JP4540041B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery using a compound represented by the general formula Li _a Ni _x Co _y Al _z O ₂ as a positive electrode active material.

  With the rapid reduction in size and weight of electronic devices, there is an increasing demand for the development of secondary batteries that are small, lightweight, have high energy density, and can be repeatedly charged and discharged with respect to the battery that is the power source. In addition, due to environmental problems such as air pollution and an increase in carbon dioxide, early commercialization of electric vehicles is desired, and an excellent secondary battery having features such as high efficiency, high output, high energy density, and light weight. Development is desired.

  As a secondary battery that satisfies these requirements, a secondary battery using a non-aqueous electrolyte has been put into practical use. This battery has an energy density several times that of a battery using a conventional aqueous electrolyte. For example, lithium-containing layered cobalt oxide (hereinafter referred to as “Co-based compound”), lithium-containing layered nickel oxide (hereinafter referred to as “Ni-based compound”), or spinel type lithium as a positive electrode of a non-aqueous electrolyte secondary battery. A long-life 4V class non-aqueous electrolyte secondary battery using a manganese composite oxide (hereinafter referred to as “Mn compound”) and using a carbon material capable of occluding and releasing lithium in a negative electrode has been put into practical use.

Among these, Ni-based compounds have a lithium amount capable of insertion / extraction within a potential range (3.0 V to 4.3 V vs. Li / Li ⁺ ) actually used in a non-aqueous electrolyte secondary battery. Due to its advantages over Mn-based compounds and abundant resources, many development studies have been made with the aim of developing batteries with high capacity and low cost.

  For example, as shown in Patent Document 1 and Patent Document 2, by replacing a part of nickel with a different metal, cycle life performance, thermal stability, storage characteristics, and the like have been improved.

  As a positive electrode active material excellent in the balance of cycle life performance, thermal stability, storage characteristics, and discharge capacity, many compositions have been conventionally proposed in which nickel in a Ni-based compound is replaced with a different metal. However, even if a compound satisfying such a composition is synthesized and evaluated in a battery, good performance is not always obtained. Even if Ni-based compounds having the same composition are used, a compound production lot Depending on the case, the internal resistance is increased and the discharge capacity is decreased.

In Patent Document 3, a positive electrode active material is a composite oxide such as LiMn ₂ O ₄ or LiNiO ₂ or a lithium composite oxide obtained by substituting a part of Mn or Ni of these composite oxides with other elements. In the non-aqueous electrolyte secondary battery used in the above, a thin film made of a binder and a conductive carbon material is provided on the surface of the positive electrode in order to prevent an internal short circuit of the battery due to a temperature rise and to provide a battery with excellent safety. In the 1s core level spectrum of oxygen measured by XPS at a photoelectron take-off angle of 35 degrees or less from the surface of the positive electrode thin film, the peak intensity maximum value in the 530 ev to 535 eV region is the peak intensity in the 528 eV to 530 eV region. A technique for making the value larger than the maximum value is disclosed.

  However, the technique described in Patent Document 3 pays attention to the XPS peak derived from the thin film formed on the positive electrode, and does not describe any XPS peak on the surface of the positive electrode active material.

JP 05-325966 A Japanese Patent Laid-Open No. 08-213015 JP 2003-338277 A

  Even in the case of using a Ni-based compound having the same composition, which is found in a positive electrode active material in which nickel in the Ni-based compound is replaced with a different metal, there is a battery in which internal resistance increases and discharge capacity decreases depending on the production lot of the compound. The obtained result was a phenomenon that was not observed in batteries using Co-based compounds or Mn-based compounds, and was considered to be a problem peculiar to Ni-based batteries.

  As a result of examining in detail the difference in the physical properties of the compound depending on the production lot in order to solve this problem, the surface state of the compound may be different from the inside of the compound even if the composition of the Ni-based compound is the same in any lot. In other words, it was found that satisfactory battery performance could not be obtained when a compound in which such a surface state change occurred was used as the positive electrode active material.

  Therefore, the object of the present invention is to define the surface state of the Ni-based compound and to use the compound satisfying the specified condition as the positive electrode active material of the non-aqueous electrolyte secondary battery, so that the Ni-based compound is excellent in nature. The object is to stably provide a non-aqueous electrolyte secondary battery in which the characteristics are utilized.

In order to achieve the above-mentioned object, the invention according to claim 1 of the present invention has a general formula Li _a Ni _x Co _y Al _z O ₂ (0.3 ≦ a ≦ 1.05, 0.7 ≦ x ≦ 0). .87, 0.1 ≦ y ≦ 0.27, 0.02 ≦ z ≦ 0.1, 0.98 ≦ x + y + z ≦ 1.02), a nonaqueous electrolyte secondary battery using a positive electrode active material In the above compound surface, a peak having an apex between 528 eV and 531 eV of the oxygen 1s spectrum measured by X-ray photoelectron spectroscopy measured under the condition of 15 kV-15 mA with 0.8 ≦ a ≦ 1.05. The ratio (Ia / Ib) of the intensity (Ia) and the intensity (Ib) of a peak having a peak between 531 eV to 533 eV is 0.5 or more.

  According to the present invention, attention is paid to the surface state of the Ni-based compound, the state is qualitatively determined by the peak intensity ratio of the oxygen 1s spectrum obtained by X-ray photoelectron spectroscopy, and the compound whose peak intensity ratio is in the specified range is determined. By using it as a positive electrode active material for water electrolyte secondary batteries, there is no increase in internal resistance or reduction in discharge capacity resulting from changes in the state of the compound surface, and the original characteristics of Ni-based compounds with the composition shown in the general formula Can be stably obtained, a battery having a large discharge capacity and excellent cycle performance and storage performance can be provided. Industrial value is high by such an effect.

The average composition of the whole compound is represented by the general formula Li _a Ni _x Co _y Al _z O ₂ (0.3 ≦ a ≦ 1.05, 0.7 ≦ x ≦ 0.87, 0.1 ≦ y ≦ 0.27, 0 0.02 ≦ z ≦ 0.1, 0.98 ≦ x + y + z ≦ 1.02), a non-aqueous electrolyte secondary battery using a lithium-containing layered nickel oxide as a positive electrode active material has an internal resistance or In many cases, the discharge capacity varied.

  As a result of detailed investigation of this cause, the present inventor has found that Ni-based compounds are inherently difficult to synthesize compared to Co-based compounds and Mn-based compounds, and the average composition of the entire compound is the above general formula. Even in the specified range, the surface state of the compound often changes, and a non-aqueous electrolyte secondary battery using such a compound as a positive electrode active material has an interface between the positive electrode and the electrolyte. It was clarified that the resistance increased and the discharge capacity decreased. It was also clarified that the surface state of the compound was changed due to the starting material, firing conditions, handling method of the compound after firing, battery preparation method, and the like.

  Therefore, the present inventor has optimized the conditions such as the starting material, firing conditions, the method of handling the compound after firing and the battery preparation method, so that the surface state of the compound is almost the same as the inside of the compound, and the change of the surface state A non-aqueous electrolyte secondary battery having a long life and a high capacity can be obtained by using a Ni-based compound that falls within the specified range as a positive electrode active material by specifying the degree of the peak intensity ratio of the oxygen 1s spectrum by X-ray photoelectron spectroscopy. Succeeded in manufacturing stably.

  Hereinafter, specific embodiments of the nonaqueous electrolyte secondary battery according to the present invention will be described.

In the present invention, the average composition of the entire lithium-containing layered nickel oxide used as the positive electrode active material and the composition of the compound surface are expressed by the general formula Li _a Ni _x Co _y Al _z O ₂ (0.3 ≦ a ≦ 1.05, 0 0.7 ≦ x ≦ 0.87, 0.1 ≦ y ≦ 0.27, 0.02 ≦ z ≦ 0.1, 0.98 ≦ x + y + z ≦ 1.02.

  In this compound, since a part of nickel is substituted by cobalt, the change of the crystal structure accompanying charging / discharging is suppressed. Moreover, the crystal structure is further stabilized by adding trivalent and stable aluminum. Note that when charging to a region where a <0.3, the crystal structure changes greatly, so it is preferable not to charge to such a region. For the same reason, it is preferable that the discharge be within a range of a ≦ 1.05. When x is less than 0.7, the discharge capacity of the conventional nonaqueous electrolyte battery using a cobalt-based compound as the positive electrode active material is reduced to the same level, and when it exceeds 0.87, the thermal stability is extremely reduced. x is preferably in the range of 0.7 to 0.87. Further, if y is less than 0.1, the crystal structure becomes unstable. Conversely, even if it exceeds 0.27, the stabilization of the crystal structure reaches its peak, and only leads to a decrease in discharge capacity. A range of .1 to 0.27 is preferred. When z is less than 0.02, the stability of the crystal structure is lowered, and the thermal stability during charging is also lowered. However, if z exceeds 0.1, the discharge capacity is remarkably reduced, so z is preferably in the range of 0.02 to 0.1.

  Next, the Ni-based compound according to the present invention has an oxygen 1s spectrum measured by X-ray photoelectron spectroscopy (XPS) measured under the condition of 15 kV-15 mA in a state of 0.8 ≦ a ≦ 1.05, 528 eV to 531 eV. The ratio (Ia / Ib) of the intensity (Ia) of the peak having a peak between and the intensity (Ib) of the peak having a peak between 531 eV to 533 eV is 0.5 or more.

Examples of XPS oxygen 1S spectra of Ni-based compounds according to the present invention are shown in FIGS. 1 and 2, and examples of XPS oxygen 1S spectra of conventional Ni-based compounds are shown in FIG. 1, 2, and 2, a peak having a peak between 528 eV and 531 eV is oxygen contained in a planar layer made of nickel, cobalt, aluminum, and oxygen in the crystal structure (hereinafter referred to as “crystalline oxygen”). caused by. On the other hand, there is a report that a peak having a peak between 531 eV and 533 eV is caused by oxygen adsorbed on the surface of the compound (hereinafter referred to as “adsorbed oxygen”), but it is not certain (Journal of Electrochemical Chemistry, 419 , 77). (1996), Thin Solid Film, 384 , 23 (2001)).

  Therefore, when comparing the ratio (Ia / Ib) of the peak intensity Ia having the peak between 528 eV to 531 eV and the peak intensity Ib having the peak between 531 eV to 533 eV in the XPS oxygen 1S spectrum of the outermost surface The conventional Ni compound shown in FIG. 3 has Ia / Ib <0.5, whereas the Ni compound according to the present invention shown in FIGS. 1 and 2 has Ia / Ib> 0.5. In particular, as shown in FIG. 2, when Ia / Ib> 1, extremely excellent characteristics can be obtained.

  The present inventor predicts that the smaller the amount of adsorbed oxygen on the compound surface and the greater the amount of crystalline oxygen, the easier the lithium ion diffusion and charge transfer reaction will proceed on the surface, and the concentration ratio of crystalline oxygen on the compound surface is determined. The means to improve was examined. As a result of examining the relationship between the concentration ratio of both oxygen and the battery performance, there are points in the starting material, the firing conditions, the handling method of the compound after firing, the battery preparation method, etc. to improve the concentration ratio of crystalline oxygen I found.

  This content will be described in the examples, but as a conclusion, in the discharge state of 0.8 ≦ a ≦ 1.05, the peak intensity (Ia) having a peak between 528 eV to 531 eV, and 531 eV to 533 eV. It has been found that if the ratio (Ia / Ib) of peak intensities (Ib) having apexes between them is 0.5 or more, good battery performance without variations in internal resistance and discharge capacity can be obtained.

  As described above, it has been found that satisfactory battery performance cannot be obtained when the surface state of the compound is different from the state inside the compound. However, in compositional analysis and XRD analysis, which are general qualitative means of Ni-based compounds, State change is not detected. Without understanding this situation, if a compound whose surface state is significantly different from the inside is used as the positive electrode active material, variations in internal resistance and discharge capacity occur between production lots.

  When synthesizing the Ni-based compound according to the present invention, it is important to pay attention to the following points. When lithium hydroxide and nickel hydroxide are used as raw materials and reacted in an oxygen atmosphere, lithium carbonate is generated by the lithium component that did not become a composite oxide, and a Ni-based compound in which lithium carbonate is present on the surface of the battery When used in a battery, lithium carbonate reacts with the electrolyte to generate gas, which causes battery blistering. Thus, when lithium hydroxide and nickel hydroxide are reacted, the amount of lithium hydroxide can be reduced to reduce the amount of lithium carbonate generated.

In addition, when lithium hydroxide and nickel hydroxide are used as raw materials, the specific surface area of the raw material powder is 1 to 100 m ² / g and the average particle size is in the range of 0.05 to 30 μm. The ratio of the average particle diameter with the hydroxide raw material powder is preferably in the range of 0.5 to 2.0.

  Furthermore, after the raw material powder is mixed, the conditions for firing are as follows. The raw material powder is mixed in advance, and then pellets are formed. The temperature is 400 to 800 ° C., the time is 10 to 100 hours, the oxygen atmosphere or the oxygen stream, It is preferable to carry out in a pressurized state.

  In addition, lithium oxide is used instead of lithium hydroxide, baking is performed at a temperature of 800 ° C. or more like Co-based and Mn-based, baking time is as long as possible, temperature distribution in the baking furnace is uniform, baking Since a large amount of moisture is generated at the time, the packing density of the raw material in the firing furnace is lowered, and the process is performed in an oxygen stream so that the moisture is easily removed. The molar ratio of lithium to nickel is 1 or less. The surface is replaced with high-concentration aluminum, the active material obtained by firing is not brought into contact with moisture or carbon dioxide, the electrode plate is manufactured in a dry room, and the electrode plate after applying the positive electrode mixture layer is vacuum It is necessary to devise such as storing it inside.

  The external appearance of the nonaqueous electrolyte secondary battery of the present invention is shown in FIG. 4, and the electrode group of the battery is shown in FIG. 4 and 5, 1 is a nonaqueous electrolyte secondary battery, 2 is an electrode group, 2a is a positive electrode, 2b is a negative electrode, 2c is a separator, 3 is a battery case, 3a is a case part of the battery case, and 3b is a battery case. , 4 is a positive terminal, 5 is a negative terminal, 6 is a safety valve, and 7 is an electrolyte injection port.

  In the nonaqueous electrolyte secondary battery of the present invention, a battery element 1 in which a positive electrode 7 and a negative electrode 8 using a compound as a positive electrode active material are wound in an oval shape via a separator 9 is housed in a battery container 2. The non-aqueous electrolyte (not shown) containing carbon black or carbon black and activated carbon is injected from the injection port 6, and then the injection port 6 is sealed.

  The negative electrode, separator, and electrolytic solution used in the non-aqueous electrolyte secondary battery of the present invention are not particularly different from those conventionally used, and those commonly used can be used. In FIG. 5, the battery element has an oval shape, but may have an oval shape. Further, the shape of the battery element is not limited to the winding type, and may be a shape in which flat plate plates are laminated.

  As a negative electrode material used for the nonaqueous electrolyte secondary battery of the present invention, various carbon materials capable of inserting and extracting lithium ions, metallic lithium and lithium alloys can be used. Transition metal oxides and nitrides may also be used.

  In addition, as the separator used in the nonaqueous electrolyte secondary battery of the present invention, a microporous membrane made of a polyolefin resin such as polyethylene or polypropylene is used, and a plurality of microporous membranes having different materials, weight average molecular weights and porosity are used. Those obtained by laminating and those microporous membranes containing appropriate amounts of various plasticizers, antioxidants, flame retardants and the like may be used.

  There are no particular restrictions on the organic solvent of the electrolyte used in the non-aqueous electrolyte secondary battery of the present invention. For example, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, halogenated hydrocarbons. , Esters, carbonates, nitro compounds, phosphate ester compounds, sulfolane hydrocarbons, etc. can be used, among these ethers, ketones, esters, lactones, halogenated hydrocarbons , Carbonates and sulfolane compounds are preferred. Examples of these are tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, 4-methyl-2-pentanone, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, 1,2-dichloroethane. , Γ-butyrolactone, dimethoxyethane, methyl formate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, vinylene carbonate, dimethylformamide, dimethyl sulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfolane, phosphorus Examples thereof include trimethyl acid, triethyl phosphate, and mixed solvents thereof, but are not necessarily limited thereto. Cyclic carbonates and cyclic esters are preferred. Most preferably, the organic solvent is a mixture of one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate and diethyl carbonate.

As the electrolyte salt used for the nonaqueous electrolyte secondary battery of the present invention is not particularly _{limited, LiClO 4, LiBF 4, LiAsF} 6, CF 3 SO 3 Li, LiPF 6, LiN (CF 3 SO 2) 2 , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiI, LiAlCl _{4 and the} like and mixtures thereof. Preferably, a lithium salt obtained by mixing one or more of LiBF ₄ and LiPF ₆ is preferable.

  In addition, a solid ion-conducting polymer electrolyte can be used as an auxiliary material for the electrolyte. In this case, the configuration of the nonaqueous electrolyte secondary battery includes a combination of a positive electrode, a negative electrode and a separator, an organic or inorganic solid electrolyte and the nonaqueous electrolyte, or an organic or inorganic solid electrolyte as the positive electrode, the negative electrode and the separator. A combination of the membrane and the non-aqueous electrolyte solution can be mentioned. When the polymer electrolyte membrane is polyethylene oxide, polyacrylonitrile, polyethylene glycol, or a modified product thereof, the polymer electrolyte membrane is lightweight and flexible, which is advantageous when used for a wound electrode plate. In addition to the polymer electrolyte, an inorganic solid electrolyte or a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte can be used.

  Other battery components include a current collector, a terminal, an insulating plate, a battery case, and the like. However, these components may be used as they are.

Examples of the present invention will be described below together with comparative examples.

[Synthesis of Ni-based compounds]
Nickel sulfate and cobalt sulfate were dissolved in water so that the molar ratio was Ni: Co = 71: 21, and a sodium hydroxide solution was added with sufficient stirring to obtain a nickel-cobalt composite coprecipitated hydroxide. .

  The produced coprecipitate was washed with water and dried, and then aluminum hydroxide having an average particle diameter of about 0.5 μm was mixed so that the molar ratio was (Ni + Co): Al = 92: 8, and then water was added. A precursor was prepared by adding lithium oxide monohydrate and adjusting the molar ratio to be Li: (Ni + Co + Al) = 105: 100.

These precursors were calcined at 700 ° C. for 10 hours in an oxygen stream, cooled to room temperature, taken out in a dry argon gas and pulverized, and composition formula Li _1.03 Ni _0.71 Co _0.21 Ai _0.08 A Ni-based compound represented by O ₂ was obtained. This was designated Ni-based compound N01.

Ni system except that the molar ratio of nickel-cobalt composite coprecipitated hydroxide is Ni: Co = 74: 22 and the molar ratio of the mixture of coprecipitate and aluminum hydroxide is (Ni + Co): Al = 96: 4. A Ni-based compound represented by the composition formula Li _1.03 Ni _0.74 Co _0.22 Ai _0.04 O ₂ was obtained under the same conditions as for the compound N01. This was designated Ni compound N02.

Ni system except that the molar ratio of nickel-cobalt composite coprecipitated hydroxide is Ni: Co = 80: 12 and the molar ratio of the mixture of coprecipitate and aluminum hydroxide is (Ni + Co): Al = 92: 8. A Ni-based compound represented by the composition formula Li _1.03 Ni _0.80 Co _0.12 Ai _0.08 O ₂ was obtained under the same conditions as for the compound N01. This was designated Ni-based compound N03.

Ni system except that the molar ratio of nickel-cobalt composite coprecipitated hydroxide is Ni: Co = 81: 16 and the molar ratio of the mixture of coprecipitate and aluminum hydroxide is (Ni + Co): Al = 97: 3. A Ni-based compound represented by the composition formula Li _1.03 Ni _0.81 Co _0.16 Ai _0.03 O ₂ was obtained under the same conditions as for the compound N01. This was designated Ni-based compound N04.

Ni system except that the molar ratio of nickel-cobalt composite coprecipitated hydroxide is Ni: Co = 85: 13 and the molar ratio of the mixture of coprecipitate and aluminum hydroxide is (Ni + Co): Al = 98: 2. Under the same conditions as for compound N01, a Ni-based compound represented by the composition formula Li _1.03 Ni _0.85 Co _0.13 Ai _0.02 O ₂ was obtained. This was designated Ni-based compound N05.

  The obtained Ni compounds N01 to N05 were vacuum-stored in a desiccator, and the subsequent analysis and battery production were performed within one week.

Nickel sulfate, cobalt sulfate, aluminum hydroxide, and lithium hydroxide monohydrate are mixed in a mortar so that the molar ratio is the same as that of the metal in the precursor when the Ni compound N01 is synthesized. After baking at 700 ° C. for 10 hours, cooling to room temperature, taking it out in dry air with a dew point of −30 ° C. or less and pulverizing it, the composition is _{expressed as} Li _1.03 Ni _0.71 Co _0.21 Ai _0.08 O ₂ . A Ni-based compound was obtained. This was designated as Ni compound N11. The obtained compound was vacuum-stored in a desiccator.

The composition formula Li _1.03 Ni _0.71 Co _0.21 Ai _0.08 O was used under the same conditions as the Ni compound N01 except that the precursor when the Ni compound N01 was synthesized was calcined in the atmosphere. A Ni-based compound represented by ₂ was obtained. This was designated Ni compound N12.

The composition formula Li _1.03 Ni _0.71 Co _0.21 Ai _0.08 is the same as the Ni compound N01 except that the firing temperature of the precursor when the Ni compound N01 is synthesized is 600 ° C. A Ni-based compound represented by O ₂ was obtained. This was designated Ni compound N13.

The composition formula Li _1.03 Ni _0.71 Co _0.21 Ai _{0.08 was used under the} same conditions as the Ni compound N01 except that the firing time of the precursor when the Ni compound N01 was synthesized was 1 hour. A Ni-based compound represented by O ₂ was obtained. This was designated Ni compound N14.

When the Ni-based compound N01 was synthesized, the composition formula Li _1.03 Ni _0.71 Co ₀ .5 was obtained under the same conditions as the Ni-based compound N01 except that the Ni-based compound N01 was taken out from the firing furnace in the atmosphere of 50% humidity after firing _. A Ni-based compound represented by ₂₁ Ai _0.08 O ₂ was obtained. This was designated Ni compound N15.

When the Ni-based compound N01 was synthesized, the composition formula Li _1.03 Ni _0.71 Co _{0 was used under the} same conditions as the Ni-based compound N01 except that the Ni-based compound N01 was left in an atmosphere of 50% humidity after firing and pulverization for one week. A Ni-based compound represented by _.21 Ai _0.08 O ₂ was obtained. This was designated Ni-based compound N16.

When the Ni compound N01 was synthesized, the composition formula Li _1.03 Ni _0.71 Co _0.21 Ai was used under the same conditions as the Ni compound N01 except that it was vacuum-stored in a desiccator for 1 year after firing and pulverization. A Ni-based compound represented by _0.08 O ₂ was obtained. This was designated Ni compound N17.

  A part of the Ni-based compounds N01 to 05 and N11 to N17 synthesized as described above was taken out from the desiccator and subjected to qualitative analysis. As a result, in powder X-ray diffraction, no peak of impurities such as unreacted hydroxide, lithium aluminate, or lithium carbonate was observed for all compounds. Table 1 shows the average composition of the Ni compounds N01 to 05 and N11 to N17 analyzed by ICP emission spectroscopy.

  Next, in order to investigate the bonding state of oxygen present on the surface portion of each compound itself, analysis was performed by X-ray photoelectron spectroscopy combined with argon ion sputtering. The intensity of the peak having a peak between 528 eV and 531 eV (Ia: the height from the baseline to the peak peak) and the intensity of the peak having a peak between 533 eV and 533 eV (Ib: the height from the baseline to the peak peak) Table 1 shows the ratio. Note that the baseline method may be any of the Linear method, the Shirley method, and the Tougaard method, but here, the Linear method was used.

  Specifically, the surface analysis by X-ray photoelectron spectroscopy was performed according to the following procedure. First, in a dry room with a dew point of −50 ° C. or less, stainless steel having a clean surface coated with a powder of compound particles on a conductive carbon tape affixed on a sample stage for X-ray photoelectron spectroscopy. The plate was placed and pressed moderately with a hydraulic press, and a flat and dense sample was produced visually. Next, the sample was horizontally mounted on a sample stage in an X-ray photoelectron spectrometer (manufactured by Shimadzu Corporation, AXIS-HS) using a transfer vessel so as not to be exposed to the atmosphere.

The X-ray source was MgKα ray, and the acceleration voltage was 15 keV and the emission current was 15 mA. Since the analysis range diameter of the X-ray photoelectron spectroscopy is 100 μmφ, the spectrum obtained is an average value from several tens of compound particles, but from the preparation of the analysis sample to the X-ray photoelectron spectroscopy measurement using the same compound No error occurred in the obtained information even if the above operation was repeated several tens of times.

  In addition, since there is a slight amount of gas and impurities adhering to the outermost surface of the compound when an analytical sample is prepared or introduced into the analyzer, here, after etching 1 nm from the outermost surface of the analytical sample, The spectrum was defined as the true compound surface spectrum. The depth was calculated by the thickness in terms of single crystal Si.

  The surface analysis of a series of compounds was carried out on the flat plate on which the powder was agglomerated and pressed as described above, but the compound was mixed with acetylene black and polyvinylidene fluoride and applied onto the flat plate, followed by compression molding. Even if the same analysis is performed for, the metal element is not contained in acetylene black or polyvinylidene fluoride, so it does not hinder the identification of the compound surface and the composition analysis of the compound surface, and the same analysis for the electrode plate Is possible. However, since the peak intensity slightly varies depending on the charged state of the active material, the peak intensity is determined to be compared in the discharged state of 0.8 ≦ a ≦ 1.05.

[Examples 1-5 and Comparative Examples 1-7]
[Example 1]
In the positive electrode, 87% by weight of Ni compound N01 as an active material, 5% by weight of acetylene black and 8% by weight of polyvinylidene fluoride were mixed, and this was mixed with N-methyl-2-pyrrolidone (hereinafter “NMP”) having a water content of 50 ppm or less. To make a paste, and then applied onto an aluminum foil and dried to form a positive electrode mixture layer. The negative electrode was prepared by mixing a carbon material (graphite) and polyvinylidene fluoride, adding NMP to the paste to form a paste, and coating and drying on a copper foil to form a negative electrode mixture layer.

  After forming the electrode group by winding the belt-like positive electrode and the negative electrode thus produced into an oval shape through a separator as shown in FIG. 3, this electrode group is formed into a long cylindrical bottomed aluminum container. Then, after filling the core portion of the electrode group with a filler, the electrolyte was injected, and the container and the lid were sealed and welded by laser welding. All processes from paste preparation to electrode processing and battery assembly were performed in a dry environment with a dew point of 50 ° C. or lower. The produced battery was the battery of Example 1, and the design capacity of this battery was 10 Ah.

[Examples 2 to 5 and Comparative Examples 1 to 7]
A battery of Example 2 was made in the same manner as Example 1 except that the Ni-based compound N02 was used as the positive electrode active material. Similarly, a battery using the Ni compound N03 was used as the battery of Example 3, a battery using the Ni compound N04 was used as the battery of Example 4, and a battery using the Ni compound N05 was used as the battery of Example 5. .

  A battery of Comparative Example 1 was fabricated in the same manner as in Example 1 except that Ni compound N11 was used as the positive electrode active material. Similarly, a battery using Ni-based compound N12 is the battery of Comparative Example 2, a battery using Ni-based compound N13 is the battery of Comparative Example 3, a battery using Ni-based compound N14 is the battery of Comparative Example 4, Ni The battery using Comparative compound N15 was used as the battery of Comparative Example 5, the battery using Ni compound N16 as the battery of Comparative Example 6, and the battery using Ni compound N17 as the battery of Comparative Example 7.

[Discharge capacity measurement]
The test battery was charged to 4.2 V at a constant current of 1 A, and then the discharge capacity when discharged to 3.0 V at a constant current of 1 A was measured to calculate the discharge capacity per gram of the positive electrode active material.

[Charge / discharge cycle test]
Next, the discharge capacity after charging and discharging the test battery for 300 cycles under the same test conditions was determined, and this was divided by the initial discharge capacity to calculate the post-cycle capacity retention rate (%).

[Preservation test]
The storage characteristics were compared with other batteries prepared at the same time as the batteries subjected to the charge / discharge cycle test and the cycle test. After charging to 4.2 V at a constant current of 1 A, charging / discharging to discharge to 3.0 V at a constant current of 1 A was repeated three times initially, and the third discharge capacity was defined as the initial capacity. Next, after charging again to 4.2 V at a constant current of 1 A, the battery was stored in an environment of 60 ° C. for 10 days, and after the storage, the charge and discharge were repeated three times under the same charge and discharge conditions as in the initial stage. The storage capacity after storage was divided by the initial discharge capacity, and the capacity retention rate (%) after storage was calculated. These test results are shown in Table 2.

From the results of Table 1 and Table 2, in the oxygen 1s spectrum of the compound itself by X-ray photoelectron spectroscopy measured under the condition of 16 kV-15 mA with 0.8 ≦ a ≦ 1.05, it is between 528 eV and 531 eV. The general formula Li _a Ni _x Co _y Al _{z in which} the ratio (Ia / Ib) of the intensity (Ia) of the peak having the apex to the intensity (Ib) of the peak having the apex between 531 eV to 533 eV is 0.5 or more. O ₂ (0.3 ≦ a ≦ 1.05, 0.7 ≦ x ≦ 0.87, 0.1 ≦ y ≦ 0.27, 0.02 ≦ z ≦ 0.1, 0.98 ≦ x + y + z ≦ 1 0.02), the nonaqueous electrolyte secondary batteries of Examples 1 to 5 using the Ni-based compound as the positive electrode active material are the nonaqueous electrolyte secondary batteries of Comparative Examples 1 to 7 where Ia / Ib <0.5. Compared to the above, the discharge capacity is large and the cycle performance and storage performance are excellent. I found out.

The figure which shows an example of the XPS oxygen 1S spectrum of the Ni type compound which becomes this invention. The figure which shows the other example of the XPS oxygen 1S spectrum of the Ni type compound which becomes this invention. The figure which shows the example of the XPS oxygen 1S spectrum of the conventional Ni type compound. The figure which shows the external appearance of the nonaqueous electrolyte secondary battery of this invention. The figure which shows the electrode group of a battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 2a Positive electrode 2b Negative electrode 2c Separator 3 Battery case 3a Case part of battery case 3b Cover part of battery case 4 Positive electrode terminal 5 Negative electrode terminal 6 Safety valve 7 Electrolyte injection port

Claims (1)

General formula Li _a Ni _x Co _y Al _z O ₂ (0.3 ≦ a ≦ 1.05, 0.7 ≦ x ≦ 0.87, 0.1 ≦ y ≦ 0.27, 0.02 ≦ z ≦ 0 .1, 0.98 ≦ x + y + z ≦ 1.02) in a nonaqueous electrolyte secondary battery using a positive electrode active material, 15 kV in a state of 0.8 ≦ a ≦ 1.05 on the surface of the compound. The intensity (Ia) of the peak having an apex between 528 eV and 531 eV and the intensity of the peak having an apex between 531 eV and 533 eV (Ib) of the oxygen 1s spectrum measured by X-ray photoelectron spectroscopy measured under the condition of −15 mA ) Ratio (Ia / Ib) is 0.5 or more (except when Ib / Ia is 1.72, 1.6, or 1.5 or less). .

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