JP2014231445A - Spinel type lithium manganese-based complex oxide and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a discharge capacity and a capacity retention rate accompanying charge/discharge cycles when a spinel type lithium manganese-based complex oxide is placed under a high temperature environment by the modification with use of a zirconium alkoxide.SOLUTION: A spinel type lithium manganese-based complex oxide is a pulverized product of a spinel type lithium manganese-based complex oxide which has a particle size such that the volume average particle size Dis 5-30 μm and the volume average particle size Dis not more than 50 μm in the secondary particle. A modified zirconia layer is formed of a decomposition product of alkoxide of zirconium and has a modification amount in the range of 0.1-1 mol% in terms of zirconia based on the spinel type lithium manganese-based complex oxide. The spinel type lithium manganese-based complex oxide has a specific surface area of not more than 1.0 cm/g.

Description

  The present invention relates to a spinel type lithium manganese composite oxide, and more particularly to a spinel type lithium manganese composite oxide coated (modified) with zirconia and a method for producing the same.

  Lithium secondary batteries are excellent in terms of electromotive force and energy density, and are widely used as batteries for portable electronic / communication devices such as small video cameras, mobile phones, and notebook computers. In recent years, it has attracted attention as a power source not only for portable electronic devices but also for mobile objects such as bicycles, electric bikes, and automobiles, and development of lithium secondary batteries for these fields has been actively promoted. .

Currently, lithium cobaltate (LiCoO ₂ ) is widely used as a positive electrode active material for lithium secondary batteries, but cobalt, the main raw material, is a rare metal and is expensive and supplied by depleting resources. Anxiety has been pointed out. In contrast, manganese, which is the main raw material of spinel-type lithium manganese oxide (chemical formula: LiMn ₂ O ₄ , lithium manganate, also referred to as lithium manganese spinel), has abundant resources and is more economical than cobalt. It is also advantageous from the aspect of sex, and its future is expected.

  In power supplies for portable electronic devices, there is a demand for shortening the time from when the device is turned on until it can be used. For automobiles as well, it is instantaneous to respond to sudden acceleration / deceleration of moving objects. There is a need for a battery that can carry a large current.

  In general, complex oxides of lithium and transition metals, including spinel-type lithium manganese complex oxides, generally have low conductivity. When used as a positive electrode active material for a secondary battery, in general, to ensure conductivity. Further, a conductive material such as carbon black and graphite and a binder are mixed to prepare a slurry, which is then applied to an aluminum foil. The positive electrode produced in this way is assembled into, for example, a coin cell type organic electrolyte secondary battery by a negative electrode including a negative electrode active material powder, a non-aqueous electrolyte solution, and a member such as a separator and a gasket.

  However, a non-aqueous electrolyte secondary battery using a spinel-type lithium manganese composite oxide as a positive electrode active material has a problem in that the capacity reduction accompanying a charge / discharge cycle in a high temperature environment is large. The cause is a disproportionation reaction in which trivalent Mn is changed to divalent Mn and tetravalent Mn due to a surface reaction in contact with the positive electrode active material and hydrogen fluoride of the non-aqueous electrolyte. It is presumed that the above-mentioned cycle deterioration occurs due to the collapse of the crystal structure because of the dissolution of Mn into the electrolyte.

In order to suppress such contact between the positive electrode active material and the non-aqueous electrolyte, it is known to coat the surface of the positive electrode active material with zirconium oxide. For example, Patent Document 1 discloses lithium manganese nickel represented by the following general formula Li _x Mn _1.5 Ni _0.5 O _4-w (where 0 <x <2, 0 ≦ w <2). Modified lithium manganese nickel composite oxide characterized in that the surface of the composite oxide is coated with a metal oxide containing at least one metal element selected from Mg, Al, Ti, Zr and Zn Things are disclosed. Further, Patent Document 2 discloses a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a nonaqueous electrolyte secondary battery including a nonaqueous electrolyte including a nonaqueous solvent in which an electrolyte salt is dissolved. The active material contains two kinds of spinel type lithium manganates having different average particle sizes, and the active material X related to the large particle size contains at least one of Mg or Al and B and F, and the average particle size X (D ₅₀ ) 10 to 30 μm, the active material Y according to the small particle size contains at least one of Mg or Al and B, and at least a part of the surface is coated with at least one of TiO ₂ or ZrO ₂ , and the average particle size Y (D ₅₀ ) is 1 to 10 μm, the mass ratio of the active material X and the active material Y contained in the positive electrode active material is 6: 4 to 9: 1, and X (D ₅₀ ) and Y (D _{50), 1.5 ≦ (X (D 50} ) / Y (D 50)) Non-aqueous electrolyte secondary battery, wherein discloses that it is 4.0.

Further, as a means for coating the surface of the positive electrode active material with zirconium oxide, Patent Document 3 discloses that in a non-aqueous lithium secondary battery using a composite oxide composed of lithium and a transition metal as a positive electrode active material, the composite oxide includes: As a means for modifying the surface of a metal compound film containing at least one of Al, Mg, Sn, Ti, Zn, and Zr having a thickness of 10 nm to 70 nm on the particle surface, an alkoxide solution of these metals is used for the composite oxidation. There is disclosed a means for performing heat treatment at a temperature of 300 ° C. or higher and 700 ° C. or lower in the air, in a nitrogen atmosphere or in an oxygen atmosphere after being mixed with an object, subjected to ultrasonic irradiation, filtered, recovered and dried. In Patent Document 4, an alkoxide of a metal element such as Zr is used in an aqueous suspension containing a composite oxide composed of lithium-transition metal element (TM) as a core particle, and fluorine is contained as a neutralizing agent. After depositing a surface treatment component containing Zr and fluorine on the surface of the composite oxide particle composed of lithium-transition metal element (TM) using a solution of the above, a temperature range of 300 to 700 ° C. in an oxygen atmosphere The method of heat-treating is disclosed.
Patent Document 5 discloses a positive electrode material obtained by separating a lithium composite oxide from an aqueous zirconium solution.

JP 2006-36545 A JP 2012-9270 A JP 2005-310744 A JP 2010-86922 A WO2011 / 052607 A1 Publication

  However, the means disclosed in Patent Documents 1 and 2 do not uniformly coat or diffuse the solid powder Zr metal oxide used to modify the spinel-type lithium manganese composite oxide. There is a problem that the effect of improving the characteristics is not sufficient. On the other hand, the means disclosed in Patent Document 3 merely suggests the use of a general metal alkoxide together with ultrasonic irradiation, and does not describe a specific means for coating an oxide of zirconium with a metal alkoxide. . The means disclosed in Patent Document 4 discloses that the surface of the composite oxide is modified using a metal alkoxide containing zirconium. In the treatment process, the means is combined with a neutralizing agent and a fluorine-containing solution. There is a problem that the process is cumbersome. Further, there is no description of specific effects when a Zr oxide is modified with zirconium alkoxide.

  The present invention provides a specific means for modifying zirconium oxide using a spinel-type lithium manganese composite oxide with zirconium alkoxide, thereby maintaining discharge capacity and capacity maintenance associated with a charge / discharge cycle when placed in a high temperature environment. The purpose is to improve the rate.

The present inventor has studied various means for modifying the spinel type lithium manganese composite oxide with zirconia, and the volume average particle diameter D ₅₀ in the secondary particles (definition: the total volume of the powder population is 100%) When the cumulative curve is obtained, the particle diameter at the point where the cumulative curve becomes 50%, the same shall apply hereinafter) is 5 to 30 μm, D ₉₀ (definition: cumulative with the total volume of the powder population as 100%. When the curve is obtained, the particle diameter at which the cumulative curve becomes 90%, the same shall apply hereinafter) is mixed with the zirconium oxide alkoxide in a wet manner and dried. The present invention has been completed by finding that heat treatment is extremely effective.

The method for producing the spinel type lithium manganese composite oxide according to the present invention,
Formula _{Li (1 + x) M y} Mn (2-x-y) O 4
Here, x and y satisfy the following conditions, respectively, and M is at least one element selected from the group consisting of B, Al, Co, Ni, Mg, Ca, Zn, and Ti. Al, Co, Ni, Mg, and Zn added as M can be expected to reduce Mn elution due to stabilization of the Mn valence by dissolving in the spinel type lithium manganese composite oxide. Further, B, Ca, and Ti can be expected to reduce Mn elution by coating a spinel type lithium manganese composite oxide.
x: 0 or more and 0.33 or less y: represented by 0 or more and 0.2 or less, and a spinel type lithium manganese composite in which the volume average particle diameter D ₅₀ is adjusted to 5 to 30 μm and the volume average particle diameter D ₉₀ is adjusted to 50 μm or less Preparing a pulverized oxide,
Zirconium alkoxide dispersed in a solvent was converted to zirconia with respect to the pulverized spinel-type lithium manganese composite oxide and added in the range of 0.1 to 1 mol%, followed by wet mixing. After the wet mixture is dried, a step of heat-treating at a temperature of 300 to 700 ° C. is sequentially performed.

Furthermore, the spinel-type lithium manganese-based composite oxide according to the present invention, the surface of the general formula _{Li (1 + x) M y} Mn (2-x-x) pulverized spinel-type lithium manganese complex oxide represented by _{O 4} In addition, the spinel-type lithium manganese composite oxide having a modified zirconia layer, wherein the pulverized product of the spinel-type lithium manganese composite oxide has a volume average particle diameter D ₅₀ of 5 to 30 μm and a volume average particle diameter D _{90 of 90} μm. The modified zirconia layer is formed by the decomposition product of zirconium alkoxide, and the amount of modification is converted to zirconia (zirconium dioxide) with respect to the spinel type lithium manganese composite oxide. In addition, the range of 0.1 to 1 mol%, and the spinel type lithium manganese composite oxide has a specific surface area ( (BET value) is 1.0 cm ² / g or less.

  According to the present invention, a charge / discharge cycle when a secondary battery using the obtained spinel-type lithium manganese composite oxide as a positive electrode material is modified in a high temperature environment by modifying the spinel-type lithium manganese composite oxide with zirconia. Therefore, it is possible to improve the discharge capacity and capacity retention rate. The reason why this effect is obtained is unknown, but the fluorine contained in the electrolyte of the secondary battery reacts with zirconium by modifying the spinel type lithium manganese composite oxide with zirconium alkoxide to modify zirconia. The formation of zirconium fluoride suppresses the generation of hydrogen fluoride generated by reacting with water. As a result, elution due to reduction of manganese generated during charging and discharging of the secondary battery is suppressed, and spinel This is presumably caused by the fact that the crystal structure of the mold is less likely to collapse. In addition, it is considered that the carbon component of the zirconium alkoxide plays a role as a sintering aid, whereby a spinel type lithium manganese composite oxide having a high tap density can be obtained.

FIG. 1 is a graph showing changes in the discharge capacity at 60 ° C. of the spinel-type lithium manganese composite oxide according to Example 4 up to 100 cycles. FIG. 2 is a graph showing changes in the discharge capacity maintenance rate at 60 ° C. of the spinel type lithium manganese composite oxide according to Example 4 up to 100 cycles.

In producing a zirconia-coated (modified) spinel type lithium manganese-based composite oxide according to the present invention, first, the chemical composition _formula: in _{Li (1 + x) M y} Mn (2-x-y) O 4 A spinel type lithium manganese oxide represented is prepared. As is apparent from the above general formula, a part of Mn in a typical lithium manganese composite oxide (chemical formula: LiMn ₂ O ₄ ) is also substituted with the third metal element M, and with respect to Mn And those containing a little excess of Li.

The substitution element M with respect to Mn is selected as one effective in suppressing elution of manganese components into the battery and improving high temperature characteristics, and is selected from B, Al, Co, Ni, Mg, Ca, Zn, and Ti. One or more of the above elements can be used. The substitution amount of the substitution element M is such that y is in the range of 0 ≦ y ≦ 0.2 in the general formula: Li _{(1 + x)} M _y Mn _(2-xy) O ₄ . This is because if the amount of substitution is too large, the discharge capacity of secondary batteries using these as a positive electrode active material tends to decrease, and an extreme decrease in discharge capacity is not preferable, so y ≦ 0.2 is limited. . Further, in the spinel type lithium manganese oxide of the present invention, the excess amount of Li atoms relative to Mn (including the substituted metal element M), x is limited to 0 ≦ x ≦ 0.33. As the ratio of Li to Mn increases, the discharge capacity of the lithium manganese secondary battery decreases. For example, at x: 0.33, Li: 1.33, and the Mn valence is almost 4, so that the theoretical 4V This is because charging and discharging are not performed in the region.

  The spinel type lithium manganese composite oxide may be obtained by any manufacturing method, and for example, according to the process of manufacturing the spinel type lithium manganese oxide shown in Japanese Patent Application Laid-Open No. 2008-156163. . At that time, by using electrolytic manganese dioxide as the manganese raw material, an improvement in tap density can be expected as compared with the case of using manganese carbonate or the like.

Synthesized spinel-type lithium manganese-based composite oxide has an average particle diameter _{D 50} of 5 to 30 [mu] _{m, D 90} is ground to 50μm or less. Tap density decreases as the average particle diameter D ₅₀ is less than 5 [mu] m. On the other hand, if it exceeds 30 μm, there is a problem that the conductivity is lowered. Further, when D ₉₀ of greater than 50 [mu] m, the greater the dispersion of particles, causing a problem that heat deteriorates likely to occur during charging and discharging. For example, a jet mill or the like can be used as the pulverizing means without any particular question.

  The spinel-type lithium manganese composite oxide whose particle size is adjusted after synthesis is wet-mixed with zirconium alkoxide, and then subjected to drying and heat treatment.

As the zirconium alkoxide (general formula: Zr (OR) ₄ ), for example, Zr (OPr) ₄ , Zr (OBu) _{4 and the} like can be selected. These are sufficiently diluted with an organic solvent such as ethanol, and added to and mixed with the adjusted spinel type lithium manganese composite oxide. Here, R is an alkyl group having 1 to 10 carbon atoms, Pr is a propyl group, and Bu is a butyl group.

  The addition amount of zirconium alkoxide is 0.1 to 1 mol% in terms of zirconia with respect to the pulverized product of the spinel type lithium manganese composite oxide. If the amount added is less than 0.1 mol%, as will be shown later in the examples, the discharge capacity and capacity maintenance rate associated with the charge / discharge cycle when the assembled secondary battery is placed in a high temperature environment are sufficiently improved. On the other hand, when the content is larger than 1 mol%, the conductivity is lowered, a sufficient capacity cannot be obtained, and the initial capacity is relatively lowered. Increasing the amount of zirconium alkoxide within the above range contributes to improvement of the tap density of the product.

  As a means for adding and mixing the zirconium alkoxide solution, a commonly used wet mixing means, for example, a method of mixing while heating using a stirring blade can be used.

The obtained wet mixture is subjected to heat treatment after drying. The drying temperature is about 100 to 200 ° C. at which the organic solvent is sufficiently volatilized, and the heat treatment is such that the alkoxide is converted to zirconia (ZrO ₂ ), and further, the spinel lithium manganese oxide can be sufficiently sintered. , At a temperature of 300 to 700 ° C. When the heat treatment temperature is less than 300 ° C., ZrO ₂ does not sinter sufficiently, and the effect cannot be obtained. On the other hand, when the temperature is higher than 700 ° C., oxygen defects are generated in the spinel type lithium manganese composite oxide, and a sufficient effect cannot be obtained. Note that the heat treatment time only needs to achieve recovery of the disorder of the crystal structure, and the heat treatment atmosphere may be an air atmosphere.

  The lithium manganese composite oxide heat-treated as described above is sieved into a product, which is provided as a positive electrode material for a secondary battery. The sieving may be performed so as to obtain the above particle diameter, and the means is not particularly limited.

Even when the above lithium manganese composite oxide according to the present invention is used as a positive electrode active material, the negative electrode active material can store and release lithium such as carbon materials and lithium storage alloys, as in the case of a normal lithium manganese composite oxide. As the electrolytic solution, a non-aqueous electrolytic solution obtained by dissolving a lithium salt in a resin or a resin is used. That is, lithium hexafluorophosphate (LiPF ₆ ) was used as the lithium salt, and a mixed solution of ethylene carbonate and dimethyl carbonate was used as the non-aqueous electrolyte. In addition, LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , LiN (SO ₃ CF ₃ ) ₂ , and the like, and mixtures thereof are used as lithium salts. In addition, as the non-aqueous electrolyte, it is possible to use a solid polymer electrolyte (resin) having high ionic conductivity having diethyl carbonate, propylene carbonate or the like or a mixture thereof and polyethyleneimine as the main chain.

(Adjustment of positive electrode active material)
A spinel-type lithium-manganese composite oxide was synthesized by dry-mixing and firing lithium carbonate, electrolytic manganese dioxide and, if necessary, a substance containing a third metal element in a precision mixer so as to have a predetermined ratio. After the obtained spinel type lithium manganese composite oxide was pulverized using a jet mill, zirconium alkoxide was added to the spinel type lithium manganese composite oxide, followed by wet mixing and drying at 80 to 200 ° C. A heat treatment was performed at a predetermined temperature to obtain a product. Table 1 shows the composition formula, average particle diameter (D ₅₀ , D ₉₀ ), addition amount of zirconium alkoxide, and heat treatment temperature of the obtained spinel-type lithium manganese composite oxide together with comparative examples. The average particle diameter was measured using SALD-2000J (laser diffraction type particle size distribution measuring device measurement range: 0.03 to 700 μm) manufactured by Shimadzu Corporation.

KF polymer # 1120 manufactured by Kureha Corporation containing acetylene black as a conductive material and polyvinylidene fluoride (PVDF) as a binder, using the obtained product as a positive electrode active material, active material: conductive material: binder The mixture was kneaded at a ratio of 90: 6: 4 (mass ratio) to obtain a positive electrode slurry. This slurry was applied to an aluminum current collector by a doctor blade method to produce a disc-shaped positive electrode having a diameter of 10.6 mm and a thickness of 0.3 mm. The positive electrode plate was pressure-molded at a pressure of 20 MPa and dried under reduced pressure at 120 ° C. for 8 hours to obtain a positive electrode plate. For the negative electrode, a lithium metal having a thickness of 0.21 mm cut out to about 15 mm square was used. For the electrolyte, 1 mol of solute LiPF ₆ was added to 1 L of a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. The one prepared by dissolving at a ratio, using a porous polypropylene membrane as a separator, CR2032 type with a diameter of 20 mm and a height of 3.2 mm (part cap, case, gasket, spacer, manufactured by Hosen Co., Ltd.) And a wave washer were used).

  The produced coin-type lithium secondary battery was charged and discharged for 100 cycles in a constant temperature bath at 60 ° C. under the conditions of charge and discharge of 0.5 C and a potential range of 3.0 V to 4.3 V. The results are summarized in Table 2. Moreover, the change to 100 cycles of the discharge capacity and volume maintenance factor which concern on Example 4 shown in Table 1 is shown in FIG. 1, FIG.

Table 1 and Table 2, the present invention limits the mean particle diameter D ₅₀ and D ₉₀ of the spinel-type lithium-manganese-based composite oxide, respectively 5 to 30 [mu] m, in 50μm or less, further modified zirconia layer is the spinel-type lithium manganese When an invention example is viewed by forming a decomposition product of zirconium alkoxide with respect to a composite oxide and making the amount of modification 0.1 to 1 mol% in terms of zirconia,
(1) The initial discharge capacity exceeds 101 mAh / g, and the discharge capacity after 100 cycles of charge / discharge repetition exceeds 97 mAh / g (while the comparative example is 97.0 mAh / g or less).
(2) The capacity retention rate after 100 cycles of charge / discharge repetition exceeds 95% (on the other hand, the comparative example is 94.7% or less).
(3) Increasing the amount of zirconium alkoxide within the above range contributes to an improvement in the tap density (1.55 g / cm ³ or more) of the product spinel type lithium manganese composite oxide. The effect was confirmed.

  On the other hand, when the modification amount of the alkoxide decomposition product with respect to the spinel type lithium manganese composite oxide is insufficient, the initial discharge capacity, the capacity retention rate after 100 cycles cannot be sufficiently improved, and the excess In this case, it was confirmed that both the initial discharge capacity and the capacity retention after 100 cycles deteriorated. In addition, in the experiment conducted in parallel, when the spinel type lithium manganese composite oxide was modified with solid zirconia powder, the initial discharge capacity, after 100 cycles, even if the modification amount was appropriate It was confirmed that a sufficient improvement effect of the capacity retention rate could not be obtained.

Further, when the average particle diameter D ₅₀ is below 5μm, it is confirmed that the tap density decreases, and if D ₉₀ of greater than 50 [mu] m, in order to create a positive electrode from the positive electrode active material powder into a paste In addition, there are problems that coarse particles are seen in the paste, making it difficult to create a uniform paste, and that the dispersion of the particles is large, and heat is likely to be generated and deteriorated during charging and discharging. .

Claims (2)

Formula _{Li (1 + x) M y} Mn (2-x-y) O 4
Here, x and y satisfy the following conditions, respectively, and M is at least one element selected from the group consisting of B, Al, Co, Ni, Mg, Ca, Zn, and Ti;
x: 0 or more and 0.33 or less y: pulverized product of spinel type lithium manganese composite oxide represented by 0 or more and 0.2 or less,
A spinel-type lithium manganese complex oxide having a modified zirconia layer on the surface of the grinding product of the spinel-type lithium manganese-based composite oxide has an average particle diameter D ₅₀ of 5 to 30 [mu] m, the particle size D ₉₀ of less 50μm The modified zirconia layer is formed by a decomposition product of zirconium alkoxide, and the amount of modification is 0.1 to 1 mol% in terms of zirconia with respect to the spinel type lithium manganese composite oxide. A spinel-type lithium manganese composite oxide having a specific surface area of 1.0 cm ² / g or less. Formula _{Li (1 + x) M y} Mn (2-x-y) O 4
Here, x and y satisfy the following conditions, respectively, and M is at least one element selected from the group consisting of B, Al, Co, Ni, Mg, Ca, Zn, and Ti.
x: 0 or more and 0.33 or less y: pulverized spinel type lithium manganese composite oxide expressed by 0 or more and 0.2 or less and having an average particle diameter D ₅₀ adjusted to 5 to 30 μm and D ₉₀ adjusted to 50 μm or less And the stage of preparing
Adding a zirconium alkoxide dispersed in a solvent in a range of 0.1 to 1 mol% in terms of zirconia to the pulverized spinel lithium manganese composite oxide, followed by wet mixing, and the obtained wet The mixture is dried and then heat-treated at a temperature of 300 to 700 ° C. to obtain a spinel-type lithium manganese composite oxide coated (modified) with zirconia. ) Produced spinel type lithium manganese composite oxide.

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