CN1091547C - Lithium battery - Google Patents

Abstract

The invention discloses a lithium battery, comprising (1) electrolyte containing borides; (2) oxides of rare earth elements used at least in battery electrode materials; (3) borides used at least in positive electrode materials; (4) ) The electrolyte contains a dehydrating agent; or (5) The part of the battery that is in contact with the electrolyte is covered with an acid-resistant thermoplastic resin, which provides a solution that can inhibit the decomposition and deterioration of the electrolyte caused by the presence of moisture, and increase the number of charge and discharge times with high capacity. long life lithium battery.

Description

lithium battery

The invention relates to lithium batteries, especially lithium accumulators.

In recent years, nonaqueous electrolyte batteries have attracted attention as high energy density batteries. In non-aqueous electrolyte batteries, light metals such as lithium, sodium, and aluminum are used as the negative active material, and manganese dioxide, carbon fluoride [(-CF _x ) _n ], thionyl chloride, etc. are used as the positive active material. , It has been used as a supporting battery for microcomputers, clock power supplies and memories.

In recent years, with the miniaturization and weight reduction of various electronic equipment such as video recorders (VTRs) and communication equipment, there is a higher demand for high-energy-density batteries as their power sources, and research on non-aqueous electrolyte batteries has become more active. For example, the use of propylene carbonate, 1,2-dimethoxyethane, γ-butyrolactone, tetrahydrofuran and other non-aqueous solvents as electrolytes is being studied to dissolve LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ and other electrolytes non-aqueous electrolyte batteries. In addition, compounds that locally chemically react with lithium, mainly TiS ₂ , MoS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , etc., as the positive electrode active material have also been studied.

However, the above storage batteries using LiCoO ₂ as a positive electrode material are now in practical use, but the others are not yet in practical use. The main reason is that the charging and discharging efficiency is low, and the life of the charging and discharging cycle (cycle) is short. The reason for this is that lithium deteriorates greatly due to the reaction between lithium as the positive electrode and the electrolyte solution. That is, lithium dissolved in the electrolytic solution as lithium ions during discharge reacts with the solvent when it is precipitated during charge, thereby deactivating a part of its surface. For this reason, through repeated charging and discharging, dendritic lithium is generated, or spherical lithium is precipitated and detached from the current collector.

On the other hand, US Pat. No. 4,668,595 and US Pat. No. 4,702,977 describe the use of a carbon material that absorbs/releases lithium as a negative electrode incorporated in a nonaqueous electrolyte storage battery. In addition, the aforementioned US Patent No. 4,668,595 describes that, as the non-aqueous solvent constituting the non-aqueous electrolytic solution, in addition to the aforementioned non-aqueous solvents, diethoxyethane, ethylene carbonate or a mixture thereof is used.

However, in the lithium battery composed of the aforementioned non-aqueous electrolyte solution, when even a small amount of water exists, the electrolyte decomposes to generate acidic substances, etc., and as a result, dissolves and corrodes metals in contact with the electrolyte solution, such as the container of the lithium battery. part, causing the disadvantage of hindering the effect of lithium in the electrolyte.

It is an object of the present invention to provide a lithium battery that suppresses the decomposition of an electrolyte solution due to water content to prevent its deterioration while normalizing the action of lithium, thereby improving the charge-discharge cycle life on a high-capacity basis.

According to an embodiment of the present invention, in a lithium battery composed of an electrolyte containing at least one selected from fluoride and chloride, and a positive electrode and a negative electrode immersed in the electrolyte, the positive electrode contains boride.

With such a structure, it is possible to provide a lithium secondary battery capable of suppressing decomposition and deterioration of the electrolytic solution due to moisture content and having a high capacity and a long life for the number of charge and discharge cycles.

Such effects can be expected even if oxides and borides of rare earth elements are added to the negative electrode material and not added to the positive electrode material. However, from the viewpoint of improving the charge-discharge cycle life, it is necessary to use these additives at least in the positive electrode material. The reasons for these additives can be easily understood from the mechanisms of the effects of these additives as described below.

That is, as an electrolyte, if lithium hexafluorophosphate (LiPF ₆ ) is used, the following reactions will first occur due to the inclusion of water.

[Formula 1]

The hydrofluoric acid generated here corrodes the inner surface of the metal container by the following reaction.

FeF ₂ is ionized according to the following formula, which hinders the charge and discharge function caused by the transfer and reception of lithium ions.

Oxides or borides of rare earth elements actually react with fluoride ions to produce hydrofluoric acid generated by containing water, for example, BF ₃ and YF ₃ . Since these products are not ionized, they do not hinder the charging and discharging function as described above.

Considering the above facts, it becomes clear that adding borides and oxides of rare earth elements to the positive electrode where a large amount of fluoride ions as anions accumulate is the most effective.

Fig. 1 shows a partial front sectional view of a lithium battery related to the present invention.

Fig. 2 shows a partial front sectional view of another lithium battery related to the present invention.

Fig. 3 is a characteristic diagram showing the relationship between the number of times of charging and discharging and the charging capacity of the lithium battery related to the present invention.

Fig. 4 is a characteristic diagram showing the relationship between the number of times of charge and discharge and the charge capacity of another example of the lithium battery related to the present invention.

Fig. 5 is a characteristic diagram showing the relationship between the number of times of charge and discharge and the charge capacity of another example of the lithium battery related to the present invention.

A specific example of the lithium battery of the present invention will be described with reference to FIG. 1 .

The bottomed cylindrical container 1 is provided with an insulator 2 at the bottom thereof. The electrode group 3 is housed in the container 1 . The structure of the electrode group 3 is that a strip formed by laminating the positive electrode 4 , the separator 5 , and the negative electrode 6 in this order is rolled into a spiral shape with the negative electrode 6 positioned outside. Container 1 is filled with non-aqueous electrolytic solution. The insulating paper 7 with an opening in the center is placed above the electrode group 3 in the container 1 . The insulating sealing plate 8 is disposed on the upper opening of the container 1, and by squeezing the vicinity of the upper opening toward the inside, the sealing plate 8 is fixed liquid-tightly on the container 1, and the positive terminal 9 is fitted into the insulating sealing. In the center of plate 8 , one end of positive electrode lead 10 is connected to positive electrode 4 , and the other end is connected to positive electrode terminal 9 . The negative electrode 6 is connected to the container 1 as a negative terminal through a negative electrode lead (not shown).

In the above-mentioned positive electrode 4, as the positive electrode of the lithium storage battery, commonly used materials can be suggested, for example, a compound containing lithium and an oxygen group element capable of local chemical changes with lithium can be used as an active material. The oxygen-group element compound includes, for example, TiS ₂ , MoS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , CoO ₂ , MnO ₂ , NiO, NbSe ₃ , and the like.

Moreover, in addition to the above-mentioned active materials, it is preferable to use conductive materials such as carbonaceous materials, binders such as fluororesins and polyolefin resins in the positive electrode, and adopt arbitrary shapes such as film, fiber, and powder for different purposes. Especially in the case of powder, the active material can be molded into any shape and used. As far as the molding method is concerned, it is generally a method of mixing the active material with a powdery binder such as polytetrafluoroethylene powder, polyethylene powder, and compression molding.

In the aforementioned negative electrode 6, an active material having a function of absorbing and releasing lithium is used. As the active material, carbonaceous material is mentioned. In addition, it is preferable to use a binder such as polyolefin resin, fluororesin, etc. for the negative electrode.

The non-aqueous electrolytic solution accommodated in the aforementioned container 1 is composed of at least one electrolyte selected from fluorides and chlorides and a non-aqueous solvent.

Examples of the electrolyte include fluorine-containing lithium compounds such as lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluorometasulfate (LiCF ₃ SO ₃ ), and peroxides. Lithium chlorate (LiClO ₄ ), etc., but because of the fluorine-containing lithium compound in them, it is difficult to oxidize and decompose when overfilled, so it is desirable, especially because LiPF ₆ has high conductivity per mol, it is the most suitable OK

As the nonaqueous solvent, organic propylene carbonate, ethylene carbonate, tetrahydrofuran γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, and the like are used. A mixture of these media can be used, and the mixing ratio can be arbitrarily determined.

A lithium battery formed in such a structure can perform the following charge and discharge. First, the positive electrode undergoes the following reaction. Turn to the right when charging, and react to the left when discharging.

[Formula 2]

Next, the negative electrode can carry out the following reactions. Here too, the charging time is to the right, and the discharge is to the left.

Taken together, the reaction shown to proceed throughout the cell is as follows.

[Formula 3]

Non-aqueous batteries have always been excellent for their high energy density, small size and light weight. However, compared with aqueous batteries, their output characteristics have shortcomings, and they have not yet reached the level of widespread application. Especially in the field of storage batteries that require output characteristics, this shortcoming is one of the reasons that hinder their practical application.

In the case of an aqueous electrolyte, the ionic conductivity is high, and in the case of a non-aqueous electrolyte, the ionic conductivity is generally low, which causes the output characteristics of the non-aqueous battery to be inferior.

As a method to solve this problem, it is the best method to make the electrode area larger, and form a thin film and a large-area electrode. For this purpose, organic polymers can be used as binders. In this case, as the coating method, there are, for example: a method of dispersing the electrode active material in a solvent in which an organic polymer is dissolved as a binder solution; a method of dispersing the electrode active material in an organic polymer water-emulsion dispersion A method in which the solution in the present invention is used as a coating solution; and a method in which a solution (dispersion) of the organic polymer is coated on a pre-formed electrode active material. The amount of the binder is not particularly limited, but it is usually in the range of (0.1-20)% of the weight of the electrode active material, preferably in the range of (0.5-10)%.

As the organic polymer, polymers such as acrylonitrile, methacrylonitrile, vinyl fluoride, vinylidene fluoride, chloroprene, vinylidene chloride, nitrocellulose, cyanoethyl cellulose, polysulfide rubber and the like can be used. Of course, these organic polymers used here are typical ones, and although not particularly limited, they are superior in terms of battery performance, charge and discharge performance, overvoltage characteristics, and the like.

When producing such an electrode, it is formed by applying the above-mentioned coating liquid on a base material and drying it. In this case, it can be formed on the base material together with the current collector material, or the current collector itself such as aluminum foil or copper foil can be used as the base material, and the above-mentioned coating liquid can be applied thereon and dried.

The present invention is characterized in that, in the non-aqueous electrolytic solution, borides are further contained in the aforementioned electrolyte and non-aqueous solvent.

In terms of borides, borides that do not have an electrolyte function, that is, borides that do not contain fluorine, chlorine, and lithium are important for lithium batteries. For example, B ₂ O ₃ , H ₃ BO ₃ , (CH ₃ O) ₃ B, (C ₂ H ₅ O) ₃ B, (CH ₃ O) ₃ BB ₂ O ₃ and the like, among which B ₂ O ₃ is particularly satisfactory.

The consumption of boride, its concentration of boron element in electrolytic solution is no more than 10% by weight, and its consumption is preferably (0.1～7)% by weight, (0.5～5)% especially.

By adding the above-mentioned borides to the electrolyte, the acidic substances generated by the water in the electrolyte can be greatly reduced, and as a result, the deterioration of the electrolyte is prevented, and the negative electrode caused by the formation of metal ions in the container due to the corrosion of the battery container activity decreased.

As for the dehydrating agent further added to the aforementioned electrolytic solution, there are, for example, activated alumina, zeolite, sodium sulfate, activated carbon, silica gel, magnesium oxide, calcium oxide, and the like. The addition amount of these dehydrating agents is usually less than 20% by weight of the electrolyte, preferably (2-15)%, and especially preferably (5-15)%. These dehydrating agents are preferably fully dried by heat treatment or the like before being added to the electrolyte.

By adding these dehydrating agents, decomposition by water in the electrolyte is prevented, and deterioration of the electrolyte solution and generation of acidic substances can be suppressed. In addition, the suppression of the generation of acidic substances prevents the pressure increase in the battery container, thereby making the outer wall of the battery thinner and reducing the weight of the battery.

Furthermore, the present invention is characterized in that the oxides of rare earth elements are contained in the battery electrodes.

In the battery electrode containing oxides of rare earth elements, although the aforementioned binders, conductive auxiliary agents, and other additives such as tackifiers, dispersants, extenders, and adhesion auxiliary agents can be added, but here refers to Containing at least one or more oxides of rare earth elements of the present invention. In addition, as the conductive auxiliary agent, there are, for example, metal powder, conductive metal oxide powder, graphite, and the like.

As for the compounds of these added elements, the important thing is that they do not have the function of electrolyte and carrier material for lithium batteries, that is, compounds that do not contain fluorine, chlorine and lithium, for example, representative examples are: Y ₂ O ₃ , La ₂ O ₃ , Ce ₂ O ₃ , Pr 2 O ₃ , Nd ₂ O _{3 ,} Pm ₂ O ₃ , Sm ₂ O _{3 ,} Fu ₂ O 3 , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ , Sc ₂ O ₃ , etc.

The content of the rare earth element compound is preferably more than 0.1% and not more than 2% by weight of the amount of the rare earth element. Moreover, the coating amount of the electrolyte solution on the electrode material is (300-500) μg/cm ² , preferably (250-400) μg/cm ² . Here, the coating amount of the electrolytic solution refers to the amount of the electrolytic solution present on the surface of the electrode when the electrode is dipped in the electrolytic solution and picked up.

As mentioned above, by including rare earth compounds in the electrode material and controlling the coating amount of the electrolyte in the electrode material, the acidic substances generated due to the moisture contained in the electrode and the electrolyte can be greatly reduced. As a result, prevention, Suppresses the decrease in the activity of the negative electrode and the oxidation of the positive electrode due to corrosion of the collector material of the electrode material, deterioration of the carrier material, deterioration of the electrolyte, deterioration of the electrolyte, corrosion of the battery container and metal ions in the container, etc. The decrease of the electrode coating film and the adhesion force of the current collector, etc.

In addition, the present invention is characterized in that the battery electrode contains boride.

Important borides are borides that do not function as electrolytes and carrier materials for lithium batteries, that is, borides that do not contain fluorine, chlorine, and lithium. For example, B ₂ O ₃ , H ₃ BO ₃ , (CH ₃ O)B, (C ₂ H ₅ O) ₃ BB ₂ O ₃ , etc. can be used, among which B ₂ O ₃ is most preferable.

Although the boron element used in the boride content can be no more than 10% by weight, it is better to use (0.5-7)%, especially (0.5-5)%.

By making the electrode material contain the above-mentioned boride, the acidic substance generated due to the moisture contained in the electrode and the electrolyte can be greatly reduced. As a result, corrosion of the collector material of the electrode, deterioration of the carrier material, and electrolyte solution The deterioration of the electrolyte, the deterioration of the electrolyte, the corrosion of the battery container, the reduction of the activity of the negative electrode, the reduction of the oxidation amount of the positive electrode, the reduction of the adhesion between the electrode coating film and the current collector, etc. are caused by the metal ions in the container.

Also, the present invention is characterized in that at least a part of the inner surface of the battery container is made of an acid-resistant thermoplastic resin. The portion that comes into contact with the electrolytic solution is typically the inner wall of the battery container. The inner wall is made, for example, of stainless steel.

As for acid-resistant thermoplastic resins, there are, for example, fluorine resins, polyolefin resins, polyvinyl chloride resins, acrylonitrile-butadiene-styrene copolymer resins, polyester resins, and the like. Two or more of them can also be used.

As for fluororesins, for example, polytetrafluoroethylene (PTFE), polychlorofluoroethylene, tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene-propylene copolymer (FED), polyvinylidene fluoride (PVDF), perfluoroalkoxy Fluorinated plastic (PFA), tetrafluoroethylene-hexafluoroethylene copolymer, etc.

As for polyolefin resins, for example, high-density polyethylene (HDPE), polypropylene (PP), propylene-ethylene copolymer, polybutane-1, polymethylpentene-1, and the like. As for the polyester resin, for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and the like.

Among the aforementioned acid-resistant thermoplastic resins, fluororesins are preferable. When the aforementioned thermoplastic resin is coated on the portion in contact with the electrolyte solution, the thickness of the coating layer is usually 100 to 200 μm.

By covering the part of the battery that is in contact with the electrolyte except the electrodes with the above-mentioned thermoplastic resin, since it can be protected from corrosion by acidic substances generated by the decomposition of the electrolyte caused by moisture, the contact part is made of stainless steel. In this case, the formation of ions such as nickel, chromium, iron, etc., which constitute the metal in the contact portion, is prevented from migrating to the electrolyte, and the absorption and release of lithium ions to the carbon material as the active material of the negative electrode can be increased. Moreover, the deterioration of the structure of the negative electrode can be suppressed, and the deterioration of the non-aqueous electrolyte solution can be suppressed, so it can be made into a high-capacity lithium storage battery with a long charge-discharge cycle life.

The present invention is characterized by the following essential conditions: the electrolyte contains borides (necessary condition 1), and the electrode material contains oxides of rare earth elements (necessary condition 2); the electrode material contains borides (necessary condition 3); the electrolyte Contains a dehydrating agent (necessary condition 4); and the part that is in contact with the electrolytic solution other than the electrodes is covered with the aforementioned thermoplastic resin (necessary condition 5). However, the present invention can not only adopt each of the necessary conditions independently, but also of course can use each of the necessary conditions in any combination, and their combination application occasions can obtain better effects than their single application occasions. This point can be understood from the description of the following examples.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1

After mixing 80% by weight of lithium cobalt oxide (LiCoO ₂ ) powder, 15% by weight of acetylene carbon black and 5% by weight of polytetrafluoroethylene powder, it is made into flakes. Then, this sheet was laminated with a current collector made of aluminum foil to produce a sheet-shaped positive electrode.

Take phenol resin and burn it at 1700°C for 2 hours in nitrogen to obtain 98% by weight of carbonaceous material powder and 2% by weight of ethylene-propylene copolymer, and stack it with a collector made of nickel foil Product, made of negative electrode.

The positive electrode, the separator made of a polypropylene porous film, and the negative electrode were laminated in this order, and wound into a spiral shape with the negative electrode on the outside to manufacture an electrode group.

In addition, after dissolving 1.0 mol of LiPF ₆ into 1 liter of a mixed solution of ethylene carbonate, propylene carbonate and 1,2 dimethoxyethane (mixing ratio 40:40:20), add boron element weight A non-aqueous electrolytic solution was prepared with boron oxide (B ₂ O ₃ ) having a concentration of 8% in the electrolytic solution.

Put the aforementioned electrode group and the aforementioned non-aqueous electrolyte into a stainless steel cylindrical container with a bottom to form a non-aqueous electrolyte lithium battery as shown in FIG. 1 .

Example 2

In Example 1, instead of B ₂ O ₃ , 5% by weight of magnesium oxide was added, and the electrolyte was prepared in the same manner as in Example 1, and then a lithium battery was assembled using this electrolyte.

Example 3

In embodiment 1, add the magnesia of its content weight 5% again, all the other prepare electrolytic solution identically with embodiment 1, then assemble lithium battery with this electrolytic solution.

Comparative example 1

In Example 1, boron oxide is not used, and the electrolyte is prepared in the same manner as in Example 1, and then a lithium battery is assembled with this electrolyte.

After the lithium batteries assembled in Examples 1-3 and Comparative Example 1 were placed for 3 hours to 35 days, the electrolyte solution was decomposed with hot sodium hydroxide aqueous solution, diluted with methanol, and the fluoride ion concentration was measured by ion chromatography. The results are shown in Table 1.

It can be seen from the results that the generation of fluoride ions is suppressed with the addition of borides and/or dehydrating agents in the electrolyte solution, which decreases significantly with time. Especially when both borides and dehydrating agents are added, the degree of reduction is greater.

Table 1

(unit: ppm) sample placement time 3 hours 20 hours 72 hours 7th 15th 20th 35 days Example 1 100 100 80 50 2 0.1 <0.01 Example 2 100 90 60 40 1 0.1 <0.01 Example 3 90 70 50 20 0.5 <0.01 <0.01 Comparative example 1 150 320 900 1150 2400 4900 7500

Example 4

The electrode group produced in Example 1 and the electrolytic solution prepared in Comparative Example 1 were put into a bottomed cylinder made of stainless steel to assemble a lithium battery. As shown in FIG. 2 , the inner wall of the bottomed cylindrical container 1 is covered with polytetrafluoroethylene (PTFE) having a thickness of 100 μm, and an inner wall protective film 11 having an acid-resistant thermoplastic resin is provided.

Example 5

A lithium battery was assembled in the same manner as in Example 1, except that the electrolyte prepared in Example 3 was used instead of the electrolyte prepared in Comparative Example 1.

After the lithium batteries assembled in Examples 4, 5 and Comparative Example 1 were discharged with a 400mA current for 10 hours respectively, the carbonaceous negative electrode powder was taken out, extracted with aqua regia, and the extract was analyzed by ICP (inductively coupled plasma) luminescence Determination of pollution metal content, the results are shown in Table 2.

From the results, it can be seen that by coating the inner wall of the battery container with PTFE, the metals constituting the container were not dissolved in the electrolytic solution, and metal ions were not contained on the negative electrode. Moreover, the effect is more pronounced when an electrolyte solution containing borides and dehydrating agents is used.

Table 2

(unit: ppm) sample Al Cv Fe Ni Example 4 <10 <10 160 20 Example 5 <10 <10 100 <10 Comparative example 1 400 600 2400 330

In addition, for the lithium batteries assembled in Examples 1 to 3 and Comparative Example 1, the charge and discharge cycle test of charging to 4.2V with a current of 50mA and discharging to 2.7V with a current of 50mA was repeated, and the discharge capacity and number of times of each battery were measured. life.

The result is shown in Figure 3.

It can be seen from FIG. 3 that the battery assembled in each embodiment has a longer charge-discharge cycle life than the battery assembled in the comparative example.

Example 6

Take 1.05 mol of lithium carbonate, 1.90 mol of cobalt oxide, and 0.084 mol of tin dioxide in a mortar, mix them in a mortar, pre-fire at 650°C for 5 hours, and then burn at 850°C in air for 12 hours, and then make the obtained composition Li _1.03 The lithium cobalt oxide of _CoSnO2 was pulverized by ball milling and processed into a powder with an average particle size of 3 μm. The powder weight of getting the lithium cobalt oxide obtained in this way is 80%, acetylene carbon black weight is 15% and polytetrafluoroethylene powder weight is 5% phase mixing, carries out kneading with isopropyl alcohol, makes paste, coats Spread on the aluminum foil as the current collector, roll it after drying, and make a thin layer of positive electrode.

On the other hand, after burning the phenol resin powder at 1700° C. for 2 hours in nitrogen, it was pulverized by a ball mill to obtain an average particle diameter of 3 μm. A 2% composition mixture was kneaded with isopropyl alcohol, coated on a copper foil as a current collector, dried and then rolled to form a thin-layer negative electrode.

The positive electrode, the separator made of a polypropylene porous film, and the negative electrode were laminated in this order, and rolled into a spiral shape with the negative electrode on the outside to manufacture an electrode group.

In addition, 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in 1 liter of a mixed solvent of ethylene carbonate, propylene carbonate and 1,2 dimethoxyethane (mixing ratio 40:40:20) After neutralization, 1.0 mol of HF was added to the solvent to prepare a non-aqueous electrolyte solution.

The aforementioned electrode group and the aforementioned non-aqueous electrolyte were put into a bottomed cylindrical container made of stainless steel, and assembled into a non-aqueous electrolyte lithium storage battery as shown in FIG. 1 above.

Example 7

Get the powder weight of the lithium cobalt oxide that the method described in embodiment 6 makes is 80%, acetylene carbon black weight is 13%, polytetrafluoroethylene powder weight is 5% and yttrium oxide weight is 2% phase mixing, adopts different Propyl ethanol is kneaded to make a paste, which is coated on the aluminum foil used as the collector, dried and then rolled to make a thin-layer positive electrode.

Similarly, the weight of the carbonaceous powder made by the method of Example 6 is 96% and the weight of the polytetrafluoroethylene powder is 4% to form a mixture, which is mixed with isopropyl alcohol and coated on the copper foil as the current collector , rolled after drying to make a thin-layer negative electrode.

The positive electrode, the separator made of a polypropylene porous film, and the negative electrode were laminated in this order, and rolled into a spiral shape with the negative electrode on the outside to form an electrode group.

In addition, 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in 1 liter of a mixed solution of ethylene carbonate, propylene carbonate and 1,2 dimethoxyethane (the mixing ratio was 40:40:20) After dissolving, add 1.0mol of HF to the solution to make a non-aqueous electrolyte.

Put the aforementioned electrode group and the aforementioned non-aqueous electrolyte into a bottomed cylindrical container made of stainless steel to form a non-aqueous electrolyte lithium battery as shown in FIG. 1 .

Example 8

Make negative pole with embodiment 6, make positive pole with the method for embodiment 7. Then, in the same manner as in Examples 6 and 7, the positive electrode, the separator made of a polypropylene porous film, and the negative electrode were stacked in this order, and the negative electrode was wound in a spiral shape with the negative electrode positioned on the outside to manufacture an electrode group.

In addition, 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in 1 liter of a mixture of ethylene carbonate, propylene carbonate and 1,2 dimethoxyethane (mixing ratio 40:40:20) After dissolving, add 1.0 mol of HF to the solvent to prepare a non-aqueous electrolyte.

Put the aforementioned electrode group and the aforementioned non-aqueous electrolyte into a bottomed cylindrical container made of stainless steel, but pack into a non-aqueous electrolyte lithium storage battery as shown in Figure 1.

Comparative example 2

The positive electrode was prepared by the method of Example 6, and the negative electrode was prepared by the method of Example 7. That is, yttrium oxide is not used. Then, in the same manner as in Examples 6 and 7, the positive electrode, the polypropylene porous film constituting the separator, and the negative electrode were laminated in this order, and then rolled into a spiral shape with the negative electrode on the outside to manufacture an electrode group.

In addition, 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in 1 liter of a mixed solution of ethylene carbonate, propylene carbonate and 1,2 dimethoxyethane (mixing ratio 40:40:20) After dissolving, 1.0 mol of HF was added to the solvent to prepare a non-aqueous electrolyte.

Put the aforementioned electrode group and the aforementioned non-aqueous electrolyte into a bottomed cylindrical container made of stainless steel to form a non-aqueous electrolyte lithium battery as shown in FIG. 1 .

Comparative example 3

The electrode group was fabricated by the method of Example 6, and then 2.0 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in 1 liter of ethylene carbonate, propylene carbonate and 1,2 dimethoxyethane mixed solution ( The mixing ratio is 40:40:20), after dissolving, 1.0 mol of HF is added to the solvent to prepare a non-aqueous electrolyte.

The aforementioned electrode group and the aforementioned non-aqueous electrolytic solution were put into a bottomed cylindrical container made of stainless steel to form a non-aqueous electrolytic solution lithium storage battery as shown in FIG. 1 .

For the lithium batteries assembled with Examples 6, 7, 8 and Comparative Examples 2 and 3, charge to 4.2V with a current of 50mA and discharge to 2.7V with a current of 50mA for 500 times of repeated charge and discharge, and then separate the negative and positive electrodes , methanol was added, and water was added and heated at 100° C. for 2 hours, then cooled to room temperature. A membrane is then used to separate the hot water soluble and insoluble components.

For hot water soluble components, ion chromatography was used for both the negative electrode and the positive electrode, and ICP (inductively coupled plasma) emission analysis was used for quantitative analysis only for the positive electrode Co.

For insoluble components, after the negative electrode is extracted with aqua regia, and the positive electrode is decomposed with nitric acid, the pollution of Al, Cu, Cr, Fe, Ni, Co and Al, Cu, Cr, Fe, Ni is quantitatively analyzed by ICP emission analysis method respectively amount of metal. The quantitative analysis results of metal pollution amount and hot water soluble components of the negative electrode are shown in Table 3, and the quantitative analysis results of metal pollution amount and hot water soluble components of the positive electrode are shown in Table 4.

table 3

(mg/piece) Al Cn Cr Fe Ni co f Example 6 <0.1 0.2 <0.1 0.2 <0.1 0.2 0.1 Example 8 <0.1 <0.1 <0.1 0.2 <0.1 <0.1 0.1 Comparative example 2 1.4 1.5 2.1 8.0 1.2 4.1 2.0 Comparative example 3 0.4 0.3 0.4 2.0 0.3 0.8 0.5

Table 4

(mg/piece) al Cn Cr Fe Ni co f Example 7 0.1 0.1 <0.1 0.1 <0.1 0.1 0.1 Example 8 0.1 0.1 <0.1 0.1 <0.1 0.1 0.1 Comparative example 2 3.1 0.4 <0.1 0.6 0.1 5.8 4.2 Comparative example 3 0.4 0.2 <0.1 0.2 <0.1 0.4 0.3

It can be seen from these results that the dissolution of metals and the generation of fluoride ions in the electrolyte are suppressed and do not increase with time for the negative and positive electrodes added with rare earth compounds. Also, the same result was obtained when the concentration of LiPF ₆ in the solvent was appropriate.

In addition, for the lithium batteries assembled with Examples 6, 7, 8 and Comparisons 2 and 3, they were charged to 4.2V with a current of 50mA and discharged to 2.7V with a current of 50mA for repeated charge and discharge, and the discharge of each battery was measured. capacity and lifespan. The result is shown in Figure 4.

It can be seen from FIG. 4 that the battery assembled in the example has a longer charge-discharge cycle life than the battery assembled in the comparative example.

Example 9

Take 1.05 mol of lithium carbonate, 1.90 mol of cobalt oxide, and 0.084 mol of tin dioxide and mix them in a mortar, pre-fire at 650°C for 5 hours, and then burn in air at 850°C for 12 hours. The obtained lithium cobalt oxide with the composition of Li _1.03 CoSnO ₂ was then pulverized by ball milling and processed into a powder with an average particle size of 3 μm. The powder weight of getting the lithium cobalt oxide obtained in this way is 80%, acetylene carbon black weight is 15% and polytetrafluoroethylene powder weight is 5% phase mixing, carries out kneading with isopropyl alcohol, makes paste, coats Spread on the aluminum foil as the current collector, roll it after drying, and make a thin layer of positive electrode.

On the other hand, after the phenol resin powder was burned at 1700° C. for 2 hours in nitrogen, it was pulverized by a ball mill to obtain an average particle size of 3 μm. The mixture is composed of 2% by weight, kneaded with isopropyl alcohol, coated on a copper foil as a collector, dried and then rolled to form a thin-layer negative electrode.

The positive electrode, the separator made of a polypropylene porous film, and the negative electrode were laminated in this order, and rolled into a spiral shape with the negative electrode on the outside to manufacture an electrode group.

In addition, 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in 1 liter of a mixed solvent of ethylene carbonate, propylene carbonate and 1,2 dimethoxyethane (mixing ratio 40:40:20) After neutralization, 1.0 mol of HF was added to the solvent to prepare a non-aqueous electrolyte solution.

Put the aforementioned electrode group and the aforementioned non-aqueous electrolyte into a bottomed cylindrical container made of stainless steel, and assemble it into a non-aqueous electrolyte lithium battery as shown in FIG. 1 .

Example 10

Take 1.05 mol of lithium carbonate, 1.90 mol of cobalt oxide, and 0.084 mol of tin dioxide in a mortar, mix them in a mortar, pre-fire at 650°C for 5 hours, and then burn at 850°C in air for 12 hours, and then make the obtained composition Li _1.03 The lithium cobalt oxide of _CoSnO2 was pulverized by ball milling and processed into a powder with an average particle size of 3 μm. The powder weight of the lithium cobalt oxide obtained in this way is 80%, the weight of acetylene carbon black is 13%, the weight of polytetrafluoroethylene powder is 5% and the weight of boron oxide is 2% and mixed, and mixed with isopropyl alcohol , made into a paste, coated on an aluminum foil as a current collector, dried and then rolled to make a thin layer of positive electrode.

On the other hand, after the phenol resin powder was burned at 1700° C. for 2 hours in nitrogen, it was pulverized by a ball mill to obtain a mixture with an average particle size of 3 μm in carbonaceous material powder weight of 96% and polytetrafluoroethylene powder weight of 4%, Kneading with isopropyl alcohol, coating on copper foil as current collector, drying and rolling to make a thin negative electrode.

The positive electrode, the separator made of a polypropylene porous film, and the negative electrode were laminated in this order, and rolled into a spiral shape with the negative electrode on the outside to manufacture an electrode group.

In addition, 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in 1 liter of a mixed solvent of ethylene carbonate, propylene carbonate and 1,2 dimethoxyethane (mixing ratio 40:40:20) After neutralization, 1.0 mol of HF was added to the solvent to prepare a non-aqueous electrolyte solution.

Put the aforementioned electrode group and the aforementioned non-aqueous electrolyte into a bottomed cylindrical container made of stainless steel, and assemble it into a non-aqueous electrolyte lithium battery as shown in FIG. 1 .

Example 11

The method of Example 9 was used to make the negative electrode, and the method of Example 10 was used to make the positive electrode. Then, in the same manner as in Examples 9 and 10, the positive electrode, the separator made of a polypropylene porous film, and the negative electrode were laminated in this order, and the negative electrode was wound in a spiral shape with the negative electrode positioned on the outside to manufacture an electrode group.

In addition, 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in 1 liter of a mixture of ethylene carbonate, propylene carbonate and 1,2 dimethoxyethane (mixing ratio 40:40:20) After dissolving, add 1.0 mol of HF to the solvent to prepare a non-aqueous electrolyte.

The aforementioned electrode group and the aforementioned non-aqueous electrolyte were put into a bottomed cylindrical container made of stainless steel, and assembled into a non-aqueous electrolyte lithium battery as shown in FIG. 1 .

Comparative example 4

The positive electrode was prepared by the method of Example 9, and the negative electrode was prepared by the method of Example 10. That is, boron oxide and rare earth oxides are not used. Then, in the same manner as in Examples 9 and 10, the positive electrode, the polypropylene porous film constituting the separator, and the negative electrode were laminated in this order, and then rolled into a spiral shape with the negative electrode on the outside to manufacture an electrode group.

In addition, 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in 1 liter of a mixed solution of ethylene carbonate, propylene carbonate and 1,2 dimethoxyethane (mixing ratio 40:40:20) After dissolving, 1.0 mol of HF was added to the solvent to prepare a non-aqueous electrolyte.

Put the aforementioned electrode group and the aforementioned non-aqueous electrolyte into a bottomed cylindrical container made of stainless steel to form a non-aqueous electrolyte lithium battery as shown in FIG. 1 .

After the lithium batteries assembled in Examples 9-11 and Comparative Example 4 were placed for 1 hour to 5 days, the carbonaceous negative electrode powder was taken out, extracted with aqua regia, and the polluting metals were determined by ICP emission analysis. And the electrolytic solution taken out of the electrode was decomposed with hot sodium hydroxide aqueous solution, diluted with methanol, and then the fluoride ion concentration was measured by ion chromatography. The results are shown in Table 5.

table 5

(unit: ppm) al Cu Cr Fe Ni f Example 9 20 50 <10 160 20 30 Example 10 30 20 <10 80 10 20 Example 11 20 10 <10 80 <10 30 Comparative example 4 400 400 600 2400 330 900

Moreover, the lithium batteries assembled in Examples 9-11 and Comparative Example 4 were placed separately for 1 hour to 5 days, and the positive electrode containing LiCoO was taken out, decomposed with nitric acid, and then the amount of polluting metals was _measured by ICP emission analysis. The results are shown in the table 5.

From these results, it can be seen that the dissolution of metal and the generation of fluorine ions in the electrolyte are suppressed for the negative and positive electrodes added with boron, and do not increase with time.

In addition, the lithium batteries assembled with Examples 9, 10, 11 and Comparative Example 4 were repeatedly charged to 4.2V with a current of 50mA and discharged to 2.7V with a current of 50mA, and the discharge capacity and number of times of each battery were measured. life. The result is shown in Figure 5.

It can be seen from FIG. 5 that the battery assembled in the example has a longer charge-discharge cycle life than the battery assembled in the comparative example.

The present invention contains borides in its electrolyte and oxides of borides and alkene elements on the battery electrodes, and can suppress the oxides generated by the action of water, especially the influence caused by hydrofluoric acid. The liquid contains a dehydrating agent, which can eliminate various disadvantages caused by containing water. By coating and protecting the inner wall of the battery container, the elution of metal in the container can be suppressed.

Moreover, with these improvements, the performance of the lithium battery does not deteriorate, and the life of the number of charge and discharge times with a high capacity can be greatly extended.

Claims (1)

1. lithium battery comprises electrolyte and is immersed in positive pole and negative pole in the described electrolyte, and this electrolyte contains at least and is selected from a kind of in fluoride and the chloride, it is characterized in that described positive pole contains boride.

Images