JP2008084743A - Positive electrode for secondary battery, and secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode for a secondary battery superior in long-term battery characteristics, and to provide the secondary battery that uses the same. <P>SOLUTION: The positive electrode for the secondary battery contains an aluminum-cobalt-containing lithium-manganese complex oxide, as expressed by the chemical Formula: Li<SB>1+x</SB>Mn<SB>2-x-y-z-w</SB>Al<SB>y</SB>Co<SB>z</SB>Mg<SB>w</SB>O<SB>4</SB>(0.03<x<0.25, 0.01<y<0.2, 0.01<z<0.2, 0≤w<0.1, and x+y+z+w<0.4) and a lithium-nickel-cobalt-manganese complex oxide, as expressed by the chemical Formula: Li<SB>1+a</SB>(Ni<SB>1-p-q-r</SB>Co<SB>p</SB>Mn<SB>q</SB>Me<SB>r</SB>)O<SB>4</SB>(Me is an element selected from among at least one of Mg, Al, Fe, Cr, Ti, and In, 0≤a<0.1, 0.2<p<0.45, 0.2<q<0.45, and 0≤r<0.15). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a positive electrode for a secondary battery and a secondary battery using the same, and in particular, has a high capacity and charge / discharge characteristics, particularly a cycle life at high temperatures, used for a lithium secondary battery or a lithium ion secondary battery. The present invention relates to a positive electrode for a secondary battery having improved capacity storage characteristics and self-discharge, and a secondary battery using the same.

  Lithium-ion secondary batteries are a composite oxidation of lithium and transition metal oxides with a negative electrode using a carbonaceous material that can be doped or dedoped with lithium, or a metal material that forms an alloy with lithium and lithium. A positive electrode using an active material as an active material is used. Each of the strip-like negative electrode side current collector and the positive electrode current collector, which is applied and laminated via a separator, is covered with an exterior material or laminated. A battery is manufactured by accommodating a wound body obtained by winding the product in a spiral shape in a battery can. As the positive electrode active material used for the positive electrode, a composite oxide of lithium and a transition metal such as lithium cobaltate, lithium nickelate, and lithium manganate is used.

  In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been widely used as power sources for mobile phones, notebook personal computers, camcorders and the like. These non-aqueous electrolyte secondary batteries have a larger volume or weight capacity density and can take out a higher voltage than secondary batteries using aqueous electrolyte such as conventional lead storage batteries and alkaline storage batteries. Therefore, it is widely adopted as a power source for small devices, and greatly contributes to the development of today's mobile devices.

  On the other hand, in recent years, the shift to a clean energy society and the establishment of environmental technologies have been attracting attention due to the growing awareness of environmental issues, and it is suitable for power storage applications, uninterruptible power supply (UPS) applications, and mobile power supply applications. Early realization of high performance secondary batteries is required. Lithium ion secondary batteries are being actively studied for such large-scale batteries due to the above-mentioned characteristics of high energy density. However, in order to spread a wide range of applicable products, the life cycle cost of existing products is high. Superiority is essential, and price reduction is an indispensable element.

  In other words, in a lithium ion secondary battery with a high operating voltage, if the charge / discharge current value can be increased using a low-cost material, it can be expressed as a high-performance UPS, hybrid vehicle (HEV), or electric vehicle (EV). That can contribute to the realization of an information society and a clean energy society. Against this background, low-cost, high capacity and high output of lithium ion secondary batteries are being actively studied.

  For example, in the past, lithium cobaltate was mainly used as the positive electrode active material for small portable devices, but as an alternative to lithium cobaltate, an attempt was made to replace Co in lithium cobaltate with other elements, or iron having an olivine structure. Development of system materials is accelerating.

  When lithium cobaltate is used for the positive electrode, vigorous research has been conducted since an electromotive force exceeding 4 V has been obtained, and conventionally, lithium cobaltate has been mainly used for small portable devices. Lithium cobalt oxide is widely used as a positive electrode active material in today's lithium ion secondary batteries because it exhibits good characteristics such as potential flatness, capacity, discharge potential, and cycle characteristics.

However, cobalt, which is an element contained in lithium cobaltate, has a small amount of crust and is an expensive material, so there is a problem in supply stability and price of raw materials. In addition, since lithium cobaltate has a layered rock salt structure (α-NaFeO ₂ structure), an oxygen layer having a large electronegativity is adjacent due to lithium desorption during charging. For this reason, it is necessary to limit the amount of lithium extracted during actual use, and if too much lithium is extracted, such as in an overcharged state, the structure will change due to electrostatic repulsion between oxygen layers and heat will be generated. In order to ensure the safety of the battery, a large protection circuit is required outside so that a positive electrode material with higher safety is required.

Although lithium nickelate has a capacity greater than that of lithium cobaltate, the crystal structure is the same layered structure as lithium cobaltate, which is due to the instability of Ni ⁴⁺ during charging, resulting in oxygen desorption from lithium cobaltate. The temperature is low and safety is more difficult to secure. Furthermore, considering that the discharge potential is lower than that of lithium cobaltate and the environmental load of Ni is high, it is not attractive as an alternative material for lithium cobaltate.

  On the other hand, materials having an olivine structure such as lithium iron phosphate have been proposed in Patent Documents 1 and 2 as a positive electrode active material of a lithium secondary battery. Because it uses cheap and abundant reserves of iron, the stability of raw materials is expected. However, since lithium iron phosphate has low conductivity and the diffusion rate of lithium ions in the crystal is low, post-treatment such as micronization and surface treatment with carbon must be performed.

  Further, lithium manganate is a material that is highly expected as one of positive electrode materials for lithium ion secondary batteries. Manganese has abundant crustal abundance compared to cobalt, is an inexpensive element, and there is no problem with the supply stability of raw materials.

This lithium manganate has a spinel structure represented by the chemical formula LiMn ₂ O ₄ and functions as a 4V-class positive electrode material between the composition and λ-MnO ₂ . Since spinel lithium manganate has a three-dimensional host structure different from the layered rock salt structure of lithium cobaltate, etc., most of the theoretical capacity can be used, and excellent cycle characteristics are expected.

Lithium manganate LiMn ₂ O ₄ is a complex oxide that is highly anticipated as an alternative to the current mainstream positive electrode active material lithium cobaltate. However, conventional secondary batteries using lithium manganate are charged and discharged at high temperatures. There were problems in practical use in two points: capacity deterioration due to repetition and reduction in storage capacity due to self-discharge. In addition, batteries for use as power storage or electric vehicle power sources have come up with new issues related to long-term reliability, such as the realization of low resistance characteristics and low resistance increase rate characteristics, and further innovations are required. ing.

  Accordingly, various methods have been studied to improve the cycle characteristics of organic electrolyte secondary batteries using lithium manganate as the positive electrode. For example, Patent Documents 3 to 7 propose improvement of characteristics by improving reactivity during synthesis, and Patent Documents 8 to 11 propose improvement of characteristics by controlling the particle size. The improvement of the cycle characteristics was not sufficient.

  Apart from this, Patent Document 12 proposes to improve the cycle characteristics by making the composition ratio of Li sufficiently larger than the stoichiometric ratio. The synthesis of the same excess Li composition composite oxide is also disclosed in Patent Documents 13 to 16 and the like.

Further, for the purpose of achieving an effect similar to that of the Li-excess composition, the Mn spinel material LiMn ₂ O ₄ and the lithium-rich lithium-manganese composite oxide Li ₂ Mn ₂ O ₄ , LiMnO ₂ , Li ₂ MnO that are more rich than this material are used. _The technique of mixing ₃ etc. and using it as a positive electrode active material is also disclosed in Patent Documents 17 and 18. However, when Li is added excessively or mixed with another Li-rich compound, the cycle characteristics are improved while the charge / discharge capacity value / charge / discharge energy value decreases, resulting in high energy density and long cycle life. There is a problem that it is difficult to achieve both.

  On the other hand, studies have been made to improve the characteristics by adding and doping another element to the three-component compound of Li—Mn—O. For example, Patent Documents 19 to 26 and the like describe addition / doping of Co, Ni, Fe, Cr, Al, or the like. The addition of these metal elements is accompanied by a reduction in charge / discharge capacity and an increase in electrode resistance, as in the case of examining the excess Li composition, and further ingenuity is required to satisfy the total performance.

  In addition, when the electrolyte contains a composition that can generate hydrogen ions by reacting with water, a charge / discharge cycle characteristic of the positive electrode containing lithium manganate can be obtained by placing a hydrogen ion scavenger at a location in contact with the electrolyte in the battery. It is known that a film-covered non-aqueous electrolyte secondary battery excellent in storage characteristics, safety, and battery external swelling suppression characteristics can be produced (see, for example, Patent Document 27).

  However, although these disclosed technologies have certain effects, further improvement is required in long-term reliability and output characteristics assuming practical use, so the charge / discharge characteristics of lithium-manganese composite oxides, In particular, the cycle characteristics, capacity storage characteristics, and low resistance increase characteristics at high temperatures were not always satisfactory.

As described above, although lithium manganate LiMn ₂ O ₄ is a complex oxide that attracts great expectations as an alternative to the currently used positive electrode active material LiCoO ₂ , batteries using conventional LiMn ₂ O ₄ are cycled. The problem is that it is difficult to extend the service life.

  Although the technical problem of battery manufacture and compatibility with electrolyte solution etc. are pointed out as this cause, the following things can be considered when paying attention to the positive electrode material itself and the influence of the positive electrode material.

  The cause of the capacity deterioration due to the charge / discharge cycle is that the average valence of Mn ions changes between trivalent and tetravalent as charge compensation accompanying Li in / out, so that Jahn-Teller distortion occurs in the crystal, In addition, the elution of Mn from lithium manganate or the impedance rise due to the elution of Mn. In other words, the causes of capacity deterioration in which the charge / discharge capacity decreases by repeating the charge / discharge cycle include the influence of impurities, elution of Mn from lithium manganate, precipitation of eluted Mn on the negative electrode active material or separator, The inactivation due to the release of the substance particles, the influence of the acid generated by the contained water, the deterioration of the electrolyte solution due to the release of oxygen from lithium manganate, and the like can be considered.

  Assuming that a single spinel phase is formed, the elution of Mn is caused by the disproportionation of trivalent Mn in the spinel structure into tetravalent Mn and divalent Mn. It can be easily dissolved, and it can be eluted from the relative shortage of Li ions. Repeated charge and discharge promotes generation of irreversible capacity and disorder of atomic arrangement in the crystal. At the same time, the eluted Mn ions are likely to be deposited on the negative electrode or the separator to prevent the movement of Li ions. Further, when Mn ions are deposited on the negative electrode or the separator, a coating having low conductivity is formed on the negative electrode or the separator, so that the direct current resistance value of the battery is increased, which causes a decrease in output. In addition, lithium manganate is distorted by the Jahn-Teller effect, and expansion / contraction of several percent of the unit cell length is caused by taking in and out Li ions. Therefore, by repeating the cycle, it is expected that some electrical contact defects will occur and the released particles will not function as an electrode active material.

  Further, it is considered that oxygen release from lithium manganate is facilitated along with elution of Mn. Lithium manganate having many oxygen defects has a 3.3 V plateau capacity that increases as the cycle progresses, resulting in deterioration of cycle characteristics. Further, it is presumed that a large amount of oxygen release affects the decomposition of the electrolytic solution, which may cause cycle deterioration due to deterioration of the electrolytic solution. To solve this problem, improvement of the synthesis method, addition of other transition metal elements, excess Li composition, etc. have been studied so far. To satisfy both of the increase in discharge capacity and the improvement in cycle life at the same time. Not reached.

  Therefore, reducing Mn elution, reducing lattice distortion, reducing oxygen vacancies, etc. are derived as countermeasures.

  Next, as a cause of the decrease in storage capacity after high temperature storage, excluding internal short-circuit phenomena such as inadequate positive and negative electrode alignment due to the battery manufacturing process and contamination of electrode metal debris, the storage characteristics can be improved. This is considered to be effective in improving the stability of lithium manganate against the above, that is, suppressing elution of Mn, reaction with the electrolyte, release of oxygen, and the like.

  In particular, when used in a high-temperature environment, both of these deteriorations are accelerated, which is a major obstacle to expanding applications. However, the charge / discharge capacity is limited because there are limited material systems that can be expected to satisfy the performance required for current high performance secondary batteries such as high electromotive force, voltage flatness during discharge, cycle characteristics, energy density, etc. There is a need for a new spinel structure lithium manganate that does not deteriorate and has excellent cycle characteristics and storage characteristics.

By the way, as a modified positive electrode active material having a layered structure, it contains Ni, Mn, or Ni, Mn and Co, for example, LiNi _0.33 Co _0.34 Mn _0.33 O _2. There are manganese complex oxides. This is a material attracting attention because it compensates for the disadvantages of lithium nickelate and lithium cobaltate, can procure raw materials at a relatively low cost, and has good thermal stability.

  For example, Patent Documents 28 to 30 propose a mixed oxide of a lithium / nickel / cobalt / manganese composite oxide and a spinel-type lithium manganate. However, simply mixing lithium-nickel-cobalt-manganese composite oxide and spinel-type lithium manganate improves the power density, but it does not necessarily satisfy the charge / discharge characteristics, especially the cycle life and capacity storage characteristics at high temperatures. The result which should have been not obtained.

  Patent Document 31 proposes to use a mixed oxide of lithium-nickel-cobalt-manganese composite oxide to which fluorine is added and lithium manganate having a spinel structure, but lithium-nickel-cobalt-manganese composite oxide. Due to the constitution in which fluorine is added to the product, the added fluorine reacts with the electrolytic solution and a small amount of moisture in the electrolytic solution, and protons are easily generated, and the high-temperature cycle characteristics are still not satisfactory.

Japanese Patent No. 3484003 Japanese Patent No. 3319258 JP-A-3-67464 Japanese Patent Laid-Open No. 3-119656 Japanese Patent Laid-Open No. 3-127453 JP 7-245106 A Japanese Patent Laid-Open No. 7-73883 JP-A-4-198028 Japanese Patent Laid-Open No. 5-283704 JP-A-6-295724 JP-A-7-97216 JP-A-2-270268 JP-A-4-123769 JP-A-4-147573 Japanese Patent Application Laid-Open No. 5-205744 JP-A-7-282798 JP-A-6-338320 JP 7-262984 A Japanese Patent Laid-Open No. 4-141954 Japanese Patent Laid-Open No. 4-160758 Japanese Patent Laid-Open No. 4-169076 JP-A-4-237970 JP-A-4-282560 JP-A-4-28962 JP-A-5-28991 JP 7-14572 A Japanese Patent No. 2996234 JP 2002-110253 A JP 2000-315503 A Japanese Patent Laying-Open No. 2005-340057 Japanese Patent Laid-Open No. 2005-267956

  Thus, the present invention has been made in view of the above problems, and has excellent battery characteristics, particularly long-term high-temperature charge-discharge cycle characteristics, long-term storage characteristics, and an excellent positive electrode for secondary batteries with reduced resistance increase rate. And a secondary battery using the same.

  The present inventors have scrutinized the prior art and made various studies in order to achieve the above object. As a result, the manganese (Mn) site of lithium manganate was changed to lithium (Li), aluminum (Al), and cobalt. Charge-discharge characteristics of Li-rich lithium / manganese composite oxide substituted simultaneously with (Co) by using a composite oxide in a specific composition region of the oxide and a lithium / nickel / cobalt / manganese composite oxide In particular, the present inventors have found that the charge / discharge capacity is specifically improved and that there is an extremely large effect on the improvement of the long-term high-temperature charge-discharge cycle characteristics, long-term storage characteristics, and further the low resistance increase rate characteristics at high temperatures. Is.

According to the present invention, the chemical formula _{Li 1 + x Mn 2-xyzw} Al y Co z Mg w O 4 (0.03 <x <0.25,0.01 <y <0.2,0.01 <z < 0.2,0 ≦ w <0.1, x + y + z + w <0.4) aluminum-cobalt-containing lithium-manganese composite oxide represented by the chemical formula _{Li 1 + a (Ni 1-} pqr Co p Mn q Me r) O ₄ (Me is an element selected from at least one of Mg, Al, Fe, Cr, Ti, and In, and 0 ≦ a <0.1, 0.2 <p <0.45, 0.2 <q <0.45, 0 ≦ r <0.15) A lithium-nickel-cobalt-manganese composite oxide represented by the following is obtained: The manganese composite oxide preferably has a spinel structure, and the lithium nickel Cobalt-manganese composite oxide is preferably a layered crystal structure.

  According to the present invention, the lithium-manganese composite oxide content in the positive electrode for secondary battery is (100-α) parts by mass, and the lithium-nickel-cobalt in the positive electrode for secondary battery is used. -When the content of the manganese composite oxide is α parts by mass, a positive electrode for a secondary battery that satisfies 3 <α ≦ 80 is obtained.

  Furthermore, according to the present invention, a power generation element including an electrolyte, a separator, and a negative electrode disposed opposite to the secondary battery positive electrode via the electrolyte and the separator is housed in an exterior body. A secondary battery is obtained.

Positive electrode active material for a secondary battery of the present invention has the formula _{Li 1 + x Mn 2-xyzw} Al y Co z Mg w O 4 (0.03 <x <0.25,0.01 <y <0.2 , 0.01 <z <0.2, 0 ≦ w <0.1, x + y + z + w <0.4) and an aluminum / cobalt-containing lithium / manganese composite oxide and a chemical formula Li _{1 + a} (Ni _{1-pqr Co p Mn q Me r) O} 4 (Me is an element selected Mg, Al, Fe, Cr, Ti, at least one of in, 0 ≦ a <0.1,0.2 < p <0. 45, 0.2 <q <0.45, 0 ≦ r <0.15) By including the lithium / nickel / cobalt / manganese composite oxide, the aluminum / cobalt-containing lithium / manganese composite oxide In the initial state before charging and discharging, overdoped lithium and cobalt To stabilize the crystal by lowering the lattice constant of the spinel structure, aluminum stabilizes the structure by exhibiting a trivalent stable oxidation degree.

  In addition, by simultaneously replacing the Mn site with cobalt and aluminum, it becomes possible to insert and desorb some of the excessively doped lithium during charging and discharging, which is higher than the conventional lithium excess composition. Lithium-manganese composite oxide can be obtained, and when it is substituted with magnesium, the resistance of the positive electrode active material particles is reduced by substituting magnesium exhibiting a stable bivalent oxidation degree. The output characteristics of the battery could be improved. In addition, lithium / nickel / cobalt / manganese composite oxides can be procured at a relatively low cost by avoiding the problems of thermal stability against lithium nickelate and lithium cobaltate, and the problem of raw material supply. The output could be obtained.

  In addition, the elution of manganese is suppressed by the proton trapping effect of the lithium / nickel / cobalt / manganese composite oxide, and the addition of other elements (Me) stabilizes the crystal structure and improves the charge / discharge cycle characteristics at high temperatures. For the effects such as, by using each of them in combination rather than being used alone, high power density and safety can be maintained, and the charge / discharge cycle life at high temperature can be improved.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing the configuration of the secondary battery of the present invention. As shown in FIG. 1, a layer 12 containing a positive electrode active material that can occlude and release lithium ions on the positive electrode current collector 11 and a negative electrode active material that occludes and releases lithium ions on the negative electrode current collector 14. The layer 13 to be contained is arranged so as to face the electrolyte solution 15 and a separator 16 including the electrolyte solution 15.

  The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode using a positive electrode active material containing the above-mentioned aluminum / cobalt-containing lithium / manganese composite oxide and the lithium / nickel / cobalt / manganese composite oxide, and lithium. The main component is a negative electrode having a negative electrode active material that can be occluded and released, and a separator that does not cause electrical connection is sandwiched between the positive electrode and the negative electrode, and the positive electrode and the negative electrode are immersed in a lithium ion conductive non-aqueous electrolyte. In a state, they are arranged to face each other via a non-aqueous electrolyte, and these are sealed in a battery case. When a voltage is applied to the positive electrode and the negative electrode, lithium ions are desorbed from the positive electrode active material, and the lithium ions are occluded in the negative electrode (active material), resulting in a charged state. In addition, by connecting the positive electrode and the negative electrode to a device outside the battery for output, lithium ions are released from the negative electrode active material, and the lithium ion is occluded in the positive electrode active material, which is opposite to that during charging. .

(Positive electrode)
Positive electrode active material for a nonaqueous electrolyte secondary battery according to the present invention has the formula _{Li 1 + x Mn 2-xyzw} Al y Co z Mg w O 4 (0.03 <x <0.25,0.01 < y <0.2, 0.01 <z <0.2, 0 ≦ w <0.1, x + y + z + w <0.4) and an aluminum / cobalt-containing lithium / manganese composite oxide and a chemical formula Li _{1 + a (Ni 1-pqr Co p Mn} q Me r) O 4 (Me is an element selected Mg, Al, Fe, Cr, Ti, at least one of in, 0 ≦ a <0.1,0.2 <P <0.45, 0.2 <q <0.45, 0 ≦ r <0.15) and a lithium / nickel / cobalt / manganese composite oxide.

Next, a method for manufacturing the positive electrode active material will be described. As a raw material for producing an aluminum / cobalt-containing lithium / manganese composite oxide, Li ₂ CO ₃ , LiOH, Li ₂ O, Li ₂ SO _4, etc. can be used as the Li raw material, but Li ₂ CO ₃ , LiOH, etc. Is suitable. As the Mn raw material, various manganese oxides such as electrolytic manganese dioxide (EMD) / Mn ₂ O ₃ , Mn ₃ O ₄ , CMD, MnCO ₃ , MnSO _{4 and the} like can be used. As the Co raw material, CoO, Co ₃ O ₄ , CoCl ₂ , Co (OH) ₂ , CoSO ₄ , CoCO ₃ , Co (NO ₃ ) ₂ or the like can be used. As the Al raw material, Al ₃ O ₄ , AlCl ₃ , Al (OH) ₃ , Al ₂ (SO ₄ ) ₃ , AlCO ₃ , Al (NO ₃ ) _3, etc. can be used. MgO, Mg (OH) ₂ , MgCl ₂ , Mg (NO ₃ ) ₂ , Mg ₃ (PO ₄ ) ₂ , MgCO ₃ or the like can be used as the Mg raw material. Mn raw materials and substitutional element raw materials may hardly cause element diffusion during firing, and Mn oxides and substitutional element oxides may remain as different phases after firing the raw materials. For this reason, a mixture of Al, Co, Mg, and Mn precipitated in the form of hydroxide, sulfate, carbonate, nitrate, etc. after dissolving and mixing Co raw material and Mn raw material, Al raw material, Mg raw material in aqueous solution Or a mixture of Al, Co, Mg, and Mn containing a substitution element can be used as a raw material. It is also possible to use Al, Co, Mg, Mn oxide or Co, Mn, Al, Mg mixed oxide obtained by firing such a mixture. When such a mixture is used as a raw material, Mn, Co, Al, and Mg are well diffused at the atomic level, and Co, Al, and Mg can be easily introduced into the 16d site of the spinel structure.

  These raw materials are weighed and mixed so as to have a target metal composition ratio. The mixing is performed by pulverizing and mixing with a ball mill, a jet mill or the like. The mixed powder is fired in air or oxygen at a temperature of 600 ° C. to 950 ° C. to obtain a positive electrode active material containing an aluminum / cobalt-containing lithium / manganese composite oxide. The firing temperature is preferably a high temperature for diffusing each element, but if the firing temperature is too high, oxygen deficiency may occur, which may adversely affect battery characteristics. For this reason, it is preferable that a calcination temperature shall be about 650 degreeC to 850 degreeC. In addition, a positive electrode active material synthesized by a liquid method such as a sol-gel process or hydrothermal synthesis can be used in a similar manner if the final composition is a predetermined one.

The specific surface area of the obtained aluminum / cobalt-containing lithium / manganese composite oxide is preferably 1.5 m ² / g or less, more preferably 0.9 m ² / g or less. This is because the larger the specific surface area, the more binders are required, which tends to be disadvantageous in terms of the capacity density of the positive electrode active material.

  The lithium / nickel / cobalt / manganese composite oxide can be produced by, for example, a method disclosed in Patent Document 28.

  The obtained lithium / nickel / cobalt / manganese composite oxide and the above-described aluminum / cobalt-containing lithium / manganese composite oxide are mixed to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention.

  In the positive electrode for a non-aqueous electrolyte secondary battery, the content of the aluminum / cobalt-containing lithium / manganese composite oxide in the positive electrode for a non-aqueous electrolyte secondary battery is (100-α) mass. When the content of the lithium / nickel / cobalt / manganese composite oxide in the positive electrode for a secondary battery is α parts by mass, 3 <α ≦ 80 may be satisfied.

  If the mixing ratio of the aluminum / cobalt-containing lithium / manganese composite oxide to the lithium / nickel / cobalt / manganese composite oxide in the positive electrode for the non-aqueous electrolyte secondary battery is within an appropriate range, the non-aqueous electrolyte is used. The characteristics of the secondary battery are stabilized, and satisfactory high-temperature cycle characteristics and output characteristics can be achieved.

  The method for producing the positive electrode is not particularly limited. For example, a powder of aluminum / cobalt-containing lithium / manganese composite oxide and a powder of lithium / nickel / cobalt / manganese composite oxide together with a conductivity-imparting agent and a binder are used. After mixing (slurry method) with an appropriate dispersion medium capable of dissolving the binder, the mixture is applied onto a current collector such as an aluminum foil, the solvent is dried, and the film is compressed by a press or the like to form a film.

  The conductivity imparting agent is not particularly limited, and carbon black, acetylene black, natural graphite, artificial graphite, carbon fiber, or the like can be used. As the binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or the like can be used.

The addition amount of the conductivity imparting agent is preferably about 1 to 10% by mass with respect to the mass of the mixture, and the addition amount of the binder is also about 1 to 10% by mass with respect to the mass of the mixture. This is because the capacity per unit weight increases as the proportion of the positive electrode active material for the non-aqueous electrolyte secondary battery increases. If the ratio between the conductivity-imparting agent and the binder is too small, the conductivity may not be maintained, or a problem of electrode peeling may occur. Moreover, it is preferable that the density of the mixture which comprises the formed secondary battery positive electrode except the electrical power collector shall be 2.55-3.05 g / cm < ³ >. When the density of the mixture is the above value, the discharge capacity at the time of use at a high discharge rate is preferably improved.

(Negative electrode)
The negative electrode active material is made of a material that can occlude and release lithium, such as lithium metal or carbon material. As the carbon material, graphite that occludes lithium, amorphous carbon, diamond-like carbon, fullerene, carbon nanotube, carbon nanohorn, or a composite thereof can be used. When lithium metal is used as the negative electrode active material, a melt cooling method, a liquid quenching method, an atomizing method, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, a thermal CVD method, a sol-gel method, etc. Thus, the layer 13 to be the negative electrode can be obtained. In the case of carbon materials, carbon and a binder such as polyvinylidene fluoride (PVDF) are mixed, dispersed and kneaded in a solvent such as NMP, and this is applied onto a substrate such as copper foil. The layer 13 containing the negative electrode active material can be obtained by the above method, vapor deposition, CVD, sputtering, or the like.

(Current collector)
Aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used as the positive electrode current collector 11, and copper, stainless steel, nickel, titanium, or an alloy thereof can be used as the negative electrode current collector 14. .

(Separator)
As the separator 16, a woven fabric, a nonwoven fabric, a porous film, or the like can be used. In particular, a polypropylene or polyethylene-based porous film is preferably used in terms of a thin film and a large area, film strength and film resistance.

  Solvents for the electrolyte include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl. Linear carbonates such as carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2- Chain ethers such as ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethyl Formamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2- Aprotic organic solvents such as oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, fluorinated carboxylic acid ester can be used alone or in combination of two or more. . Of these, propylene carbonate, ethylene carbonate, γ-butyl lactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like are preferably used alone or in combination.

A lithium salt is dissolved as a supporting salt in these organic solvents. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , Li (C ₂ F ₅ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides, etc. . Further, a polymer electrolyte may be used instead of the electrolytic solution. The electrolyte concentration is, for example, 0.5 mol / l to 1.5 mol / l. If the concentration is too high, density and viscosity increase. If the concentration is too low, the electrical conductivity may decrease.

  The lithium secondary battery according to the present invention is obtained by laminating a negative electrode and a positive electrode through a separator in a dry air or an inert gas atmosphere, or winding the laminated one, and then inserting it into an outer package and impregnating with an electrolytic solution. Then, it is obtained by sealing the battery outer package.

  There are no restrictions on the battery shape, and it can take the form of a positive electrode and negative electrode facing each other with a separator in between, a wound type, a laminated type, etc., and the cell can also be a coin type, laminate pack, square cell, cylinder Type cells can be used.

  Examples of the present invention will be described in detail below, but the present invention is not limited to the following examples.

(Synthesis of aluminum-cobalt-containing lithium-manganese composite oxide)
First, lithium carbonate (Li ₂ CO ₃ ) pulverized and classified to an average particle size of 5 μm or less, manganese oxide (Mn ₂ O ₃ ), cobalt oxide (CoO), aluminum hydroxide pulverized and classified to an average particle size of 10 μm or less (Al (OH) ₃ ) and magnesium hydroxide (Mg (OH) ₂ ) are prepared and mixed at a predetermined ratio and mixed for 2 hours by a planetary ball mill. In the inside, primary baking was performed at 800 ° C. Next, the primary fired product was crushed and remixed, followed by secondary firing in air at 600 ° C. Next, the fired product obtained in the above-described step is pulverized using an Ishikawa-type Reika machine, so that an aluminum / cobalt-containing lithium / manganese composite oxide (Li _{1 + x} Mn) having a spinel structure and an average particle diameter of 10 μm is obtained. _{2-xyzw Al y Co z Mg} w O 4 (0.03 <x <0.25,0.01 <y <0.2,0.01 <z <0.2,0 ≦ w <0.1, x + y + z + w <0.4) was obtained.

(Synthesis of lithium / nickel / cobalt / manganese composite oxide)
Next, nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ), manganese sulfate (MnSO ₄ ) are prepared, and these are prepared at a predetermined ratio, and this mixture is dissolved in water to prepare an aqueous solution. Sodium hydroxide (NaOH) is added to obtain a nickel-cobalt-manganese composite coprecipitate. Further, the composite coprecipitate, lithium hydroxide (LiOH), and hydroxide of an element selected from at least one of Mg, Al, Fe, Cr, Ti, and In are prepared so as to have a predetermined ratio. After mixing for 2 hours by a mold ball mill, the mixture was put in a crucible and fired at 850 ° C. for 12 hours in an oxygen atmosphere. Next, the fired product obtained in the above step is pulverized using an Ishikawa-type Reika machine, so that the lithium-nickel-cobalt-manganese composite oxide Li _{1 + a} (Ni _{1 -pqr Co p Mn q Me r)} O 4 (Me is an element selected Mg, Al, Fe, Cr, Ti, at least one of in, 0 ≦ a <0.1,0.2 < p < 0.45, 0.2 <q <0.45, 0 ≦ r <0.15).

(Production of battery)
The obtained powdered positive electrode active material and conductivity imparting agent are dry-mixed and uniformly dispersed in N-methyl-2-pyrrolidone (NMP) in which vinylidene fluoride resin (PVDF) as a binder is dissolved. Was made. Carbon black was used as the conductivity imparting agent. The slurry was applied on an aluminum metal foil (thickness 20 μm) serving as a positive electrode current collector, and then NMP was evaporated to obtain a positive electrode sheet having a film thickness of 85 μm. The solid content ratio in the positive electrode was positive electrode active material: conductivity imparting agent: PVDF = 89: 4: 7 (mass%). On the other hand, when the negative electrode active material is made of a carbon material, it is mixed so as to have a ratio of carbon: PVDF = 90: 10 (mass%), dispersed in NMP, and on a copper foil (thickness 10 μm) serving as a negative electrode current collector. To prepare a negative electrode sheet having a thickness of 47 μm. When metallic lithium was used as the negative electrode, a rolled lithium sheet formed to 20 μm by rolling on the copper foil surface was used. As the electrolyte solution, 1 mol / l LiPF6 as an electrolyte was used. Thereafter, the negative electrode and the positive electrode were laminated via a separator made of polyethylene to produce a cylindrical secondary battery.

(Charge / discharge characteristics test)
High temperature cycle characteristics were evaluated using a cylindrical cell using a carbon material as the negative electrode active material. At a temperature of 60 ° C., the charge rate was 1.0 C, the discharge rate was 1.0 C, the charge end voltage was 4.3 V, the charge time was 2.5 hours, and the discharge end voltage was 2.5 V. The capacity retention rate (%) is a value obtained by dividing the discharge capacity (mAh) after 100 cycles by the discharge capacity (mAh) at the 10th cycle.

(Measurement of internal DC resistance)
A cylindrical cell using a carbon material as a negative electrode active material was prepared, and the initial internal DC resistance was measured. At a temperature of 20 ° C., the battery was charged to 4.3 V at a charge rate of 0.5 C. After reaching 4.3 V, constant voltage charging was performed for 2 hours for charging. The discharged battery was discharged at 0.1 C to a depth of discharge (DOD) of 50%, and then the voltage when discharged at a current of 1 C for 10 seconds was measured. Subsequently, after standing for 10 minutes, the voltage when charged for 10 seconds at a current of 3 C was measured. Furthermore, the voltage when discharged for 10 seconds at a current of 5 C after standing for 10 minutes was measured, and the voltage when charged for 10 seconds at a current of 3 C after standing again for 10 minutes was measured. After that, with the 10-minute leaving interval, the charge / discharge current was set to 7C and 10C, and the same measurement was repeated to obtain the V-I straight line. The slope of this straight line was defined as the initial internal DC resistance (initial resistance). did. Moreover, after adjusting the cylindrical cell after measuring internal resistance to the state of DOD60%, it preserve | saved for four weeks in a 55 degreeC thermostat. Thereafter, the internal DC resistance was measured, and the resistance increase ratio of the internal DC resistance (= [internal DC resistance after storage] / [internal DC resistance before storage]) was calculated.

  The composition ratio of the lithium / manganese composite oxide containing aluminum / cobalt and the lithium / nickel / cobalt / manganese composite oxide used in the produced cylindrical cell was changed, and the above-mentioned high temperature cycle characteristics and the rate of increase in internal DC resistance were measured. . Table 1 summarizes the compositions of the positive electrode active materials used in the fabricated battery. Mixing ratio of aluminum / cobalt-containing lithium / manganese composite oxide and lithium / nickel / cobalt / manganese composite oxide (aluminum / cobalt-containing lithium / manganese composite oxide: lithium / nickel / cobalt / manganese composite oxide) Was 7: 3 by weight. Table 2 shows the evaluation results of these batteries.

In addition, aluminum / cobalt-containing lithium / manganese composite oxide (Li _1.10 Al _0.07 Co _0.07 Mn _1.76 O ₄ ) and lithium / nickel / cobalt / manganese composite oxide (LiNi _0.33 Co _0.34 Mn _0.33 O) used in the produced cylindrical cell were used. ₂ ) The mixing ratio (aluminum / cobalt-containing lithium / manganese composite oxide: lithium / nickel / cobalt / manganese composite oxide) was changed, and the above-described high temperature cycle characteristics and the rate of increase in internal DC resistance were measured. Table 3 summarizes the mixing ratio of the positive electrode active materials used in the manufactured battery and the battery evaluation results.

(Verification of effects due to simultaneous substitution of excess lithium, aluminum and cobalt: high-temperature cycle characteristics)
Capacity after cycle of cylindrical batteries using lithium-manganese composite oxide and lithium-nickel-cobalt-manganese composite oxide containing aluminum / cobalt in which lithium excess and aluminum and cobalt are simultaneously substituted in Examples 1 to 4 The retention rate is higher than the capacity retention rate after the cycle of the cylindrical battery using the lithium-manganese composite oxide in which lithium excess and aluminum and cobalt are not simultaneously substituted in Comparative Examples 1 to 4. . This is because, by simultaneously replacing cobalt and aluminum of the present invention, overdoped lithium and cobalt reduce the lattice constant of the spinel structure to stabilize the crystal, and aluminum has a stable trivalent oxidation degree. Since the structure is stabilized by showing the above, it is considered that the capacity retention rate was higher than that of the conventional lithium excess composition. The same results as in Examples 1 to 3 were obtained for the samples in which magnesium was added in addition to lithium, aluminum, and cobalt in Examples 3 and 4.

(Verification of the effect of simultaneous replacement of excess lithium, aluminum and cobalt: resistance increase ratio)
After high-temperature storage of a cylindrical battery using lithium-manganese composite oxide and lithium-nickel-cobalt-manganese composite oxide containing lithium / excess lithium, aluminum and cobalt simultaneously substituted in Examples 1 to 4 The resistance increase ratio is lower than the resistance increase ratio of the cylindrical battery using the lithium-manganese composite oxide in which the excess of lithium in Comparative Examples 1 to 4, aluminum and cobalt are not substituted simultaneously. This is because, by using the aluminum-cobalt-containing lithium-manganese composite oxide in which cobalt and aluminum are simultaneously substituted according to the present invention, the overdoped lithium and cobalt are stabilized by reducing the lattice constant of the spinel structure. The structure of aluminum is stabilized by exhibiting a trivalent and stable degree of oxidation. Therefore, it is considered that the capacity retention rate was higher than that of the conventional lithium excess composition. In addition, the same results as in Examples 1 and 2 were obtained for the samples obtained by adding magnesium in addition to lithium, aluminum and cobalt in Examples 3 and 4. This is because, by simultaneously replacing cobalt and aluminum of the present invention, overdoped lithium and cobalt reduce the lattice constant of the spinel structure to stabilize the crystal, and aluminum has a stable trivalent oxidation degree. It is considered that the Mn elution amount was lower than that of the conventional lithium excess composition because the structure was stabilized by showing.

(Verification of effects due to simultaneous substitution of excess lithium, aluminum and cobalt)
Capacity after cycle of cylindrical battery using lithium-manganese composite oxide and lithium-nickel-cobalt-manganese composite oxide containing aluminum / cobalt in which aluminum excess and aluminum and cobalt are simultaneously substituted in Examples 5 to 10 Both the retention rate and the resistance increase ratio are superior to those of the cylindrical battery using the layered structure positive electrode active material having the composition of Comparative Examples 5 to 7 and the aluminum / cobalt-containing lithium / manganese composite oxide. . This is because the lithium-manganese composite oxide in which cobalt and aluminum of the present invention are substituted at the same time is mixed and used as a positive electrode active material. It is considered that the capacity retention ratio was higher than that of mixing with the conventional lithium composite oxide because it was sustained. Moreover, the result similar to Examples 5-8 was obtained also about the sample which added magnesium, iron, and titanium as another element in Examples 8-10. Similar effects can be obtained when aluminum, chromium, or indium is added as other elements.

(Verification of the optimum range of the mixing ratio of aluminum / cobalt-containing lithium / manganese composite oxide and lithium / nickel / cobalt / manganese composite oxide)
Cylindrical battery cycle in which the mixture ratio of the lithium / manganese composite oxide containing aluminum / cobalt and the lithium / nickel / cobalt / manganese composite oxide in which lithium excess and aluminum and cobalt are simultaneously substituted in Examples 11 to 15 was changed The capacity retention ratio and the resistance increase ratio afterwards are both higher than those of the cylindrical battery using the positive electrode active material having a layered structure having the composition of Comparative Examples 8 to 10 and the aluminum / cobalt-containing lithium / manganese composite oxide. Are better. In the case of Comparative Example 8 with a small amount of lithium / nickel / cobalt / manganese composite oxide in the positive electrode active material, the proton scavenging effect of the lithium / nickel / cobalt / manganese composite oxide is not sufficiently exhibited. Charge / discharge characteristics could not be obtained. Further, in the case of Comparative Example 9 where there are many lithium / nickel / cobalt / manganese composite oxides in the positive electrode active material, contact between the lithium / nickel / cobalt / manganese composite oxide particles cannot be secured stably. Satisfactory charge / discharge characteristics could not be obtained.

  In the above, this invention was demonstrated based on the Example. It is to be understood by those skilled in the art that this embodiment is merely an example, and that various modifications are possible and that such modifications are within the scope of the present invention.

The schematic diagram which shows the structure of the secondary battery of this invention.

Explanation of symbols

11 Positive Electrode Current Collector 12 Layer Containing Positive Electrode Active Material 13 Layer Containing Negative Electrode Active Material 14 Negative Electrode Current Collector 15 Electrolytic Solution 16 Separator

Claims (5)

Formula _{Li 1 + x Mn 2-xyzw} Al y Co z Mg w O 4 (0.03 <x <0.25,0.01 <y <0.2,0.01 <z <0.2,0 ≦ w <0.1, x + y + z + w <0.4) aluminum-cobalt-containing lithium-manganese composite oxide and the chemical formula Li ₁ + a (Ni represented _{by-1 pqr Co p Mn q Me} r) O 4 (Me is Mg , Al, Fe, Cr, Ti, In, an element selected from at least one of the following: 0 ≦ a <0.1, 0.2 <p <0.45, 0.2 <q <0.45, 0 A positive electrode for a secondary battery comprising a lithium / nickel / cobalt / manganese composite oxide represented by ≦ r <0.15).   2. The positive electrode for a secondary battery according to claim 1, wherein the aluminum / cobalt-containing lithium / manganese composite oxide has a spinel structure.   2. The positive electrode for a secondary battery according to claim 1, wherein the lithium / nickel / cobalt / manganese composite oxide has a layered crystal structure.   4. The secondary battery positive electrode according to claim 1, wherein the content of the lithium-manganese composite oxide in the secondary battery positive electrode is (100−α) parts by mass, and the secondary battery. A positive electrode for a secondary battery, wherein 3 <α ≦ 80 is satisfied, where the content of the lithium / nickel / cobalt / manganese composite oxide in the positive electrode is α parts by mass.   A power generation element comprising the positive electrode for a secondary battery according to any one of claims 1 to 4, an electrolyte, a separator, and a negative electrode disposed opposite to the positive electrode for a secondary battery via the electrolyte and the separator. A secondary battery stored in an exterior body.

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