Lithium electrochemical systems

The study of the internal resistance of the lithium-ion battery designed and manufactured by JSC «Saturn» as the original, and after a long cycle life by pulse chronopotentiometry and electrochemical impedance was carried out. It is shown that the higher the hexagonal ordering of the material and the closer the degree of cation mixing to the optimal value, the less polarization resistance of the battery as original, and after a long cycle life. It was found that the less the original polarization resistance of the battery, the more its cyclic life.

In article experience of application of chemical sources of a current of electrochemical system lithium – tionilchloride and batteries on their basis, in onboard systems of electrosupply of modern and perspective space-rocket technics of Russia is presented.

On basis of analysis of literature data as well as of own experimental results we suggest some regularity for degradation of silicon electrodes upon cycling. It was shown that an electrode capacity Q at n-th cycle can be calculated from equation Q = Q₀ exp(kn+βn²/2), where Q₀ is initial capacity value, k и β are empiric constants.

In this paper, we investigated the possibility of determining the internal resistance of the battery by pulsed method with followed Fourier transformation in transition characteristics. The changes of internal resistance of lithium sulfur cells were studied in dependence on the discharge and charge depths during continuous cycling by proposed method. It was shown that the internal resistance of lithium sulfur cell was maximal at the point corresponding to the transition between high-voltage and low-voltage plateaus both at the charge curves and at the discharge curves. The most significant increase in the internal resistance of lithium sulfur cells occurs at the initial stages of cycling. It was found that the internal resistance of lithium sulphur cell is governed by the way the state of charge is achieved. This is due to the difference in densities of products, generated in positive electrodes by electrochemical reactions at charge (ρ(S) = 2.07 g/cm³) and discharge (ρ(Li₂S) = 1.63 g/cm³).

The effect of lithium polysulphides on the cyclic deposition/and dissolution of lithium metal on an inert stainless steel electrode and on a lithium metal electrode in sulfolane solutions has been studied. It has been shown that the addition of lithium polysulphides to sulfolane solutions leads to a significant increase in the cycle life (2 or more times) and cycling efficiency of a lithium metal electrode and a lithium metal on inert stainless steel electrode. It also results in the reduction of the corrosion rate of the lithium cathodic deposits. The positive influence of lithium polysulphideson the electrochemical behaviour of the lithium electrode is explained by the formation, in the presence of lithium polysulphides, of a «sulphide» surface film, which has a higher lithium-ion conductivity and better protection properties in comparison to the surface film formed on the lithium in the presence of LiClO₄.

Structure of thin-film electrodes manufactured by layer-by-layer magnetron sputtering of Si and Al in the environment with small oxygen additives has been studied. Charge-discharge behavior of these electrodes was studied as well. It is shown that such electrodes are able to stable cycling with marginal irreversible capacity.

Cycling tests of lithium-ion batteries in wide temperature and load ranges have been carried out. The existence of certain threshold discharge load corresponding abrupt decrease of discharge capacity was found.

Discharge behavior of lithium nano-titanate samples synthesized by solid-state methods from titania (anatase) and various lithium compounds has been studied. The shape of discharge curves was shown to change along with increasing current. This change was explained with due account for the model of heterogeneous lithium nano-titanate grain. It is found that the dependence of discharge capacity on current density does not obey to common Peukert equation but consists of two segments. In any cases the exponent in the Peukert equation does not exceed 0.2.

Silicon nano- and microwires have been obtained by KCl-KF-K₂SiF₆-SiO₂ melt electrolysis in air; this material is suitable as anode component for lithium ion batteries. Optimal conditions of electrolysis were determined. Morphology, phase and chemical composition of silicon deposits were established. Electrochemical behavior of silicon nanowires as anode component was evaluated using solid polymer electrolyte cells.

A series of solid phases (mixed lithium-iron-manganese phosphates) of the common formula LiMn_yFe_1-yPO₄ (0 ≤ y ≤ 1) with a carbon coating on the particle surface was synthesized by mechanochemical activation with carbothermal reduction. The synthesized mixed phosphates were examined as promising cathode materials for lithium-ion batteries. The positive effect of replacement of a rather small fraction of iron by manganese is shown, which improves the electrochemical performance at the rates C/10–10C. The highest discharging capacity (above 160 mA·h/g at the C/10 rate, about 100 mA·h/g at the 10C rate) and cycling stability (the capacity decrease rate less than 0.05 mA·h/g per cycle at the 10 C rate) were established for the weakly doped cathode material LiMn_0.05Fe_0.95PO₄.