JP5155498B2 - Method for producing positive electrode active material for lithium secondary battery - Google Patents

Description

The present invention relates to the production how the positive active material for a rechargeable lithium battery.

LiMPO ₄ (M is a transition metal), which is an olivine-type lithium metal phosphate, has a relatively large electric capacity and is less expensive than LiCoO ₂ that has been widely used as a positive electrode active material for lithium secondary batteries. Since a battery can be made, it is expected as a positive electrode active material for a lithium secondary battery, particularly a large-sized lithium secondary battery for automobiles (see Patent Documents 1 and 2).

The positive electrode active material using olivine-type lithium metal phosphate has lower conductivity than LiCoO ₂ and the electrode reaction polarization increases with charge / discharge. The capacity is not obtained. For this reason, various proposals for increasing the capacity have been made.

In Patent Document 3, electrode growth polarization is promoted by suppressing the crystal growth of LiMPO ₄ by using a crystal growth inhibitor to facilitate the entry and exit of lithium ions between the inside of the positive electrode active material and the electrolyte. In addition, the proposal has been made to improve the conductivity and increase the capacity by increasing the contact area between the positive electrode material and the conductivity-imparting material.

In Patent Document 4, the crystallite diameter of olivine-type lithium metal phosphate is reduced to 35 nm or less by a solvothermal method or spray pyrolysis method, and lithium ions between phosphorus and oxygen (PO) tetrahedrons are formed. Proposals have been made to shorten the moving distance, shorten the moving distance of electrons for changing the valence of the metal, improve the insertion / desorption efficiency of lithium ions, and consequently increase the capacity. By this proposal, a capacity of about 105 mAh / g is obtained with LiCoPO ₄ and a capacity of about 135 mAh / g with LiFePO ₄ .

  Since olivine type lithium metal phosphate has poor surface crystallinity, there is a problem that divalent metal is oxidized and changed to high resistance trivalent phosphate, and coarse particles are formed by secondary aggregation. There is a problem that it is easy to make and the capacity is difficult to obtain due to its poor electrical conductivity. Patent Document 5 proposes a method for calcination of a sintered body of lithium metal phosphate by a ball mill or the like, adding a carbon source, and firing. However, since ball milling requires solid-liquid separation, waste liquid treatment, and the like, the cost is high, and there is a problem of contamination, resulting in low productivity.

  In Patent Document 6, olivine-type lithium metal phosphate is washed with a reducing acid or the like to remove iron phosphate or lithium phosphate present as a high-resistance impurity on the surface of the lithium metal phosphate particles. Thus, a method for reducing the electrical resistance has been proposed. However, this method has a problem in that productivity decreases because the charged lithium, phosphorus, and iron are washed away.

  In Patent Document 7, when olivine type lithium iron phosphate is produced by a solid phase method, divalent Fe contained in the raw material is oxidized by air or moisture contained in the raw material and does not function as an active material. As a method of solving the problem that the capacity is reduced by changing to Fe, a method of reducing the amount of trivalent Fe by taking two-stage firing conditions has been proposed. However, when the present inventors made additional trials, a sufficient capacity could not be obtained.

  Patent Document 8 proposes a method of substituting with a different element because the transition of lithium ions is hindered when a transition metal ion is present at a site where lithium ions are present. However, if another ion is present at the site where the lithium ion is present, the movement of the lithium ion is hindered, and there is a possibility that a satisfactory capacity cannot be obtained.

Patent Document 9 proposes to increase the capacity and improve cycle characteristics by firing a mixture of LiFePO ₄ raw material and carbon material fine particles to produce a positive electrode active material in which carbon material fine particles are combined with LiFePO _4. Has been made. By this method, a capacity of about 110 mAh / g is obtained.

Japanese Patent Laid-Open No. 9-171827 JP-A-9-134725 JP 2003-45430 A Japanese Patent No. 4190912 JP 2009-81002 A JP 2009-200013 A JP 2005-190882 A Special table 2010-524820 Japanese Patent No. 4186507

As described above, various methods for increasing the capacity have been proposed so far, but a sufficient capacity has not been obtained compared to the theoretical capacity (170 mAh / g in LiFePO ₄ ).

As a result of intensive studies to solve the above-mentioned problems, the present inventor has obtained a lithium metal phosphate (LiMPO _{4) as} a starting material in a production method for producing a positive electrode active material by firing lithium metal phosphate. When the composition ratio of (M is a transition metal) is less than Li: M: P = 1: 1: 1, replenishing the shortage of elements or raw materials and firing is performed to obtain a high capacity positive electrode active The inventors have found that a substance can be obtained and have come up with the present invention. If there is a deficient element or material less than the composition ratio Li: M: P = 1: 1: 1, the fired positive electrode active material will have an incomplete crystal structure, but this deficiency must be compensated. Thus, a more complete crystal structure is considered. It is speculated that the completeness of the crystal structure enables rapid insertion / extraction of lithium ions in the active material, resulting in high capacity. That is, the present inventor brought the viewpoint of how to ensure the completeness of the crystal structure of the positive electrode active material to the problem of increasing the capacity and arrived at the present invention.
In addition, the present inventor completed the present invention by improving the conductivity of the positive electrode active material by combining a carbonaceous material with lithium metal phosphate to further increase the capacity.

An object of the present invention is to provide a method for producing a positive electrode active material for a lithium secondary battery comprising a composite of olivine type lithium metal phosphate and carbon, which can realize a high discharge rate characteristic with a high capacity. To do.
The present invention also provides a positive electrode comprising a composite of an olivine-type lithium metal phosphate and carbon obtained by a method for producing a positive electrode active material for a lithium secondary battery capable of realizing a high capacity and good discharge rate characteristics. An object is to provide an active material and a lithium secondary battery including the positive electrode active material.

In order to achieve the above object, the present invention provides the following means.
[1] Compositional formula LiMPO ₄ (element M is Fe, Mn, or Ti, V, Cr, Co, Ni, Nb, Ta, Mo, W, or one or more transition metals) Measuring a composition ratio of the phosphoric acid compound to identify an element whose composition ratio is less than Li: M: P = 1: 1: 1; a lithium source as an element source corresponding to the identified element; A step of kneading a metal (M) source or a phosphoric acid source, the phosphoric acid compound, a carbonaceous material or a carbonaceous material precursor to obtain a first carbon-containing mixture, and firing the first carbon-containing mixture And a process of
The manufacturing method of the positive electrode active material for lithium secondary batteries characterized by having.
[2] represented by the composition formula LiMPO ₄ (the element M is Fe, Mn, or any one or two or more transition metals of Ti, V, Cr, Co, Ni, Nb, Ta, Mo, W) Measuring a composition ratio of the phosphoric acid compound to identify an element whose composition ratio is less than Li: M: P = 1: 1: 1; a lithium source as an element source corresponding to the identified element; A step of kneading a metal (M) source or a phosphoric acid source and the phosphoric acid compound to obtain a first mixture, a step of firing the first mixture, a fired product obtained in the step, and carbon A positive electrode active material for a lithium secondary battery, comprising: a step of kneading a carbonaceous material or a carbonaceous material precursor to obtain a second carbon-containing mixture; and a step of firing the second carbon-containing mixture. Manufacturing method.
[3] represented by the composition formula LiMPO ₄ (the element M is Fe, Mn, or one or more transition metals of Ti, V, Cr, Co, Ni, Nb, Ta, Mo, W) Measuring a composition ratio of the phosphoric acid compound to identify an element having a composition ratio of less than Li: M: P = 1: 1: 1, the phosphoric acid compound, and a carbonaceous material or a carbonaceous material precursor A step of obtaining a third carbon-containing mixture by kneading the body, a step of firing the third carbon-containing mixture, a fired product obtained in the step, and lithium as an element source corresponding to the specified element A lithium secondary battery comprising: a step of kneading a source, a metal (M) source, or a phosphoric acid source to obtain a fourth carbon-containing mixture; and a step of firing the fourth carbon-containing mixture. For producing a positive electrode active material for use.
[4] The carbonaceous material precursor is at least one selected from the group consisting of sugars, hydrocarbons, fatty acids, ethers, esters, alcohols, thiols, fats and oils, pitches, and polymers. [1] The method for producing a positive electrode active material for a lithium secondary battery according to any one of [3].
[5] As the carbonaceous material, at least one selected from the group consisting of graphite, carbon nanotubes, amorphous carbon, glassy carbon, carbon black, and graphene is used. 4] The manufacturing method of the positive electrode active material for lithium secondary batteries as described in any one of 4) .

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the positive electrode active material for lithium secondary batteries which consists of a composite of an olivine type lithium metal phosphate and carbon by which a favorable discharge rate characteristic is implement | achieved can be provided.
In addition, the present invention provides a positive electrode comprising a composite of an olivine type lithium metal phosphate and carbon obtained by a method for producing a positive electrode active material for a lithium secondary battery that realizes a high capacity and good discharge rate characteristics. A lithium secondary battery including the active material and the positive electrode active material can be provided.

  Hereinafter, the manufacturing method of the positive electrode active material for lithium secondary batteries, the positive electrode active material for lithium secondary batteries, and a lithium secondary battery which are embodiments of the present invention will be described.

(Method for manufacturing positive electrode active material for lithium secondary battery (first embodiment))
In the method for producing a positive electrode active material for a lithium secondary battery according to the present embodiment, the composition ratio of the phosphoric acid compound represented by the composition formula LiMPO ₄ is measured, and the composition ratio is Li: M: P = 1: 1: 1. For identifying elements that do not satisfy the requirements (identifying process for deficient elements), lithium sources, metal (M) sources, or phosphoric acid sources, phosphoric acid compounds, and carbonaceous materials as element sources corresponding to the identified elements Or it has the process of knead | mixing a carbonaceous material precursor and obtaining a 1st carbon containing mixture, and the process of baking a 1st carbon containing mixture. Here, the element M of LiMPO ₄ is Fe, Mn, or any one or two or more transition metals of Ti, V, Cr, Co, Ni, Nb, Ta, Mo, and W.

<Identification process for missing elements>
In this step, the composition ratio of the phosphoric acid compound represented by the composition formula LiMPO _{4 as} a starting material is measured, and the composition ratio is less than Li: M: P = 1: 1: 1 (desired composition ratio). This is a process of specifying an element.

The method for measuring the ratio of Li, M, and P that are constituent elements of the active material LiMPO ₄ is not particularly limited, and examples thereof include ICP (Inductively Coupled Plasma) emission spectroscopy and atomic absorption. Further, a spectroscopic method such as EPMA (Electron Probe Micro-Analysis) or fluorescent X-ray analysis may be used. A plurality of analysis methods with high accuracy may be combined. For example, analytical values obtained by an atomic absorption method for Li and a fluorescent X-ray analysis method for M and P may be used.

Method for producing a phosphoric acid compound represented by the composition formula LiMPO ₄ is the starting material is not particularly limited, it is possible to use a hydrothermal synthesis method, a solid phase synthesis method, a sol-gel method or the like.

<Step of obtaining a first carbon-containing mixture>
In this step, the element source (lithium source or metal (M) source) or raw material source (phosphoric acid source) specified as less than Li: M: P = 1: 1: 1 in the previous step (hereinafter, appropriately, This is a step of generating a mixture (first carbon-containing mixture) by kneading the measured phosphoric acid compound and the carbonaceous material or carbonaceous material precursor, omitting the raw material source). .

The element source for measuring the composition ratio of the constituent elements of the active material and replenishing elements that do not satisfy the desired composition ratio is not particularly limited, but it is desirable that the counter anion decomposes and volatilizes at the firing temperature. . Furthermore, from the viewpoint of performing a solid-phase reaction, each element source is preferably dissolved in a liquid such as water or an organic solvent. This is because the phosphoric acid compound before addition of the deficient element is in a solid phase, and this is mixed with each element source uniformly.
Specifically, as the lithium source, for example, one or more compounds of LiOH, LiCl, Li ₂ CO ₃ , CH ₃ COOLi, and (COO) ₂ Li ₂ can be used.
As the metal (M) source, when the metal (M) is Fe, for example, any one or more compounds of FeCl ₂ , FeSO ₄ , Fe (NO ₃ ) ₂ or (COO) ₂ Fe are used. be able to. When the metal (M) is Mn, for example, one or more compounds of MnCl ₂ , MnSO ₄ , Mn (NO ₃ ) ₂ or (COO) ₂ Mn can be used.
Is not particularly restricted but includes phosphoric acid source, _{e.g., H 3 PO 4, NH 4} H 2 PO 4, may be used _(NH 4) any one or more compounds of the 2 HPO _4.

The carbonaceous material is not particularly limited as long as it is a material made of carbon having conductivity through a firing process. For example, artificial graphite and natural graphite used as lithium ion battery negative electrode materials, oriented graphite such as highly oriented pyrolytic graphite HOPG, coke, carbon nanotube, carbon nanofiber, graphene, acetylene black and ketjen black Carbon black such as black pearl, amorphous carbon and glassy carbon, or those obtained by graphitizing these carbon materials can be used.
In particular, it is preferable to use one or more of graphite, carbon nanotube, amorphous carbon, glassy carbon, and graphene. This is because all of them are highly conductive, and in particular, graphite, carbon nanotubes, and graphene are highly conductive because the graphite structure is clear.

The metal (M) may be two or more kinds of transition metals. In this case, for example, in LiFe _0.75 Mn _0.25 PO ₄ , the desired composition ratio is Li: Fe: Mn: P = 1: 0.75: 0.25: 1. Each element source will be supplemented.

  The addition amount of the lithium source, the metal (M) source, and the phosphate source added to make up for the insufficient element source is such that the composition ratio of each element source is Li: M: P = 1: 1: Although it is preferable to adjust so that it may be set to 1, it is not limited to this. For example, when a lithium source is added as an insufficient element source, it is preferably added at a composition ratio of more than 0 and less than 1. The reason why the above range is preferable as the addition amount of the lithium source is that the addition amount of the lithium source can move in the range of 0 to 1 when iron is oxidized. When a metal (M) source is added as an insufficient element source, it is preferably added at a composition ratio of more than 0 and 0.33 or less. The reason why the above range is preferable as the addition amount of the metal (M) source is that the metal (M) source is insufficient and a compound having a composition ratio of Li: M: P = 3: 2: 3 may be generated. This is because it is necessary to supplement the metal (M) source. When a phosphoric acid source is added as an insufficient element source, it is preferably added at a composition ratio of more than 0 and 0.2 or less. The reason why the above range is preferable as the addition amount of the phosphoric acid source is that if the addition amount of the phosphoric acid source exceeds the composition ratio of 0.2, the olivine structure may not be maintained.

Examples of the carbonaceous material precursor include saccharides such as sucrose, lactose, glucose, maltose, and fructose; hydrocarbon gases such as methane, ethylene, ethane, propane, propylene, butane, and isobutane; not gaseous but liquid or solid Hydrocarbons; unsaturated and saturated fatty acids such as oleic acid, linoleic acid, palmitic acid, linolenic acid; ethers, esters, monovalent, divalent, trivalent, primary, secondary, tertiary alcohols, thiols , Ketones, oils and fats, pitches such as coal tar, tar, and general organic substances such as polyethylene glycol, polyvinyl alcohol, rubber, synthetic fiber, synthetic resin, copolymer, melamine, urea can be used. .
In particular, it is preferable to use one or more of saccharides, hydrocarbons, fatty acids, ethers, esters, alcohols, thiols, fats and oils, pitches, or polymers. This is because particularly liquid ones of the above can be coated with a high coverage, excellent handling properties, and relatively low cost.

  It is essential that the amount of carbonaceous material or carbonaceous material precursor added does not significantly reduce the capacity of the battery active material. For that purpose, in the battery active material consisting of lithium metal phosphate and carbon finally obtained, the amount of carbon to battery active material may be added in an amount of 0.5 wt% or more and 5 wt% or less. Preferably, an amount that is 0.6 wt% or more and 4 wt% or less is more preferable, and an amount that is 0.7 wt% or more and 3 wt% or less is most preferable. This is because if the carbon ratio is greater than 5 wt%, the capacity decreases, and if it is less than 0.5 wt%, the conductivity is too low to be used as an active material.

  The mixing method of the phosphoric acid compound, each element source and the carbonaceous material or carbonaceous material precursor is not particularly limited. However, since the former is a solid (usually a powder), it is preferable to mix a liquid or a solution dissolved in a solvent as the latter two. A solid can also be used as the latter. In this case, for example, by performing sufficient mixing with a ball mill or a powerful stirrer, a solid phase reaction can be caused in the subsequent firing step to obtain a uniform composition.

  The obtained mixture (first carbon-containing mixture) is dried using a dryer or the like. It is preferable to select conditions so as not to oxidize the mixture during drying. A vacuum drying method is preferably used for drying.

<Step of firing the first carbon-containing mixture>
In this step, the mixture (first carbon-containing mixture) obtained in the previous step is fired to produce a positive electrode active material for a lithium secondary battery composed of lithium metal phosphate and carbon.

The firing temperature in this step is preferably 120 ° C. or higher and 700 ° C. or lower when a carbonaceous material is used, and preferably 200 ° C. or higher and 700 ° C. or lower when a carbonaceous material precursor is used. This is because it is considered that the resynthesis of LiMPO ₄ does not substantially occur when the firing temperature is less than 120 ° C. when the carbonaceous material is used, and when the firing temperature is less than 200 ° C., the carbonaceous material is used when the carbonaceous material precursor is used. This is because the material precursor cannot be sufficiently converted into the carbonaceous material. Further, if the firing temperature exceeds 700 ° C., sintering starts to occur and the particle size becomes large.
In addition, the firing time in this step may be within a range where the firing can be completed and the material is not damaged (including sintering), and is preferably, for example, 2 hours or more and 100 hours or less.

In addition, in the case where the olivine type lithium metal phosphate is easily oxidized, for example, in the case of LiFePO ₄ , the firing is preferably performed in an inert atmosphere such as nitrogen or argon.

(Method for producing positive electrode active material for lithium secondary battery (second embodiment))
In the method for producing a positive electrode active material for a lithium secondary battery according to the present embodiment, the composition ratio of the phosphoric acid compound represented by the composition formula LiMPO ₄ is measured, and the composition ratio is Li: M: P = 1: 1: 1. Kneading the phosphoric acid compound with a step of identifying an element that is less than (a step of identifying a deficient element), a lithium source, a metal (M) source, or a phosphoric acid source as an element source corresponding to the identified element And then kneading the step of obtaining the first mixture, the step of firing the first mixture, the fired product obtained in the step and the carbonaceous material or the carbonaceous material precursor to obtain a second carbon-containing mixture. And a step of firing the second carbon-containing mixture. Here, the element M of LiMPO ₄ is Fe, Mn, or any one or two or more transition metals of Ti, V, Cr, Co, Ni, Nb, Ta, Mo, and W.

<Identification process for missing elements>
This step is the same as in the first embodiment.

<Step of obtaining the first mixture>
In this embodiment, first, only the element source whose deficiency is specified and the measured phosphoric acid compound are kneaded to obtain a mixture (first mixture).
As the element source (raw material source), the same element as in the first embodiment can be used.
The mixing method of the phosphoric acid compound and the element source whose deficiency is specified is not particularly limited. However, since the former is solid (usually powder), the latter is preferably mixed with a liquid or a solution dissolved in a solvent. A solid can also be used as the latter. In this case, for example, by performing sufficient mixing with a ball mill or a powerful stirrer, a solid phase reaction can be caused with a uniform composition in the subsequent firing step.

  The obtained mixture (first mixture) is dried using a dryer or the like. It is preferable to select conditions so as not to oxidize the mixture during drying. A vacuum drying method is preferably used for drying.

<Step of firing the first mixture>
Next, the obtained mixture (first mixture) is fired.
The firing temperature in this step is preferably 120 ° C. or higher and 700 ° C. or lower. This is because it is considered that the resynthesis of LiMPO ₄ does not substantially occur when the firing temperature is less than 120 ° C., and LiMPO ₄ starts to sinter when the firing temperature exceeds 700 ° C.
In addition, the firing time in this step may be within a range in which firing can be performed and the material is not damaged (including sintering), and is preferably, for example, 1 hour or more and 100 hours or less.

  Further, when the mixture (first mixture) is a material that is easily oxidized, the firing is preferably performed in an inert atmosphere such as nitrogen or argon.

<Step of obtaining a second carbon-containing mixture>
Next, the mixture (first mixture) obtained in the previous step and the carbonaceous material or the carbonaceous material precursor are kneaded to obtain a carbon-containing mixture (second carbon-containing mixture).
The mixing method of the mixture (first mixture) and the carbonaceous material or the carbonaceous material precursor is not particularly limited. However, since the former is a solid and is usually a powder, it is preferable to use a liquid or a solution dissolved in a solvent as the latter. A solid can also be used. In this case, for example, by performing sufficient mixing with a ball mill or a powerful stirrer, a solid phase reaction can be caused with a uniform composition in the subsequent firing step.

  The obtained carbon-containing mixture (second carbon-containing mixture) is dried using a dryer or the like. It is preferable to select conditions so as not to oxidize the mixture during drying. A vacuum drying method is preferably used for drying.

<Step of firing the second carbon-containing mixture>
Next, the carbon-containing mixture (second carbon-containing mixture) obtained in the previous step is fired to produce a positive electrode active material for a lithium secondary battery composed of lithium metal phosphate and carbon.
The firing temperature in this step is preferably 120 ° C. or higher and 700 ° C. or lower when a carbonaceous material is used, and preferably 200 ° C. or higher and 700 ° C. or lower when a carbonaceous material precursor is used. This is because when the carbonaceous material is used, it is considered that the resynthesis of LiMPO ₄ does not substantially occur when the firing temperature is less than 120 ° C., and when the firing temperature is less than 200 ° C. when the carbonaceous material precursor is used, This is because the carbonaceous material precursor is not sufficiently thermally decomposed. Moreover, it is because sintering of LiMPO ₄ will start when a calcination temperature exceeds 700 degreeC.
In addition, the firing time in this step is not limited as long as the firing can be completed and the material is not damaged (including sintering), and is preferably, for example, 1 hour or more and 100 hours or less.
In this firing step, carbon supplied from the carbonaceous material or the carbonaceous material precursor contributes to reducing a trace amount of trivalent metal present on the surface of the lithium metal phosphate (LiMPO ₄ ). Conceivable. The optimum temperature for this reaction is 300 ° C. or higher and 700 ° C. or lower. When the temperature is lower than 300 ° C., a reaction of forming a carbon-lithium metal phosphate (LiMPO ₄ ) complex and reducing a trace amount of trivalent metal existing on the surface of the lithium metal phosphate (LiMPO ₄ ) occurs. This is because the sintering of LiMPO ₄ starts when the temperature exceeds 700 ° C.

  Moreover, when the carbon-containing mixture (second carbon-containing mixture) is a material that is easily oxidized, the firing is preferably performed in an inert atmosphere such as nitrogen or argon.

  The obtained mixture (second carbon-containing mixture) is dried using a dryer or the like. It is preferable to select conditions so as not to oxidize the mixture during drying. A vacuum drying method is preferably used for drying.

(Method for Producing Positive Electrode Active Material for Lithium Secondary Battery (Third Embodiment))
In the method for producing a positive electrode active material for a lithium secondary battery according to the present embodiment, the composition ratio of the phosphoric acid compound represented by the composition formula LiMPO ₄ is measured, and the composition ratio is Li: M: P = 1: 1: 1. A step of identifying an element less than 3 (a step of identifying a deficient element), a step of kneading the phosphoric acid compound and a carbonaceous material or a carbonaceous material precursor to obtain a third carbon-containing mixture, and the third A step of calcining the carbon-containing mixture, a calcined product obtained in the step, and a lithium source, a metal (M) source, or a phosphoric acid source as an element source corresponding to the specified element are kneaded, and the fourth is performed. A step of obtaining a carbon-containing mixture, and a step of firing the fourth carbon-containing mixture. Here, the element M of LiMPO ₄ is Fe, Mn, or any one or two or more transition metals of Ti, V, Cr, Co, Ni, Nb, Ta, Mo, and W.

<Identification process for missing elements>
This step is the same as in the first embodiment.

<Step of obtaining a third carbon-containing mixture>
In this embodiment, first, only the measured phosphate compound and the carbonaceous material or the carbonaceous material precursor are kneaded to obtain a mixture (third carbon-containing mixture).
The mixing method of the phosphoric acid compound and the carbonaceous material or the carbonaceous material precursor is not particularly limited. However, since the former is a solid and is usually a powder, it is preferable to use a liquid or a solution dissolved in a solvent as the latter. Solids can also be used. In this case, for example, by performing sufficient mixing with a ball mill or a powerful stirrer, a solid phase reaction can be caused with a uniform composition in the subsequent firing step.

  The obtained mixture (third carbon-containing mixture) is dried using a dryer or the like. It is preferable to select conditions so as not to oxidize the mixture during drying. A vacuum drying method is preferably used for drying.

<Step of firing the third carbon-containing mixture>
Next, the carbon-containing mixture (third carbon-containing mixture) obtained in the previous step is fired.
The firing temperature in this step is preferably 120 ° C. or higher and 700 ° C. or lower when a carbonaceous material is used, and preferably 200 ° C. or higher and 700 ° C. or lower when a carbonaceous material precursor is used. This is because when the carbonaceous material is used, it is considered that the resynthesis of LiMPO ₄ does not substantially occur when the firing temperature is less than 120 ° C., and when the firing temperature is less than 200 ° C. when the carbonaceous material precursor is used, This is because the carbonaceous material precursor is not sufficiently thermally decomposed. Further, because the sintering of the LiMPO ₄ the firing temperature exceeds 700 ° C. exceeds 700 ° C. begins.
In addition, the firing time in this step may be within a range where the firing can be completed and the material is not damaged (including sintering), and is preferably, for example, 1 hour or more and 100 hours or less.

  In addition, when the carbon-containing mixture (third carbon-containing mixture) is a material that is easily oxidized, the firing is preferably performed in an inert atmosphere such as nitrogen or argon.

<Step of obtaining a fourth carbon-containing mixture>
Next, the calcined product obtained in the previous step and the lithium source, metal (M) source, or phosphoric acid source of the specified element are kneaded to obtain a carbon-containing mixture (fourth carbon-containing mixture). .
The mixing method of the fired product and each element source is not particularly limited. However, since the former is a solid and is usually a powder, the latter is preferably a liquid or a solution dissolved in a solvent. A solid can also be used as the latter. In this case, for example, by performing sufficient mixing with a ball mill or a powerful stirrer, a solid phase reaction can be caused with a uniform composition in the subsequent firing step.

  The obtained mixture (fourth carbon-containing mixture) is dried using a dryer or the like. It is preferable to select conditions so as not to oxidize the mixture during drying. A vacuum drying method is preferably used.

<Step of firing the fourth carbon-containing mixture>
Next, the carbon-containing mixture (fourth carbon-containing mixture) obtained in the previous step is fired to produce a positive electrode active material for a lithium secondary battery composed of lithium metal phosphate and carbon.
The firing temperature in this step is preferably 120 ° C. or higher and 700 ° C. or lower. This is because it is considered that the resynthesis of LiMPO ₄ does not substantially occur when the firing temperature is less than 120 ° C., and LiMPO ₄ starts to sinter when the firing temperature exceeds 700 ° C.
Further, the firing time in this step may be within a range in which the firing can be completed and the material is not damaged (including sintering), and is preferably, for example, 2 hours or more and 100 hours or less.

  Moreover, when the carbon-containing mixture (second carbon-containing mixture) is a material that is easily oxidized, the firing is preferably performed in an inert atmosphere such as nitrogen or argon.

(Lithium secondary battery)
A lithium secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. In this lithium secondary battery, the positive electrode active material contained in the positive electrode is manufactured by the above method. By providing such a positive electrode active material, the capacity and discharge rate of the lithium secondary battery can be improved. Hereinafter, the positive electrode, the negative electrode, and the nonaqueous electrolyte constituting the lithium secondary battery will be described in order.

(Positive electrode)
In the lithium secondary battery of the present embodiment, as a positive electrode, a sheet comprising a positive electrode mixture containing a positive electrode active material, a conductive additive and a binder, and a positive electrode current collector bonded to the positive electrode mixture Shaped electrodes can be used. Further, as the positive electrode, a pellet type or sheet-shaped positive electrode formed by forming the above positive electrode mixture into a disk shape can also be used.

  As the positive electrode active material, the lithium metal phosphate produced by the above-described method is used. However, a conventionally known positive electrode active material may be mixed with the lithium metal phosphate and used.

  Binders include polyethylene, polypropylene, ethylene propylene copolymer, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, polytetrafluoroethylene, poly (meth) acrylate, polyvinylidene fluoride, polyethylene oxide, polypropylene oxide, poly Examples include epichlorohydrin, polyphasphazene, polyacrylonitrile, and the like.

  Furthermore, examples of the conductive aid include conductive metal powders such as silver powder; conductive carbon powders such as furnace black, ketjen black, and acetylene black; carbon nanotubes, carbon nanofibers, and vapor grown carbon fibers. As the conductive aid, vapor grown carbon fiber is preferable. The vapor grown carbon fiber preferably has a fiber diameter of 5 nm to 0.2 μm. The fiber length / fiber diameter ratio is preferably 5 to 1000. The content of the vapor grown carbon fiber is preferably 0.1 to 10% by mass with respect to the dry mass of the positive electrode mixture.

  Furthermore, examples of the positive electrode current collector include a conductive metal foil, a conductive metal net, and a conductive metal punching metal. As the conductive metal, aluminum or an aluminum alloy is preferable.

  Furthermore, the positive electrode mixture may contain an ion conductive compound, a thickener, a dispersant, a lubricant, and the like as necessary. Examples of the ion conductive compound include polysaccharides such as chitin and chitosan, and cross-linked products of the polysaccharides. Examples of the thickener include carboxymethyl cellulose and polyvinyl alcohol.

The positive electrode can be formed, for example, by applying a paste-like positive electrode mixture to a positive electrode current collector, drying, and pressure forming, or by pressing a powdery positive electrode mixture on the positive electrode current collector. can get. The thickness of the positive electrode is usually 0.04 mm or more and 0.15 mm or less. A positive electrode having an arbitrary electrode density can be obtained by adjusting the pressure applied during molding. The pressure applied during the molding is 1t / cm ² ~3t / cm ² is preferably about.

(Negative electrode)
The negative electrode is a sheet-like electrode composed of a negative electrode active material, a binder, and a negative electrode mixture containing a conductive additive added as necessary, and a negative electrode current collector bonded to the negative electrode mixture. Can be used. Further, as the negative electrode, a pellet-type or sheet-shaped negative electrode obtained by forming the above-described negative electrode mixture into a disk shape can also be used.

  As the negative electrode active material, conventionally known negative electrode active materials can be used. For example, carbon materials such as artificial graphite and natural graphite, metals such as Sn and Si, or metalloid materials can be used.

As the binder, the same binder as that used in the positive electrode can be used.
Furthermore, the conductive additive may be added as necessary, or may not be added. For example, conductive carbon powders such as furnace black, ketjen black, and acetylene black; carbon nanotubes, carbon nanofibers, vapor grown carbon fibers, and the like can be used. As the conductive additive, vapor grown carbon fiber is particularly preferable. The vapor grown carbon fiber preferably has a fiber diameter of 5 nm to 0.2 μm. The fiber length / fiber diameter ratio is preferably 5 to 1000. The content of the vapor grown carbon fiber is preferably 0.1 to 10% by mass with respect to the dry mass of the negative electrode mixture.

  Furthermore, examples of the negative electrode current collector include a conductive metal foil, a conductive metal net, and a conductive metal punching metal. As the conductive metal, copper or a copper alloy is preferable.

The negative electrode can be formed by, for example, applying a paste-like negative electrode mixture to a negative current collector, drying, and pressure molding, or by pressure molding a granular negative electrode mixture on the negative electrode current collector. can get. The thickness of the negative electrode is usually 0.04 mm or more and 0.15 mm or less. A negative electrode having an arbitrary electrode density can be obtained by adjusting the pressure applied during molding. The pressure applied during the molding is 1t / cm ² ~3t / cm ² is preferably about.

(Nonaqueous electrolyte)
Next, examples of the non-aqueous electrolyte include a non-aqueous electrolyte in which a lithium salt is dissolved in an aprotic solvent.

The aprotic solvent is preferably at least one or a mixed solvent selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and vinylene carbonate. .
Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , CH ₃ SO ₃ Li, and CF ₃ SO ₃ Li.

A so-called solid electrolyte or gel electrolyte can also be used as the nonaqueous electrolyte.
Examples of the solid electrolyte or gel electrolyte include a polymer electrolyte such as a sulfonated styrene-olefin copolymer, a polymer electrolyte using polyethylene oxide and MgClO ₄ , and a polymer electrolyte having a trimethylene oxide structure. The non-aqueous solvent used for the polymer electrolyte is preferably at least one selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and vinylene carbonate.

  Furthermore, the lithium secondary battery according to the present embodiment is not limited to the positive electrode, the negative electrode, and the nonaqueous electrolyte, and may include other members as necessary. For example, the lithium secondary battery includes a separator that separates the positive electrode and the negative electrode. May be. The separator is essential when the non-aqueous electrolyte is not a polymer electrolyte, and examples thereof include nonwoven fabrics, woven fabrics, microporous films, and combinations thereof. More specifically, the separator is porous. A polypropylene film, a porous polyethylene film, etc. can be used suitably.

  The lithium secondary battery according to the present embodiment can be used in various fields. For example, personal computer, tablet computer, notebook computer, mobile phone, wireless device, electronic notebook, electronic dictionary, PDA (Personal Digital Assistant), electronic meter, electronic key, electronic tag, power storage device, electric tool, toy, Electric and electronic devices such as digital cameras, digital video, AV equipment and vacuum cleaners; electric vehicles, hybrid vehicles, electric bikes, hybrid bikes, electric bicycles, electric assist bicycles, railway engines, aircraft, ships and other transportation systems; sunlight Examples include power generation systems such as power generation systems, wind power generation systems, tidal power generation systems, geothermal power generation systems, heat differential power generation systems, and vibration power generation systems.

Example 1
Example 1 uses the positive electrode active material for a lithium secondary battery according to the first embodiment of the present invention.
(1) Synthesis of Phosphate Compound First, lithium iron phosphate (LiFePO ₄ ) as a starting material was synthesized by the following procedure by a hydrothermal synthesis method.
Dissolve 973.11 g of FeSO ₄ · 7H ₂ O (special grade manufactured by Kanto Chemical Co., Ltd.) and 6.52 g of L-ascorbic acid (C ₆ H ₈ O ₆ , manufactured by Kanto Chemical Co., Ltd.) in 1 liter of deionized water. did. Next, 322.80 g of H ₃ PO ₄ (Kanto Chemical Co., Ltd., special grade 85.0% aqueous solution) and 92.44 g of (NH ₄ ) ₂ HPO ₄ (Kanto Chemical Co., Ltd., special grade) were deionized into 1 liter. Dissolved in water. 440.63 g of LiOH.H ₂ O (special grade manufactured by Kanto Chemical Co., Inc.) was dissolved in 2 liters of deionized water. The two solutions were mixed and shaken well until a uniform solution was obtained. Next, a LiOH aqueous solution was added to this mixed solution and shaken well to obtain a raw slurry for hydrothermal synthesis. While washing the vessel wall, a total of 1 liter of deionized water was added. This was placed in an 8 liter autoclave and the lid was closed.
Next, the temperature of the autoclave was raised to 220 ° C. in 1 hour, and maintained at 220 ° C. for 7 hours, thereby proceeding with the hydrothermal synthesis reaction. After holding for 7 hours, heating was stopped and the mixture was cooled to room temperature.
Thereafter, the lid of the autoclave was opened, the suspension containing the hydrothermal compound was taken out, and after centrifugation and washing, drying was performed with a vacuum dryer controlled at 95 ° C. In this way, lithium iron phosphate LiFePO ₄ was obtained.

(2) Production of positive electrode active material When the composition ratio of the lithium iron phosphate salt obtained as described above was measured by ICP emission spectroscopy, Li: Fe: P = 0.972: 1: 0.964. And was found to be deficient for Li and PO ₄ .
Therefore, in the measured lithium iron phosphate salt, lithium hydroxide monohydrate (LiOH.H ₂ O) at a composition ratio of 0.028 with respect to Fe, and H ₃ PO ₄ as a phosphate source with Fe ₃ Is added at a composition ratio of 0.036 to the mixture, and 4.3 wt% of sucrose as a carbonaceous material precursor is added and kneaded to form a carbon-containing mixture (first carbon-containing mixture). Dried.
Next, the obtained carbon-containing mixture was baked at 700 ° C. for 48 hours to obtain a positive electrode active material composed of lithium iron phosphate and carbon. About the obtained positive electrode active material, the ratio of carbon to the positive electrode active material was 2.5 wt%.

(3) Production of lithium secondary battery A positive electrode active material comprising lithium iron phosphate salt and carbon, acetylene black (DENKA BLACK HS-100, manufactured by Denki Kagaku Kogyo) as a conductive additive, and PVdF (as a binder) # 1300 manufactured by Kureha Chemical Co., Ltd. was weighed at a mass ratio of 7: 2: 1.
N-methyl-2-pyrrolidinone (hereinafter abbreviated as NMP) was added thereto and mixed well to obtain a slurry having a solid content concentration of 25 to 45 wt%.
The slurry thus obtained was applied on an aluminum foil having a length of 10 cm, a width of 20 cm, and a thickness of 20 μm using a test coater and an applicator so as to have a thickness of 0.1 mm.
Next, after drying NMP from the aluminum foil to which the slurry was applied, an electrode was produced by punching out so that a tab margin (tab space) was formed in 2 cm long × 2 cm wide. The area of the electrode is 2 cm × 2 cm = 4 cm ² .
Further, this electrode was pressed at a pressure of 5 MPa and vacuum-dried at a temperature of 50 ° C. for 24 hours to be used as a positive electrode. The mass of the positive electrode was 0.045 g, and the portion of the positive electrode excluding the aluminum foil, that is, the mass of the positive electrode mixture was 0.023 g. Lithium foil of 21 mm x 21 mm x 0.023 mm thickness is used for the negative electrode as the counter electrode, 3 mm x 3 mm lithium foil is used for the reference electrode, and 30 mm x 50 mm Celgard 2400 (manufactured by Hoechst Celanese) Name) was used as a battery for evaluation.
In a glove box filled with argon and controlled to a dew point of −75 ° C. or lower, an evaluation battery was produced as follows.
The positive electrode obtained as described above and the negative electrode sandwiched between the separators were folded so that the coating film surface of the positive electrode and the negative electrode face each other, and these were laminated with two 30 mm × 30 mm × 1 mm glass plates. I caught it.
This was put in a 150 ml sealed glass container, and the leads of the positive electrode and the negative electrode were fixed with clips connected to the outside of the sealed glass container. Place the electrolyte (EC + EMC solution (EC: EMC = (2: 3) V / V) in which 1M LiPF ₆ is dissolved) in a sealed glass container so that the portion sandwiched between the glass plates is completely immersed, and cover A battery for evaluation was obtained.
A parafilm was wound around the closed portion of the evaluation battery thus obtained to improve the airtightness.

(4) Battery evaluation The performance of the lithium secondary battery manufactured as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test First, only the potential of the positive electrode based on the reference electrode was monitored without charging / discharging for 2 hours in order to soak the electrolyte into the electrode.
Next, a current value of 0.2 C was calculated when it was assumed that the positive electrode active material used in each cell had a capacity of 150 mAh / g, and constant current charging / discharging was performed for 3 cycles at this current value. The charge / discharge current value at this time is referred to as a current value corresponding to “0.2 C”. A 10 minute rest period was interposed between each charge and discharge. Three cells were prepared for each example and comparative example, and the average of the discharge capacity at the second cycle was defined as the “initial capacity” of the active material.
The initial capacity of Example 1 was 165 mAh / g.
(Ii) Discharge rate characteristic test Assuming that the positive electrode active material has a capacity of 150 mAh / g, charging is performed at 0.2 C equivalent, and discharging is performed at 0.5 C equivalent, 1.0 C equivalent, 2.0 C equivalent. Performed at 0C equivalent. 100 × (capacity when discharged at a current value equivalent to 3.0 C) / (initial capacity) = discharge rate characteristics (%).
The discharge rate of Example 1 was 90%.
(Iii) Cyclic Voltammetry (CV) Test The CV result is considered to reflect the reaction activity of the surface of the LiFePO ₄ crystal, which is an active material in which lithium ion insertion / extraction reaction actually occurs. That is, in the CV test, the closer the crystal structure of the active material LiFePO ₄ and near the surface is to a perfect crystal structure, the faster lithium ions are inserted and desorbed in LiFePO ₄ , resulting in a larger current value and output. The value is considered to be obtained. Therefore, a CV test was conducted to evaluate the completeness of the crystal structure of the LiFePO ₄ crystal as the positive electrode active material.
Specifically, the current value is measured by changing the scanning speed from the charging side at a scanning speed of 0.1 mV / s and the scanning range from 2.5 V to 4.2 V with respect to the lithium electrode, and the output value (closed curve is surrounded by a CV graph). Area).
The output value of CV in Example 1 was 107 mW / g.
(Iv) Potential difference between peaks in CV In CV, the potential difference between peaks is a value reflecting a voltage drop due to a resistance component during charging and discharging. If the structures of the evaluation batteries are all the same, it can be considered that the peak-to-peak potential difference reflects the characteristics of the positive electrode active material used in the evaluation battery. Therefore, this potential difference was also measured and compared. In this case, it is estimated that the smaller the potential difference between the peaks, the higher the completeness of the crystal structure of the positive electrode active material.
The peak-to-peak potential difference of Example 1 was 0.18V.

(Example 2)
Example 2 uses the positive electrode active material for a lithium secondary battery according to the second embodiment of the present invention.
(1) Synthesis of phosphoric acid compound and (3) production of lithium secondary battery were carried out in the same manner as in Example 1.
(2) The production of the positive electrode active material is as follows.
In the lithium iron phosphate salt whose composition ratio was measured, lithium hydroxide monohydrate (LiOH.H ₂ O) as a lithium source at a composition ratio of 0.028 to Fe and H ₃ as a phosphate source PO ₄ was added at a composition ratio of 0.036 to Fe and kneaded to form a mixture (first mixture), which was dried.
The resulting mixture was then fired at 700 ° C. for 48 hours.
Next, 4.3% by weight of sucrose as a carbonaceous material precursor is added and kneaded to produce a carbon-containing mixture (second carbon-containing mixture), which is then dried. It was.
Next, the obtained carbon-containing mixture was baked at 700 ° C. for 48 hours to obtain a positive electrode active material composed of lithium iron phosphate and carbon.
About the obtained positive electrode active material, the ratio of carbon to the positive electrode active material was 2.5 wt%.
(4) Battery evaluation The performance of the lithium secondary battery manufactured as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 165 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 89%.
(Iii) Cyclic Voltammetry (CV) Test Similarly to Example 1, the output value (area surrounded by the closed curve) was determined from the CV graph. The output value of CV was 105 mW / g.
Next, the output value is divided by the surface area (BET specific surface area) of the calcined product (lithium iron phosphate (LiFePO ₄ )) obtained after the “step of calcining the first mixture”, and normalized CV Output value (mW / m ² ) was obtained.
The output value obtained from the CV graph includes the influence of the size of the surface area in addition to the completeness of the crystal structure. For this reason, the output value (mW / m ² ) of CV normalized by dividing by the surface area (BET specific surface area) increases the accuracy of evaluation of the integrity of the crystal structure.
The output value of the standardized CV was 7.00 mW / m ² .
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.17V.

Example 3
Example 3 uses the positive electrode active material for a lithium secondary battery according to the third embodiment of the present invention.
(1) Synthesis of phosphoric acid compound and (3) production of lithium secondary battery were carried out in the same manner as in Example 1.
(2) The production of the positive electrode active material is as follows.
A sucrose as a carbonaceous material precursor was added to the lithium iron phosphate salt whose composition ratio was measured at 4.3 wt% of the total, and kneaded to form a mixture (third carbon-containing mixture), which was dried. .
The resulting mixture was then fired at 700 ° C. for 48 hours.
Next, to the obtained fired product, lithium hydroxide monohydrate (LiOH.H ₂ O) was added in a composition ratio of 0.028 to Fe, and H ₃ PO ₄ as a phosphoric acid source was converted into Fe. On the other hand, it was added at a composition ratio of 0.036 and kneaded to produce a carbon-containing mixture (fourth carbon-containing mixture), which was dried.
Next, the obtained carbon-containing mixture was baked at 700 ° C. for 48 hours to obtain a positive electrode active material composed of lithium iron phosphate and carbon.
(4) Battery evaluation The performance of the lithium secondary battery manufactured as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 165 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 88%.
(Iii) Cyclic voltammetry (CV) test The output value of CV was 103 mW / g.
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.20V.

Example 4
Example 4 uses the positive electrode active material for a lithium secondary battery according to the first embodiment of the present invention.
(1) Synthesis of phosphoric acid compound and (3) production of lithium secondary battery were carried out in the same manner as in Example 1. In addition, (2) in the production of the positive electrode active material, instead of adding 4.3 wt% of sucrose in Example 1, 2.5 wt% of acetylene black was added. The same was done.
(4) Battery evaluation The performance of the lithium secondary battery manufactured as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 163 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 88%.
(Iii) Cyclic voltammetry (CV) test The output value of CV was 108 mW / g.
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.21V.

(Comparative Example 1)
Comparative Example 1 was produced under exactly the same conditions as in Example 1 except that the lithium source and the phosphoric acid source, which were specified to lack elements, were not added.
(Battery evaluation)
The performance of the lithium secondary battery produced as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 140 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 80%.
(Iii) Cyclic voltammetry (CV) test The output value of CV was 90 mW / g.
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.30V.

(Comparative Example 2)
Comparative Example 2 was produced under exactly the same conditions as Example 2 except that the lithium source and the phosphoric acid source identified as insufficient for the element were not added.
(Battery evaluation)
The performance of the lithium secondary battery produced as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 138 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 75%.
(Iii) Cyclic voltammetry (CV) test The output value of CV was 91 mW / g.
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.31V.

(Comparative Example 3)
Comparative Example 3 was produced under exactly the same conditions as Example 3 except that the lithium source and the phosphoric acid source identified as insufficient for the element were not added.
(Battery evaluation)
The performance of the lithium secondary battery produced as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 141 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 78%.
(Iii) Cyclic voltammetry (CV) test The output value of CV was 89 mW / g.
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.32V.

(Comparative Example 4)
Comparative Example 4 was produced under exactly the same conditions as in Example 4 except that the lithium source and the phosphoric acid source identified as insufficient for the element were not added.
(Battery evaluation)
The performance of the lithium secondary battery produced as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 135 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 80%.
(Iii) Cyclic voltammetry (CV) test The output value of CV was 89 mW / g.
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.29V.

(Comparative Example 5)
Comparative Example 5 was produced under exactly the same conditions as Example 1 except that sucrose was not added as a carbonaceous material precursor.
(Battery evaluation)
The performance of the lithium secondary battery produced as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 136 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 79%.
(Iii) Cyclic voltammetry (CV) test The output value of CV was 90 mW / g.
The output value of normalized CV (mW / m) obtained by dividing this output value by the surface area (BET specific surface area) of the finally obtained calcined product (lithium iron phosphate (LiFePO ₄ )) ² ) was 6.00 mW / m ² .
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.34V.

(Comparative Example 6)
Comparative Example 6 was produced under exactly the same conditions as Example 2 except that sucrose was not added as a carbonaceous material precursor.
(Battery evaluation)
The performance of the lithium secondary battery produced as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 144 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 76%.
(Iii) Cyclic voltammetry (CV) test The output value of CV was 87 mW / g.
The output value of normalized CV (mW / m) obtained by dividing this output value by the surface area (BET specific surface area) of the finally obtained calcined product (lithium iron phosphate (LiFePO ₄ )) ² ) was 6.21 mW / m ² .
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.30V.

(Comparative Example 7)
Comparative Example 7 was produced under exactly the same conditions as Example 3 except that sucrose was not added as a carbonaceous material precursor.
(Battery evaluation)
The performance of the lithium secondary battery produced as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 142 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 77%.
(Iii) Cyclic voltammetry (CV) test The output value of CV was 88 mW / g.
The output value of normalized CV (mW / m) obtained by dividing this output value by the surface area (BET specific surface area) of the finally obtained calcined product (lithium iron phosphate (LiFePO ₄ )) ² ) was 5.50 mW / m ² .
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.28V.

(Comparative Example 8)
Comparative Example 8 was produced under exactly the same conditions as Example 4 except that sucrose was not added as a carbonaceous material precursor.
(Battery evaluation)
The performance of the lithium secondary battery produced as described above was evaluated. The evaluation results are shown in Table 1.
(I) Initial capacity test The initial capacity was 139 mAh / g.
(Ii) Discharge rate characteristic test The discharge rate was 76%.
(Iii) Cyclic voltammetry (CV) test The output value of CV was 88 mW / g.
The output value of normalized CV (mW / m) obtained by dividing this output value by the surface area (BET specific surface area) of the finally obtained calcined product (lithium iron phosphate (LiFePO ₄ )) ² ) was 5.50 mW / m ² .
(Iv) Potential difference between peaks at CV The potential difference between peaks was 0.33V.

From the above results, the initial capacity, discharge rate, CV output value, standardized CV output value, and peak-to-peak potential difference of Examples 1 to 4 are superior to those of Comparative Examples 1 to 8. It was confirmed. This is because, before final firing, lithium metal phosphate is replenished with a sufficient amount of elements or raw materials less than the composition ratio Li: M: P = 1: 1: 1, and then fired. As a result of improving the conductivity of the positive electrode active material by making the crystal structure of the acid salt more complete, and further by combining carbon with lithium metal phosphate, the capacity increased, high discharge rate, high output In addition, it is considered that low resistance has been realized.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the positive electrode active material for lithium secondary batteries which consists of a composite of an olivine type lithium metal phosphate and carbon by which a favorable discharge rate characteristic is implement | achieved can be provided. In addition, the present invention provides a positive electrode comprising a composite of an olivine type lithium metal phosphate and carbon obtained by a method for producing a positive electrode active material for a lithium secondary battery that realizes a high capacity and good discharge rate characteristics. A lithium secondary battery including the active material and the positive electrode active material can be provided. Therefore, this invention can be used suitably in the manufacturing method of the positive electrode active material for lithium secondary batteries, the positive electrode active material for lithium secondary batteries, and a lithium secondary battery.

Claims (5)

Phosphoric acid represented by a composition formula LiMPO ₄ (element M is Fe, Mn, or one, or two or more transition metals of Ti, V, Cr, Co, Ni, Nb, Ta, Mo, W) Measuring the composition ratio of the compound and identifying an element having the composition ratio less than Li: M: P = 1: 1: 1;
A lithium source, a metal (M) source, or a phosphoric acid source as an element source corresponding to the specified element, the phosphoric acid compound, and a carbonaceous material or a carbonaceous material precursor are kneaded to contain a first carbon. Obtaining a mixture;
Firing the first carbon-containing mixture;
The manufacturing method of the positive electrode active material for lithium secondary batteries characterized by having. Phosphoric acid represented by a composition formula LiMPO ₄ (element M is Fe, Mn, or one, or two or more transition metals of Ti, V, Cr, Co, Ni, Nb, Ta, Mo, W) Measuring the composition ratio of the compound and identifying an element having the composition ratio less than Li: M: P = 1: 1: 1;
A step of kneading a lithium source, a metal (M) source, or a phosphoric acid source as an element source corresponding to the identified element and the phosphoric acid compound to obtain a first mixture;
Firing the first mixture;
A step of kneading the fired product obtained in the above step and a carbonaceous material or a carbonaceous material precursor to obtain a second carbon-containing mixture;
Firing the second carbon-containing mixture;
The manufacturing method of the positive electrode active material for lithium secondary batteries characterized by having. Phosphoric acid represented by a composition formula LiMPO ₄ (element M is Fe, Mn, or one, or two or more transition metals of Ti, V, Cr, Co, Ni, Nb, Ta, Mo, W) Measuring the composition ratio of the compound and identifying an element having the composition ratio less than Li: M: P = 1: 1: 1;
Kneading the phosphoric acid compound and a carbonaceous material or a carbonaceous material precursor to obtain a third carbon-containing mixture;
Firing the third carbon-containing mixture;
A step of kneading the fired product obtained in the step and a lithium source, a metal (M) source, or a phosphoric acid source as an element source corresponding to the identified element to obtain a fourth carbon-containing mixture;
Firing the fourth carbon-containing mixture;
The manufacturing method of the positive electrode active material for lithium secondary batteries characterized by having.   The at least one selected from the group consisting of saccharides, hydrocarbons, fatty acids, ethers, esters, alcohols, thiols, fats and oils, pitches, and polymers is used as the carbonaceous material precursor. 4. The method for producing a positive electrode active material for a lithium secondary battery according to any one of 3 above.   4. The carbonaceous material according to claim 1, wherein at least one selected from the group consisting of graphite, carbon nanotubes, amorphous carbon, glassy carbon, and graphene is used. A method for producing a positive electrode active material for a lithium secondary battery.