II.2. Expanders and additives to the paste

Organic expanders of ligno-sulphonates, BaSO₄ and active carbon are added to the negative paste. It has been established that although BaSO₄ is isomorphic with PbSO₄ it has no effect on the phase composition of the paste. Ligno-sulphonates suppress fully the formation of 4PbO.PbSO₄ and orthorhombic-PbO phases. Formation of 4BS is suppressed due to the suppressed formation of orthorhombic-PbO, which is a component of the 4BS phase. A family of eight lingo-sulphonates produced by Borregaard Ligno-Tech (Norway) has been investigated. The beneficial effect of the expander has been found to correlate positively with low average molecular weight of the lignins and of their derivates, high - COOH content, low OCH₃ group and organic S content, optimum ArOH content and high lignin purity. Expanders with different chemical composition should be selected for different battery type applications. It has also been established that phenol groups of the expander structure react with Sb, Sn and Ca ions forming organometallic compounds, which influences battery performance.

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