion secondary battery is shown. A separator is sandwiched between the positive electrode and the negative electrode as necessary to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside using a current collecting lead or the like, an electrolytic solution is added to the electrode body to form a lithium ion secondary battery. It is good to do. Moreover, the lithium ion secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.

  The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The lithium ion secondary battery using the first to fifth positive electrodes of the present invention exhibits a suitable capacity maintenance rate because the active material surface layer is stable and the active material is unlikely to deteriorate. As a result, the lithium ion secondary battery using the first to fifth positive electrodes of the present invention can exhibit a good capacity retention rate even under high potential driving conditions. Therefore, the lithium ion secondary battery using the first to fifth positive electrodes of the present invention maintains a large charge / discharge capacity and has excellent cycle performance. Here, the high potential driving condition means that the operating potential of lithium ions with respect to lithium metal is 4.3 V or higher, and further 4.5 V to 5.5 V. In the lithium ion secondary battery using each positive electrode of the present invention, the charging potential of the positive electrode can be set to 4.3 V or more, and further, 4.5 V to 5.5 V on the basis of lithium. Note that, under the driving conditions of a general lithium ion secondary battery, the operating potential of lithium ions with respect to lithium metal is less than 4.3V.

  The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or a part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with lithium ion secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office devices, and industrial devices in addition to vehicles. Furthermore, the lithium ion secondary battery of the present invention is a wind power generation, solar power generation, hydroelectric power generation and other power system power storage device and power smoothing device, power of ships and / or power supply sources of auxiliary equipment, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

  As mentioned above, although embodiment of the electrolyte solution of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples, Production Examples, Reference Examples, Reference Comparative Examples, and Evaluation Examples. In addition, this invention is not limited by these Examples. In the following, unless otherwise specified, “part” means part by mass, and “%” means mass%.

(Production Example 1)
The following treatment was performed on the lithium composite metal oxide as a starting material.
A lithium composite metal oxide represented by LiNi _1/3 Co _1/3 Mn _1/3 O ₂ prepared by a coprecipitation method was prepared. An aqueous solution for surface modification containing 4.0% by mass of (NH ₄ ) ₂ HPO ₄ and 5.8% by mass of Mg (NO ₃ ) ₂ when the total aqueous solution was 100% by mass was prepared. The lithium composite metal oxide was immersed in an aqueous solution for surface modification and stirred and mixed at room temperature. The immersion time was 1 hour.

  Filtration was performed after immersion, and then the surface-modified lithium composite metal oxide was dried at 130 ° C. for 6 hours. Thereafter, the obtained lithium composite metal oxide was heated at 700 ° C. in an air atmosphere for 5 hours. The product obtained by these treatments was used as the active material of Production Example 1.

(Production Example 2)
The active material of Production Example 2 was produced in the same manner as in Production Example 1, except that the time for immersing the lithium composite metal oxide in the aqueous solution for surface modification was changed to 36 hours.

(Production Example 3)
The surface modification aqueous solution was changed to one containing 2.1% by mass of (NH ₄ ) ₂ HPO ₄ and 3.0% by mass of Mg (NO ₃ ) ₂ when the total aqueous solution was 100% by mass. Produced the active material of Production Example 3 in the same manner as Production Example 1.

(Production Example 4)
The surface modification aqueous solution was manufactured in the same manner as in Production Example 1, except that the aqueous solution for surface modification was changed to one containing 5.4% by mass of (NH ₄ ) ₂ HPO ₄ when the total aqueous solution was 100% by mass. 4 active materials were produced.

(Production Example 5)
The active material of Production Example 5 was produced in the same manner as Production Example 1 except that a lithium composite metal oxide represented by LiNi _5/10 Co _2/10 Mn _3/10 O ₂ was used.

(Evaluation example 1)
The surface layer of the active material of Production Example 1 was measured at an acceleration voltage of 200 kV while performing spherical aberration correction using a high-angle scattering annular dark field scanning transmission electron microscope: JEM-ARM200F (JEOL: manufactured by JEOL Ltd.). .

  FIG. 2 shows the first to third superlattice structures of the present invention obtained by observing the 3b site of the layered rock salt structure of the active material from the <1-100> orientation by high-angle scattering annular dark field scanning transmission electron microscopy. The image applicable to a part is shown. The length of the long side of the rectangular parallelepiped in the lower left of FIG. 2 is 1 nm.

As a comparison, FIG. 3 shows a comparison of the normal superlattice plane obtained by observing the 3b site of the commercially available layered rock salt structure LiNi _1/3 Co _1/3 Mn _1/3 O ₂ itself from the <1-100> orientation. Show the image. The length of the long side of the rectangular parallelepiped in the lower left of FIG. 3 is 1 nm.

  When the images in FIGS. 2 and 3 are observed, an image with the same intensity is regularly observed in FIG. 3, whereas in FIG. 2, an image with a set of “bright and dark” intensities is a period. Observed.

  FIG. 4 shows a phase having a crystal structure including the first to third superlattice structures according to the present invention obtained by observing the 3b site of the layered rock salt structure of the active material from the <1-100> orientation and the normal superstructure. An image near the interface with a phase having a crystal structure including a lattice plane is shown.

  5 and FIG. The integrated intensity data of the image of the 3b site shown by 1-7 is shown. 4 and FIG. 1 to 7 are attached for the sake of convenience. 1 does not mean the outermost surface of the active material.

  The numerical values in FIG. 1, 1004416 is an integrated intensity that appears at a location a for convenience. It means the integrated intensity that is continuous in the order of a, b, and c. The numerical value described in the lower column of the integrated intensity, for example, 0.822 in the lower column of the integrated intensity of c is an intensity ratio obtained by dividing the minimum value of the three consecutive integrated intensity a, b, c by the maximum value. . 0.813 in the lower column of the integrated intensity of d is an intensity ratio obtained by dividing the minimum value of the three consecutive integrated intensity b, c, d by the maximum value. The average value n in the right column of the table is an average value of seven sets of the intensity ratio.

  In FIG. 5, the first superlattice structure portion is No. 1 in which the average value n satisfies less than 0.9. 1 to 4.

Further, in FIG. 1, a, b, c, No. 1 2 b, c, d, No. 2 3 d, e, f, No. 3 4 c, d, and e satisfy the conditions of the second superlattice structure of the present invention.
Therefore, the active material of Production Example 1 is No. 1 in FIG. 1-4 have first to third superlattice structures.

(Evaluation example 2)
The surfaces of the active materials in Production Examples 1 to 4 were measured by X-ray photoelectron spectroscopy, and the Ni, Co, and Mn composition ratios of the surface layer of the active material were calculated. As a control, the surface of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ itself was measured by X-ray photoelectron spectroscopy, and the Ni, Co, and Mn composition ratio of the surface layer was calculated. The results are shown in Table 1.

  It was confirmed by analyzing the internal composition from the particle cross-sectional direction with TEM-EDX that the internal composition ratio of the active material was not changed. At this time, Mg and P signals obtained from the surface layer and the inside of the active material were below the detection limit of the TEM-EDX analysis. In other words, the surface layer of the active material obtained in the treatments 1 to 4 is not modified by the compound added in the treatments 1 to 4 but the composition of the elements contained in the active material is changed in advance. It can be said that it was modified by.

  When each production example and the control are compared with respect to the Ni, Co, and Mn composition ratio of the surface layer of the active material, the Mn composition ratio is high in each production example, whereas the Co composition ratio is low. I understand.

Example 1
The positive electrode of the present invention was prepared as follows.
An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. 94 parts by mass of the active material of Production Example 5, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride (PVDF) as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The slurry was placed on the surface of the aluminum foil, and applied using a doctor blade so that the slurry became a film. The aluminum foil coated with the slurry was dried at 80 ° C. for 20 minutes, whereby NMP was removed by volatilization, and a positive electrode active material layer was formed on the aluminum foil surface. The mass per square centimeter of the positive electrode active material layer was 18 mg. 90 parts by mass of LiFePO ₄ as a high resistance metal compound, 5 parts by mass of acetylene black as a conductive auxiliary agent, and 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. The slurry was placed on the positive electrode active material layer, and applied using a doctor blade so that the slurry became a film. The aluminum foil coated with the slurry was dried at 80 ° C. for 20 minutes to remove NMP by volatilization, thereby forming a high resistance metal compound layer on the positive electrode active material layer on the aluminum foil. The mass per square centimeter of the high resistance metal compound layer was 9 mg. The aluminum foil on which the high-resistance metal compound layer and the positive electrode active material layer were formed was compressed using a roll press machine, and the aluminum foil and each layer were firmly bonded. The joined product was heated with a vacuum dryer at 120 ° C. for 6 hours, cut into a predetermined shape (rectangular shape of 25 mm × 30 mm), and the positive electrode of Example 1 was obtained.

(Comparative Example 1)
A positive electrode of Comparative Example 1 was obtained in the same manner as in Example 1, except that LiNi _5/10 Co _2/10 Mn _3/10 O ₂ itself that was not surface-modified was used as the positive electrode active material.

(Comparative Example 2)
A positive electrode of Comparative Example 2 was obtained in the same manner as in Example 1 except that the mass per square centimeter of the positive electrode active material layer was 25 mg and that the high resistance metal compound layer was not formed.

(Example 2)
The lithium ion secondary battery of the present invention was prepared as follows.
The positive electrode used in Example 1 was used.
The negative electrode was produced as follows.

Carbon-coated SiO _x (0.3 ≦ x ≦ 1.6) 32 parts by mass, graphite 50 parts by mass, acetylene black (AB) 8 parts by mass as a conductive additive, and polyamide imide (PAI) 10 parts by mass as a binder And the mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. This slurry was applied to a copper foil having a thickness of 20 μm as a negative electrode current collector so as to form a film using a doctor blade, and the current collector coated with the slurry was dried and pressed. Heated with a vacuum dryer for a time, cut into a predetermined shape (rectangular shape of 25 mm × 30 mm), and made a negative electrode having a thickness of about 85 μm.

A laminate type lithium ion secondary battery was manufactured using the positive electrode and the negative electrode. Specifically, a rectangular sheet (27 × 32 mm, thickness 25 μm) made of a resin film having a three-layer structure of polypropylene / polyethylene / polypropylene was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. As the electrolytic solution, a solution in which LiPF ₆ was dissolved to 1 mol / L in a solvent in which ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed at a volume ratio of 3: 3: 4 was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. Note that the positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery.
Through the above steps, a laminate type lithium ion secondary battery of Example 2 was produced.

(Comparative Example 3)
A laminated lithium ion secondary battery of Comparative Example 3 was produced in the same manner as Example 2 except that the positive electrode of Comparative Example 1 was used.

(Comparative Example 4)
A laminated lithium ion secondary battery of Comparative Example 4 was produced in the same manner as Example 2 except that the positive electrode of Comparative Example 2 was used.

(Evaluation example 3)
The discharge capacity of the lithium ion secondary batteries of Example 2 and Comparative Examples 3 and 4 was measured by the following method, and the energy density was calculated. The results are shown in Table 2.

  Discharge when the battery to be measured is CCCV charged (constant current constant voltage charge) at 25 ° C., 0.33 C rate, voltage 4.5 V, and CC discharge (constant current discharge) is performed at 0.33 C rate The capacity was measured. The energy density was calculated by multiplying the discharge capacity and potential and dividing by the volume of the battery.

  The lithium ion secondary batteries of Example 2 and Comparative Examples 3 and 4 were subjected to the following nail penetration test, the surface temperature of the lithium ion secondary battery at the time of internal short circuit was measured, and the state of the battery was observed. The results are shown in Table 2.

  The lithium ion secondary battery was charged at a constant voltage until stabilized at a potential of 4.5V. The lithium ion secondary battery after charging was placed on a restraint plate having a hole with a diameter of 20 mm. A restraint plate was placed on a press machine with a nail attached to the top. Until the nail penetrates the lithium ion secondary battery on the restraining plate and the tip of the nail is located inside the hole of the restraining plate, the nail is 20 mm / sec. Moved at a speed of. The surface temperature of the battery after penetrating the nail was measured, and the state of the battery was observed at room temperature and atmospheric conditions. After the nail penetration, the surface temperature of each battery once increased and then gradually decreased. Table 2 shows the maximum temperature among the observed surface temperatures. The nail used had a diameter of 8 mm and a tip angle of 60 °, and the nail material was S45C defined by JIS G 4051.

In Table 2, when no smoke was generated from the battery, a mark was given, and when smoke was generated from the battery, a mark was marked.

  From the results in Table 2, thermal runaway of the internally short-circuited lithium ion secondary battery and the accompanying smoke generation are caused by the presence of both the surface-modified positive electrode active material and the high resistance metal compound even under high voltage driving. It turns out that it was suppressed.

(Reference Example 1)
The lithium ion secondary battery of Reference Example 1 was produced as follows.
The positive electrode was prepared as follows.

  An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. 94 parts by mass of the active material of Production Example 1, 3 parts by mass of acetylene black as a conductive auxiliary agent, and 3 parts by mass of polyvinylidene fluoride (PVDF) as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The slurry was placed on the surface of the aluminum foil, and applied using a doctor blade so that the slurry became a film. The aluminum foil coated with the slurry was dried at 80 ° C. for 20 minutes, thereby removing NMP by volatilization and forming an active material layer on the surface of the aluminum foil. The aluminum foil having the active material layer formed on the surface was compressed using a roll press machine, and the aluminum foil and the active material layer were firmly bonded. The joined product was heated with a vacuum dryer at 120 ° C. for 6 hours and cut into a predetermined shape (rectangular shape of 25 mm × 30 mm) to obtain a positive electrode.

The negative electrode was produced as follows.
97 parts by mass of graphite, 1 part by mass of KB as a conductive additive, 1 part by mass of styrene-butadiene rubber (SBR) and 1 part by mass of carboxymethyl cellulose (CMC) as a binder are mixed, and this mixture is subjected to an appropriate amount of ion exchange. A slurry was prepared by dispersing in water. This slurry was applied to a copper foil having a thickness of 20 μm as a negative electrode current collector so as to form a film using a doctor blade, and the current collector coated with the slurry was dried and pressed. Heated with a vacuum dryer for a time, cut into a predetermined shape (rectangular shape of 25 mm × 30 mm), and made a negative electrode having a thickness of about 85 μm.

A laminate type lithium ion secondary battery was manufactured using the positive electrode and the negative electrode. Specifically, a rectangular sheet (27 × 32 mm, thickness 25 μm) made of a resin film having a three-layer structure of polypropylene / polyethylene / polypropylene was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. As the electrolytic solution, a solution in which LiPF ₆ was dissolved at 1 mol / L in a solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 3: 7 (volume ratio) was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. Note that the positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery.
Through the above steps, the lithium ion secondary battery of Reference Example 1 was produced.

(Reference Example 2)
A lithium ion secondary battery of Reference Example 2 was produced in the same manner as Reference Example 1, except that the active material of Production Example 2 was used.

(Reference Example 3)
A lithium ion secondary battery of Reference Example 3 was produced in the same manner as Reference Example 1, except that the active material of Production Example 3 was used.

(Reference Example 4)
A lithium ion secondary battery of Reference Example 4 was produced in the same manner as Reference Example 1 except that the active material of Production Example 4 was used.

(Reference Comparative Example 1)
A laminated lithium ion secondary battery was produced in the same manner as in Reference Example 1 except that LiNi _1/3 Co _1/3 Mn _1/3 O ₂ itself was used as the active material.

(Evaluation example 4)
The initial capacities of the laminated lithium ion secondary batteries of Reference Examples 1 to 4 and Reference Comparative Example 1 were measured. CCCV charge (constant current constant voltage charge) at 25 ° C, 0.33C rate, voltage 4.5V, and CC discharge (constant current discharge) at voltage 3.0V, 0.33C rate. The discharge capacity when measured was measured and used as the initial capacity.

Furthermore, CCCV charge (constant current constant voltage charge) is performed at 55 ° C., 1C rate, voltage 4.5V, and after 2.5 hours, CC discharge (constant current discharge) is performed at voltage 3.0V, 0.33C rate. The 4.5V-3.0V charge / discharge cycle to be performed was performed 25 times on the battery to be measured, and then the discharge capacity at the 0.33C rate was measured to calculate the capacity retention rate.
The capacity retention rate (%) was obtained by the following formula.
Capacity maintenance rate (%) = capacity after cycle / initial capacity × 100
For example, the current rate for discharging in 1 hour is referred to as 1C.

  Table 3 shows the results of the composition ratio of Ni, Co and Mn on the surface layer of the active material, the initial capacity, the capacity after 25 cycles, and the capacity retention ratio.

  Comparing each reference example and the reference comparative example with respect to the capacity retention rate, it can be seen that the capacity retention rate is remarkably improved as compared with the reference comparative example in any reference example.

  From these results, it can be said that when the Mn composition ratio of the surface layer of the active material is made higher than the Mn composition ratio of the original (or internal) active material, the active material exhibits a good capacity retention rate.

Consideration is made by paying attention to the Mn composition ratio (d2).
Regarding the relationship between the Mn composition ratio (d2) and the capacity retention ratio in the reference example, Reference Example 2 in which d2 = 0.62, Reference Example 1 in which d2 = 0.47, d2 = Reference Example 3 is 0.38, and Reference Example 4 is d2 = 0.44. Here, the capacity retention rates of Reference Examples 1 and 2 are remarkably excellent. Therefore, it is presumed that there is a Mn composition ratio (d2) at which a suitable capacity retention ratio is obtained in the vicinity of the Mn composition ratio of 0.47 to 0.62.
Regarding the relationship between d2 and the initial capacity in the reference example, in order of increasing initial capacity, Reference Example 1 with d2 = 0.47, Reference Example 4 with d2 = 0.44, Reference Example 3 with d2 = 0.38, Reference example 2 in which d2 = 0.62 is obtained. Here, the initial capacity of Reference Example 1 is remarkably excellent. Therefore, it is presumed that there is a Mn composition ratio (d2) at which a suitable initial capacity can be obtained near d2 = 0.47.
Considering the capacity retention rate and the initial capacity together, it can be said that d2 is optimally around 0.47.

Consideration is made by paying attention to the Co composition ratio (c2).
Regarding the relationship between the Co composition ratio (c2) and the capacity retention ratio in the reference example, the reference example 2 in which c2 = 0.10, the reference example 1 in which c2 = 0.21, and the c2 = Reference Example 3 of 0.17 and Reference Example 4 of c2 = 0.25 are obtained. Here, the capacity retention rates of Reference Examples 1 and 2 are remarkably excellent. Therefore, it is presumed that there is a Co composition ratio (c2) at which a suitable capacity retention ratio is obtained near the Co composition ratio of 0.10 to 0.21.

Regarding the relationship between c2 and the initial capacity in the reference example, Reference Example 1 with c2 = 0.21, Reference Example 4 with c2 = 0.25, Reference Example 3 with c2 = 0.17 in descending order of initial capacity, Reference Example 2 in which c2 = 0.10 is obtained. Here, the initial capacity of Reference Example 1 is remarkably excellent. Therefore, it is presumed that there is a Co composition ratio (c2) in which a suitable initial capacity can be obtained near c2 = 0.21.
Considering the capacity retention rate and the initial capacity together, it can be said that c2 is optimally around 0.21.

Consideration is made by paying attention to the Ni composition ratio (b2).
As for the relationship between the Ni composition ratio (b2) and the capacity retention rate, the case where the ratio is higher than the Ni composition ratio (b) of the original active material (Reference Example 3) is also lower (Reference Example 1, Both 2 and 4) showed good capacity retention rates. Therefore, it can be said that the change in the Ni composition ratio does not particularly affect the capacity retention rate.

  Regarding the relationship between the Ni composition ratio (b2) and the initial capacity in the reference example, Reference Example 1 in which b2 = 0.32, Reference Example 4 in which b2 = 0.31, and b2 = 0.45 in descending order of initial capacity. Reference Example 3 in this example, and Reference Example 2 in which b2 = 0.28. Therefore, there is a Ni composition ratio (b2) at which a suitable initial capacity can be obtained in the vicinity of b2 = 0.32, or the Ni composition ratio (b2) is less changed from the original composition ratio (b). It is estimated to show a suitable initial capacity.

These test results show that Mn in the active material is most inactive during Li charge / discharge reaction, and the capacity decreases as the Mn content increases in the active material, but on the other hand, the Mn content in the active material increases. It is not inconsistent with the characteristic that it is excellent in stability. Therefore, the results shown in Reference example, not only the actually _LiNi 1/3 _Co 1/3 _Mn 1/3 _{O 2} was used, the general _{formula: Li a Ni b Co c Mn} d D e O f (0. 2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, It is considered to be valid over all materials represented by at least one element selected from Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 2.1).

  From the above results that the lithium ion secondary battery using the surface-modified active material showed a good capacity retention rate, it was confirmed that the secondary battery was excellent in cycle characteristics. It was also confirmed that the surface-modified active material can maintain its capacity even under a high potential driving condition of 4.5V. From the results and discussion of the reference examples and reference comparative examples, the relationship between the active material having a high manganese portion in the surface layer and the capacity retention rate in the lithium ion secondary battery using the same was clarified. That is, it is supported that the active material has a high manganese part in the surface layer, so that the capacity retention rate is suitably maintained, and further, the Ni, Co, and Mn composition ratio of the high manganese part exhibiting a more preferable capacity maintenance rate It became clear that can also be estimated. It was also revealed that the Ni, Co, and Mn composition ratios with suitable initial capacities can be estimated in the high manganese portion of the surface-modified active material.

  In addition, in the surface-modified active material, it can be said that the presence of the first to third superlattice structures improves the stability of the active material surface layer in direct contact with the electrolyte and suppresses the deterioration of the active material.

  1: positive electrode current collector, 2: positive electrode active material layer, 3: high resistance metal compound layer, 4: separator, 5: negative electrode active material layer, 6: negative electrode current collector, 7: lithium ion secondary battery

Claims (7)

General formula of layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, At least one element selected from Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 2 .1) and is the minimum of the integral intensities of three consecutive high-angle scattering annular dark field scanning transmission electron microscope images obtained by observing the same 3b site of the layered rock salt structure from the <1-100> orientation A positive electrode active material having a first superlattice structure portion on the surface layer, where an average value n of the seven strength ratios is less than 0.9 when seven strength ratios obtained by dividing the value by the maximum value are calculated; and A positive electrode comprising a high-resistance metal compound having a higher resistance than the positive electrode active material. General formula of layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, At least one element selected from Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 2 .1), and the integrated intensities of any three consecutive high-angle scattering annular dark-field scanning transmission electron microscope images obtained by observing the same 3b site of the layered rock salt structure from the <1-100> orientation are sequentially p1, p2, q (0.9 × p1 ≦ p2 ≦ 1.1 × p1, q is q <0.9 × p2 when p1 ≦ p2, and q <0.9 × when p2 ≦ p1 a positive electrode active material having a second superlattice structure portion represented by p1) as a surface layer, and a high resistance having higher resistance than the positive electrode active material A positive electrode comprising an antimetal compound. General formula of layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, At least one element selected from Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 2 .1) having a third superlattice structure portion on the surface layer that satisfies both the conditions of the first superlattice structure portion according to claim 1 and the second superlattice structure portion according to claim 2 A positive electrode comprising a positive electrode active material and a high-resistance metal compound having higher resistance than the positive electrode active material. General formula of layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, At least one element selected from Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 2 .1) and contains at least Ni, Co and Mn, and the composition ratio of Ni, Co and Mn is Ni: Co: Mn = b2: c2: d2 (where b2 + c2 + d2 = 1, 0 <b2 <1, 0 A positive electrode comprising: a positive electrode active material having a high manganese portion represented by <c2 <c, d <d2 <1) in a surface layer; and a high-resistance metal compound having a higher resistance than the positive electrode active material. The positive electrode according to any one of claims 1 to 4 , wherein the high-resistance metal compound is a lithium silicate transition metal lithium salt and / or a lithium phosphate transition metal lithium salt. The high resistance metal compound is Li ₂ MSiO ₄ (M is one or more elements selected from transition elements) and / or LiMPO ₄ (M is one or more elements selected from transition elements). The positive electrode according to any one of claims 1 to 5 . The lithium ion secondary battery provided with the positive electrode in any one of Claims 1-6 .