Nonaqueous electrolyte lithium secondary batteries

Details Nonaqueous electrolyte lithium secondary batteries Nonaqueous electrolyte lithium secondary batteries

2001-11-13

2004-06-01

Weiner, Laura (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S231400, C429S231800, C429S330000, C429S324000, C429S332000, C429S341000, C429S342000, C429S323000, C429S251000, C429S249000, C252S182100, C252S062200

Reexamination Certificate

active

06743549

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to electrolyte solution compositions and lithium-ion batteries employing these electrolyte solutions. These electrolytes feature lower volatility than solutions known in the art while retaining excellent battery performance using graphite based negative electrode active materials
BACKGROUND OF THE INVENTION
Lithium-ion batteries are now under intensive development around the world to provide a new generation of secondary, or rechargeable, batteries. Whatever the specific design approach, all have in common an electrolyte comprising an ionic species and an aprotic liquid, referred to herein as an electrolyte solvent, to provide a physical medium through which the ionic species can move. Commercial lithium-ion batteries generally exhibit a high open-circuit voltage, typically 3.6 to 3.8 volts. This means that during charging, a voltage as high as ca. 4.2 volts will normally be died, with localized transient voltages even higher. Secondary lithium-ion batteries are distinguishable over the primary lithium metal batteries of the art not only in that the voltages to which battery components are exposed are generally higher, but also in that the battery components of a lithium-ion battery must endure repeated exposure to these highly oxidizing conditions during numerous charge/discharge cycles.
Every component of the lithium-ion battery must be able to endure the repeated exposure to the very high electrochemical oxidation and reduction potentials which these voltages represent. Many well-known electrolyte solvents suitable for use in other types of batteries simply do not exhibit the requisite stability for lithium-ion battery use. There appears to be no generalized scheme accepted in the art beyond trial and error for selecting those electrolyte solvents which will exhibit the requisite stability. In practice, this has constrained the choice of electrolyte solvents employed in the art of lithium-ion batteries to the acyclic and cyclic organic carbonates, primarily dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethylene carbonate (EC), and monoesters such as methyl acetate (MA), ethyl acetate (EA), methyl formate (MF), methyl propionate (MP), ethyl propionate), and gamma-butyrolactone (GBL) as described in B. A. Johnson, and R. E. White, “Characterization of Commercially Available Li-ion Batteries”,
Journal of Power Sources,
70, 48-54, (1998). Most often, these electrolyte solvents are used in combinations comprising a cyclic organic carbonate, usually EC or PC, and an acyclic carbonate, usually DMC, DEC, or EMC, as disclosed in U.S. Pat. No. 5,525,443 to Matsushita. These combinations have been found in practice to achieve an excellent combination of desirable properties such as high ionic conductivity over a wide temperature range and relatively low volatility while achieving excellent lifetime and performance in lithium-ion batteries. The state-of-the-art is also well described in “Organic Electrolytes for Rechargeable Lithium Batteries,” by M. Morita, M. Ishikawa, and Y. Matsuda, in Ch. 7 of
Lithium
-
Ion Batteries, Fundamentals and Performance,
Ed. By M. Wakihara and O. Yamamoto, Wiley VCH, 1998.
The patent art disclosing electrolyte solvents for use in lithium-ion batteries is voluminous. The disclosed electrolyte solvents suitable for use in lithium-ion batteries fall into three broad categories: (1) halogen-substituted organic carbonates such as 2-fluoroethylene carbonate, (2) mixes of organic carbonates with acyclic or cyclic esters such as EC+DMC+methyl formate, and (3) unsaturated organic carbonates such as vinylene carbonate.
Representative of the scope of the art are the following: U.S. Pat. No. 5,192,629 wherein is disclosed mixtures of ethylene carbonate and dimethyl carbonate in ratios of from 20/80 to 80/20; U.S. Pat. No. 5,474,862 wherein is disclosed a combination of cyclic and acyclic organic carbonates with CH
3
CHC(O)OR where R=C
1
to C
3
alkyl; U.S. Pat. No. 5,571,635 wherein is disclosed a combination of EC, PC, and chloroethylene carbonate; U.S. Pat. No. 5,578,395, wherein is disclosed a combination of EC, dimethoxyethane (DME), and butylene carbonate (BC); U.S. Pat. No. 5,626,981, wherein is disclosed a combination of a cyclic and acyclic organic carbonate, and an unsaturated organic carbonate such as vinylene carbonate (VC); U.S. Pat. No. 5,626,985, wherein is disclosed a combination of a cyclic and an acyclic organic carbonate with 40-80% ether such as DME; U.S. Pat. No. 5,633,099 wherein is disclosed acyclic asymmetric fluorine-substituted organic carbonates; U.S. Pat. No. 5,659,062, wherein is disclosed CH
3
OC(O)OCH
2
CR
3
where RC=C
1
to C
2
alkyl, F-substituted alkyl, or F; and, U.S. Pat. No. 5,773,165, wherein is disclosed EC/PC (50-60%) in combination with GBL (10-25%), DMC, and EC/MA.
In every case in the art, an acyclic ester or acyclic organic carbonate is a required component in the composition in order to achieve the ionic conductivity thought to be required for most lithium-ion battery applications. However, the acyclic esters and acyclic organic carbonates are undesirably fugitive and flammable under some conditions contemplated for battery manufacturing. There is a clear need in the art for high conductivity electrolyte compositions having reduced volatility and flammability.
Webber, U.S. Pat. No. 5,219,683, discloses the use of solvents of the type Y—O—X—O—C(O)—R where R is a C
1
-C
10
alkyl group, X is a C
1
-C
8
acyclic group and Y is a C
1
-C
10
alkyl group or a carbonyl group. Their preferred composition includes ethylene glycol diacetate preferably mixed with propylene carbonate and a salt such as lithium trifluoromethane sulfonate. Claimed is the use of diacetate solvents in lithium primary batteries such as the Li/FeS
2
battery. The maximum voltage to which the solvents are exposed is about 2 volts.
Horiba et al., JP 86017106, employs diesters from dicarboxylic acids in lithium primary batteries. The battery exemplified had an open circuit voltage of 2.9 V, and was not subject to recharging.
Liu et al., WO 99/44246, describes lithium-ion polymer batteries prepared using plasticizers based on dialkyl adipate dibasic esters. According to Liu et al., the adipate ester plasticizer is substantially removed from the battery by an extraction process prior to addition of battery electrolyte. However, Liu et al. teaches that residual adipate ester plasticizer up to as much as 20 wt-% does not affect battery performance.
Chang in WO 00/01027 discloses the use of malonate diesters containing no alpha hydrogens as electrolyte solvent in lithium-ion batteries.
SUMMARY OF THE INVENTION
The present invention provides for an electrode composition comprising a lithium electrolyte solution in ionically conductive contact with a graphite-based electrode-active material, wherein the solution comprises a lithium electrolyte and a solvent represented by the formula
R
1
C(O)OR
2
OC(O)R
3
  (I)
or by the formula
R
1
OC(O)R
2
C(O)OR
3
  (II)
where R
1
and R
3
each independently designates an acyclic alkyl radical of 1-4 carbons, C(O) designates a carbonyl radical, and R
2
is an alkenyl radical of 2 or 3 carbons.
The present invention further provides for a lithium-ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte solution comprising a solvent, and lithium ions, at least one of said anode, cathode, or separator being in ionically conductive contact with said electrolyte solution; and said solvent being represented by the formula
R
1
C(O)OR
2
OC(O)R
3
  (I)
or by the formula
 R
1
OC(O)R
2
C(O)OR
3
  (II)
where R
1
and R
3
each independently designates an acyclic alkyl radical of 1-4 carbons, C(O) designates a carbonyl radical, and R
2
is an alkenyl radical of 2 or 3 carbons.
DETAILED DESCRIPTION OF THE INVENTION
For the purposes of the present invention,

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