JP5634362B2 - Electrode active material and method for producing the same - Google Patents

Description

  The present invention relates to a lithium ion secondary battery, and more particularly to a technique for improving charge / discharge rate characteristics of a lithium ion secondary battery.

  In an in-vehicle lithium ion secondary battery, a plurality of single cells (cells) each having a positive electrode, a negative electrode, and an electrolyte are arranged in series to form an assembled battery, and a cell controller for charge / discharge control is connected. Then, the battery module is formed so as to obtain a necessary voltage.

  In such a secondary battery cell, an electrode sheet and a separator are stacked, and a wound type electricity storage element that is crushed after being wound into a flat shape or a cylindrical shape, or an electrode and a separator cut into a flat plate shape are stacked. There are two types of stacked power storage elements, and those that are housed in a cylindrical case, and those that are housed in a rectangular or flat case are known.

  Among the constituent elements of the unit cell, the electrode sheet of the positive electrode or the negative electrode is applied with a paste of an electrode active material containing electrode active material particles, a binder, a solvent and the like on the surface of a current collecting foil that is a thin metal foil and dried. Become.

  When charging / discharging the unit cell, lithium ions diffuse between the electrolytic solution and the electrode active material particles to enter and exit. For this reason, conventionally, when charging / discharging with a large current is performed, lithium ions do not flow in and out smoothly, which causes a reduction in rate characteristics (performance of maintaining capacity even in high rate charging / discharging). In order to perform charging / discharging with a large current while maintaining this rate characteristic, it is necessary to promptly and smoothly move between the lithium ion electrode active material particles and the electrolytic solution.

  Conventionally, however, the crystals constituting the electrode active material particles are amorphous or polycrystalline with crystal lattices randomly oriented, which complicates the migration path for lithium ion diffusion, resulting in a certain level. The above high rate charge / discharge was difficult.

  In order to solve such a problem, in the lithium ion battery, the positive electrode active material is made of single crystal manganese dioxide, and the diffusion transfer path of lithium ions between the electrolytic solution and the electrode active material is minimized. In other words, a positive electrode structure in which this single crystal is oriented so as to be perpendicular to the positive electrode current collector is known (see, for example, Patent Document 1).

  However, in the technique described in Patent Document 1, since it is necessary to electrochemically grow a single crystal on the current collector, there is a problem that the types of active materials are limited, and it takes a long time to grow the single crystal. There is a problem that it is difficult to form a thick layer, a problem that the blending of the conductive material and the binder is limited, and the like. Therefore, realizable dimensions and specifications are limited, and the cost for practical use is high. Therefore, it is difficult to apply this technique to a battery that charges and discharges with a large current while maintaining high rate characteristics as required for automobile applications.

JP 2007-005281 A

  The present invention has been made in order to solve the above-described problems of the prior art, and an object thereof is to provide an electrode active material that has improved rate characteristics and can be charged / discharged by a large current, and a method for manufacturing the same. It is said.

  The electrode active material of the present invention is an electrode active material composed of secondary particles in which primary particles of an active material selected from lithium layered compounds and olivine compounds are aggregated, and the primary particles are single crystals The primary particles in the secondary particles are characterized by being laminated in the primary ion diffusion direction so that the primary particles have the same lithium ion diffusion direction.

  In the present invention having the above configuration, since the primary particles in the secondary particles constituting the electrode active material are oriented so that the lithium ion diffusion directions are the same, the lithium ion electrolyte during charge and discharge The diffusion movement path between the electrode and the electrode active material is shortened. Thereby, rapid insertion and removal of lithium ions is possible, and the rate characteristics and output density are improved by improving the electrochemical reaction speed on the electrode surface. Thereby, the battery which can respond also to rapid charging / discharging and charging / discharging of a large current can be comprised.

In the present invention, the primary particles have a long surface and a shorter short surface, the long surface intersects the lithium ion diffusion direction, and the short surface is parallel to the lithium ion diffusion direction. It is a further feature .

  In the present invention having the above configuration, the long surface intersects the lithium ion diffusion direction, and the short surface is parallel to the lithium ion diffusion direction. That is, since the entrance / exit surface where insertion / extraction of lithium ions occurs is a long surface and is relatively wide, lithium ions enter / exit more smoothly and the electrochemical reaction rate is improved. In addition, since the plane parallel to the direction in which lithium ion diffusion and movement occurs is a short surface, the movement distance of lithium ions is relatively shortened, and similarly, lithium ions enter and exit more smoothly, resulting in an electrochemical reaction. Increases speed.

  The method for producing an electrode active material according to the present invention includes a step of generating primary particles of a single crystal made of an active material selected from either a lithium layered compound or an olivine compound, and coating the primary particles with a metal alkoxide. The method comprises a step and a step of aggregating the coated primary particles to produce secondary particles.

  In the present invention having the above structure, a large number of alkoxy groups are formed on the surface of the primary particles that are single crystals of the electrode active material, and the alkoxy groups on the surface of the adjacent primary particles are aggregated and dehydrated and condensed to form ether groups. By forming, the adjacent primary particles are combined to form secondary particles. At this time, since the long surface has more alkoxy groups than the short surface, the adjacent primary particles The long surfaces of each other will aggregate more selectively. Thereby, the secondary particle | grains with which the diffusion direction of the lithium ion of this invention was equal can be grown.

It is sectional drawing which shows typically the positive electrode structure using the electrode active material of this invention. It is an enlarged view of the electrode active material secondary particle of this invention. It is a schematic diagram which shows the crystal structure of the electrode active material primary particle in 1st Embodiment of this invention. It is a schematic diagram which shows the crystal structure of the electrode active material primary particle in 2nd Embodiment of this invention. It is a schematic diagram which shows the crystal structure of the layered compound in 1st Embodiment of this invention. It is a schematic diagram which shows the crystal structure of the olivine compound in 2nd Embodiment of this invention. It is a chart which shows the X-ray-diffraction analysis result of the Example of this invention, and a comparative example (layered compound). It is a chart which shows the X-ray-diffraction analysis result of the Example and comparative example (olivine compound) of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing a positive electrode in a lithium ion battery according to an embodiment of the present invention. The positive electrode E is configured by, for example, electrode active material secondary particles 2 and conductive material particles 3 being bound by a binder 4 on a current collector 1 made of a metal foil such as aluminum. The electrode E can be manufactured by, for example, a known method in which the electrode active material secondary particles 2, the conductive material 3, and the binder 4 are kneaded together with a solvent to form a paste on the current collector 1.

  FIG. 2 is an enlarged view of the electrode active material secondary particles 2. The electrode active material secondary particles 2 are constituted by aggregation of a large number of electrode active material primary particles 5. In the present invention, as shown in FIG. 2, the electrode active material primary particles 5 have a long surface and a short surface, and the primary particles 5 are aggregated between the long surfaces to form secondary particles. The ratio L / D between the long and short lengths is preferably 1.1 or more. If it is less than 1.1, the long surface and the short surface are substantially the same, and if it is less than 1, the long surface and the short surface are reversed, which is not preferable. The primary particle size is preferably in the range of 0.05 to 100 μm, particularly 0.1 to 20 μm.

First embodiment (layered compound)
FIG. 3 shows the first embodiment of the present invention in which the electrode active material primary particles 5 are composed of a layered compound of lithium, and FIG. 5 is a diagram for explaining the crystal structure of the layered compound. The layered compound of lithium according to the present invention is a complex oxide having a general formula Li _x MO _{2 ± y} (0.8 ≦ x ≦ 2.5, y varies depending on x), where M is A transition metal containing at least one of Al, Mg, V, Ti, Ni, Co, Mn, Fe, and Cu.

  As shown in FIG. 5, the crystal of the layered compound has a structure in which oxide layers and lithium layers of transition metal M are alternately arranged. The extending direction of the oxide layer and the lithium layer of the transition metal M coincides with the 003 plane (00N plane, N: integer, hereinafter the same) of the crystal lattice, and intersects the 110 plane (NN0 plane) perpendicularly. Therefore, in the electrochemical reaction accompanying charging / discharging, lithium ions diffuse and move along a direction parallel to the 003 plane.

  Therefore, in the present invention, as shown in FIG. 3, the long surface L of the electrode active material primary particles 5 is coincident with the 110 surface (NN0 surface) of the layered compound, and the short surface D is the 003 surface (00N surface). The primary particles are configured so as to coincide with each other, and the primary particles 5 are combined with the long surfaces so that the lithium ion diffusion directions in the respective particles coincide with each other to constitute the secondary particles 2.

  As described above, in the present invention, the long surface L is used as the entrance / exit of lithium ions, thereby smoothly inserting and releasing lithium ions into / from the electrode active material, and the lithium of each primary particle 5 in the secondary particle 2. By aligning the direction of the ion diffusion transfer path, bending of the lithium ion diffusion transfer path during the electrochemical reaction can be eliminated and the shortest distance can be achieved.

Second embodiment (olivine compound)
FIG. 4 shows a second embodiment of the present invention in which the electrode active material primary particles 5 are composed of a lithium olivine compound, and FIG. 6 is a diagram for explaining the crystal structure of the olivine compound. The lithium olivine compound of the present invention is a composite oxide having the general formula LiMPO ₄ , where M is at least one of Al, Mg, V, Ti, Ni, Co, Mn, Fe, and Cu. Including transition metals.

As shown in FIG. 6, the crystal of the olivine compound has a structure in which Li is present in layers between the crystal structures of MPO _{4 and} the layer in which this Li is present coincides with the 200 plane (N00 plane). The extending direction of the lithium layer intersects the 020 plane (0N0 plane) of the crystal perpendicularly. Therefore, in the electrochemical reaction accompanying charging / discharging, lithium ions diffuse and move along a direction parallel to the 200 plane.

  Therefore, in the present invention, as shown in FIG. 4, the long surface L of the electrode active material primary particles 5 coincides with the 020 surface (0N0 surface) of the layered compound, and the short surface D becomes the 200 surface (N00 surface). The primary particles are configured so as to match, and the primary particles 5 are combined with the long surfaces so that the lithium ion diffusion directions in the respective particles match, thereby forming the secondary particles 2.

  As described above, in the present invention, the long surface L is used as the entrance / exit of lithium ions, thereby smoothly inserting and releasing lithium ions into / from the electrode active material, and the lithium of each primary particle 5 in the secondary particle 2. By aligning the direction of the ion diffusion transfer path, bending of the lithium ion diffusion transfer path during the electrochemical reaction can be eliminated and the shortest distance can be achieved.

Production method of primary particles and secondary particles of the present invention 1: sol-gel method Secondary particles in which the individual primary particles in the present invention described above are aligned with a specific crystal plane aligned can be produced by the following method.

<Process 1: Crystal growth in molten salt>
A transition metal oxide is charged into the crucible, and Li ₂ O and LiCl that are flux and Li sources are charged, respectively. The transition metal oxide is converted to Li and crystal growth is performed by firing at 300 to 1000 ° C. using an electric furnace or the like in an air atmosphere and melting flux. Thereby, the single crystal of the electrode active material primary particle can be grown. After the reaction, the reaction system is cooled to room temperature. The crystal growth time can be arbitrarily set according to the dimensions of the target single crystal.

<Process 2: Excessive flux removal>
Next, the produced crystal is washed with distilled water to remove excess flux remaining without reacting in the above step. By changing the type and amount of flux to be used, the crystal growth conditions, and the particle diameter of the transition metal oxide introduced into the crucible, the size of the primary particles to be generated can be arbitrarily controlled within the range of 0.05 μm to 100 μm. it can. The number of times of flux washing and time are arbitrary. Also, the washing temperature is not particularly specified, but if hot water is used, the solubility of flux increases, so that it can be efficiently removed. Specifically, water in the range of 10 to 90 ° C. can be used.

<Process 3: Organic coating>
A metal alkoxide containing an arbitrary composite oxide is prepared and subjected to a sol-gel method. When the composite oxide is LiAlO ₂ , Li—OR and Al—OR are used. RO- is preferably an ethoxy group. These double alkoxide solutions are prepared in a solvent such as ethanol. H ₂ O is titrated with stirring, and the solution in a state where gelation is promoted is spray-coated on the primary particles of the electrode active material by spray drying.

<Process 4: Formation of secondary particles>
When the H ₂ O is further titrated while the sprayed primary particles are stirred in an ethanol solvent, aggregates of primary particles are formed. This is because the organic substances bonded to the surface of the active material are aligned and aggregated by bonding the active material between the surfaces including the long length through the metal in the alkoxide. When the agglomerates to a desired size and grow, stirring is stopped, and the solvent is put into a container of an isostatic press and pressed. In the case of LiAlO ₂ , a pressure of 1 ton / cm ² is maintained for 30 seconds. Thereby, the organic component containing the alkoxide metal of the aggregate is further aggregated while being pushed out to the aggregate surface. Finally, these aggregates are sintered to obtain desired secondary particles. In the case of LiAlO ₂ , hold at 500 degrees for 30 minutes.

Production method 2 of primary particles and secondary particles of the present invention: precipitation method <process 1: precipitation of transition metal carbonate>
The transition metal nitrate is dissolved in distilled water. An aqueous sodium carbonate solution and an aqueous ammonium hydroxide solution are added dropwise to the aqueous solution. When the solution is basic, the transition metal precipitates as carbonates, and the precipitates are spherical secondary particles composed of fine primary particles. The type of the transition metal salt is not particularly limited, and sulfates and acetates may be used, but nitrates that can be easily removed in the subsequent water washing / firing process are desirable.

<Process 2: Washing with water>
The produced transition metal carbonate precipitate is washed with distilled water. In this step, Na ions and nitrate ions present as impurities are removed. The number of washings and the time are arbitrary. Further, although the washing temperature is not particularly specified, impurities can be efficiently removed by using warm water.

<Process 3: Liification of precipitate and crystal plane alignment of primary particles>
A transition metal carbonate precipitate is put into a crucible, and Li ₂ O and LiCl as flux and Li sources are put in, respectively. Firing is performed in an air atmosphere using an electric furnace or the like, and flux is melted to form carbonate Li and align primary particle crystals. Cool to room temperature.

  During firing, the carbonate is decarboxylated, reacts with Li, and changes to a Li-containing transition metal oxide. In addition, each primary particle made of a polycrystal is converted into secondary particles in which a specific crystal plane is aligned during the cooling process. The aligned crystal planes can be controlled by changing the type and amount of flux used and the crystal growth conditions. In addition, the time of the cooling process necessary for aligning the crystal planes of the primary particles is not particularly limited, but it is desirable to cool as long as possible from the highest temperature to room temperature.

Hereinafter, each component of the present invention will be described in detail.
The positive electrode sheet constituting the positive electrode sheet lithium ion secondary battery has a structure in which a positive electrode material is bound on both surfaces of a positive electrode current collector made of aluminum. As the positive electrode material of the present invention, the electrode active material secondary particles of the present invention are used, and examples of the conductive filler include acetylene black, ketjen black, and VGCF. The conductive fillers of the positive electrode and the negative electrode may be the same or different.

  As the binder for the positive electrode sheet, any thermoplastic resin or thermosetting resin can be used as long as it is chemically stable in the battery. Examples thereof include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, and the like, and these can be used alone or in combination. Among these, PVDF and PTFE that can exhibit a binding force in a small amount are particularly preferable.

The negative electrode sheet constituting the negative electrode sheet storage element has a structure in which a negative electrode material is bound on both surfaces of a negative electrode current collector made of copper or the like. As the negative electrode material of this embodiment, a carbon material that occludes and releases lithium ions, and an alloy or oxide containing Sn, Si, Pb, and Co can be used. Examples of the carbon material include natural graphite, artificial graphite, activated carbon, a low-temperature carbon body calcined at 600 to 1200 ° C. (for example, pitch, mesophase pitch as an easily graphitizable carbon precursor, or phenol as a non-graphitizable carbon precursor). Resin, xylene resin, PPS, cellulose, etc.) synthesized by heat treatment in an inert atmosphere. The electrode active materials of the central element and the peripheral element may be the same or different. For example, the element in the central part is likely to deteriorate because the temperature is high, so that hard carbon with high deterioration toughness and small expansion is used for the negative electrode in the central part, and soft carbon and graphite materials are used for the outer electrode. You can also.

  As the binder for the negative electrode sheet, the same binders as those used for the positive electrode described above can be used, and among them, styrene butadiene rubber, polyvinylidene fluoride, and the like are particularly preferable.

As the separator sheet constituting the separator sheet power storage element, a polyolefin microporous separator such as polyethylene, polypropylene or a nonwoven fabric separator such as polyester fiber or aramid fiber can be used.

Examples of the electrolyte solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (γ- BL), sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran and the like. A solvent may be used independently or may be used in mixture of 2 or more types. Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium boron tetrafluoride (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), and lithium trifluoromethanesulfonate. Examples include lithium salts such as (LiCF ₃ SO ₃ ) and bistrifluoromethylsulfonylimide lithium [LiN (CF ₃ SO ₃ ) ₂ ]. The electrolyte may be used alone or in combination of two or more. The amount of electrolyte dissolved in the solvent is usually about 0.2 mol / L to 2 mol / L. Various ionic liquids may be mixed. In addition, it may be a gel electrolyte retained by the electrolytic solution, and the retaining material may be polyethylene oxide, polypropylene oxide, vinylidene fluoride (VdF), hexafluoropropylene (HFP) or a derivative thereof, or a copolymer. Can do.

As the electrode terminal of the electrode terminal positive electrode terminal and the negative electrode terminal, a metal such as copper, nickel, aluminum, stainless steel, an alloy containing these, or a metal plated with these metals as a base material can be used. In order to increase the bonding area between the current collector foil and the terminal portion, a plate shape is preferable.

As the lead plate positive electrode and negative electrode lead plate, metals such as copper, nickel, aluminum, and stainless steel, alloys containing these metals, and those plated with nickel based on these metals can be used.

To process the shape of the battery case bottom surface, aluminum, stainless alloy, or resin can be used, but an aluminum alloy produced by impact molding or transfer press processing is preferable. The case preferably has a structure that is in close contact with the power storage element. This reduces the space between the case and the power storage element, and the liquid level rises when the electrolyte is injected. There is an effect that can be shortened.

Hereinafter, specific production examples of the present invention will be described. The electrode active material secondary particles of Examples and Comparative Examples of the present invention were produced by the following method.
[Example 1] (Production method 1: Sol-gel method)
In the crucible, 1.0 g of Co oxide (Co ₃ O ₄ ) was charged, and 4.0 g of Li ₂ O and LiCl as flux and Li sources were charged. In an air atmosphere, it was baked at 800 ° C. for 24 hours using an electric furnace, and the flux was melted to convert the Co oxide to Li and grow the crystal until D50 = 15 μm. After the reaction, it was cooled to room temperature over 72 hours. The produced LiCoO ₂ crystals were washed with distilled water to remove the remaining flux without reacting in the above step.

A double alkoxide solution of Li alkoxide and Al alkoxide was prepared in an ethanol solvent. While stirring, H ₂ O was titrated around 150 ppm, and the solution in a state where gelation was promoted was spray-coated on the primary particles of LiCoO ₂ by spray drying.

While stirring the spray-coated primary particles in an ethanol solvent, H ₂ O was further titrated to obtain aggregates (secondary particles) of primary particles having crystal orientations aligned in one direction. When the desired size was formed, the stirring was stopped, the solvent was placed in a container of an isostatic press, pressed, further agglomerated, and finally, these agglomerates were sintered. Next particles were obtained.

[Example 2] (Production method 1: Sol-gel method)
Instead of Co oxide (Co ₃ O ₄ ), a 1: 1: 1 molar ratio Ni / Co / Mn mixed oxide was used, and a double alkoxide solution of Li alkoxide and Al alkoxide was used. The secondary particles of Example 2 shown in Table 1 were obtained in the same manner except that D50 = 10 μm.

[Example 3] (Production method 2: Precipitation method)
Transition metal nitrate (a 1: 1: 1 molar ratio Ni / Co / Mn nitrate mixture) was dissolved in distilled water to 0.2M. To this aqueous solution, 0.2M Na ₂ CO ₃ aqueous solution and 0.2M NH ₄ OH aqueous solution were added dropwise to precipitate the transition metal carbonate to obtain spherical secondary particles composed of fine primary particles. . The produced carbonate precipitate was washed with distilled water to remove Na ions and nitrate ions present as impurities.

1.0 g of Ni / Co / Mn carbonate precipitate was put into a crucible, and 4.0 g of Li ₂ O and LiCl as flux and Li sources were added. Firing was performed in an air atmosphere at 800 ° C. for 24 hours using an electric furnace, and the flux was melted to convert the carbonate into Li and align the primary particle crystals. Cooled to room temperature over 72 hours.

[Examples 4 to 8] (Production method 2: Precipitation method)
Secondary particles of Examples 4 to 8 shown in Table 1 were obtained in the same manner except that the molar ratio of the transition metal nitrate mixture and the primary particle dimensions were changed to the ratios and dimensions shown in Table 1.

[Example 9] (Production method 1: Sol-gel method)
_{Fe (NO 2) 3 · 9H} 2 O, a solution of 0.1 mol / L was dissolved Na ₂ HPO 4 · 12H ₂ O to each of distilled water, and mixing these aqueous solutions. The obtained precipitate was filtered and washed with water, dried, and calcined in air at 600 ° C. for 3 hours to obtain FePO ₄ . In a crucible, 1.0 g of FePO ₄ and flux, and Li ₂ O as a Li source and 4.0 g of LiCl were charged, respectively. Further, 0.1 g of sucrose is added as a reducing agent for FePO ₄ , calcined in a mixed gas of argon and hydrogen at 800 ° C. for 24 hours, and flux is melted until LiPO of FePO ₄ and D50 = 3 μm are obtained. Crystal growth was performed. After the reaction, it was cooled to room temperature over 72 hours. The produced LiFePO ₄ crystals were washed with distilled water to remove the remaining flux and sucrose without reacting in the above step.

A double alkoxide solution of metal alkoxide (Li alkoxide and Al alkoxide) was prepared in an ethanol solvent. While stirring, H ₂ O was titrated around 150 ppm, and the solution in a state where gelation was promoted was spray-coated on the primary particles of LiFePO ₄ by spray drying.

While stirring the spray-coated primary particles in an ethanol solvent, H ₂ O was further titrated to obtain aggregates (secondary particles) of primary particles having crystal orientations aligned in one direction. When the desired size was formed, the stirring was stopped, the solvent was put into a container of an isostatic press, pressed, further agglomerated, and finally these agglomerates were sintered. Next particles were obtained.

[Comparative Example 1] (Ternary system)
Sodium hydroxide was added to the reaction vessel to prepare 2% by mass of ammonia water adjusted to a pH of about 12. A mixed aqueous solution containing a transition metal nitrate adjusted so that the molar ratio of Ni, Co, and Mn was 1/6: 1/6: 2/3 was dropped into the alkaline solution in the reaction vessel. At this time, 25% by mass of aqueous ammonia and aqueous sodium hydroxide solution were also added dropwise so that the reaction solution was maintained at a pH of about 12. The temperature of the reaction solution was maintained at about 50 ° C., and nitrogen gas was purged so that the reaction atmosphere became an inert atmosphere. The obtained product was filtered and washed with water to obtain a hydroxide having a molar ratio of Ni: Co: Mn = 1/6: 1/6: 2/3. 1 mol of this hydroxide and 1.4 mol of lithium hydroxide monohydrate were mixed. The mixture was put in an alumina crucible and baked at 800 ° C. for 24 hours to synthesize Li _1.4 (Ni _1/6 Co _1/6 Mn _2/3 ) O ₂ .

[Comparative Example 2] (Iron olivine)
Iron acetate (Fe (CH ₃ COO) ₂ ), diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), and lithium carbonate (Li ₂ CO ₃ ) have a stoichiometric ratio of lithium iron phosphate (LiFePO ₄ ). Weighed as follows. Acetone and zirconia balls were added to the weighed raw materials and mixed using a planetary ball mill. The mixture was dried, pre-calcined with argon and hydrogen at 300 ° C. for 2 hours, and subsequently calcined at 800 ° C. for 24 hours to synthesize lithium iron phosphate (LiFePO ₄ ).

X-Ray Diffraction Analysis X-ray diffraction analysis was performed on the electrode active material secondary particles of each Example and Comparative Example prepared above. The results are shown in FIG. 7 for the layered compound and in FIG. 8 for the olivine compound. As shown in FIG. 7, in the example of the layered compound, it was confirmed that the 110 peak was relatively stronger than the 003 peak and was 110-oriented. Further, as shown in FIG. 8, in the example of the olivine compound, the 020 peak was relatively stronger than the 200 peak, and the 020 orientation was confirmed.

Rate characteristic test A battery cell was fabricated using the electrode active material secondary particles of each Example and each Comparative Example. A 14 μm thick Cu foil was used as the negative electrode current collector foil, and an 20 μm thick Al foil was used as the positive electrode current collector foil. As the negative electrode active material, artificial graphite particles having a particle size of 22 μm were used. An electrode was prepared using a PVDF binder, and the thickness of the active material layer after pressing the electrode body was 100 μm. Electrode density of the negative electrode 1.5 g / cm ^3, the electrode density of the positive electrode was 3.8 g / cm ^3. The positive electrode side was 110 mm coated and 8 mm uncoated, the negative electrode was 114 mm coated and 8 mm uncoated, and the separator was sandwiched between positive and negative electrodes with a thickness of 25 μm.

  Positive and negative electrodes were inserted between the separators and wound with a core. After completion, the winding core was removed to obtain a flat type storage element having an element thickness of 12 mm. As the current collector foil, uncoated portions of Al and Cu were left and right on the positive electrode and the negative electrode, respectively.

After the storage element was vacuum-dried at 80 ° C. for 24 hours, the storage element was put into a container for impregnation in the glove box, the inside of the container was depressurized, and then LiPF ₆ / (EC + DMC + EMC) of 1.0 M electrolyte was injected. Then, impregnation was performed.

  A battery case having a case plate thickness of 0.5 mm and a case outer dimension of L130 × W25 × H80 mm was produced by impact molding using an aluminum alloy of 3003. The electricity storage device produced above was inserted into the battery case. The battery case was inserted, the upper part was sealed with a battery lid, the lid and case were sealed by YAG welding, and then CCCV charge was performed for 8 hours at a current of 0.2 C up to 4.2 V with a charge / discharge device. . Thereafter, degassing was performed under reduced pressure, and a rubber stopper was plugged into the injection port to complete the cell. Discharge was performed to SOC 50%, and initial performance measurement was performed.

  About each battery, discharge at high rate (5C) and discharge at low rate (0.1C) were performed, the capacity of the battery was calculated from each discharge, the ratio was obtained, and the high rate capacity maintenance rate was obtained. The results are shown in Table 1.

  In the example, since the primary particles form secondary particles by aligning crystal planes in which insertion and release of Li ions are smooth, rapid charge / discharge characteristics are high. In addition, since each of the primary particles forming the secondary particles is fine, the Li ion diffusion path in the solid is short, which is advantageous for rapid charge / discharge. In addition, since each primary particle is formed of a single crystal, there are no lattice defects, and there is very little that inhibits the diffusion of Li into the solid, so the rapid charge / discharge characteristics are superior to the comparative examples (rate characteristics) test).

  When the fine particle powder is obtained by firing at a low temperature in order to shorten the Li ion diffusion path in the solid as in the comparative example, the crystallinity is lowered. When charging / discharging is repeated using such an active material, amorphization gradually proceeds, and the charge / discharge cycle characteristics deteriorate. Further, if firing is simply performed at a high temperature in order to increase the crystallinity, sintering proceeds between the particles, and the crystallinity is increased, but the particles are enlarged but the rapid charge / discharge characteristics are impaired.

  According to the present invention, charging / discharging with a large current is possible and rate characteristics are improved. Therefore, the present invention is extremely promising when applied to an in-vehicle lithium ion secondary battery.

E ... Positive electrode,
1 ... positive electrode current collector,
2 ... electrode active material secondary particles,
3 ... Conductive material,
4 ... Binder
5: Primary particles of electrode active material.

Claims (8)

An electrode active material composed of secondary particles in which primary particles of an active material selected from lithium layered compounds and olivine compounds are assembled,
The primary particles is a single crystal having a long face, short short side than it,
The long surface intersects the lithium ion diffusion direction, and the short surface is parallel to the lithium ion diffusion direction,
The electrode active material, wherein the primary particles in the secondary particles are laminated so that the lithium ion diffusion direction in each primary particle is the same and at least in the lithium ion diffusion direction. In the primary particle of the lithium layered compound, the NN0 face of the crystal lattice is the long face, the 00N face is the short face, and lithium ions diffuse in a direction parallel to the 00N face. The electrode active material according to claim 1. In the primary particles of the lithium olivine compound, the 0N0 plane of the crystal lattice is the long plane, the N00 plane is the short plane, and lithium ions diffuse in a direction parallel to the N00 plane. The electrode active material according to claim 1. 4. The electrode active material according to claim 1, wherein a ratio L / D of a length L of the long surface to a length D of the short surface is 1.1 or more. The electrode active material according to claim 1, wherein the laminated primary particles are bonded to each other by an ether group. Producing primary particles of single crystals composed of an active material selected from any one of a layered compound of lithium and an olivine compound;
Coating the primary particles with a metal alkoxide;
And a step of agglomerating the coated primary particles to produce secondary particles. The method for producing an electrode active material according to claim 6 , wherein a metal of the metal alkoxide is the same as a constituent metal of the layered or olivine compound. The lithium ion secondary battery using the electrode active material material in any one of Claims 1-5 .

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