The CSIRO have been working on a new lead acid battery that is called an ULTRA battery, the problem with lead acid batteries is that they do not like to be fast charged, what the CSIRO did was change one of the electrodes, they made it into an an electrode that would accept a fast charge, it acted like a fat capacitor which accepted a fast charge and then discharged that to the electrode slowly, it basically meant that the battery could be fast charged and still have the benefits of large storage.
During normal lead-acid battery operation, lead sulfate crystals grow on the negative electrode during discharging and dissolve again during charging. The formation of these crystals is called sulfation. Over time sulfation can become permanent, as some crystals grow and resist being dissolved. This is particularly the case when the battery is forced to perform at very high rates of discharge, which tends to promote lead sulfate crystal growth on the surface of the electrode. At moderate rates of discharge, the lead sulfate crystals grow throughout the cross section of the electrode plate (which has a sponge-like consistency) since the electrolyte (dilute sulfuric acid) is drawn diffused through the body of the electrode to allow the reaction can take place throughout the plate.[10]
But at very fast rates of discharge, the acid already inside the body of the plate is used up quickly and fresh acid cannot diffuse through the electrode in time to continue the reaction. Hence the reaction is favored toward the outer wall of the electrode, where crystals may form in a dense mat, rather than in dispersed clumps throughout the plate. This mat of crystals further impedes electrolyte transfer. The crystals then grow larger, and because the larger crystals have a large volume compared to their surface area it becomes difficult to remove them chemically during charging, particularly as the concentration of the sulfuric acid in the electrolyte is likely to be high (since only limited lead sulfate has been created on the surface of the plate) and lead sulfate is less soluble in concentrated sulfuric acid (above about 10% concentration by weight) than it is in dilute sulfuric acid.
This condition is sometimes termed the “hard” sulfation of the battery electrode [REF]. Hard sulfation increases the battery's impedance (since the lead sulfate crystals tend to insulate the electrode from the electrolyte) and decreases its power, capacity and efficiency due to increased undesirable side reactions, some of which occur inside the negative plate due to charging taking place with low availability of lead sulfate (inside the plate body). One undesirable effect is the production of hydrogen inside the plate, further reducing the efficiency of the reaction. “Hard” sulfation is generally irreversible since the side reactions tend to dominate as more and more energy is pushed into the battery.[11]
To reduce the likelihood of hard sulfation, conventional VRLA batteries should therefore be discharged at specific rates, determined by various charging algorithms. [REF] Furthermore, they must be frequently refreshed and are most suited to operation toward the top end of the SoC (between 80% and 100% charged). [REF] While operating in this limited state of charge mitigates permanent sulfation on the negative electrode, battery operation exclusively at or near a full SoC is highly inefficient. [REF] The inefficiency is largely due to increases the incidence of side reactions (for instance electrolysis) which dissipate energy.
The presence of the ultracapacitor integrated in the UltraBattery acts to limit the formation of hard sulfation inside the cell. [REF] This supports the battery's ability to operate for long periods in a partial SoC where the battery operates more efficiently. [REF] Conventional VRLAs are somewhat constrained to operate in the inefficient region toward the top of their charge capacity in order to protect them against damage by sulfation. Research continues into the reasons why the presence of the ultracapacitor reduces sulfation so successfully. Experimental results show that the presence of carbon within VRLA cells has some mitigating effect but the protective effects of the parallel-connected ultracapacitor within the UltraBattery are much more significant. Hund et al., for instance, found that typical VRLA battery failure modes (water loss, negative plate sulfation, and grid corrosion) are all minimized in the UltraBattery. Hund's results also showed that the UltraBattery, used in a high rate partial state of charge application, exhibits reduced gassing, mimimized negative plate hard sulfation, enhanced power performance and minimized operating temperature compared with conventional VRLA cells.
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