Negative active mass

SLI batteries are also supplied in a dry charged state and are activated simply by filling with electrolyte. Plates for such batteries have extra additives, such as antioxidants in the negative active mass, and forming is followed by one of a number of controlled drying processes. 

FORMATION OF LEAD-ACID BATTERIES AND STRUCTURE OF POSITIVE AND NEGATIVE ACTIVE MASSES... 

Positive and negative active-mass formation. The cured pastes of both positive and negative plates comprise identical mixtures of bivalent lead compounds (3BS, 4BS, PbO), which cannot create electromotive forces when the pasted plates are assembled into cells. The purpose of the formation step is to convert the cured pastes into electrochemically active porous materials — Pb02 in the positive plates and Pb in the negative plates — which are connected mechanically and electrically to the grids. The process of formation can be conducted via two basic schemes, as shown in Fig. 3.1. 

Recipes for the positive and negative active masses are well known and are aimed at achieving a positive mass that is as porous as possible and a negative mass that can withstand the formation process, which can involve very high temperatures. The majority of separators are pure glass-mats, but present research is focusing on the use of synthetic fibre additives to make manufacturing simpler and cheaper. 

All of the future vehicle concepts listed in Table 17.1 call upon increased electrical capacity and power compared with today s conventional automobiles. The battery requirements of these future vehicles will not be met by present lead-acid products. Adjustments to the grid design and to the surface area and conductivity of the negative active-mass, as well as the deployment of elements capable of reducing the proclivity of the cell to evolve gas (especially hydrogen) during charging, all show... 

Let us first see how carbon additives affect the structure of the negative active mass. 

Let us now see how the structure of the negative active mass looks like when it contains both BaS04 and carbon black additives. Figure 7.12 c and d shows SEM images of NAM with 0.8 wt% BaS04 and two different concentrations of PRU carbon black. The carbon black particles are adsorbed on the lead surface and it is strongly folded. The surface area of NAM has increased. 

SLI plates were kept in contact with air for different periods of time. The obtained kinetic curves of oxidation of the plates by the air are presented in Fig. 13.6. After reaching a definite critical temperature and moisture content, a vigorous oxidation or burning of the plates commences. This phenomenon is quite similar to the processes observed during curing of the pasted plates. At the end of this period of rapid oxidation, the active mass contains 50—60% sponge lead and up to 40—50% lead oxide and lead sulfate. This composition of the negative active mass yields only a very low capacity, and often none at all. 

Active mass utilization coefficient, (rj). This coefficient gives the share (by weight) of the energetic structure in the total amount of positive or negative active mass per cell ... 

The value is determined experientially for each particular technology of positive or negative active mass production. It depends on battery type as well. 

An increase of cycle life under high-rate working conditions, and also of high-power capability of lead acid batteries can be achieved by adding expanded graphite and some other materials to the negative active mass formulation (Pavlov et al., 2005 Muneret et al., 2005). 

Amotint of elecIriciCy clouded or diKhorged, in comparison to the negative active mass (mAh g)... 

Figure 5.6. Voltage curves for charge and discharge of a graphite negative electrode depending on the degree of insertion xi (lower axis) or the amount of electricity in comparison to the negative active mass (upper axis)...

For the negative plate, according to Faraday s law, when 1 Ah of electricity passes through the cell, theoretically 3.866 g of Pb would react at the negative plate. The theoretical capacity of the negative active mass is equal to... 

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