It is very important operation in a battery manufacturing process to disperse electrode materials because battery performance is decided by the dispersion states of electrode materials. A batch operation is generally used as a conventional method, and it needs long operation time to make dispersion slurry. Getting dispersion slurry using some of the next generation active materials having modified-surface and fine grain size is difficult for the conventional method. To provide a dispersing device capable of efficiently obtaining dispersion force is required. We use twin screw type continuous kneading machine. This continuous kneader can disperse a wide range of viscosity. The continuous kneader is also applied in various industries such as food and chemical in order to have excellent dispersing ability. Due to continuous process, automation and cost reduction become possible, and production speed is improved.
The continuous kneader is closed horizontal twin screw type. The twin screws are constructed of many paddles which are mounted on the twin shafts. Each paddle is separate piece that can be arranged to suit various mixing characteristics. The shafts rotate in the same direction. The paddles are arranged in pairs along the mixing circuit, and have a constant clearance between the tip of the paddle and the inner barrel wall, as well as the tip of the paddle to the surface of the opposite piece. This gives the benefit of mixing efficiency. Volume of material is changed in compression and expansion according to paddle's rotation. Shearing actions between the barrel and paddle, and between paddles increases efficiency of kneading and dispersion.
The continuous kneader was applied to the tape for manufacturing magnetic recording medium, because dispersion plays important role. The magnetic powder became finer according to enhance data capacity, the continuous kneader could manufacture good dispersion magnetic coating material in response to this change. Manufacturing of lithium ion battery electrode slurry is kneading powder materials in binder resin in the similar way of making the magnetic tape. The authors included the know-how obtained by improving manufacturing of the magnetic tape in continuous kneading process of lithium ion battery electrode slurry.
The authors have performed examination of suitable kneading conditions of dispersion slurry production by using Li(Ni1/3Mn1/3Co1/3)O2 (NMC) and LiFePO4(LFP) as cathode active materials. The dispersion state of the slurry using the continuous kneader is controlled by the paddle arrangement, the rotary speed of the shaft and the supply conditions of raw materials. Several elements of kneading conditions have beneficial effect on slurry viscosity and battery performance. After changing some of kneading conditions, excellent dispersion slurries were obtained. The slurry from optimized continuous process showed high battery performance. Cyclic performance of laminated pouch type cell showed a stable characteristic about 2,000 cycles at the charge-discharge rate of 3C. The battery performance was comparison with the slurry made by using batch operation. Rate characteristics and cyclic performance of the slurry made by continuous kneading process showed better than made by batch operation. The paddle arrangement and the supply conditions of raw materials influence the dispersion state of slurry. The solid content concentration in the continuous kneader changes when supply conditions of raw materials was changes, it was considered that the dispersion of raw materials advanced by adjusting the solid content concentration appropriately.
This high speed continuous kneading process greatly improves not only the battery performance but also productivity of the electrode slurry. Our high speed continuous kneading process can manufacture about 60 times faster than the conventional batch operation according to our estimates. Therefore the cost reduction may be practiced in LIB mass production. The above-mentioned results indicate that the high speed process of high performance electrode slurry made by the continuous kneader is effective method.