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Solid-state polymer electrolytes are key components for future batteries with higher energy density as well as increased safety and processability. In this context, a solid polymer electrolyte is developed from statistical copolymers containing flame-retardant phosphonate units and ion-conductive cyclocarbonate moieties mixed with lithium salts. Ionic conductivity measured at room temperature for those copolymers (≈10 −5 S cm −1 ) are in the same range as typical solid polymeric electrolytes not based on poly(ethylene oxide). Moreover, those copolymers electrolytes are stable in a wide electrochemical window (0.5 -4.5 V vs Li + /Li) and at high temperature (>120 °C) and they lead to a better ionic conductivity than the corresponding homopolymer blends of a similar composition, which is explained by a better lithium salt solubility and better-defined ion-conduction pathways in case of the copolymer. Finally, it has demonstrated the possibility to have fire-retardant properties afforded by phosphonate groups in copolymers without impacting the ionic conductivity.

A model is proposed for the description of the discharging of porous graphite electrodes. The model takes into account the nonequivalence of the different layers of the internal porous surface, as well as change in the potential and current density in these layers depending on the amount of passed charge. The model uses a special Balgorithmic approach^for calculating current distribution in such a non-stationary system, based on consistent computer formulation and solution of Kirchhoff's algebraic equations for the equivalent electrical circuit that simulates a porous electrode with the given thickness on different time intervals. The analysis of the model enables a better understanding of the mechanism of current generation in porous graphite electrodes and offers and explanation of the effect of electrochemical process penetration into the thick electrodes during the discharge process. It is shown, particularly, that classical almost exponential current distributions in the initial quasi-stationary period of time changes considerably during the further discharge process. After some period of discharge, the current peaks originate in the electrode. These discharge currents travel into the depth of the electrode, involving again and again new layers the porous electrode. The effect of some design and technological parameters (like the electrode thickness, current density, resistor of separator, polymer binders, etc.) has been analyzed. This gives a possibility to estimate the influence of such parameters on the discharge curves and operating characteristics of lithium-ion batteries and hybrid electrochemical capacitors with negative graphite electrode.

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Lithium-ion batteries are today among the most efficient devices for electrochemical energy storage. However, an improvement of their performance is required to address the challenges of modern grid management, portable technology, and electric mobility. One of the most important limitations to solve is the slow kinetics of redox reactions associated to inorganic cathodic materials, directly impacting on the charging time and the power characteristics of the cells. In sharp contrast, redox polymers such as poly(2,2,6,6-tetramethyl-1-piperidinyloxy methacrylate) (PTMA) exhibit fast redox reaction kinetics and pseudocapacitors characteristics. In this contribution, we have hybridized high energy Li(NixMnyCoz)O2 mixed oxides (NMC) with PTMA. In this hybrid cathode configuration, the higher voltage NMC (ca. 3.7 V vs. Li/Li+) is able to transfer its energy to the lower voltage PTMA (3.6 V vs. Li/Li+) improving the discharge power performances and allowing high power cathodes to be obtained. However, the NMC-PTMA hybrid cathodes show an important capacity fading. Our investigations indicate the presence of an interface degradation reaction between NMC and PTMA transforming NMC into an electrochemically dead material. Moreover, the aqueous process used here to prepare the cathode is also shown to enable the degradation of NMC. Indeed, once NMC is immersed in water, alkaline surface species dissolve, increasing the pH of the slurry, and corroding the aluminum current collector. Additionally, the NMC surface is altered due to delithiation which enables the interface degradation reaction to take place. This reaction by surface passivation of NMC particles did not succeed in preventing the interfacial degradation. Degradation was, however, notably decreased when Li(Ni0.8Mn0.1Co0.1)O2 NMC was used and even further when alumina-coated Li(Ni0.8Mn0.1Co0.1)O2 NMC was considered. For the latter at a 20C discharge rate, the hybrids presented higher power performances compared to the single constituents, clearly emphasizing the benefits of the hybrid cathode concept.