JP3316403B2 - Lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to an improvement in a lithium ion storage material used for a negative electrode for the purpose of obtaining a lithium secondary battery having excellent charge / discharge cycle characteristics. .

[0002]

2. Description of the Related Art In recent years,
Unlike alkaline rechargeable batteries, such as nickel-cadmium rechargeable batteries, which use an aqueous alkaline solution as the electrolyte, lithium secondary batteries do not need to consider the decomposition voltage of water. For reasons, attention has been paid.

Conventionally, metallic lithium was initially considered as a negative electrode material for this type of secondary battery. When this negative electrode material is used, lithium is deposited on the surface of the lithium negative electrode during charging, and the lithium deposited during discharging becomes lithium ions and elutes into the electrolyte. However, when metal lithium is used, an internal short circuit may occur due to the growth of dendritic lithium. Therefore, in a practical battery, a carbon material that does not have such a problem and that can electrochemically occlude and release lithium ions during charge and discharge is used.

[0004] Typical carbon materials capable of electrochemically storing and releasing lithium ions include:
There are a coke type and a graphite type. The coke type carbon material has a specific capacity of about 200 mAh / g, and the graphite type carbon material has a specific capacity of about 370 mAh / g.

[0005] Recently, a demand for a longer charging interval for a power supply for a portable device or the like has led to a demand for higher battery capacity. Therefore, Sn as a lithium ion storage material having a higher specific capacity than a carbon material is used.
Oxides of tin such as O ₂ and SnO have been proposed (see Japanese Patent Application Laid-Open No. 7-122274).

However, lithium secondary batteries using tin oxide as the lithium ion storage material for the negative electrode have a problem that the charge / discharge cycle characteristics are extremely poor because the crystal structure of tin oxide is unstable. is there.

[0007] Tin oxide having excellent charge-discharge cycle characteristics includes tin, lithium, sodium, potassium, magnesium, calcium, titanium, zirconium, vanadium, and tin, which are less likely to undergo a crystal structure collapse due to repeated charge and discharge. Niobium, tantalum, molybdenum, tungsten, manganese, iron, rhodium, iridium, copper, silicon,
A composite oxide with germanium or bismuth has been proposed (see JP-A-6-338325). When this composite oxide is used, the charge / discharge cycle characteristics can be considerably improved as compared with the case where the tin oxide is used.

However, since the crystal structure of the above-mentioned composite oxide is not sufficiently stable, the crystal structure gradually collapses due to repetition of expansion and contraction during a charge / discharge cycle. Therefore, the lithium secondary battery using this as the lithium ion storage material of the negative electrode also has a problem that the charge / discharge cycle characteristics are not yet sufficient.

The present invention has been made in view of the above circumstances, and has as its object to provide a lithium secondary battery having extremely excellent charge / discharge cycle characteristics.

[0010]

[Summary of The lithium secondary battery according to the present invention for achieving the object (hereinafter, referred to as "present battery".) Has a tin, lithium, sodium, Ca
Lium, titanium , zirconium, vanadium, niobium,
Tantalum, molybdenum, tungsten, manganese, iron,
At least one element M ¹ selected from the group consisting of rhodium, iridium, copper, zinc and bismuth ;
A composite oxide of at least one element M ² selected from phosphorus and the group consisting of sulfur, is obtained by using as a lithium ion storage material of the negative electrode.

The composite oxide according to the present invention has a layered crystal structure, in which lithium ions intrude between the layers during charging and release lithium ions from the layers during discharging.

As a specific example of the composite oxide, a composition formula Sn
M ¹ _X M ² _y O _z (where x is 0.9 or more and 2.1 or less, y is 0.01 or more and 0.3 or less, preferably 0.0
5 or more and 0.2 or less, and z is 1.5 or more and 10.0 or less).

A feature of the present invention is to provide a lithium secondary battery having extremely excellent charge / discharge cycle characteristics by using a composite oxide of tin and a specific element, which has a crystal structure that does not easily collapse during charge / discharge cycles, as a negative electrode. In that it was used as a lithium ion storage material. Therefore, other materials constituting the battery such as the positive electrode material and the electrolyte are not particularly limited, and various materials conventionally used or proposed for lithium secondary batteries can be used. .

As a cathode material (cathode active material), LiC
_{oO 2, LiNiO 2, LiFeO 2} , LiMn 2 O 4
And the like.

As the electrolyte, ethylene carbonate,
Diethyl carbonate, dimethyl carbonate, 1,2
- dimethoxyethane, sulfolane, or a mixture of these _{solvents, LiPF 6, LiClO 4, LiCF} 3 SO 3
A solution in which 0.7 to 1.5 mol / liter of an electrolyte salt such as described above is dissolved is exemplified.

Since the battery of the present invention uses a composite oxide of tin and a specific element as the lithium ion storage material of the negative electrode, it exhibits extremely excellent charge / discharge cycle characteristics.
The reason is not clear at present also in the present inventors, the crystal structure of the composite oxide of tin and elemental M ¹ and the element M ² is considered very stable for.

[0017]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

[Preparation of positive electrode] LiC as positive electrode active material
oO ₂ and a carbon material as a conductive agent in a weight ratio of 18:
And 95 parts by weight of this mixture and a solution of 5 parts by weight of polyvinylidene fluoride in NMP (N-methyl-2-pyrrolidone) to prepare a slurry. The foil was applied to both sides of the foil by a doctor blade method and vacuum dried at 150 ° C. for 2 hours to produce a positive electrode.

[Production of negative electrode] Stannic oxide (SnO ₂ )
When a M ¹ a raw material (compound containing an element M ^1), pentoxide, boron (B ₂ O _5), phosphorus pentoxide (P ₂ O ₅₎ or sulfur (or three containing an element M ² M ² The mixture was fired at 900 ° C. for 2 hours in the air to obtain a composite oxide. Next, 90 parts by weight of each composite oxide, 5 parts by weight of carbon powder as a conductive agent, and an NMP solution of 5 parts by weight of polyvinylidene fluoride were kneaded to prepare a slurry, and this slurry was used as a negative electrode current collector. The copper foil was applied to both sides by a doctor blade method and vacuum dried at 150 ° C. for 2 hours to produce a negative electrode.

[Preparation of Electrolyte Solution] LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 1 at 1 mol / liter to prepare an electrolyte solution.

[Preparation of Battery] Using the above positive electrode, negative electrode and electrolytic solution, an outer diameter of 14 mm was used.
Cylindrical lithium secondary batteries A1 to A3 having a height of 50 mm
A6 to A18, A23, B1 to B3, B6 to B18, B
23, C1 to C3, C6 to C18, C23, D1 to D
3, D6-D18, D23, E1-E3, E6-E1
8, E23, F1 to F3, F6 to F18, F23, G1
-G3, G6-G18, G23, H1-H3, H6-H
18, H23, I1 to I3, I6 to I18, and I23 were produced. Furthermore, batteries J1 to J3 were prepared in the same manner except that a composite oxide containing no boron pentoxide, phosphorus pentoxide, and sulfur was used as the lithium ion storage material of the negative electrode .
J6 to J18 and J23 were produced. In each of the batteries, a microporous polypropylene membrane was used as a separator.

FIG. 1 is a schematic cross-sectional view of a manufactured lithium secondary battery. The illustrated battery BA has a positive electrode 1, a negative electrode 2, a separator 3 separating them from each other, a positive electrode lead 4, a negative electrode lead 5, and a positive external terminal. 6, a negative electrode can 7 and the like. The positive electrode 1 and the negative electrode 2 are housed in a negative electrode can 7 while being spirally wound through a separator 3 into which a non-aqueous electrolyte is injected. The terminal 6 and the negative electrode 2 are connected to a negative electrode can 7 via a negative electrode lead 5, so that chemical energy generated inside the battery can be extracted to the outside as electric energy.

Tables 1 to 4 show the composite oxides used for producing the negative electrodes of the batteries, and Tables 5 and 6 show M ¹
Raw material, M ² raw material, M ¹ : Sn of M ¹ raw material and stannic oxide: Sn
Atom conversion ratio (M ¹ / Sn; composition formula SnM ¹ _X M ² _y O
corresponds to x in _z), and, M ² and M ² material and stannic oxide: atomic conversion ratio of Sn (M ² / Sn; formula SnM
¹ _X M ² _y O _z ).

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

[Table 5]

[0029]

[Table 6]

<Charge / Discharge Cycle Characteristics of Each Battery> Each battery is charged at room temperature to 4.1 V at 200 mA and then discharged to 2.75 V at 200 mA.
By repeating the cycle, the capacity deterioration rate per cycle up to the 200th cycle of each battery was calculated based on the following equation. Tables 5 and 6 above show the capacity deterioration rate (% / cycle) of each battery. The number below the battery code is the capacity deterioration rate.

Capacity deterioration rate = {(discharge capacity at first cycle−discharge capacity at 200th cycle) / discharge capacity at first cycle} charge / discharge cycle (199 cycles) × 100

From Tables 5 and 6, batteries A1 to A3, A6 to A18, A23, B1 to B3 and B using the composite oxide specified in the present invention as a lithium ion storage material for a negative electrode were obtained.
6 to B18, B23, C1 to C3, C6 to C18, C2
3, D1 to D3, D6 to D18, D23, E1 to E3
E6 to E18, E23, F1 to F3, F6 to F18, F
23, G1 to G3, G6 to G18, G23, H1 to H
3, H6-H18, H23, I1-I3, I6-I1
8, I23 is battery using the composite oxide containing no element M ² J1~J3, J6~J18, compared to J23,
It can be seen that the capacity deterioration rate is small and the charge / discharge cycle characteristics are excellent.

In the above embodiment, the case where the present invention is applied to a cylindrical lithium secondary battery has been described as an example.
The shape of the battery is not particularly limited, and the present invention can be applied to lithium secondary batteries having various shapes such as a flat shape and a square shape.

Although a liquid electrolyte is used in the above embodiment, the present invention is also applicable to a solid electrolyte battery.

[0035]

The battery of the present invention uses a composite oxide of tin, a specific element M ¹ and a specific element M ² as a lithium ion storage material for the negative electrode, and therefore has extremely excellent charge-discharge cycle characteristics. Is expressed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cylindrical lithium secondary battery manufactured in an example.

[Explanation of symbols]

 BA lithium secondary battery 1 positive electrode 2 negative electrode 3 separator 4 positive electrode lead 5 negative electrode lead 6 positive external terminal 7 negative electrode can

Continued on the front page (72) Inventor Masahisa Fujimoto 2-5-5 Keihanhondori, Moriguchi City, Osaka Prefecture Inside Sanyo Electric Co., Ltd. (72) Inventor Toshiyuki Noma 2-5-5 Keihanhondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-1, Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-7-288123 (JP, A) JP-A-8 -130035 (JP, A) JP-A-8-130036 (JP, A) JP-A-8-203526 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/00- 4/62

Claims (3)

(57) [Claims] 1. Tin and lithium, sodium, potassium,
At least one element M ¹ selected from the group consisting of titanium , zirconium, vanadium, niobium, tantalum, molybdenum, tungsten, manganese, iron, rhodium, iridium, copper, zinc and bismuth; and a group consisting of boron, phosphorus and sulfur At least one element M ² selected from
Wherein the composite oxide is used as a lithium ion storage material for a negative electrode. Wherein said composite oxide is represented by the composition formula SNM ¹ _X M ²
_y O _z (where x is 0.9 or more and 2.1 or less, and y is 0.
2. The lithium secondary battery according to claim 1, wherein the composite oxide is a complex oxide represented by the formula: 01 to 0.3, z is 1.5 to 10.0. Wherein the composite oxide has a composition formula SnM ¹ _X M ²
_y O _z (where x is 0.9 or more and 2.1 or less, and y is 0.
The lithium secondary battery according to claim 1, wherein the composite oxide is a composite oxide represented by the following formula: