JP5403337B2 - Method for producing positive electrode active material - Google Patents

Description

  The present invention relates to a method for producing a positive electrode active material of a lithium secondary battery. In detail, it is related with the manufacturing method of the positive electrode active material which consists of an olivine type lithium phosphate compound.

  In recent years, lithium secondary batteries, nickel metal hydride batteries, and other secondary batteries have become increasingly important as power sources for mounting on vehicles or as power sources for personal computers and portable terminals. In particular, a lithium secondary battery that is lightweight and has a high energy density is expected to be preferably used as a high-output power source for mounting on a vehicle.

A lithium secondary battery includes an electrode having a configuration in which a material (electrode active material) capable of reversibly occluding and releasing lithium ions serving as a charge carrier is held in a conductive member (electrode current collector), and further increases energy. In order to achieve higher density and higher output, studies have been made on the electrode active material. For example, as a positive electrode active material used for a positive electrode, a material having a layered rock salt type crystal structure such as NiCo-type or NiCoMn-type, or a material having a spinel type crystal structure such as LiMn ₂ O ₄ is generally known. However, as a positive electrode active material having a high theoretical capacity, low cost and excellent safety, the general formula is LiMPO ₄ (M is at least one element of Co, Ni, Mn, and Fe; for example, LiFePO ₄ , LiMnPO ₄ ). A lithium-containing phosphate compound having an olivine-type crystal structure represented by (hereinafter, sometimes simply referred to as an olivine-type phosphate compound) has been proposed.

  As a synthesis method of the olivine-type phosphate compound, in general, a powdery compound as a raw material is weighed and mixed so as to have a predetermined composition, and then subjected to heat treatment (firing) to synthesize, A liquid phase method in which the raw materials are uniformly mixed in the liquid phase and then fired is used. In addition, attempts have been made to increase the conductivity of the olivine-type phosphoric acid compound, which is a positive electrode active material, by adding carbon powder as a conductive raw material to the positive electrode active material during or after the synthesis process. For example, in Patent Document 1 and Patent Document 2, when the raw material of the positive electrode material is fired at 300 to 450 ° C., the positive electrode material is synthesized by adding carbon powder at a predetermined stage. In the technique of Patent Document 3, carbon powder is uniformly mixed with a positive electrode material in advance, and the positive electrode material is synthesized by further adding and baking the carbon powder to one fired at 300 to 600 ° C.

JP 2004-63386 A JP 2004-303496 A JP 2002-260659 A

  According to the techniques described in Patent Documents 1 to 3, the conductivity of the olivine-type phosphoric acid compound is enhanced by adding carbon powder or the like. As a result, a part of the phosphoric acid compound is crystallized. If carbon powder is added and mixed there, the particles of the phosphoric acid compound may be crushed and the crystal structure may be destroyed. As a result, the crystallinity of the olivine-type phosphoric acid compound, which is the positive electrode active material, decreases, making it difficult to obtain desired battery characteristics.

  This invention is made | formed in view of this point, The main objective is to provide the method of manufacturing the positive electrode active material which consists of an olivine type | mold phosphate compound with high crystallinity and high electroconductivity. . Another object is to provide a lithium secondary battery including a positive electrode active material manufactured by the method disclosed herein for a positive electrode.

In order to achieve the above object, according to the present invention, the general formula Li _x MPO ₄ (wherein M is at least one element selected from the group consisting of Co, Ni, Fe and Mn, and 0 <x ≦ The method of manufacturing the positive electrode active material which consists of the olivine type lithium containing phosphate compound represented by 1) is provided.
In the method for producing a positive electrode active material according to the present invention, (1) a gel raw material obtained by mixing starting materials for constituting the positive electrode active material including a lithium source, a phosphoric acid source and an M element source in an aqueous solvent. A step of preparing a mixture, (2) a step of heating and calcining the raw material mixture in a predetermined temperature range where the starting material does not crystallize, and (3) a calcined product obtained in the calcining step. A step of adding conductive powder, mixing and firing.

In the present specification, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged / discharged by transfer of electric charges associated with lithium ions between the positive and negative electrodes. A secondary battery generally referred to as a lithium ion battery is a typical example included in the lithium secondary battery in this specification.
In the present specification, the “positive electrode active material” means a positive electrode side capable of reversibly occluding and releasing (typically inserting and desorbing) chemical species (for example, lithium ions) serving as charge carriers in the secondary battery. The active material.

The method for producing a positive electrode active material provided by the present invention is a method for producing a positive electrode active material comprising an olivine type lithium-containing phosphate compound using a sol-gel method.
Here, the term “sol-gel method” means a sol-gel method known to those skilled in the art as a method for producing various solid materials starting from a solution, and does not require any special definition. That is, it refers to a method of synthesizing a desired material by preparing a sol in a particle dispersed state from a solution in which a predetermined raw material is mixed with a solvent, and changing the sol to a non-flowable gel and performing heat treatment.

According to the production method of the present invention, the general formula Li _x MPO ₄ (wherein M is at least one element selected from the group consisting of Co, Ni, Fe and Mn, and 0 <x ≦ 1 The olivine-type lithium-containing phosphate compound represented by the above can be provided. Although such a compound has a high theoretical capacity, it has a low conductivity. Therefore, in order to obtain desired battery characteristics, it is important to provide conductivity or to obtain a compound with high crystallinity. As a means for imparting conductivity, a method of adding a conductive powder to the compound is used, but in order to supplement the conductivity, the conductive powder is added to the compound and mixed (stirred). Since the crystal structure of the lithium-containing phosphate compound is crushed and destroyed by the mechanical energy of the stirring device, it is difficult to obtain an olivine-type lithium-containing phosphate compound having high crystallinity. However, according to the method for producing a positive electrode active material provided by the present invention, a gel raw material mixture (sol, sol) prepared by mixing starting materials including the lithium source, phosphoric acid source and M element source in an aqueous solvent. (Including colloidal liquids, dispersions, and suspensions, the same applies hereinafter) is calcined by heating in a predetermined temperature range that does not crystallize, and conductive powder is added to the calcined product. In a low temperature range where crystallization does not occur, crystal growth is suppressed, and each component of the gel-like raw material mixture (typically, various ions such as Li ⁺ and PO ₄ ³⁻ ) is uniformly diffused. Mix at a ratio close to the stoichiometric composition. Therefore, even if conductive powder is added to and mixed with the calcined product, there is no possibility that the crystal structure will be broken, and there is no possibility that the crystal growth of the compound will be hindered by mechanical energy. Therefore, in the subsequent firing step, a crystal of a lithium-containing phosphoric acid compound close to the stoichiometric composition can be stably grown, and a positive electrode active material having high crystallinity and excellent conductivity can be provided.

Moreover, it is preferable to heat at 80-150 degreeC as a predetermined temperature range in which the prepared starting material does not crystallize in a temporary baking process. By heating or holding in such a low temperature range, a part of the aqueous solvent volatilizes slowly from the raw material mixture over time, so that each component of the gel-like raw material mixture ( (Various ions such as Li ⁺ , Mn ²⁺ and PO ₄ ³⁻ ) are uniformly diffused. When the components of the raw material mixture are uniformly diffused, they are mixed at a ratio close to the stoichiometric composition, and a positive electrode active material having a high degree of crystallinity can be obtained.

In a preferred embodiment of the method disclosed herein, an organic acid is added in the step of preparing the raw material mixture. By adding an organic acid to a starting material including a lithium source, a phosphoric acid source, and an M element source, a coating of the organic acid is formed on the fine lithium-containing phosphoric acid compound in a state where crystal growth is suppressed in the pre-baking step. Can be formed. Such a film made of an organic acid can be heated and carbonized in a subsequent firing step to form a carbon film uniformly coated on the surface of the compound. As a result, a positive electrode active material having a highly conductive carbon film can be provided.
In a preferred embodiment, the addition amount of the organic acid is set to an amount corresponding to 10% by mass or less with respect to 100% by mass of the raw material mixture. Since the positive electrode active material made of an olivine-type lithium-containing phosphate compound has low electronic conductivity, it is important to provide conductivity or obtain a compound with high crystallinity in order to obtain desired battery characteristics. . Therefore, a lithium-containing phosphoric acid compound having higher conductivity can be produced by setting the organic acid to the above-mentioned addition amount.

Moreover, in one preferable aspect of the production method provided by the present invention, in the firing step, the conductive powder is added to and mixed with the temporarily fired product and fired at a temperature not exceeding 350 ° C. And a second firing step in which conductive powder is further added to and mixed with the fired product obtained in the first firing step and fired at a temperature of 600 ° C. or higher.
In the baking step, before the rapid high-temperature baking, first, the first baking is performed at a temperature not exceeding 350 ° C., whereby crystals of the lithium-containing phosphate compound can be grown stepwise. In addition, by adding conductive powder to the fired product obtained in the first firing step and mixing it, the surface of the compound on which crystals are being deposited is coated (coated) with the conductive powder. ) Or the like, and the crystal structure of the compound is hardly broken. Further, by firing at a higher temperature of 600 ° C. or higher, a lithium secondary battery having high crystallinity and excellent battery characteristics (particularly battery capacity, charge / discharge cycle characteristics or high rate characteristics) can be constructed. A positive electrode active material can be manufactured.

Furthermore, in another preferable embodiment, the olivine-type lithium-containing phosphate compound is LiMnPO ₄ containing Mn as the M element. Alternatively, Li _x Mn _y M′PO ₄ (wherein M ′ is a condition of 0 <x ≦ 1, 0 <y <1 which can allow the presence of impurity components with Co, Ni and Fe as main constituent elements) Lithium manganese phosphate represented by: Such lithium manganese phosphate has lower ionic conductivity and electronic conductivity than other olivine-type phosphate compounds (for example, LiFePO ₄ ). In particular, the resistance increases during charge / discharge at a high rate. However, according to the production method disclosed herein, it is possible to produce lithium manganese phosphate having a dense crystal structure and fine grains. Therefore, the lithium secondary battery constructed using such lithium manganese phosphate has excellent battery performance (for example, battery capacity, charge / discharge cycle characteristics or high rate characteristics).

Moreover, this invention provides a lithium secondary battery as another aspect. That is, it is a lithium secondary battery provided with a positive electrode active material manufactured by any one of the manufacturing methods disclosed herein. A lithium secondary battery including such a positive electrode is excellent in conductivity and can be a battery in which an increase in internal resistance is suppressed even with respect to high rate charge / discharge.
Furthermore, according to this invention, the vehicle provided with the lithium secondary battery disclosed here is provided. The lithium secondary battery provided by the present invention may exhibit quality (for example, prevention of internal short circuit) and performance (for example, high output) suitable as a power source for a battery mounted on a vehicle. Therefore, the lithium secondary battery disclosed herein can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile equipped with an electric motor such as a hybrid vehicle or an electric vehicle.

It is a process flow figure showing a manufacturing process of an olivine type lithium content phosphate compound concerning one embodiment. It is a figure which shows typically the lithium secondary battery which concerns on one Embodiment. It is the III-III sectional view taken on the line in FIG. It is the graph which showed the specific capacity of the test battery which concerns on Examples 1-6 and a comparative example. It is a graph of X-ray diffraction pattern of the crystal structure of LiMnPO ₄ according to Example 3 and Comparative Example. It is the graph which showed the specific capacity of the test battery which concerns on Example 3, 7-9, and a comparative example. It is a side view showing typically a vehicle (automobile) provided with a lithium secondary battery concerning one embodiment.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

As one preferred embodiment of a method for producing a positive electrode active material comprising an olivine-type lithium-containing phosphate compound disclosed herein, a general formula Li _x MPO ₄ (wherein M is Co, Ni, Fe and Lithium manganese phosphate containing at least one element selected from the group consisting of Mn and satisfying the condition of 0 <x ≦ 1. The method for producing a positive electrode active material according to the present embodiment will be described by taking as an example a case of producing a positive electrode active material made of LiMnPO _4. . “Manganese source” in the following description can be read as other M element (Co, Ni, Fe) sources.
In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, the configuration and manufacturing method of an electrode body including a positive electrode and a negative electrode, the configuration and manufacturing method of a separator and an electrolyte, General techniques relating to the construction of lithium secondary batteries and other batteries, etc.) can be understood as design matters for those skilled in the art based on the prior art in this field.

As shown in FIG. 1, the method for producing lithium manganese phosphate LiMnPO _{4 according to} the present embodiment is roughly divided into a raw material mixture preparation step (S10), a temporary firing step (S20), and a firing step (S30). And have. Hereinafter, each step will be described in detail.

<Raw material mixture preparation process>
First, the raw material mixture preparation step (S10) will be described. In the raw material mixture preparation step (S10), the starting raw materials for constituting the positive electrode active material including the lithium source, the M element source (manganese source in the present embodiment), and the phosphoric acid source are set to have a predetermined mixing ratio. These are weighed, mixed in an aqueous solvent and dissolved or dispersed to prepare a gel-like raw material mixture. When mixing a starting material with a solvent, you may stir as needed. Dissolution can be stably performed in a short time by stirring.

As the starting material, one or more compounds including at least a lithium source, a manganese source and a phosphate source can be appropriately selected and used.
First, the compound including the lithium source is not particularly limited as long as it can be dissolved or uniformly dispersed in the aqueous solvent, and various lithium compounds can be used. For example, lithium organic acid compounds such as lithium acetate and lithium oxalate, and lithium inorganic acid compounds such as lithium carbonate, lithium hydroxide, and lithium phosphate may be used. As a particularly preferred example, lithium acetate dihydrate [Li (CH ₃ COO) · 2H ₂ O] which is easily soluble in an aqueous solvent can be mentioned.

The compound including the M element source is not particularly limited as long as it can be dissolved or uniformly dispersed in the aqueous solvent, and organic acid salts of Co, Ni, Fe and Mn can be used. For example, acetate and oxalate are mentioned. Further, as the manganese source when the M element is Mn, manganese organic acid compounds such as manganese acetate and manganese oxalate can be used. As a particularly preferable example, manganese acetate (II) tetrahydrate [Mn (CH ₃ COO) ₂ .4H ₂ O] which is easily soluble in an aqueous solvent can be mentioned.

The compound including the phosphoric acid source is not particularly limited as long as it can be dissolved or uniformly dispersed in the aqueous solvent, and various phosphoric acid compounds can be used. For example, ammonium hydrogen phosphate such as ammonium dihydrogen phosphate [NH ₄ H ₂ PO ₄ ] or diammonium hydrogen phosphate can be used. Alternatively, phosphoric acid or a solution containing phosphoric acid may be used as the phosphoric acid source.

  In the raw material mixture preparation step (S10), it is preferable to further add an organic acid to the starting raw material including the lithium source, the manganese source, and the phosphoric acid source. By adding an organic acid, in the pre-baking step (S20), which will be described later, the raw material mixture to which organic oxidation has been added is heated in a low temperature range, so that the fine grain manganese phosphate in which crystal growth is suppressed A film made of an organic acid can be uniformly formed on the surface of lithium. Such a film made of an organic acid is heated and carbonized in the subsequent baking step (S30), and is coated on the surface of the compound, so that it can be a highly conductive carbon film.

  Although it does not specifically limit as an organic acid added here, What can melt | dissolve or disperse | distribute uniformly to an aqueous solvent can be used, For example, saccharides, a fatty acid, and these salts are used suitably. it can. Examples of sugars include monosaccharides, disaccharides and polysaccharides, and derivatives thereof. For example, as monosaccharide, aldose such as glucose, mannose, galactose, allose, talose, ribose, arabinose, erythrose, threose, ketose such as fructose, tagatose, sorbose ribulose, xylulose, erythrose or pyranose which is a cyclic structure thereof. And furanose. Examples of the disaccharide include sucrose, lactose, and maltose. Examples of the polysaccharide include starch and cellulose. The fatty acids include saturated fatty acids such as acetic acid and butyric acid, unsaturated fatty acids such as oleic acid, linoleic acid, and arachidonic acid, or phthalic acid, citric acid, isocitric acid, malic acid, tartaric acid, lactic acid, and oxalic acid. And other fatty acids such as succinic acid. In particular, saccharides such as sucrose can be preferably used.

  As the addition amount of the organic acid, the addition amount of the organic acid is an amount corresponding to 10% by mass or less with respect to 100% by mass of the mixture of the starting materials including the lithium source, the manganese source and the phosphoric acid source. Is preferred. More preferably, it is 5 mass% or less, for example, 3-4 mass% organic acid can be added.

  The aqueous solvent in which the starting material is mixed is typically water, but may be any water-based solvent as a whole. For example, an aqueous solution containing a lower alcohol (methanol, ethanol, etc.) is preferable. That is, water or a mixed solvent mainly composed of water can be preferably used. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use a solvent in which about 80% by mass or more (more preferably about 90% by mass or more, more preferably about 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is a solvent consisting essentially of water.

The above starting materials are dissolved or uniformly dispersed in an aqueous solvent to prepare a gel-like raw material mixture. The method of gelation is not particularly limited, but a gelling agent may be added to the raw material mixture in order to promote gelation. As the gelling agent, for example, glycolic acid [C ₂ H ₄ O ₃ ] can be preferably used. The addition amount of a gelling agent is not specifically limited, It is good to adjust suitably so that a desired gel form may be exhibited. Moreover, you may heat a raw material mixture above room temperature (for example, about 25-50 degreeC). By heating, gelation is promoted, and the sol state in a particle dispersed state can be changed to a gel state having no fluidity. The gel-like raw material mixture thus prepared constitutes a state in which the fluidity is lost while retaining the aqueous solvent. In addition, in order to heat a raw material mixture in a predetermined temperature range in the temporary baking process (S20) mentioned later, the heating for the gelatinization in this process (S10) may be abbreviate | omitted. Therefore, the raw material mixture in a state where a part of the fluidity is maintained can be used for the next step (S20).

<Temporary firing process>
Next, the temporary firing step (S20) will be described. In the pre-baking step (S20), the raw material mixture is heated and pre-baked in a predetermined temperature range where the prepared starting material does not crystallize. As a predetermined temperature range which does not crystallize, it can heat at 80-350 degreeC, A preferable temperature range is 80-150 degreeC, Most preferably, it is 100-150 degreeC, for example, heating at about 120 degreeC Can do.
By heating or holding in such a low temperature range, a part of the aqueous solvent volatilizes slowly from the raw material mixture over time, so that each component of the gel-like raw material mixture (Li ⁺ , Various ions such as Mn ²⁺ and PO ₄ ³⁻ are diffused uniformly. When the components of the raw material mixture are uniformly diffused, they are mixed at a ratio close to the stoichiometric composition, and further heated in the firing step (S30) described later, so that the stoichiometric composition or the lithium manganese phosphate close thereto is obtained. Fine-grained crystals grow stably. As a result, a desired positive electrode active material having a high degree of crystallinity can be obtained.

  The heating and holding time in the pre-baking step (S20) is not particularly limited, but the heating time is kept long to sufficiently reach the stoichiometric value and the diffusion of various ions proceeds sufficiently. It is better to let them. However, when all the solvent is volatilized and dried, the temporarily fired product is solidified and cannot enjoy the merit of the sol-gel method. Therefore, it is preferable to confirm the drying state of the solvent and appropriately adjust the holding time. In addition, the holding atmosphere may be an atmosphere that can keep the gel state stable, and depending on the type of solvent and starting material used, if necessary, in an air atmosphere or an inert gas atmosphere such as nitrogen gas. Alternatively, it can be held in a sealed container.

<Baking process>
Next, the firing step (S30) will be described. In the firing step (S30), conductive powder is added to the temporarily fired calcined product, mixed and fired. In the above-mentioned pre-baking step (S20), various ions are mixed at a ratio close to the stoichiometric composition, so that the fine particle crystal of lithium manganese phosphate grows at a stoichiometric composition or a composition ratio close thereto by further heating. To do. Thereby, a positive electrode active material with high crystallinity can be obtained.

Here, the conductive powder is added to the calcined product in which various ions are mixed at a ratio close to the stoichiometric composition through the calcining step (S20).
An olivine-type positive electrode active material, such as lithium manganese phosphate, has high theoretical capacity but low conductivity. Therefore, in order to obtain desired battery characteristics, it is necessary to impart conductivity or obtain a compound with high crystallinity. However, as a means for imparting conductivity, a conductive powder can be added to the compound and mixed (stirred). When the conductive powder is mixed using a mixing device or the like, the crystal structure is crushed and destroyed by the mechanical energy of the device, so it is difficult to obtain an olivine-type lithium-containing phosphate compound having high crystallinity. However, according to the manufacturing method disclosed herein, the crystal growth of lithium manganese phosphate is suppressed in the pre-baking step (S20), so even if conductive powder is added and mixed, the crystal structure is broken. There is no fear, and there is no possibility that the crystal growth of the compound is inhibited by mechanical energy. Therefore, by adding conductive powder in the previous stage of crystal growth (before the firing step), the conductive powder can be uniformly diffused into the temporarily fired product, and the conductivity of lithium manganese phosphate can be increased. Can be increased.

As the conductive powder to be added, carbon powder (carbon powder) is preferably used. For example, various carbon blacks such as acetylene black, furnace black, and ketjen black, or carbon powders such as graphite can be suitably used. Moreover, you may use 1 type or 2 types or more together among these.
Further, the above-mentioned apparatus used for mixing (including stirring and pulverization) is not particularly limited, but for example, by using a planetary mixer, a planetary stirring apparatus, a desper, a ball mill, a kneader, a mixer, etc. Powder and pre-baked product can be suitably mixed. The mixing time is not particularly limited as long as the conductive powder is uniformly diffused with respect to the temporarily fired product, but a suitable mixed state can be formed by mixing for about 20 hours.

  The firing temperature is not particularly limited as long as it is a temperature capable of synthesizing a desired compound (here, lithium manganese phosphate), but can be fired at a temperature of 600 ° C. or higher, for example, 600 ° C. According to the production method disclosed herein, since an olivine-type positive electrode active material having high crystallinity, for example, lithium manganese phosphate, is obtained, it is heated in a high temperature range (for example, a temperature exceeding 900 ° C.) like a general firing temperature. It does not have to be. Rather, if the firing temperature is too high, coarse crystal particles grow and impurities may increase. Further, the firing atmosphere is not particularly limited, and for example, firing may be performed in an air atmosphere, or may be performed in an inert gas atmosphere such as nitrogen gas as necessary.

Moreover, in a baking process (S30), after adding and mixing electroconductive powder to the said temporary baked material, it baked at the temperature which does not exceed 350 degreeC (S310), and obtained by a 1st baking process. A second firing step (S320) in which conductive powder is further added to the fired product and mixed and fired at a temperature of 600 ° C. or higher can be performed.
In the firing step (S30), before the rapid high-temperature firing, first, the first firing is performed at a temperature not exceeding 350 ° C., whereby crystals of lithium manganese phosphate can be grown stepwise. Further, conductive powder is further added to and mixed with the fired product obtained in the first firing step (S310), whereby the surface of the compound on which crystals are precipitated is coated (coated) stepwise with the conductive powder. Therefore, it becomes difficult to receive mechanical damage by an apparatus such as mixing (or stirring), and the crystal structure of the compound is hardly broken. Thus, by adding conductive powder stepwise and firing at a temperature of 600 ° C. or higher in the high temperature region, a positive electrode active material having high crystallinity and excellent conductivity can be suitably produced. it can.

In the example described above, the case of synthesizing lithium manganese phosphate whose basic composition is represented by LiMnPO ₄ is illustrated, but the present invention is not limited to this. For example, Li _x Mn _y M′PO ₄ (M ′ in the formula is composed of Co, Ni and Fe as main constituent elements while changing the composition ratio of lithium, manganese and phosphoric acid while maintaining the olivine type crystal structure. And the condition that 0 <x ≦ 1 and 0 <y <1 are satisfied, which can allow the presence of impurity components). In that case, in the raw material mixture preparation step (S10), the blending ratio of the starting materials including the lithium source, manganese source, phosphate source and M ′ element source may be appropriately changed so as to obtain a desired composition compound. . Similarly for LiCoPO ₄ , LiNiPO ₄ and LiFePO ₄ , which are olivine-type lithium-containing phosphate compounds other than lithium manganese phosphate, the mixing ratio of starting materials should be appropriately changed so that a desired composition compound can be obtained. Can be manufactured.

As described above, since the olivine-type lithium-containing phosphate compound obtained by the manufacturing method of the present embodiment has high crystallinity, the configuration of various forms of lithium secondary batteries (typically lithium ion batteries) It can be preferably used as an element or a constituent element (positive electrode active material) of a positive electrode incorporated in the lithium secondary battery.
A positive electrode current collector obtained by mixing the positive electrode active material made of the olivine-type lithium-containing phosphate compound thus produced and other positive electrode material components (for example, a binder) used as necessary A positive electrode can be produced by holding it in layers.

  The step of forming the positive electrode is the same as that for producing a conventional positive electrode for a lithium secondary battery, except that the olivine type lithium-containing phosphate compound obtained by the method of the present embodiment is used as the positive electrode active material. Can be done. For example, a paste-like composition in which the above-described positive electrode active material and other positive electrode material components (for example, a binder) used as necessary are dispersed in a suitable dispersion medium and kneaded is prepared. What is necessary is just to produce a positive electrode by apply | coating on a positive electrode electrical power collector, and drying.

  Hereinafter, an embodiment of a lithium secondary battery constructed using a positive electrode active material obtained by the manufacturing method disclosed herein will be described with reference to schematic diagrams shown in FIGS.

  2 is a perspective view schematically showing a rectangular lithium secondary battery according to an embodiment, and FIG. 3 is a cross-sectional view taken along line III-III in FIG. As shown in FIGS. 2 and 3, the lithium secondary battery 100 according to the present embodiment includes a rectangular parallelepiped battery case 10 and a lid 14 that closes the opening 12 of the case 10. A flat electrode body (wound electrode body 20) and an electrolyte can be accommodated in the battery case 10 through the opening 12. The lid 14 is provided with a positive terminal 38 and a negative terminal 48 for external connection, and a part of the terminals 38 and 48 protrudes to the surface side of the lid 14.

  As shown in FIG. 3, in this embodiment, the wound electrode body 20 is accommodated in the case 10. The electrode body 20 includes a positive electrode sheet 30 in which a positive electrode active material layer 34 is formed on the surface of a long sheet-like positive electrode current collector 32, and a negative electrode active material layer 44 on the surface of a long sheet-like negative electrode current collector 42. Are formed of a negative electrode sheet 40 on which is formed, and a long sheet-like separator 50. Then, the positive electrode sheet 30 and the negative electrode sheet 40 are overlapped and wound together with the two separators 50, and the obtained wound electrode body 20 is formed into a flat shape by crushing and ablating from the side surface direction.

  In the wound positive electrode sheet 30, the positive electrode current collector 32 is exposed without forming the positive electrode active material layer 34 at one end portion along the longitudinal direction, while the negative electrode is wound. Also in the sheet 40, the negative electrode current collector 42 is exposed at one end portion along the longitudinal direction without forming the negative electrode active material layer 44. Then, the positive electrode terminal 38 is joined to the exposed end portion of the positive electrode current collector 32, and the negative electrode terminal 48 is joined to the exposed end portion of the negative electrode current collector 42, respectively. The positive electrode sheet 30 or the negative electrode sheet 40 is electrically connected. The positive and negative terminals 38 and 48 and the positive and negative current collectors 32 and 42 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

  The positive electrode sheet 30 may be formed by applying a positive electrode active material on a long positive electrode current collector. As the positive electrode current collector, an aluminum foil or other metal foil suitable for the positive electrode is preferably used. As the positive electrode active material, a positive electrode active material made of an olivine-type lithium-containing phosphate compound manufactured by applying any of the methods disclosed herein can be used.

  On the other hand, the negative electrode sheet 40 may be formed by applying a negative electrode active material layer for a lithium secondary battery on a long negative electrode current collector. For the negative electrode current collector, a copper foil (this embodiment) or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or more of materials conventionally used in lithium secondary batteries can be used without any particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium-containing transition metal oxides and transition metal nitrides.

  Moreover, as a suitable separator sheet 50 used between the positive / negative electrode sheets 30 and 40, what was comprised with porous polyolefin resin is mentioned. For example, a porous separator sheet made of synthetic resin (for example, made of polyolefin such as polyethylene) can be suitably used. When a solid electrolyte or a gel electrolyte is used as the electrolyte, there may be a case where a separator is unnecessary (that is, in this case, the electrolyte itself can function as a separator).

  In addition, a rough procedure for constructing the lithium secondary battery 100 according to an embodiment will be described. The produced positive electrode sheet 30 and negative electrode sheet 40 are stacked and wound together with two separators 50, and are crushed from the stacking direction to be crushed to form an electrode body into a flat shape, accommodated in a battery case 10 and accommodated in an electrolyte. After injecting the lithium secondary battery 100 of this embodiment, the lid 14 is attached to the case opening 12 and sealed. There is no particular limitation on the structure, size, material (for example, metal or laminate film) of the battery case 10 and the like.

  Since the lithium secondary battery constructed in this way is constructed using a positive electrode active material composed of an olivine-type lithium-containing phosphate compound having high crystallinity and excellent conductivity as described above, it is excellent. The battery performance (particularly battery capacity, charge / discharge cycle characteristics or high rate characteristics).

  Hereinafter, although the test example regarding this invention is demonstrated, it is not intending to limit this invention to what is shown to this specific example.

  A lithium secondary battery was constructed using a positive electrode active material comprising an olivine-type lithium-containing phosphate compound obtained by the positive electrode active material manufacturing method disclosed herein, and the battery performance of the battery was evaluated.

<Example 1: Synthesis of LiMnPO ₄ (1)>
In this example, lithium acetate dihydrate [Li (CH ₃ COO) · 2H ₂ O], manganese acetate (II) tetrahydrate [Mn (CH ₃ COO) ₂ · 4H ₂ O] and , Ammonium dihydrogen phosphate [NH ₄ H ₂ PO ₄ ] was weighed so as to have a molar ratio of 1: 1: 1, and dissolved in ion-exchanged water as a solvent to prepare a raw material mixture. Next, the obtained raw material mixture was heated to 80 ° C. and calcined. When the solvent was appropriately evaporated, carbon powder was added as a conductive powder to the temporarily fired product and mixed (stirred) for 20 hours using a ball mill apparatus. And it baked at 350 degreeC, and also carbon powder was added, and it mixed using the ball mill apparatus. Furthermore, LiMnPO _{4 according} to Example 1 was synthesized by firing at 600 ° C.

<Example 2: Synthesis of LiMnPO ₄ (2)>
In this example, LiMnPO _{4 according} to Example 2 was synthesized by the same procedure as in Example 1 except that the heating temperature for pre-baking was set to 100 ° C.

<Example 3: Synthesis of LiMnPO ₄ (3)>
In this example, LiMnPO _{4 according} to Example 3 was synthesized by the same procedure as in Example 1 except that the heating temperature for pre-baking was set to 120 ° C.

<Example 4: Synthesis of LiMnPO ₄ (4)>
In this example, LiMnPO _{4 according} to Example 4 was synthesized by the same procedure as in Example 1 except that the heating temperature for pre-baking was set to 150 ° C.

<Example 5: Synthesis of LiMnPO ₄ (5)>
In this example, LiMnPO _{4 according} to Example 5 was synthesized by the same procedure as in Example 1 except that the heating temperature for pre-baking was set to 200 ° C.

<Example 6: Synthesis of LiMnPO ₄ (6)>
In this example, LiMnPO _{4 according} to Example 6 was synthesized by the same procedure as in Example 1 except that the heating temperature for pre-baking was set to 350 ° C.

<Example 7: Synthesis of LiMnPO ₄ (7)>
In this example, LiMnPO _{4 according} to Example 7 was synthesized by the same procedure as in Example 1 except that sucrose was further added as an organic acid to the raw material mixture.
Specifically, lithium acetate dihydrate [Li (CH ₃ COO) · 2H ₂ O], manganese acetate (II) tetrahydrate [Mn (CH ₃ COO) ₂ · 4H ₂ O] and , Ammonium dihydrogen phosphate [NH ₄ H ₂ PO ₄ ] was weighed so as to have a molar ratio of 1: 1: 1, and sucrose 3 as an organic acid with respect to 100% by weight of the mixture of the weighed raw materials. Mass% was added and dissolved in ion exchange water to prepare a raw material mixture. Next, the obtained raw material mixture was heated to 80 ° C. and calcined. When the solvent was appropriately evaporated, carbon powder was added as a conductive powder to the temporarily fired product and mixed (stirred) for 20 hours using a ball mill apparatus. And it baked at 350 degreeC, and also carbon powder was added, and it mixed using the ball mill apparatus. Furthermore, LiMnPO _{4 according} to Example 7 was synthesized by baking at 600 ° C.

<Example 8: Synthesis of LiMnPO ₄ (8)>
In this example, LiMnPO _{4 according} to Example 8 was synthesized by the same procedure as in Example 7 except that the heating temperature for pre-baking was set to 120 ° C.

<Example 9: Synthesis of LiMnPO ₄ (9)>
In this example, LiMnPO _{4 according} to Example 9 was synthesized by the same procedure as in Example 7 except that the heating temperature for pre-baking was set to 150 ° C.

<Comparative Example: Synthesis of LiMnPO ₄ (10)>
In this comparative example, the preliminary baking step of heating the raw material mixture in Example 1 at 80 ° C. was omitted, and LiMnPO _{4 according} to the comparative example was synthesized.
Specifically, lithium acetate dihydrate [Li (CH ₃ COO) · 2H ₂ O], manganese acetate (II) tetrahydrate [Mn (CH ₃ COO) ₂ · 4H ₂ O] and , Ammonium dihydrogen phosphate [NH ₄ H ₂ PO ₄ ] was weighed so as to have a molar ratio of 1: 1: 1, and dissolved in ion-exchanged water as a solvent to prepare a raw material mixture. Next, the obtained raw material mixture was fired at 350 ° C., carbon powder was added, and mixing was performed using a ball mill apparatus. Furthermore, LiMnPO _{4 according} to the comparative example was synthesized by firing at 600 ° C. In addition, the carbon powder used the same amount as the addition amount for 2 times added in the baking process in Example 1.

<Preparation of positive electrode>
Using the synthesized Examples 1 to 9 and LiMnPO _{4 according} to the comparative example, positive electrodes were produced. That is, 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder was dissolved in N-methylpyrrolidone (NMP), 75 parts by mass of LiMnPO ₄ as the synthesized positive electrode active material, and carbon as a conductive additive. A paste-like composition for forming a positive electrode active material layer was prepared by adding 20 parts by mass of black (CB) and kneading until uniform mixing. Such a paste-like composition was applied to one surface of a positive electrode current collector (aluminum foil having a thickness of 15 μm), the solvent was volatilized and dried to form a positive electrode active material layer. Thereafter, the sheet was stretched into a sheet shape by a press machine and punched into a circular shape with a punch having a diameter of 16 mm to produce a positive electrode.

<Construction of lithium secondary battery>
Test lithium secondary batteries were constructed using positive electrodes produced using LiMnPO _{4 according} to Examples 1 to 9 and Comparative Examples. The prepared positive electrode and a negative electrode (19 mm in diameter) made of metallic lithium were arranged so as to face each other with a polypropylene porous separator interposed therebetween, and this was accommodated in a coin-type case (CR 2032 type cell) together with an electrolytic solution. As the electrolytic solution, a solution obtained by dissolving about 1 mol / L LiPF ₆ as a supporting salt in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) was used. In this way, a lithium secondary battery was constructed using LiMnPO ₄ according to Examples 1 to 9 and Comparative Examples was a test cell according to each of Examples 1 to 9 and Comparative Examples.

<Charge / discharge test>
The following tests were conducted using the test battery constructed as described above. That is, for the test batteries according to Examples 1 to 6 using LiMnPO ₄ synthesized by pre-baking and the test batteries according to comparative examples using LiMnPO ₄ synthesized by omitting the pre-baking step The charge / discharge test was conducted to evaluate the rate characteristics. The charge / discharge test is performed at a measurement temperature of 25 ° C. and charged to an upper limit voltage of 4.8 V by a constant current-constant voltage method. It was measured. The measurement results are shown in FIG. 1C represents a current value for discharging a theoretical capacity of 150 mAh / g in 1 hour.

As shown in FIG. 4, the test batteries according to Examples 1 to 6 using LiMnPO ₄ synthesized by pre-baking are related to a comparative example using LiMnPO ₄ synthesized without the pre-baking step. Compared with the test battery, the specific capacity was large and excellent rate characteristics were exhibited. In particular, the specific capacity of the test batteries according to Examples 1 to 4 that were pre-fired at a heating temperature of 80 to 150 ° C. was large, and the specific capacity was the largest when Example 3 was pre-baked at 120 ° C. This was a test battery.
From this, it was confirmed that the rate characteristics were improved by performing preliminary firing. In addition, it was confirmed that the pre-baking was more effective when heated in a temperature range of 80 to 150 ° C.

<XRD analysis>
Using an X-ray diffractometer, the crystal structure of LiMnPO _{4 according to} Example 3 synthesized by performing preliminary calcination by heating at 120 ° C. and LiMnPO _{4 according} to a comparative example synthesized by omitting the calcination step was analyzed. . FIG. 5 is a diagram showing the results of measuring each diffraction pattern. The diffraction patterns of LiMnPO _{4 according} to Example 3 and the comparative example are shown in order from the top.

According to FIG. 5, the diffraction pattern of LiMnPO ₄ according to Example 3 was sharp in all peaks. On the other hand, the diffraction pattern of LiMnPO _{4 according} to the comparative example has few sharp peaks as a whole, and the peak at 2θ = about 20-40 ° is observed to be broader than the peak at the same position in Example 3. It was. From this, it was confirmed that LiMnPO _{4 according to} Example 3 synthesized by performing preliminary calcination by heating at 120 ° C. has a higher crystallinity than the comparative example.

<Charge / discharge test>
Furthermore, the charge / discharge test was performed in the same manner as described above on the test batteries according to Examples 7 to 9 using LiMnPO ₄ synthesized by adding sucrose to the raw material mixture and performing preliminary firing. The rate characteristics were evaluated together with the results of the test battery according to Example 3 using LiMnPO ₄ synthesized by performing pre-baking at 120 ° C. and the test battery according to the comparative example. The measurement results are shown in FIG.

As shown in FIG. 6, the test cell according to an 7-9 that addition of sucrose to the raw material mixture was used LiMnPO ₄ synthesized by performing the calcination, the LiMnPO ₄ synthesized by omitting the pre-baking step Compared with the test battery according to the comparative example used, the specific capacity was large and the rate characteristics were excellent. Further, the test battery according to Example 8 was constructed using LiMnPO ₄ synthesized by adding sucrose to a raw material mixture and pre-baking at 120 ° C., but also without adding sucrose. The specific capacity was larger than that of the test battery according to Example 3, which was constructed using LiMnPO ₄ synthesized by performing preliminary firing at ° C. From this, it was confirmed that the rate characteristics were most improved by adding sucrose as an organic acid to the raw material mixture and performing pre-baking.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here. For example, the battery of the various content from which an electrode body structural material and electrolyte differ may be sufficient. Further, the size and other configurations of the battery can be appropriately changed depending on the application (typically for in-vehicle use).

  Since the lithium secondary battery using the positive electrode active material obtained by the method of the present invention is excellent in battery characteristics as described above, it is particularly suitable as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Can be used. Therefore, as schematically shown in FIG. 7, the present invention provides a vehicle (typically an automobile, particularly a hybrid automobile) provided with such a lithium secondary battery (typically, a battery pack formed by connecting a plurality of series batteries) 100 as a power source. , An automobile equipped with an electric motor such as an electric vehicle and a fuel cell vehicle.

S10 Raw material mixture preparation step S20 Temporary firing step S30 Firing step S310 First firing step S320 Second firing step 1 Vehicle 10 Battery case 12 Opening portion 14 Lid 20 Winding electrode body 30 Positive electrode sheet (positive electrode)
32 Positive electrode current collector 34 Positive electrode active material layer 38 Positive electrode terminal 40 Negative electrode sheet (negative electrode)
42 Negative electrode current collector 44 Negative electrode active material layer 48 Negative electrode terminal 50 Separator 100 Lithium secondary battery

Claims (8)

It is represented by the general formula Li _x MPO ₄ (wherein M is at least one element selected from the group consisting of Co, Ni, Fe and Mn, and satisfies the condition of 0 <x ≦ 1). A method for producing a positive electrode active material comprising an olivine-type lithium-containing phosphate compound, comprising the following steps:
Mixing a starting material for constituting the positive electrode active material including a lithium source, a phosphoric acid source and an M element source in an aqueous solvent to prepare a gel-like raw material mixture;
Step temporarily baked by heating the pre-Symbol raw material mixture to a temperature range of 80 to 150 ° C.; and,
A step of adding conductive powder to the pre-baked product obtained by heating to the temperature range in the pre-baking step, mixing and baking;
A method for producing a positive electrode active material.   The positive electrode active material manufacturing method according to claim 1, wherein an organic acid is added in the preparation step of the raw material mixture.   The method for producing a positive electrode active material according to claim 1 or 2, wherein the addition amount of the organic acid is set to an amount corresponding to 10% by mass or less with respect to 100% by mass of the raw material mixture. In the firing step, the conductive powder is added to the calcined product, mixed, and fired at a temperature not exceeding 350 ° C .; and
A second baking step in which conductive powder is further added to and mixed with the fired product obtained in the first baking step and fired at a temperature of 600 ° C. or higher;
Encompassing, positive electrode active material manufacturing method according to any one of claims 1-3. The olivine-type lithium-containing phosphate compound, containing Mn as the element M, the positive electrode active material manufacturing method according to any one of claims 1-4. Wherein the conductive powder is carbon powder, the positive electrode active material manufacturing method according to any one of claims 1-5. Lithium secondary battery comprising the positive electrode active material obtained in the cathode by the method of any of claims 1-6. A vehicle comprising the lithium secondary battery according to claim 7 .

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