Lithium anode with solid electrolyte interface

Details Lithium anode with solid electrolyte interface Lithium anode with solid electrolyte interface

1999-02-04

2002-01-08

Brouillette, Gabrielle (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S231800, C429S231950, C429S218200

Reexamination Certificate

active

06337159

ABSTRACT:

INTRODUCTION/BACKGROUND
Safety considerations lead to the replacement of pure lithium by heavier carbonaceous materials, with the general formula Li
x
C
6
, as anodes for lithium batteries.
In order to minimize the loss in energy density due to this replacement, X which is the molar ratio between 6 carbons and Li, in Li
x
C
6
must be maximized and the irreversible capacity loss (Q
IR
) in the first charge of the battery must be minimized. The maximum value for the reversible intercalation of lithium (DX) depends on the carbon type and is typically between 0.5 (186 mAh/g carbon) for non-graphitic carbon to 1 (372 mAh/g carbon) for graphites. There is a larger variation in Q
IR
between 30% to 90%. It was generally found that Q
IR
is larger for graphites than for petroleum coke. Therefore in order to be able to benefit from the use of graphite, (having X=1), means should be taken to decrease its Q
IR
. Q
IR
is attributed to SEI (Solid Electrolyte Interphase) formation and to exfoliation of the graphite.
When a carbonaceous electrode is cathodically polarized to potentials lower than 2.0 V vs. lithium, several reactions take place: Lithium intercalation with or without co-intercalation of solvent molecules, partial or complete reduction of solvent molecules and anions, precipitation of insoluble reduction products to form a Solid Electrolyte Interphase (SEI), diffusion of partially reduced species (such as semicarbonates) from the surface of the carbon into the solution, reduction-induced polymerization of solvent molecules (such as cyclic ethers and esters). At potentials lower than 0.5V, dissolution of solvated electrons into the electrolyte takes place. The fraction or yield of each reaction depends on: type of carbon, type of salt and solvents, temperature, impurities and potential (current density). Further reactions depend on electrolyte stability. In highly purified electrolytes which consist of thermodynamically stable anions (like I) and kinetically stable solvents such as ammonia, some amines and ethers, the solvated electrons exist for long periods of time (hours). These electrolytes are for obvious reasons, not suitable for use in practical lithium batteries. In “battery-grade” ether-based electrolytes, or when reducible anions such as AsF
6
or reducible solvents such as PC are used, these solvated electrons immediately react to form SEI on the electrode.
Highly graphitized carbons have a large capacity, but suffer from solvent co-intercalation and degradation in performance. In ether-, PC- and MF-rich solutions, the solvent co-intercalation is a significant problem, while EC addition alleviates the problem. If reversible, it may cause disintegration (exfoliation) of the graphite crystallites as a result of large variation in the lattice spacing (large changes in d
002
). The large variation in dimension may cause cracks in the “protective” SEI which lead to further (and faster) electrolyte reduction and more co-intercalation. Reduction of the intercalated molecules may yield gasses (such as ethane and propane in EC and PC solutions) inside the graphite crystallites. This may cause exfoliation and cracks in the SEI. Once the co-intercalation of solvent molecules starts, it will be very difficult to prevent. Therefore it must be prevented from the outset i.e. prior to or in the first charge. We believe that high quality SEI can eliminate or effectively prevent the co-intercalation of solvent molecules and the degradation process described above.
SUMMARY OF THE INVENTION
The present invention relates to non-aqueous batteries whose anode comprise carbon-based particles bounded by appropriate binders, which binders may also be a carbon-based material, which carbonaceous particles (beads, powder, wiskers, etc.), are coated by a thin, submonolayer of up to 0.1 &mgr;m solid electrolyte interphase (SEI), which film is an M
+
conductor and electronic insulator and consists of alkali (M) or alkaline-earth metal (MA) salts, oxides or sulfides or a mixture of these which optionally contains up to 30% organic binder or polymers, which salts are insoluble in the battery electrolyte and which preferably are fluorides, chlorides, carbonates, semicarbonates, surface carboxylic salts or a mixture of these, which SEI is chosen to be compatible with the particular electrolyte of the battery. According to a preferred embodiment the solid electrolyte interphase is chemically bonded to the surface of the carbonaceous particles, preferable through oxygen bonds.
The carbonaceous material can be chosen amongst others from graphite and non-graphitic carbons which optionally contains up to 10% (atomic weight) additional elements chosen from the group of N,B,Al,Ca,Mg and Si.
Preferably, the carbonaceous particles are partially oxidized at a suitable temperature by a suitable gas selected from: dry or wet air, O
2
or Cl
2
to form very narrow, up to 1 nm in width, preferably 0.3 to 0.6 nm holes, pits, cracks or flaws, the carbon losses in this process being up to 30% of its weight, preferably 3 to 15%.
A suitable temperature range for this process in air and for nongraphitized carbons is 300 to 500° C. and for graphitized carbons it is 450 to 640° C., depending on carbon structure, degree of graphitization surface area and impurities. Following this oxidation process, the carbon may be treated with alkali or alkaline earth hydroxides (or basic salts, such as carbonates) to neutralize the surface acidic groups and turn them into a thin layer of surface carboxylic salts, chemically bound to the carbon surface. If not, these acidic surface groups will be neutralized (turn into lithium salt) in the first charge of the battery.
The carbonaceous based particles are preferably partially oxidized by dry or wet air or oxygen, where the temperature and time are optimized for each carbon material to obtain a maximum of surface acidic groups and minimum surface basic groups at a minimal weight loss (less than 3% weight loss) optionally followed by neutralization by alkali or alkaline metal hydroxides.
Anodes of the batteries of the invention may comprise carbon-based particles which were oxidized to form surface acidic groups by the use of oxidizing agents such as aqueous solutions of H
2
O
2
, H
2
SO
4
, HNO
3
, KClO
4
, KClO, etc., washed and neutralized by an alkali metal or alkaline earth metal hydroxide or their basic salts.
The carbon based particles can be coated by a thin, up to 2 nm layer of chemically bonded alkali metal or alkaline metal carbonate formed by:
a) first formation of surface basic group by reaction of clean surface (free of surface groups) carbon with wet air at low temperatures (up to 150° C.);
b) reaction with an alkali or alkaline earth metal hydroxide at preferably 100-200° C. or with MAH
2
or MH to form C—O—M or (C—(O)
2
—MA surface groups;
c) reaction with CO
2
gas at room temperature to form C—O—CO
2
M or C—O—CO
2
)
2
MA surface groups, i.e. a thin chemically bound alkali carbonate surface film.
The SEI or a part of can be formed by a dissolution of the SEI materials or its precursors in a proper solvent or solvents mixture and casting a thin layer on the carbonaceous particles followed by a heat treatment if needed. Organic elastomer up to 30% (V/V) can be added to the casting solution. A preferred SEI can be formed by treatment of these carbon particles by an appropriate amount of aqueous solution of an alkali metal carbonate optionally with water soluble polymer such as PEO and evaporating the water to form 1-10 nm thick carbonate layer. The SEI or a part of it may be formed by chemical vapor deposition or thermal decomposition of an appropriate SEI precursors.
The invention further relates to a non-aqueous battery consists of a carbon based anode, an appropriate aprotic non-aqueous electrolyte and suitable cathode the carbon of which was formed by dehydration of a carbohydrate such as (C
6
O
6
H
12
), a polysaccharide, cellulose or starch with general formula (C
6
O
5
H
10
)n either by reaction with concentrated H
2
SO
4
or by moderate temperature pyrol

Affiliated with

Also associated with

Rating

Lithium anode with solid electrolyte interface does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Lithium anode with solid electrolyte interface, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lithium anode with solid electrolyte interface will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2827036