JP3504195B2 - Lithium secondary battery positive electrode active material and lithium secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a positive electrode active for a lithium secondary battery.
The present invention relates to materials and lithium secondary batteries, and particularly to improvement of positive electrode active materials, and aims to increase discharge capacity and charge / discharge cycle characteristics of batteries.

[0002]

2. Description of the Related Art A lithium secondary battery using a negative electrode active material made of lithium metal, a lithium alloy, or a material capable of inserting and extracting lithium ions is characterized by high voltage and excellent reversibility. In particular, a lithium-ion secondary battery that uses a composite oxide of lithium and a transition metal as the positive electrode active material and a carbon-based material as the negative electrode active material is compared to conventional lead secondary batteries or nickel-cadmium secondary batteries. Because of its light weight and large capacity, it is widely used in electronic devices such as mobile phones and notebook personal computers.

LiCoO ₂ is mainly used as a positive electrode active material of a lithium ion secondary battery which is currently generally used, but cobalt, which is a raw material of LiCoO ₂ , has a small reserve and is used in a limited area. Therefore, it is not preferable as a positive electrode active material for a lithium ion secondary battery in terms of price and stable supply of raw materials.

On the other hand, it has been clarified by Japanese Laid-Open Patent Publication No. 9-134725 that LiFePO _4, which uses a large amount of iron and is inexpensive as a raw material, operates as a positive electrode material of a lithium secondary battery. Further, it is possible to replace the iron of LiFePO ₄ with cobalt to control the battery voltage.
No. 34724.

[0005]

However, LiFePO
No. ₄ has a slow lithium insertion / desorption reaction during battery charging / discharging, and LiFe is used to increase the packing density of the positive electrode active material in the battery.
When the size of the PO ₄ particles is increased, there is a problem that charging / discharging with a satisfactory capacity can be performed only with an extremely small current.

When cobalt is added to LiFePO ₄ , the redox reaction of cobalt occurs at a potential as high as about 5 V with respect to the standard potential of lithium metal, but when the charging voltage exceeds 4.3 V, the current lithium is present. In the electrolytic solution used in the ion secondary battery, oxidative decomposition of the electrolytic solution itself occurs,
Charging / discharging at such a high voltage is likely to deteriorate cycle characteristics. Although stable electrolytes are being developed even at high voltage, none have been put to practical use at present and it is preferable to add more cobalt than necessary from the viewpoint of cost and battery life. Absent.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, and its object is to use a lithium iron phosphate-based material, which is inexpensive and can be charged and discharged at a voltage of 4 V or less, as a positive electrode. This is to increase the discharge capacity of the used lithium secondary battery at a practical current.

[0008]

In order to achieve such an object, the lithium secondary battery positive electrode active material according to the present invention has a general formula Li _z Fe _1-y X _y PO ₄ (0 <z ≦ 1). In a given phosphate compound having an olivine structure, the element X is a substance that is electrochemically stable in a potential region of 3 V to 4 V with respect to the standard potential of lithium metal in a state of constituting the phosphate compound, Furthermore, y is a substance in which 0 <y ≦ 0.3, and the element X in the phosphoric acid compound is magnesium.
And at least one of zinc and zinc .

The lithium secondary battery according to the present invention is
The lithium secondary battery positive electrode active material according to claim 1,
Quality, including lithium metal, lithium alloy or lithium
The negative electrode active material is a substance that can store and release um ions.
In addition, lithium ions are added to the positive electrode active material and the negative electrode.
A substance that can move to cause an electrochemical reaction with an active material
Is contained as an electrolyte .

The present invention will be described in more detail. The positive active material of the lithium secondary battery according to the present invention has the general formula Li _z.
Fe _1-y X _y PO ₄ (0 <z ≦ 1) is a phosphate compound having an olivine structure, and the element X is 3 V with respect to the standard potential of lithium metal in the state where the phosphate compound is formed. Is a substance that is electrochemically stable in a potential region of 4 V to 4 V, and y is 0 <y ≦ 0.3.

The above-mentioned substance generally called lithium iron phosphate is represented by LiFePO ₄ (z = 1),
No more lithium can be inserted while maintaining the structure. When this material is used as the positive electrode of a battery, lithium escapes from the positive electrode when charging and the composition is Fe.
When approaching PO ₄ (z becomes small) and discharging the charged battery, lithium in the electrolytic solution is inserted into the positive electrode, and the composition returns to LiFePO ₄ (z = 1). Considering the discharge capacity and production of the battery, the material with z = 1 is the most preferable, but since the value of z changes continuously in this way, even a substance with a composition such as z = 0.9, which is a non-stoichiometric composition, can be used. A battery that operates with a mechanism equivalent to that of lithium iron phosphate with z = 1, which is a general stoichiometric composition, can be prepared. Therefore, in the above formula, z is represented by 0 <z ≦ 1.

In a lithium secondary battery using LiFePO ₄ as a positive electrode material, lithium is desorbed during charging and iron ions change from divalent to trivalent. Results lithium is eliminated, that portion of the crystal structure would be (olivine structure) partially moving path of lithium becomes unstable is blocked, may be difficult further away lithium in the interior are removed, LiFePO ₄ This is considered to be the reason why a lithium secondary battery using as a positive electrode material cannot obtain a sufficient capacity at a practical charge / discharge current.

Further, it is considered that the instability of this structure causes a decrease in discharge capacity due to repeated charge / discharge cycles. On the other hand, when a part of iron is replaced with an element such as zinc which is electrochemically stable in the potential region of 3 V to 4 V with respect to the standard potential of lithium metal in the state that the phosphoric acid compound is constituted, charging is performed. Even if is performed, the substituted element such as zinc remains divalent and is not oxidized, and lithium adjacent to the substituted element remains in the crystal without being desorbed. Therefore, it is considered that the crystal structure of the replaced portion is unlikely to change even after charging, and the lithium migration path is secured, so that the capacity is increased and the cycle stability is improved.

However, since lithium that is not desorbed does not participate in charging and discharging, if the amount of such substitution is too large, the capacity of the battery will decrease. The inventor conducted various experiments and found that the substitution amount of the iron element, which has the effect of increasing the capacity, was 30% (0 <
y ≦ 0.3) or less, preferably 10% to 30% (0.
1 ≦ y ≦ 0.3), more preferably 10 to 20%
It was found that (0.1 ≦ y ≦ 0.2).

Incidentally, the element which is electrochemically stable in the potential region of 3 V to 4 V with respect to the standard potential of lithium metal described above is, first of all, an alkali metal, an alkaline earth metal or the like. Redox occurs at a potential of less than 3 V with respect to the standard potential, and at higher voltages, it is a stable element, or when it is replaced with iron in lithium iron phosphate, such as cobalt and nickel, the standard of lithium metal. At a potential lower than 3 V with respect to the potential, divalent metal is reduced, and redox does not occur in a potential region of 3 V to 4 V,
An element that is oxidized from divalent to trivalent at a potential exceeding 4V.

[0016] Thus, the metal to be replaced in order to replace the iron while maintaining an olivine structure lithium iron phosphate, and even divalent ions in 4V potential region from 3V
Good. As the element to be replaced in the present invention using magnesium <br/> c arm, the zinc.

[0017]

Embodiments of the present invention will now be described in more detail with reference to the drawings. The present invention is not limited to the following examples.

[0018]

Reference Example 1 FIG. 1 is a sectional view of a battery showing a structure according to an embodiment of a lithium secondary battery according to the present invention. 1 in the figure
Is a sealing plate, 2 is a metal lithium negative electrode, 3 is a gasket, 4
Is a separator, 5 is a positive electrode pellet, and 6 is a positive electrode case.

LiFe _0.7 Co _0.3 PO _4, which is the positive electrode active material contained in the positive electrode pellet 5 of FIG. 1, was prepared by the following method.

First, the raw material lithium carbonate (Li ₂ CO
₃ ) and iron oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O)
And cobalt acetate tetrahydrate _{(Co (CH 3 COO) 2} · 4
H ₂ O) and diammonium hydrogen phosphate ((NH ₄ ) ₂ H
PO ₄ ) was mixed in a molar ratio of 0.5: 0.7: 0.3: 1 and put in a crucible, and the mixture was heated to 800 in an argon atmosphere.
It was prepared by firing at 24 ° C. for 24 hours. The X-ray diffraction chart of the obtained substance is shown in FIG.

It is almost in agreement with the reported X-ray diffraction chart of LiFePO ₄ (JCPDS 15-0760), which shows that iron is replaced by cobalt while maintaining the olivine structure. This positive electrode active material 70
% By weight, 25% by weight of acetylene black as a conductive agent and 5% by weight of polytetrafluoroethylene as a binder were kneaded into a clay-like lump, which was rolled by a biaxial roller to a thickness of about 0.6 mm. After that, a punch was punched into a disk shape having a diameter of 15 mm to prepare a positive electrode pellet (5). FIG. 3 shows the olivine structure of LiFePO ₄ . Black circles represent lithium atoms, octahedrons represent iron surrounded by 6 oxygens, and tetrahedra represent phosphorus surrounded by 4 oxygens.

Next, a metallic lithium negative electrode 2 placed under pressure on a stainless steel sealing plate 1 was inserted into the recess of a polypropylene gasket 3, and a polypropylene microporous separator 4 and a positive electrode were placed on the negative electrode. The pellets 5 are arranged in this order, and 1 mol of LiPF ₆ is added as an electrolytic solution to an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate.
A proper amount of an electrolytic solution dissolved in a concentration of 1 / dm ³ was injected and impregnated, and then a positive electrode case 6 made of stainless steel was covered and caulked to manufacture a coin type battery having a thickness of 2 mm and a diameter of 23 mm. The charging / discharging characteristics of the manufactured battery were evaluated by charging / discharging under the conditions of a final charge voltage of 4.0 V, a final discharge voltage of 3.0 V, and a constant current of 1 mA.

FIG. 4 shows a charge / discharge curve at the 10th cycle. The discharge potential is almost the same as the voltage of a battery in which lithium iron phosphate, which has not been substituted, is used as the positive electrode and lithium metal is used as the negative electrode, which is already known. I know that Discharge capacity is 1
It increased somewhat from the 10th cycle to the 10th cycle, and showed a substantially constant capacity thereafter.

The capacity at the 50th cycle is 5.6 mA.
It was h. The relationship between the number of cycles of the initial 50 cycles and the discharge capacity is shown in FIG. Also, the substitution amount y of iron by the element X
FIG. 6 shows the relationship between the discharge capacity at the 50th cycle and the discharge capacity at the 50th cycle. Further, Table 1 shows the composition formula of the positive electrode active material of the battery, the substitution amount y and the discharge capacity at the 50th cycle.

[0025]

Comparative Example 1 LiF which is a positive electrode active material containing no element X
ePO ₄ was prepared by the following method. First, lithium carbonate (Li ₂ CO ₃ ) as a raw material and iron oxalate dihydrate (Fe
C ₂ O ₄ .2H ₂ O) and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) were mixed in a molar ratio of 0.5: 1: 1 and put into a crucible, and the mixture was placed under an argon atmosphere. 8
It was produced by firing at 00 ° C. for 24 hours.

Using the obtained positive electrode active material, a positive electrode pellet and a coin type battery were produced by the same method as in Reference Example 1. Evaluation of the charge-discharge characteristics under the same conditions as in Reference Example 1, although the discharge capacity at the first cycle was higher than that of the battery described in Reference Example 1, the battery discharge capacity shown in Reference Example 1 from 5 cycle It is lower than that in the 50th cycle
4.7 mAh corresponding to 84% of the battery shown in Reference Example 1
Only the capacity of was obtained.

The relationship between the number of cycles of the initial 50 cycles and the discharge capacity is shown in FIG.
The relationship of the discharge capacity at the 0th cycle is shown in FIG. 6, and the composition formula of the positive electrode active material of the battery, the substitution amount y and the discharge capacity at the 50th cycle are shown in Table 1 together with the values of Reference Example 1.

[0028]

[Table 1]

[0029]

Reference Example 2 LiFe _0.8 Co _0.2 PO ₄ , which is the positive electrode active material contained in the positive electrode pellet, was produced by the following method. A first raw material of lithium carbonate _(Li 2 CO ₃₎ and iron oxalate dihydrate _{(FeC 2 O 4 · 2H 2} O) and cobalt acetate tetrahydrate _{(Co (CH 3 COO) 2} · 4H 2 O)
And diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ )
Were mixed in a crucible at a molar ratio of 0.5: 0.8: 0.2: 1 and placed in an argon atmosphere at 800 ° C. for 24 hours.
It was produced by firing for a time.

Using the obtained positive electrode active material, a positive electrode pellet and a coin type battery were produced by the same method as in Reference Example 1. When the charge / discharge characteristics were evaluated under the same conditions as in Reference Example 1, the discharge capacity was higher than that of the battery shown in Comparative Example 1 from the second cycle, and 1.43 of the battery shown in Comparative Example 1 was found at the 50th cycle. A doubled capacity of 6.7 mAh was obtained.

The relationship between the number of cycles of the initial 50 cycles and the discharge capacity is shown in FIG.
The relationship of the discharge capacity at the 0th cycle is shown in FIG. 6, the composition formula of the positive electrode active material of the battery, the substitution amount y and the discharge capacity at the 50th cycle are shown in Table 1, together with the characteristics of Reference Example 1 and Comparative Example 1, respectively. Show.

[0032]

Reference Example 3 LiFe _0.9 Co _0.1 PO ₄ , which is the positive electrode active material contained in the positive electrode pellet, was produced by the following method. A first raw material of lithium carbonate _(Li 2 CO ₃₎ and iron oxalate dihydrate _{(FeC 2 O 4 · 2H 2} O) and cobalt acetate tetrahydrate _{(Co (CH 3 COO) 2} · 4H 2 O)
And diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ )
Were mixed in a crucible at a molar ratio of 0.5: 0.9: 0.1: 1 and placed in an argon atmosphere at 800 ° C. for 24 hours.
It was produced by firing for a time.

A coin type battery was produced by the same method as in Reference Example 1 using the obtained positive electrode active material. When the charge and discharge characteristics were evaluated under the same conditions as in Reference Example 1, the discharge capacity was higher than that of the battery shown in Comparative Example 1 from the 5th cycle,
At the 50th cycle, a capacity of 4.9 mAh corresponding to 1.04 times that of the battery shown in Comparative Example 1 was obtained.

The relationship between the number of cycles of the initial 50 cycles and the discharge capacity is shown in FIG.
The relationship of the discharge capacity at the 0th cycle is shown in FIG. 6, and the composition formula of the positive electrode active material of the battery, the substitution amount y and the discharge capacity at the 50th cycle are shown in Table 1 together with the characteristics of Reference Examples 1 and 2 and Comparative Example 1, respectively. Indicate.

[0035]

Comparative Example 2 LiFe _0.6 Co _0.4 PO ₄ , which is the positive electrode active material contained in the positive electrode pellet, was produced by the following method. A first raw material of lithium carbonate _(Li 2 CO ₃₎ and iron oxalate dihydrate _{(FeC 2 O 4 · 2H 2} O) and cobalt acetate tetrahydrate _{(Co (CH 3 COO) 2} · 4H 2 O)
And diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ )
Were mixed in a crucible at a molar ratio of 0.5: 0.6: 0.4: 1 and placed in an argon atmosphere at 800 ° C. for 24 hours.
It was produced by firing for a time.

A coin type battery was produced by the same method as in Reference Example 1 using the obtained positive electrode active material. When the charge and discharge characteristics were evaluated under the same conditions as in Reference Example 1, the discharge capacity was always lower than that of the battery shown in Comparative Example 1 from the first cycle to the 50th cycle, and the discharge capacity was shown in Comparative Example 1 at the 50th cycle. It only showed a capacity of 4.3 mAh, which is 0.91 times that of the battery.

The relationship between the number of cycles of the initial 50 cycles and the discharge capacity is shown in FIG.
The relationship between the discharge capacity at the 0th cycle and the composition of the positive electrode active material of the battery, the substitution amount y and the discharge capacity at the 50th cycle are shown in Table 1, and the characteristics of Reference Examples 1 to 3 and Comparative Example 1, respectively. Shown together.

[0038]

Example 1 LiFe _0.8 Zn _0.2 PO ₄ , which is a positive electrode active material contained in a positive electrode pellet, was produced by the following method. First, the raw material lithium hydroxide monohydrate (LiOH
· _H 2 O) and iron oxalate dihydrate _{(FeC 2} O 4 · 2H
₂ O) and zinc acetate dihydrate (Zn (CH ₃ COO) ₂ ·
2H ₂ O) and diammonium hydrogen phosphate ((NH ₄ ) ₂
HPO ₄ ) was mixed in a molar ratio of 1: 0.8: 0.2: 1 and put in a crucible, and the temperature was 800 ° C. under an argon atmosphere.
It was prepared by firing for 24 hours.

A coin-type battery was manufactured by using the obtained positive electrode active material in the same manner as in Reference Example 1. When the charge and discharge characteristics were evaluated under the same conditions as in Reference Example 1, the discharge capacity was higher than that of the battery shown in Comparative Example 1 from the first cycle,
The cycle number dependency slightly higher than that of Reference Example 2 was shown. In addition, at the 50th cycle, 1.4% of the battery shown in Comparative Example 1 was used.
A capacity of 7.0 mAh corresponding to 9 times was obtained.

The relationship between the number of cycles in the initial 50 cycles and the discharge capacity is shown in FIG. 5, and the composition formula of the positive electrode active material of the battery, the substitution amount y and the discharge capacity at the 50th cycle are shown in Table 1.
The characteristics of Reference Examples 1 to 3 and Comparative Examples 1 and 2 are shown together.

[0041]

Example 2 LiFe _0.85 Mg _0.15 PO ₄ , which is the positive electrode active material contained in the positive electrode pellet, was produced by the following method. First, the raw material lithium hydroxide monohydrate (Li
OH · H ₂ O) and iron oxalate dihydrate (FeC ₂ O ₄ ·
2H ₂ O), magnesium oxide (MgO) and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) were mixed in a molar ratio of 1: 0.85: 0.15: 1 and put in a crucible. It was manufactured by baking at 800 ° C. for 24 hours in an argon atmosphere.

A coin type battery was produced by the same method as in Reference Example 1 using the obtained positive electrode active material. When the charge and discharge characteristics were evaluated under the same conditions as in Reference Example 1, the discharge capacity was higher than that of the battery shown in Comparative Example 1 from the first cycle,
Approximately the same cycle number dependence as in Reference Example 2 was shown.

At the 50th cycle, a capacity of 6.8 mAh, which is 1.45 times that of the battery shown in Comparative Example 1, was obtained.
The composition formula of the positive electrode active material, the substitution amount y, and the discharge capacity at the 50th cycle of the battery shown in Example 2 are shown in Table 1 together with the characteristics of Example 1, Reference Examples 1 to 3 and Comparative Examples 1 and 2. .

[0044]

Reference Example 4 LiFe _0.8 Ni _0.2 PO ₄ , which is the positive electrode active material contained in the positive electrode pellet, was produced by the following method. First, the raw material lithium hydroxide monohydrate (LiOH
· _H 2 O) and iron acetate _{((CH 3 COO) 2 Fe} ) and nickel oxide (NiO) and diammonium hydrogenphosphate ((N
H ₄ ) ₂ HPO ₄ ) in a molar ratio of 1: 0.8: 0.2: 1
It was prepared by mixing the above so as to be put into a crucible and firing at 800 ° C. for 24 hours in an argon atmosphere.

Using the positive electrode active material thus obtained, a coin-type battery was manufactured by the same method as in Reference Example 1. When the charge and discharge characteristics were evaluated under the same conditions as in Reference Example 1, the discharge capacity was higher than that of the battery shown in Comparative Example 1 from the first cycle,
The number of cycles was slightly lower than that of Reference Example 2. Further, at the 50th cycle, 1.3% of the battery shown in Comparative Example 1 was used.
A capacity of 6.5 mAh corresponding to 8 times was obtained. Reference example
The positive electrode active material composition formula of battery shown in 4, the discharge capacity of the substitution amount y and the 50th cycle in Table 1, the characteristics of Examples 1 and 2 Example 1 or <br/> et 3 and Comparative Examples 1 and 2 Shown together with.

In the above-mentioned examples, the positive electrode formed into a pellet shape was used. However, a positive electrode active material and a binder such as polyvinylidene fluoride were added to a solvent such as N-methyl-2-pyrrolidone. To make a slurry,
It may have a shape such as a coating electrode in which it is thinly coated on a metal foil and dried.

Although lithium metal was used as the negative electrode material, other lithium-based materials, carbon-based materials such as graphite and coke, and metal oxides such as tungsten oxide, niobium oxide, vanadium oxide, and tin oxide. A lithium transition metal composite nitride such as lithium manganese nitride, lithium cobalt nitride, or lithium iron nitride, or metal chalcogenite such as iron sulfide or molybdenum sulfide may be used.

Further, as the electrolytic solution, LiPF ₆ was added to an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate.
Was used as an electrolytic solution in which was dissolved at a concentration of 1 mol / dm ³ .
The same non-aqueous lithium secondary battery as the conventional one can be used.

For example, the solvent is dimethoxyethane, 2
-Methyltetrahydrofuran, ethylene carbonate,
It is possible to use methyl formate, dimethyl sulfoxide, propylene carbonate, acetonitrile, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc. alone or in combination of two or more.

As the solute, other than LiPF ₆ used in the examples, for example, LiClO ₄ and LiBF ₆ are used.
₄ , LiAsF ₆ , LiCF ₃ SO ₃ or the like may be used.
Further, a polymer electrolyte, a solid electrolyte, a room temperature molten salt and the like can also be used. In addition, conventionally known various materials can be used for other elements such as a structural material such as a separator and a battery case. Further, although the battery shape is a button shape in the embodiment, it is not particularly limited and may be a cylindrical shape, a rectangular shape or the like.

[0051]

As described above, according to the lithium secondary battery of the present invention, iron in lithium iron phosphate is used as the positive electrode active material, and when the phosphoric acid compound is formed, the standard lithium metal is used. Battery life due to decomposition of electrolytic solution compared with unsubstituted lithium iron phosphate by using a compound in which a substance that is electrochemically stable in an electric potential region of 3 V to 4 V with respect to the electric potential is substituted at a ratio of 30% or less It was possible to improve the discharge capacity and the cycle characteristics in charge and discharge at 4 V or less, where the decrease of the discharge does not easily occur. Therefore, it is possible to realize a lithium secondary battery which is economically excellent and has good battery characteristics.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configuration of an embodiment of a lithium secondary battery according to the present invention.

FIG. 2 shows LiFe _0.7 Co _0.3 PO used as a positive electrode active material in Reference Example 1 of the lithium secondary battery of the present invention.
_The figure which showed the X-ray-diffraction pattern of ₄ .

FIG. 3 is a diagram showing an olivine structure of LiFePO ₄ .

FIG. 4 is a diagram showing a charge / discharge curve of a battery in Reference Example 1 of the lithium secondary battery of the present invention.

FIG. 5: Reference examples 1 to 3 of the lithium secondary battery of the present invention
The figure which showed the relationship between the number of cycles and discharge capacity in Example 1 together with the relationship in Comparative Examples 1 and 2.

FIG. 6 is a diagram showing the relationship between the amount y of iron replaced by element X and the discharge capacity in Reference Examples 1 to 3 of the lithium secondary battery of the present invention together with the relationship in Comparative Examples 1 and 2.

[Explanation of symbols]

1 Seal plate 2 Metal lithium negative electrode 3 gasket 4 separator 5 Positive electrode pellet 6 Positive case

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Youji Sakurai 2-3-1, Otemachi, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (56) Reference JP-A-9-134724 (JP, A) Hei 9-134725 (JP, A) International publication 00/060679 (WO, A1) International publication 00/060680 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 10/40

Claims (2)

(57) [Claims] 1. The general formula Li _z Fe _1-y X _y PO ₄ (0
In a phosphoric acid compound having an olivine structure given by <z ≦ 1), the element X is in the state of constituting the phosphoric acid compound,
It is a substance that is electrochemically stable in the potential region of 3 V to 4 V with respect to the standard potential of lithium metal, and y is 0 <
a substance in which y ≦ 0.3, in the phosphoric acid compound,
Element X is at least one of magnesium and zinc
A positive electrode active material for a lithium secondary battery, comprising: 2. The positive electrode active material of the lithium secondary battery according to claim 1.
Including substances as positive electrode active materials, lithium metal, lithium
Negative materials that can store and release alloys or lithium ions
As a polar active material, lithium ions are further added to the positive electrode active material.
Quality and transfer for electrochemical reaction with the negative electrode active material.
Lithium characterized by containing a substance capable of conducting as an electrolyte
Um secondary battery.