Overcharge Reaction Research Articles

Lead acid battery performance and cycle life increased through addition of discrete carbon nanotubes to both electrodes

Contemporary applications are changing the failure mechanisms of lead acid batteries. Sulfation at the negative electrode, acid stratification, and dendrite formation now precede positive electrode failures such as grid corrosion and active material shedding. To attenuate these failures, carbon has been explored as a negative electrode additive to increase charge acceptance, eliminate sulfation, and extend cycle life. Frequently, however, carbon incorporation decreases paste density and hinders manufacturability.Discrete carbon nanotubes (dCNT), also known as Molecular Rebar®, are lead acid battery additives which can be stably incorporated into either electrode to increase charge acceptance and cycle life with no change to paste density and without impeding the manufacturing process.Here, full-scale automotive batteries containing dCNT in the negative electrode or both negative and positive electrodes are compared to control batteries. dCNT batteries show little change to Reserve Capacity, improved Cold Cranking, increased charge acceptance, and enhanced overall system efficiency. Life cycle tests show >60% increases when dCNT are incorporated into the negative electrode (HRPSoC/SBA) and up to 500% when incorporated into both electrodes (SBA), with water loss per cycle reduced >20%. Failure modes of cycled batteries are discussed and a hypothesis of dCNT action is introduced: the dCNT/Had Overcharge Reaction Mechanism.

Overcharge Protection Effect of Cyclohexylbenzene and New Overcharge Protection Agent for Lithium Ion Batteries

We investigated the overcharge protection property of cyclohexylbenzene (CHB). CHB prevents overcharging by consuming the overcharge current through the electrochemical reaction of CHB. However, the CHB reactants do not increase resistance, and the overcharge reaction will restart after the CHB reaction has finished. A new overcharge protection agent (OPA) needed to be developed that has a shut-down function. We developed the new OPA, which consists of a polymer with an aromatic group and a high polar functional group. The new OPA forms a high-resistance film during overcharging, and its concept is validated.

High temperature versus low temperature Zebra (Na/NiCl2) cell performance

The effect of operating temperature on performance and aging of Zebra cells was investigated. The cells were cycled at 260°C and 350°C using a modified charging regime to accelerate damage. The cathode and solid electrolyte of degraded cells at the end of cycling were analyzed by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. It is hypothesized that the formation of AlF3 on the surface of the β″ alumina electrolyte contributes to the failure of cells at low temperatures. A mechanism based on the overcharge reaction is proposed for the formation of this phase. At 350°C, a significant capacity loss was observed with cycle life, which correlates to nickel particle growth as the cause of this phenomenon. The factors responsible for Ni grain growth are discussed.

Overcharge protection effect and reaction mechanism of cyclohexylbenzene for lithium ion batteries

We studied the relationship between the structure of aromatic compounds and the overcharge protection effect, using cyclohexylbenzene, isopropylbenzene, and toluene as the overcharge protection agents. Cyclohexylbenzene proved to be the most effective overcharge protection agent among these aromatic compounds. The effect is enhanced using a higher concentration of cyclohexylbenzene and elevated temperatures. The reaction product of cyclohexylbenzene was analyzed using field desorption mass spectrometry to elucidate its reaction mechanism. The results suggested that some of the overcharge reaction products of CHB were more reactive than that of IPB, which is consistent with the better suppressing effect on overcharging of the active material in the positive electrode.

Morphological and Structural Changes of Mg-Substituted Li(Ni,Co,Al)O2 during Overcharge Reaction

The effect of Mg-substitution in Li(Ni,Co,Al)O2 during overcharge was studied by scanning electron microscopy (SEM) observations and in situ synchrotron X-ray Diffraction (XRD) measurements. The higher Mg-substituted samples showed higher electrochemical stability during the overcharge cycling. After overcharge, the non Mg-substituted sample featured many cracks, not only at the grain boundaries in secondary particles but also inside the primary particles. This morphological change is assigned to the drastic shrinking of the c-axis during overcharge. The Mg-substitution suppressed the c-axis shrinking and consequently avoided the cracking of the particles. This effect of Mg-substitution in Li(Ni,Co,Al)O2 correlates with the electrochemical stability during the overcharge cycling.

Structural and Morphological Changes of Mg Substituted Li(Ni,Co,Al)O2 during Overcharge Reaction

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Overcharge reaction of lithium-ion batteries

Overcharge reaction was studied in detail using 650 mAh prismatic hermetically sealed lithium-ion batteries with LiCoO 2 cathodes, graphitic carbon anodes and ethylene carbonate/ethyl methyl carbonate (EC/EMC) electrolytes. Several varieties of gases (CO 2, CO, H 2, CH 4, C 2H 6 and C 2H 4) were evolved in the overcharge reaction. The amount of gas increased with the increase in the cell temperature and rose rapidly at the end of the overcharge. In particular, the amount of CO 2 gas produced by the oxidation of the electrolyte at the cathode increased markedly. The exothermic oxidation reaction of the electrolyte was accelerated at the temperature above 60 °C, causing the cell temperature to increase rapidly thereafter. The heating tests of the overcharged anode samples enclosed in cylindrical cell cases with EC/EMC electrolytes resulted in thermal runaways. In contrast, the overcharged cathodes tested in the same manner showed no thermal runaway. The thermal runaway reaction during overcharge was caused by the violent reaction between the overcharged anode (deposited lithium) and the electrolyte solvent at high temperature that was the result of the rapid exothermic reaction of the delithiated cathode and the electrolyte.

A study of the overcharge reaction of lithium-ion batteries

A study of the overcharge reaction of lithium-ion batteries

A study of the overcharge reaction of lithium-ion batteries

The overcharge behavior of prismatic lithium ion batteries was studied under abusive conditions. Experimental cells were constructed with a systematic variation in cell balance and overcharge tested to the point of failure. This test demonstrated that the point of cell rupture tracked the amount of cathode in the cell, independent of the amount of anode material. The rate of charge was found to be an important parameter, as cells overcharged at low charge rates remained hermetic while high charge rates (C/2 and above) resulted in cell rupture. The internal temperature of the cells monitored during overcharge was found to be as high as 199°C, which was 93°C higher than the external skin temperature of the cell. Coin cell tests identified the cathode as the source of heat produced in the cell, and Rdc measurements identified a large increase in cell resistance past the full delithiation point of Li x CoO 2.

Abuse Testing of Lithium-Ion Batteries: Characterization of the Overcharge Reaction of LiCoO2/Graphite Cells

The short-circuit and overcharge behavior of prismatic lithium-ion batteries containing cathodes and graphite anodes were studied in detail. Internal thermocouples were used to characterize the thermal profiles of the cells under abusive conditions. Differences between the internal and surface temperatures of the cells during the safety tests highlighted the importance of the internal measurement for obtaining more meaningful data. Under short-circuit conditions the cells remained hermetically sealed, reached an internal temperature of 132°C (the shutdown temperature of the separator), and then slowly cooled to ambient temperature. However, on extreme overcharge testing different results were obtained depending on the current used to charge the battery. At low currents the cells remained hermetic, but swelled significantly. When higher currents were used, the cells ruptured during overcharge. Experimental cells were constructed with a systematic variation in cell balance and the point of cell rupture tracked to the amount of cathode in the cell, independent of the amount of anode material. The internal dc resistance of the cell was also measured during the overcharge reaction and remained low throughout most of the test, although a large increase was observed at the end of the test due to the melting of the shutdown separator. The cells overcharged with high currents all reached high temperatures immediately prior to rupturing, which suggests that the melting of lithium is a key underlying factor leading to the rupture of the cells. To test this proposal, cells were assembled with lithium removed from the cathode, so that lithium metal would not plate on the anode during the overcharge test. These cells reached a significantly higher temperature prior to rupture. © 2001 The Electrochemical Society. All rights reserved.

Mathematical Modeling of the Lithium Deposition Overcharge Reaction in Lithium‐Ion Batteries Using Carbon‐Based Negative Electrodes

The processes that lead to capacity fading affect severely the cycle life and rate behavior of lithium‐ion cells. One such process is the overcharge of the negative electrode causing lithium deposition, which can lead to capacity losses including a loss of active lithium and electrolyte and represents a potential safety hazard. A mathematical model is presented to predict lithium deposition on the negative electrode under a variety of operating conditions. The , 2:1 ethylene carbonate/dimethyl carbonate, poly(vinylidene fluoride‐hexalfuoropropylene)| cell is simulated to investigate the influence of lithium deposition on the charging behavior of intercalation electrodes. The model is used to study the effect of key design parameters (particle size, electrode thickness, and mass ratio) on the lithium deposition overcharge reaction. The model predictions are compared for coke and graphite‐based negative electrodes. The cycling behavior of these cells is simulated before and after overcharge to understand the effect of overcharge on extended cycling. These results can be used to establish operational and design limits within which safety hazards and capacity fade problems, inherent in these cells, can be minimized. © 1999 The Electrochemical Society. All rights reserved.

96/06108 Simple model for the overcharge reaction in valve regulated lead/acid batteries under fully stationary conditions

96/06108 Simple model for the overcharge reaction in valve regulated lead/acid batteries under fully stationary conditions

Improvements of the Rechargeable Alkaline MnO2 ‐ Zn Cell

Rechargeable versions of alkaline manganese dioxide‐zinc batteries need to be protected against overcharge especially in multiple‐cell series arrangements. It is necessary to shift the cathodic overcharge reaction to pure oxygen evolution instead of manganate(VI,VII) formation and to consume the oxygen produced either via a recombination reaction with hydrogen upon a suitable catalyst or by reaction with a chemically active zinc anode.

Simple model for the overcharge reaction in valve regulated lead/acid batteries under fully stationary conditions

A mode for the float charge of valve regulated lead/acid batteries is presented. The model relies on a description of the intrinsic kinetics of hydrogen and oxygen evolution, and corrosion. The mass transport is characterized by a single parameter. An important result is that polarizations are highly dependent on both the hydrogen and oxygen overvoltages. The model enables the calculation of the minimum float charge voltage.