Lithium secondary batteries have common structural features that include a cathode, an anode, an organic electrolyte and a lithium ion-permeable separator disposed between the electrodes. The electrical energy is generated by redox reactions occurring on the electrodes. A lithium ion secondary battery contains a positive electrode, a negative electrode, and an ion conducting layer sandwiched between these electrodes as a main component. Lithium ion secondary batteries generally employ a positive electrode plate prepared by applying to an aluminum current collector a mixture comprising a powdered active material, such as a lithium-cobalt complex oxide, a powdered electron conductor, and a binder resin; a negative electrode plate prepared by applying to a copper current collector a mixture of a powdered carbonaceous active material and a binder resin; and an ion conducting layer made of a porous film of polyethylene, polypropylene, etc. filled with a nonaqueous solvent containing lithium ions. The negative electrode has a negative current collector contacting the negative electrode active material, and a positive current collector contacting the positive electrode active material. The negative electrode active material releases lithium ions upon discharging of the battery cell and absorbs lithium ions upon charging of the battery cell. The positive electrode active material reacts with lithium ions upon discharging of the battery cell and releases lithium ions upon charging of the battery cell. A cathode for lithium-ion secondary battery comprises a metal oxide active material for releasing and inserting lithium, a conductive material added to give conductivity, and a coupling material for fixing the metal oxide active material and the conductive material to an aluminum collecting body. A lithium ion battery can secure its stability and can maintain high capacitance characteristics by employing graphite as an anode-forming material. A graphite anode reversibly enables storage and separation of lithium through intercalation of lithium ions. In lithium ion secondary batteries, a separator is interposed between positive and negative electrodes in order to electronically insulate the electrodes and to retain an electrolyte. Lithium ion secondary batteries typically utilize a separator comprising a microporous thin film made of polyolefin resin such as polyethylene.

Lithium ion secondary batteries produce an electromotive force by lithium doping/dedoping. The cathode made of lithium doped transition metal oxides function as electron donors. Atoms of the electron donor undergo an oxidation reaction to form ions of lithium, and free electrons. These ions travel through the membrane and are absorbed by the anode by a reduction reaction, and the free electrons travel through an electrical circuit to provide electrical current. The anode is generally made of materials comprising carbon, such as graphite or carbon fibers. The carbon materials can readily intercalate lithium ions. The lithium ion liquid secondary battery comprises an anode including carbonaceous material as an anode active material and a cathode including metal oxide of lithium cobalt oxide as a cathode active material, and is prepared by intercalating a porous polyolefin-based separator between the anode and the cathode, then by injecting a non-aqueous electrolyte having a lithium salt of lithium hexafluorophosphate. Lithium ions move back and forth between electrodes during the charging and discharging processes of the battery. During the battery charging process, Li ions from the cathode move through an electrolyte, collect an electron and proceed to intercalate within the carbon structure of the anode. During charging of this type of battery, lithium ions are removed from the cathode when the oxidation state of the transition metal component of the cathode increases. Lithium ions are inserted in the cathode during reduction at the cathode when the oxidation state of the transition metal component is lowered. The opposite reaction takes place during discharging. When the battery discharges, the opposite occurs with the lithium ions of a carbon layer of an anode being released and then inserted into the cathode active material. The ability to intercalate lithium into the carbon structure of the anode usually determines the performance of the battery. The performance of lithium ion secondary batteries, such as the charge/discharge capacity, voltage profile and cyclic stability, strongly depends on the microstructure of the carbon anode material. Types of carbon materials that have been investigated for use in lithium ion batteries include both graphitic carbons and non-graphitic carbons, such as semi-coke and glass-like carbons.

Lithium secondary batteries are classified as lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries according to kinds of separator and electrolyte, and as cylindrical, prismatic, and coin-type batteries according to their shapes. Depending on the types of solid polymer electrolyte, the lithium polymer batteries are classified into full-solid type lithium polymer batteries in which organic electrolytic liquid is not included at all, and lithium ion polymer batteries employing gel type polymer electrolyte containing organic electrolytic liquid. In general, a battery using a liquid electrolyte is referred to as a lithium-ion battery, and a battery using a polymeric electrolyte is referred to as a lithium polymer battery. The lithium ion polymer battery uses a solid electrolyte such as a polymer, unlike the lithium ion battery that uses a liquid electrolyte. Lithium ion polymer batteries are generally preferred over lithium ion batteries because of no risk of liquid electrolyte leakage and the capability of shaping it into any form. A lithium ion polymer secondary battery is formed by laminating a positive-electrode sheet and a negative-electrode sheet. The positive-electrode sheet is prepared by forming an active material on a surface of a positive-electrode collector foil, and the negative-electrode sheet is prepared by forming an active material on a surface of a negative-electrode collector foil. A polymer electrolyte layer is disposed between the active material on the positive-electrode sheet and the active material on the negative-electrode sheet. In polymer solid electrolytes, electrolytes are homogeneously dissolved into polymers. The polymer solid electrolytes are flexible and are suitable for use in sheet batteries.

The lithium-ion battery has been the preferred power sources for various applications because of its higher energy density, longer cycle life of charge-discharge and the absence of a memory effect problem. Lithium is the lightest of all the metals, with a high electrochemical potential, thus providing high energy densities. Rechargeable batteries using lithium as the electrochemical material are capable of providing higher energy to weight ratios than those using other chemistries. Lithium ion secondary batteries have superior electromotive force and battery capacity, and are more advantageous than nickel-cadmium battery etc. in that they show high energy density, high voltage etc. In spite of the advantage of high energy density, the lithium ion secondary battery is required to provide a sufficient measure for safety because lithium metal and a non-aqueous electrolyte are used. It is typical to use protection circuitry with lithium ion batteries to avoid potential deleterious effects. Protection circuitry is frequently employed to terminate charging if the voltage or temperature of the battery exceeds a certain level. It is also common to incorporate a low voltage cutoff to disconnect the battery from its load if the voltage of the battery (or any cell) falls below a certain lower level, to prevent permanent damage to the battery which can occur if a voltage greater than a damage potential threshold (DPT) is applied to one of the electrodes.