A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer supported by the negative electrode current collector, when dividing the negative electrode active material layer into two layers of a first region and a second region having the same thickness, the second region is closer to the negative electrode current collector than the first region, the first region and the second region each contains graphite particles, a ratio P1/P2 of interparticle porosity P1 of the first region to interparticle porosity P2 of the second region is greater than 1, and the nonaqueous electrolyte includes at least one additive selected from the group consisting of a sulfite compound and a sulfate compound.

A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer supported by the negative electrode current collector, when dividing the negative electrode active material layer into two layers of a first region and a second region having the same thickness, the second region is closer to the negative electrode current collector than the first region, the first region and the second region each contains graphite particles, a ratio P1/P2 of interparticle porosity P1 of the first region to interparticle porosity P2 of the second region is greater than 1, and the nonaqueous electrolyte includes at least one additive selected from the group consisting of a sulfite compound and a sulfate compound.

Disclosed is a secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte comprises a lithium salt, an organic solvent, and an additive, wherein the additive comprises a fluorinated compound that accounts for 5-20% of the total mass of the electrolyte, and a polynitrile compound that accounts for 0.2-4% of the total mass of the electrolyte and a sulfate compound that accounts for 0.3-5% of the total mass of the electrolyte; and the negative electrode has a compacted density of not less than 1.55 g/cm3. When the secondary battery is used, the battery can still have both a high temperature characteristic and a low temperature charging ability under the conditions of a higher negative electrode density, thereby having market application prospects, and overcoming the problem of the performance of existing secondary batteries deteriorating when the compacted density of a negative electrode is improved.

Disclosed is a secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte comprises a lithium salt, an organic solvent, and an additive, wherein the additive comprises a fluorinated compound that accounts for 5-20% of the total mass of the electrolyte, and a polynitrile compound that accounts for 0.2-4% of the total mass of the electrolyte and a sulfate compound that accounts for 0.3-5% of the total mass of the electrolyte; and the negative electrode has a compacted density of not less than 1.55 g/cm3. When the secondary battery is used, the battery can still have both a high temperature characteristic and a low temperature charging ability under the conditions of a higher negative electrode density, thereby having market application prospects, and overcoming the problem of the performance of existing secondary batteries deteriorating when the compacted density of a negative electrode is improved.

The present disclosure provides a non-aqueous electrolyte including an additive including a repeating unit represented by Formula 1 and a repeating unit represented by Formula 2 below:

##STR00001##

##STR00002##

wherein X, R, R.sub.1 and R.sub.2 are described herein.

The present disclosure provides a non-aqueous electrolyte including an additive including a repeating unit represented by Formula 1 and a repeating unit represented by Formula 2 below:

##STR00001##

##STR00002##

wherein X, R, R.sub.1 and R.sub.2 are described herein.

A non-aqueous electrolyte, with a coulombic efficiency with respect to lithium of at least 80%, that includes a Group 1 salt dissolved in a mixture containing two sulfone compounds, a mixture containing a sulfone compound and a sultone compound, and/or a mixture containing a sulfone compound and a sulfonamide compound. The Group 1 salt can be a lithium salt, the sulfone compound can be a cyclic sulfone such as thietane-1,1-dioxide and sulfolane, the sultone compound can be a cyclic sultone such as 1,3-propane sultone, and the sulfonamide compound can be a partially fluorinated sulfonamide such as 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide and N-butyl-1,1,1-trifluoro-N-methylmethanesulfonamide. Additives such as another lithium salt, a polyunsaturated compound, a cyclic anhydride, a cyclic unsaturated sultone, and/or a cyclic phosphate can be included in the non-aqueous electrolyte.

A non-aqueous electrolyte, with a coulombic efficiency with respect to lithium of at least 80%, that includes a Group 1 salt dissolved in a mixture containing two sulfone compounds, a mixture containing a sulfone compound and a sultone compound, and/or a mixture containing a sulfone compound and a sulfonamide compound. The Group 1 salt can be a lithium salt, the sulfone compound can be a cyclic sulfone such as thietane-1,1-dioxide and sulfolane, the sultone compound can be a cyclic sultone such as 1,3-propane sultone, and the sulfonamide compound can be a partially fluorinated sulfonamide such as 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide and N-butyl-1,1,1-trifluoro-N-methylmethanesulfonamide. Additives such as another lithium salt, a polyunsaturated compound, a cyclic anhydride, a cyclic unsaturated sultone, and/or a cyclic phosphate can be included in the non-aqueous electrolyte.

Systems and methods for a lithium-ion battery cell are disclosed. In one example, a method for forming a cathode for a lithium-ion battery cell includes forming a pre-lithiated cathode with a pre-lithiation reagent and positioning the pre-lithiated cathode in contact with an electrolyte. An electrolyte additive is injected into the electrolyte to form a passivation layer at the pre-lithiated cathode, the passivation layer inhibiting continued decomposition of the pre-lithiation reagent of the pre-lithiated cathode after completion of a formation cycle of the lithium-ion battery cell.

Systems and methods for a lithium-ion battery cell are disclosed. In one example, a method for forming a cathode for a lithium-ion battery cell includes forming a pre-lithiated cathode with a pre-lithiation reagent and positioning the pre-lithiated cathode in contact with an electrolyte. An electrolyte additive is injected into the electrolyte to form a passivation layer at the pre-lithiated cathode, the passivation layer inhibiting continued decomposition of the pre-lithiation reagent of the pre-lithiated cathode after completion of a formation cycle of the lithium-ion battery cell.