Insertion compounds (hereinafter also referred to as electroactive materials or redox materials) are well known, and their operation is based on the exchange of alkaline ions, in particular lithium ions, and valence electrons of at least one transition element, in order to keep the neutrality of the solid matrix. The partial or complete maintenance of the structural integrity of the material allows the reversibility of the reaction. Redox reactions resulting in the formation of several phases are usually not reversible, or only partially. It is also possible to perform the reactions in the solid phase through the reversible scission of the sulphur-sulphur bonds or the redox reactions involved in the transformation of the aromatic organic structures in quinonoid form, including in conjugated polymers.
The insertion materials are the electrochemical reactions active components used in particular in electrochemical generators, supercapacitors or light transmission modulating system (electrochromic devices).
The progression of the ions-electrons exchange reaction requires the existence within the insertion material of a double conductivity, simultaneous with the electrons and the ions, in particular lithium ions, either one of these conductivities being eventually too weak to ensure the necessary kinetic exchanges for the use of the material, in particular for electrochemical generators or supercapacitors. This problem is partly solved by using so-called “composite” electrodes, wherein the electrode material is dispersed in a matrix containing the electrolyte and a polymer binder. When the electrolyte is a polymer electrolyte or a polymer gel working in the presence of a solvent, the mechanical binding role is carried out directly by the macromolecule. Gel means a polymer matrix, solvating or not, and retaining a polar liquid and a salt, to confer to the mixture the mechanical properties of a solid while retaining at least a part of the conductivity of the polar liquid. A liquid electrolyte and the electrode material can also be maintained in contact with a small fraction of an inert polymer binder, i.e., not interacting with the solvent. With any of these means, each electrode material particle is thus surrounded by an electrolyte capable of bringing the ions in direct contact with almost the totality of the electrode material surface. To facilitate electronic exchanges, it is usual, according to the prior art, to add particles of a conductive material to one of the mixtures of the electrode material and electrolyte mentioned above. Such particles are in a very divided state. Generally, carbon-based materials are selected, and especially carbon blacks (Shawinigan or Ketjenblack®). However, the volume fractions used must be kept low because such material modifies strongly the rheology their suspension, especially in polymers, thereby leading to an excessive porosity and loss of operating efficiency of the composite electrode, in terms of the fraction of the usable capacity as well as the kinetics, i.e, the power available. At these low concentrations used, the carbon particles structure themselves in chains, and the contact points with the electrode materials are extremely reduced. Consequently, such configuration results in a poor distribution of the electrical potential within the electroactive material. In particular, over-concentrations or depletion can appear at the triple junction points:

These excessive variations of the mobile ions local concentrations and the gradients within the electroactive materials are extremely prejudicial to the reversibility of the electrode operation over a high number of cycles. These chemical and mechanical constraints or stresses, result at the microscopic level in the disintegration (particulation) of the electroactive material particles, a part of which being susceptible to lose the contact with the carbon particles and thus becoming electrochemically inactive. The material structure can also be destroyed, with the appearance of new phases and eventual release of transition metal derivatives, or other fragments in the electrolyte. These harmful phenomenons appear even more easily the larger the current density or the power requested at the electrode is.
USPTO Backgrounds
USPTO Backgrounds