CA2250719A1 - Carbon for a lithium secondary battery, a lithium secondary battery, and manufacturing methods therefor - Google Patents
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Abstract
A method of manufacturing carbon for a lithium secondary battery comprising the first step of bringing dry-distilled charcoal into contact with a halogen gas to obtain halogenated dry-distilled charcoal, the second step of bringing the halogenated charcoal into contact with a thermally decomposable hydrocarbon to obtain preliminary pore adjusted charcoal, the third step of eliminating a part or all of the halogen from the preliminary pore adjusted charcoal to obtain dehalogenated charcoal, and the fourth step of bringing the preliminary pore adjusted charcoal into contact with a thermally decomposable hydrocarbon. Carbon for a lithium secondary battery manufactured by the method and a lithium secondary battery comprising this carbon.
Description
CA 022~0719 1998-10-20 ~ CARBON FOR A LITHIUM SECONDARY BATTERY, A LITHIUM: SECONDARY BATTERY, AND MANUFACTURING METHODS THEREFOR
FIELD OF THE INVENTION
This invention relates to carbon for a lithium secondary battery which is suitable as an electrode material for a rechargeable lithium secondary battery and a manufacturing method for the carbon. It also relates to a lithium secondary battery comprising the carbon7 and a manufacturing method for the battery.
BACKGROUND
As startin~, materials for carbon for an electrode, carbonized plant and animal materials such as lignite, brown coal, anthracite coal, coke, wood charcoal, coconut shell char; any kind of resin such as phenol resin, furan resin, vinylidene chloride copolymer, etc., which have been heated in an inert gas (dry~ till~tion), and the like may be used.
Because carbonaceous materials are chemically inactive7 they are used in a wide range of applications such as adsorption agents, catalysts, electrode materials, structural materials for use in machines, etc. This use is closely related to the structure of the carbon.
The carbon which is referred to as porous carbon has specific effects due to thedevelopment of pores. For example, it is used for mixture separation and purification by means of the adsorption phenomena. In addition, the carbon used in electrical double layer capacitors, the carbon used in lithium secondary batteries, and the like display electrochemical energy-storing effects.
The structure of the carbonaceous material can take various forms depending on the starting material and the m:~nllf~c.turing method. Char and active carbon obtained by activating char comprise microcrystalline carbon (crystallites), and carbon which takes on a chain structure. When the carbonaceous material is nongraphitizing carbon, randomly layered crystallites are formed, and a wide range of pores, from micropores to macropores, is formed in the gaps between these crystallites.
The crystallites are made of net planes of six-membered carbon rings that are piled up to form several parallel layers, and graphite carbon forming six-membered carbon rings is bonded each other using the Sp2 hybrid orbital. A net plane comprising a si~-membered CA 022~0719 1998-10-20 carbon ring is called a basal plane.
Graphitizing carbon develops crystallites by means of heating at a high temperature, and finally becomes graphite.
Nongraphitizing carbon, and graphitizing carbon which has not been completely graphitized usually contain unorganized carbon Unorganized carbon is carbon other than graphite carbon which is chemically bonded to graphite carbon only. The unorganized carbon includes carbon which has a chain structure7 carbon which is stuck around six-membered ring carbon, carbon which is in the outermost (prism plane) six-membered carbon rings, and carbon which is held in cross-linked structures with other six-membered carbon rings (crystallites).
Some of the unorganized carbon is bonded with oxygen atoms, hydrogen atoms, and the like in forms such as C-H, C-OH7 C-OOH, and C=O; or is in the form of double bonded carbons (-C=C-).
Lithium secondary batteries which utilize porous carbonaceous material in the negative electrode are charged by means of the uptake (doping) of lithium ions by the carbonaceous material of the negative electrode and are discharged by the release (un-doping) of lithium ions In the lithium secondary battery, the charging capacity is determined by the amount of lithium ions with which the carbonaceous material is doped, and the discharging capacity is determined by the de-doping amount. The efficiency of the electrical charging and discharging is defined as the ratio of the discharging capacity to the charging capacity When using graphite as the above-mentioned carbonaceous material, the lithium ions are taken in between the layers of the net planes of the carbon In this case, it is reported that the theoretically maximal doping quantity is when there is one lithium ion for every six carbon atoms. However, there are reports that, when non-graphitizing carbonaceous material is used, charging capacities which exceed the above-mentioned theoretically maximal amount can be obtained To date, a variety of methods for m~nuf~cturing carbon for a lithium battery have been proposed~ for example, in Japanese Patent Applications Laid-Open numbers H02-66856, H06-187972, S61-218060, H05-335017, H02-230660, H05-89879, H05-182668, H03-245473, and H05- 14440.
The Japanese Patent Application Laid-Open number H02-66856 discloses that carbon CA 022~0719 1998-10-20 with a distance between faces of lattice doo2=3 80A and true density of 1.55g/cm3 can be obtained by carbonizing furfurylalcohol resins at 500 C and then heating at 1100 ~C, and that a large amount of lithium ions can be doped between the carbon net planes.
The Japanese Patent Application Laid-Open number H06-187972 discloses a carbonaceous material obtained by reacting a condensed polycyclic aromatic compound with a cross-linking agent such as paraxyleneglycol and then baking the generated resins at a temperature higher than 1000~C. The resulting substance comprises a crystallized graphite structure made of an aromatic componentl and non-crystallized domain formed by the cross-linking agent. This substance is suitable for carbon for a lithium secondary battery.
The Japanese Patent Application Laid-Open number S61-218060 discloses that the suitable material includes condensed aromatic resins such as polyacene, that is m~nllf~c.tllred by heat-treatment to have H/C atomic ratio of 0.5-0.05, a BET specific surface area of 600m2/g or greater, and an average pore size of 10 ,~ m or smaller. It also discloses that carbon with the above-mentioned properties can be obtained by heat-treatment at 350-800~C, since such treatment enables the substance to form a 3-dimensional net structure.
A lithium secondary battery has a general problem of irreversible charging and discharging, which makes the efficiency low. Thus, not only a lithium secondary battery with a large capacity but also a carbonaceous material with a large discharging capacity are expected.
We have discovered that the discharging capacity and its efficiency are improvedwhen halogenated dry-distilled charcoal that is obtained by halogenation of dry-distilled charcoal is preliminarily pore adjusted before dehalogenation and pore adjustment treatments.
SUMMARY OF THE INVENTION
This invention relates to a method of m~nllf~cturing carbon for a lithium secondary battery comprising a halogenation treatment of bringing dry-distilled charcoal in contact with a halogen gas to obtain halogenated dry-distilled charcoal; a preliminary pore adjustment treatment of bringing said halogenated charcoal obtained in the halogenation treatment in contact with a thermally decomposable hydrocarbon to obtain preliminarily pore adjusted charcoal; a dehalogenation treatment of elimin~ting a part or all of the halogen from said CA 022~0719 1998-10-20 charcoal obtained in the preliminary pore adjustment treatment to obtain dehalogenated charcoal. and a pore adjustment treatment of bringing said charcoal obtained in the dehalogenation treatment into contact with a thermally decomposable hydrocarbon.This invention also relates to carbon for a lithium secondary battery m~nnf~ctllred by the above-mentioned method.
This invention relates to a lithium secondary battery comprising a carbon electrode, a lithium electrode, an electrolytic solution provided between said electrodes, wherein said carbon electrode is the above-mentioned carbon for a lithium secondary battery.
This invention is also directed to a method of m~nnf~cturing a lithium secondarybattery comprising a carbon electrode, a lithium electrode, and an electrolytic solution provided between said electrodes wherein said lithium secondary battery is assembled, in an inert gas, with above-mentioned carbon for a lithium secondary battery.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig I is a process diagram showing a m:~nllf~ch~ring method for the lithium secondary battery of the present invention.
Fig. 2 is a cross section of the evaluation cells used in the Examples and the Comparative Examples.
Fig. 3 is a diagram of a typical current-potential curve when measuring charging and discharging capacities.
Fig. 4 is a cross section of the coin-shaped lithium secondary battery m~nnf~c.tured in the Examples.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, an inert gas is nitrogen, rare gases such as helium and argon, or a mixture of these gases.
A preferred halogenated dry-distilled charcoal of this invention is in a powder state.
A preferred dehalogenated dry-distilled charcoal of this invention is in a powder state. A
preferred preliminary pore adjustment step of this invention is heating at the temperature between 300 and 900 ~C in a thermally decomposable hydrocarbon that is diluted with an inert gas. A preferred thermally decomposable hydrocarbon of this invention used in the - CA 022~0719 1998-10-20 preliminary pore adjustment step is at least one type of aromatic hydrocarbons, cyclic hydrocarbons, saturated chain hydrocarbons, and unsaturated chain hydrocarbons.
Carbonaceous materials Dry-distilled charcoal that can be used for manufacturing the lithium secondary battery of this invention includes a variety of dry distilled materials such as carbonized plant or animal materials like lignite, brown coal, anthracite coal, coke, wood charcoal and coconut shell char, and resins like phenol resin, furan resin, and vinylidene chloride copolymer. A preferred resin is phenol resin.
Dry-distillation Starting materials such as phenol resin are heated at a temperature between 500 and 1000 ~C optionally under a current of an inert gas such as nitrogen and argon Halo~;enation treatment The dry-distilled charcoal obtained above is then brought into contact with halogen gas such as chlorine, thereby the carbon (in the charcoal) is reacted with halogen. Although any kindsQf halo~en can be used, chlorine and bromine are preferably used.
The degree of chlorination of the halogenated dry-distilled charcoal is expressed by the atomic ratio of chlorine to carbon (Cl/C). The atomic ratio in the chlorination tre~tment is a molar ratio of the numbers of atoms which are obtained by the conversion from the weight of carbon and the weight of chlorine, in which the weight of the carbonized charcoal before the chlorination step is ~csllmecl to be the weight of carbon and the weight increase due to the chlorination step is assumed to be the weight of chlorine. In the dehalogenation treatment, it is assumed that the decrease of the weight is solely due to the dehalogenation, and this is converted to the numbers of the decreased chlorine atoms for subtraction from the numbers of the halogen atoms in the halogenized dry-distilled carbon.
in the reai halogenaiion step, due io the dry-dis~illa~ion action accolllpaïïyiïï$ the process of carbonization and the activated action by steam (the gasification of carbon), the ratio of the numbers of atoms according to the above definition can be a negative value.
The halogenation treatment is, when using chlorine gas for example, carried out by heating dry-distilled charcoal at a temperature between 350 and 1000 ~C, preferably 400 and 800 ~C, and more preferably 500 and 700 ~C in chlorine gas diluted with an inert gas such as CA 022~0719 1998-10-20 nitrogen. When bromine is used instead of chlorine, heating is conducted at a temperature between 350 to 1000~C, and preferably 400 and 800 ~C in bromine gas diluted with an inert gas such as nitrogen.
In the halogenation treatment, when the temperature of the heat treatment of thechlorination, for example, exceeds 1000 ~C, the degree of chlorination is reduced, as the carbonation progresses, due to the reduction in the quantity of hydrogen atoms and therefore this is not desirable. In addition, when the temperature of the heat treatment of the chlorination is less than 350~C, a long period of time is required for the chlorination treatment because the reaction rate between the unorganized carbon and the chlorine is too low, therefore this is not desirable. This is the same for the bromination treatments.
By means of the above-mentioned halogenation treatment, halogenated dry-distilled charcoal such as a chlorinated dry-distilled charcoal having an atomic ratio of chlorine to carbon (Cl/C) of 0.03 or greater, and preferably of 0.07 or greater, and a bromin~ted dry-distilled charcoal having an atomic ratio of bromine to carbon (Br/C) of 0.01 or greater, and preferably 0.03 or greater can be obtained. It is not desirable for this atomic ratio to be less than the above-mentioned minimllm value, since the formation of micropores is insufficient.
When the m~nllf~ctured carbonaceous material with such atomic ratio is used in a lithium secondary battery. good charging and discharging properties cannot be obtained In addition, the upper limit of the above-mentioned atomic ratio is determined by the quantity of hydrogen atoms in the halogenated dry-distilled charcoal, that is the carbonization temperature.
Although the ratio is not particularly limited, it is understood that when the atomic ratio (Cl/C) is 0 315 or less, the charging and discharging properties of the battery m~n~lf~ctured with the carbonaceous material are improved.
Preliminary pore adjustment treatment We have previously found that a carbonaceous material with better charging and discharging properties can be obtained by pore adjustment and halogenation treatments as disclosed in Japanese Patent Application Laid-Open number H07-230803 and PCT
International Patent Publication W097/01192. As a result of further in-depth investigation, we have found that the charging capacity and charge-discharge efficiency can be greatly improved by conducting a preliminary pore adjustment treatment on halogenated dry-distilled CA 022~0719 1998-10-20 charcoal, and this is disclosed in this application.
In one embodiment of the preliminary pore adjustment treatment, halogenated dry-distilled charcoal is heated at a temperature between 300 and 900 ~C, and preferably 400 and 700 ~C in a thermally decomposable hydrocarbon diluted with an inert gas. When the heating temperature exceeds 900 ~C, it becomes difficult to control the preliminary pore adjustment treatment, therefore the desired effect of this invention cannot be obtained When the temperature is less than 300 ~C, the rate of the thermal decomposition of hydrocarbon becomes low, therefore it takes longer for preliminary pore adjustment treatment to be completed and this is not desirable.
The above-mentioned thermally decomposable hydrocarbons may be at least one typeof hydrocarbon selected from the group consisting of aromatic hydrocarbons, cyclic hydrocarbons, saturated chain hydrocarbons, and unsaturated chain hydrocarbons Examples of the thermally decomposable hydrocarbons include benzene, toluene, xylene, ethylbenzene, naphthalene, methylnaphthalene, biphenyl, cyclohexane, methylcyclohexane, 1,1-dimethylcyclohexane, 1,3,5-trimethylcyclohexane, cycloheptane, methane, isobutane, hexane, heptane, isooctane, acetylene, ethylene, butadiene, ethanol, isopropanol, and isobutylene.
Among these, benzene or toluene is preferably used.
In another embodiment, the preliminary pore adjustment tre~tm~nt is conducted bymeans of thermal decomposition of the liquid hydrocarbon compounds with which the halogenated dry-distilled charcoal is impregnated. For example, with 2,4-xylenol, quinoline, or creosote, a precursor in I to 20 % by weight is impregnated, and then, under a current of nitrogen gas, the precursor is heated at the temperature which enables the reaction of the hydrocarbon compound with the halogenated dry-distilled charcoal to take place (for example, 400 to gO0~C). At these temperatures, the hydrocarbon compound is decomposed to make carbons educed, and the educed carbon is replaced with a part of the halogen in the halogenated dry-distilled charcoal. Pitch and resins are also used as thermally decomposable hydrocarbon compounds.
After preliminary pore adjustment treatment is conducted to granular or cylindrical halogenated dry-distilled charcoal, crushing treatment can be conducted. However, it is possible and desirable to first prepare halogenated dry-distilled charcoal in a granular state, and CA 022~0719 1998-10-20 then to conduct the preliminary pore adjustment treatment to the charcoal.
Dehalo~enation treatment Low temperature dehalogenation is a treatment in which the above-mentioned preliminary pore adjusted and halogenated dry-distilled charcoal is heated, to make the halogen detached from the charcoal, at a temperature between 600 and 850 ~C, and preferably 650 and 7~0 ~C in a steam of a lower hydrocarbon gas that is diluted with an inert gas. Alternatively, the low temperature dehalogenation is a treatment in which the halogenated dry-distilled charcoal is heated, to make the halogen detached from the charcoal, at a temperature between 600 and 1400 ~C, and preferably 650 and 1200 ~C in a hydrogen gas diluted with an inert gas.
The heatin~s~ time is approximately 20 to 60 min. With regard to a preferred degree of dehalogenation, in the case of chlorine, the above-mentioned ratio of the numbers of atoms (Cl/C) is equal to or less than 0.02, and in the case of bromine, the above -mentioned ratio of the numbers of atoms (Br/C) is equal to or less than 0.01. However, the ratio is not limited to these values and the effect of the present invention can be achieved even if some of the halogen atoms is left in the charcoal.
High temperature dehalogenation is a heating treatment at a temperature between 700 and 1400 ~C, and preferably 800 and 1300 ~C in an inert gas. Alternatively, high tenperature dehalogenation is a treatment at a temperature between 700 and 1400 ~C, and preferably 800 and 1300 ~C in vacuum evacuation. The degree of the vacuum evacuation is not specifically limited, however, approximately 10 Torr is preferred. The time for heating is approximately 30 to 120 minutes. When the temperature ofthe high temperature dehalogenation treatment is less than 700 ~C, a long period of time is required therefore it is not efficient; and when the temperature exceed 1400 ~C, the effects of thermal shrinking are too large, therefore it is not preferable for pore structure formation High temperature dehalogenation treatment has effects of porosity reduction, as well as dehalogenation, by heat shrinking the entire porous carbonaceous material.
Pore adjustment treatment Dehalogenated carbonaceous materials are subjected to a pore adjustment treatment by contact with a thermally decomposable hydrocarbon. The carbon without pore adjustment treatment is referred to as an electrode carbon precursor.
In one embodiment of the pore adjustment treatment in which contact is made with a thermally decomposable hydrocarbon, the heating treatment of the electrode carbon precursor may be conducted in a thermally decomposable hydrocarbon diluted with an inert gas at a temperature between 600 and 1100 ~C, preferably 700 and 1050 ~C, and more preferably 800 and 1000 ~C A pore adjustment treatment is conducted for adjusting the size of the pores so that the organic solvent in the electrolytic solution does not enter the pores By properly selecting the kind of the thermally decomposable hydrocarbon, the temperature of the treatment, and the time of the treatment, pores of the desired size can be obtained When the temperature exceeds 1100 ~C, it becomes more diff1cult to control the eduction of the thermally decomposed carbons, therefore it becomes more difficult to obtain pores of the desired size. When the temperature is less than 600 ~C, the rate of the thermal decomposition becomes low, therefore it takes longer to conduct pore adjustment treatment, and this is not preferable.
In another embodiment, the pore adjustment treatment in which contact is made with a thermally decomposable hydrocarbon is conducted by thermal decomposition of the liquid hydrocarbon compounds with which the electrode carbon precursor was impregn~tecl In one example, the above-mentioned precursor is impregnated with 2,4-xylenol, quinoline, or creosote, in 1 to 20 % by weight, and then under a current of nitrogen gas, heated at the temperature which enables the thermal decomposition to proceed (ex. 600-1200~C)~ thereby the hydrocarbon compounds are decomposed so that carbon is educed and the educed carbon makes the pores of the precursor narrower As thermally decomposable hydrocarbon compounds, pitch, resin and the like can be also used.
After the pore adjustment treatment, crushing is conducted and the resulting powder can be used for m~n~lf~cturing an electrode However, it is preferrable to prepare dehalogenated carbon in a powder state in advance and then to conduct the above-mentioned pore adjustment treatment since if the average particle size after the crushing is too small, the effect of the pore adjustment treatment may become low.
Hereinafter, pore adjusted carbon and the carbon that is molded into the desired shape in order to measure its charging and discharging properties are referred to as carbon for an electrode or simply as carbon; and the carbon that is impregnated with an electrolytic solution is CA 022~0719 1998-10-20 referred to as a carbon electrode.
The carbon for a lithium secondary battery that is obtained by the above-mentioned manufacturing method has a superior discharging capacity and efficiency.
Figure 2 shows an evaluation cell for measuring charging and discharging capacity and efficiency This evaluation cell comprises a carbon electrode 1, and a lithium electrode 2 as an opposite electrodel a separator 3 between the electrodes, an electrolytic solution 4 that is in contact with the electrodes, and reference electrode S comprising lithium, said lithium being placed in the electrolytic solution. Although strictly speaking~ the carbon electrode 1 is a cathode and the doping of lithium ions to the carbon electrode I is discharging with regard to the evaluation cell shown in Fig. 2; this process is referred to as charging, for convenience sake, as is in a real battery, and therefore the process in which lithium ions are taken out of the carbon electrode 1 is referred to as discharging.
The test method for evaluation of charging and discharging capacity and efficiency is clarified in referring to the current-potential curve shown in Fig. 3.
In the initial charging process, the initial electric potential of the carbon electrode (ne~ative) to the lithium electrode 5 is approximately 1.5 (V), and the application of electric current is begun at a fixed electric current having a current density of 0.53 mA/cm2 . When the electric potential of the carbon electrode 1 is gradually reduced to be O mV, a switch from a fixed electric current to a fixed electric potential is made, and thereafter the electric source is turned offwhen the electric current density is small enough. When the recovery of the electric potential is equal to or less than 10 mV after 2 hours pause, the charging is completed.
After a 2 hour pause from the completion of the charging, discharging is conducted.
Discharging is continuously conducted at a fixed current of 0.53 mA/cm2 and then when the electric potential reaches 1.5 (V), the discharging is completed.
Charging capacity A and discharging capacity B are represented by the shaded area A
and B in Fig. 3 respectively. Charging capacity and discharging capacity are expressed as a capacity per 1 g of carbonaceous materials. The loss of the capacity is the difference of charging capacity and discharging capacity (A - B). Discharging efficiency K is expressed as B/A x loo (%) A variety of electrolytic materials that are dissolved in an organic solvent can be used CA 022~0719 1998-10-20 as an electrolytic solution. For example, LiC104, LiAsF6~ LiPF6, LiBF4 and the like can be used as an electrolytic material, and propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2- diethoxyethane, r -butyllactone, tetrahydrofuran, 2-methyltetrahydrofuran, diethyl ether, acetonitrile and the like can be used as organic solvents.
Hereinafter, the basis for manufacturing carbon for a lithium secondary battery with a superior discharging property by means of the above-mentioned method is clarified.
In the halogenation treatment, the halogen which is brought into contact with dry-distilled charcoal, for example chlorine, reacts with unorganized carbon. These reactions include addition of chlorine to carbon double bonds, substitution of hydrogen atoms bonded to the unorganized carbon with chlorine atoms (hydrogen chloride in equimolar amount is generated), dehydrogenation (hydrogen chloride in an amount double that of chlorine is generated) and the like.
The preliminary pore adjustment treatment is conducted to adjust the pore size in advance so that it is a preferable size for the pore adjustment treatment in the later step. In the preliminary pore adjustment treatment, the thermally decomposable hydrocarbons are replaced with halogen near the surface of carbon primary particles to make the pores near the surface narrower. When a pore adjustment treatment is conducted after conducting the preliminary pore adjustment and dehalogenation treatments, the amount of impregnated thermally decomposable hydrocarbons can be reduced compared to the case where a pore adjustment treatment is conducted once without having a preliminary pore adjustment treatment. It is believed that the smaller amount of carbon impregnation m~int~in~ the level of the occlusion amount of lithium ions in the carbonaceous materials that are attained by halogenation treatment.
It is possible to prepare carbon in a powder state after the preliminary pore adjustment treatment However, it is possible and preferable to conduct the preliminary pore adjustment treatment on the halogenated dry-distilled charcoal in a powder state. It is thought that the pore size near the surface of the carbon particles in a powder state is narrowed by conducting the preliminary pore adjustment treatment on the halogenated dry-distilled charcoal in the powder state, and that a high level of occlusion of lithium ions in the inside of the particles can CA 022~0719 1998-10-20 be maintained due to the halogen.
In the dehalogenation treatment, the aforementioned halogen bonded to the unorganized carbonl for example chlorine, is removed. It is thought that, in the halogenation (chlorination) treatment, the preliminary pore adjustment treatment, the low temperature dehalogenation (dechlorination) treatment, and the high temperature dehalogenation (dechlorination) treatment; the following reaction takes place due to the dehalogenation (dechlorination) and thermal shrinking, and new carbon atom - carbon atom bonding (hereinafter referred to as a carbon bond) is formed. In the following formula (i), the * mark shown next to the C indicates an unorganized carbon.
C*-CI + C*-H ~ C-C + HCI (i) Although the formation of new carbon bonds is thought to have an action of restoring defects in the graphite structure of the carbon net plane or crystallites, an action of crystallite growth, an action of changing the aggregation condition of crystallites, and so on, and details of these actions are not known. However, it is thought that by these actions, lots of micropores (0.8-2.0 nm) and/or submicropores (<0.8 nm) that are suitable for adsorbing gases with smaller molecular size such as nitrogen and oxygen are formed. These pores are thought to function effectively for charging and discharging lithium ions Another action of the high temperature dehalogenation is the action of reducing the porosity by thermally shrinking the entire porous carbon obtained by the halogenation treatment.
In other words, tightening of the aggregation of crystallites is carried out. As a result, pore size is also reduced.
Although the mech~ni~m~ of the pore adjustment have not been established yet, it is thought that the molecules of the solvent which have large molecular diameters cannot penetrate into the pores as a result of the narrowing the openings of the micropores by thermally decomposed carbons. However, since the lithium ions which have small ionic diameters can pass, charging and discharging are possible.
It is thought that the carbon for the lithium secondary battery m~nllf~ctured by the method of this invention has improved charging and discharging efficiency due to the above-mentioned effects acting synergistically.
A lithium secondary battery can be composed of carbon as an anode m~nllf~ctured by the methods of the present invention and a lithium compound as a cathode. The combination CA 022~0719 1998-10-20 , 13 of carbon electrode of this invention and the components of the cathode, the shape, and the composition concentration of the electrolytic solution, and the like are all suitably set in accordance with the use of the lithium secondary battery.
EXAMPLES
The present invention is illustrated by the following examples. However, it should be understood that the invention is not limited to the specific details of these examples.
The carbonaceous materials of the examples 1 to 6 were manufactured and their charging and discharging properties were compared to those of the carbonaceous materials of Comparative Examples I to 4.
~ry-distilled charcoal Phenol resin, PGA-4560 (m~nllf~ctllred by Gun-ei Chemical Industry (Ltd), sold under the name of Resitop) as a binder was added to Phenol resin R 800 (m~nl1f~ct11red by Kanebo Co.. Ltd., sold under the name of Bell Pearl), and the mixture was molded into a cylindrical shape of approximately 2 mm (~) x 5-6 mm, and then dry-distilled at 700 ~C under a current of nitrogen gas to obtain a dry-distilled charcoal starting material.
Halooen treatment The dry-distilled charcoal starting materials were then treated with halogen to form porous carbonaceous materials. In the case of chlorination, the dry-distilled charcoal starting material (approximately 15 g) was heated at 600 ~C for two hours under a current of nitrogen gas (2.7NL/min) cont~inin~ chlorine at 5% by yolume. In the case of bromination, the dry-distilled charcoal starting material was heated at 600 ~C for two hours under a current of nitrogen gas (3NL/min) cont~inin~ bromine at 5 % by volume .
Preliminary pore adjustment treatment A preliminary pore adjustment treatment was conducted by heating at 400 to 550 ~C
for 25 to 120 minutes under a current of nitrogen gas saturated with benzene or toluene at 25 ~C .
Dehalo enation treatment Low temperature dehalogenation treatment: After the preliminary pore adjustment treatment, the dry-distilled charcoal was heated at 700 ~C for 30 minutes under a current of CA 022~0719 1998-10-20 nitrogen gas saturated with steam at 25 ~C (lNL/min).
High temperature dehalogenation treatment: After preliminary pore adjustment treatment, the dry-distilled charcoal was heated at 1000 ~C for 60 minutes under a current of nitrogen gas (3NL/min).
Pore adjustment treatment After dehalogenation treatment, the dry-distilled charcoal was heated at 900 ~C for 10 minutes under a current of nitrogen gas saturated with toluene at 25 ~C.
Crushin~r After the pore adjustment treatment, the dry-distilled charcoal was crushed to pieces using a small size vibrating ball mill7 NB-0, manufactured by Nitto Kagaku (Ltd) for 30 minutes.
Carbon for Battery To the carbon obtained after the halogenation treatment, the preliminary pore adjustment treatment7 the dehalogenation treatment, and the pore adjustment treatment, poiyfluorovinyiidene (9 % by weight of the carbon) as a binder was added, and then, N-methyi-2-pyrrolidone was added to the mixture to form a paste. The resulting paste was poured onto a collecting electrode made of stainless steel ( 10 mm diameter) to obtain carbon for a battery.
Evaluati~n test for Char~ing and Dischar~in~ Capacity The electrolytic solution used was a solution of a 1:1 mixture of propylene carbonate and dimethoxyethanel to which lithium perchlorate (LiC~04) (1.0 mol/l) was added as a supporting electrolyte. The carbon electrode was formed by immersing the above-mentioned carbon for a battery in the electrolytic solution.
With regard to charging and discharging, the above-mentioned charging capacity (A) and dischargin~ capacity (B) were measured using a charging and discharging testing device (model HJ-201B) m~mlf~c.tllred by Hokuto Denko (Ltd).
Comparative Example No preliminary pore adjustment; with chlorination, high temperature dehalogenation, steam dehalogenation, and post-dehalogenation crushing.
Dry-distilled charcoal was subjected to the halogenation treatment, and the resulting charcoal was then heated at 1000 ~C under a current of nitrogen gas (high temperature CA 022~0719 1998-10-20 dehalogenation treatment). The charcoal was further heated under a current of nitrogen gas containing steam (low temperature dehalogenation treatment). After crushing and pore adjustment treatment, the carbon for battery was manufactured according to the above shown method. The battery was tested for its charging and discharging properties using evaluation cells: A=772 mAh/g, B=652 mAh/g, discharging efficiency (K) =84.~S%, and the loss of capacity= 120 mAh/g.
Comparative Example 2 No preliminary pore adjustment; with chlorination, high temperature dehalogenation, steam dehalogenation, and post-halogenation crushing.
The dry-distilled charcoal was subjected to chlorination and then crushed into pieces.
The resulting charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperature dechlorination treatment), and then heated again under a current of nitrogen gas cont~ining steam (low temperature dehalogenation treatment). The charcoal thus obtained was subjected to the pore adjustment treatment and carbon for battery was m~nllf~ctured by the above-mentioned method, and its charging and discharging properties were measured using an evaluation cell: A=773 mAh/g, B=649mAh/g, discharging efficiency = 84.0%, and the loss of capacity = 124 mAh/g.
Comparative Example 3 No preliminary pore adjustment; with chlorination, steam dechlorination, high temperature dechlorination, and post-dechlorination crushing.
Dry-distilled charcoal was subjected to chlorination. The charcoal was heated under a current of nitrogen gas conl~ining steam (low temperature dehalogenation treatment) and then heated at 1000 ~C under a current of nitrogen gas (high temperature dehalogenation treatment). After crushing and pore adjustment treatments, carbon for battery was manufactured by the above-mentioned method, and its charging and discharging properties were measured: A=764 mAh/g, B=642 mAh/g, discharging efficiency = 84.0%, and the loss of capacity= 122 mAh/g.
Comparative Example 4 No preliminary pore adjustment; with bromination, steam debromination~ high temperature debromination and post-debromination crushing.
CA 022~0719 1998-10-20 lG
Dry-distilled charcoal was subjected to bromination. The charcoal was then heated under a current of nitrogen gas (low temperature debromination treatment) and heated at 1000 ~C under a current of nitrogen gas (high temperature debromination treatment). After crushing and pore adjustment treatments, carbon for battery was manufactured by the above-mentioned method, and then its charging and discharging properties were measured using an evaluation cell: A=774 mAh/g, B=660 mAh/g, discharging efficiency = 85.3%, and the loss of capacity = 114 mAh/g.
Example 1 With chlorination, preliminary pore adjustment (toluene, 550~C x 25 min), high temperature dechlorination, steam dechlorination and post-dechlorination crushing.
Dry-distilled charcoal was subjected to chlorination, and by using toluene a preliminary pore adjustment treatment was conducted at 550~C for 25 min. Then, the charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperature dechlorination tre~tment), and the resulting charcoal was heated under a current of nitrogen gas cont~ining steam (low iemperai:ure chlorinaiion trealmeni). Af~eF cFushirrg and pore adjustmeni ireaimenis, carbon for battery was m~n~lf~c.tllred by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=798 mAh/g, B=688 mAh/g, discharging efficiency = 86.2%, and the loss of capacity = 110 mAh/g.
Example 2 With chlorination, prelimin~ry pore adjustment (toluene, 550 ~C X 25 min), high temperature dechlorination, steam dechlorination and post-chlorination crushing.Dry-distilled charcoal was subjected to chlorination and then the reslllting charcoal was crushed into pieces. By using toluene a prelimin:~ry pore adjustment treatment was conducted at 550~C for 25 min. Then, the charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperature dechlorination treatment), and the resulting charcoal was heated under a current of nitrogen gas cont~ininsg steam (low temperature chlorination treatment). After the pore adjustment treatment, carbon for battery was m~nllf~ctured by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=816 mAh/~, and B=720 mAh/g, discharging efficiency = 88.2%, and the loss of capacity = 96 mAh/g.
CA 022~0719 1998-10-20 Example 3 With chlorination, preliminary pore adjustment (benzene, 550~C X 50 min), high temperature dechlorination and post-chlorination crushing.
Dry-distilled charcoal was subjected to chlorination and then the resulting charcoal was crushed into pieces. By using toluene a preliminary pore adjustment treatment was conducted at 550~C for 50 min. Then, the charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperature dechlorination treatment), and the resulting charcoal was heated under a current of nitrogen gas cont~ining steam (low temperature chlorination treatment) After the pore adjustment treatment, carbon for battery was m:~nllf~ctured by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=819 mAh/g, B=721 mAh/g, discharging efflciency = 88.0%, and the loss of capacity = 9g mAh/g.
Example 4 With chlorination, pr~.limin~ry pore adjustment (toluene, 550~C x 25 min), steamdechlorinatiGn, high terllperature dec~'orinztion and post-dechlorination cr.,shing.
Dry-distilled charcoal was subjected to chlorination, and then, using toluene, apreliminary pore adjustment treatment was conducted at 550~C for 25 min Then, the charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperaturedechlorination treatment), and the resulting charcoal was heated under a current of nitrogen gas cont~ining steam (low temperature chlorination treatment). After crushing and pore adjustment treatments, carbon for battery was m~nllf~ctllred by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=812 mAh/g, B=700 mAh/g, discharging efficiency = 86.2%, and the loss of capacity = 1 12 mAh/g.
Example 5 With chlorination, preliminary pore adjustment (toluene, 400~C x 120 min), steamdechlorination, high temperature dechlorination, and post-dechlorination crushing.
Dry-distilled charcoal was subjected to chlorination and then resulting charcoal was subjected to the preliminary pore adjustment treatment (toluene, 400~C x 120 min). Then, the charcoal was heated at 1000~C under a current of nitrogen gas (high temperature dechlorination treatment), and the resulting charcoal was heated under a current of nitrogen gas CA 022~0719 1998-10-20 containing steam (low temperature chlorination treatment). The resulting charcoal was crushed into pieces and after the pore adjustment treatment, carbon for battery was manufactured by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=797 mAh/g, B=687 mAh/g, discharging efficiency =
86.2%, the loss ofthe capacity = 110 mAh/g.
Example 6 With bromination, preliminary pore adjustment (toluene, 550~C X 25 min), steam debromination, high temperature debromination, and post-debromination crushing.
Dry-distilled charcoal was subjected to bromination. By using toluene, a preliminary pore adjustment treatment was conducted at 550~C for 25 min. Then7 the charcoal was heated under a current of nitrogen gas cont~ining steam (low temperature debromination treatment), and the resulting charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperature debromination treatment). After crushing and pore adjustment treatments, carbon for battery was m~nuf~ctured by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=796 mAh/g, B=693 mAh/g, discharging efficiency = 87 1%, and the loss of capacity = 103 mAh/g.
Table 1 shows charging and discharging properties of Comparative Examples 1-4 and Examples 1-6 together with trç~tmçnt conditions Table 1.
[1~ [2~ [3~ [~ [~ A B A-B K
Cl Cl 2 - - - 772 652 120 84.5 C2 Cl 1 - - - 773 649 124 84.0 C3 Cl 2 - - - 764 642 122 84.0 C4 Br 2 - - - 774 660 114 85.3 El Cl 2 t 550 25 798 688 110 86 2 E2 Cl 1 t 550 25 816 720 96 88.2 E3 Cl 1 b 550 50 819 721 98 88.0 E4 Cl 2 t 550 25 812 700 112 86.2 E5 Cl 2 t 400 120 797 687 110 86.2 E6 Br 2 t 550 25 796 693 103 87.1 CA 022~0719 1998-10-20 C l-C4: Comparative Examples 1-4, El-E6: E?~ample 1-6;
[ I ]: kind of halogen;
[2]: timin, of crushin~;
1: after halogenation treatment, before preliminary pore adjustment treatment, 2: after dehalogenation treatment, before pore adjustment treatment, [3]: I;ind of thermally decomposable hydrocarbon used in the preliminary pore adjustment treatment;
t: toluene, b: ben~ene, [4]: temperature of preliminary pore adjustment treatment (~C);
FIELD OF THE INVENTION
This invention relates to carbon for a lithium secondary battery which is suitable as an electrode material for a rechargeable lithium secondary battery and a manufacturing method for the carbon. It also relates to a lithium secondary battery comprising the carbon7 and a manufacturing method for the battery.
BACKGROUND
As startin~, materials for carbon for an electrode, carbonized plant and animal materials such as lignite, brown coal, anthracite coal, coke, wood charcoal, coconut shell char; any kind of resin such as phenol resin, furan resin, vinylidene chloride copolymer, etc., which have been heated in an inert gas (dry~ till~tion), and the like may be used.
Because carbonaceous materials are chemically inactive7 they are used in a wide range of applications such as adsorption agents, catalysts, electrode materials, structural materials for use in machines, etc. This use is closely related to the structure of the carbon.
The carbon which is referred to as porous carbon has specific effects due to thedevelopment of pores. For example, it is used for mixture separation and purification by means of the adsorption phenomena. In addition, the carbon used in electrical double layer capacitors, the carbon used in lithium secondary batteries, and the like display electrochemical energy-storing effects.
The structure of the carbonaceous material can take various forms depending on the starting material and the m:~nllf~c.turing method. Char and active carbon obtained by activating char comprise microcrystalline carbon (crystallites), and carbon which takes on a chain structure. When the carbonaceous material is nongraphitizing carbon, randomly layered crystallites are formed, and a wide range of pores, from micropores to macropores, is formed in the gaps between these crystallites.
The crystallites are made of net planes of six-membered carbon rings that are piled up to form several parallel layers, and graphite carbon forming six-membered carbon rings is bonded each other using the Sp2 hybrid orbital. A net plane comprising a si~-membered CA 022~0719 1998-10-20 carbon ring is called a basal plane.
Graphitizing carbon develops crystallites by means of heating at a high temperature, and finally becomes graphite.
Nongraphitizing carbon, and graphitizing carbon which has not been completely graphitized usually contain unorganized carbon Unorganized carbon is carbon other than graphite carbon which is chemically bonded to graphite carbon only. The unorganized carbon includes carbon which has a chain structure7 carbon which is stuck around six-membered ring carbon, carbon which is in the outermost (prism plane) six-membered carbon rings, and carbon which is held in cross-linked structures with other six-membered carbon rings (crystallites).
Some of the unorganized carbon is bonded with oxygen atoms, hydrogen atoms, and the like in forms such as C-H, C-OH7 C-OOH, and C=O; or is in the form of double bonded carbons (-C=C-).
Lithium secondary batteries which utilize porous carbonaceous material in the negative electrode are charged by means of the uptake (doping) of lithium ions by the carbonaceous material of the negative electrode and are discharged by the release (un-doping) of lithium ions In the lithium secondary battery, the charging capacity is determined by the amount of lithium ions with which the carbonaceous material is doped, and the discharging capacity is determined by the de-doping amount. The efficiency of the electrical charging and discharging is defined as the ratio of the discharging capacity to the charging capacity When using graphite as the above-mentioned carbonaceous material, the lithium ions are taken in between the layers of the net planes of the carbon In this case, it is reported that the theoretically maximal doping quantity is when there is one lithium ion for every six carbon atoms. However, there are reports that, when non-graphitizing carbonaceous material is used, charging capacities which exceed the above-mentioned theoretically maximal amount can be obtained To date, a variety of methods for m~nuf~cturing carbon for a lithium battery have been proposed~ for example, in Japanese Patent Applications Laid-Open numbers H02-66856, H06-187972, S61-218060, H05-335017, H02-230660, H05-89879, H05-182668, H03-245473, and H05- 14440.
The Japanese Patent Application Laid-Open number H02-66856 discloses that carbon CA 022~0719 1998-10-20 with a distance between faces of lattice doo2=3 80A and true density of 1.55g/cm3 can be obtained by carbonizing furfurylalcohol resins at 500 C and then heating at 1100 ~C, and that a large amount of lithium ions can be doped between the carbon net planes.
The Japanese Patent Application Laid-Open number H06-187972 discloses a carbonaceous material obtained by reacting a condensed polycyclic aromatic compound with a cross-linking agent such as paraxyleneglycol and then baking the generated resins at a temperature higher than 1000~C. The resulting substance comprises a crystallized graphite structure made of an aromatic componentl and non-crystallized domain formed by the cross-linking agent. This substance is suitable for carbon for a lithium secondary battery.
The Japanese Patent Application Laid-Open number S61-218060 discloses that the suitable material includes condensed aromatic resins such as polyacene, that is m~nllf~c.tllred by heat-treatment to have H/C atomic ratio of 0.5-0.05, a BET specific surface area of 600m2/g or greater, and an average pore size of 10 ,~ m or smaller. It also discloses that carbon with the above-mentioned properties can be obtained by heat-treatment at 350-800~C, since such treatment enables the substance to form a 3-dimensional net structure.
A lithium secondary battery has a general problem of irreversible charging and discharging, which makes the efficiency low. Thus, not only a lithium secondary battery with a large capacity but also a carbonaceous material with a large discharging capacity are expected.
We have discovered that the discharging capacity and its efficiency are improvedwhen halogenated dry-distilled charcoal that is obtained by halogenation of dry-distilled charcoal is preliminarily pore adjusted before dehalogenation and pore adjustment treatments.
SUMMARY OF THE INVENTION
This invention relates to a method of m~nllf~cturing carbon for a lithium secondary battery comprising a halogenation treatment of bringing dry-distilled charcoal in contact with a halogen gas to obtain halogenated dry-distilled charcoal; a preliminary pore adjustment treatment of bringing said halogenated charcoal obtained in the halogenation treatment in contact with a thermally decomposable hydrocarbon to obtain preliminarily pore adjusted charcoal; a dehalogenation treatment of elimin~ting a part or all of the halogen from said CA 022~0719 1998-10-20 charcoal obtained in the preliminary pore adjustment treatment to obtain dehalogenated charcoal. and a pore adjustment treatment of bringing said charcoal obtained in the dehalogenation treatment into contact with a thermally decomposable hydrocarbon.This invention also relates to carbon for a lithium secondary battery m~nnf~ctllred by the above-mentioned method.
This invention relates to a lithium secondary battery comprising a carbon electrode, a lithium electrode, an electrolytic solution provided between said electrodes, wherein said carbon electrode is the above-mentioned carbon for a lithium secondary battery.
This invention is also directed to a method of m~nnf~cturing a lithium secondarybattery comprising a carbon electrode, a lithium electrode, and an electrolytic solution provided between said electrodes wherein said lithium secondary battery is assembled, in an inert gas, with above-mentioned carbon for a lithium secondary battery.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig I is a process diagram showing a m:~nllf~ch~ring method for the lithium secondary battery of the present invention.
Fig. 2 is a cross section of the evaluation cells used in the Examples and the Comparative Examples.
Fig. 3 is a diagram of a typical current-potential curve when measuring charging and discharging capacities.
Fig. 4 is a cross section of the coin-shaped lithium secondary battery m~nnf~c.tured in the Examples.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, an inert gas is nitrogen, rare gases such as helium and argon, or a mixture of these gases.
A preferred halogenated dry-distilled charcoal of this invention is in a powder state.
A preferred dehalogenated dry-distilled charcoal of this invention is in a powder state. A
preferred preliminary pore adjustment step of this invention is heating at the temperature between 300 and 900 ~C in a thermally decomposable hydrocarbon that is diluted with an inert gas. A preferred thermally decomposable hydrocarbon of this invention used in the - CA 022~0719 1998-10-20 preliminary pore adjustment step is at least one type of aromatic hydrocarbons, cyclic hydrocarbons, saturated chain hydrocarbons, and unsaturated chain hydrocarbons.
Carbonaceous materials Dry-distilled charcoal that can be used for manufacturing the lithium secondary battery of this invention includes a variety of dry distilled materials such as carbonized plant or animal materials like lignite, brown coal, anthracite coal, coke, wood charcoal and coconut shell char, and resins like phenol resin, furan resin, and vinylidene chloride copolymer. A preferred resin is phenol resin.
Dry-distillation Starting materials such as phenol resin are heated at a temperature between 500 and 1000 ~C optionally under a current of an inert gas such as nitrogen and argon Halo~;enation treatment The dry-distilled charcoal obtained above is then brought into contact with halogen gas such as chlorine, thereby the carbon (in the charcoal) is reacted with halogen. Although any kindsQf halo~en can be used, chlorine and bromine are preferably used.
The degree of chlorination of the halogenated dry-distilled charcoal is expressed by the atomic ratio of chlorine to carbon (Cl/C). The atomic ratio in the chlorination tre~tment is a molar ratio of the numbers of atoms which are obtained by the conversion from the weight of carbon and the weight of chlorine, in which the weight of the carbonized charcoal before the chlorination step is ~csllmecl to be the weight of carbon and the weight increase due to the chlorination step is assumed to be the weight of chlorine. In the dehalogenation treatment, it is assumed that the decrease of the weight is solely due to the dehalogenation, and this is converted to the numbers of the decreased chlorine atoms for subtraction from the numbers of the halogen atoms in the halogenized dry-distilled carbon.
in the reai halogenaiion step, due io the dry-dis~illa~ion action accolllpaïïyiïï$ the process of carbonization and the activated action by steam (the gasification of carbon), the ratio of the numbers of atoms according to the above definition can be a negative value.
The halogenation treatment is, when using chlorine gas for example, carried out by heating dry-distilled charcoal at a temperature between 350 and 1000 ~C, preferably 400 and 800 ~C, and more preferably 500 and 700 ~C in chlorine gas diluted with an inert gas such as CA 022~0719 1998-10-20 nitrogen. When bromine is used instead of chlorine, heating is conducted at a temperature between 350 to 1000~C, and preferably 400 and 800 ~C in bromine gas diluted with an inert gas such as nitrogen.
In the halogenation treatment, when the temperature of the heat treatment of thechlorination, for example, exceeds 1000 ~C, the degree of chlorination is reduced, as the carbonation progresses, due to the reduction in the quantity of hydrogen atoms and therefore this is not desirable. In addition, when the temperature of the heat treatment of the chlorination is less than 350~C, a long period of time is required for the chlorination treatment because the reaction rate between the unorganized carbon and the chlorine is too low, therefore this is not desirable. This is the same for the bromination treatments.
By means of the above-mentioned halogenation treatment, halogenated dry-distilled charcoal such as a chlorinated dry-distilled charcoal having an atomic ratio of chlorine to carbon (Cl/C) of 0.03 or greater, and preferably of 0.07 or greater, and a bromin~ted dry-distilled charcoal having an atomic ratio of bromine to carbon (Br/C) of 0.01 or greater, and preferably 0.03 or greater can be obtained. It is not desirable for this atomic ratio to be less than the above-mentioned minimllm value, since the formation of micropores is insufficient.
When the m~nllf~ctured carbonaceous material with such atomic ratio is used in a lithium secondary battery. good charging and discharging properties cannot be obtained In addition, the upper limit of the above-mentioned atomic ratio is determined by the quantity of hydrogen atoms in the halogenated dry-distilled charcoal, that is the carbonization temperature.
Although the ratio is not particularly limited, it is understood that when the atomic ratio (Cl/C) is 0 315 or less, the charging and discharging properties of the battery m~n~lf~ctured with the carbonaceous material are improved.
Preliminary pore adjustment treatment We have previously found that a carbonaceous material with better charging and discharging properties can be obtained by pore adjustment and halogenation treatments as disclosed in Japanese Patent Application Laid-Open number H07-230803 and PCT
International Patent Publication W097/01192. As a result of further in-depth investigation, we have found that the charging capacity and charge-discharge efficiency can be greatly improved by conducting a preliminary pore adjustment treatment on halogenated dry-distilled CA 022~0719 1998-10-20 charcoal, and this is disclosed in this application.
In one embodiment of the preliminary pore adjustment treatment, halogenated dry-distilled charcoal is heated at a temperature between 300 and 900 ~C, and preferably 400 and 700 ~C in a thermally decomposable hydrocarbon diluted with an inert gas. When the heating temperature exceeds 900 ~C, it becomes difficult to control the preliminary pore adjustment treatment, therefore the desired effect of this invention cannot be obtained When the temperature is less than 300 ~C, the rate of the thermal decomposition of hydrocarbon becomes low, therefore it takes longer for preliminary pore adjustment treatment to be completed and this is not desirable.
The above-mentioned thermally decomposable hydrocarbons may be at least one typeof hydrocarbon selected from the group consisting of aromatic hydrocarbons, cyclic hydrocarbons, saturated chain hydrocarbons, and unsaturated chain hydrocarbons Examples of the thermally decomposable hydrocarbons include benzene, toluene, xylene, ethylbenzene, naphthalene, methylnaphthalene, biphenyl, cyclohexane, methylcyclohexane, 1,1-dimethylcyclohexane, 1,3,5-trimethylcyclohexane, cycloheptane, methane, isobutane, hexane, heptane, isooctane, acetylene, ethylene, butadiene, ethanol, isopropanol, and isobutylene.
Among these, benzene or toluene is preferably used.
In another embodiment, the preliminary pore adjustment tre~tm~nt is conducted bymeans of thermal decomposition of the liquid hydrocarbon compounds with which the halogenated dry-distilled charcoal is impregnated. For example, with 2,4-xylenol, quinoline, or creosote, a precursor in I to 20 % by weight is impregnated, and then, under a current of nitrogen gas, the precursor is heated at the temperature which enables the reaction of the hydrocarbon compound with the halogenated dry-distilled charcoal to take place (for example, 400 to gO0~C). At these temperatures, the hydrocarbon compound is decomposed to make carbons educed, and the educed carbon is replaced with a part of the halogen in the halogenated dry-distilled charcoal. Pitch and resins are also used as thermally decomposable hydrocarbon compounds.
After preliminary pore adjustment treatment is conducted to granular or cylindrical halogenated dry-distilled charcoal, crushing treatment can be conducted. However, it is possible and desirable to first prepare halogenated dry-distilled charcoal in a granular state, and CA 022~0719 1998-10-20 then to conduct the preliminary pore adjustment treatment to the charcoal.
Dehalo~enation treatment Low temperature dehalogenation is a treatment in which the above-mentioned preliminary pore adjusted and halogenated dry-distilled charcoal is heated, to make the halogen detached from the charcoal, at a temperature between 600 and 850 ~C, and preferably 650 and 7~0 ~C in a steam of a lower hydrocarbon gas that is diluted with an inert gas. Alternatively, the low temperature dehalogenation is a treatment in which the halogenated dry-distilled charcoal is heated, to make the halogen detached from the charcoal, at a temperature between 600 and 1400 ~C, and preferably 650 and 1200 ~C in a hydrogen gas diluted with an inert gas.
The heatin~s~ time is approximately 20 to 60 min. With regard to a preferred degree of dehalogenation, in the case of chlorine, the above-mentioned ratio of the numbers of atoms (Cl/C) is equal to or less than 0.02, and in the case of bromine, the above -mentioned ratio of the numbers of atoms (Br/C) is equal to or less than 0.01. However, the ratio is not limited to these values and the effect of the present invention can be achieved even if some of the halogen atoms is left in the charcoal.
High temperature dehalogenation is a heating treatment at a temperature between 700 and 1400 ~C, and preferably 800 and 1300 ~C in an inert gas. Alternatively, high tenperature dehalogenation is a treatment at a temperature between 700 and 1400 ~C, and preferably 800 and 1300 ~C in vacuum evacuation. The degree of the vacuum evacuation is not specifically limited, however, approximately 10 Torr is preferred. The time for heating is approximately 30 to 120 minutes. When the temperature ofthe high temperature dehalogenation treatment is less than 700 ~C, a long period of time is required therefore it is not efficient; and when the temperature exceed 1400 ~C, the effects of thermal shrinking are too large, therefore it is not preferable for pore structure formation High temperature dehalogenation treatment has effects of porosity reduction, as well as dehalogenation, by heat shrinking the entire porous carbonaceous material.
Pore adjustment treatment Dehalogenated carbonaceous materials are subjected to a pore adjustment treatment by contact with a thermally decomposable hydrocarbon. The carbon without pore adjustment treatment is referred to as an electrode carbon precursor.
In one embodiment of the pore adjustment treatment in which contact is made with a thermally decomposable hydrocarbon, the heating treatment of the electrode carbon precursor may be conducted in a thermally decomposable hydrocarbon diluted with an inert gas at a temperature between 600 and 1100 ~C, preferably 700 and 1050 ~C, and more preferably 800 and 1000 ~C A pore adjustment treatment is conducted for adjusting the size of the pores so that the organic solvent in the electrolytic solution does not enter the pores By properly selecting the kind of the thermally decomposable hydrocarbon, the temperature of the treatment, and the time of the treatment, pores of the desired size can be obtained When the temperature exceeds 1100 ~C, it becomes more diff1cult to control the eduction of the thermally decomposed carbons, therefore it becomes more difficult to obtain pores of the desired size. When the temperature is less than 600 ~C, the rate of the thermal decomposition becomes low, therefore it takes longer to conduct pore adjustment treatment, and this is not preferable.
In another embodiment, the pore adjustment treatment in which contact is made with a thermally decomposable hydrocarbon is conducted by thermal decomposition of the liquid hydrocarbon compounds with which the electrode carbon precursor was impregn~tecl In one example, the above-mentioned precursor is impregnated with 2,4-xylenol, quinoline, or creosote, in 1 to 20 % by weight, and then under a current of nitrogen gas, heated at the temperature which enables the thermal decomposition to proceed (ex. 600-1200~C)~ thereby the hydrocarbon compounds are decomposed so that carbon is educed and the educed carbon makes the pores of the precursor narrower As thermally decomposable hydrocarbon compounds, pitch, resin and the like can be also used.
After the pore adjustment treatment, crushing is conducted and the resulting powder can be used for m~n~lf~cturing an electrode However, it is preferrable to prepare dehalogenated carbon in a powder state in advance and then to conduct the above-mentioned pore adjustment treatment since if the average particle size after the crushing is too small, the effect of the pore adjustment treatment may become low.
Hereinafter, pore adjusted carbon and the carbon that is molded into the desired shape in order to measure its charging and discharging properties are referred to as carbon for an electrode or simply as carbon; and the carbon that is impregnated with an electrolytic solution is CA 022~0719 1998-10-20 referred to as a carbon electrode.
The carbon for a lithium secondary battery that is obtained by the above-mentioned manufacturing method has a superior discharging capacity and efficiency.
Figure 2 shows an evaluation cell for measuring charging and discharging capacity and efficiency This evaluation cell comprises a carbon electrode 1, and a lithium electrode 2 as an opposite electrodel a separator 3 between the electrodes, an electrolytic solution 4 that is in contact with the electrodes, and reference electrode S comprising lithium, said lithium being placed in the electrolytic solution. Although strictly speaking~ the carbon electrode 1 is a cathode and the doping of lithium ions to the carbon electrode I is discharging with regard to the evaluation cell shown in Fig. 2; this process is referred to as charging, for convenience sake, as is in a real battery, and therefore the process in which lithium ions are taken out of the carbon electrode 1 is referred to as discharging.
The test method for evaluation of charging and discharging capacity and efficiency is clarified in referring to the current-potential curve shown in Fig. 3.
In the initial charging process, the initial electric potential of the carbon electrode (ne~ative) to the lithium electrode 5 is approximately 1.5 (V), and the application of electric current is begun at a fixed electric current having a current density of 0.53 mA/cm2 . When the electric potential of the carbon electrode 1 is gradually reduced to be O mV, a switch from a fixed electric current to a fixed electric potential is made, and thereafter the electric source is turned offwhen the electric current density is small enough. When the recovery of the electric potential is equal to or less than 10 mV after 2 hours pause, the charging is completed.
After a 2 hour pause from the completion of the charging, discharging is conducted.
Discharging is continuously conducted at a fixed current of 0.53 mA/cm2 and then when the electric potential reaches 1.5 (V), the discharging is completed.
Charging capacity A and discharging capacity B are represented by the shaded area A
and B in Fig. 3 respectively. Charging capacity and discharging capacity are expressed as a capacity per 1 g of carbonaceous materials. The loss of the capacity is the difference of charging capacity and discharging capacity (A - B). Discharging efficiency K is expressed as B/A x loo (%) A variety of electrolytic materials that are dissolved in an organic solvent can be used CA 022~0719 1998-10-20 as an electrolytic solution. For example, LiC104, LiAsF6~ LiPF6, LiBF4 and the like can be used as an electrolytic material, and propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2- diethoxyethane, r -butyllactone, tetrahydrofuran, 2-methyltetrahydrofuran, diethyl ether, acetonitrile and the like can be used as organic solvents.
Hereinafter, the basis for manufacturing carbon for a lithium secondary battery with a superior discharging property by means of the above-mentioned method is clarified.
In the halogenation treatment, the halogen which is brought into contact with dry-distilled charcoal, for example chlorine, reacts with unorganized carbon. These reactions include addition of chlorine to carbon double bonds, substitution of hydrogen atoms bonded to the unorganized carbon with chlorine atoms (hydrogen chloride in equimolar amount is generated), dehydrogenation (hydrogen chloride in an amount double that of chlorine is generated) and the like.
The preliminary pore adjustment treatment is conducted to adjust the pore size in advance so that it is a preferable size for the pore adjustment treatment in the later step. In the preliminary pore adjustment treatment, the thermally decomposable hydrocarbons are replaced with halogen near the surface of carbon primary particles to make the pores near the surface narrower. When a pore adjustment treatment is conducted after conducting the preliminary pore adjustment and dehalogenation treatments, the amount of impregnated thermally decomposable hydrocarbons can be reduced compared to the case where a pore adjustment treatment is conducted once without having a preliminary pore adjustment treatment. It is believed that the smaller amount of carbon impregnation m~int~in~ the level of the occlusion amount of lithium ions in the carbonaceous materials that are attained by halogenation treatment.
It is possible to prepare carbon in a powder state after the preliminary pore adjustment treatment However, it is possible and preferable to conduct the preliminary pore adjustment treatment on the halogenated dry-distilled charcoal in a powder state. It is thought that the pore size near the surface of the carbon particles in a powder state is narrowed by conducting the preliminary pore adjustment treatment on the halogenated dry-distilled charcoal in the powder state, and that a high level of occlusion of lithium ions in the inside of the particles can CA 022~0719 1998-10-20 be maintained due to the halogen.
In the dehalogenation treatment, the aforementioned halogen bonded to the unorganized carbonl for example chlorine, is removed. It is thought that, in the halogenation (chlorination) treatment, the preliminary pore adjustment treatment, the low temperature dehalogenation (dechlorination) treatment, and the high temperature dehalogenation (dechlorination) treatment; the following reaction takes place due to the dehalogenation (dechlorination) and thermal shrinking, and new carbon atom - carbon atom bonding (hereinafter referred to as a carbon bond) is formed. In the following formula (i), the * mark shown next to the C indicates an unorganized carbon.
C*-CI + C*-H ~ C-C + HCI (i) Although the formation of new carbon bonds is thought to have an action of restoring defects in the graphite structure of the carbon net plane or crystallites, an action of crystallite growth, an action of changing the aggregation condition of crystallites, and so on, and details of these actions are not known. However, it is thought that by these actions, lots of micropores (0.8-2.0 nm) and/or submicropores (<0.8 nm) that are suitable for adsorbing gases with smaller molecular size such as nitrogen and oxygen are formed. These pores are thought to function effectively for charging and discharging lithium ions Another action of the high temperature dehalogenation is the action of reducing the porosity by thermally shrinking the entire porous carbon obtained by the halogenation treatment.
In other words, tightening of the aggregation of crystallites is carried out. As a result, pore size is also reduced.
Although the mech~ni~m~ of the pore adjustment have not been established yet, it is thought that the molecules of the solvent which have large molecular diameters cannot penetrate into the pores as a result of the narrowing the openings of the micropores by thermally decomposed carbons. However, since the lithium ions which have small ionic diameters can pass, charging and discharging are possible.
It is thought that the carbon for the lithium secondary battery m~nllf~ctured by the method of this invention has improved charging and discharging efficiency due to the above-mentioned effects acting synergistically.
A lithium secondary battery can be composed of carbon as an anode m~nllf~ctured by the methods of the present invention and a lithium compound as a cathode. The combination CA 022~0719 1998-10-20 , 13 of carbon electrode of this invention and the components of the cathode, the shape, and the composition concentration of the electrolytic solution, and the like are all suitably set in accordance with the use of the lithium secondary battery.
EXAMPLES
The present invention is illustrated by the following examples. However, it should be understood that the invention is not limited to the specific details of these examples.
The carbonaceous materials of the examples 1 to 6 were manufactured and their charging and discharging properties were compared to those of the carbonaceous materials of Comparative Examples I to 4.
~ry-distilled charcoal Phenol resin, PGA-4560 (m~nllf~ctllred by Gun-ei Chemical Industry (Ltd), sold under the name of Resitop) as a binder was added to Phenol resin R 800 (m~nl1f~ct11red by Kanebo Co.. Ltd., sold under the name of Bell Pearl), and the mixture was molded into a cylindrical shape of approximately 2 mm (~) x 5-6 mm, and then dry-distilled at 700 ~C under a current of nitrogen gas to obtain a dry-distilled charcoal starting material.
Halooen treatment The dry-distilled charcoal starting materials were then treated with halogen to form porous carbonaceous materials. In the case of chlorination, the dry-distilled charcoal starting material (approximately 15 g) was heated at 600 ~C for two hours under a current of nitrogen gas (2.7NL/min) cont~inin~ chlorine at 5% by yolume. In the case of bromination, the dry-distilled charcoal starting material was heated at 600 ~C for two hours under a current of nitrogen gas (3NL/min) cont~inin~ bromine at 5 % by volume .
Preliminary pore adjustment treatment A preliminary pore adjustment treatment was conducted by heating at 400 to 550 ~C
for 25 to 120 minutes under a current of nitrogen gas saturated with benzene or toluene at 25 ~C .
Dehalo enation treatment Low temperature dehalogenation treatment: After the preliminary pore adjustment treatment, the dry-distilled charcoal was heated at 700 ~C for 30 minutes under a current of CA 022~0719 1998-10-20 nitrogen gas saturated with steam at 25 ~C (lNL/min).
High temperature dehalogenation treatment: After preliminary pore adjustment treatment, the dry-distilled charcoal was heated at 1000 ~C for 60 minutes under a current of nitrogen gas (3NL/min).
Pore adjustment treatment After dehalogenation treatment, the dry-distilled charcoal was heated at 900 ~C for 10 minutes under a current of nitrogen gas saturated with toluene at 25 ~C.
Crushin~r After the pore adjustment treatment, the dry-distilled charcoal was crushed to pieces using a small size vibrating ball mill7 NB-0, manufactured by Nitto Kagaku (Ltd) for 30 minutes.
Carbon for Battery To the carbon obtained after the halogenation treatment, the preliminary pore adjustment treatment7 the dehalogenation treatment, and the pore adjustment treatment, poiyfluorovinyiidene (9 % by weight of the carbon) as a binder was added, and then, N-methyi-2-pyrrolidone was added to the mixture to form a paste. The resulting paste was poured onto a collecting electrode made of stainless steel ( 10 mm diameter) to obtain carbon for a battery.
Evaluati~n test for Char~ing and Dischar~in~ Capacity The electrolytic solution used was a solution of a 1:1 mixture of propylene carbonate and dimethoxyethanel to which lithium perchlorate (LiC~04) (1.0 mol/l) was added as a supporting electrolyte. The carbon electrode was formed by immersing the above-mentioned carbon for a battery in the electrolytic solution.
With regard to charging and discharging, the above-mentioned charging capacity (A) and dischargin~ capacity (B) were measured using a charging and discharging testing device (model HJ-201B) m~mlf~c.tllred by Hokuto Denko (Ltd).
Comparative Example No preliminary pore adjustment; with chlorination, high temperature dehalogenation, steam dehalogenation, and post-dehalogenation crushing.
Dry-distilled charcoal was subjected to the halogenation treatment, and the resulting charcoal was then heated at 1000 ~C under a current of nitrogen gas (high temperature CA 022~0719 1998-10-20 dehalogenation treatment). The charcoal was further heated under a current of nitrogen gas containing steam (low temperature dehalogenation treatment). After crushing and pore adjustment treatment, the carbon for battery was manufactured according to the above shown method. The battery was tested for its charging and discharging properties using evaluation cells: A=772 mAh/g, B=652 mAh/g, discharging efficiency (K) =84.~S%, and the loss of capacity= 120 mAh/g.
Comparative Example 2 No preliminary pore adjustment; with chlorination, high temperature dehalogenation, steam dehalogenation, and post-halogenation crushing.
The dry-distilled charcoal was subjected to chlorination and then crushed into pieces.
The resulting charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperature dechlorination treatment), and then heated again under a current of nitrogen gas cont~ining steam (low temperature dehalogenation treatment). The charcoal thus obtained was subjected to the pore adjustment treatment and carbon for battery was m~nllf~ctured by the above-mentioned method, and its charging and discharging properties were measured using an evaluation cell: A=773 mAh/g, B=649mAh/g, discharging efficiency = 84.0%, and the loss of capacity = 124 mAh/g.
Comparative Example 3 No preliminary pore adjustment; with chlorination, steam dechlorination, high temperature dechlorination, and post-dechlorination crushing.
Dry-distilled charcoal was subjected to chlorination. The charcoal was heated under a current of nitrogen gas conl~ining steam (low temperature dehalogenation treatment) and then heated at 1000 ~C under a current of nitrogen gas (high temperature dehalogenation treatment). After crushing and pore adjustment treatments, carbon for battery was manufactured by the above-mentioned method, and its charging and discharging properties were measured: A=764 mAh/g, B=642 mAh/g, discharging efficiency = 84.0%, and the loss of capacity= 122 mAh/g.
Comparative Example 4 No preliminary pore adjustment; with bromination, steam debromination~ high temperature debromination and post-debromination crushing.
CA 022~0719 1998-10-20 lG
Dry-distilled charcoal was subjected to bromination. The charcoal was then heated under a current of nitrogen gas (low temperature debromination treatment) and heated at 1000 ~C under a current of nitrogen gas (high temperature debromination treatment). After crushing and pore adjustment treatments, carbon for battery was manufactured by the above-mentioned method, and then its charging and discharging properties were measured using an evaluation cell: A=774 mAh/g, B=660 mAh/g, discharging efficiency = 85.3%, and the loss of capacity = 114 mAh/g.
Example 1 With chlorination, preliminary pore adjustment (toluene, 550~C x 25 min), high temperature dechlorination, steam dechlorination and post-dechlorination crushing.
Dry-distilled charcoal was subjected to chlorination, and by using toluene a preliminary pore adjustment treatment was conducted at 550~C for 25 min. Then, the charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperature dechlorination tre~tment), and the resulting charcoal was heated under a current of nitrogen gas cont~ining steam (low iemperai:ure chlorinaiion trealmeni). Af~eF cFushirrg and pore adjustmeni ireaimenis, carbon for battery was m~n~lf~c.tllred by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=798 mAh/g, B=688 mAh/g, discharging efficiency = 86.2%, and the loss of capacity = 110 mAh/g.
Example 2 With chlorination, prelimin~ry pore adjustment (toluene, 550 ~C X 25 min), high temperature dechlorination, steam dechlorination and post-chlorination crushing.Dry-distilled charcoal was subjected to chlorination and then the reslllting charcoal was crushed into pieces. By using toluene a prelimin:~ry pore adjustment treatment was conducted at 550~C for 25 min. Then, the charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperature dechlorination treatment), and the resulting charcoal was heated under a current of nitrogen gas cont~ininsg steam (low temperature chlorination treatment). After the pore adjustment treatment, carbon for battery was m~nllf~ctured by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=816 mAh/~, and B=720 mAh/g, discharging efficiency = 88.2%, and the loss of capacity = 96 mAh/g.
CA 022~0719 1998-10-20 Example 3 With chlorination, preliminary pore adjustment (benzene, 550~C X 50 min), high temperature dechlorination and post-chlorination crushing.
Dry-distilled charcoal was subjected to chlorination and then the resulting charcoal was crushed into pieces. By using toluene a preliminary pore adjustment treatment was conducted at 550~C for 50 min. Then, the charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperature dechlorination treatment), and the resulting charcoal was heated under a current of nitrogen gas cont~ining steam (low temperature chlorination treatment) After the pore adjustment treatment, carbon for battery was m:~nllf~ctured by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=819 mAh/g, B=721 mAh/g, discharging efflciency = 88.0%, and the loss of capacity = 9g mAh/g.
Example 4 With chlorination, pr~.limin~ry pore adjustment (toluene, 550~C x 25 min), steamdechlorinatiGn, high terllperature dec~'orinztion and post-dechlorination cr.,shing.
Dry-distilled charcoal was subjected to chlorination, and then, using toluene, apreliminary pore adjustment treatment was conducted at 550~C for 25 min Then, the charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperaturedechlorination treatment), and the resulting charcoal was heated under a current of nitrogen gas cont~ining steam (low temperature chlorination treatment). After crushing and pore adjustment treatments, carbon for battery was m~nllf~ctllred by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=812 mAh/g, B=700 mAh/g, discharging efficiency = 86.2%, and the loss of capacity = 1 12 mAh/g.
Example 5 With chlorination, preliminary pore adjustment (toluene, 400~C x 120 min), steamdechlorination, high temperature dechlorination, and post-dechlorination crushing.
Dry-distilled charcoal was subjected to chlorination and then resulting charcoal was subjected to the preliminary pore adjustment treatment (toluene, 400~C x 120 min). Then, the charcoal was heated at 1000~C under a current of nitrogen gas (high temperature dechlorination treatment), and the resulting charcoal was heated under a current of nitrogen gas CA 022~0719 1998-10-20 containing steam (low temperature chlorination treatment). The resulting charcoal was crushed into pieces and after the pore adjustment treatment, carbon for battery was manufactured by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=797 mAh/g, B=687 mAh/g, discharging efficiency =
86.2%, the loss ofthe capacity = 110 mAh/g.
Example 6 With bromination, preliminary pore adjustment (toluene, 550~C X 25 min), steam debromination, high temperature debromination, and post-debromination crushing.
Dry-distilled charcoal was subjected to bromination. By using toluene, a preliminary pore adjustment treatment was conducted at 550~C for 25 min. Then7 the charcoal was heated under a current of nitrogen gas cont~ining steam (low temperature debromination treatment), and the resulting charcoal was heated at 1000 ~C under a current of nitrogen gas (high temperature debromination treatment). After crushing and pore adjustment treatments, carbon for battery was m~nuf~ctured by the above-mentioned method and its charging and discharging properties were measured using an evaluation cell: A=796 mAh/g, B=693 mAh/g, discharging efficiency = 87 1%, and the loss of capacity = 103 mAh/g.
Table 1 shows charging and discharging properties of Comparative Examples 1-4 and Examples 1-6 together with trç~tmçnt conditions Table 1.
[1~ [2~ [3~ [~ [~ A B A-B K
Cl Cl 2 - - - 772 652 120 84.5 C2 Cl 1 - - - 773 649 124 84.0 C3 Cl 2 - - - 764 642 122 84.0 C4 Br 2 - - - 774 660 114 85.3 El Cl 2 t 550 25 798 688 110 86 2 E2 Cl 1 t 550 25 816 720 96 88.2 E3 Cl 1 b 550 50 819 721 98 88.0 E4 Cl 2 t 550 25 812 700 112 86.2 E5 Cl 2 t 400 120 797 687 110 86.2 E6 Br 2 t 550 25 796 693 103 87.1 CA 022~0719 1998-10-20 C l-C4: Comparative Examples 1-4, El-E6: E?~ample 1-6;
[ I ]: kind of halogen;
[2]: timin, of crushin~;
1: after halogenation treatment, before preliminary pore adjustment treatment, 2: after dehalogenation treatment, before pore adjustment treatment, [3]: I;ind of thermally decomposable hydrocarbon used in the preliminary pore adjustment treatment;
t: toluene, b: ben~ene, [4]: temperature of preliminary pore adjustment treatment (~C);
[5]: time of preliminary pore adjustment tr~tment (min);
A: Charging capacity (mAh/g);
B: Discharging capacity (mAh/g);
K: Discharging efficiency (%) The dry distilled charcoal samples of the Examples that were subjected to chlorination and preliminary pore adjustment treatments showed favorable properties as a carbon material for lithium secondary battery in that they have a larger discharging capacity and smaller loss of the capacity, compared to the samples of comparative examples without the prl~.limin~ry pore adjustment treatment. In this case, the pr~limin~ry pore adjustment treatment after crushing gave a more favorable result than prf~.limin~ry pore adjustment treatment after dehalogenation treatment. With regard to the preliminary pore adjustment trç~tment both of toluene and benzene gave better properties compared to the case where no prclimin~ry tr~ tm~.nt was given.
Also in the brominated samples, similar effects of prelimin~ry adjustment were found.
Table 2 shows the relative discharging capacity of each of the Examples to that of corresponding Comparative Examples. The capacity of the Comparative Example is set to be 1. As is shown in this Table2, both the discharging capacity and efficiency in Examples 1 to 6 are improved. The maximum increase of discharging capacity and efficiency were I.11 fold (11% increase) and 1.05 fold (5% increase), respectively.
CA 022~0719 1998-10-20 , 20 Table 2 Discha~ 7~ cal~acit~ Effici~ c~
El/Cl 1.06 1.02 E2/C2 1 I 1 1.05 E3/C2 1.11 1.05 E4/C3 1.09 1 03 ES/C3 1.07 1 03 E6/C4 1 04 1.02 El-E6: Examples 1-6 C l-C4: Comparative Examples 1-4 Example 7 Us;ng the electrode according to the Examples 1-6, a coin-shaped lithium secondary battery as shown in Fig. 4 was assembled in a dry inert gas. This battery comprises a cathode 22 consisting mainly of LiCoO2; an anode 23 according to the Example 1-3 as an opposite electrode; a separator 21 between the electrodes, immersed with an organic solvent, as an electrolytic solution, cont~inin~ lithium ions; a metal can 24 and a cap 25 surrounding the electrodes and the separator; packing 26 for fixing the boundary between the can 24 and cap 25 in an i~ ting state.
The charging and discharging properties of this lithium secondary battery were evaluated according to the aforementioned charging and discharging test, and this revealed that the batteries have a similarly improved efflciency as was shown for the evaluation cells.
As explained above, this invention provides carbon for a lithium secondary battery which gives the battery a greater discharging capacity, a smaller loss of the capacity, and high efficiency; and provides the high per-formance lithium secondary battery m~nllf~ctured using the carbon.
A: Charging capacity (mAh/g);
B: Discharging capacity (mAh/g);
K: Discharging efficiency (%) The dry distilled charcoal samples of the Examples that were subjected to chlorination and preliminary pore adjustment treatments showed favorable properties as a carbon material for lithium secondary battery in that they have a larger discharging capacity and smaller loss of the capacity, compared to the samples of comparative examples without the prl~.limin~ry pore adjustment treatment. In this case, the pr~limin~ry pore adjustment treatment after crushing gave a more favorable result than prf~.limin~ry pore adjustment treatment after dehalogenation treatment. With regard to the preliminary pore adjustment trç~tment both of toluene and benzene gave better properties compared to the case where no prclimin~ry tr~ tm~.nt was given.
Also in the brominated samples, similar effects of prelimin~ry adjustment were found.
Table 2 shows the relative discharging capacity of each of the Examples to that of corresponding Comparative Examples. The capacity of the Comparative Example is set to be 1. As is shown in this Table2, both the discharging capacity and efficiency in Examples 1 to 6 are improved. The maximum increase of discharging capacity and efficiency were I.11 fold (11% increase) and 1.05 fold (5% increase), respectively.
CA 022~0719 1998-10-20 , 20 Table 2 Discha~ 7~ cal~acit~ Effici~ c~
El/Cl 1.06 1.02 E2/C2 1 I 1 1.05 E3/C2 1.11 1.05 E4/C3 1.09 1 03 ES/C3 1.07 1 03 E6/C4 1 04 1.02 El-E6: Examples 1-6 C l-C4: Comparative Examples 1-4 Example 7 Us;ng the electrode according to the Examples 1-6, a coin-shaped lithium secondary battery as shown in Fig. 4 was assembled in a dry inert gas. This battery comprises a cathode 22 consisting mainly of LiCoO2; an anode 23 according to the Example 1-3 as an opposite electrode; a separator 21 between the electrodes, immersed with an organic solvent, as an electrolytic solution, cont~inin~ lithium ions; a metal can 24 and a cap 25 surrounding the electrodes and the separator; packing 26 for fixing the boundary between the can 24 and cap 25 in an i~ ting state.
The charging and discharging properties of this lithium secondary battery were evaluated according to the aforementioned charging and discharging test, and this revealed that the batteries have a similarly improved efflciency as was shown for the evaluation cells.
As explained above, this invention provides carbon for a lithium secondary battery which gives the battery a greater discharging capacity, a smaller loss of the capacity, and high efficiency; and provides the high per-formance lithium secondary battery m~nllf~ctured using the carbon.
Claims (9)
1. A method of manufacturing carbon for a lithium secondary battery comprising a) a halogenation treatment of bringing dry-distilled charcoal into contact with a halogen gas to obtain halogenated dry-distilled charcoal, b) a preliminary pore adjustment treatment of bringing said halogenated charcoalobtained in a) into contact with a thermally decomposable hydrocarbon to obtain preliminary pore adjusted charcoal;
c) a dehalogenation treatment of eliminating a part or all of halogen from said charcoal obtained in b) to obtain dehalogenated charcoal; and d) a pore adjustment treatment of bringing said charcoal obtained in c) into contact with a thermally decomposable hydrocarbon
c) a dehalogenation treatment of eliminating a part or all of halogen from said charcoal obtained in b) to obtain dehalogenated charcoal; and d) a pore adjustment treatment of bringing said charcoal obtained in c) into contact with a thermally decomposable hydrocarbon
2. A method of manufacturing carbon for a lithium secondary battery according toclaim 1, wherein said halogenated dry-distilled charcoal in step a) is in a powder state.
3. A method of manufacturing carbon for a lithium secondary battery according toclaim 1, wherein said dehalogenated charcoal in step c) is in a powder state.
4. A method of manufacturing carbon for a lithium secondary battery according toany one of the claims 1 to 3, wherein said preliminary pore adjustment step comprises heating at a temperature between 300 and 900 °C in a thermally decomposable hydrocarbon that is diluted with an inert gas.
5 A method of manufacturing carbon for a lithium secondary battery according to claim 4, wherein said thermally decomposable hydrocarbon used in said preliminary pore adjustment treatment is at least one type of hydrocarbon selected from the group consisting of aromatic hydrocarbons, cyclic hydrocarbons, saturated chain hydrocarbons, and unsaturated chain hydrocarbons.
6 A method of manufacturing carbon for a lithium secondary battery according to claim 5, wherein said thermally decomposable hydrocarbon used in said preliminary pore adjustment treatment is benzene or toluene.
7. Carbon for a lithium secondary battery manufactured by the method according to any one of the claims 1 to 6.
8. A lithium secondary battery comprising a carbon electrode, a lithium electrode. an electrolytic solution provided between said electrodes, wherein said carbon electrode is carbon for a lithium secondary battery according to claim 7.
9. A method of manufacturing a lithium secondary battery comprising a carbon electrode, a lithium electrode, and an electrolytic solution provided between said electrodes;
wherein said lithium secondary battery is assembled, in an inert gas, with said carbon for a lithium secondary battery according to claim 7.
wherein said lithium secondary battery is assembled, in an inert gas, with said carbon for a lithium secondary battery according to claim 7.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9-295980 | 1997-10-28 | ||
| JP9295980A JPH11135108A (en) | 1997-10-28 | 1997-10-28 | Carbon for lithium secondary battery and its manufacture, and lithium secondary battery and its manufacture |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2250719A1 true CA2250719A1 (en) | 1999-04-28 |
Family
ID=17827589
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002250719A Abandoned CA2250719A1 (en) | 1997-10-28 | 1998-10-20 | Carbon for a lithium secondary battery, a lithium secondary battery, and manufacturing methods therefor |
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| JP (1) | JPH11135108A (en) |
| CA (1) | CA2250719A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014034857A1 (en) * | 2012-08-30 | 2014-03-06 | 株式会社クレハ | Carbon material for nonaqueous electrolyte secondary battery and method for manufacturing same, and negative electrode using carbon material and nonaqueous electrolyte secondary battery |
| US10504635B2 (en) | 2013-02-19 | 2019-12-10 | Kuraray Co., Ltd. | Carbonaceous material for nonaqueous electrolyte secondary battery negative electrode |
| CN115636405A (en) * | 2022-10-31 | 2023-01-24 | 湖州强大分子筛科技有限公司 | Preparation method of high-capacity hard carbon negative electrode material |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2009081106A (en) * | 2007-09-27 | 2009-04-16 | Central Res Inst Of Electric Power Ind | Nonaqueous electrolyte secondary battery |
| KR102405983B1 (en) | 2016-08-16 | 2022-06-07 | 주식회사 쿠라레 | Carbonaceous material for negative electrode active material of nonaqueous electrolyte secondary battery, negative electrode for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery, and manufacturing method of carbonaceous material |
| KR102267675B1 (en) * | 2018-08-30 | 2021-06-22 | 한국화학연구원 | Method for controlling the ratio of carbon monoxide and hydrogen produced by electrochemical CO2 conversion |
-
1997
- 1997-10-28 JP JP9295980A patent/JPH11135108A/en not_active Withdrawn
-
1998
- 1998-10-20 CA CA002250719A patent/CA2250719A1/en not_active Abandoned
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014034857A1 (en) * | 2012-08-30 | 2014-03-06 | 株式会社クレハ | Carbon material for nonaqueous electrolyte secondary battery and method for manufacturing same, and negative electrode using carbon material and nonaqueous electrolyte secondary battery |
| EP2892096A4 (en) * | 2012-08-30 | 2016-04-13 | Kureha Corp | Carbon material for nonaqueous electrolyte secondary battery and method for manufacturing same, and negative electrode using carbon material and nonaqueous electrolyte secondary battery |
| US10573891B2 (en) | 2012-08-30 | 2020-02-25 | Kuraray Co., Ltd. | Carbon material for nonaqueous electrolyte secondary battery and method for manufacturing same, and negative electrode using carbon material and nonaqueous electrolyte secondary battery |
| US10504635B2 (en) | 2013-02-19 | 2019-12-10 | Kuraray Co., Ltd. | Carbonaceous material for nonaqueous electrolyte secondary battery negative electrode |
| CN115636405A (en) * | 2022-10-31 | 2023-01-24 | 湖州强大分子筛科技有限公司 | Preparation method of high-capacity hard carbon negative electrode material |
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| JPH11135108A (en) | 1999-05-21 |
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