Water processed LNMO cathodes

Abstract

Post-treatment of LNMO active material is an effective means of bringing down the pH levels for water- processed LNMO cathode slurries. pH levels between 8.4 ± 0.3 are obtained in this experiment compared to ph levels of ph = 9 - 10 of untreated LNMO active material an important step towards reducing the undesired side reactions with transition metals and lithium which causes capacity fading in the processed electrodes by forming bubbling and current collector corrosion. Three variations of water-processed binder combinations using LiPaa, SBR and CMC, have been pro- cessed and bench-marked to conventional PVDF, and results from rheology emphasizes the importance of diligence in tuning the relationship between solid content, binder ratio in relation to the viscosity in preparing the coating. Post-treatment of LNMO has a 10-15 % better capacity retention for positive-electrode post-treated active materials compared to untreated reference material for specific capacity of 8.5 ± 0.8 mg/cm2 < 30 cycles for half-cells at 1C. Water-processed samples with measured pH = 8.4 ± 0.3 with LNMO CMC/SBR produced the highest capacity retention compared to NMP/PVDF LNMO post-treated samples. Un- quantified bubbling effects on water-processed electrodes, caused by undesired side-reactions was present for all water-processed electrodes. Cracking of electrodes was not present for mass loading between 8 - 19 mg/cm2 . A binder screening by half-cells comparing CMC/SBR(1/2), CMC/LiPaa(1/1) and CMC/SBR/LiPaa(1/1/1) detected that the binder combination with LiPAA/CMC binder has superior capacity retention of 98% over the first 30 cycles CMC/SBR/LiPAA 95% PVDF 94% and 78% CMC/SBR.The LiPaa combinations has 10% lower initial capacity compared to CMC/SBR and PVDF combinations 30 cycles and a factor of 10 inferior precision at 30 cycles. EIS analysis for water processed aligns well with theory for estimation of ionic resistance elements and for ionic resistance. Ionic resistance is higher for water-process electrodes compared to NMP at the corresponding porosities between 25 and 50. The results show good alignment with the Bruggeman theory for both MacMullin Number and tortuosity with increasing MacMullin number with decreasing porosity and values between 4-20. The values for tortuosity are aligned with the Bruggeman theory with numbers corresponding to the ones found in the industry. For a comparison of binders the study show that the lowest ionic resistance is obtained with the combina- tion of CMC/SBR/LiPaa(1/1/1) which indicates that the combination has the most favorable properties from EIS and capacity retention testing.