JP2006286208A - Lithium-ion secondary battery and cathode active material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium-ion secondary battery having an excellent safety property as well as an excellent output characteristics, and a cathode active material necessary for making the above battery. <P>SOLUTION: The cathode active material consists of a phosphoric acid compound having a general formula LiMn<SB>1-x</SB>M<SB>x</SB>PO<SB>4</SB>of which the space group is rhombic with a symmetry of Pmnb with a lattice constant of the a-axis, b-axis, and c-axis being 1.060≤a≤1.120 nm, 0.620≤b≤0.66 nm, and 0.486≤c≤0.515 nm respectively. In the general formula, M stands for a bivalent cation other than Mn, and 0.01≤X≤0.4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery and a positive electrode active material used therefor.

  A lithium ion secondary battery has a positive electrode active material at its positive electrode, and a negative electrode has a negative electrode active material mainly composed of carbon such as graphite or amorphous carbon that occludes lithium. And it has the non-aqueous electrolyte which has the lithium ion which couple | bonds a positive electrode and a negative electrode electrochemically.

As a positive electrode active material of a lithium ion secondary battery, a layered oxide typified by LiNiO ₂ , LiCoO ₂ and LiMnO ₂ and a spinel positive electrode material typified by LiMn ₂ O ₄ are well known. The theoretical capacity of the layered oxide is about 270 mAh / g, and although the practical capacity is as high as 140 mAh / g to 200 mAh / g, the charged product is inferior in thermal stability, and there is a problem in safety especially during overcharging. It is well known. On the other hand, the spinel positive electrode material has excellent thermal stability of the charged product and high safety, but its practical capacity is 100
The current situation is as small as about mAh / g.

Recently, a phosphate compound represented by a general formula LiMPO ₄ (M is Mn, Fe, etc.), which is generically referred to as an olivine compound, has been attracting attention as a positive electrode active material of a lithium ion secondary battery. For example, Patent Document 1 discloses LiMnPO ₄ as one of phosphoric acid compounds.

The above phosphoric acid compound has a capacity of about 170 mAh / g, and a practical capacity exceeding 100 mAh / g is being synthesized. And it is becoming clear that the above-mentioned phosphoric acid compound is excellent in the thermal stability of a charge product, and the high safety | security of a battery can also be anticipated. As for the phosphoric acid compound as the positive electrode active material, studies on LiFePO ₄ and LiMnPO ₄ are currently in progress. The former discharge voltage is about 3.5V, while the latter discharge voltage is around 3.8V. Yes, LiMnPO ₄ is excellent in terms of energy density.

However, the conventional lithium ion secondary battery using LiMnPO ₄ has a problem that its battery resistance is high and output characteristics are inferior. This is considered to be caused by the high resistance of LiMnPO ₄ which is a positive electrode active material. Therefore, it has been difficult to realize a lithium ion secondary battery having excellent safety and capacity and output characteristics by the conventional technology.

JP-A-11-259593

  An object of the present invention is to realize a lithium ion secondary battery having excellent safety and output characteristics, and a positive electrode active material necessary for realizing the lithium ion secondary battery.

The lithium ion secondary battery of the present invention is a lithium ion secondary battery having a positive electrode having a positive electrode active material, a negative electrode, and an electrolyte solution, wherein the positive electrode active material has the general formula LiMn _1-x M _x PO _4.
(M: a divalent cation other than Mn, 0.01 ≦ X ≦ 0.4) having an orthorhombic phosphate compound having the symmetry of the space group Pmnb, and the a-axis of the phosphate compound , B-axis and c-axis lattice constants are 1.060 nm ≦ a ≦ 1.120 nm, 0.620 nm ≦ b ≦ 0.66 nm, 0.486 nm ≦ c ≦ 0.515 nm, respectively.

The positive electrode active material for a lithium ion secondary battery of the present invention is of the general formula LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn, 0.01 ≦ X ≦ 0.4). It has an orthorhombic phosphate compound having symmetry of the space group Pmnb, and the lattice constants of the a-axis, b-axis and c-axis of the phosphate compound are 1.060 nm ≦ a ≦ 1.120 nm and 0.1, respectively. The main features are 620 nm ≦ b ≦ 0.66 nm and 0.486 nm ≦ c ≦ 0.515 nm.

A lithium ion secondary battery according to another embodiment of the present invention is a lithium ion secondary battery having a positive electrode having a positive electrode active material, a negative electrode, and an electrolyte solution, wherein the positive electrode active material has the general formula LiMn _{1− x M x PO 4 (M:} 2 -valent cations other than Mn, 0 ≦ X ≦ 0.4) having a phosphoric acid compound orthorhombic with symmetry space group Pmnb is, and the phosphoric acid compound The lattice constants of the a-axis, b-axis and c-axis are 1.060 nm ≦ a ≦ 1.120 nm, 0.620 nm ≦ b ≦ 0.66 nm and 0.486 nm ≦ c ≦ 0.515 nm, respectively. The main feature is that it has 1 to 10% by weight of carbon black or acetylene black and 5 to 20% by weight of carbon material particles having an average grain size of 1 to 20 μm.

  According to the present invention, it is possible to provide a lithium ion secondary battery that is excellent in safety, excellent in capacity and output characteristics, and a positive electrode active material necessary for the realization thereof.

The lithium ion secondary battery of the present invention has a general formula LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn, 0.01 ≦ X ≦ 0.4) as the positive electrode active material, The space group is an orthorhombic crystal having Pmnb symmetry, and the lattice constants of its a-axis, b-axis, and c-axis are 1.060 nm ≦ a ≦ 1.120 nm, 0.620 nm ≦ b ≦ 0.66 nm, and 0, respectively. .486 nm ≦ c ≦
It has the phosphoric acid compound of the present invention which is 0.515 nm. It is considered that Mn in the phosphoric acid compound represented by LiMn _1-x M _x PO ₄ exists as a divalent cation in the compound. The phosphoric acid compound of the present invention is mainly composed of Mn as a divalent cation, and is composed of a divalent cation other than Mn.

It is considered that the phosphoric acid compound in the positive electrode active material of the present invention is excellent in output characteristics due to excellent diffusion of Li ions in the crystal structure and low resistance by appropriately controlling the lattice constant. That is, the lattice constants of the a-axis, b-axis, and c-axis are 1.060 nm ≦ a ≦ 1.120, respectively.
Desirably, nm, 0.620 nm ≦ b ≦ 0.66 nm, 0.486 nm ≦ c ≦ 0.515 nm. If the lattice constant is smaller than this, the space necessary for the diffusion of Li ions is narrowed, and the lattice constant is If it is larger than the above, it is considered that the diffusion of Li ions is inhibited by the crystal structure being significantly disturbed.

  In addition, although the mechanism of excellent output characteristics due to the presence of a divalent cation different from Mn in the phosphate compound of the present invention is not necessarily clear, a divalent cation having an ionic radius different from Mn in the crystal structure is not suitable. It is considered that the presence at a ratio is effective in promoting the diffusion movement of Li ions in the crystal structure.

In the present invention, the abundance ratio x of divalent cations M different from Mn in the phosphoric acid compound having the general formula LiMn _1-x M _x PO ₄ is in the range of 0.01 ≦ X ≦ 0.4. If X is less than 0.01, the effect of the above-mentioned divalent cation on the low resistance is insufficient, and if X exceeds 0.4, it becomes difficult to synthesize a single-phase phosphate compound. It is not desirable.

  As the divalent cation other than Mn in the phosphoric acid compound of the present invention, a transition metal element that can be a divalent cation is preferable, and the synthesis is particularly easy by using at least one selected from Co, Fe, Ni, and Cu. It is more preferable because a positive electrode active material having a lower resistance can be obtained.

  The composition of the phosphoric acid compound in the present invention can be determined by quantifying the ratio of each element in an atomic absorption spectrum or the like in a solution in which the phosphoric acid compound is dissolved in, for example, sulfuric acid.

  In order to determine the lattice constant of the phosphoric acid compound in the present invention, a reflection diffraction type powder X-ray diffraction method is used. Using Cu as a target, a positive electrode active material is irradiated with CuKα rays at a tube voltage of 50 kV and a tube current of 150 mA, and diffraction lines are measured with a goniometer to obtain a powder X-ray diffraction spectrum. A lattice constant is obtained by using a value indexed by an orthorhombic crystal having a diffraction angle of the obtained diffraction line and a symmetry of Pmnb.

  Although the method for realizing the phosphoric acid compound which is the positive electrode active material of the present invention is not particularly limited, it is preferably fired at 500 to 900 ° C. in order to appropriately control the lattice constant of the phosphoric acid compound. For this purpose, compared to the so-called solid phase method in which powder raw materials are mixed and fired, the liquid phase method in which the precursor is obtained from the raw material as a solution is mixed more uniformly with the raw material elements at a lower temperature. This is preferable because it can be synthesized. At the same time, the liquid phase method is preferable because a plurality of elements other than Li, Mn and P can be homogeneously mixed. As a liquid phase method, for example, a so-called sol-gel method in which an alkali component is added to an acidic solution in which raw materials are dissolved to precipitate a constituent element of an active material to obtain a precursor, and this precursor is fired, or a solution is heated to a high-temperature gas phase There is a so-called spray drying method in which a precursor is obtained by spray-drying and the precursor is fired. In particular, in the spray drying method, the constituent ratio of each element in the solution in which the raw material is dissolved can be easily set as the element constituent ratio of the precursor as it is. The raw material for each element used in the liquid phase method is not particularly limited. For Li and divalent cations, inorganic acid salts such as nitrates and phosphates and organic acid salts such as acetates can be used. , P can be an ammonium salt or the like.

As a form of the synthesized positive electrode active material, the average particle diameter can be preferably 0.1 to 30 μm, and the specific surface area is preferably ² to 50 m ² / g. These forms can be realized by controlling the formation method and conditions of the precursor and the firing conditions.

The positive electrode active material of the present invention has the general formula LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn, 0.01 ≦ X ≦ 0.4), and its space group is Pmnb symmetry. The lattice constants of the a-axis, b-axis, and c-axis are 1.060 nm ≦ a ≦ 1.120 nm, respectively.
The phosphoric acid compound of the present invention satisfying 0.620 nm ≦ b ≦ 0.66 nm and 0.486 nm ≦ c ≦ 0.515 nm may be used alone, or may be another material such as a carbon material. A composite material with a material may be used. For example, in a composite material in which a carbon coating is formed on a phosphoric acid compound using a gas phase reaction, the electron conductivity as a positive electrode active material is improved, and a lithium ion secondary battery with a lower resistance positive electrode active material and excellent output Can be expected.

A lithium ion secondary battery according to another embodiment of the present invention is a lithium ion secondary battery having a positive electrode having a positive electrode active material, a negative electrode, and an electrolyte solution, wherein the positive electrode active material has the general formula LiMn _{1− x M x PO 4 (M:} 2 -valent cations other than Mn, 0 ≦ X ≦ 0.4) having a phosphoric acid compound orthorhombic with symmetry space group Pmnb is, and the phosphoric acid compound The lattice constants of the a-axis, b-axis and c-axis are 1.060 nm ≦ a ≦ 1.120 nm, 0.620 nm ≦ b ≦ 0.66 nm and 0.486 nm ≦ c ≦ 0.515 nm, respectively, and 1 to 20% by weight of carbon black or acetylene black and an average grain system of 1 to 20
It is a lithium ion secondary battery having 5 to 20% by weight of carbon material particles of μm.

  Here, carbon black or acetylene black is an extremely small carbonaceous particle having an average particle diameter of about 5 to 100 nm, and these carbon material particles adhere to the surface of the positive electrode active material, and the electron conduction of the positive electrode active material particles. Has the effect of improving the battery output. In the present invention, carbon black or acetylene black is not necessarily limited as long as the average particle diameter of the carbon material particles is in the range of 5 to 100 nm.

  The carbon material particles having an average particle size of 1 to 20 μm are graphite particles and amorphous carbon particles having a particle size comparable to that of the positive electrode active material, and these are between the positive electrode active materials and between the positive electrode active material and the current collector. It improves the electron conductivity with the body and improves battery output. The form of the carbon material particles is not particularly limited, and for example, flakes and lumps can be used.

An orthorhombic phosphate compound having the symmetry of the space group Pmnb having the general formula LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn, 0 ≦ X ≦ 0.4) in the present invention And the lattice constant of the a-axis, b-axis and c-axis of the phosphoric acid compound is 1.060 nm ≦ a ≦ 1.120, respectively.
In the lithium ion secondary battery using the positive electrode active material satisfying nm, 0.620 nm ≦ b ≦ 0.66 nm, 0.486 nm ≦ c ≦ 0.515 nm, the above-described carbon black or acetylene black and an average grain system 1 Furthermore, by blending the carbon material particles of 20 μm with the positive electrode at an appropriate ratio, more excellent output characteristics are expressed. That is, the lithium ion secondary battery using a phosphoric acid compound having no divalent cation other than Mn in the above general formula composition has excellent output characteristics. Here, the effect of carbon black or acetylene black on the battery output is different from that of carbon material particles having an average grain size of 1 to 20 μm, so that sufficient output characteristics can be obtained even if only one of them is contained in the positive electrode. I can't.

  In addition, when the content of carbon black or acetylene black is less than 1% by weight, a sufficient effect for improving the conductivity of the positive electrode active material cannot be obtained. On the other hand, the output characteristics deteriorate even when the amount exceeds 10% by weight. This is because the above-described carbon black or acetylene black covers the surface of the positive electrode active material and inhibits the reaction between lithium ions and the positive electrode active material. Guessed.

  Furthermore, if the content of carbon material particles having an average grain size of 1 to 20 μm is less than 5% by weight, a sufficient effect for improving the conductivity between the positive electrode active materials cannot be obtained. On the other hand, even when the content exceeds 20% by weight, the output characteristics are deteriorated. This is presumably because the weight ratio of the positive electrode active material is decreased.

  Next, an example of specific means for realizing the lithium ion secondary battery of the present invention will be described.

  First, a positive electrode is produced as follows. The positive electrode active material powder of the present invention and a conductive agent are mixed well. As the conductive agent, carbon black or acetylene black is desirably 1 to 10% by weight with respect to the amount of the positive electrode mixture, and further, carbon material particles having an average particle size of 1 to 20 μm are desirably 5 to 20% by weight with respect to the positive electrode mixture. . To this, a solution prepared by dissolving polyvinylidene fluoride (PVDF) or the like as a binder in a solvent such as N-methylpyrrolidone (NMP) is added and further mixed to form a slurry. This slurry is applied to an aluminum foil having a thickness of 10 to 20 μm and dried at a temperature of 80 to 100 ° C. Apply and dry both sides of the aluminum foil in the same procedure. Thereafter, it is compression-molded by a roll press machine or the like and cut into a predetermined size to produce a positive electrode.

Next, a negative electrode is produced. As the negative electrode active material used for the negative electrode, for example, metallic lithium, a carbon material, a material capable of inserting lithium or forming a compound can be used, and carbon materials such as graphite and amorphous carbon are particularly used. Is preferred. In the lithium secondary battery of the present invention, the peak intensity in the peak intensity in the range of 1300～1400Cm ^-1 as measured by Raman spectroscopy on the negative electrode and (I _D) in the range of 1580~1620cm ^-1 (I _G By using a carbon material having a carbon material having an R ratio (I _D / I _G ) that is an intensity ratio of 0.4 or more and 1.5 or less, a higher-power lithium ion secondary battery can be obtained. Peak in the range of 1580～1620Cm ^-1 as measured by Raman spectroscopy spectra is intended to indicate a regular stacking of the hexagonal plane of graphite, the peak in the range of 1300～1400Cm ^-1 lamination of hexagonal network It is supposed to show the disturbance. The insertion / desorption reaction of the negative electrode active material of Li ion proceeds on the end face of the laminated hexagonal mesh surface. Therefore, when the R value is less than 0.4, the ratio of the regularly stacked carbon hexagonal mesh faces is high, and therefore the ratio of the end faces is small, so that the output is reduced. On the other hand, if the R value exceeds 1.5, the stacking disorder is too great, which may hinder Li ion insertion / desorption reaction, and the output may decrease.

  The negative electrode is produced as follows. A carbon material having an R value of 0.4 or more and 1.5 or less is desirably used as the negative electrode active material. A solution prepared by dissolving PVDF or the like as a binder in a solvent such as NMP was added to the negative electrode active material and mixed to obtain a slurry. The slurry is applied to a copper foil and dried at a temperature of 80 to 100 ° C. Apply and dry on both sides of the copper foil using the same procedure. Thereafter, it is compression molded by a roll press and cut into a predetermined size to produce a negative electrode.

When producing a cylindrical battery, it is as follows. As a mechanism for electrically insulating the positive electrode and the negative electrode obtained from each other, a separator made of a porous insulating film having a thickness of 15 to 50 μm is sandwiched between the positive electrode and the negative electrode, and this is wound into a cylindrical shape. An electrode group is prepared and inserted into a battery container made of SUS or aluminum. What can be used as the separator may be a resin porous insulating film such as polyethylene (PE) or polypropylene (PP), a laminate thereof, or an inorganic compound such as alumina dispersed therein.

A nonaqueous electrolyte solution in which a lithium salt that electrochemically bonds the positive electrode and the negative electrode is dissolved in a nonaqueous solvent is poured into the battery container in a working container in dry air or an inert gas atmosphere, and the container is sealed. Battery. Lithium salt supplies lithium ions that move in the electrolyte by charging and discharging the battery, and LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF _6, etc. may be used alone or in combination of two or more. it can. Examples of the organic solvent include carbonates, esters, ethers and the like. For example, ethylene carbonate (EC), propylene carbonate, butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate, diethyl carbonate, Examples thereof include γ-butyrolactone. A nonaqueous solvent in which these are used alone or in combination is used.

  Various additives may be added as necessary for the purpose of suppressing side reactions of the battery and increasing stability at high temperatures. Examples of the additive used include sulfur compounds and phosphorus compounds that dissolve in the above-mentioned solvents and those that also serve as solvents.

  Further, in order to obtain a square battery, it is as follows. The application of the positive electrode and the negative electrode is the same as that for producing the cylindrical battery. In order to produce a prismatic battery, a wound group is produced around a square center pin. As in the case of the cylindrical battery, the battery can is sealed after storing it in a battery container and injecting an electrolyte. Further, instead of the wound group, a laminate in which a separator, a positive electrode, a separator, a negative electrode, and a separator are laminated in this order can also be used.

  The use of the lithium ion secondary battery of the present invention is not particularly limited, but as a power source for various portable devices, information devices, household electrical devices, etc., or a generator or fuel driven by an electric vehicle, an internal combustion engine, or the like As a power source for hybrid vehicles equipped with power generation engines such as batteries, motor vehicles equipped with generators driven by internal combustion engines, etc., and power equipment such as elevators, power storage systems for various business and household use Can be used as a power source.

  Hereinafter, more detailed examples of the lithium ion secondary battery of the present invention and the positive electrode active material used therefor will be shown and described in detail. However, the present invention is not limited to the examples described below.

Example 1
The positive electrode active material 1 to the positive electrode active material 6 of the present invention were prepared as follows. As raw materials, lithium acetate, manganese acetate, cobalt acetate, nickel acetate, iron acetate, copper acetate, and ammonium dihydrogen phosphate were selected. These raw materials were weighed so that each element had a predetermined molar ratio and dissolved in distilled water to obtain a raw material solution. This raw material solution was introduced into a spray drying apparatus to obtain a precursor powder. The obtained precursor powder was pyrolyzed in an inert gas atmosphere at 350 ° C. for 1 hour and then calcined in an inert gas at 550 ° C. for 8 hours to obtain a positive electrode active material. The obtained positive electrode active material 1 to positive electrode active material 6 were each pulverized in a mortar, and the powder X-ray diffraction spectrum by CuKα ray was measured, and the obtained diffraction line was orthorhombic with symmetry of diffraction angle and Pmnb. Lattice constants were obtained with the indexed values.

Table 1 shows the compositions and lattice constants of the positive electrode active material 1 to the positive electrode active material 6 of Example 1. The lattice constants of the a-axis, b-axis, and c-axis of each of the positive electrode active material 1 to the positive electrode active material 6 are 1.060 nm ≦ a ≦ 1.120 nm, 0.620 nm ≦ b ≦ 0.66 nm, and 0.486 nm ≦ c ≦, respectively.
It was in the range of 0.515 nm.

(Comparative Example 1)
As Comparative Example 1, LiMnPO ₄ (positive electrode active material H1) was produced in the same manner as in Example 1. Moreover, as positive electrode active material H2, preparation of LiMn _0.5 Fe _0.5 PO ₄ was attempted in the same manner as in Example 1, but the result of powder X-ray diffraction was a mixture of two types of phosphate compounds. Further, as the positive electrode active material H3, a positive electrode active material having the composition formula LiMn _0.9 Fe _0.1 PO ₄ was produced in the same manner as in Example 1 except that the firing temperature was 500 ° C. A positive electrode active material having the composition formula LiMn _0.9 Fe _0.1 PO ₄ was prepared by the same heat treatment as in Example 1 using the same raw material as in Example 1 as a positive electrode active material H4 and a precursor obtained by mixing the raw materials with a ball mill. did. Lattice constants were determined in the same manner as in Example 1 for the positive electrode active material H1, the positive electrode active material H3, and the positive electrode active material H4.

  Table 1 shows the composition and lattice constant of the positive electrode active material H1, the positive electrode active material H3, and the positive electrode active material H4 of Comparative Example 1. The lattice constant of the positive electrode active material H1 is in the range of the positive electrode active material of the present invention, but does not include a divalent cation other than Mn. Moreover, although the composition of positive electrode active material H3 and positive electrode active material H4 contains Fe as a bivalent cation other than Mn, its lattice constant was outside the range of the positive electrode active material of the present invention.

(Example 2)
Coin-type lithium ion secondary batteries (battery 1 to battery 6) of the present invention were produced as follows.

First, a positive electrode was produced. The positive electrode active material 1 to the positive electrode active material 6 prepared in Example 1 were used as the positive electrode active material. 80% by weight of the positive electrode active material, 3% by weight of flaky graphite having an average particle diameter of 10 μm as a conductive agent, 10% by weight of acetylene black, and a solution prepared by previously dissolving 7% by weight of PVDF as a binder in NMP In addition, the mixture was further mixed to prepare a positive electrode mixture slurry. The slurry was applied to a 20 μm thick aluminum foil (positive electrode current collector) substantially uniformly and evenly, and then dried at a temperature of 80 ° C. At this time, the coating amount was adjusted so that the coating amount of the positive electrode was constant regardless of the difference in the positive electrode active material. After that, the punched material having a diameter of 15 mm was compression-molded by a press to produce a positive electrode.

Next, a negative electrode was produced. As the negative electrode active material, graphite (negative electrode active material 1) whose surface was coated with amorphous carbon was used. Peak intensity ratio in the range of peak and 1580～1620Cm ^-1 in the range of 1300～1400Cm ^-1 by Raman spectroscopy of the negative electrode active material 1 R was 0.94. A negative electrode mixture slurry was prepared by adding and mixing a solution of 5 wt% acetylene black as a conductive agent and 4 wt% PVDF in NMP in advance to 91 wt% of the negative electrode active material. This slurry was applied substantially uniformly and evenly to a rolled copper foil (negative electrode current collector) having a thickness of 15 μm in the same procedure as that for the positive electrode, and then dried at a temperature of 80 ° C. Thereafter, a punched-out piece having a diameter of 16 mm was compression-molded by a press machine to produce a negative electrode.

A coin-type lithium ion secondary battery shown in FIG. 1 was produced using the produced positive electrode and negative electrode. The positive electrode 11 and the negative electrode 12 were sandwiched by a microporous polypropylene separator 13 having a thickness of 25 μm, and inserted into a SUS battery can 14 also serving as a negative electrode terminal. After injecting the electrolyte into the battery can, the sealing lid portion 15 to which the positive electrode terminal was attached was caulked and sealed to the battery can 14 via the packing 16 to obtain a coin-type battery. As the non-aqueous electrolyte, a solution obtained by dissolving 1 mol / liter of LiPF ₆ in a mixed solvent of EC, DMC, and DEC in a volume ratio of 1: 1: 1 was used.

(Comparative Example 2)
As Comparative Example 2, a coin-type lithium ion secondary battery was fabricated in the same manner as in Example 2 except that the positive electrode active material H1, the positive electrode active material H3, and the positive electrode active material H4 of Comparative Example 1 were used.

(Measurement of battery output)
The outputs of the produced lithium ion secondary batteries of Example 2 and Comparative Example 2 were measured as follows.

  About the produced lithium ion secondary battery, charge and discharge were repeated 3 times at 20 degreeC, and the discharge capacity of the 3rd time was defined as the rated capacity of a battery. The charging conditions were constant current and constant voltage charging with an upper limit voltage of 3.9 V at a current equivalent to 0.33 C for 5 hours, and then a constant current discharge with a current equivalent to 0.33 C and a lower limit voltage of 2.5 V.

Next, the output of the battery was measured. Output measurement was started after charging with constant current and constant voltage for 4 hours at an upper limit voltage of 3.9 V at a current corresponding to 0.33 C. When the rated capacity is 1 C, the discharge current is discharged at 1 C for 10 seconds, the open circuit voltage (V ₀ ) before the discharge and the voltage (V ₁₀ ) at the _10th discharge are measured, and the difference (V ₀ − The voltage drop (ΔV) which is V ₁₀ ) was determined. Thereafter, charging corresponding to the discharged amount of electricity was performed, and the discharge current was sequentially changed to 5C and 10C to similarly obtain the voltage drop (ΔV). Extrapolate the voltage drop (ΔV) to the discharge current value, find the maximum current value (I _MAX ) when it is assumed that the discharge end voltage of 2.5 V is reached in 10 seconds, and multiply I _MAX by 2.5 V The output of the lithium ion secondary battery was used.

  Table 2 shows the results of the positive electrode active material and the battery output used for each battery (Battery 1 to Battery 6) of Example 2 and each battery (Battery H1, Battery H3, and Battery H4) of Comparative Example 2. The lithium ion secondary battery of Example 2 using the positive electrode active material of Example 1 has a higher battery output than the lithium secondary battery of Comparative Example 2 using the positive electrode active material of Comparative Example 1. It was.

(Example 3)
Coin-type lithium ion secondary batteries (battery A2 to battery A5) of the present invention were produced. The positive electrode active material 3 in Example 1 was used as the positive electrode active material. As the negative electrode active material, amorphous carbon-coated graphite (negative electrode active material 2 to negative electrode active material 5) having different R values in Raman spectroscopy was selected. Other than that was carried out similarly to Example 1, and produced the coin-type lithium ion secondary battery for every negative electrode active material.

Table 3 shows the results of the negative electrode active material and the battery output used for each battery (battery A2 to battery A5) of Example 3 and battery 3 of Example 2. The lithium ion secondary battery of Example 3 uses the positive electrode active material 3 in Example 1, and has a higher battery output than the lithium secondary battery of Comparative Example 2 using the positive electrode active material of Comparative Example 1. was gotten. In addition, the battery 3, the battery A3, and the battery A4 using the negative electrode active material whose R value (I _D / I _G ) measured by the Raman spectrum is 0.4 or more and 1.5 or less are the battery A2 and the battery There was an effect that a higher battery output was obtained compared to A5.

Example 4
Coin-type lithium ion secondary batteries (batteries D1 to D3) of the present invention were produced. In the production of the positive electrode, the positive electrode active material H1 in Comparative Example 1 was used, the scale-like graphite having an average particle diameter of 10 μm as the conductive agent was in the range of 5 to 20% by weight, and the acetylene black was in the range of 1 to 10% by weight. Used in. Further, amorphous carbon was used as the negative electrode active material. The intensity ratio R of the peak in the range of peak and 1580～1620Cm ^-1 in the range of 1300～1400Cm ^-1 by Raman spectroscopy of the amorphous carbon was 1.05. A lithium ion secondary battery was produced in the same manner as in Example 2 except for the above.

(Comparative Example 3)
As Comparative Example 3, the battery H5 using 3% by weight of flaky graphite having an average particle diameter of 10 μm and 15% by weight of acetylene black on the positive electrode, 25% by weight of flaky graphite having an average particle diameter of 10 μm, and 0.1% of acetylene black. A coin-type lithium ion secondary battery was produced in the same manner as in Example 3 except that 5% by weight of the battery H6 was used.

  Table 4 shows the results of the weight% of graphite used, the weight% of acetylene black, and the battery output for each battery (battery D1 to battery D3) of Example 4 and battery H5 and battery H6 of Comparative Example 3. The lithium ion secondary battery of Example 4 uses flaky graphite having an average particle diameter of 10 μm in the range of 5 to 20% by weight and acetylene black in the range of 1 to 10% by weight. Compared to the ion secondary battery, there was an effect that a high battery output was obtained.

The schematic diagram which shows an example of the coin-type lithium ion secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Positive electrode, 12 ... Negative electrode, 13 ... Separator, 14 ... Battery can, 15 ... Lid, 16 ... Packing, 17 ... Negative electrode collector, 18 ... Negative electrode mixture, 19 ... Positive electrode mixture, 20 ... Positive electrode collector .

Claims (8)

A lithium ion secondary battery having a positive electrode having a positive electrode active material, a negative electrode, and an electrolyte solution, wherein the positive electrode active material has the general formula LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn) ,
0.01 ≦ X ≦ 0.4) having orthorhombic phosphate compound having symmetry of space group Pmnb, and lattice constants of a-axis, b-axis and c-axis of said phosphate compound are respectively 1. A lithium ion secondary battery characterized in that 1.060 nm ≦ a ≦ 1.120 nm, 0.620 nm ≦ b ≦ 0.66 nm, and 0.486 nm ≦ c ≦ 0.515 nm. The divalent cation M of LiMn _1-x M _x PO ₄ in the phosphate compound according to claim 1 is:
A lithium ion secondary battery comprising at least one of Co, Fe, Ni, and Cu. A negative electrode, R value is the intensity ratio of the peak intensity (I _G) in the range of the peak intensity (I _D) and 1580～1620Cm ^-1 in the range of 1300～1400Cm ^-1 it measured by Raman spectrum (I 3. The lithium ion secondary battery according to claim 1, comprising a carbon material having a ratio of _D / I _G ) of 0.4 or more and 1.5 or less. A lithium ion secondary battery having a positive electrode having a positive electrode active material, a negative electrode, and an electrolyte solution, wherein the positive electrode active material has the general formula LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn) ,
0 ≦ X ≦ 0.4) having an orthorhombic phosphate compound having the symmetry of the space group Pmnb, and the lattice constants of the a-axis, b-axis and c-axis of the phosphate compound are 1. 060 nm ≦ a ≦ 1.120 nm, 0.620 nm ≦ b ≦ 0.66 nm, 0.486 nm ≦ c ≦ 0.515 nm, and the positive electrode has 1 to 10% by weight of carbon black or acetylene black and an average particle size A lithium ion secondary battery comprising 5 to 20% by weight of carbon material particles having a size of 1 to 20 μm. The divalent cation M of LiMn _1-x M _x PO ₄ in the phosphate compound according to claim 4 is:
A lithium ion secondary battery comprising at least one of Co, Fe, Ni, and Cu. A negative electrode, R value is the intensity ratio of the peak intensity (I _G) in the range of the peak intensity (I _D) and 1580～1620Cm ^-1 in the range of 1300～1400Cm ^-1 measured by Raman spectrum (I 3. The lithium ion secondary battery according to claim 1, comprising a carbon material having a ratio of _D / I _G ) of 0.4 or more and 1.5 or less. A positive electrode active material used for a positive electrode of a lithium ion secondary battery, wherein the positive electrode active material is a general formula LiMn _1-x M _x PO ₄ (M: a divalent cation other than Mn, 0.01 ≦ X ≦ 0.0. 4) an orthorhombic phosphate compound having the symmetry of the space group Pmnb, and the lattice constants of the a-axis, b-axis and c-axis of the phosphate compound are 1.060 nm ≦ a ≦ 1. A positive electrode active material for a lithium ion secondary battery, wherein 120 nm, 0.620 nm ≦ b ≦ 0.66 nm, 0.486 nm ≦ c ≦ 0.515 nm. The divalent cation M of LiMn _1-x M _x PO ₄ in the phosphate compound according to claim 4 is:
A positive electrode active material for a lithium ion secondary battery, wherein the positive electrode active material is one or more of Co, Fe, Ni, and Cu.

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