Understanding Function and Performance of Carbon Additives in Lead-Acid Batteries

Abstract

While the low cost and strong safety record of lead-acid batteries make them an appealing option compared to lithium-ion technologies for stationary storage, they can be rapidly degraded by the extended periods of high rate, partial state-of-charge operation required in such applications. Degradation occurs primarily through a process called hard sulfation, where large PbSO 4 crystals are formed on the negative battery plates, hindering charge acceptance and reducing battery capacity. Various researchers have found that the addition of some forms of excess carbon to the negative active mass in lead-acid batteries can mitigate hard sulfation, but the mechanism through which this is accomplished is unclear. In this work, the effect of carbon composition and morphology was explored by characterizing four discrete types of carbon additives, then evaluating their effect when added to the negative electrodes within a traditional valve-regulated lead-acid battery design. The cycle life for the carbon modified cells was significantly larger than an unmodified control, with cells containing a mixture of graphitic carbon and carbon black yielding the greatest improvement. The carbons also impacted other electrochemical aspects of the battery (e.g., float current, capacity, etc.) as well as physical characteristics of the negative active mass, such as the specific surface area. Valve-regulated lead-acid (VRLA) batteries are a mature rechargeable energy storage technology. Low initial cost, well-established manufacturing base, proven safety record, and exceptional recycling efficiency make VRLA batteries a popular choice for emerging energy storage needs.1,2 VRLA batteries are employed in stationary storage applications such as: utility ancillary regulation services, wind farm energy smoothing, and solar photovoltaic energy smoothing.3 Stationary applications may require short duration, high-rate, and partial state-of-charge cycling (HRPSoC). 4 Under HRPSoC duty, conventional VRLA cells fail prematurely from irreversible PbSO 4 formation within the negative plates.5 Regular cycling to 100% state-of-charge (SoC) mitigates PbSO 4 crystal formation and growth. However, regularly cycling to 100% SoC is not viable for many stationary storage applications. Large PbSO 4 crystals are not easily reduced back to metallic lead during HRPSoC charging, reducing cycle life. Reduced cycle life of VRLA batteries increases the operating cost, thereby limiting their practicality for stationary applications.VRLA battery HRPSoC cycle life can be increased with carbon modification of the negative active material (NAM).6-10 Adding carbon to the negative plate inhibits PbSO 4 crystal formation and/or limits PbSO 4 crystal growth.11-13 The underlying mechanism responsible for reducing PbSO 4 formation/accumulation is dependent on the size of the PbSO 4 crystallites. Controlling PbSO 4 microstructure has been found to be difficult while maintaining low cost. Other methods exist to limit PbSO 4 crystal size; including utilization of a carbon honeyco...

Modification of Graphite Felt with Lead (II) Formate and Acetate—An Approach for Preparation of Lightweight Electrodes for a Lead-Acid Battery

“…Furthermore, a push towards LAB applications in electric vehicles has led to a lot of research in carbon material application in LAB, mixing of carbon materials in negative active material (NAM) in particular. The addition of carbon materials in NAM increases charge-discharge cycle amount at high-rate partial state of charge and higher charge acceptance, which are crucial parameters for batteries in EV application [7][8][9]. More importantly, the new LAB technologies propose to completely or partially replace negative electrode with carbon materials [10].…”

Applications of carbon in lead-acid batteries: a review

“…There are however some negative effects. Carbon lowers the initial capacity and hydrogen overpotential; so, in large amounts, it leads to a higher NAM self-discharge and a lower charge efficiency [12]. Additionally, the reactions between lead oxides and carbon during the charging and discharging are possible, especially with the rise of the temperature of the electrode due to the ohmic resistance.…”

Enhancing the Performance of Motive Power Lead-Acid Batteries by High Surface Area Carbon Black Additives

“…The lead-acid battery has a history of over 150 years and has a dominant position in electrochemical power supplies due to its low price, easy availability of raw materials and its full reliability in use, which is suitable for a wide range of environmental temperatures [1][2][3][4][5]. In the past decade, the electric bike industry has been unprecedentedly prosperous and electric bikes (e-bikes) have been gaining increasing attention in China [6].…”