Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-05-26
2003-01-07
Kalafut, Stephen (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C429S217000, C429S309000, C429S314000, C429S317000
Reexamination Certificate
active
06503284
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electrochemical devices and, more articularly, to methods of fabricating electrochemical cells whereby the amount of organic solvents used in the manufacturing process is minimized.
BACKGROUND OF THE INVENTION
Non-aqueous lithium electrochemical cells typically include an anode, an electrolyte comprising a lithium salt that is dissolved in one or more organic solvents and a cathode of an electrochemically active material, typically a chalcogenide of a transition metal. During discharge, lithium ions from the anode pass through the liquid electrolyte to the electrochemically active cathode material of the cathode where the ions are taken up with the simultaneous release of electrical energy. During charging, the flow of ions is reversed so that lithium ions pass from the electrochemically active material through the electrolyte and are plated back onto the anode.
Recently, the lithium metal anode has been replaced with a carbon anode such as coke or graphite intercalated with lithium ions to form Li
x
C. In operation of the cell, lithium ions pass from the carbon through the electrolyte to the cathode where it is taken up just as in a cell with a metallic lithium anode. During recharge, the lithium is transferred back to the anode where it reintercalates into the carbon. Because no metallic lithium is present in the cell, melting of the anode does not occur even under abuse conditions. Also, because lithium is reincorporated into the anode by intercalation rather than by plating, dendritic and spongy lithium growth does not occur. Non-aqueous lithium electrochemical cells are discussed in U.S. Pat. Nos. 4,472,487, 4,668,595, 5,028,500, 5,441,830, 5,460,904 and 5,540,741.
Conventional methods of fabricating electrochemical cells typically consist of using organic solvents in making the electrodes and polymeric matrix (e.g., separator). For example, a solid electrolyte containing the polymeric matrix is prepared by curing a mixture comprising an organic solvent and solid matrix forming monomers and/or partial polymers thereof. Alternatively, the solid electrolyte is formed by solvent casting whereby a mixture comprising an organic solvent and a polymer is first coated onto the appropriate substrate. Thereafter, a polymeric film is formed upon removal of the solvent. Electrodes can also be fabricated by similar solvent casting techniques.
As is apparent, conventional methods of preparing electrochemical cell components require the use of significant organic solvents which pose environmental and health risks. These risks are particularly evident in the case of solvent casting since an evaporative step is required to extract the casting solvent (e.g., acetone) prior to insertion of the electrolyte solvent and inorganic salt. The organic solvents must therefore be recovered which further adds to the manufacturing costs.
SUMMARY OF THE INVENTION
The present invention is based in part on the discovery that the anode, cathode, and/or solid electrolyte (or separator layer) components of an electrochemical cell can be fabricated using aqueous compositions containing a binding material or polymer.
In one aspect, the invention is directed to a method of fabricating an electrode that includes the steps of:
(a) providing a latex composition comprising an aqueous phase and a solid phase that comprises a polymer;
(b) mixing an electrode active material into said latex composition to form a mixture; and
(c) removing water from said mixture to form an electrode.
In a further aspect, the invention is directed a method of fabricating a polymer electrolyte that includes the steps of:
(a) providing a latex composition comprising an aqueous phase and a solid phase that comprises a polymer to form mixture;
(b) removing water from said mixture to form a polymeric layer; and
(c) adding an electrolyte solution comprising an electrolyte solvent and a salt to the polymeric layer.
In another aspect, the invention is directed to a method of fabricating an electrochemical cell that includes the steps of:
(a) forming an anode by a process comprising the steps of:
(i) providing a first latex composition comprising an aqueous phase and a solid phase that comprises a first polymer;
(ii) mixing an anode active material into said first latex composition to form a first mixture; and
(iii) removing water from said first mixture to form an anode;
(b) forming a cathode by a process comprising the steps of:
(i) providing a second latex composition comprising an aqueous phase and a solid phase that comprises a second polymer;
(ii) mixing a cathode active material into said second latex composition to form a second mixture; and
(iii) removing water from said second mixture to form a cathode and;
(c) forming an electrolyte layer comprising a polymeric matrix by a process comprising the steps of:
(i) providing a third latex composition comprising an aqueous phase and a solid phase that comprises a third polymer;
(ii) removing water from the third latex composition to form a polymeric film; and
(iii) adding a solution comprising an electrolyte solvent and a salt to said polymeric film to form said electrolyte layer, which is positioned between said anode and said cathode.
In preferred embodiments, the polymer is a fluoropolymer including polyvinylidenedifluoride, poly(vinlylidene difluoride-co-hexafluoropropylene), and mixtures thereof.
In another aspect, the invention is directed to a method of making an electrode that includes the steps of:
(a) providing an aqueous composition comprising a binding material that is selected from the group consisting of a polyester represented by formula I, a terpolymer represented by formula II, a melamine-formaldehyde represented by formula III, and mixtures thereof, wherein
where R and R′ are independently selected from (CH
2
)
n
, where n is an integer from about 2 to about 10, and a substituted or unsubstituted benzyl, m is an integer that ranges from about 100 to about 10,000, x ranges from about 0.3 to about 0.7, y ranges from about 0.3 to about 0.7, and z ranges from about 0.02 to about 0.1;
(b) mixing an electrode active material into said aqueous composition to form a mixture; and
(c) causing said binding material to polymerize and removing water from said mixture to form an electrode.
In a further aspect, the invention is directed to a method of fabricating a polymeric electrolyte that includes the steps of:
(a) providing an aqueous composition comprising a binding material that is selected from the group consisting of a polyester represented by formula I, a terpolymer represented by formula II, a melamine-formaldehyde represented by formula III, and mixtures thereof, as described above;
(b) causing said binding material to polymerize and removing water from said mixture to form a polymeric layer; and
(c) adding an electrolyte solution comprising an electrolyte organic solvent and a salt to the polymeric layer.
In yet another aspect, the invention is directed to a method of making an electrochemical cell that includes the steps of:
(a) forming an anode by a process comprising the steps of:
(i) preparing an aqueous anode composition comprising an anode active material and a first binding material that is selected from the group consisting of a polyester represented by formula I, a terpolymer represented by formula II, a melamine-formaldehyde represented by formula III, and mixtures thereof as described above; and
(ii) causing the first binding material to polymerize and removing water from the anode composition to form said anode;
(b) forming a cathode by a process comprising the steps of:
(i) preparing an aqueous cathode composition comprising a cathode active material and an effective amount of a second binding material that is selected from the group consisting of a polyester represented by formula I, a terpolymer represented by formula II, a melamine-formaldehyde represented by formula III, as defined above and mixtures thereof; and
(ii) causing the second binding material to polymerize and removing water from the c
Gao Feng
Liu Peikang
Mitchell Porter
Kalafut Stephen
Kovacevic Cynthia S.
Williams Roger A.
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