KR101115392B1 - Anode Material for Lithium Secondary Battery Having Excellent Conductivity and Energy Density, and High Power Lithium Secondary Battery Employed with the Same - Google Patents

Abstract

The present invention is a negative electrode material produced by uniformly mixing the copper oxide and the amorphous carbon-based compound, and then calcined and carbonized, the copper nanoparticles are uniformly contained in the inside and the surface of the negative electrode material, micropores or communication therein The present invention provides a negative electrode material for electrode mixture in which a large amount of fine passages are generated. The lithium secondary battery using the negative electrode material exhibits excellent battery characteristics by improving output density and energy density.

Description

Anode Material for Lithium Secondary Battery Having Excellent Conductivity and Energy Density, and High Power Lithium Secondary Battery Employed with the Same}

The present invention relates to a negative electrode material for a lithium secondary battery having excellent electrical conductivity and energy density, and to a high output lithium secondary battery including the same. More particularly, after uniformly mixing a copper oxide and an amorphous carbon-based compound, firing and carbonizing As a negative electrode material manufactured by using a negative electrode material, copper nanoparticles are uniformly contained in the inside and the surface of the negative electrode material, the negative electrode material for electrode mixture and a high output lithium secondary containing the same, a large amount of fine pores or communication therein is generated It relates to a battery.

The present invention relates to a negative electrode material for a lithium secondary battery having excellent electrical conductivity and energy density, and to a high output lithium secondary battery including the same. More particularly, after uniformly mixing a copper oxide and an amorphous carbon-based compound, firing and carbonizing As a negative electrode material manufactured by using the same, the negative electrode material and the high-output lithium secondary including the electrode mixture negative electrode material containing copper nanoparticles uniformly contained in the inside and the surface of the negative electrode material, and a large amount of fine pores or communication therein is generated therein It relates to a battery.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing, and lithium secondary batteries having high energy density and voltage are commercially used in such secondary batteries. When a secondary battery is used as a power source for a mobile phone or a laptop, a secondary battery that provides a stable output is required, whereas when used as a power source of a power tool such as an electric drill, it provides instantaneous high output while vibrating There is a need for a secondary battery that can be stable against external physical shocks such as falling and the like.

In addition, as interest in environmental problems grows, research on electric vehicles and hybrid electric vehicles that can replace vehicles using fossil fuel, such as gasoline and diesel vehicles, which are one of the main causes of air pollution, is being conducted. . As a power source of such electric vehicles and hybrid electric vehicles, nickel-metal hydride secondary batteries are mainly used, but researches using lithium secondary batteries with high energy density and discharge voltage have been actively conducted and some commercialization stages are in progress.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode on which an active material is coated on a current collector. The positive electrode active material is mainly composed of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium composite oxide, etc., the negative electrode active material is mainly composed of carbon-based materials.

The carbon-based active material is composed of soft carbon having an almost graphitized graphene structure (a structure in which hexagonal honeycomb planes of carbon are arranged in layers), and these structures are mixed with amorphous portions. It is classified as hard carbon, which is classified as hard carbon, and is classified as graphite when the layered crystal structure is completely formed like natural graphite.

In particular, since the graphite-based material, which is a layered crystal, is mainly used as a negative electrode active material, the negative electrode made of such a graphite-based material has a theoretical maximum capacity of 372 mAh / g (844 mAh / cc) and has a limited capacity increase, thus rapidly changing the next generation. It is difficult to play a sufficient role as an energy source of mobile devices.

In addition, although lithium metal, which has been examined as a negative electrode material, has a very high energy density and can realize a high capacity, there are problems of safety due to dendrite growth and short cycle life during repeated charging and discharging. In addition, attempts have been made to use carbon nanotubes as negative electrode active materials, but problems such as low productivity, high price, and low initial efficiency of 50% or less have been pointed out.

As another cathode material, it has been known that silicon, tin, or alloys thereof can reversibly occlude and release a large amount of lithium through a compound formation reaction with lithium. Is going on. For example, silicon is promising as a high capacity cathode material because the theoretical maximum capacity is about 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is much larger than graphite-based materials. However, the negative electrode material has a disadvantage in that the cycle characteristics are poor due to the large volume change during charge and discharge.

On the other hand, the amorphous carbon-based compound has a very high discharge capacity of 280 to 450 mAh / g, whereas the initial efficiency is very low, such as 70 to 80%, the energy density is not good due to the large irreversible capacity and low bulk density and electrical conductivity There is a problem.

In this regard, a negative electrode material coated with an amorphous carbon layer on the graphite-based carbon compound may be considered. However, in this case, although the energy density is improved, it is difficult to expect high output characteristics because the proportion of the amorphous carbon-based compound contained in the negative electrode material is low, and there is a problem in that the life characteristics of the battery are deteriorated due to poor electrical conductivity of the coating layer.

In addition, a technique for facilitating the movement of electrons by doping a conductive metal or the like on the surface of the negative electrode active material in order to improve the conventional output characteristics. For example, Korean Patent Application Publication No. 2002-062193 includes a battery active material having an average particle diameter of 0.1 to 100 μm and conductive powders such as nickel and aluminum having an average particle size of 10 nm to 10 μm attached around the active material. A carbon material for secondary batteries is disclosed. However, according to the above technique, the conductivity on the surface of the negative electrode active material may be partially improved. However, in the case of an active material having low conductivity such as an amorphous carbon compound, the conductivity inside the particle is difficult to be improved. have.

In addition, a technology for replacing a carbon-based material with a material having excellent rate capability as a negative electrode active material has been proposed, but these active materials have a problem in that high temperature characteristics and capacity reduction of a battery are caused.

Therefore, while minimizing the above problems in the secondary battery, there is an urgent need to develop a negative electrode material with improved output characteristics.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application, after continuing in-depth research and various experiments, uniformly mixed the precursor of the copper oxide and the amorphous carbon-based compound, and then calcined and carbonized to produce a negative electrode material, the copper on the inside and surface of the negative electrode material Since the nanoparticles are uniformly contained and a large amount of fine passages are formed inside or in communication with each other, the movement path of lithium ions can be diversified. Thus, a lithium secondary battery using the same improves output density and energy density, thereby providing excellent battery characteristics. It has been found to have, and came to complete the present invention.

Therefore, the negative electrode material for electrode mixture according to the present invention is a negative electrode material prepared by uniformly mixing the copper oxide and the precursor of the amorphous carbon-based compound, and then calcined and carbonized, the copper nanoparticles uniformly inside and on the surface of the negative electrode material It is included, and consists of a large amount of fine passages are formed in the micropores or communication therein.

The negative electrode material according to the present invention is prepared by uniformly mixing the precursor of the copper oxide and the amorphous carbon-based compound, and then calcining and carbonizing, the oxygen of the copper oxide is carbon of the precursor of the amorphous carbon-based compound in the firing and carbonization process It is reduced by and discharged in the form of water vapor (H ₂ O) and carbon dioxide (CO ₂ ), thereby generating a large amount of fine passages or pores in the final manufactured negative electrode material, and at the same time to the inside and surface of the amorphous carbon compound Copper nanoparticles are uniformly distributed.

Therefore, by supplementing the low bulk density and the electrical conductivity of the amorphous carbon compound by the high electrical conductivity of copper nanoparticles uniformly distributed on the inside and the surface of the amorphous carbon compound, a cathode material having high energy density and improved output characteristics can be obtained. have. Furthermore, since the movement path of lithium ions is diversified by a plurality of micro-paths through which pores and communicating inside the negative electrode material generated while the water vapor and carbon dioxide are discharged, the discharge capacity and rate characteristics of the negative electrode material can be further improved, such a negative electrode Electrochemical cells containing ash can exhibit excellent battery properties.

The mixing ratio of the copper oxide and the precursor of the amorphous carbonaceous compound can be appropriately adjusted in consideration of the desired degree of improvement in electrical conductivity, battery capacity, and the like. However, when the ratio of the copper oxide is too high, the improvement in electrical conductivity is not great, and the battery capacity may be reduced by decreasing the content of the amorphous carbon material in the relatively negative electrode material, which is relatively undesirable. Since the effect of improving the desired electrical conductivity and increasing the migration path of lithium can not be exerted, the copper oxide and the precursor of the amorphous carbon-based compound may preferably be mixed in a weight ratio of 0.1: 100 to 10: 100.

The average particle diameter of the copper nanoparticles is not particularly limited as long as it can be uniformly distributed on the inside and the surface of the negative electrode material, it may be several to several hundred nm, preferably 5 to 500 nm. If the particle size of the metal powder is too small, uniform distribution becomes difficult due to cohesion, and thus it is difficult to exert a desired effect. On the contrary, if the particle size of the metal powder is too large, it may be difficult to distribute inside the amorphous carbon-based negative electrode material.

The amorphous carbon is a metastable solid state produced by an equilibrium process in a liquid phase or a gaseous phase, and has a structure in which particles of several tens of nanometers to hundreds of nanoscales are aggregated. Therefore, unlike crystalline carbon having a variety of amorphous shapes, a large surface area per unit volume, and a path through which lithium ions are inserted and desorbed is approximately two-dimensional, it is relatively large, and thus excellent output characteristics can be exhibited.

The precursor of the amorphous carbon-based compound is not particularly limited as long as it can occlude and release lithium ions. For example, hard carbon, coke, needle coke, and the like, which are thermally decomposed phenol resin, furan resin, and the like, Soft carbon carbonized pitch and the like, and preferably selected from the group consisting of phenol resin, furan resin, coke, needle coke, pitch and liquid mesophase pitch. One or more than one may be used.

Such an amorphous carbon-based compound basically has a relatively high discharge capacity of 280 to 450 mAh / g can implement a high capacity battery.

The present invention also provides

(1) uniformly mixing a precursor of an amorphous carbon compound and copper oxide under a solvent;

(2) drying, calcining and carbonizing the mixed mixture; And

(3) pulverizing the produced carbide;

It provides a method for producing the negative electrode material comprising a.

In the present invention, the mixing of the precursor of the amorphous carbonaceous compound and the copper oxide is performed by a wet mixing method performed under a predetermined solvent. Dry mixing may be possible, however, in this case, a uniform distribution of the copper nanoparticles requires the use of a very small anode material precursor or a long time process.

When mixing copper oxide powder by the said wet mixing method, alcohol is preferable as a solvent, Especially, methanol can be used especially preferable. In some cases, a surfactant may be further added to the solvent to prevent the copper oxide particles from agglomerating in the solvent. The surfactant may be, for example, polyoxyethylene and polyoxypropylene, or a copolymer thereof, but is not limited thereto.

The precursor of the amorphous carbon-based compound is not particularly limited, and may be preferably a phenol resin powder or a phenol resin solution.

In addition, the copper oxide is preferably added in an amount of 0.05 to 10% by weight based on the total weight of the negative electrode material mixture in consideration of the desired degree of improvement in electrical conductivity, battery capacity, and the like, as described above.

The firing and carbonization process may be performed in a vacuum or inert atmosphere, preferably in a nitrogen or argon atmosphere to prevent oxidation of the amorphous carbonaceous compound precursor material.

On the other hand, the firing process may be performed at a sufficiently high temperature above the carbonization temperature of the precursor, so that the copper nanoparticles can be uniformly distributed on the inside and the surface of the amorphous carbon-based compound precursor, It may vary depending on the type, for example, may be carried out at a temperature of 600 to 2000 ℃.

In the grinding process, it is preferable to grind the carbide mixed with the precursor and the copper oxide powder to a size of 8 to 25 μm. When the average particle diameter of the carbide is too large, there is a problem that the bulk density of the negative electrode material is lowered. If the average particle diameter is too small, the irreversible capacity of the negative electrode material is high and it is not preferable because the desired discharge capacity is difficult to be expected.

The present invention also provides a negative electrode mixture comprising the negative electrode material, a binder and a conductive material.

The binder is a component that assists in mutual bonding of the negative electrode material and the conductive material and bonding to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the negative electrode material. Examples of such binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose Roses, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers And polymer high polymerized polyvinyl alcohol.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Specific examples of commercially available conductive materials include Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, Ketjenblack and EC, which are acetylene black series. Family (Armak Company), Vulcan XC-72 (manufactured by Cabot Company) and Super P (manufactured by Timcal).

The negative electrode mixture may also optionally include a filler, an adhesion promoter, and the like.

The filler is not particularly limited as long as it is a fibrous material that does not cause chemical change in the battery as a component that suppresses the expansion of the negative electrode. For example, the filler may be an olefin polymer such as polyethylene or polypropylene, glass fiber, carbon fiber, or the like. Fibrous materials are used.

The adhesion promoter may be added in an amount of 10% by weight or less based on the binder, for example, oxalic acid, adipic acid, Formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.

The invention also relates to an electrochemical cell comprising the negative electrode mixture comprising a negative electrode applied on a current collector.

Generally, the negative electrode is prepared by adding a negative electrode mixture to a solvent such as NMP to prepare a slurry, and then applying the same to a current collector to dry and press. Preferred examples of the solvent used in the preparation of the electrode slurry include dimethyl sulfoxide (DMSO), alcohol, N-methylpyrrolidone (NMP), acetone, and the like. Up to 400% by weight can be used and removed during drying.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The method of evenly applying the negative electrode mixture slurry on the negative electrode current collector may be selected from known methods or may be performed by a new suitable method in consideration of the properties of materials and the like. For example, the slurry may be distributed on the current collector and then uniformly dispersed using a doctor blade or the like. In some cases, a method of distributing and dispersing in one process may be used. In addition, die casting, comma coating, screen printing, or the like may be used. Alternatively, a separate substrate may be formed and then joined with a current collector by pressing or lamination. You can also It is preferable to dry the slurry applied on the current collector for 1 to 3 days in a vacuum oven at 50 to 200 ℃.

The electrochemical cell is a device for providing electricity through an electrochemical reaction, preferably a high output lithium secondary battery containing a lithium salt-containing nonaqueous electrolyte. The lithium secondary battery may have a structure in which a lithium salt-containing non-aqueous electrolyte is impregnated in an electrode assembly having a structure in which a separator is interposed between the negative electrode and the positive electrode.

The lithium secondary battery according to the present invention may be preferably used as a unit cell for a high output large capacity battery or a battery pack, and in particular, it may be preferably used as a vehicle power source such as an electric vehicle, a hybrid electric vehicle, etc. that require high output even at low temperatures.

In general, graphite and digraphitized carbon mainly use ethylene carbonate (EC) as an electrolyte solvent due to the properties of the material in a lithium secondary battery, whereas nongraphitized carbon uses propylene carbonate (PC) as an electrolyte solvent. Can be. According to experiments conducted by the inventors of the present application, since the PC has a characteristic of having a lower freezing point than EC, it has been found to be preferable for a material of a battery that requires operation at low temperatures.

That is, in the lithium secondary battery according to the present invention, by using a non-graphitizing carbonaceous material as a negative electrode active material, it is possible to use PC having a high dielectric constant and relatively low viscosity at a low temperature as the main component of the electrolyte solvent. Therefore, since the output characteristics at low temperatures are excellent, it can be preferably used in medium and large battery systems that must be operated under harsh conditions such as electric vehicles, hybrid electric vehicles, and the like.

In some cases, mixed solvents containing linear carbonates such as diethyl carbonate (DEC) and dimethyl carbonate (DMC) may be used in addition to PCs to increase the conductivity of lithium ions and to ensure reaction stability. have.

Other components of the lithium secondary battery according to the present invention will be described in detail below.

The positive electrode is produced by, for example, applying a positive electrode mixture containing a positive electrode active material onto a positive electrode current collector and then drying it.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _2-y O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _{1 - y} M _y O ₂ (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and y = 0.01 to 0.3); Formula LiMn _2-y M _y O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separation membrane, for example, a sheet or a nonwoven fabric made of an olefin-based polymer such as polypropylene which is chemically resistant and hydrophobic, glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

As the lithium salt-containing non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, or the like may be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymerizers containing ionic dissociating groups and the like can be used.

As the inorganic solid electrolyte, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO _4- LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , _{Li 4 SiO 4 - LiI-LiOH} , Li 3 PO 4 - there is a Li nitrides, halides, sulfates, etc., such as Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, in the electrolyte solution, for the purpose of improving the charge and discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride and the like may be added. . In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

As described above, the negative electrode material according to the present invention is prepared by uniformly mixing the copper oxide and the precursor of the amorphous carbon-based compound, and then calcining and carbonizing, thereby uniformly including copper nanoparticles in the inside and the surface of the negative electrode material. In addition, since a large amount of fine passages are formed inside the micro-pores or communication, the secondary battery comprising the same has a high electrical conductivity and energy density, the lithium ion movement path can be increased to exhibit excellent high output characteristics, the amorphous carbon-based compound of High discharge capacity can be exhibited.

Claims (15)

The copper oxide and the precursor of the amorphous carbonaceous compound are uniformly mixed in a weight ratio of 0.1: 100 to 10: 100, and then calcined and carbonized, and the copper nanoparticles are uniformly contained inside and on the surface of the anode material. The negative electrode material for electrode mixture, characterized in that a large amount of fine passages are formed in or communicate with the micropores. delete The negative electrode material according to claim 1, wherein the average particle diameter of the copper nanoparticles is 5 to 500 nm. The electrode mixture of claim 1, wherein the precursor of the amorphous carbonaceous compound is at least one selected from the group consisting of a phenol resin, a furan resin, coke, needle coke, a pitch, and a liquid mesophase pitch. Cathode material for use. Uniformly mixing the precursor of the amorphous carbonaceous compound with copper oxide in a solvent at a weight ratio of 100: 0.1 to 100: 10, drying, calcining and carbonizing the mixture, and grinding the resulting carbide A method for producing a negative electrode material according to any one of claims 1, 3 and 4, comprising. The method of claim 5, wherein the precursor of the amorphous carbonaceous compound is a phenol resin powder and / or a phenol resin solution. delete The method of claim 5, wherein the calcining and carbonization are performed in a nitrogen or argon atmosphere. The method of claim 5, wherein the firing process is performed at 600 to 2000 ° C. 7. The method of claim 5, wherein the carbide is ground to a size of 8 to 25 μm in the grinding process. A negative electrode mixture comprising the negative electrode material according to any one of claims 1, 3 and 4, and a binder and a conductive material. An electrochemical cell consisting of a negative electrode on which a negative electrode mixture according to claim 11 is applied on a current collector. The electrochemical cell of claim 12, wherein the electrochemical cell is a lithium secondary battery containing a lithium salt-containing nonaqueous electrolyte. The electrochemical cell of claim 13, wherein the solvent of the electrolyte comprises propylene carbonate. delete