New Solef® Grades
for Binder Application
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Solef® New grades for Binder Application
Solvay Solexis has developed new PVDF grades in order to improve binder performances in Lithium Batteries electrodes, in particular adhesion of active materials to metal collector and cohesion between particles of active material.
朗诵伴奏Two new grades of Solef®are prented: Solef®5130 and Solef®5320. This Data Sheet shows main properties of the two products related to binder application; a comparison with standard Solef® 1013 and Solef® 6020 as references is also reported.
Adhesion Properties
The target for new materials is to increa adhesion in binder application in order to obtain better performances of lithium batteries even with a lower amount of PVDF in the electrode. Following graph shows results obtained on different cathode samples prepared with Solef®PVDF grades, carbon black and LiCoO2 as active material and dried at 130°C. Adhesion of the coating to aluminum foil has been measured by a peeling test. Relative values, referred to performances of Solef® 6020 as reference, are reported in Fig. 1.
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Fig. 1: Adhesion measured on cathodes with different polymer dry content.
Good results are obtained with new Solef®grades: in particular by using the same PVDF content in the electrode it is possible to achieve an adhesion higher respect to standard Solef 6020. Excellent results are obtained also by verely reducing PVDF dry content in the final electrode.
The same trend of adhesion results has been obtained on cathodes dried at 80°C.
析组词Processability
怎么清洗打印机Viscosity of slurries containing PVDF and active materials plays a key role in the electrodes preparation. It is possible to easily control this parameter by varying PVDF content or by changing concentration of the final slurry.
Several tests have been performed in cathode slurries with a standard composition of active materials (LiCoO2 and carbon black). The graph in Fig. 2 shows a comparison between values obtained with different grades of PVDF: viscosity of Solef® 1013 and Solef® 6020 slurries has been maintained as reference for the relative comparison with new grades.
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Fig. 2: Slurry viscosity measured in slurries with different polymer content.
In particular the two new grades give a different slurry processability compared to standard grades Solef® 1013 and Solef® 6020. Thanks to improved adhesion properties, as shown in following paragraph, viscosities clor to standard references are easily achieved for instance by reducing PVDF content in the electrode or by slightly diluting the slurry.
Thermal Properties
DSC datas refer to 2nd melting curve after crystallization of 1st running curve. The curve itlf is ud to extract datas such as Tm (°C) and fusion enthalpy, dHf (J/g). Crystallinity index can be estimated by dividing dHf by the fusion enthalpy of a 100% theoretical crystalline PVDF.
Intrinsic viscosity
Values of intrinsic viscosity have been extrapolated from viscosity data of DMF solutions, measured with Ubbelohde viscosimeter at 25°C. Results are reported in following table.
婴儿黄疸指数正常值Dissolution time in NMP
Dissolution time is an important parameter linked to PVDF processability in solution. Times necessary to obtain a clear solution in NMP at 8% weight and 50°C are reported in following table. Powders have been slowly added to NMP solutions (1 g/min) under magnetic stirring. Low speed of powder addition and low concentration of PVDF in NMP can reduce dissolution time; also geometry of stirrer have a strong influence on dissolution process and time.
Viscosity in NMP solution
Solef® PVDF homopolymers such as 1013 and 6020 and new experimental grades are well dissolved by solvents as dimethylformamide (DMF), dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP), typically utilized in Lithium Batteries manufacturing process. PVDF type and molecular weight, concentration of the solution and temperature are key factors in determing the solution viscosity as indicated below, in the ca of NMP solutions. Shear rate can be a factor above 10 s-1, especially for ultra high molecular weight such as Solef® 6020 and Solef® 5130.
Following graph shows flow curves related to solutions of PVDF in NMP at 8% weight and 25°C for a comparison of different Solef®grades for Lithium Batteries application. In this ca differences in viscosity are determined by the different molecular weight of polymers.
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Fig. 3: Viscosity of different PVDF grades in NMP at 8% weight and 25°C.
It is possible to vary concentration of PVDF in the solution or temperature of dissolution process in order to obtain a better processability of Solef®grades in NMP: for instance following graph shows a comparison between Solef® 5130, Solef® 5320 and standard Solef®6020 at two different concentrat
ions. All measurements have been performed at 25°C.
Fig. 4: Viscosity of different concentration of PVDF in NMP at 25°C.
