Electrodes based on Li4Ti5O12 (LTO) with sodium alginate (SA) binder featuring high percentage of active material and operating in glyme-based electrolyte are here proposed for the first time. Three electrode formulations operating in ethylene carbonate: dimethyl carbonatee1M LiPF6 (LP30) and 1m lithium bis(trifluoromethane) sulfonimide - tetraglyme were tested in half-cell vs. Li and compared to conventional 80% LTO and 10% polyvinylidene fluoride binder. Electrodes with 87% LTO and 3% SA binder show the best performance, with good rate capability and excellent cycling stability over 600 cycles at 1C in both electrolytes. The use of SA is beneficial as it allows made-in-water electrode manufacturing in absence of N-methyl-2-pyrrolidone, a toxic and expensive solvent required by fluorinated binders. SA also permits to decrease its amount to 3% increasing the active material percentage, and to develop a final device with higher specific energy.
The fast charge and discharge capability of lithium-ion batteries is improved by applying a lamination step during cell assembly. Electrode sheets and separator are laminated into one stack which improves the electrochemical performance as well as the stack assembly process. The effect of non-laminated and laminated interfaces on the reversible capacity during cycling are studied thoroughly in half-cell and full-cell configurations.
The fully-laminated cells show a reduction in the capacity losses of 3%, 5% and 12% upon cycling at 2C, 3C and 5C-rate, respectively, while capacity losses of 6%, 11% and 23% are observed in non-laminated cells at the same C-rates. A significant reduction in the capacity fading at high C-rates is observed upon lamination. Additional compression is applied on the cells to compare the effect of lamination and compression on the cell performance.
The laminated cells show an improvement in the fast charging capability in comparison to the non-laminated cells.
This paper presents a comprehensive study of the influences of lamination at both electrode-separator interfaces of lithium-ion batteries consisting of LiNi1/3Mn1/3Co1/3O2 cathodes and graphite anodes. Typically, electrode-separator lamination shows a reduced capacity fade at fast-charging cycles. To study this behavior in detail, the anode and cathode were laminated separately to the separator and compared to the fully laminated and non-laminated state in single-cell format. The impedance of the cells was measured at different states of charge and during the cycling test up to 1500 fast-charging cycles. Lamination on the cathode interface clearly shows an initial decrease in the surface resistance with no correlation to aging effects along cycling, while lamination on both electrode-separator interfaces reduces the growth of the surface resistance along cycling. Lamination only on the anode-separator interface shows up to be suffcient to maintain the enhanced fast-charging capability for 1500 cycles, what we prove to arise from a significant reduction in growth of the solid electrolyte interface.
The accumulation of solid electrolyte interphases (SEI) in graphite anodes related to elevated formation rates (0.1C, 1C and 2C), cycling rates (1C and 2C), and electrode-separator lamination is investigated. As shown previously, the lamination technique is beneficial for the capacity aging in graphite-LiNi1/3Mn1/3Co1/3O2 cells. Here, surface resistance growth phenomena are quantified using electrochemical impedance spectroscopy (EIS). The graphite anodes were extracted from the graphite NMC cells in their fully discharged state and irreversible accumulations of lithium in the SEI are revealed using neutron depth profiling (NDP). In this post-mortem study, NDP reveals uniform lithium accumulations as a function of depth with lithium situated at the surface of the graphite particles thus forming the SEI. The SEI was found to grow logarithmically with cycle number starting with the main formation in the initial cycles. Furthermore, the EIS measurements indicate that benefits from lamination arise from surface resistance growth phenomena aside from SEI growth in superior anode fractions.
This study shows the feasibility of the Electrospinning method as a process step for advanced and fast production Li ion cells. Lamination is a key technology for Lithium-ion battery production. It bares different advantages, such as a fast production line speed by fixing the separator to the electrodes. Unfortunately, this technology is inapplicable for separator and electrode formulations not based on thermoplastic binders. Using Electrospinning, this disadvantage can be overcome. In our study, beaded PVDF polymer nanofibres were spun onto a fibre-reinforced, inorganic-filled separator. This modified separator was then laminated onto a NMC111-cathode using a temperature profile of 110/110/120˚C within the laminator. After Lamination, the separator was pulled-off again and placed in a SEM to see the adhesive behaviour of the applied polymer. The information gathered with SEM clearly shows a successful lamination of the separator to the electrode.