Electrolytes comprising trialkylsilyl phosphorus ester additives
An electrolyte for an electrochemical cell that cycles lithium ions includes an organic solvent, an inorganic lithium salt, and an additive including a chemical compound having a phosphorus, oxygen, and silicon bond (POS additive). The organic solvent includes a mixture of a cyclic carbonate and a linear carbonate. The POS additive includes a trialkylsilyl ester of at least one of phosphoric acid, polyphosphoric acid, phosphonic acid, and phosphorous acid. The electrochemical cell may include a positive electrode comprising a nickel-based electroactive material and a negative electrode comprising a silicon-based electroactive active material.
1 . An electrolyte for an electrochemical cell that cycles lithium ions, the electrolyte consisting of:
an organic solvent consisting of a mixture of at least one cyclic carbonate and at least one linear carbonate;
an inorganic lithium salt in the organic solvent;
fluoroethylene carbonate;
vinylene carbonate; and
≥0.2% and ≤1.5%, by weight, of an additive that is a chemical compound having a phosphorus, oxygen, and silicon bond (POS additive),
the POS additive consisting of at least one trialkylsilyl phosphorus ester having the formula X a —P(═O) b (OZ) c , where:
X is hydrogen (H) or an alkyl group,
Z is a trialkylsilyl group (—Si—R 3 ), where R is an alkyl group,
a is zero or 1,
b is zero or 1,
c is 2 or 3,
when c is 2, a=1 and b=1, and
when c is 3, a=0 and b=0 or 1.
2 . The electrolyte of claim 1 , wherein the POS additive consists of tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, bis(trimethylsilyl) phosphite, trimethylsilyl polyphosphate, or a combination thereof.
3 . The electrolyte of claim 1 , wherein the organic solvent consists of a mixture of ethylene carbonate and dimethyl carbonate.
4 . The electrolyte of claim 3 , wherein the ethylene carbonate and the dimethyl carbonate comprise, by weight, greater than or equal to about 70% to less than or equal to about 90% of the electrolyte, and wherein a ratio of the ethylene carbonate to the dimethyl carbonate (EC:DMC) in the organic solvent is in a range from 2:8 to 4:6.
5 . The electrolyte of claim 4 , wherein the inorganic lithium salt consists of lithium hexafluorophosphate, wherein the inorganic lithium salt constitutes, by weight, greater than or equal to about 5% to less than or equal to about 20% of the electrolyte.
6 . The electrolyte of claim 5 , wherein the fluoroethylene carbonate constitutes, by weight, greater than or equal to about 1% to less than or equal to about 3% of the electrolyte and the vinylene carbonate constitutes, by weight, greater than or equal to about 0.5% to less than or equal to about 1.5% of the electrolyte.
7 . An electrochemical cell that cycles lithium ions, the electrochemical cell comprising:
a positive electrode comprising a nickel-based electroactive material;
a negative electrode comprising a silicon-based electroactive active material;
a porous separator sandwiched between the positive electrode and the negative electrode; and
an electrolyte infiltrating at least one of the positive electrode, the negative electrode, and the porous separator, the electrolyte consisting of:
an organic solvent consisting of a mixture of at least one cyclic carbonate and at least one linear carbonate;
an inorganic lithium salt in the organic solvent;
fluoroethylene carbonate;
vinylene carbonate; and
≥0.2% and ≤1.5%, by weight, of an additive that is a chemical compound having a phosphorus, oxygen, and silicon bond (POS additive),
the POS additive consisting of a trialkylsilyl phosphorus ester having the formula X a —P(═O) b (OZ) c , where:
X is hydrogen (H) or an alkyl group,
Z is a trialkylsilyl group (—Si—R 3 ), where R is an alkyl group,
a is zero or 1,
b is zero or 1,
c is 2 or 3,
when c is 2, a=1 and b=1, and
when c is 3, a=0 and b=0 or 1.
8 . The electrochemical cell of claim 7 , wherein the POS additive consists of tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, bis(trimethylsilyl) phosphite, trimethylsilyl polyphosphate, or a combination thereof.
9 . The electrochemical cell of claim 8 , further comprising:
a first interphase layer disposed on a major surface of the positive electrode; and
a second interphase layer disposed on a major surface of the negative electrode, wherein the first interphase layer and the second interphase layer are respectively formed in situ on the major surfaces of the positive electrode and the negative electrode during cycling of the electrochemical cell,
wherein the first interphase layer and the second interphase layer each comprise a chemical compound having a phosphorus, oxygen, and silicon bond (P—O—Si bond), and
wherein electrochemical oxidation of the POS additive occurs at the positive electrode during charge of the electrochemical cell, and wherein the first interphase layer comprises byproducts of the electrochemical oxidation of the POS additive.
10 . The electrochemical cell of claim 9 , wherein the organic solvent consists of a mixture of ethylene carbonate and dimethyl carbonate.
11 . The electrochemical cell of claim 10 , wherein intermediate chemical compounds are formed within the electrochemical cell via electrochemical reduction of the ethylene carbonate at the negative electrode during cycling of the electrochemical cell, and wherein the second interphase layer comprises byproducts of chemical reactions between the intermediate chemical compounds and the POS additive.
12 . The electrochemical cell of claim 11 , wherein the ethylene carbonate and the dimethyl carbonate comprise, by weight, greater than or equal to about 70% to less than or equal to about 90% of the electrolyte, and wherein a ratio of the ethylene carbonate to the dimethyl carbonate (EC:DMC) in the organic solvent is in a range from 2:8 to 4:6.
13 . The electrochemical cell of claim 12 , wherein the inorganic lithium salt consists of lithium hexafluorophosphate, and wherein the inorganic lithium salt constitutes, by weight, greater than or equal to about 5% to less than or equal to about 20% of the electrolyte.
14 . The electrochemical cell of claim 13 , wherein the nickel-based electroactive material comprises lithium nickel cobalt manganese aluminum oxide, lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide, or a combination thereof, and wherein the positive electrode comprises, by weight, greater than 80% nickel.
15 . The electrochemical cell of claim 14 , wherein the silicon-based electroactive material comprises silicon, silicon oxide, lithium silicon oxide, or a combination thereof, and wherein the negative electrode comprises, by weight, greater than 5% silicon.
16 . The electrochemical cell of claim 15 , wherein the fluoroethylene carbonate constitutes, by weight, greater than or equal to about 1% to less than or equal to about 3% of the electrolyte and the vinylene carbonate constitutes, by weight, greater than or equal to about 0.5% to less than or equal to about 1.5% of the electrolyte.
17 . The electrochemical cell of claim 16 , wherein the POS additive consists of tris(trimethylsilyl)phosphite.
18 . The electrochemical cell of claim 16 , wherein the POS additive consists of bis(trimethylsilyl) phosphite.
19 . An electrochemical cell that cycles lithium ions, the electrochemical cell comprising:
a positive electrode comprising a nickel-based electroactive material;
a negative electrode comprising a silicon-based electroactive material;
an electrolyte infiltrating at least one of the positive electrode or the negative electrode, the electrolyte consisting of:
an organic solvent consisting of a mixture of ethylene carbonate and dimethyl carbonate;
lithium hexafluorophosphate in the organic solvent at a concentration of about 1 Molar;
about 2%, by weight, fluoroethylene carbonate
about 2%, by weight, vinylene carbonate; and
about 1%, by weight, of an additive that is a chemical compound having a phosphorus, oxygen, and silicon bond (POS additive), the POS additive consisting of tris(trimethylsilyl)phosphite, tris(trimethylsilyl)phosphate, bis(trimethylsilyl) phosphite, trimethylsilyl polyphosphate, or a combination thereof.
20 . The electrochemical cell of claim 19 , wherein the POS additive consists of tris(trimethylsilyl)phosphite.