JP2009129721A - Non-aqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery which has a high capacity and superior preservation characteristics and cycle characteristics, and in which the charging completion potential of the positive electrode can be charged as 4.4-4.6 V in lithium standard. <P>SOLUTION: The non-aqueous electrolyte secondary battery is provided with a positive electrode having a positive electrode active material capable of storing and releasing lithium. The positive electrode active material consists of a core oxide composed of a lithium metal complex oxide and a coating oxide composed of a lithium-contained manganese complex oxide having a spinel structure and in which a part of manganese is substituted by aluminum, and the surface of the core oxide is covered with the coating oxide. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolyte secondary battery that can be charged at a high charge voltage. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery that has a high capacity, is excellent in storage characteristics and cycle characteristics, and can be charged at a positive charge end potential of 4.4 V to 4.6 V based on lithium.

  Non-aqueous electrolyte secondary typified by lithium-ion secondary battery with high energy density and high capacity as a driving power source for portable electronic devices such as mobile phones, portable personal computers, portable music players, etc. Batteries are widely used. Among these, nonaqueous electrolyte secondary batteries using graphite particles as the negative electrode active material are widely used because of their high safety and high capacity.

  By the way, in a device in which this type of non-aqueous electrolyte secondary battery is used, the space for accommodating the battery is often a square (flat box shape), so the power generation element is accommodated in a rectangular outer can. The formed rectangular nonaqueous electrolyte secondary battery is often used. The configuration of such a rectangular nonaqueous electrolyte secondary battery will be described with reference to the drawings.

  FIG. 1 is a perspective view of a conventional non-aqueous electrolyte secondary battery manufactured by cutting in the longitudinal direction. In this nonaqueous electrolyte secondary battery 10, a flat wound electrode body 14 in which a positive electrode plate 11 and a negative electrode plate 12 are wound via a separator 13 is accommodated in a rectangular battery outer can 15. The battery outer can 15 is sealed with a sealing plate 16.

  The wound electrode body 14 is wound so that the positive electrode plate 11 is exposed at the outermost periphery, and the exposed outermost positive electrode plate 11 is formed on the inner surface of the battery outer can 15 that also serves as a positive electrode terminal. Direct contact and electrical connection. The negative electrode plate 12 is formed at the center of the sealing plate 16 and is electrically connected to a negative electrode terminal 18 attached via an insulator 17 via a negative electrode tab 19.

  Since the battery outer can 15 is electrically connected to the positive electrode plate 11, in order to prevent a short circuit between the negative electrode plate 12 and the battery outer can 15, the upper end of the wound electrode body 14 and the sealing plate The insulating spacer 20 is inserted between the negative electrode plate 12 and the battery outer can 15 so as to be electrically insulated.

  In this rectangular nonaqueous electrolyte secondary battery 10, after the wound electrode body 14 is inserted into the battery outer can 15, the sealing plate 16 is laser welded to the opening of the battery outer can 15, and then the electrolyte injection hole The non-aqueous electrolyte is injected from 21 and the electrolyte injection hole 21 is sealed. Such a rectangular non-aqueous electrolyte secondary battery has an excellent effect that there is little wasted space during use, and the battery performance and battery reliability are high.

  As the negative electrode active material used in this non-aqueous electrolyte secondary battery, carbonaceous materials such as graphite and amorphous carbon have a discharge potential comparable to that of lithium metal or lithium alloy, but dendrite grows. Therefore, it is widely used because it has excellent properties such as high safety, excellent initial efficiency, good potential flatness, and high density.

  In addition, as the non-aqueous solvent of the non-aqueous electrolyte, carbonates, lactones, ethers, esters and the like are used alone or in combination of two or more, and among these, the dielectric constant is particularly high. Many carbonates which are large and have a high ionic conductivity of the non-aqueous electrolyte are used.

On the other hand, as a positive electrode active material, lithium represented by Li _x MO ₂ (wherein M is at least one of Co, Ni, and Mn) capable of reversibly occluding and releasing lithium ions. Transition metal composite oxides, that is, LiCoO ₂ , LiNiO ₂ , LiNi _y Co _1-y O ₂ (y = 0.01 to 0.99), LiMnO ₂ , LiMn ₂ O ₄ , LiCo _x Mn _y Ni _z O ₂ (X + y + z = 1), LiFePO ₄ or the like is used singly or in combination.

  Among these, since various battery characteristics are particularly superior to others, lithium cobaltate and lithium metal oxide doped with a different metal element are often used. However, cobalt is expensive and has a small abundance as a resource. Therefore, in order to continue to use these lithium cobaltate and lithium cobaltate added with different metal elements as the positive electrode active material of the nonaqueous electrolyte secondary battery, further enhancement of the performance of the nonaqueous electrolyte secondary battery is desired.

  As methods for meeting such demands, increasing the density of electrode materials, reducing the thickness of current collectors, separators, and the like, and increasing the battery voltage are generally known. Among these, when the electrode material is densified and the current collector and the separator are thinned, the productivity of the nonaqueous electrolyte secondary battery is lowered. On the other hand, increasing the charging voltage of the battery voltage is essential for the development of high-capacity batteries in the future because it can minimize the impact on the productivity of non-aqueous electrolyte secondary batteries and increase the capacity. Technology.

  In a nonaqueous electrolyte secondary battery using these lithium-containing transition metal oxides as a positive electrode active material and a carbon material such as graphite as a negative electrode active material, the charging voltage is generally 4.1 to 4.2 V (positive electrode potential). Is 4.2 to 4.3 V on a lithium basis. Under such charging conditions, the positive electrode is used only 50 to 60% of the theoretical capacity. Therefore, if the charging voltage can be further increased, the capacity of the positive electrode can be used at 70% or more of the theoretical capacity, and the capacity and energy density of the battery can be increased.

  In addition, extending the life of non-aqueous electrolyte secondary batteries and improving safety are indispensable issues for future high performance. However, for example, in the case of a positive electrode material mainly composed of lithium cobaltate, the crystal structure of lithium cobaltate in a charged state becomes unstable. Therefore, side reactions such as dissolution of the positive electrode active material and decomposition of the electrolytic solution occur, and there is a problem that battery characteristics such as storage characteristics and cycle characteristics deteriorate. That is, when lithium cobaltate is used as the positive electrode active material and the end-of-charge potential is set to 4.4 V or higher with respect to lithium, the positive electrode active material dissolves and oxygen (or oxygen radicals) are released at a relatively high temperature. The organic solvent which is the main component of the non-aqueous electrolyte is oxidatively decomposed by the oxygen or oxygen radical. Therefore, due to such a side reaction, the charge / discharge coulomb efficiency is reduced on the positive electrode side, and the storage characteristics and cycle characteristics are deteriorated.

Therefore, in order to obtain a positive electrode active material that can be charged at such a high voltage, in Patent Document 1 below, LiCoO ₂ to which a different metal element is added as a positive electrode active material and layered nickel cobalt cobalt manganate are mixed. An invention of a non-aqueous electrolyte secondary battery that can be stably charged at a high charging voltage is disclosed. The positive electrode active material disclosed in Patent Document 1 improves structural stability at high voltage by adding at least Zr and Mg different metal elements to LiCoO ₂ , and further has high thermal stability at high voltage. The safety is ensured by mixing layered nickel cobalt lithium manganate. By combining a positive electrode using these positive electrode active materials and a negative electrode having a negative electrode active material made of a carbon material, the charging voltage is set to a voltage exceeding 4.2 V (the positive electrode potential is a voltage exceeding 4.3 V based on lithium). However, a non-aqueous electrolyte secondary battery that can achieve good cycle characteristics and thermal stability has been obtained.

On the other hand, spinel-type lithium manganate (LiMn ₂ O ₄ ) has high crystal structure stability at high potentials and excellent thermal stability, and is therefore suitable for improving the performance of nonaqueous electrolyte secondary batteries. It is. However, in the case of spinel type lithium manganate, the theoretical capacity is smaller than that of lithium cobaltate and the filling ability is low, so that it is difficult to achieve high capacity. In addition, the spinel type lithium manganate has a problem that the cycle characteristics are inferior because manganese itself is dissolved in the electrolyte at a high temperature.

Therefore, in Patent Documents 2 to 4 below, a positive electrode active material in which the surface of a lithium composite oxide serving as a core is coated with spinel lithium manganate and thermal stability is imparted to the lithium composite oxide of the core. The invention of the used nonaqueous electrolyte secondary battery is disclosed. Further, Patent Documents 5 to 7 below describe inventions of non-aqueous electrolyte secondary batteries using a positive electrode active material in which elution of Mn is suppressed by substituting a part of Mn of spinel type lithium manganese oxide with Al. It is disclosed.
JP 2005-317499 A JP 2000-164214 A JP 2004-127695 A JP 2006-12426 A JP 2001-151511 A JP 2001-143705 A JP 2000-331682 A

  As shown in the above-mentioned Patent Document 1, various non-aqueous electrolyte secondary batteries conventionally containing a lithium composite oxide as a positive electrode active material can be charged with various voltages in order to increase the capacity and energy density. Improvements have been made. However, if the charging potential of the non-aqueous electrolyte secondary battery is further increased to increase the charging depth of the positive electrode active material, the non-aqueous electrolyte is decomposed on the surface of the positive electrode active material and the structure of the positive electrode active material itself is likely to deteriorate. Such decomposition of the non-aqueous electrolyte and the structure deterioration of the positive electrode active material increase with an increase in the end-of-charge voltage. Therefore, the secondary battery has a high capacity non-aqueous electrolyte that maintains the same cycle characteristics and charge storage characteristics as conventional models. It has been difficult to provide a battery.

  On the other hand, when a positive electrode active material in which the surface of a lithium composite oxide that is a core as shown in Patent Documents 2 to 4 is coated with a spinel-type lithium manganate is used, Thermal stability can be imparted. However, since the lithium composite oxide as a core deteriorates in structure when charged at a high charge voltage, the non-aqueous electrolyte secondary battery disclosed in Patent Documents 2 and 3 has a charge end voltage of 4.1 V to 4.V. It is performed at 2 V or less (4.2 V to 4.3 V or less based on lithium) (Note that Patent Document 4 does not show anything about the charging voltage). Furthermore, in the nonaqueous electrolyte secondary batteries disclosed in the above cited examples 5 to 7, the end-of-charge voltage is 4.2 V (4.3 V based on lithium).

  The present invention has been made to solve the problems of the non-aqueous electrolyte secondary battery using the positive electrode active material in which the surface of the lithium composite oxide as the core described above is coated with spinel type lithium manganate. . That is, according to the present invention, when a positive electrode active material in which the surface of the core lithium composite oxide is coated with spinel type lithium manganate is used, charging is performed at a high charge end potential of 4.4 V to 4.6 V based on lithium. Even so, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that has a high capacity and that has excellent storage characteristics and cycle characteristics at high temperatures.

In order to achieve the above object, the nonaqueous electrolyte secondary battery of the present invention comprises:
In a non-aqueous electrolyte secondary battery including a positive electrode having a positive electrode active material capable of inserting and extracting lithium,
The positive electrode active material is composed of a core oxide composed of a lithium metal composite oxide and a coating oxide composed of lithium manganese oxide having a spinel structure in which a part of manganese is replaced with aluminum. The surface of the product is coated with the coating oxide.

  In the present invention, the coating oxide covering the surface of the core oxide needs to be made of lithium manganese oxide in which a part of manganese having a spinel structure is replaced with aluminum. The lithium manganese oxide having a spinel structure has a reaction region at 4.6 V on the basis of lithium. When this reaction region is used, the crystal structure of the lithium manganese oxide having a spinel structure becomes extremely unstable, and when used as a positive electrode active material, the battery characteristics are significantly deteriorated. The reaction region of 4.6 V based on lithium of this lithium manganese oxide having a spinel structure does not disappear even if a part of manganese is replaced with lithium, magnesium, zinc, or other 3d transition metal elements. It disappears when the part is replaced with aluminum. Therefore, according to the nonaqueous electrolyte secondary battery of the present invention, even when charged with a charge end voltage of 4.6 V at least based on lithium, it maintains a high capacity and has excellent storage characteristics and cycle characteristics at high temperatures. A water electrolyte secondary battery is obtained.

  The non-aqueous electrolyte secondary battery of the present invention may be a cylindrical or rectangular non-aqueous electrolyte secondary battery using a wound electrode body in which the positive electrode is wound together with a separator and a negative electrode, or the positive electrode and the separator And a square non-aqueous electrolyte secondary battery in which a negative electrode is laminated.

As the core oxide, Li _x MO ₂ (however, M is at least one of Co, Ni, and Mn) capable of reversibly occluding and releasing lithium ions conventionally used. lithium transition metal composite oxide represented, _{namely, LiCoO 2, LiNiO 2, LiNi} y Co 1-y O 2 (y = 0.01~0.99), LiMnO 2, LiCo x Mn y Ni z O 2 ( x + y + z = 1), LiNi _1-xy Co _y Al _y O _2, LiFePO _4, or the like can be used singly or in combination. However, from the viewpoint of increasing the capacity at a high charge voltage and increasing the energy density, lithium cobaltate and lithium cobaltate doped with a different metal element are preferable.

  In the non-aqueous electrolyte secondary battery of the present invention, as the negative electrode active material, natural graphite, artificial graphite, carbon black, coke, glassy carbon, carbon fiber, or a mixture of one or more of these fired bodies, etc. It is preferable to use a negative electrode mainly composed of a carbonaceous material. However, in addition to the carbonaceous material, an alloy of lithium and aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, or other known negative electrode actives for non-aqueous electrolyte secondary batteries. A negative electrode using a substance can also be used.

  Further, as the non-aqueous solvent (organic solvent) constituting the non-aqueous solvent-based electrolyte in the non-aqueous electrolyte secondary battery of the present invention, carbonates, lactones, ethers, esters and the like can be used. Two or more types of solvents can be mixed and used. Among these, carbonates, lactones, ethers, ketones, esters and the like are preferable, and carbonates are more preferably used.

  Specific examples include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl. -1,3-oxazolidine-2-one, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, γ -Butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, 1,4-dio Xanthan can be mentioned.

In addition, as a solute of the nonaqueous electrolyte in the present invention, a lithium salt generally used as a solute in a nonaqueous electrolyte secondary battery can be used. Such lithium salts include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , and mixtures thereof Illustrated. Among these, LiPF ₆ (lithium hexafluorophosphate) is preferably used. The amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L.

In the non-aqueous electrolyte secondary battery of the present invention, the core oxide is represented by the general formula Li _{1 + a} Co _1-x M _x O ₂ (M = Mg, Al, Ti, and Zr, −0 0.1 ≦ a ≦ 0.2, 0 ≦ x ≦ 0.1), which is preferably a lithium-containing cobalt composite oxide having a layered structure.

  When the core oxide is a lithium-containing cobalt composite oxide having a layered structure represented by the above general formula, when used in a charged state in which the charge end potential is 4.4 V to 4.6 V on the basis of lithium, The capacity can be made close to the theoretical capacity, and the capacity and energy density of the battery can be increased.

In the non-aqueous electrolyte secondary battery of the present invention, the core oxide has the general formula Li _{1 + a} Co _1-xy Al _x Mg _y O ₂ (−0.1 ≦ a ≦ 0.2, 0 ≦ x ≦ A lithium-containing cobalt composite oxide having a layered structure represented by 0.1, 0 ≦ y ≦ 0.1, 0 <x + y ≦ 0.1) is preferable.

  In a lithium-containing cobalt composite oxide having a layered structure, when a part of cobalt is replaced with both aluminum and magnesium, the charge end potential is higher than that of lithium cobaltate even in a charged state of 4.4 V to 4.6 V based on lithium. The crystal structure is stable. Therefore, according to the nonaqueous electrolyte secondary battery of this aspect, the above effect is particularly noticeable. Note that it is preferable to substitute a part of cobalt with equimolar amounts of aluminum and magnesium because the crystal structure is further stabilized.

In the nonaqueous electrolyte secondary battery of the present invention, the coating oxide has a general formula of Li _{1 + b} Al _z Mn _2−z−b O ₄ (0 ≦ b ≦ 0.15, 0 <z ≦ 0.3, 0 A lithium-containing manganese composite oxide having a spinel structure represented by ≦ b + z ≦ 0.5) is preferable.

  When the coating oxide is a lithium-containing manganese composite oxide having a spinel structure represented by the above general formula, the reaction region of 4.6 V clearly disappears with respect to the lithium of the lithium manganese oxide having a spinel structure. Therefore, a non-aqueous electrolyte secondary battery that exhibits the above effects can be obtained. In addition, when a part of manganese is substituted with lithium, magnesium, zinc, or the like, the same effect as when aluminum is substituted is not obtained.

  In the nonaqueous electrolyte secondary battery of the present invention, the amount of the coating oxide is preferably 0.1 to 25 mol% with respect to the amount of the core oxide.

  When the amount of the coating oxide is less than 0.1 mol% with respect to the amount of the core oxide, the battery capacity is increased, but the storage characteristics and cycle characteristics at high temperatures are deteriorated, which is not preferable. When the amount of the coating oxide is less than 25 mol% with respect to the amount of the core oxide, the storage characteristics and the cycle characteristics at high temperatures are good, but the battery capacity becomes small, which is not preferable. A more preferable amount of the coating oxide in consideration of all of the battery capacity, storage characteristics at high temperature and cycle characteristics is 0.5 to 20 mol% with respect to the amount of the core oxide.

  In the nonaqueous electrolyte secondary battery of the present invention, the end-of-charge potential of the positive electrode active material can be set to 4.4 V to 4.6 V based on lithium.

  According to the nonaqueous electrolyte secondary battery of the present invention, the end-of-charge voltage can be set to 4.4 to 4.6 V on the basis of lithium, which is higher than that of the conventional battery, so that the end-of-charge voltage is 4.3 V on the basis of lithium. Thus, the nonaqueous electrolyte secondary battery is superior in storage characteristics and cycle characteristics at high temperatures while having a higher capacity than the conventional nonaqueous electrolyte secondary battery.

  Hereinafter, the best mode for carrying out the present invention will be described in detail using various examples and comparative examples. However, the following examples show examples of non-aqueous electrolyte secondary batteries for embodying the technical idea of the present invention, and are not intended to specify the present invention to these examples. The present invention can be equally applied to various modifications without departing from the technical idea shown in the claims.

[Preparation of positive electrode plate]
(Production of core oxide)
As a starting material, lithium carbonate (Li ₂ CO ₃ ) was used as a lithium source. As the cobalt source, 1 mol% of magnesium (Mg) and aluminum (Al) are coprecipitated with respect to cobalt as different elements during the synthesis of cobalt carbonate, and then the different element-added tricobalt tetroxide (Co) obtained by thermal decomposition reaction is obtained. ₃ O ₄ ) was used. These compounds were weighed so that the molar ratio of lithium to cobalt was 1: 1, then mixed in a mortar, and then fired at 850 ° C. for 20 hours in an air atmosphere to obtain magnesium and aluminum-added lithium cobalt oxide. . This was pulverized with a mortar until the average particle size became 10 μm to obtain a core oxide. The molecular formula of this core oxide is Li [Co _0.98 Al _0.01 Mg _0.01 ] O ₂ . This core oxide was commonly used in Examples 1 to 8 and Comparative Examples 1 to 5.

(Formation of coating layer)
The core oxide particles thus obtained are added to pure water and stirred, and an aqueous solution having manganese ions having a predetermined composition is dropped. Next, an aqueous solution of ammonium hydrogen carbonate is added, and manganese ions are precipitated as ammonium hydroxide on the surface of the core oxide to form a coating layer. Next, the particles having manganese hydroxide deposited on the surface of the core oxide particles are filtered, washed with water, heat treated, and then lithium carbonate, aluminum hydroxide (Al (OH) ₃ ) and boron oxide (B ₂ O ₃ ) (calcination aid). Agent). Thereafter, the positive electrode active material particles were fired at 700 ° C. for 20 hours, and the resulting oxide was pulverized in an mortar to an average particle size of 10 μm, and the surface of the core oxide particles was coated with spinel-structured aluminum-substituted lithium manganate Got. In addition, the coating layer was prepared so that it might become a composition and a coating | coated ratio as shown in following Table 1 about Examples 1-8 and Comparative Examples 2-5. However, Comparative Example 1 did not form a coating layer.

(Formation of positive electrode plate)
94 parts by mass of positive electrode active material particles having the surface of the core oxide particles thus obtained coated with aluminum-substituted lithium manganate, 3 parts by mass of carbon powder as a conductive agent, and polyfluoride as a binder. A slurry was prepared by mixing with an N-methylpyrrolidone (NMP) solution so that the vinylidene chloride (PVdF) powder was 3 parts by mass. This slurry was applied to both surfaces of an aluminum current collector having a thickness of 20 μm by a doctor blade method to form an active material layer on both surfaces of the positive electrode current collector. Then, after passing through the dryer and drying, it is compressed to a thickness of 130 μm using a compression roller, and cut to produce a positive electrode plate with a short side length of 30 mm and a long side length of 450 mm did.

  In addition, the addition amount of the different atom except magnesium of the positive electrode active material particles was analyzed by ICP (Inductivity Coupled Plasma) emission spectrometry. The amount of magnesium added was analyzed by atomic absorption method. Further, the cobalt content was obtained by dissolving the sample in hydrochloric acid, drying, diluting with water, adding alcorbic acid, and then titrating using an EDTA (ethylene diamine tetraacetic acid) standard solution. The lithium content was quantified by dissolving the sample in hydrochloric acid, drying it, diluting it with water, and measuring the flame intensity at 670.8 nm.

[Production of negative electrode plate]
95 parts by weight of a negative electrode active material made of graphite powder, 3 parts by weight of a thickener made of carboxymethyl cellulose (CMC), and 2 parts by weight of a binder made of styrene butadiene rubber (SBR) are mixed with an appropriate amount of water. To make a slurry. This slurry was applied to both surfaces of a 20 μm thick copper current collector by a doctor blade method to form an active material layer. Then, after passing through a dryer and drying, the negative electrode plate having a short side length of 32 mm and a long side length of 460 mm is prepared by compressing to 150 μm in thickness using a compression roller and cutting. did. This negative electrode plate was used in common with Examples 1 to 8 and Comparative Examples 1 to 5.

  The potential of graphite during charging is about 0.1 V with respect to lithium. The positive electrode and negative electrode active material filling amount was adjusted so that the positive electrode / negative electrode charge capacity ratio (negative electrode charge capacity / positive electrode charge capacity) was 1.25 at the potential of the positive electrode active material as a design standard.

[Production of electrode body]
The positive electrode plate and the negative electrode plate produced as described above are arranged so as to face each other with a separator made of a polyethylene microporous film having a width of 44 mm and a thickness of 25 μm, and then around the cylindrical winding core. Winding was performed to produce a cylindrical electrode body. Furthermore, the outermost periphery was fixed with a polypropylene tape so that the cylindrical electrode body could not be unwound. Next, this cylindrical electrode body was pressed to obtain an electrode body having an oval cross-sectional shape. The pressure of the press was controlled so that the thickness of the electrode body after pressing was 4.2 mm. After pressing, a tape was affixed to the surface of the electrode body that contacted the bottom of the can to insulate it from the bottom of the can.

[Preparation of electrolyte]
LiPF ₆ was dissolved in a mixed solvent of EC (30 vol%) and MEC (70 vol%) to a concentration of 1 mol / L to prepare an electrolyte, which was used for battery production.

[Production of battery]
The flat wound electrode body produced as described above is inserted into an outer can (5.5 × 35 × 40 mm), 2.5 g of the above-described electrolytic solution is injected, and the injection hole is made of aluminum. By installing the plate and sealing with laser welding, the rectangular nonaqueous electrolyte secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 having the shapes shown in FIG. 1 were produced.

[Preservation test]
About each battery of Examples 1-8 and Comparative Examples 1-5, it charged with the constant current of 1 It = 700mAh at 25 degreeC, and battery voltage reached to 4.4V (the electric potential of a positive electrode is 4.5V on the basis of lithium). After that, the battery was charged at a constant voltage of 4.4 V until the current value reached 20 mA. Thus, the capacity | capacitance at the time of discharging until the battery voltage became 3.0V with the constant current of 1 It each at 25 degreeC was calculated | required as the discharge capacity before a storage test. After that, it was charged again at 25 ° C. with a constant current of 1 It = 700 mAh, and after the battery voltage reached 4.4 V, it was charged with a constant voltage of 4.4 V until the current value reached 20 mA, and then the atmosphere at 60 ° C. Stored for 10 days. About each battery after a preservation | save, the capacity | capacitance at the time of discharging until the battery voltage became 3.0V at 1 It was measured, and it calculated | required as the discharge capacity after a preservation | save test. And the remaining capacity was measured by the following formula. The results of Examples 1 to 3 and Comparative Examples 1 to 5 are collectively shown in Table 1, and the results of Examples 4 to 8 are shown together with the results of Example 1 in Table 2.
Residual capacity (%) = (discharge capacity after storage test / discharge capacity after storage test) × 100

[Cycle characteristic test]
About each battery of Examples 1-8 and Comparative Examples 1-5, it charged with the constant current of 1 It = 700mAh at 25 degreeC, and after the battery voltage reached 4.4V, it is a current value with the constant voltage of 4.4V. Was charged to 20 mA. The battery thus charged was discharged at 25 ° C. with a constant current of 1 It each until the battery voltage reached 3.0 V, and the discharge capacity at this time was determined as the discharge capacity of the first cycle. Next, the above charge / discharge cycle was repeated 500 times, and the 500th discharge capacity was determined. And the capacity | capacitance maintenance factor was calculated | required with the following formulas. The results of Examples 1 to 3 and Comparative Examples 1 to 5 are collectively shown in Table 1, and the results of Examples 4 to 8 are shown together with the results of Example 1 in Table 2.
Capacity maintenance rate (%)
= (Discharge capacity at 500th cycle / discharge capacity at the first cycle) × 100

  Table 1 shows the results of examining how the battery characteristics change by changing the composition of the coating layer while keeping the composition of the core oxide and the coating ratio of the coating layer constant. In Comparative Example 1, a coating layer is not formed on the surface of the core oxide particles, and in Comparative Example 2, manganese in the coating layer is not replaced with a different element. Further, in Comparative Examples 3 to 5, a part of manganese in the coating layer was replaced with lithium (Comparative Example 3), magnesium (Comparative Example 4) and zinc (Comparative Example 5) as different elements. In Examples 1 to 3, a part of manganese in the coating layer was replaced with aluminum as a different element, and the replacement ratio was 0.1 mol (Example 1), 0, 2 mol (Example 2) and 0. 3 mol (Example 3). Further, the coating ratio of the coating layer is constant at 5 mol% in both Comparative Examples 2 to 5 and Examples 1 to 3.

  According to the results shown in Table 1, in Comparative Example 1 in which the coating layer was not formed on the surface of the core oxide particles, the battery capacity was the largest, but both the high temperature storage characteristics and the cycle characteristics were the worst. This is because the covering layer has a smaller theoretical capacity than the core layer, and the batteries of Comparative Examples 2 to 5 and Examples 1 to 3 using the positive electrode active material on which the covering layer was formed had a reduced battery capacity. It is estimated to be. Moreover, since the structure of the core layer is unstable in a charged state at a high voltage, the battery of Comparative Example 1 using the positive electrode active material having no coating layer is estimated to have deteriorated high-temperature storage characteristics and cycle characteristics. The

  Moreover, the following can be understood from the results of Comparative Examples 2 to 5 and Example 1 in which the substitution ratio of manganese in the coating compound to a different element is constant and the kind of the different element is changed. That is, in the case of a battery using a positive electrode active material in which the different elements are lithium (Comparative Example 3), magnesium (Comparative Example 4), and zinc (Comparative Example 5), the battery capacity, high-temperature storage characteristics and cycle characteristics are substantially reduced. Equivalent results are obtained. However, in the case of a battery using a positive electrode active material whose dissimilar element is aluminum (Example 1), the battery capacity is substantially the same as in Comparative Examples 2 to 5, but both the high-temperature storage characteristics and the cycle characteristics are compared. The results are much better than those of Examples 2-5.

  Further, according to the results of Examples 1 to 3 in which the different element is aluminum and the substitution ratio is changed, the battery capacity tends to decrease as the substitution ratio increases, but both the high-temperature storage characteristics and the cycle characteristics. Substantially equivalent results were obtained, and results much better than those of Comparative Examples 2 to 5 were obtained. Therefore, it can be seen that when the end-of-charge voltage is made higher than that of the conventional one, it is most preferable to replace with aluminum if manganese in the coating layer is replaced with a different element.

  Table 2 shows that the composition of the core oxide and the coating layer is constant, and the coating ratio of the coating layer is 0.1 mol% (Example 4), 1 mol% (Example 5), 5 mol% (Example 1). The results of examining how the battery characteristics change when changed to 10 mol% (Example 6), 20 mol% (Example 7) and 25 mol% (Example 8) are shown. As this coating layer, a layer in which a part of manganese having the same composition as in Example 1 is replaced with aluminum is used.

  According to the results shown in Table 2, when the coating ratio of the coating layer is in the range of 0.1 mol% to 25 mol%, the battery capacity tends to decrease as the coating ratio increases. Further, both the high temperature storage characteristics and the cycle characteristics have maximum values when the coating ratio is in the range of 5 to 10 mol%, and a tendency to decrease as the ratio goes out of this range is recognized. However, even when the coating ratio of the coating layer is 0.1 mol% and 25 mol%, the same results as Comparative Examples 3 to 5 in which manganese in the coating layer is replaced with lithium, magnesium, or zinc are obtained for high temperature storage characteristics and cycle characteristics. ing. Therefore, it is understood that the coating ratio of the coating layer is preferably in the range of 1 mol% to 25 mol%, and more preferably in the range of 1 mol% to 20 mol% if a good effect is expected with respect to high temperature storage characteristics and cycle characteristics.

  Thus, the positive electrode active material coated with a coating oxide composed of lithium manganese oxide in which the surface of the core oxide composed of lithium metal composite oxide has a spinel structure and a part of manganese is substituted with aluminum It can be seen that a non-aqueous electrolyte secondary battery with a high capacity and excellent high-temperature storage characteristics and cycle characteristics can be obtained even when the end-of-charge potential is 4.4 V or more on the basis of lithium. Such characteristics cannot be obtained when lithium cobaltate is used alone or when lithium cobaltate and aluminum-substituted lithium manganate are mixed.

It is a perspective view which cut | disconnects the square nonaqueous electrolyte secondary battery manufactured conventionally from the longitudinal direction.

Explanation of symbols

10: non-aqueous electrolyte secondary battery, 11: positive electrode plate, 12: negative electrode plate, 13: separator, 14: wound electrode body, 15: battery outer can, 16: sealing plate, 17: insulator 18: negative electrode Terminal, 19: Negative electrode tab, 20: Insulating spacer, 21: Electrolyte injection hole

Claims (6)

In a non-aqueous electrolyte secondary battery including a positive electrode having a positive electrode active material capable of inserting and extracting lithium,
The positive electrode active material is composed of a core oxide composed of a lithium metal composite oxide and a coating oxide composed of lithium manganese oxide having a spinel structure in which a part of manganese is replaced with aluminum. A non-aqueous electrolyte secondary battery, characterized in that the surface of the product is coated with the coating oxide. The core oxide has a general formula Li _{1 + a} Co _1-x M _x O ₂ (M = at least one selected from Mg, Al, Ti, and Zr, −0.1 ≦ a ≦ 0.2, 0 ≦ x The nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium-containing cobalt composite oxide has a layered structure represented by ≦ 0.1). The core oxide has the general formula Li _{1 + a} Co _1-xy Al _x Mg _y O ₂ (−0.1 ≦ a ≦ 0.2, 0 ≦ x ≦ 0.1, 0 ≦ y ≦ 0.1, 3. The nonaqueous electrolyte secondary battery according to claim 2, wherein the lithium-containing cobalt composite oxide has a layered structure represented by 0 <x + y ≦ 0.1). The coating oxide is a spinel represented by the general formula Li _{1 + b} Al _z Mn _2−z−b O ₄ (0 ≦ b ≦ 0.15, 0 <z ≦ 0.3, 0 ≦ b + z ≦ 0.5). The nonaqueous electrolyte secondary battery according to claim 1, which is a lithium-containing manganese composite oxide having a mold structure.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the amount of the coating oxide is 0.1 to 25 mol% with respect to the amount of the core oxide.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein an end-of-charge potential of the positive electrode active material is 4.4V to 4.6V on a lithium basis.

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