JP2005108738A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with superior safety and storing property by suppressing reaction due to deterioration in the vicinity of a compound surface by obtaining an improved effect proposed by conventional inventions by stipulating the composition of the composite as a whole in the composite used for positive electrode active substance in the nonaqueous electrolyte secondary battery and using the compound with the composition in the vicinity of the surface within the range of stipulation. <P>SOLUTION: In the nonaqueous electrolyte secondary battery using lithium content stratified nickel oxide particle for positive electrode active substance, the average composition of the lithium content stratified nickel oxide particle as a whole and the composition of the particle surface is expressed by a general formula of Li<SB>a</SB>Ni<SB>x</SB>Co<SB>y</SB>Al<SB>z</SB>O<SB>2</SB>(0.3≤a≤1.05), 0.7≤x≤0.87, 0.1≤y≤0.27, 0.02≤z≤0.1, 0.02≤z≤0.1, 0.98≤x+y+z≤1.01. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  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, a lithium-containing layered cobalt oxide (hereinafter referred to as a Co-based compound), a lithium-containing layered nickel oxide (hereinafter referred to as a Ni-based compound) or a spinel-type lithium manganese composite oxide (hereinafter referred to as a Mn-based) is used as a positive electrode of a nonaqueous electrolyte secondary battery. And a long-life 4V class non-aqueous electrolyte secondary battery using a carbon material capable of inserting and extracting lithium in the negative electrode has been put into practical use.

Among these, the Ni-based compound has a lithium-based amount of lithium that can be inserted and desorbed within the potential range (3.0 to 4.3 V vs. Li / Li ⁺ ) actually used in the nonaqueous electrolyte secondary battery. In addition to its advantages over Mn-based compounds and abundant resources, many development studies have been conducted 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.

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

  However, many compositions have been proposed so far in which nickel in a Ni-based compound is replaced with a dissimilar metal and has an excellent balance between cycle life performance, thermal stability, storage characteristics, and discharge capacity. The composition is an averaged composition of the entire compound, and the composition in the vicinity of the interface (= near the compound surface) with the electrolyte that plays an important role in the charge / discharge reaction has not been studied deeply.

  At the interface between the electrolyte and the compound, degradation reactions different from those in the solid layer proceed, such as decomposition of the electrolyte, generation of gas, and elution of metal ions. Therefore, composition control in the vicinity of the compound surface is very important for suppressing these reactions.

  In the case where only the composition of the entire compound is specified as in the conventional proposals, the composition often differs greatly between the inside of the compound and the vicinity of the surface. This is considered to be caused by the fact that the synthesis of the Ni-based compound itself is relatively difficult and that the Ni-based compound easily reacts with moisture and carbon dioxide gas.

  Thus, when the composition of the compound surface portion is different from the inside, the above-described characteristic deterioration reaction proceeds at the compound interface, and the effect of substituting nickel with a different metal may not be sufficiently obtained.

  Therefore, the object of the present invention is to specify the composition of the entire compound to obtain the improvement effect proposed in the conventional invention, and also pay attention to the composition in the vicinity of the surface. By using a compound in the above as a positive electrode active material of a non-aqueous electrolyte secondary battery, a reaction resulting from deterioration near the surface of the compound is also suppressed, and a non-aqueous electrolyte secondary battery with better safety and storage characteristics is obtained. There is to get.

In order to achieve the above object, the first aspect of the present invention provides a nonaqueous electrolyte secondary battery using lithium-containing layered nickel oxide particles as a positive electrode active material. The average composition and the particle surface composition of the general formula Li _a Ni _x Co _y Al _z O ₂ (0.3 ≦ a ≦ 1.05, 0.7 ≦ x ≦ 0.98, 0.1 ≦ y ≦ 0 .27, 0.02 ≦ z ≦ 0.1, 0.98 ≦ x + y + z ≦ 1.01).

The invention according to claim 2 is the nonaqueous electrolyte secondary battery according to claim 1, wherein z ₀ −0.01 ≦ z ≦ z ₀ +0.01 at all locations in the particle of the lithium-containing layered nickel oxide particles. (Where z ₀ is an arbitrary value).

  The invention according to claim 3 is the nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the lithium-containing layered nickel oxide particles have an average particle diameter of 1 to 50 μm.

  In the nonaqueous electrolyte secondary battery of the present invention, the cathode crystal structure is prevented from collapsing due to repeated charge and discharge, and the thermal stability at the time of temperature increase is improved. Since the increase in resistance, gas generation, elution of metal ions, and the like are also suppressed, the various performances expected by the substitution of different metals can be surely obtained.

  Further, since the nonaqueous electrolyte secondary battery of the present invention has a homogeneous composition from the surface portion to the inside of the positive electrode active material, between the expected performance and the actual performance, between the vicinity of the surface and the inside. An effect of suppressing the possibility of variation in charge / discharge capacity and thermal stability resulting from the difference in composition can be obtained.

  Furthermore, since the nonaqueous electrolyte secondary battery of the present invention is not mixed with fine powder or coarse powder with low crystallinity and inferior charge / discharge performance, the life performance and storage characteristics are further improved.

  According to the present invention, the composition of the entire nickel-based compound is specified to obtain the improvement effect that has been proposed in the conventional invention, and the composition in the specified range is also focused on the composition near the surface. By using the compound as a positive electrode active material for a non-aqueous electrolyte secondary battery, the reaction resulting from deterioration near the surface of the compound is also suppressed to ensure a non-aqueous electrolyte secondary battery with better safety and storage characteristics. Since it can be manufactured, the quality and reliability of a non-aqueous electrolyte secondary battery using a nickel-based compound as a positive electrode active material can be improved, and its industrial value is high.

The average composition of the entire 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 , 0.02 ≦ z ≦ 0.1, 0.98 ≦ x + y + z ≦ 1.01), in a nonaqueous electrolyte secondary battery using a lithium-containing layered nickel oxide as a positive electrode active material, discharge is performed for each production lot. There were many variations in capacity, output performance, and storage performance.

  As a result of investigating the cause in detail, the present inventor has found that the average composition of the entire lithium-containing layered nickel oxide particles is within the range defined by the above general formula, and about 10 nm from the outermost surface of the particles toward the inside. It has been clarified that the composition in the vicinity of the surface up to the depth of the surface often deviates from the above general formula, and in such a case, the interface performance increases and the battery swells due to gas generation, resulting in a decrease in battery performance. . It has also been clarified that the reason why the composition in the vicinity of the compound surface deviates from the general formula is the starting material, the firing conditions, the method of handling the compound after firing, the battery preparation method, and the like.

  Accordingly, the present inventor has optimized the conditions such as the starting material, the firing conditions, the method of handling the compound after firing and the method of producing the battery so that the average composition in the vicinity of the compound surface and the average composition of the entire compound are within a predetermined range. Thus, a non-aqueous electrolyte secondary battery excellent in safety and storage characteristics was obtained.

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

The present invention relates to a non-aqueous electrolyte secondary battery using lithium-containing layered nickel oxide particles as a positive electrode active material, wherein the average composition of the entire lithium-containing layered nickel oxide particles and the composition of the particle surface are 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, 0.02 ≦ z ≦ 0.1, 0.98 ≦ x + y + z ≦ 1.01).

  The term “particle surface” means a portion of the lithium-containing layered nickel oxide particle that has a depth of 10 nm from the particle surface excluding adsorbate adhering to the outermost surface of the particle. "" Means the remaining part of the particle excluding the particle surface.

Therefore, the lithium-containing layered nickel oxide particles used for the positive electrode active material of the present invention are not significantly different from the composition of the particle surface and the composition inside the particles. The value z ₀ −0.01 ≦ z ≦ z ₀ +0.01 (where z ₀ is an arbitrary value) holds at all locations in the particle, that is, the composition of aluminum on the particle surface and inside the particle is It is preferable that it is substantially uniform.

  In the lithium-containing layered nickel oxide particles of the present invention, since a part of nickel is replaced by cobalt, changes in the crystal structure accompanying charge / discharge are suppressed. In addition, the crystal structure is further stabilized by including trivalent and stable aluminum.

  When the lithium-containing layered nickel oxide of the present invention is charged to a region where a <0.3, the crystal structure changes greatly. Therefore, it is preferable not to charge to such a region. For the same reason, the discharge is preferably 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. Furthermore, 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, since the discharge capacity is significantly reduced when z exceeds 0.1, z is preferably in the range of 0.02 to 0.1.

  The reason why the composition of the lithium-containing layered nickel oxide particles on the particle surface deviates from the composition of the above general formula is that the mixing of the raw materials is insufficient or the raw material has a large particle size and is unreacted on the surface of the compound after firing. When a raw material residue (lithium hydroxide, etc.) adheres, or when the compound absorbs moisture or carbon dioxide gas after firing to produce a lithium compound (lithium carbonate, etc.) on the surface, In addition to the case where moisture is absorbed to produce a lithium compound, it occurs when the firing temperature deviates from an appropriate temperature (depending on the composition, but generally 650 to 750 ° C.) or the firing time is too short.

  In this way, even if the composition of the particle surface is different from the composition inside the particle, if the composition of the entire compound is qualitatively determined by emission spectroscopy used in general composition analysis, the composition deviation of the particle surface will be In many cases, the average composition of the entire compound falls within a predetermined range without being detected. If a compound whose particle surface composition deviates from the specified value is used as a positive electrode active material without understanding such a situation, variations in discharge capacity, output performance, storage performance, etc. occur for each production lot.

  Even if the composition of the particle surface falls within the specified composition range, variation in charge / discharge capacity and thermal stability due to the difference in composition between the particle surface and the inside of the particle between expected performance and actual performance In order to suppress this, it is desirable that the entire particle has a composition as homogeneous as possible, that is, the difference in composition between the particle surface and the inside of the particle is as small as possible.

  In particular, it has a great effect on stabilizing the crystal structure and improving the thermal stability during charging, but the amount of aluminum added, which also affects the decrease in discharge capacity and the increase in interfacial resistance, reduces variation among production lots. In order to do so, it is desirable to be constant. Of course, it is needless to say that a certain composition is desirable for nickel and cobalt.

As described above, the average composition of the entire lithium-containing layered nickel oxide particles and the composition of the particle surface are both expressed 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, 0.02 ≦ z ≦ 0.1, 0.98 ≦ x + y + z ≦ 1.01) In addition to defining raw materials, firing methods, and handling methods, it is necessary to inspect the compound surface by Auger electron spectroscopy, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and the like.

  In addition, it is preferable that the particle diameter of a compound falls in 1 micrometer or more and 50 micrometers or less. In general, a fine powder having a particle size of 1 μm or less is a poor compound with low crystallinity, and there are many particles whose average composition of the whole particle and composition of the particle surface are not within the range specified in claim 1. Even if such a fine powder is mixed in a small amount in the compound powder, the influence on the average composition of the powder as a whole and the average composition of the surface may be small. I want to avoid mixing.

  On the other hand, a coarse powder having a particle size of 50 μm or more has a disadvantage that firing is difficult to proceed to the inside, and therefore, even when the composition of the entire particle and the composition of the surface satisfy claim 1, a portion having low crystallinity is generated in the particle. there is a possibility. For these reasons, the particle diameter of the compound is preferably in the range of 1 to 50 μm. The particle size distribution can be adjusted by adjusting the raw material preparation or classifying the compound after firing.

  As shown in FIG. 1 and FIG. 2, the nonaqueous electrolyte secondary battery of the present invention has a positive electrode and a negative electrode using the above compound as a positive electrode active material in a circular shape or an oval shape through a separator. The wound electrode group is housed in a battery container, and the electrode group is impregnated with a nonaqueous electrolyte.

  FIG. 1 is a perspective view showing an external appearance of a long cylindrical nonaqueous electrolyte secondary battery, and FIG. 2 is a perspective view showing a configuration of an electrode group housed in the long cylindrical nonaqueous electrolyte secondary battery. 1 and 2, 1 is a non-aqueous electrolyte secondary battery, 2 is a power generation element, 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 inlet.

  The negative electrode, separator, electrolyte, and the like used for this nonaqueous electrolyte secondary battery are not particularly different from those conventionally used, and those that are normally used can be used. That is, as the negative electrode material used in the nonaqueous electrolyte secondary battery of the present invention, various carbon materials that can occlude and release 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 polyolefin resin such as polyethylene is used, and a plurality of microporous membranes having different materials, weight average molecular weights and porosity are laminated. Or those containing a suitable amount of various plasticizers, antioxidants, flame retardants and the like in these microporous membranes.

  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, 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.

[Production of Nickel Compounds Used in Examples 1 to 5 and Comparative Examples 1 to 10]
Nickel sulfate and cobalt sulfate were dissolved at a predetermined blending ratio, and a sodium hydroxide solution was added with sufficient stirring to obtain a nickel-cobalt composite coprecipitated hydroxide. The resulting coprecipitate was washed with water, dried, and thoroughly mixed with aluminum hydroxide having an average particle diameter of 1 μm, and then lithium hydroxide monohydrate was added. The molar ratio of lithium to nickel + cobalt + aluminum was 1.05: The precursor was prepared by adjusting to 1.

Next, the precursor was calcined at 700 ° C. for 20 hours in an oxygen atmosphere, cooled to room temperature, taken out in a dry argon gas and pulverized, and the composition 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, x + y + z = 1). 5 and various nickel compounds used in Comparative Examples 1 to 10 were obtained. In addition, the obtained compound was vacuum-stored in the desiccator.

Subsequently, as a starting material, lithium carbonate and tricobalt tetroxide are mixed, calcined in the atmosphere at 800 ° C. for 20 hours, cooled to room temperature, pulverized in the atmosphere, and expressed by the composition formula LiCoO _2. A cobalt-based compound (Comparative Example 11) was obtained. The obtained compound was vacuum-stored in a desiccator.

  A part of the compound was removed 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 compound particles.

  Next, in order to investigate the composition of the particle surface portion of each compound, composition analysis in the depth direction was performed by X-ray photoelectron spectroscopy combined with argon ion sputtering. The analysis 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, this sample was mounted in an X-ray photoelectron spectrometer so as not to be exposed to the atmosphere using a transfer vessel. 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. Since the gas and impurities are slightly adsorbed on the outermost surface of the compound, the spectrum after etching 1 nm from the outermost surface of the compound is defined as the spectrum of the true compound surface. The depth was calculated by the thickness in terms of single crystal Si.

  In addition, the surface analysis about a series of compounds was performed about the flat plate which carried out the aggregation pressure of the powder as mentioned above. Even if the compound is mixed with acetylene black and polyvinylidene fluoride, applied onto a flat plate, and the same analysis is performed on the compression-molded electrode plate, the metal element is not contained in acetylene black or polyvinylidene fluoride. It does not interfere with the surface identification and composition analysis of the compound surface. Therefore, the same analysis is possible for the electrode plate.

Table 1 shows the average composition of the entire compound particles analyzed by ICP emission spectroscopy, and Table 2 shows the composition of a certain depth portion of the particles calculated from the area ratio of the spectrum of each element by X-ray photoelectron spectroscopy. Shown in The composition formula is 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 ≦ When z ≦ 0.1 and x + y + z = 1), the values of a were all set to 1.03.

[Examples 1 to 5 and Comparative Examples 1 to 11]
[Example 1]
87% by weight of the compound of Example 1 shown in Table 1 and Table 2, 5% by weight of acetylene black and 8% by weight of polyvinylidene fluoride (PVdF) were mixed, and this was mixed with N-methyl-2-pyrrolidone having a water content of 50 ppm or less. (NMP) was added to form a paste, and this paste was applied onto an aluminum foil and dried to form a positive electrode mixture layer, thereby producing a positive electrode plate. For the negative electrode, a carbon material (graphite) and PVdF were mixed, and NMP was added thereto to form a paste, which was further coated on a copper foil and dried to form a negative electrode mixture layer, thereby producing a negative electrode plate.

  As shown in FIG. 2, the thus produced belt-like positive electrode plate and negative electrode plate are wound into an oval shape through a separator to form an electrode group. After inserting into the bottom aluminum container and filling the core part of the electrode group with the filler, the electrolytic solution 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 obtained battery was referred to as the battery of Example 1.

[Examples 2 to 5]
A battery of Example 2 was produced in the same manner as Example 1 except that the compound of Example 2 shown in Table 1 and Table 2 was used as the positive electrode active material. Similarly, batteries of Examples 3 to 5 were fabricated in the same manner as in Example 1 except that the compounds of Examples 3 to 5 shown in Table 1 and Table 2 were used as the positive electrode active material.

[Comparative Examples 1 to 11]
A battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the compound of Comparative Example 1 shown in Table 1 and Table 2 was used as the positive electrode active material. Similarly, batteries of Comparative Examples 2 to 11 were produced in the same manner as in Example 1 except that the compounds of Comparative Examples 2 to 11 shown in Table 1 and Table 2 were used as the positive electrode active material.

[Discharge capacity measurement and charge / discharge cycle test]
After the batteries of Examples 1 to 5 and Comparative Examples 1 to 11 were charged to a voltage of 4.2 V with a current of 1 CA, the discharge capacity was measured when discharged to a voltage of 3.0 V with a current of 1 CA. The discharge capacity per gram of active material was calculated. Next, the discharge capacity after charging and discharging these batteries for 300 cycles under the same test conditions was calculated, and the capacity retention ratio obtained by dividing this by the initial discharge capacity was calculated, and this was referred to as “post-cycle capacity retention ratio”. did.

[Thermal stability test]
In the batteries of Examples 1 to 5 and Comparative Examples 1 to 11, the battery was charged at a current of 0.2 CA until it reached a state of Li0.3, and the battery of Comparative Example 11 was changed to a state of Li0.5 at a current of 0.2 CA. Charged until After charging, a safety test was conducted in accordance with the nail penetration test method described in “Lithium Secondary Battery Safety Evaluation Standard Guidelines (SBA G101)” issued by Japan Storage Battery Industry Association.

[Preservation test]
After charging to a voltage of 4,2V with a current of 1CA, charging / discharging of discharging to 3.0V with a current of 1CA was repeated three times in the initial stage, and the third discharge capacity was defined as the initial capacity. Next, after charging again to a voltage of 4.2 V with a current of 1 CA, the battery was stored in an environment of 60 ° C. for 10 days, and after the storage, the battery was repeatedly charged and discharged three times under the same charge / discharge conditions as in the initial stage. The discharge capacity at the second time was taken as the capacity after storage, and this was divided by the initial discharge capacity to calculate the capacity retention after storage, which was designated as “capacity retention after storage”.

  These test results are shown in Table 3. In Table 3, in the column of thermal stability test, compared to the result of Comparative Example 11, when the safety was equivalent, it was ◯, when the safety was slightly lowered, △, When it fell, it was described as x.

From the results shown in Tables 1 to 3, compared to conventional non-aqueous electrolyte secondary batteries using cobalt compounds, the battery, which is comprehensively superior in terms of discharge capacity, cycle life performance, thermal stability, storage performance, etc. And the composition of the particle surface have 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 ≦ It was found that the battery uses a nickel-based compound represented by 0.27, 0.02 ≦ z ≦ 0.1, x + y + z = 1) as the positive electrode active material.

[Examples 6 to 9 and Comparative Examples 12 to 14]
[Example 6]
The nickel-based compound was produced under the same conditions as in Example 3 except that the firing conditions were 750 ° C. and 10 hours. And the battery of Example 6 was produced on the same conditions as Example 3 except having used this nickel-type compound for the positive electrode active material.

[Example 7]
The nickel-based compound was produced under the same conditions as in Example 3 except that the firing conditions were 750 ° C. and 20 hours. And the battery of Example 7 was produced on the same conditions as Example 3 except having used this nickel-type compound for the positive electrode active material.

[Example 8]
The nickel-based compound was produced under the same conditions as in Example 3 except that the firing conditions were 800 ° C. and 20 hours. And the battery of Example 8 was produced on the same conditions as Example 3 except having used this nickel-type compound for the positive electrode active material.

[Example 9]
The nickel-based compound was produced under the same conditions as in Example 5 except that the average particle diameter of aluminum hydroxide used for the synthesis was 50 μm. And the battery of Example 9 was produced on the conditions same as Example 5 except having used this nickel-type compound for the positive electrode active material.

[Comparative Example 12]
The nickel-based compound was produced under the same conditions as in Example 5 except that the average particle diameter of aluminum hydroxide used for the synthesis was 0.01 μm. And the battery of the comparative example 12 was produced on the conditions same as Example 5 except having used this nickel-type compound for the positive electrode active material.

[Comparative Example 13]
The nickel-based compound was produced under the same conditions as in Example 5 except that the fired compound was taken out from the furnace in the atmosphere at 50% humidity and then vacuum-stored. And the battery of the comparative example 13 was produced on the conditions same as Example 5 except having used this nickel-type compound for the positive electrode active material.

[Comparative Example 14]
The nickel-based compound was produced under the same conditions as in Example 5, except that the compound after firing was taken out of the furnace in the atmosphere at 50% humidity and stored in the atmosphere thereafter. And the battery of the comparative example 14 was produced on the conditions same as Example 5 except having used this nickel-type compound for the positive electrode active material.

  Qualitative analysis of the nickel-based compounds prepared in Examples 6-9 and Comparative Examples 12-14 was performed. As a result, in powder X-ray diffraction, no peak of impurities such as unreacted hydroxide and lithium aluminate was observed for all compounds.

The average composition of the entire compound particles analyzed by ICP emission spectroscopy is shown in Table 4, and the constant depth of the particles calculated from the area ratio of the spectrum of each element by X-ray photoelectron spectroscopy combined with argon ion sputtering. The composition of the parts is shown in Table 5. The composition formula is 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 ≦ When z ≦ 0.1 and x + y + z = 1), the values of a were all set to 1.03.

  Table 6 shows the discharge capacity per gram of the positive electrode active material of the batteries produced in Examples 6 to 9 and Comparative Examples 12 to 14, the capacity retention after the charge / discharge cycle, the thermal stability test results, and the storage performance. The test method is the same as in Example 1. Table 6 also shows the measurement results of Example 3 and Example 5 for comparison.

From the results shown in Tables 4 to 6, the composition of the entire particle is expressed 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, 0.02 ≦ z ≦ 0.1, x + y + z = 1), and shows various performances better than the battery using a conventional cobalt compound. Even in a battery that is expected to be soldered, the composition of the particle surface may deviate from the composition of the entire particle due to the raw materials, firing conditions, handling method of the compound after firing, etc., and as a result, the expected performance cannot be obtained. It became clear that there is.

  In other words, in order to obtain good performance as expected in a battery using a nickel-based compound as a positive electrode active material, it is essential to use particles that satisfy the general formula representing the composition of the entire particle even on the particle surface. Became clear by the present invention.

  Even when the composition of the particle surface is within the range represented by the general formula representing the composition of the entire particle, it is preferable that the variation of the composition is as small as possible in order to obtain the expected performance. However, it is preferable that the Al composition that greatly affects various performances be within about ± 0.01.

[Examples 10 to 13 and Comparative Examples 15 and 16]
[Example 10]
The nickel-based compound was produced under the same conditions as in Example 3 except that the particle size distribution of the obtained particles was in the range of 2 to 30 μm. And the battery of Example 10 was produced on the same conditions as Example 3 except having used this nickel-type compound for the positive electrode active material.

[Example 11]
The nickel-based compound was prepared under the same conditions as in Example 3 except that the amount of sodium hydroxide added during preparation of the coprecipitated hydroxide was adjusted and the particle size distribution of the obtained particles was in the range of 5 to 50 μm. And the battery of Example 11 was produced on the same conditions as Example 3 except having used this nickel-type compound for the positive electrode active material.

[Example 12]
The nickel-based compound was prepared under the same conditions as in Example 3 except that the amount of sodium hydroxide added during preparation of the coprecipitated hydroxide was adjusted and the particle size distribution of the obtained particles was in the range of 1 to 20 μm. And the battery of Example 12 was produced on the same conditions as Example 3 except having used this nickel-type compound for the positive electrode active material.

[Example 13]
For the nickel compound, compound particles produced under the same conditions as in Example 12 were dry classified, and the particle size distribution was adjusted to a range of 5 to 10 μm. A battery of Example 13 was made under the same conditions as Example 3 except that this nickel-based compound was used as the positive electrode active material.

[Comparative Example 15]
The nickel-based compound was prepared under the same conditions as in Example 3 except that the amount of sodium hydroxide added during preparation of the coprecipitated hydroxide was adjusted and the particle size distribution of the obtained particles was in the range of 20 to 80 μm. And the battery of the comparative example 15 was produced on the conditions same as Example 3 except having used this nickel-type compound for the positive electrode active material.

[Comparative Example 16]
The nickel-based compound is prepared under the same conditions as in Example 3 except that the amount of sodium hydroxide added during preparation of the coprecipitated hydroxide is adjusted and the particle size distribution of the obtained particles is in the range of 0.5 to 15 μm. did. And the battery of the comparative example 16 was produced on the conditions same as Example 3 except having used this nickel-type compound for the positive electrode active material.

  The qualitative analysis of the nickel-based compounds prepared in Examples 10 to 13 and Comparative Examples 15 and 16 was performed. As a result, in powder X-ray diffraction, no peak of impurities such as unreacted hydroxide and lithium aluminate was observed for all compounds.

The average composition of the entire compound particles analyzed by ICP emission spectroscopy was all of the general formula Li _1.03 Ni _0.80 Co _0.12 Al _0.08 O ₂ . Table 7 shows the composition of a constant depth portion of the particles calculated from the area ratio of the spectrum of each element by X-ray photoelectron spectroscopy combined with argon ion sputtering.

  Table 8 shows the discharge capacity per gram of the positive electrode active material of the batteries prepared in Examples 10 to 13 and Comparative Examples 15 and 16, the capacity retention after the charge / discharge cycle, the thermal stability test results, and the storage performance. The test method is the same as in Example 1.

  From the results shown in Table 7 and Table 8, when coarse powder exceeding 50 μm is mixed in the powder, the discharge capacity and life performance of the whole positive electrode tend to be reduced due to low charge / discharge performance of the coarse powder. It is confirmed. In addition, even when fine powder of less than 1 μm is mixed, it is confirmed that poor charge / discharge performance and life performance of the fine powder are affected and the performance of the entire positive electrode is lowered.

  In addition, if fine powder of less than 1 μm is mixed in the powder, the electrode coating property may be lowered and the packing density of the electrode may be reduced. On the other hand, if coarse powder having a particle diameter of more than 50 μm is mixed, electrode coating may be performed. In this sense, the particle diameter is preferably in the range of 1 to 50 μm because the yield of the work may be reduced.

The perspective view which shows the external appearance of a long cylindrical nonaqueous electrolyte secondary battery. The perspective view which shows the structure of the electrode group accommodated in the long cylindrical nonaqueous electrolyte secondary battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Power generation element 2a Positive electrode 2b Negative electrode 2c Separator 3 Battery case 3a Battery case case 3b Battery case cover 4 Positive electrode terminal 5 Negative electrode terminal 6 Safety valve 7 Electrolyte injection port

Claims (3)

In a non-aqueous electrolyte secondary battery using lithium-containing layered nickel oxide particles as a positive electrode active material, the average composition of the entire lithium-containing layered nickel oxide particles and the composition of the particle surface are expressed 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 ≦ 0.27,0.02 ≦ z ≦ 0.1,0.98 ≦ x + y + z ≦ 1.01). The nonaqueous electrolyte secondary battery characterized by the above-mentioned. In the lithium-containing layered nickel oxide particles, z ₀ −0.01 ≦ z ≦ z ₀ +0.01 (where z ₀ is an arbitrary value) is established at all locations in the particle. The nonaqueous electrolyte secondary battery according to 1. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the lithium-containing layered nickel oxide particles have an average particle diameter of 1 to 50 µm.

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