JP2003272613A - Negative electrode material for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode material for a nonaqueous electrolyte secondary battery capable of satisfying capacity per unit cubic volume, cycle characteristics and rate characteristics at the same time. <P>SOLUTION: The composition is expressed in (Al<SB>1-x</SB>Si<SB>x</SB>)<SB>a</SB>Ni<SB>b</SB>M<SB>c</SB>(provided, M is a kind of element selected from a group consisting of C, Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Ga, Ge, La, Zr, W, Mo, and Ba, and the atomic percentages a, b, c and x denote; a+b=100 atom %, 60≤a≤90, 0≤c≤5, 0.2≤x≤0.8 and includes an alloy satisfying a formula: (β/α)≤0.6. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a negative electrode material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, a non-aqueous electrolyte battery using metallic lithium as a negative electrode active material has attracted attention as a high energy density battery, and manganese dioxide (Mn 2
O ₂ ), fluorocarbon [(CF ₂ ) n], thionyl chloride (S
A primary battery using OC1 ₂ ) or the like is already widely used as a power source for calculators and watches and a backup battery for memories. Further, with the recent miniaturization and weight reduction of various electronic devices such as VTRs and communication devices, the demand for high energy density secondary batteries as their power source has increased, and research on lithium secondary batteries using lithium as a negative electrode active material has been conducted. It is active.

As a lithium secondary battery, metallic lithium is used.
Negative electrode containing propylene carbonate (PC), 1,2-dimension
Toxyethane (DME), γ-butyrolactone (γ-B
L), in a non-aqueous solvent such as tetrahydrofuran (THF)
LiClO_Four, LiBF_Four, LiAsF₆Richiu, etc.
Non-aqueous electrolyte or lithium-conducting solid in which aluminum salt is dissolved
Topochemical reaction between electrolyte and lithium
Compound (eg TiS ₂, MoS₂, V₂O_Five, V₆O₁₃,
MnO₂Etc.) as a positive electrode active material
Things are being researched.

However, the lithium secondary battery described above has not yet been put into practical use. The main reason for this is that the metallic lithium used for the negative electrode becomes fine powder during repeated charging and discharging, and becomes reactive dendrites, which impairs the safety of the battery and also causes damage to the battery, short circuit, and thermal runaway. This is because it may cause it. In addition, there is a problem that deterioration of lithium metal lowers charge / discharge efficiency and shortens cycle life.

In view of the above, it has been proposed to use a carbonaceous material that absorbs and releases lithium, such as coke, a resin fired body, carbon fiber, and pyrolytic vapor phase carbon, instead of metallic lithium. In recent years, commercialized lithium ion secondary batteries include a negative electrode containing a carbonaceous material and LiCoO 2.
It is provided with a positive electrode containing ₂ and a non-aqueous electrolyte. In such a lithium ion secondary battery, a reaction occurs in which lithium ions released from the negative electrode are taken into the non-aqueous electrolyte during discharging, and lithium ions in the non-aqueous electrolyte are occluded in the positive electrode during charging.

By the way, due to recent demands for further miniaturization of electronic equipment and continuous use for a long time, there is a strong demand for further improvement of battery capacity. However,
With conventional carbon materials, there is a limit to the improvement of charge and discharge capacity,
In addition, since low-temperature fired carbon, which is considered to have a high capacity, has a low material density, it is difficult to increase the charge / discharge capacity per unit volume. Therefore, it is necessary to develop new negative electrode materials to realize high capacity batteries.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a negative electrode material for a non-aqueous electrolyte secondary battery capable of simultaneously satisfying the capacity per unit volume, cycle life and rate characteristics, and a non-aqueous electrolyte provided with this negative electrode material. It is an object to provide a water electrolyte secondary battery.

[0008]

The negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention has a composition of (Al _1-x Si _x ) _a Ni _b
M _c (where M is C, Mg, Ca, Ti, V, C
r, Mn, Fe, Co, Cu, Zn, Ga, Ge, L
at least one element selected from the group consisting of a, Zr, W, Mo and Ba, and atomic ratios a, b, c and x
Is a + b = 100 atomic%, 60 ≦ a ≦ 90, 0 ≦ c ≦
5, showing 0.2 ≦ x ≦ 0.8) and containing an alloy satisfying the following formula (1).

(Β / α) ≦ 0.6 (1) However, α has the maximum intensity of the peaks in which 2θ is 45 ° ≦ 2θ ≦ 48 ° in the X-ray diffraction pattern using CuKα rays. Is the intensity of the peak, and β
Is 2θ in an X-ray diffraction pattern using CuKα rays.
Is the intensity of the peak having the maximum intensity among the peaks appearing at 25 ° ≦ 2θ ≦ 30 °.

The non-aqueous electrolyte secondary battery according to the present invention comprises a negative electrode containing a negative electrode material, a positive electrode, and a non-aqueous electrolyte, and the negative electrode material has a composition of (Al _1-x Si _x ) _a Ni _b M
_c (However, M is C, Mg, Ca, Ti, V, C
r, Mn, Fe, Co, Cu, Zn, Ga, Ge, L
at least one element selected from the group consisting of a, Zr, W, Mo and Ba, and atomic ratios a, b, c and x
Is a + b = 100 atomic%, 60 ≦ a ≦ 90, 0 ≦ c ≦
5, showing 0.2 ≦ x ≦ 0.8) and containing an alloy satisfying the following formula (1).

(Β / α) ≦ 0.6 (1) However, α has the maximum intensity of the peaks in which 2θ is 45 ° ≦ 2θ ≦ 48 ° in the X-ray diffraction pattern using CuKα rays. Is the intensity of the peak, and β
Is 2θ in an X-ray diffraction pattern using CuKα rays.
Is the intensity of the peak having the maximum intensity among the peaks appearing at 25 ° ≦ 2θ ≦ 30 °.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention has a composition of (Al _1-x Si _x ) _a Ni _b M _c (where M is C, Mg, Ca, Ti, V, Cr, M
n, Fe, Co, Cu, Zn, Ga, Ge, La, Z
At least one element selected from the group consisting of r, W, Mo and Ba, and the atomic ratios a, b, c and x are a +
b = 100 atomic%, 60 ≦ a ≦ 90, 0 ≦ c ≦ 5, 0.
2 ≦ x ≦ 0.8) and satisfies the following formula (1).

(Β / α) ≦ 0.6 (1) However, α has the maximum intensity among the peaks appearing when 2θ is 45 ° ≦ 2θ ≦ 48 ° in the X-ray diffraction pattern using CuKα rays. Is the intensity of the peak, and β
Is 2θ in an X-ray diffraction pattern using CuKα rays.
Is the intensity of the peak having the maximum intensity among the peaks appearing at 25 ° ≦ 2θ ≦ 30 °.

First, the composition of the negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention will be described.

(Si atomic ratio x) Si (silicon) is L
Li can be occluded and released by reversibly combining and dissociating with i. The theoretical charge / discharge capacity when Si metal was used as the negative electrode material for a non-aqueous electrolyte secondary battery was 4200 mAh / g (9800 mAh / cc: specific gravity: 2.
33). The theoretical maximum capacity of this Si metal is 3 of the theoretical maximum capacity of the carbon material currently in practical use.
It is much larger than 72 mAh / g (844 mAh / cc: specific gravity of 2.27), and the theoretical maximum capacity of metallic lithium is 3900 mAh / g (2100 mAh / c).
Compared with c: specific gravity 0.53), Si metal has a significantly larger discharge capacity per unit volume, which is important from the viewpoint of battery miniaturization. However, since the negative electrode material made of Si undergoes a large volume change due to storage / release of Li, it is easily broken into fine particles. For this reason, the capacity is drastically reduced with charge / discharge cycles, and the cycle life is extremely shortened.

The atomic ratio x of Si is preferably in the range of 0.2 or more and 0.8 or less. This is for the reason explained below. When the atomic ratio x is less than 0.2, the irreversible capacity of the alloy increases, so that the charge / discharge cycle life decreases. That is, Al is very likely to be oxidized, and the oxide Al ₂ O ₃ formed on the surface causes the initial Coulomb efficiency to deteriorate. The atomic ratio x of Si is 0.
If it is less than 2, the Al content in the alloy relatively increases and the alloy surface is coated with a large amount of oxide, so that the irreversible capacity of the alloy increases. On the other hand, the atomic ratio x of Si is 0.8
When it exceeds, the volume expansion of the alloy due to the occlusion and release of lithium becomes large, resulting in a decrease in cycle life. A more preferable range of the atomic ratio x of Si is 0.5 ≦ x ≦ 0.7.

(Total atomic ratio a of Al and Si) Al and Si
The total atomic ratio a of is preferably in the range of 60 to 90 atomic%. This is for the reason explained below. When the total atomic ratio a is outside the above range, α
It is not possible to obtain an alloy having a desired peak intensity ratio of β and β. Further, when the total atomic ratio exceeds 90 atomic%, the ratio of the Al and Si simple phases relatively increases, so that the initial capacity becomes very high, but the cycle deterioration becomes severe. On the other hand, if the total atomic ratio a is less than 60 atomic%,
A large number of phases other than the first phase A and the second phase B, which are inactive with respect to the elements, particularly Li, exist, leading to a decrease in capacity.
A more preferable range of the total atomic ratio a is 70 ≦ a ≦ 75.
Is.

(Ni atomic ratio b) Ni atomic ratio b is 1
It is desirable to set it within the range of 0 to 40 atomic%. This is for the reason explained below. When the total atomic ratio b is out of the above range, an alloy having a desired peak intensity ratio of α and β cannot be obtained. Further, if the total atomic ratio b is less than 10 atomic%, the ratio of the simple phases of Al and Si relatively increases, so that the initial capacity becomes very high, but the cycle deterioration becomes severe. On the other hand, when the total atomic ratio b exceeds 60 atomic%, many capacities are inactive with respect to elements other than the first phase A and the second phase B, especially Li, and thus the capacity is lowered. A more preferable range of the atomic ratio b of Ni is 25 ≦ b ≦ 30.

(Atomic ratio c of element M) The element M is not particularly specified, and may or may not form an alloy with Si, Ni, or Al. When a new alloy is formed, the alloy phase may or may not occlude Li. As the element M, C, Mg, Ca, Ti, V, C
r, Mn, Fe, Co, Cu, Zn, Ga, Ge, L
At least one element selected from the group consisting of a, Zr, W, Mo and Ba can be used. Further, it is desirable that the atomic ratio c of the element M be within a range of 5 atomic% or less (including 0). This is because when the atomic ratio c of the element M exceeds 5 atomic%, it is difficult to obtain an alloy having a peak strength (β / α) of 0.6 or less, and the newly generated alloy phase is capable of occluding Li or not. Regardless of the possibility, the initial capacity decreases or the cycle characteristics deteriorate.

By adding the element M, it is possible to improve the battery performance. For example, when C is added, the second
It is presumed that Si and C in the phase B react with each other to form SiC in the second phase B. Since SiC is a very hard ceramic, the volume expansion of the second phase B can be suppressed when Li is occluded. On the other hand, for example, when Mg is added, Si in the second phase B and a new alloy SiMg ₂ can be formed. SiMg ₂ can form an alloy with Li. Although SiMg ₂ has a smaller initial capacity than Si, the volume expansion during storage of Li is much smaller than that. Therefore, like SiC, although the initial capacity is slightly reduced, the cycle characteristics are considered to be improved.

The alloy of the negative electrode material according to the present invention comprises Al and N.
First phase A containing intermetallic compound containing i and Si
And a second phase B containing Al as a main component. The second phase B may be an elemental elemental phase B of Al, or may contain Si or Ni in addition to Al. However, it is desirable that the Al content in the second phase B be higher than the contents of other constituent elements.

The Al content in the first phase A is X _Al atom%, the Ni content in the first phase A is X _Ni atom%, and the Si content in the second phase B is Y. _{When Si} atomic% and the Ni content in the second phase B are Y _Ni atomic%, 35 ≦ X _Al
≦ 50, 30 ≦ X _Ni ≦ 40, 0 ≦ Y _Si ≦ 10, 0 ≦ Y _Ni
It is desirable to satisfy ≦ 5. Note that the first phase and the second
The compositional analysis of the phase can be performed using a transmission electron microscope (TEM).

The Al content X _Al in the first phase A is 35
If it is less than atomic%, the lattice constant of the first phase A becomes small, so that the diffusion path of Li deteriorates, and further, the lithium conductivity of the intermetallic compound decreases, and the discharge rate characteristic may deteriorate. On the other hand, when the Al content X _Al exceeds 50 atomic%, the crystallinity of the intermetallic compound of the first phase A is lowered, so that the volume expansion of the second phase B due to lithium occlusion / release can be suppressed. In addition, the lithium storage capacity of the first phase A is almost lost. A in the first phase A
The more preferable range of the 1 content X _Al is 36 ≦ X _Al ≦ 40
Is.

The Ni content X _{Ni in} the first phase A is 30.
When the amount is out of the range of 40 atomic%, the crystallinity of the intermetallic compound of the first phase A is deteriorated, and the volume expansion of the second phase B during lithium absorption cannot be suppressed, which causes deterioration of the cycle. is there. More preferable range is 33 ≦ X
_Ni ≦ 38.

The Si content Y _{Si in} the second phase B is 10
When it exceeds atomic%, although the initial capacity increases, the volume expansion during lithium occlusion becomes severe and the cycle life may decrease. A more preferable range of the Si content Y _Si in the second phase B is 0 ≦ Y _Si ≦ 7.

Further, since Ni is inactive to lithium, it is desirable that the Ni content Y _{Ni in} the second phase B is within the range of 5 atomic% or less. The second phase B
The more preferable range of the Ni content Y _Ni is 0 ≦ Y _Ni ≦
It is 5.

The first phase A containing the intermetallic compound containing Al, Ni and Si has almost no volume expansion during charging and discharging, specifically, the volume expansion change rate is 3% or less. Is preferred. The first phase A is preferably a NiSi ₂ phase having a fluorite type structure of CaF ₂ or a phase having a crystal structure similar to NiSi ₂ . The case where the first phase A is the NiSi ₂ phase will be described. In the negative electrode material according to the present invention, the second phase B mainly containing Al
Is considered to have contributed to the increase in charge / discharge capacity. On the other hand, the first phase A is composed of, for example, NiSi ₂ having a fluorite structure of CaF ₂ . First phase A
When the intermetallic compound (1) has a crystal structure equivalent to that of NiSi ₂ , Li diffusion inside the metal solid cannot be secured, and Li
Since neither occlusion nor release is performed, volume expansion hardly occurs during charge / discharge. Therefore, the first phase A can suppress the volume change during the Li insertion / release reaction of the second phase B.

The lattice constant of the NiSi ₂ phase is 5.406Å
This NiSi ₂ phase can suppress the volume change at the time of Li insertion / release reaction, but on the other hand, it tends to become a factor to inhibit Li diffusion of the entire system at the time of charge / discharge,
The rate characteristics of the secondary battery may be deteriorated. Therefore, it is desirable to replace the Ni site or a part of the Si site of the NiSi ₂ phase with Al so that the lattice constant is larger than that of NiSi ₂ . Specifically, the lattice constant of the intermetallic compound of the first phase A is preferably in the range of 5.45Å or more and 5.7Å or less. By setting the lattice constant to 5.45 Å or more, the lithium diffusion rate and the lithium conductivity of the negative electrode material can be increased, so that the rate characteristics of the secondary battery can be improved. On the other hand, when the lattice constant exceeds 5.7 Å, the amount of Al substitution at the Ni site or Si site of the NiSi ₂ phase increases, so that it becomes difficult to maintain the crystal structure of NiSi ₂ and the volume of the second phase B increases. The original purpose of suppressing expansion may not be achieved. Therefore, it is desirable that the lattice constant is within the range of 5.45Å or more and 5.7Å or less. First
A more preferable range of the lattice constant of the intermetallic compound of phase A is 5.5 Å or more and 5.65 Å or less.

The average crystal grain size of the first phase A containing the intermetallic compound containing Al, Ni and Si is 5 to 500 nm.
It is desirable to be within the range. The average crystal grain size is a photograph (for example, 100,000 times) obtained by TEM observation with the longest part of the crystal grain obtained in the transmission electron microscope (TEM) photograph as the crystal grain size, and 50 grains adjacent to each other. The crystal grain size of the crystal grains was measured and expressed as an average. If the average crystal grain size is less than 5 nm, the crystal grains are too fine, and it may be difficult to store Li and a high capacity may not be obtained. On the other hand, if the average crystal grain size exceeds 500 nm,
The cycle life may be shortened. A more preferable range of the average crystal grain size is 10 to 400 nm.

The second phase B mainly composed of Al preferably has an area ratio within the range of 1 to 50% when the total area of the alloy is 100%. This is for the reason explained below. When the area ratio is less than 1%, it may be difficult to store Li and a high capacity may not be obtained. On the other hand, when the area ratio exceeds 50%, the proportion of the first phase A relatively decreases, so that it is difficult to suppress the volume expansion, and the cycle characteristics may deteriorate. A more preferable range of the area ratio is 10 to 40%. The magnification of the TEM photograph for obtaining the average crystal grain size and the area ratio of the second phase B can be changed according to the size of the crystal grain to be measured.

At least some of the crystal grains of the first phase A containing the intermetallic compound containing Al, Ni and Si are isolated from each other and fill the gaps between the isolated crystal grains. As described above, it is desirable that the second phase B mainly containing Al is precipitated. With such a configuration, the second phase B can be constrained by the first phase A, so that the expansion and contraction of the second phase B due to lithium occlusion and release can be reduced. As a result, pulverization of the alloy can be suppressed, so that the cycle life of the secondary battery can be improved. However, when the crystal grains of the second phase B are isolated from each other and the first phase A is deposited so as to fill the space between the crystal grains, Li between the crystal grains of the second phase B is separated. Since a sufficient conduction path cannot be secured, there is a possibility that a high capacity cannot be obtained. In addition, it is difficult to reduce the volume expansion and contraction of the second phase B due to the lithium occlusion and release, which may lead to the pulverization of the alloy.

Next, the peak intensity ratio (β / α) will be described.

In the negative electrode material according to the present invention, a peak derived from Al is observed in the X-ray diffraction peak, and 2θ is 25 ° ≦ 2θ ≦ 30 ° and 45 ° ≦ 2θ ≦ 48.
° Each peak appears. Of course, other peaks may appear. If there is a peak other than the above,
The peak intensity is preferably 1/10 or less, and more preferably 1/50 or less of the peak having the maximum intensity among the peaks appearing at 45 ° ≦ 2θ ≦ 48 °.

The above α is the intensity of the peak having the maximum intensity among the peaks appearing when 2θ is 45 ° ≦ 2θ ≦ 48 ° in the X-ray diffraction pattern using CuKα rays. On the other hand, β is the intensity of the peak having the maximum intensity among the peaks in which 2θ is 25 ° ≦ 2θ ≦ 30 ° in the X-ray diffraction pattern using CuKα rays. When the negative electrode material according to the present invention contains a phase having a fluorspar structure, α is the intensity of the peak derived from the (111) plane of the fluorspar structure, and β is the fluorspar structure. It is the intensity of the peak derived from the (220) plane.

The peak intensity ratio (β / α) is preferably 0.6 or less. Peak intensity ratio (β / α) is 0.6
If it exceeds, the progress of pulverization of the negative electrode material is rapid and the cycle life of the secondary battery is reduced. Although the cycle life is improved as the peak intensity ratio is reduced, if the peak intensity ratio is less than 0.2, the crystallinity of the intermetallic compound of the first phase A is lowered and the initial capacity and the cycle are reduced. Both lifespan may be reduced. Peak intensity ratio (β
A more preferable range of / α) is 0.2 to 0.5.

The negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention is, for example, a single roll method, a twin roll method, a rotating disk method, a water atomizing method, a gas atomizing method, or the like. It is produced by the method. The rotating disk method, the water atomizing method, and the gas atomizing method are suitable for producing a spherical sample, and are effective when close packing of the material is required at the time of producing the negative electrode. It can also be manufactured by mechanical alloying or mechanical gliding.

The single roll method is a method in which a molten alloy prepared so as to have a predetermined composition is injected from a small nozzle hole onto a cooling body which rotates at a high speed, and is rapidly cooled. Here, the roll diameter and the roll width are not particularly limited, but when producing a large amount, a large amount of heat needs to be taken from the molten alloy, and a large heat capacity is a condition. Roll diameter is 300
The diameter is preferably at least mmφ, and more preferably at least 500 mmφ. The roll width is preferably wide for the same reason. The roll width is preferably 50 mm or more, more preferably 100 mm or more.

The cooling rate is mainly governed by the plate thickness of the sample obtained by rapid cooling, which is determined by manufacturing parameters such as nozzle hole diameter, molten metal injection pressure, roll peripheral speed, roll material, and roll-nozzle gap. Is. Nozzle hole diameter is 0.3
The range of 1 mm is preferable. When the nozzle hole diameter is less than 0.3 mm, it becomes difficult to inject the molten metal, while when the nozzle hole diameter exceeds 1 mm, it is easy to obtain a thick sample and it is difficult to obtain a sufficient cooling rate.

Although the roll peripheral speed depends on the material composition, it is mainly 2
Non-equilibrium phase at 0 to 60 m / s (non-equilibrium phase in forced solid solution,
Amorphous phase, quasi-crystalline phase, etc.) are facilitated.

The optimum material for the roll is determined by the wettability with the molten alloy, but the preferable material for the roll is Cu.
Base alloy (eg Cu, TiCu, ZrCu, BeC
u), an Fe-based alloy. 1-100 μm on roll surface
You may use what was Cr-plated and Ni-plated with the thickness of.

The gap between the roll and the nozzle is 0.2 to 10
The range of mm is preferable, but even if it exceeds 10 mm, there is no problem if the flow of the molten metal is a laminar flow. However, since a thicker sample can be obtained by widening the gap, widening the gap gradually slows the cooling rate.

The non-aqueous electrolyte secondary battery according to the present invention will be described below.

This non-aqueous electrolyte secondary battery comprises a positive electrode, a negative electrode containing the negative electrode material according to the present invention, and a non-aqueous electrolyte layer arranged between the positive electrode and the negative electrode.

1) Negative Electrode In this negative electrode, for example, the powder of the negative electrode material according to the present invention and a binder are kneaded in an organic solvent, the obtained suspension is applied to a current collector, and after drying, It is produced by pressing.

As the binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVD)
F), ethylene-propylene-diene copolymer (EPD
M), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) and the like can be used.

The mixing ratio of the powder of the negative electrode material and the binder is preferably 90 to 98% by weight of the negative electrode material and 1 to 10% by weight of the binder.

The current collector can be used without particular limitation as long as it is a conductive material. For example, copper, stainless steel,
Alternatively, a nickel foil, mesh, punched metal, lath metal, or the like can be used.

The sample prepared by the quenching method or mechanical alloying may be pulverized by a method such as a pin mill, a jet mill, a hammer mill, a ball mill, or at a temperature near the crystallization temperature of 0.1 to 0.1. It is also possible to pulverize after heat treatment for 24 hours.

2) Positive Electrode The positive electrode includes a current collector and a positive electrode active material-containing layer carried on one side or both sides of the current collector.

In this positive electrode, for example, a positive electrode active material, a conductive agent and a binder are suspended in a suitable solvent, and the obtained suspension is applied onto a current collector surface such as an aluminum foil and dried. It is produced by pressing.

The positive electrode active material can be used without any particular limitation as long as it can occlude an alkali metal at the time of discharging a battery and release the alkali metal at the time of charging.

Various oxides and sulfides can be mentioned, for example,
For example, manganese dioxide (MnO_Two), Lithium manganese compound
Compound oxide (eg LiMn_TwoO_FourOr LiMn
O_Two), Lithium nickel composite oxide (eg LiNi
O_Two), Lithium cobalt composite oxide (LiCo
O_Two), Lithium nickel cobalt composite oxide (eg
LiNi_{1- x}Co_xO_Two), Lithium manganese cobal
Complex oxide (eg LiMn_xCo _1-xO_Two),
Nadium oxide (eg V_TwoO₅) And the like.
In addition, conductive polymer materials, disulfide-based polymer materials
Organic materials such as materials are also included.

A more preferable positive electrode active material has a high battery voltage.
Lithium manganese composite oxide (LiMn_TwoO_Four),
Titanium nickel composite oxide (LiNiO_Two),lithium
Cobalt composite oxide (LiCoO_Two), Lithium nickel
Rucobalt composite oxide (LiNi_0.8Co
_0.2O_Two), Lithium manganese cobalt composite oxide
(LiMn _xCo_1-xO_Two) And the like.

As the current collector, any electrically conductive material can be used without particular limitation. Particularly, as the current collector for the positive electrode, it is preferable to use a material that is not easily oxidized during the battery reaction, such as aluminum. , Stainless steel, titanium, etc. may be used.

Examples of the conductive agent include acetylene black, carbon black, graphite and the like.

Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (P).
VdF), fluorocarbon rubber, and the like.

The compounding ratio of the positive electrode active material, the conductive agent, and the binder is 80 to 95 wt% of the positive electrode active material and 3 to 20 w of the conductive agent.
It is preferable that t% and the binder are in the range of 2 to 7 wt%.

3) Non-Aqueous Electrolyte Layer The non-aqueous electrolyte layer imparts ionic conductivity between the positive electrode and the negative electrode.

As the non-aqueous electrolyte layer, it is possible to use a non-aqueous electrolytic solution prepared by dissolving an electrolyte in a non-aqueous solvent in a separator made of a porous material.

The separator holds the non-aqueous electrolytic solution and insulates between the positive electrode and the negative electrode, is made of an insulating material, and has pores that enable ion transfer between the positive electrode and the negative electrode. There is no particular limitation as long as it can be used, and specific examples include synthetic resin non-woven fabrics, polyethylene porous films and polypropylene porous films.

The non-aqueous solvent is ethylene carbonate (E
A non-aqueous solvent mainly composed of a cyclic carbonate such as C) or propylene carbonate (PC) or a mixed solvent of these cyclic carbonate and a non-aqueous solvent having a viscosity lower than that of the cyclic carbonate can be used.

Examples of the low viscosity non-aqueous solvent include, for example:
Chain carbonate (eg, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, etc.), γ-butyrolactone, acetonitrile, methyl propionate, ethyl propionate, cyclic ether (eg, tetrahydrofuran, 2-methyltetrahydrofuran, etc.), chain ether ( For example, dimethoxyethane,
Diethoxyethane and the like).

A lithium salt is used as the electrolyte. Specifically, lithium hexafluorophosphate (LiP
F ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), and the like. . In particular, lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ) are preferred examples.

The amount of the electrolyte dissolved in the non-aqueous solvent is
It is preferably 0.5 to 2 mol / L.

It is also possible to use a gel-like body in which a non-aqueous electrolyte solution is contained in a polymer material for the non-aqueous electrolyte layer, and the electrolyte layer formed by the gel-like body alone is used as a positive electrode. It may be arranged between the negative electrode and the electrolyte layer in which the gel-like material is formed in the separator may be arranged between the positive electrode and the negative electrode.

Examples of the polymer material used for preparing the gel-like material include polymers of monomers such as polyacrylonitrile, polyacrylate, polyvinylidene fluoride (PVdF), polyethylene oxide (PECO) and others. And a copolymer with the above monomer.

It is also possible to dissolve the electrolyte in the polymer material and use the solidified solid polymer electrolyte as the non-aqueous electrolyte layer. Examples of the polymer material used for preparing the solid polymer electrolyte include a polymer of a monomer such as polyacrylonitrile, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), or other polymer. A copolymer is mentioned. Further, it is possible to use an inorganic solid electrolyte as the non-aqueous electrolyte layer. Examples of the inorganic solid electrolyte include a lithium-containing ceramic material. Specifically, Li
_{3 N, Li 3 PO 4 -Li} 2 S-SiS 2, LiI-L
such as i ₂ S-SiS ₂ glass and the like.

A cylindrical non-aqueous electrolyte secondary battery, which is an example of the non-aqueous electrolyte secondary battery according to the present invention, will be described with reference to FIG.

That is, the insulator 2 is arranged at the bottom of the bottomed cylindrical container 1 made of, for example, stainless steel. The electrode group 3 is housed in the container 1. The electrode group 3 has a structure in which a band-shaped material in which a positive electrode 4, a separator 5, a negative electrode 6 and a separator 5 are laminated is spirally wound so that the separator 5 is located outside.

The non-aqueous electrolyte is held in the electrode group 3. The insulating paper 7 having an opening at the center is arranged above the electrode group 3 in the container 1. The insulating sealing plate 8 is
The sealing plate 8 is arranged in the upper opening of the container 1 and the vicinity of the upper opening is caulked inward.
Is fixed to the container 1. The positive electrode terminal 9 is fitted in the center of the insulating sealing plate 8. One end of the positive electrode lead 10 is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9.

Next, a thin non-aqueous electrolyte secondary battery as another example of the non-aqueous electrolyte secondary battery according to the present invention will be described with reference to FIG. FIG. 2 is a partial cross-sectional view showing a thin non-aqueous electrolyte battery according to an embodiment of the present invention.

The container 11 surrounds the electrode group 12.
The electrode group 12 has a structure in which a laminate including a positive electrode, a negative electrode, and a separator is wound into a flat shape. The non-aqueous electrolyte is
It is held by the electrode group 12 in the container 11. One end of the strip-shaped positive electrode lead 13 is connected to the positive electrode current collector of the electrode group 12, and the other end thereof extends from the container 11. On the other hand, the strip-shaped negative electrode lead 14 has one end connected to the negative electrode current collector of the electrode group 12 and the other end extending from the container 11.

[0073]

Embodiments of the present invention will now be described in detail with reference to the drawings.

(Examples 1 to 25 and Comparative Examples 1 and 2) <Preparation of Negative Electrode Material> After mixing the respective elements in the ratios shown in Tables 1 and 2 and heating and melting, elements were formed into a ribbon by a single roll method. An alloy was prepared. That is, a molten alloy is injected from a nozzle hole of 0.5 to 2 mmφ onto a cooling roll (roll material: BeCu) that rotates at a peripheral speed of 1 to 50 m / s in an inert atmosphere, and is rapidly cooled to be thin. A band-shaped alloy was prepared.
The roll speed and nozzle holes were changed according to the alloy composition.

The obtained alloy was subjected to X-ray diffraction measurement using CuKα ray, and the intensity of the peak α having the maximum intensity among the peaks appearing at 2θ of 45 ° or more and 48 ° or less and 2θ of 25 °. As described above, the peak intensity ratio (β / α) calculated from the intensity of the peak β having the maximum intensity among the peaks appearing at 30 ° or less has the values shown in Table 1 below, and 25 and the alloys of Comparative Examples 1 and 2.

Here, the intensity of the peak α and the intensity of the peak β are the divergence slit of 1 deg or less, the scattering slit of 1 deg or less, and the light receiving slit of 0.15 mm in X-ray diffraction measurement using a vertical goniometer. Hereinafter, the peak top value observed when the scan speed was measured at 10 ° / min or less was used.

Regarding the alloys of Examples 1 to 25 and Comparative Examples 1 and 2, the peak position (2θ) having the maximum intensity in the X-ray diffraction pattern was determined, and the strongest peak was determined to be the peak derived from the cubic fluorite structure. The lattice constants under the assumption were calculated, and the results are shown in Tables 1 and 2 below.

The alloys of Examples 1 to 25 and Comparative Examples 1 and 2 were observed by a transmission electron microscope (TEM). As a result, the metallographic structures of the alloys were Al and S as shown in FIG.
In the crystal grains of the first phase A containing the intermetallic compound of i and Ni (the crystal grains shown by the diagonal lines in FIG. 3), although some of the crystal grains A are precipitated adjacently, most of the crystals are The grains A were isolated from each other. A second phase B mainly composed of Al is precipitated so as to fill the space between the isolated crystal grains A, and has a sea-island structure in which the first phase A is an island and the second phase B is the sea. I was able to confirm that. Figure 4
In addition, the transmission electron microscope (TE
M) Shows a photograph. In FIG. 4, the crystal grains that appear black are Al.
The crystal grains of the intermetallic compound phase of Si and Ni (first phase A), and the phase that appears light gray is the second phase B mainly composed of Al. Most of the crystal grains of the intermetallic compound phase A are isolated and precipitated, but some are in contact with each other.

With respect to the alloys of Examples 1 to 25 and Comparative Examples 1 and 2, the composition of the first phase A and the composition of the second phase B were analyzed by using a transmission electron microscope (TEM). The results are shown in Tables 1 and 2 below.

Cylindrical lithium ion secondary batteries were assembled by the methods described below using the alloys of Examples 1 to 25 and Comparative Examples 1 and 2, respectively.

<Preparation of Negative Electrode> Each of the alloys of Examples 1 to 25 and Comparative Examples 1 and 2 was cut and then pulverized by a jet mill to obtain an alloy powder having an average particle size of 50 μm.

94% by weight of each alloy powder, 3% by weight of graphite powder as a conductive material, 2% by weight of styrene-butadiene rubber as a binder resin, and 1% by weight of carboxymethylcellulose as an organic solvent were mixed with water. A suspension was prepared by dispersing. This suspension was applied to a copper foil having a film thickness of 18 μm, which is a current collector, dried, and then pressed to produce a negative electrode.

<Production of Positive Electrode> 91 wt% lithium cobalt oxide powder, 6 wt% graphite powder and 3 wt% polyvinylidene fluoride were mixed and dispersed in N-methyl-2-pyrrolidone to prepare a slurry. did.
This slurry was applied to an aluminum foil as a current collector, dried, and then pressed to produce a positive electrode.

<Assembly of Battery> A separator made of a polyethylene porous film was prepared, the separator was placed between a positive electrode and a negative electrode, and these were spirally wound to form an electrode group.

Further, lithium hexafluorophosphate as an electrolyte was dissolved in a mixed solvent of ethylene carbonate and methyl ethyl carbonate (volume ratio 1: 2) at 1 mol / liter to prepare a non-aqueous electrolytic solution.

The electrode group was housed in a bottomed cylindrical container made of stainless steel, and the bottomed cylindrical container was filled with a nonaqueous electrolytic solution to hold the nonaqueous electrolytic solution in the pores of the separator. A cylindrical lithium ion secondary battery having the structure shown in FIG. 1 was manufactured.

Comparative Example 3 A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 above, except that NiSi ₂ having a fluorite structure was used as the negative electrode material.

With respect to NiSi ₂ , X-ray diffraction measurement using CuKα ray was carried out to measure the lattice constant, the position of the peak having the maximum intensity (2θ) and the peak intensity ratio (β / α),
The results are also shown in Table 2 below. Further, the NiSi _2, was subjected to TEM observation, it was confirmed to consist of a single phase of NiSi ₂ phase. The results of composition analysis of the NiSi ₂ phase by TEM are shown in Table 2 below.

Comparative Example 4 As a negative electrode material, 3250 ° C.
Heat-treated mesophase pitch carbon fiber (average fiber diameter 10 μm, average fiber length 25 μm, average surface spacing d ₍₀₀₂₎
Of 0.3355 nm, BET specific surface area of 3 m ²
/ G) of the carbonaceous powder was used, and a cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 above.

(Comparative Example 5) As the negative electrode material, the average particle size was 1
A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that 0 μm Si powder was used.

(Comparative Example 6) As the negative electrode material, the average particle size was 1
A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that 0 μm of Al powder was used.

Obtained Examples 1 to 25 and Comparative Examples 1 to 6
Regarding the secondary battery of, the initial capacity by the method described below,
Measure the capacity retention rate and rate characteristics at the 100th cycle,
The results are shown in Tables 3 to 4 below.

<Initial capacity and capacity retention rate at 100th cycle> For each secondary battery, charging current was 1.5 A at 20 ° C.
After charging to 4.2V for 2 hours, the charging / discharging cycle of discharging 1.5V to 2.7V was repeated, and the discharge capacity per unit volume (mAh / cc) and 1
The capacity retention rate at the 00th cycle was measured, and the results are shown in Tables 3 and 4 below. The capacity retention rate at the 100th cycle is represented by the discharge capacity ratio at the 100th cycle when the discharge capacity at the 1st cycle is 1.

<Rate characteristics> For each secondary battery, 20
The battery was charged at a charging current of 1.5 A at 4.2 ° C. for 2 hours and then discharged to 2.7 V at 0.1 C, and the discharge capacity was measured to obtain a discharge capacity at 0.1 C. Also, 20
The battery was charged at a charging current of 1.5 A at 4.2 ° C. for 2 hours and then discharged to 2.7 V at 1 C, and the discharge capacity was measured to obtain the discharge capacity at 1 C. The discharge capacity ratio at 1C when the discharge capacity at 0.1 is 1 is shown in Tables 3 and 4 below as rate characteristics.

[0095]

[Table 1]

[0096]

[Table 2]

[0097]

[Table 3]

[0098]

[Table 4]

As is clear from Tables 1 to 4, when the compositions of the first phase A and the second phase B are compared with the lattice constant / strength ratio, the smaller the peak strength ratio, the first The proportion of Al in the phase A is large, while the lattice constant is small and the strength ratio is large, the Si occupied in the first phase A is large.
It can be seen that the ratio of is increasing.

As is clear from Tables 1 to 4, a negative electrode whose composition is represented by (Al _1-x Si _x ) _a Ni _b and whose peak intensity ratio (β / α) is 0.6 or less. It can be understood that the secondary batteries of Examples 1 to 25 containing the materials have an excellent balance between the capacity per unit volume, the capacity retention ratio at the 100th cycle, and the rate characteristics. The larger peak intensity ratio (β / α), the shorter the cycle life. It is considered that this is because the amount of Si in the second phase B is large and the volume expansion change is large during the Li insertion / release process.

Further, it is seen that as the lattice constant increases and the peak intensity ratio (β / α) decreases, the rate characteristics tend to be superior.

Although it cannot be clearly determined, the present inventors presume as follows. By increasing the lattice constant, the diffusion of Li in the intermetallic compound smoothly proceeds at the time of insertion, and it is considered that the rate characteristic is improved. Generally, when Al having a large atomic radius is substituted for Si or Ni, the lattice constant tends to increase regardless of any crystal phase. However, the lattice constant does not become so large simply by solidly dissolving Al in Si and Ni. In the case where the peak intensity ratio decreases like the negative electrode material in the present invention, Al is not simply replaced by Si or Ni but solid-dissolved in a specific crystallographic site of the intermetallic compound phase A. You should think that you are doing. As described above, the solid solution of Al in a specific crystallographic site causes the intermetallic compound phase A
It is believed that the lattice constant of can be further increased, and as a result, high rate characteristics can be realized.

On the other hand, in the secondary battery of Comparative Example 3, the lithium occlusion reaction did not occur and the charge / discharge characteristics could not be evaluated. It can be seen that the secondary battery of Comparative Example 4 using the carbonaceous material as the negative electrode material has excellent cycle characteristics, but the capacity per unit volume and rate characteristics are significantly lower than those of Examples 1 to 25. On the other hand, Si metal or Al
It can be seen that the secondary batteries of Comparative Examples 5 and 6 using the metal as the negative electrode material have excellent capacity per unit volume, but the cycle characteristics are significantly lower than those of Examples 1 to 25.

FIG. 5 shows X-ray diffraction patterns of the negative electrode material of Example 3 and the negative electrode material of Comparative Example 3. As is clear from FIG. 5, in the negative electrode material of Example 3, in the X-ray diffraction pattern, the (111) plane of the fluorite structure and the (22)
0) plane, (311) plane, (400) plane and (331) plane
A peak derived from the plane appears, and the lattice constant is comparative example 3.
It can be understood that the X-ray intensity ratio is lower than that of Comparative Example 3 because In the X-ray diffraction pattern of the negative electrode material of Example 3, 2θ is 25 to 30 ° and 45 to 48.
The peak appearing at ° originates from the intermetallic compound of the first phase A, and the peaks observed at 2θ around 38 °, around 45 °, and around 68 ° (indicated by black circles in FIG. 5) are A.
It is a peak derived from 1.

[0105]

As described in detail above, according to the present invention, a negative electrode material for a non-aqueous electrolyte secondary battery which simultaneously satisfies the initial capacity, cycle life and discharge rate characteristics, and a non-aqueous electrolyte comprising this negative electrode material. A secondary battery can be provided.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a cylindrical non-aqueous electrolyte secondary battery which is an example of a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a partial cross-sectional view showing a thin non-aqueous electrolyte secondary battery which is another example of the non-aqueous electrolyte secondary battery according to the present invention.

FIG. 3 is a schematic diagram showing a metallographic structure of negative electrode materials of Examples 1 to 25.

FIG. 4 is a transmission electron microscope (TEM) photograph of the negative electrode material of Example 3.

FIG. 5 shows X of the negative electrode material of Example 3 and the negative electrode material of Comparative Example 3.
The characteristic view which shows a line diffraction pattern.

[Explanation of symbols]

1 ... container, 3 ... electrode group, 4 ... Positive electrode, 5 ... Separator, 6 ... Negative electrode, 8 ... Seal plate, A ... First-phase crystal grains B ... Crystal grains of the second phase.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takao Sawa             8th Shinsugita Town, Isogo Ward, Yokohama City, Kanagawa Prefecture             Ceremony company Toshiba Yokohama office (72) Inventor Norio Takami             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center F-term (reference) 4K018 AA08 AA16 AB01 AB05 AC01                       BA02 BA04 BA08 KA38                 5H029 AJ02 AJ03 AJ05 AK02 AK03                       AK05 AK16 AL11 AM03 AM04                       AM05 AM07 BJ02 BJ04 BJ14                       CJ02 CJ03 CJ08 DJ17 HJ02                       HJ13                 5H050 AA02 AA07 AA08 BA17 CA02                       CA07 CA11 CA20 CB11 FA19                       GA02 GA03 GA10 HA02 HA13

Claims (4)

[Claims] 1. A composition of (Al _1-x Si _x ) _a Ni _b M _c (wherein M is C, Mg, Ca, Ti, V, Cr, M).
n, Fe, Co, Cu, Zn, Ga, Ge, La, Z
At least one element selected from the group consisting of r, W, Mo and Ba, and the atomic ratios a, b, c and x are a +
b = 100 atomic%, 60 ≦ a ≦ 90, 0 ≦ c ≦ 5, 0.
2 ≦ x ≦ 0.8), and an alloy satisfying the following formula (1) is included: a negative electrode material for a non-aqueous electrolyte secondary battery. (Β / α) ≦ 0.6 (1) where α is the intensity of the peak having the maximum intensity among the peaks appearing when 2θ is 45 ° ≦ 2θ ≦ 48 ° in the X-ray diffraction pattern using CuKα rays. And the above β
Is 2θ in an X-ray diffraction pattern using CuKα rays.
Is the intensity of the peak having the maximum intensity among the peaks appearing at 25 ° ≦ 2θ ≦ 30 °. 2. The alloy includes a first phase containing an intermetallic compound containing Al, Ni, and Si, and a second phase containing Al as a main component, and Al in the first phase is included. X _Al content
Atomic%, Ni content in the first phase is X _Ni atomic%, Si content in the second phase is Y _Si atomic%, Ni content in the second phase is Y _Ni atomic%. Then 35 ≦ X _Al ≦
50, 30 ≦ X _Ni ≦ 40, 0 ≦ Y _Si ≦ 10, 0 ≦ Y _Ni ≦
The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, which satisfies No. 5. 3. At least some of the crystal grains of the first phase are isolated from each other, and the second phase is precipitated so as to fill the spaces between the isolated crystal grains. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 2. 4. A non-aqueous electrolyte secondary battery comprising a negative electrode containing the negative electrode material according to claim 1, a positive electrode, and a non-aqueous electrolyte.