Determination of the relationship between particle size and electrochemical performance of uncoated LiFePO4 materials

Abstract

The current literature generally reports the relationship between particle size and electrochemical performance of carbon-coated LiFePO4 (LFP). However, besides the factor of particle size, the quality of carbon coating will affect the electrochemical performance of LiFePO4 simultaneously. Logistically, each independent equation is solvable when it contains just one variable and is not solvable when it contains two or more variables. Therefore, we decide to study the relationship between particle size and electrochemical performance of uncoated LiFePO4, of which the relevant literature is sparse. To prepare samples within a wide range for average particle sizes, a traditional precipitation approach was employed to prepare the LFP materials with different average particle sizes of 30–500 nm. Carbon-coated LiFePO4 materials were prepared for the purpose of comparison studies. Both pristine LiFePO4 and carbon-coated LiFePO4 were investigated by XRD, FESEM, as well as charge/discharge testing (in the form of coin cells). The details of materials syntheses were discussed. Without the influence of carbon coating, the discharge capacity of pristine LiFePO4 exhibited a “volcano”-type relationship versus the average primary particle size in the size range of 50–500 nm and reaches a maximum value at the optimum size of about 200 nm. This finding may drive the development of power grade LFP cathode nanomaterials toward more precise particle size optimization.