DE4320140A1 - Composite anode for sec. batteries with non-aq. electrolytes - contains alkali metal alloy powder as active material, with oxygen-contg. carbon powder and ethylene@]-propylene] copolymer binder - Google Patents

Abstract

A composite anode for sec. batteries with non-aq. electrlytes is claimed. The anode is based on powdered alkali metal alloy (I), carbon powder (II) and a binder (III), with the alkali metal as active anode material, and the electrolyte soln. is a soln. of electrolyte in organic solvent. The carbon (II) contains oxygen atoms, with oxygen content 0.1-5 wt%. Also claimed is a process for prodn. of the anode, by mixing binder (III) (an olefin copolymer) in aromatic solvent with (I) and (II), applying the mixt. to an electrode substrate and forming the coated substrate. Also claimed are sec. batteries with non-aq. electrolytes, contg. an anode as above together with a cathode. ADVANTAGE - The binder prevents particles of (I) from falling off the anode, and the presence of (II) in the spaces between the alloy particles moderates the effect of vol. changes caused by charging and discharging and helps to maintain electrical contact between alloy particles; (II) can also adsorb and desorb (I) and thus acts as a reservoir of (I) for the charge-discharge process. The overall effect is to delay inactivation and prevent collapse of the anode and thus prolong the service life of the battery.

Description

The present invention is concerned with composite anodes for use in secondary batteries with non-aqueous electrolyte, and in particular special such a composite anode using powdered Alkali metal alloy, carbon powder and binder is formed, as well a process for their manufacture.

The increase in the number of possible charge and discharge cycles is the most important task for secondary batteries with non-aqueous electrical is to be solved in which an alkali metal is used as the active anode material and as an electrolytic solution, one by dissolving an electrolyte in one organic solvent solution is used. To a side reaction between the electrolyte solution and that when charging at the anode to inhibit deposited active alkali metal, which is a dominant It is a factor for the possible number of charge and discharge cycles required the optimal combination of anode and electrolyte system choose.

Accordingly, there are mixed solutions regarding the electrolyte system systems and electrolyte solutions with excellent stability at the Anode developed and additives tested to inhibit side reactions been. Regarding the anode materials is to prevent an out falling of active alkali metal on the anode surface during charging the use of alloys of alkali metals or carbon have been investigated as anode materials, the goal being one as possible rapid diffusion of the alkali metal deposited during charging the alloy or carbon was to have a side reaction between the Prevent electrolytic solution and the alkali metal.

However, the development of new anode materials is under One problem in using carbon material is that this is only one have low capacitance density per electrode volume. When using Alkali metal alloys experience this if the  Anode during charging and charging volume changes, and their re- then leads to a breakdown of the electrodes, which results in how therefore a reduction in the achievable number of charging and discharging cycles results.

To solve these problems, there has been a method (JP-A-60-262351) in which a composite material made of an alkali metal alloy and a conductive capable polymer is used, and a method (JP-A-60-131776) in which the electrode was made using polytetrafluor ethylene is produced as a binder.

However, these processes also prove to be unsatisfactory, since conductive polymers release alkali metal during the discharge, so that the conductivity is reduced, and because of their small specific surface area of only about 10 m ² / g, they do not bring about a sufficient bond between the individual particles can, while when using polytetra fluorethylene as a binder, this reacts with the alkali metal and thus leads to damage to the anode.

The present invention has for its object the above Darge put difficulties to overcome and a composite anode for secondary to create batteries with non-aqueous electrolyte, which is characterized by a distinguishes high number of achievable charge and discharge cycles.

For this purpose, an anode material is used within the scope of the invention, which consists of an alkali metal alloy and carbon powder, which is a bin demittel is added.

The present invention provides a solution to the above problem a composite anode made of powdered alkali metal alloy, carbon powder and binders used for secondary batteries with non-aqueous Electrolytes is determined in which the active anode material is alkali metal and as an electrolyte solution, an electrolyte dissolved in an organic solvent is used, wherein according to the invention, the carbon powder ent ent atoms holds and the oxygen content in a range of 0.1 to 5% by weight lies.  

The present invention further relates to a method for Manufacture of a composite anode from powdered alkali metal alloy, Carbon powder and binder for secondary batteries with non-aqueous Electrolytes in which the active anode material is alkali metal and Serves electrolyte solution dissolved in organic solvent, wherein according to the invention a binder from a copolymer of in the Mainly monomers composed of olefins in aromatic solution medium with powdered alkali metal alloy and carbon powder with mixed an oxygen content of 0.1 to 5% by weight and the obtained Mixture applied to an electrode substrate and the coated substrate is brought into shape.

Before a description of the invention in all details, the drawing will be briefly discussed first; the only figure of which is a graphical representation of the relationships between the capacity density or the service life in the form of the achievable number of charge and discharge cycles and the oxygen content in carbon, curve 11 representing the capacity density for the deposition and detachment process for lithium , while curve 12 shows the lifetime for a lead-based composite anode.

The present invention is explained in detail below.

First, the expected effects of binders and conductive capable materials to strengthen the bond between the particles of the active material in a combination of alkali metal alloy Particle and conductive material shaped composite anode for different materia lien has been examined. With regard to the binder, it has been shown that of hydrocarbon polymers without foreign atoms, copolymers of olefins such as ethylene and propylene as the main ingredients are best suited the reaction with the alkali metal forming the active anode material to in hibernate.

Since the alkali metal alloys are generally brittle, this results in the problem of shedding them into a plate electrode. To a slices it is possible to produce electrodes as used in button cells  Molding presses are worked. If, however, a spiral wound The electrode is to be produced as required for cylindrical batteries there are considerable difficulties for the manufacturing technology both when molding an alloy in powder form and when casting the alloy into a plate. The mainly from olefins like Ethylene and propylene are soluble in aromatic solvents. Therefore the solution obtained with an alkali metal alloy and carbon powder mixed to make a paste, and then electrodes can be made by simply applying this paste using a method similar to that used in Manufacture of electrodes for conventional secondary batteries with aqueous electr trolyten current method is spread on a current arrester. The composite anode thus produced may have a larger surface area than a plate electrode because the alkali metal serving as the active material alloy in powder form is used, and the result is one better discharge characteristics.

On the other hand, with regard to the conductive materials, the composition of the alkali metal alloy forming the active material, namely the ratio M ₁ / M ₂ in which M _{1 represents} one alkali metal and M _{2 represents} another metal forming the alloy, changes in the course of Charges and discharges and causes expansion and contraction on the particles of the alkali metal alloy, so that the electrical contact between the alloy particles is lost. To prevent this loss of electrical contact due to expansion and contraction, it is necessary to create a binding effect between the particles. In order to maintain the electrical contact between the particles, those materials with low bulk density are required which have a high electrical conductivity and can be filled effectively into the space between the particles of the alkali metal alloy in order to obtain effective contact between the particles and the To mitigate the change in volume of the alloy particles.

It has been shown that as such materials carbon materials conductive polymer materials such as those mentioned in JP-A-60-262351 are. When making electrodes by loosening one in the main copolymer composed of ethylene and propylene in an aromatic  Solvent and then adding the solution obtained to a Mixture of alkali metal alloy particles and carbon powder for loading preparation of a paste there is a possibility that part of the as a bandage medium acting, mainly consisting of ethylene and propylene Copolymer onto the alkali metal alloy forming the active material particles and the separation and detachment process of the alkali metal handicapped. However, it is possible to deposit the in the main thing consisting of ethylene and propylene copolymer on the alkali metal to prevent alloy particles by working with a carbon material works with a relatively large specific surface.

Another advantage of using carbon materials lies in that carbon involves a deposition and detachment process brings, whereby not only the binding effect between the alkali metal alloy particles but also the effect of carbon as such shows active anode material. When examining the capacity density and the Reversibility of the different carbon materials for the separation Formation and detachment reaction with alkali metal has been shown that coal material materials with a higher oxygen content at a higher capacity lead density, as can also be seen from the drawing. If for example the deposition and stripping process for lithium using by thermal decomposition by polymerization of furfuryl alcohol Resin produced carbon with an oxygen content of The capacity density was 3.8% by weight when the electrode was carried out a reversible deposition and detachment reaction 150 mAh / g. In the event of The capa was of acetylene black with an oxygen content of 0.2% by weight density for the reversible deposition and separation process for Lithium at 140 mAh / g. On the other hand, the capacity density for the reversible deposition and detachment process for lithium in the case of Using graphite with an oxygen content of 0.01% by weight what is below the detection limit, 30 mAh / g.

Such an effect on the oxygen-containing functional group the carbon surface can be explained by ent holding functional group on the surface as an adsorption site for the Alkali metal ion. The amount of functional oxygen-containing  Groups on the surface are preferably 0.1% by weight and above as mentioned above. If the amount of oxygen-containing functional Groups on the surface exceeding 5% by weight, the electrical takes Conductivity decreases, and the function as a composite anode is impaired. The most preferred functional group on the surface is that Aether bond (C-O-C), which has been shown to be mild in the interaction with the Alkali metal ion proves.

Methods for the extraction of carbon materials with oxygen containing functional groups on the surface include, for example a process with thermal decomposition of phenol and phenol derivatives alcohols, acrylates and furans or polymers thereof, Oxygen-containing compounds and a process with oxidation of Low oxygen carbon materials.

The composite anode can be made in the following manner. A well-known alkali metal alloy with aluminum, gallium, indium, tin, bismuth, Lead or the like is after metallurgical or electrochemical Ver drive or manufactured, then ground and finally sieved to Legie obtain powder. The powders obtained are mixed with carbon powders mixed, and a solution is added to the mixture by dissolution a copoly composed mainly of ethylene and propylene Mers have been prepared as a binder in an aromatic solvent is. The mixture is kneaded and spread on a current arrester, and this is molded and dried to obtain an anode. The Mixing ratio of alkali metal and carbon is convenient in a range of 0.2 to 1.0 in the volume ratio of the carbon powder the alloy particles so the carbon powder in the gaps can be filled between the alloy particles by the Charging and discharging caused volume changes in the alloy part diminish. The mixing ratio by weight must be based on the specific weights of alloy and carbon can be determined. This The method allows mass production of uniform electrodes production with simple devices and enables effective production of batteries on an industrial scale.  

Batteries are manufactured using the compo thus obtained sitanode in combination with a cathode and filling with an electrolyte solution solution. Oxides or sulfides of manganese, molybdenum, titanium, Vanadium, chromium, cobalt or the like can be used. As an electrolyte solution can be used by dissolving an alkali electrolytes containing metal ions such as LiBF4, NaBF4, LiPF6, NaPF6, LiClo4 or LiCF3SO3 in a polar organic solvent. There are no restrictions on the shape of the electrodes and batteries, however, the present invention is particularly suitable for use with cylindrical batteries with spirally wound electrodes or at large format batteries.

The operating behavior of the composite anode is explained below. The microstructure of the composite anode is such that carbon powder fills the spaces between the alkali metal alloy particles, and these particles are bound by a binder with a copolymer mainly composed of ethylene and propylene. In this composite electrode, alkali metal ions are reduced to alkali metal during charging. The alkali metal quickly diffuses into the alloy. This diffusion into the alloy leads to an increase in the ratio M1 / M2 in the alloy, which in turn leads to a reduction in the density of the alloy and an expansion of the alloy particles. During the discharge, the alkali metal is oxidized on the surface of the alkali metal alloy particles and dissolves in the electrolyte solution in the form of alkali metal ions. Therefore, the ratio M ₁ / M ₂ in the alkali metal alloy decreases and the volume of the alloy particles shrinks. If this expansion and contraction of the alkali metal alloy particles constituting the active material is repeated by continued charging and discharging in this manner, the electrode body collapses when using a plate-shaped alloy of monolithic structure as an anode. When using an alkali metal alloy part by molding Chen manufactured electrode, the volume change can be mitigated thanks to the inter mediate spaces between the powder particles, but nevertheless there is a similar breakdown if the utilization of the anode is increased.

In the composite anode, this is caused by charging and discharging gentle volume change of the alkali metal alloy particles macroscopically softens the spaces between the alloy particles filling carbon powder, and at the same time prevents the binder from coming out mainly copolymer composed of ethylene and propylene The particles of the active material fall out of the electrode body. In addition, the in the spaces between the alloy particles filled carbon microscopically even if the alkali metals The alloy particles shrink in volume during discharge and the immit Contact between the alloy particles is lost, the electri maintain contact between the particles of the active material. In addition, the added carbon is capable of charging and discharging charge to adsorb or desorb alkali metal ions and thus acts as Reserve of alkali metal alloy for charging and discharging.

This means that when the active material is formed Alkali metal alloy deteriorates during charging and discharging and the capacity decreases, active alkali metal on the surface of the anode falls when there is no carbon and there is inactivation of the precipitated alkali metal comes. If, however, as in the composite anode Carbon is present, this introduces and extracts alkali metal ions it instead of the alkali metal alloy and thus prevents deposition and Detachment of alkali metal on the surface of the alloy and takes over charging and discharging, so that the result is inactivation of the anode can be prevented. Specifically, by adjusting the oxygen content in the carbon in a range between 0.1 and 5% by weight Increase the carbon density for charging and discharging, and this causes an improvement in battery life.

The present invention is now intended to be further illustrated by examples are illustrated.  

example 1

88% by weight alloy particles made by grinding an alloy made of lithium and lead with a ratio Li / Pb of 3.5 on one mesh number of 200 corresponding grain size or less were obtained with 9% by weight acetylene black with an oxygen content of 0.2% by weight mixed, and a solution was added to the mixture by dissolution of ethylene / propylene rubber in an amount of 3% by weight in xylene was to get a paste. This paste was applied to a current arrester spread and dried in vacuo to produce a composite anode. A battery was made using this composite anode, one Cathode with active mainly composed of manganese dioxide Material and one by dissolving lithium hexafluorophosphate in one Solvent mixture obtained from propylene carbonate and 1,2-dimethoxyethane Solution as an electrolyte solution. This battery has been charged and discharged subjected to de-test. In this case, the capacitance density of the cathode set to 150 mAh / g and that of the anode to 90 mAh / g (corresponding to 22% the anode utilization), and the charging and discharging were carried out with two hours repeated current. The result was a number of 380 cycles before the Discharge capacity had dropped to half the initial value as in the drawing is illustrated.

Example 2

88% by weight of alloy particles obtained by grinding a β-phase Alloy of lithium and aluminum with a mesh size of 200 corresponds grain size or less were obtained with 9% by weight one by polymerizing furfuryl alcohol in aqueous solution with Schwe rock acid and subsequent thermal decomposition of the polymer obtained in a nitrogen atmosphere at 1000 ° C with carbon powder mixed with an oxygen content of 3.8% by weight, and the obtained A solution was added to the mixture which was obtained by dissolving an ethylene / Propylene gums in an amount of 3% by weight in xylene was prepared to to get a paste. This paste was spread on a current arrester and dried in vacuo to produce a composite anode. A  Battery was made using this composite anode, one Cathode with active mainly composed of manganese dioxide Material and one by dissolving lithium hexafluorophosphate in one Solvent mixture obtained from propylene carbonate and 1,2-dimethoxyethane Solution as an electrolyte solution. This battery has been charged and discharged subjected to de-test. In this case, the capacitance density of the cathode set to 150 mAh / g and that of the anode to 120 mAh / g (corresponding to 15% the anode utilization), and the charging and discharging were carried out with two hours repeated current. The result was a cycle number of 280 before the Discharge capacity had dropped to half the initial value.

Example 3

88% by weight alloy particles made by grinding an alloy made of lithium and indium with a Li / In ratio of 1.0 on one mesh number of 200 corresponding grain size or less were obtained with 9% by weight acetylene black with an oxygen content of 0.2% by weight mixed, and a solution was added to the mixture by dissolution of an ethylene / propylene rubber in an amount of 3% by weight in xylene was riding to get a paste. This paste was on a stream arrester spread and dried in vacuo to produce a composite anode deliver. A battery was made using this composite anode, a cathode mainly composed of manganese dioxide active material and one by dissolving lithium hexafluorophosphate in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane obtained solution as an electrolytic solution. This battery has been charged and subjected to discharge test. In this case, the capacity density of the Cathode set to 150 mAh / g and the anode set to 45 mAh / g (corresponding to 20% of the anode utilization), and the charging and discharging were two hour stream repeated. The result was a cycle number of 430, before the discharge capacity had dropped to half the initial value.  

Example 4

88% by weight alloy particles made by grinding an alloy made of lithium and lead with a ratio Li / Pb of 3.5 on one mesh number of 200 corresponding grain size or less were obtained with 9% by weight of one by polymerizing furfuryl alcohol in aqueous Solution with sulfuric acid and subsequent thermal decomposition of the The polymer produced in a nitrogen atmosphere at 1000 ° C. Koh mixed with an oxygen content of 3.8% by weight, and a solution was added to the resulting mixture by dissolution of an ethylene / propylene rubber in an amount of 3% by weight in xylene was riding to get a paste. This paste was on a stream arrester spread and dried in vacuo to produce a composite anode deliver. A battery was made using this composite anode, a cathode mainly composed of manganese dioxide active material and one by dissolving lithium hexafluorophosphate in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane obtained solution as an electrolytic solution. This battery has been charged and subjected to discharge test. In this case, the capacity density of the Cathode set to 150 mAh / g and the anode set to 90 mAh / g (corresponding to 22% of the anode utilization), and the charging and discharging were two hour stream repeated. The result was a cycle number of 320, before the discharge capacity had dropped to half the initial value, as illustrated in the drawing.

Comparative Example 1

Alloy particles obtained by grinding an alloy of lithium and lead with a ratio Li / Pb of 3.5 to a mesh size of 200 or less corresponding grain size or less were press-formed into an anode at a pressure of 200 kg / cm ² . A battery was manufactured using this anode, a cathode with an active material mainly composed of manganese dioxide and a solution obtained by dissolving lithium hexafluorophosphate in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane as an electrolytic solution. This battery has been subjected to a charge and discharge test. In this case, the capacitance density of the cathode was set to 150 mAh / g and that of the anode to 90 mAh / g (corresponding to 22% of the anode utilization), and the charging and discharging were repeated with two hours of current. The result was a number of cycles of 120 before the discharge capacity had dropped to half the initial value.

Comparative Example 2

88% by weight alloy particles made by grinding an alloy made of lithium and lead with a ratio Li / Pb of 3.5 on one mesh number of 200 corresponding grain size or less were obtained mixed with 9% by weight of graphite powder, and the mixture obtained was added a solution by dissolving an ethylene / propylene rubber in an amount of 3% by weight in xylene was prepared to make a paste hold. This paste was spread on a current conductor and in the Vacuum dried to make a composite anode. A battery was produced using this composite anode, a cathode with in the The main thing is active material composed of manganese dioxide and one by dissolving lithium hexafluorophosphate in a mixed solvent solution obtained from propylene carbonate and 1,2-dimethoxyethane as an electro lyt solution. This battery has been subjected to a charge and discharge test. In this case, the capacitance density of the cathode was set to 150 mAh / g and that of the anode is set to 90 mAh / g (corresponding to 22% of the anode use), and the charging and discharging were carried out with two-hour electricity repeated. The result was a cycle number of 200 before the discharge capacity had dropped to half the initial value, as in the Drawing is illustrated.

According to the present invention, the use of a Composite anode with a powdered alkali metal alloy, an acid Carbon powder containing atoms and a binder from a Copolymer of mainly ethylene and propylene Monomers in a secondary containing an alkali metal as an active material batteries with non-aqueous electrolyte breakdown of the anode and  prevent deterioration due to charging and discharging and build secondary batteries with non-aqueous electrolytes an excellent service life in the form of possible loading and unloading mark charging cycles.

A first object of the present invention is a compo powdered alkali metal alloy, carbon powder and bin titanium anode Detergent for secondary batteries with non-aqueous electrolytes, in which as active anode material alkali metal and as electrolyte solution in organic Solvent electrolyte is used, which is characterized in that the carbon powder contains oxygen atoms, the oxygen content in is in the range of 0.1 to 5% by weight.

Another object of the present invention is a method for producing a composite anode from powdered alkali metal alloy, Carbon powder and binder for secondary batteries with non-aqueous Electrolytes in which the active anode material is alkali metal and the elec trolyte solution in organic solvent is used electrolyte with the Steps mixing a binder from a copolymer of in the main monomers composed of olefins in aromatic solvent with powdered alkali metal alloy and carbon powder with one Oxygen content from 0.1 to 5% by weight, applying the mixture to a Electrode substrate and molding of the coated substrate.

Finally, the present invention also relates to a second intestinal battery with non-aqueous electrolyte, which is a composite anode of the above contains mentioned type in combination with a cathode.

Claims (7)

1. Composite anode made of powdered alkali metal alloy, carbon powder and binder for secondary batteries with non-aqueous electr trolytes in which the active anode material is alkali metal and Electrolyte solution dissolved in organic solvent serves, wherein the carbon powder contains oxygen atoms and the Oxygen content is in a range from 0.1 to 5% by weight. 2. Anode according to claim 1, wherein the volume ratio of carbon powder for powdered alkali metal alloy in a range of 0.2 to 1.0. 3. Anode according to claim 1, wherein the carbon atoms containing oxygen atoms Powder by thermal decomposition of phenol and phenol derivatives, alcohols, acrylates and furans or polymers thereof selected oxygen-containing organic compound in one inert atmosphere is preserved. 4. Anode according to claim 1, wherein the carbon atoms containing oxygen atoms cloth powder by heat treatment of a low carbon Oxygen content obtained in an oxidizing atmosphere Is carbon. 5. A method of making a powdered alkali composite anode metal alloy, carbon powder and binder for secondary batteries s with non-aqueous electrolytes, in which as an active anode material Alkali metal and as an electrolyte solution in organic solvent dissolved electrolyte is used with the steps of mixing a binder from a copolymer composed mainly of olefins ten monomers in aromatic solvent with powdered alkali metal alloy and carbon powder with an oxygen content of 0.1 up to 5% by weight, application of the mixture to an electrode substrate and shaping the coated substrate.   6. The method according to claim 5, in which as a binder, a copolymer of in the main ge composed of ethylene and propylene monomers is chosen. 7. Secondary battery with non-aqueous electrolyte with a composite anode according to claim 1 in combination with a cathode.