Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-09-11
2003-03-04
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231100, C429S231950, C429S245000
Reexamination Certificate
active
06528212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lithium battery comprising a positive electrode, a negative electrode and a nonaqueous electrolyte and more particularly, to a lithium battery adapted for dissolution and deposition of lithium metal in the negative electrode, the battery directed to a suppressed formation of lithium dendrite on the negative electrode and to a suppressed reaction between the lithium metal in the negative electrode and a solvent in the nonaqueous electrolyte in the lithium dissolution/deposition process associated with the charging and discharging of the battery.
2. Description of the Related Art
As a novel secondary battery of high power and high energy density, a lithium battery have gained widespread use. Such a battery employs the nonaqueous electrolyte and is capable of being charged and discharged through oxidation/reduction of lithium.
This lithium battery uses a variety of negative-electrode materials for forming the negative electrode.
Where lithium metal is employed as the negative-electrode material, the battery can achieve the highest theoretical capacity of 3.86 Ah/g. Accordingly, studies have been made on the use of lithium metal as the negative-electrode material.
However, if the lithium battery employing lithium metal as the negative-electrode material is subjected to repeated charging/discharging processes involving lithium-metal dissolution/deposition in the negative electrode, the negative electrode encounters a gradual growth of lithium dendrite thereon. The lithium dendrite will further grow through a separator to come into contact with the positive electrode. Furthermore, the dendrite growth leads to an increased contact area between the lithium metal of the negative electrode and the solvent of the nonaqueous electrolyte so that the lithium metal of the negative electrode is more likely to react the solvent of the nonaqueous electrolyte. As a result, the lithium battery is decreased in the charge/discharge efficiency and hence in the cycle performance.
More recently, Japanese Unexamined Patent Publication No.11-3713(1999) has proposed a lithium battery employing a negative electrode collector formed from a porous material, such as carbon, for suppression of the formation of lithium dendrite during charging and discharging of the lithium battery.
Unfortunately, the lithium battery with the negative electrode collector formed from the porous material, such as carbon, still suffers the drawback that the charge/discharge efficiency is decreased due to the reaction between the solvent or the like in the nonaqueous electrolyte and the lithium metal retained at the negative electrode collector or the porous material, such as carbon, forming the negative electrode collector.
SUMMARY OF THE INVENTION
A first object of the invention is to prevent the growth of lithium dendrite on the negative electrode during charging/discharging of the lithium battery adapted for the dissolution/deposition of lithium metal in the negative electrode.
A second object of the invention is to prevent the reaction between the lithium metal in the negative electrode and the solvent in the nonaqueous electrolyte in the lithium battery adapted for the dissolution/deposition of lithium metal in the negative electrode.
A third object of the invention is to enhance the charge/discharge efficiency and thence the cycle performance of the lithium battery adapted for the dissolution/deposition of lithium metal in the negative electrode.
In accordance with a first aspect of the invention, a lithium battery comprises a positive electrode, a negative electrode with a negative electrode collector retaining lithium metal, and a nonaqueous electrolyte, wherein an activated carbon with a minimum pore size in the range of 5 Å to 16 Å is used as the negative electrode collector.
In accordance with a second aspect of the invention, a lithium battery comprises a positive electrode, a negative electrode with a negative electrode collector retaining lithium metal, and a nonaqueous electrolyte, wherein an activated carbon with a specific surface area in the range of 960 m
2
/g to 2000 m
2
/g is used as the negative electrode collector.
With the minimum pore size of 5 Å, the activated carbon used as the negative electrode collector has a specific surface area of about 960 m
2
/g. With the minimum pore size of 16 Å, the activated carbon used as the negative electrode collector has a specific surface area of about 2000 m
2
/g.
If the activated carbon with the minimum pore size in the range of 5 Å to 16 Å and the specific surface area in the range of 960 m
2
/g to 2000 m
2
/g is used for forming the negative electrode collector of the negative electrode, as in the lithium batteries of the first and second aspects hereof, lithium ions with the solvent desorbed therefrom are inserted into the activated carbon pores so as to be deposited as lithium metal in the activated carbon pores when the lithium battery is charged for lithium metal retention at the negative electrode collector. Thus, the growth of lithium dendrite on the negative electrode is suppressed while the lithium metal deposited in the activated carbon pores is prevented from reacting the solvent in the nonaqueous electrolyte. Hence, the lithium battery is not degraded in the charge/discharge efficiency, accomplishing the improved cycle performance.
If the negative electrode collector is formed from the activated carbon with the minimum pore size of less than 5 Å, lithium ions are not readily inserted in the activated carbon pores, resulting in the deposition of lithium metal on the surface of the activated carbon.
Consequently, the lithium dendrite is formed on the negative electrode or the lithium metal of the negative electrode is in contact with the solvent in the nonaqueous electrolyte, reacting the same. If, on the other hand, the negative electrode collector is formed from the activated carbon with the minimum pore size in excess of 16 Å, solvated lithium ions are inserted into the activated carbon pores to be deposited as lithium metal. The resultant lithium metal is in contact with the solvent and the like of the nonaqueous electrolyte infiltrating into the activated carbon pores and the reaction therebetween occurs. Hence, both of the above cases entail the decreased charge/discharge efficiency and thence, the degraded cycle performance of the lithium battery.
The activated carbon for use in the negative electrode collector may take any form of grains, fibers and the like so long as the aforementioned properties are |presented. However, a fibrous activated carbon may be preferred from the standpoint of easy handling when used for forming the negative electrode collector.
In accordance with a third aspect of the invention, a lithium battery comprises a positive electrode, a negative electrode with a negative electrode collector retaining lithium metal, and a nonaqueous electrolyte, wherein a graphitized carbon is used as the negative electrode collector.
If the graphitized carbon is used as the negative electrode collector as in the lithium battery of the third aspect hereof, the lithium dendrite growth on the negative electrode is suppressed during charging of the lithium battery for lithium metal retention at the negative electrode collector. In addition, the negative electrode collector is prevented from reacting the solvent and the like in the nonaqueous electrolyte during charging. Thus, the lithium battery is improved in the charge/discharge efficiency.
Where graphitized carbon is used as the negative electrode collector, the higher the graphitization degree of the graphitized carbon, the greater the effect of suppressing the reaction between the negative electrode collector and the solvent and the like in the nonaqueous electrolyte during charging. The graphitized carbon having spacing d
002
of lattice planes (002) in the range of 3.35 Å to 3.43 Å or more preferably of 3.35 Å to 3.36 Å, or contai
Fujimoto Masahisa
Kusumoto Yasuyuki
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