JPH06302315A - Electrode for nonaqueous electrolytic secondary battery and its manufacture - Google Patents

Abstract

PURPOSE:To provide an electrode which can provide nonaqueous electrolytic secondary battery excellent in charge/discharge cycle by at least containing active substance powder, which has reversibility to charge and discharge, and chemically and electrochemically inert whiskers. CONSTITUTION:An electrode contains at least active substance powder, which has reversibility to charge and discharge, and chemically and electrochemically inert whiskers. It is to be desired that this electrode active substance should be an object in which lithium can be inserted or broken away reversibly Moreover, the mixture contains a binder and constitutes a solid structure. The whisker is at least one kind being selected from among the group consisting of a silicon carbide whisker, silicon nitride whisker, a potassium titanate whisker, and an aluminum oxide whisker. Furthermore, the surface of the whisker is covered with at least on kind being selected from among the group consisting of carbon, nickel, copper, and stainless steel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in electrodes for non-aqueous electrolyte secondary batteries. More specifically, it relates to an improvement of an electrode containing a powder of an electrode material capable of reversibly inserting and releasing lithium.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using lithium as a negative electrode have high electromotive force and are expected to have higher energy density than conventional nickel-cadmium storage batteries and lead storage batteries, and many studies have been conducted. However, when metallic lithium is used for the negative electrode, a dendrite is generated during charging and a short circuit is likely to occur due to the dendrite, resulting in a battery with low reliability. In order to solve this problem, the use of an alloy negative electrode of lithium and aluminum or lead was studied. When these alloy negative electrodes are used, Li is occluded in the negative electrode alloy by charging, and dendrite is not generated, so that the battery has high reliability. However, since the discharge potential of the alloy negative electrode is about 0.5 V more noble than that of metallic Li, the voltage of the battery is also 0.5 V lower, which lowers the energy density of the battery.

[0003] On the other hand, researches using an intercalation compound of a carbon material such as graphite and Li as a negative electrode active material have been actively conducted. Also in this compound negative electrode, dendrite does not occur because Li enters the carbon layer during charging. Since the discharge potential is no more than about 0.1 V as compared with metallic Li, the decrease in battery voltage is small. This can be said to be a more preferable negative electrode. Usually, a carbonaceous material is obtained by decomposing an organic substance by heating at about 400 to 3000 ° C. in an inert atmosphere, carbonizing, and further graphitizing. The starting material of the carbonaceous material is almost always an organic substance, and by heating up to around 1500 ° C., which is a carbonization step, almost only carbon atoms remain and heating up to a high temperature near 3000 ° C. develops a graphite structure. As the organic raw material, pitch in the liquid phase, cortal, or a mixture of coke and pitch is used, and in the solid phase, a wood raw material,
Furan resin, Cellulose, Polyacrylonitrile, Ray
Yeon is used. In the gas phase, hydrocarbon gas such as methane and propane is used.

Up to now, so-called easily graphitizable carbon materials having a developed graphite structure obtained by firing petroleum pitch or the like as a starting material, generally at a high temperature of 2000 ° C. or higher, and furan resin, etc. A non-aqueous electrolyte secondary that absorbs and releases lithium from a so-called non-graphitizable carbon material having a turbostratic structure, which is obtained by firing a thermosetting resin as a starting material at a relatively low temperature of 2000 ° C. or less. Attempts have been made to use it as a negative electrode material for batteries.

On the other hand, MnO ₂ and TiS ₂ are often studied as the active material for the positive electrode. These positive electrode active materials have a potential with respect to Li of about 3 V, but more recently, LiMn ₂ O ₄ , LiNiO ₂ , and LiCoO ₂ are Li.
On the other hand, it has attracted attention as a positive electrode active material showing a charge / discharge potential near 4 V, and research and development have been very active, and some of them have been put into practical use. That is, efforts are being made to increase the battery voltage as well as the capacity as a means for obtaining a high energy density of the battery.

[0006]

As described above, there is a serious problem even when a carbon material such as graphite and an intercalation compound of Li are used as a negative electrode active material. That is, the capacity decreases as the charging and discharging are repeated. As a countermeasure against this,
It is also practiced to mix glass fiber coated with fibrous graphite or a carbon material into the negative electrode. These fibrous substances are generally produced by spinning a carbon precursor or a glass material, and the fiber diameter is relatively large at a minimum of about 6 μm and becomes bulky. Therefore, when these fibrous substances are mixed in the negative electrode, it is necessary to increase the amount of the binder in order to increase the strength of the electrode plate, which causes a problem such as a decrease in initial capacity. Further, when the amount of the binder is not increased in order to maintain the initial capacity, the electrode plate strength becomes weak and, as a result, the cycle characteristics become insufficient.

The same problem was encountered with the positive electrode. That is, one of the problems to be solved for the positive electrode is to prevent the capacity from decreasing due to charge / discharge. In order to solve this problem, many efforts have been made so far such as improvement of the positive electrode active material, examination of the electrolytic solution, and improvement of the separator. One of the causes of a decrease in discharge capacity when charging and discharging are repeated is that even in a compound capable of inserting and releasing lithium, such as the positive electrode active material described above, when deep charging and discharging are repeated, the active material becomes This means that miniaturization will occur. As the number of charge and discharge cycles increases, the phenomenon that the active material is miniaturized becomes remarkable, and as a result, the electrode collapses when the miniaturization is most advanced. Therefore, many ideas have been made for the binder. For example, fluororesins, rubber-based resins and polyolefins are preferably used.

However, even in this case, as a result of the expansion and contraction of the positive electrode active material due to the insertion and desorption of lithium, defective active material retention and poor current collection occur, and sufficient cycle characteristics cannot be obtained. Have As a countermeasure against this, it has been practiced to mix fibrous graphite or glass fiber coated with a carbon material as in the case of the negative electrode. As mentioned above, these fibrous materials are generally bulky. Similar to the case of the negative electrode, it is necessary to increase the amount of the binder to increase the strength of the electrode plate, which causes a problem such as a decrease in initial capacity. Further, when the amount of the binder is not increased in order to maintain the initial capacity, the electrode plate strength becomes weak and, as a result, the cycle characteristics become insufficient. The present invention solves the above-mentioned decrease in discharge capacity due to charge / discharge, that is, the problem of insufficient cycle characteristics, and provides an electrode that provides a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics. The purpose is to do.

[0009]

The electrode of the present invention is characterized by containing at least an active material powder having reversibility to charge and discharge and a whisker which is chemically and electrochemically inactive. . The electrode active material is preferably one that reversibly inserts and releases lithium. As such a negative electrode active material, there is a carbon material. On the other hand, as a positive electrode active material that reversibly inserts and releases lithium, Li is
CoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFeO ₂ ,
γ-type LiV ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , V
Those selected from ₂ O ₅ and V ₆ O ₁₃ are preferable.

The whiskers used in the electrode of the present invention include silicon carbide whiskers, silicon nitride whiskers,
At least one selected from the group consisting of potassium titanate whiskers and aluminum borate whiskers is preferable. More preferably, these whiskers have carbon coated on the surface thereof. The negative electrode may be coated with nickel, copper or stainless steel, and the positive electrode may be coated with titanium, aluminum or stainless steel. The mixing ratio of these whiskers is 0.5% by weight to 20% by weight of the electrode active material.
It is desirable to be equivalent to the weight%. The whisker has an average diameter of 0.1 to 3 μm and an average length of 3 to 50 μm.
It is preferably m.

The method for producing an electrode of the present invention comprises a step of mixing the above-mentioned whiskers with a raw material of an electrode active material and heating the mixture to produce an active material intimately mixed with the whiskers. It is characterized by

[0012]

According to the present invention, it is possible to obtain an electrode in which the capacity decrease with charge / discharge cycle is extremely small. It is considered that the improvement of the charge / discharge cycle characteristics according to the present invention is due to the whisker functioning to compensate the current collection failure due to the expansion and contraction of the active material during charge / discharge. Although the active material particles are in contact with each other during battery construction to ensure a good electrical contact state, crystal expansion and Li desorption during Li insertion (charge in negative electrode, discharge in positive electrode) are performed. It is speculated that the particles are separated due to repeated contraction during separation (discharge at the negative electrode, charge at the positive electrode), resulting in insufficient electrical contact.

The whiskers mixed with the active material play a role of suppressing a gap between the active material particles due to repeated expansion and contraction of the active material, in other words, maintaining a structure in which the initial internal state of the electrode is maintained. it is conceivable that. Further, when the surface of the whisker is coated with the above metal such as carbon or stainless steel, in addition to the above structure-maintaining action, a current collecting action is also performed, which is particularly effective for improving rapid charge / discharge cycle performance. Is. By using the electrode of the present invention, it is possible to obtain a non-aqueous electrolyte secondary battery having a high energy density and a decrease in capacity with charge / discharge cycles.

[0014]

EXAMPLE An electrode for a non-aqueous electrolyte secondary battery according to the present invention is
Preferably, it is composed of a mixture of an electrode active material powder capable of reversibly inserting and releasing lithium, a whisker and a binder, and a conductive agent added as necessary, and a conductive support. The mixture is pelletized by pressure molding, or is pelletized by pressure molding on a conductive support to be integrated with the support. In another embodiment, the mixture is made into a paste by adding a suitable medium, applied to a conductive support, dried and rolled to be integrally bonded to the support.

In the electrode constructed as a solid structure as described above, the whiskers are, as described above,
Demonstrate the structure maintenance function. As a result of various studies on the fibrous reinforcing material to be added to the electrode, the present inventors have found that the above-mentioned whiskers have appropriate strength and size as a reinforcing material for the electrode structure, and the capacity decreases with charge / discharge cycles of the electrode. It was found that the above can be effectively suppressed. If the whiskers are coated with the above-mentioned metal such as carbon or stainless steel as described above, the rapid charge / discharge characteristics of the electrode can be improved due to the conductivity of the coating layer.

As a method for coating the whisker with a metal such as carbon or stainless steel, a vapor phase method such as a CVD method known as a thin film forming method, a sputtering method or a deposition method in a solution is used. it can. Further, in order to obtain an intimate mixture of the active material and the whisker, a method of mixing a whisker with a raw material of the active material and heating the mixture to synthesize an active material in intimate contact with the whisker is adopted. Is preferred. As a raw material of the carbon material of the negative electrode active material, an organic substance which carbonizes by heating to give a carbon material, preferably petroleum pitch, coal tar, coke or a mixture thereof is used.

The positive electrode active material used in the present invention includes the following 3
Classified into species. (1) LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , Li
A lithium-containing composite oxide such as FeO ₂ or γ-type LiV ₂ O 5. (2) Metal oxides such as MnO ₂ , V ₂ O ₅ , and V ₆ O ₁₃ . (3) Sulfides such as TiS ₂ and MoS ₂ . Examples of the raw material of the composite oxide of (1) above include lithium oxides such as lithium oxides, carbonates, hydroxides, sulfates, nitrates, and chlorides, or lithium salts that give the same oxides by heating. , A metal forming a composite oxide together with lithium, for example, cobalt oxide, carbonate, hydroxide,
Cobalt oxides such as sulfates, nitrates and chlorides, or a combination with a salt that gives the same oxide by heating are used. As a raw material of the metal oxide of (2), a low order oxide, carbonate, hydroxide, sulfate, nitrate, chloride or the like of the corresponding metal is used. As the sulfide of (3), metallic titanium or molybdenum and sulfur are used, and the sulfide is synthesized by heating in vacuum.

Example 1 In this example, graphite was used as the negative electrode material. As whiskers to be mixed therein, silicon carbide whiskers, silicon nitride whiskers, potassium titanate whiskers, and aluminum borate whiskers were used. Each of these whiskers has an average diameter of 1 μm and an average length of 10 μm. Graphite powder 100g
On the other hand, 10 g of whiskers and 5 g of polyethylene powder as a binder were mixed to obtain a mixture. 0.1 g of this mixture is pressure-molded into a disk having a diameter of 17.5 mm to obtain an electrode according to the present invention.

FIG. 1 shows the construction of the test cell used to evaluate this electrode. Reference numeral 1 denotes the above electrode, which is arranged at the center of a stainless steel case 2. A separator 3 made of a microporous polypropylene film is arranged on the electrode 1. As the non-aqueous electrolytic solution, a mixed solution of 1 mol / 1 lithium perchlorate (LiClO ₄ ) dissolved in ethylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 1 is used. After injecting this electrolytic solution onto the separator, a disc-shaped metallic lithium plate 4 having a diameter of 17.5 mm is attached to the inside, and a stainless steel sealing plate 6 having a polypropylene gasket 5 on the outer peripheral portion is attached to the case 2. A test cell is constructed by combining and sealing.

As a comparative example, a cell using an electrode not mixed with a whisker, a cell using an electrode mixed with the same amount of fibrous graphite instead of the whisker, and carbon-coated glass fiber instead of the whisker. A cell using electrodes mixed with was prepared in the same manner as above. The fibrous graphite used here had an average diameter of 8 μm and an average length of 20 μm.
m, the carbon-coated glass fiber has an average diameter of 6 μm and an average length of 18 μm. For these test cells,
At a constant current of 0.8 mA, the electrode 1 is cathode-polarized (corresponding to charging when the electrode 1 is regarded as a negative electrode) until the voltage becomes 0 V with respect to the lithium counter electrode 4, and then the electrode 1 is opposed to the counter electrode 4. Anodic polarization (corresponding to discharge) was performed until the voltage reached 1.0V. The electrode characteristics were evaluated by repeating this cathode polarization and anode polarization. Table 1 shows the discharge capacity per 100 g of the electrode active material of the first cycle of each cell, that is, 100 g of graphite.
The discharge capacity at the cycle and the capacity retention rate at the 100th cycle are shown.

[0021]

[Table 1]

As is clear from Table 1, the discharge capacities in the first cycle are almost the same. However, as is clear from the comparison of the capacity retention ratios at the 100th cycle, the cell using the electrode to which the whisker was added has a much smaller capacity decrease due to repeated charging and discharging than the cell of the comparative example. Although graphite was used as the negative electrode material in this embodiment, it is needless to say that the same effect can be obtained as long as it is a carbon material or a graphite material having reversibility with respect to charge and discharge. As described above, the whiskers mixed with the active material serve to suppress the separation between the active material particles due to repeated expansion and contraction of the electrodes due to charge and discharge, in other words, to maintain the initial internal state of the electrodes. It seems to play a role. Moreover, since the diameter and length of the whiskers are smaller than those of carbon fibers, glass fibers, etc., the whiskers are easily dispersed efficiently in the spaces between the active material particles inside the electrodes. No problem occurs.

Example 2 Next, the mixing ratio of whiskers was examined in detail. Here, graphite was used as the negative electrode material, and potassium titanate whiskers having an average diameter of 1 μm and an average length of 10 μm were used as the whiskers. Table 2
As shown in, nine kinds of electrodes were prepared by adding whiskers from 0 g to 30 g to 100 g of graphite and 5 g of a binder. A test cell having the same configuration as that of Example 1 was prepared using these electrodes, and the electrodes were evaluated under the same charge and discharge conditions as in Example 1. Table 2 shows the discharge capacity per 1 g of the electrode active material at the first cycle, the discharge capacity at the 100th cycle, and 1
The capacity retention rate at the 00th cycle was shown.

[0024]

[Table 2]

Mixing about 0.5% by weight of whiskers with graphite has the effect of improving the capacity retention rate.
The capacity retention rate increases as the mixing ratio increases. However, when the mixing ratio exceeds 10% by weight, the capacity retention rate gradually increases, and when the mixing ratio exceeds 20% by weight, it hardly changes. Also, the initial discharge capacity decreases with increasing whisker-mixing ratio. From these results, the mixing ratio of whiskers was 0.5% by weight based on the graphite powder.
-20% by weight is suitable. As a whisker,
Similar results were obtained when silicon carbide whiskers, silicon nitride whiskers and aluminum borate whiskers were used.

[Embodiment 3] In this embodiment, graphite is used as a negative electrode material, and whiskers mixed with this are silicon carbide whiskers, silicon nitride whiskers and titanium nitride having an average diameter of 1 μm and an average length of 10 μm. The surface of each of the potassium acid whisker and the aluminum borate whisker coated with carbon was used. The carbon coating on the whiskers was performed by the CVD method. That is, the whiskers were put into a reaction furnace, and benzene was added to about 10 in an argon stream.
The mixture was heated to 00 ° C to generate carbon on the whisker surface. A test cell was prepared in the same manner as in Example 1, and each electrode was repeatedly subjected to cathodic polarization and anodic polarization at a constant current of 3 mA to evaluate the characteristics. This charging / discharging current of 3 mA is larger than 0.8 mA of Example 1 and Example 2, and the charging / discharging condition of this example is the rapid charging / discharging condition. Table 3 shows the characteristics of each cell.

[0027]

[Table 3]

Cell No. In Nos. 3.1 to 3.4, the capacity decrease due to charge and discharge was much smaller than that of the comparative cell (No. 3.5), and the cycle characteristics were excellent. A cell using an electrode mixed with whiskers not coated with carbon (No.
In No. 3.6), the capacity retention ratio is higher than that of the comparative cell (No. 3.5), and the effect of whisker mixing with the carbon material is recognized even in the rapid charge / discharge cycle test in this example. However, no. It is inferior to 3.1 to 3.4 and is insufficient from the viewpoint of practical application to batteries. As described above, by using the whiskers whose surface is coated with carbon, the rapid charge / discharge cycle performance can be improved. It is considered that this is because the action of collecting current was added to the structure maintaining action of the whiskers. In this example, the CVD method was used as the carbon coating method for the whiskers, but the same effect can be obtained by using another carbon thin film forming method, for example, a vapor phase method such as a sputtering method or a deposition method in a solution. Is obtained.

[Embodiment 4] In this embodiment, a whisker whose surface is coated with nickel, copper, stainless steel, or carbon was examined. Here, graphite was used as the negative electrode material, and potassium titanate whiskers having an average diameter of 1 μm and an average length of 10 μm were used as the whiskers. The whiskers were coated with nickel, copper, and stainless steel by vacuum deposition. That is, the whiskers were placed in a reaction furnace, and the whiskers were coated by heating the metal of the coating material with an electron beam. The carbon coating method is the same as in Example 3. A test cell was prepared in the same manner as in Example 1 and charged and discharged under the same conditions as in Example 3. Table 4 shows the discharge capacity per 1 g of electrode active material in the first cycle and 100
The discharge capacity and capacity retention rate at the cycle are shown.

[0030]

[Table 4]

Cell No. 4.1 to 4.4 are all 1
The discharge capacity at the first cycle and the capacity retention rate at the 100th cycle were the cell numbers of the comparative examples. The value is higher than that of 4.5. As a material for coating the whisker surface, nickel,
Copper, stainless steel and carbon are all preferred, with carbon being most preferred. Although the potassium titanate whisker has been described here, the silicon carbide whisker,
Silicon nitride whiskers, aluminum borate whiskers
The same result as above was obtained. Needless to say, the same result can be obtained by using another thin film forming method such as a vapor phase method such as a sputtering method or a precipitation method in a solution as a method of coating the whiskers with nickel or the like. .

[Example 5] The mixing ratio of whiskers was examined in detail. Here, graphite was used as the negative electrode material, and a silicon carbide whisker having an average diameter of 1 μm and an average length of 10 μm whose surface was coated with a carbon material was used as the whisker. As shown in Table 5, whiskers were added from 0 g to 30 g with respect to 100 g of graphite and 5 g of a binder.
Different types of electrodes were made. A test cell was prepared using these electrodes, and a charge / discharge test was performed under the same conditions as in Example 3. Table 5 shows the discharge capacity per 1 g of electrode active material in the first cycle and 1
The discharge capacity and capacity retention rate at the 00th cycle are shown.

[0033]

[Table 5]

Mixing about 0.1% by weight of whiskers with graphite has the effect of improving the capacity retention rate.
The capacity retention rate increases as the mixing ratio increases. However, when the mixing ratio exceeds 10% by weight, the capacity retention rate gradually increases, and when the mixing ratio exceeds 20% by weight, it hardly changes. Also, the initial discharge capacity decreases with increasing whisker-mixing ratio. From these results, the mixing ratio of whiskers was 0.5% by weight based on the graphite powder.
-20% by weight is suitable. As a whisker,
Similar results were obtained when potassium titanate whiskers, silicon nitride whiskers and aluminum borate whiskers were used instead of the silicon carbide whiskers.

Example 6 The diameter and length of whiskers were examined. Here, graphite is used as the negative electrode material,
An electrode was prepared by mixing 100 g of this with 10 g of potassium titanate whisker coated with carbon and 5 g of a binder. As the potassium titanate whiskers, those having various average diameters and average lengths as shown in Tables 6 and 7 were used. A test cell similar to that of Example 1 was prepared using these electrodes, and charged and discharged under the same conditions as in Example 3. Tables 6 and 7 show the discharge capacities and 1
The discharge capacity and capacity retention rate at the 00th cycle are shown.

[0036]

[Table 6]

[0037]

[Table 7]

Average diameter 0.1 to 3 μm, average length 3 to 5
The initial capacity is large when 0 μm whiskers are used,
Moreover, it can be seen that the capacity retention rate at the 100th cycle is high. In addition, instead of potassium titanate whiskers,
When silicon carbide whiskers, silicon nitride whiskers, and aluminum borate whiskers are used, whiskers having an average diameter of 0.1 to 3 μm and an average length of 3 to 50 μm are suitable as described above. Was confirmed.

[Embodiment 7] In this embodiment, whiskers are mixed with an organic material which is a raw material of a carbon material of a negative electrode active material, and the mixture is heated to carbonize the organic material to mix the whiskers. An example of obtaining the active material will be described. Here, petroleum pitch was used as the organic substance of the active material raw material, and potassium titanate whiskers having an average diameter of 1 μm and an average length of 10 μm were used as whiskers. First, 2% by weight of potassium titanate whisker was added to the organic substance and mixed well, and the mixture was heated in the range of 300 ° C to 1600 ° C as shown in Table 8. An electrode was obtained by mixing 5 g of the binder with 100 g of the carbon material in which the whiskers were mixed as obtained above and press molding. A test cell similar to that of Example 1 was prepared using these electrodes, and a charge / discharge test was performed under the same conditions as in Example 3. Table 8 shows the discharge capacity per 1 g of the electrode active material in the first cycle, the discharge capacity in the 100th cycle, and the capacity retention rate.

[0040]

[Table 8]

From these results, the heating temperature shows a large initial capacity and a high capacity retention rate after 100 cycles.
It can be seen that 00 ° C to 1400 ° C is desirable. In the comparative example (No. 7.9) in which no whiskers were added, the initial capacity was large, but the cycle capacity retention rate was extremely small. In addition, a comparative example (No.
7.10) showed high values for both the initial capacity and the cycle capacity retention rate, but No. It can be seen that the cells of 7.2 to 7.7 are more excellent in cycle performance. If the heating temperature is lower than 400 ° C, the carbonization of the organic matter is insufficient and the capacity is small. On the other hand, when the temperature is higher than 1400 ° C., the thermal decomposition of the whiskers remarkably progresses, so that the original function of maintaining the structure of the whiskers cannot be exhibited, and the capacity retention ratio is poor.

In the above examples, petroleum pitch was used as the organic substance of the active material raw material, but the same examination was made in the case of coal tar and coke. Further, the same examination was conducted when silicon carbide whiskers, silicon nitride whiskers, and aluminum borate whiskers were used instead of potassium titanate whiskers. As a result, in any case, the heating temperature is 400 ° C to 1400 ° C.
Was confirmed to be desirable. Further, even when the whiskers whose surface is coated with nickel, copper, stainless steel, or carbon are used, the same preferable capacity retention rate can be obtained.

[Embodiment 8] In this embodiment, a cylindrical battery having the structure shown in FIG. 2 was produced and its characteristics were examined. A battery was manufactured by the following procedure. LiMn _1.8 which is a positive electrode active material
Co _0.2 O ₄ was synthesized by mixing Li ₂ CO ₃ , Mn ₃ O _4, and CoCO ₃ in a predetermined molar ratio and heating at 900 ° C. To 100 g of this that was classified to 100 mesh or less, 10 g of carbon powder as a conductive agent, 8 g of an aqueous dispersion of polytetrafluoroethylene as a binder in resin content, and pure water were added to form a paste. It was applied to the core material of a titanium sheet, dried and rolled to obtain a positive electrode. On the other hand, 5 g of potassium titanate whiskers having an average diameter of 1 μm and an average length of 10 μm coated with carbon per 100 g of graphite powder as a negative electrode active material and polyvinylidene fluoride powder 7
g was added, and a paste was formed using dimethylformamide. This was applied to a nickel sheet core material, dried, and rolled to obtain a negative electrode.

Between the positive electrode plate 11 to which the positive electrode lead 14 of the same material as the core material is attached by spot welding and the negative electrode plate 12 to which the negative electrode lead 15 of the same material as the core material is attached by spot welding, the bipolar plate An electrode group is formed by interposing a separator 13 made of a wider band-shaped porous polypropylene film and spirally winding the whole. Insulating plates 16 and 17 made of polypropylene are respectively provided above and below this electrode group.
Is placed in the metal case 18 to form a step on the upper part of the case 18, and then an equal volume mixed solution of ethylene carbonate and 1,2-dimethoxyethane in which 1 mol / l of lithium perchlorate is dissolved. Is injected and the container is sealed with a polypropylene sealing plate 19 provided with a positive electrode terminal 20. The battery thus manufactured is designated as A. On the other hand, 10 g of polyvinylidene fluoride was added to 100 g of graphite powder and made into a paste using dimethylformamide. This was applied to a nickel core material, dried, and rolled to obtain a negative electrode containing no whiskers. A battery manufactured by the same method as above using this negative electrode and the above positive electrode is designated as B. Further, 5 g of fibrous graphite and 10 g of polyvinylidene fluoride were added to 100 g of graphite powder and made into a paste using dimethylformamide, which was applied to a nickel core material, dried and rolled to obtain a negative electrode. A battery manufactured in the same manner as above using this negative electrode and the above positive electrode is designated as C.

For these batteries, the charge / discharge current was 0.5.
A charge / discharge cycle test was performed at mA / cm ² and a charge / discharge voltage range of 4.3V to 3.0V. The result is shown in FIG. The capacity of the battery B was drastically decreased due to charge / discharge cycles, and was about half or less of the initial capacity after about 50 cycles. When this battery was disassembled, precipitation of lithium was observed on the entire surface of the negative electrode. Regarding the cycle performance of the battery C, the battery capacity is not lower than that of the battery B, but the battery capacity is smaller than that of the other two batteries. When Battery C was disassembled after 100 cycles, lithium was deposited on the surface of the negative electrode, although not as large as Battery B. On the other hand, the battery A of the present invention has a slightly smaller battery capacity than the battery B, but the cycle performance is very good, and the capacity after 100 cycles maintains 95% of the initial capacity. When this battery A was disassembled after 100 cycles, the lithium deposition on the negative electrode surface, which was found in the batteries B and C, was not observed. From these results, it can be seen that the battery using the negative electrode according to the present invention has extremely excellent cycle characteristics.

As described above, the present invention provides a battery having high discharge voltage, high capacity and excellent cycle characteristics. In the examples, as the positive electrode active material, Li
Was used Mn _1.8 Co _0.2 O _4, the negative electrode of the present invention, in addition, has a reversible relative _{LiCoO 2, LiNiO 2, LiFeO 2} , γ -type LiV ₂ O _5, etc. beginning with charging and discharging the It goes without saying that the same effect can be obtained when combined with the positive electrode. Further, although the cylindrical battery has been described in the embodiment, it is needless to say that the present invention is not limited to this structure because the technical ideas such as capacity increase according to the present invention are the same.

Example 9 In this example, a positive electrode using LiCoO ₂ as an active material was examined. As whiskers to be mixed therein, silicon carbide whiskers, silicon nitride whiskers, potassium titanate whiskers, and aluminum borate whiskers were used. Each of these whiskers has an average diameter of 1 μm and an average length of 10
μm. 100 g of LiCoO _{2 as the} positive electrode active material was mixed with 2.0 g of graphite as a conductive agent, 2.0 g of the above whiskers was added thereto, and further 3.0 g of polytetrafluoroethylene resin powder as a binder was mixed. It was used as a positive electrode mixture. 0.1 g of the positive electrode mixture was press-molded at a pressure of 1 ton / cm ² into a disk having a diameter of 17.5 mm to obtain a positive electrode.

The structure of the obtained battery is similar to that of the test cell shown in FIG. However, the above positive electrode is used for the electrode 1, and the electrode 4 has a diameter of 17.5 mm and a thickness of 0.3 mm.
Each of the negative electrodes made of the lithium plate was used. Further, as the electrolytic solution, a solution prepared by dissolving 1 mol / l of lithium perchlorate in an equal volume mixed solvent of propylene carbonate and 1,2-dimethoxyethane was used. Also, as a comparative example,
A battery using a positive electrode not mixed with whiskers and a battery using a positive electrode mixed with fibrous graphite or carbon-coated glass fibers instead of whiskers were also produced by the same method as described above.

With respect to the coin type battery manufactured as described above, the charging / discharging current was 0.5 mA, and the voltage range was from 4.2V to 3.V.
A charging / discharging cycle test was performed by performing constant current charging / discharging between 0V. Table 9 shows the initial discharge capacity, the discharge capacity at the 100th cycle, and the capacity retention rate. The number of samples n was 50 for each. The discharge capacity is 1 g of the positive electrode active material.
The value per hit is shown.

[0050]

[Table 9]

As shown in Table 9, the discharge capacity at the first cycle is the largest in the battery of Comparative Example 1 (No. 9.5), and that of Comparative Examples 2 and 3 (No. 9.6 to 9.7). The battery is the smallest. On the other hand, regarding the capacity maintenance ratio, the battery No. 9.1-
9.4 shows a much higher value than the comparative battery. As described above, it was found that the electrode to which the whiskers were added had a slight decrease in initial capacity, but the decrease in capacity with the subsequent charge / discharge cycle was very small. Although LiCoO _{2 was} used as the positive electrode active material in the examples, it goes without saying that the same effect can be obtained as long as it is a material having reversibility with respect to charge and discharge. As shown above, it is considered that the whiskers act to suppress the separation between the active material particles due to repeated expansion and contraction, in other words, to play a role of maintaining the structure in which the initial state inside the electrode is maintained.

[Example 10] The mixing ratio of whiskers was examined. Here, TiS ₂ is used as the positive electrode active material, and the whiskers have an average diameter of 1 μm and an average length of 10 μm.
A μm potassium titanate whisker was used. As shown in Table 10, 9 types of electrodes were prepared by adding whiskers from 0 g to 30 g to 100 g of TiS ₂ , 2.0 g of graphite and 3.0 g of a binder. The method for producing the test battery is the same as in Example 9. The conditions of the charge / discharge cycle test in this example are as follows: charge / discharge current 0.5 mA, voltage range 2.
It was set between 5V and 1.5V. Table 10 shows the discharge capacity per 1 g of the electrode active material at the first cycle, the discharge capacity at the 100th cycle, and the capacity retention rate.

[0053]

[Table 10]

Mixing about 0.5% by weight of whiskers with respect to the positive electrode active material has the effect of improving the capacity retention rate, and the capacity retention rate increases as the mixing rate increases.
However, when the mixing ratio exceeds 10% by weight, the capacity retention rate gradually increases, and when the mixing ratio exceeds 20% by weight, it hardly changes. Also, the initial capacity decreases with increasing whisker-mix ratio. From these results, the mixing ratio of whiskers was 0.5% by weight with respect to the positive electrode active material.
-20% by weight is suitable. As a whisker,
It was also confirmed that when using silicon carbide whiskers, silicon nitride whiskers, or aluminum borate whiskers, the mixing ratio with respect to the positive electrode active material is appropriately 0.5% by weight to 20% by weight.

[Embodiment 11] In this embodiment, LiMn ₂ O ₄ is used as a positive electrode active material, and a whisker mixed with this is used.
As a result, a silicon carbide whisker having an average diameter of 1 μm and an average length of 10 μm, a silicon nitride whisker, a potassium titanate whisker, and an aluminum borate whisker each having a surface coated with carbon was examined. In addition, as comparative examples, those not mixed with whiskers and those mixed with potassium titanate whiskers whose surface was not coated with carbon were used. In order to study the characteristics of each of these positive electrodes, a test battery was prepared in the same manner as in Example 9, and a test was performed in which the battery was charged and discharged at a constant current of 3 mA in a voltage range of 4.3 V to 3.0 V. The charging / discharging condition in this example is a rapid charging / discharging condition in which the current is larger than 0.5 mA in Examples 9 and 10. Table 11 shows the result of the charge / discharge test.

[0056]

[Table 11]

Battery No. 11.1 to 11.4 have much less capacity decrease due to charge and discharge than the comparative battery, and have excellent cycle characteristics. Comparative Example Battery No. 11.6
No. The capacity retention rate is higher than that of 11.5, and the effect of whisker mixing with the positive electrode is recognized even in the above rapid charge / discharge cycle test. However, no.
It is inferior to 11.1 to 11.4 and is insufficient from the viewpoint of practical application to batteries. As described above, by using the whiskers whose surface is coated with carbon, the rapid charge / discharge cycle performance can be improved. It is considered that this is because the action of collecting current was added to the structure maintaining action of the whiskers.

[Embodiment 12] In this embodiment, a whisker whose surface was coated with titanium, aluminum, stainless steel, or carbon was examined. Here, LiCoO ₂ was used as the positive electrode active material, and potassium titanate whiskers having an average diameter of 1 μm and an average length of 10 μm were used as whiskers. The whisker was coated with titanium, aluminum, and stainless steel by the same vacuum deposition method as in Example 4. The carbon coating method is the same as in Example 3. A test battery was prepared in the same manner as in Example 9,
Charging and discharging were performed under the same conditions as in Example 11. Table 12 shows the discharge capacity per 1 g of the electrode active material at the first cycle, the discharge capacity at the 100th cycle, and the capacity retention rate.

[0059]

[Table 12]

Battery No. In all of Nos. 12.1 to 12.4, the discharge capacity at the first cycle and the capacity retention rate at the 100th cycle were battery Nos. The value is higher than that of 12.5. From the above results, as the material for coating the whisker surface, titanium, aluminum, stainless steel,
Carbon is preferable, but carbon is most preferable. Although the potassium titanate whiskers have been described here, the same results as above can be obtained for silicon carbide whiskers, silicon nitride whiskers, and aluminum borate whiskers.

[Example 13] The mixing ratio of whiskers was examined in detail. Here, as the positive electrode active material, Li
Using NiO ₂ , a silicon carbide whisker having an average diameter of 1 μm and an average length of 10 μm, the surface of which was covered with a carbon material, was used as a whisker. As shown in Table 13, nine kinds of electrodes were produced by adding whiskers from 0 g to 30 g to 100 g of LiNiO _{2 as} a positive electrode active material, 2.0 g of graphite and 3.0 g of a binder. A test battery was produced using these electrodes and charged and discharged under the same conditions as in Example 11.
Table 13 shows the discharge capacity per 1 g of the electrode active material in the first cycle, the discharge capacity in the 100th cycle, and the capacity retention rate.

[0062]

[Table 13]

Mixing about 0.1% by weight of whiskers with respect to the positive electrode active material has the effect of improving the capacity retention rate, and the capacity retention rate increases as the mixing rate increases.
However, when the mixing ratio exceeds 10% by weight, the capacity retention rate gradually increases, and when the mixing ratio exceeds 20% by weight, it hardly changes. Also, the initial capacity decreases with increasing whisker-mix ratio. From these results, the mixing ratio of whiskers was 0.5% by weight with respect to the positive electrode active material.
-20% by weight is suitable. As a whisker,
Similar results were obtained when potassium titanate whiskers, silicon nitride whiskers and aluminum borate whiskers were used instead of the silicon carbide whiskers.

Example 14 The diameter and length of whiskers were examined. Here, LiCo is used as the positive electrode active material.
O ₂ was used, and 100 g thereof was mixed with 2.0 g of graphite, 2.0 g of carbon-coated potassium titanate whiskers and 3.0 g of a binder to prepare a positive electrode. As the potassium titanate whiskers, those having various average diameters and average lengths were used as shown in Tables 14 and 15. A test battery similar to that of Example 9 was produced using these positive electrodes, and charged and discharged under the same conditions as in Example 9. Tables 14 and 15 show the discharge capacity per 1 g of the electrode active material in the first cycle, the discharge capacity in the 100th cycle, and the capacity retention rate.

[0065]

[Table 14]

[0066]

[Table 15]

From these results, the initial capacity is large and 1
It can be seen that the high value of the capacity retention ratio after 00 cycles is obtained when the whiskers having an average diameter of 0.1 to 3 μm and an average length of 3 to 50 μm are used. Instead of potassium titanate whiskers, silicon carbide whiskers,
Silicon nitride whiskers, aluminum borate whiskers
When using, the diameter is 0.1 to 3μ as in the above.
It was confirmed that a whisker having a length of m and a length of 3 to 50 μm is suitable.

[Embodiment 15] In this embodiment, a cylindrical battery having the structure shown in FIG. 2 was produced and its characteristics were examined. 100 g of LiCoO _{2 as a} positive electrode active material, 2.0 g of acetylene black as a conductive agent, 2.0 g of carbon-coated whisker having an average diameter of 1 μm and an average length of 10 μm, and polytetrafluoride as a binder. 4.0 g of an aqueous dispersion of ethylene as a resin component and pure water were added to form a paste, which was applied to a core material of a titanium sheet, dried and rolled to obtain a positive electrode.
On the other hand, the negative electrode was obtained by pressure-bonding metallic lithium onto a nickel sheet core material. Example 8 except that the above positive electrode and negative electrode were used
A cylindrical battery as shown in FIG. 2 was obtained in the same manner as in. Let this battery be a. As a comparative example, a battery using a positive electrode in which whiskers are not mixed is designated as b, and a battery using a positive electrode in which fibrous graphite is mixed instead of whiskers is designated as c.

For these batteries, the charge / discharge current was 0.5.
A charge / discharge cycle test was performed at mA / cm ² and a charge / discharge voltage range of 4.2V to 3.0V. The result is shown in FIG. The capacity of the battery b was drastically reduced due to charge / discharge cycles, and was about half or less of the initial capacity after about 50 cycles. Also,
Regarding the cycle performance of the battery c, the battery capacity is smaller than that of the other two batteries, although the capacity is not reduced as much as that of the battery b. On the other hand, the battery a using the positive electrode according to the present invention
Although the battery capacity is slightly smaller than that of the battery b, the cycle performance is very good, and the capacity after 100 cycles maintains 98% of the initial capacity. As described above, the present invention provides a battery having high discharge voltage, high capacity, and excellent cycle characteristics. Although LiCoO ₂ was used as the positive electrode active material in the examples, the same effect can be obtained even when the present invention is applied when another positive electrode active material having reversibility for charge and discharge is used. Needless to say.

[Embodiment 16] In this embodiment, an example of obtaining a whisker-mixed active material by mixing whiskers with the starting material in advance during the synthesis of the positive electrode active material and heating the mixture is described. To do. Here, LiMn ₂ O ₄ was selected as the positive electrode active material. As the whiskers, potassium titanate whiskers having an average diameter of 1 μm and an average length of 10 μm were used. Li ₂ CO ₃ and MnO ₂ which are raw materials of the positive electrode active material LiMn ₂ O ₄ were sufficiently mixed in a predetermined stoichiometric ratio, and 5 wt% of potassium titanate whiskers was added to the mixture, and the mixture was sufficiently mixed. Mixed. Table 16
It heated on each temperature condition shown in. Further, this was classified into 100 mesh or less. The above whiskers were mixed in advance with 100 g of the positive electrode active material, and 2.0 g of graphite and 3.0 g of polytetrafluoroethylene powder were mixed to obtain a positive electrode mixture. The diameter 17 of the cathode mixture at a pressure 1 ton / cm ^2.
A 5 mm disc was press-molded to obtain a positive electrode. A test battery similar to that of Example 9 was produced using these positive electrodes, and a charge / discharge test was performed under the same conditions as in Example 9. Table 16 shows the discharge capacity per 1 g of the electrode active material in the first cycle, the discharge capacity in the 100th cycle, and the capacity retention rate.

[0071]

[Table 16]

From this result, the heating temperature shows a large initial capacity and a high capacity retention ratio after 100 cycles.
It can be seen that 00 ° C to 1400 ° C is desirable. The comparative example (No. 16.9) in which no whiskers were added had a large initial capacity, but the capacity retention rate at the 100th cycle was extremely small.
Further, the comparative example (No. 16.10) in which whiskers were added to the finished active material showed high values for both the initial capacity and the cycle capacity retention rate, but the battery of this example, for example, No. 16. It can be seen that 16.2 to 16.7 are more excellent in cycleability. When the heating temperature is lower than 400 ° C, the crystal structure of the positive electrode active material is insufficiently developed and the capacity is small. On the other hand, when the temperature is higher than 1400 ° C., the thermal decomposition of the whisker material remarkably progresses, and the original function of maintaining the structure of the whisker cannot be exhibited, resulting in a poor capacity retention rate.

Similar investigations were carried out when silicon carbide whiskers, silicon nitride whiskers and aluminum borate whiskers were used as whiskers.
As a result, in any case, the heating temperature is 400 ° C to 140 ° C.
It was confirmed that 0 ° C. is desirable. Further, even if the whiskers whose surface is coated with titanium, aluminum, stainless steel or carbon are used, the same preferable capacity retention rate can be obtained. In Examples 9 to 16 above, metallic lithium was used as the negative electrode to be combined, but it goes without saying that the same effect can be obtained as long as the negative electrode can be reversibly charged and discharged. For example, as the active material of such a negative electrode, a carbon material, a graphite material, a metal oxide and the like can be mentioned.

In the above examples, the present invention was applied to one electrode and the performance as a negative electrode or a positive electrode was examined. However, it is preferable that the negative electrode and the positive electrode according to the present invention are combined to form a battery. Needless to say. Further, in the above examples, a specific electrolytic solution was used, but as a solute, lithium perchlorate, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium borofluoride, etc., as a solvent, propylene carbonate, ethylene carbonate. It is possible to use a non-aqueous electrolytic solution containing a lithium salt that is well known in this field, such as carbonates, gamma-butyrolactone, esters such as methyl acetate, and electrolytes using ethers such as dimethoxyethane and tetrahydrofuran. it can.

[0075]

As described above, the electrode of the present invention contains a whisker that exerts a structure-maintaining function. Therefore, the capacity is less likely to decrease with charge and discharge, has a high energy density, and has excellent cycle characteristics. Provide an electrolyte secondary battery. Also,
When the whiskers are coated with carbon, stainless steel, or the like, the rapid charge / discharge characteristics of the electrodes can be improved.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a test cell used in an example of the present invention.

FIG. 2 is a vertical cross-sectional view of a non-aqueous electrolyte secondary battery according to an example of the present invention.

FIG. 3 is a diagram showing cycle characteristics of a battery of an example of the present invention and a battery of a comparative example.

FIG. 4 is a diagram showing cycle characteristics of a battery of an example of the present invention and a battery of a comparative example.

[Explanation of symbols]

 1 Test electrode or positive electrode 2 Case 3 Separator 4 Metal Li or negative electrode 5 Gasket 6 Sealing plate 11 Positive electrode 12 Negative electrode 13 Separator 14 Positive electrode lead plate 15 Negative electrode lead plate 16 Upper insulating plate 17 Lower insulating plate 18 Battery case 19 Sealing plate 20 Positive electrode terminal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Ito 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor, Toyokuchi ▲ Yoshi ▼ 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. In the company

Claims (8)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a mixture containing at least active material powder having reversibility for charge and discharge and a chemically and electrochemically inactive whisker. electrode. 2. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the active material is a material that reversibly inserts and releases lithium. 3. The electrode for a non-aqueous electrolyte secondary battery according to claim 2, wherein the mixture contains a binder to form a solid structure. 4. The whisker is at least one selected from the group consisting of silicon carbide whiskers, silicon nitride whiskers, potassium titanate whiskers, and aluminum borate whiskers. Electrode for water electrolyte secondary battery. 5. The whisker is at least one selected from the group consisting of silicon carbide whiskers, silicon nitride whiskers, potassium titanate whiskers, and aluminum borate whiskers, and the whiskers.
The negative electrode for a non-aqueous electrolyte secondary battery according to claim 3, wherein the surface of the negative electrode is coated with at least one selected from the group consisting of carbon, nickel, copper and stainless steel. 6. The whisker is at least one selected from the group consisting of silicon carbide whiskers, silicon nitride whiskers, potassium titanate whiskers, and aluminum borate whiskers, and the surface thereof is carbon. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 3, which is coated with at least one selected from the group consisting of titanium, aluminum, and stainless steel. 7. A non-aqueous electrolyte secondary having a step of mixing a chemically and electrochemically inactive whisker with an organic substance carbonized by heating and heating the mixture to carbonize or graphitize the organic substance. Manufacturing method of negative electrode for battery. 8. A non-aqueous electrolyte secondary battery having a step of synthesizing an active material by previously mixing chemically and electrochemically inactive whiskers at the time of synthesizing a positive electrode active material and heating the mixture. Positive electrode manufacturing method.