NTU Singa­pore sci­ent­ists use fruit peel to turn old bat­ter­ies into new

The team demon­strated their concept using orange peel, which recovered pre­cious metals from bat­tery waste effi­ciently. They then made func­tion­al bat­ter­ies from these recovered metals, cre­at­ing min­im­al waste in the pro­cess. The sci­ent­ists say that their waste-to-resource approach tackles both food waste and elec­tron­ics waste, sup­port­ing the devel­op­ment of a cir­cu­lar eco­nomy with zero waste, in which resources are kept in use for as long as pos­sible. An estim­ated 1.3 bil­lion tonnes of food waste and 50 mil­lion tonnes of e‑waste are gen­er­ated glob­ally each year. Spent bat­ter­ies are con­ven­tion­ally treated with extreme heat (over 500°C) to smelt valu­able metals, which emits haz­ard­ous tox­ic gases. Altern­at­ive approaches that use strong acid solu­tions or weak­er acid solu­tions with hydro­gen per­ox­ide to extract the metals are being explored, but they still pro­duce sec­ond­ary pol­lut­ants that pose health and safety risks, or rely on hydro­gen per­ox­ide which is haz­ard­ous and unstable. Pro­fess­or Madhavi Srinivas­an, co-dir­ect­or of the NTU Singa­pore-CEA Alli­ance for Research in Cir­cu­lar Eco­nomy (NTU SCARCE) lab, said: ​“Cur­rent indus­tri­al recyc­ling pro­cesses of e‑waste are energy-intens­ive and emit harm­ful pol­lut­ants and liquid waste, point­ing to an urgent need for eco-friendly meth­ods as the amount of e‑waste grows. Our team has demon­strated that it is pos­sible to do so with bio­de­grad­able sub­stances. ​“These find­ings build on our exist­ing body of work at SCARCE under NTU’s Energy Research Insti­tute (ERI@N). The SCARCE lab was was set up to devel­op green­er ways of recyc­ling e‑waste. It is also part of the NTU Smart Cam­pus ini­ti­at­ive, which aims to devel­op tech­no­lo­gic­ally advanced solu­tions for a sus­tain­able future.” Assist­ant Pro­fess­or Dalton Tay of the NTU School of Mater­i­als Sci­ence and Engin­eer­ing and School of Bio­lo­gic­al Sci­ences said: ​“In Singa­pore, a resource-scarce coun­try, this pro­cess of urb­an min­ing to extract valu­able metals from all kinds of dis­carded elec­tron­ics becomes very import­ant. With this meth­od, we not only tackle the prob­lem of resource deple­tion by keep­ing these pre­cious metals in use as much as pos­sible, but also the prob­lem of e‑waste and food waste accu­mu­la­tion – both a grow­ing glob­al crisis.”
The find­ings were pub­lished in the sci­entif­ic journ­al Envir­on­ment­al Sci­ence & Tech­no­logy in July.

A low-cost, sus­tain­able approach

With indus­tri­al approaches to recyc­ling bat­tery waste gen­er­at­ing harm­ful pol­lut­ants, hydro­me­tal­lurgy – using water as a solvent for extrac­tion – is increas­ingly being explored as a pos­sible altern­at­ive. This pro­cess involves first shred­ding and crush­ing used bat­ter­ies to form a crushed mater­i­al called black mass. Research­ers then extract valu­able metals from black mass by dis­solv­ing it in a mix of strong acids or weak acids plus oth­er chem­ic­als like hydro­gen per­ox­ide under heat, before let­ting the metals pre­cip­it­ate. While rel­at­ively more eco-friendly than con­ven­tion­al meth­ods, the use of such strong chem­ic­als on an indus­tri­al scale could gen­er­ate a sub­stan­tial amount of sec­ond­ary pol­lut­ants, pos­ing sig­ni­fic­ant safety and health risks, said Asst Prof Tay. The NTU team found that the com­bin­a­tion of orange peel that has been oven-dried and ground into powder, and cit­ric acid, a weak organ­ic acid found in cit­rus fruits, can achieve the same goal. In lab exper­i­ments, the team found that their approach suc­cess­fully extrac­ted around 90 per cent of cobalt, lith­i­um, nick­el, and man­ganese from spent lith­i­um-ion bat­ter­ies – a com­par­able effic­acy to the approach using hydro­gen per­ox­ide.
Asst Prof Tay explained: ​“The key lies in the cel­lu­lose found in orange peel, which is con­ver­ted into sug­ars under heat dur­ing the extrac­tion pro­cess. These sug­ars enhance the recov­ery of metals from bat­tery waste. Nat­ur­ally-occur­ring anti­ox­id­ants found in orange peel, such as flavon­oids and phen­olic acids, could have con­trib­uted to this enhance­ment as well.” Import­antly, sol­id residues gen­er­ated from this pro­cess were found to be non-tox­ic, sug­gest­ing that this meth­od is envir­on­ment­ally sound, he added.
From the recovered mater­i­als, they then assembled new lith­i­um-ion bat­ter­ies, which showed a sim­il­ar charge capa­city to com­mer­cial ones. Fur­ther research is under­way to optim­ise the charge-dis­charge cyc­ling per­form­ance of these new bat­ter­ies made from recovered mater­i­als. This sug­gests that this new tech­no­logy is ​“prac­tic­ally feas­ible for recyc­ling spent lith­i­um ion bat­ter­ies in the indus­tri­al sense”, said the research­ers.
The team is now look­ing to fur­ther improve the per­form­ance of their bat­ter­ies gen­er­ated from treated bat­tery waste. They are also optim­ising the con­di­tions to scale up pro­duc­tion and explor­ing the pos­sib­il­ity of remov­ing the use of acids in the pro­cess. Prof Madhavi, who is also from NTU’s School of Mater­i­als Sci­ence and Engin­eer­ing and ERI@N, said: ​“This waste-to-resource approach could also poten­tially be exten­ded to oth­er types of cel­lu­lose-rich fruit and veget­able waste, as well as lith­i­um-ion bat­tery types such as lith­i­um iron phos­phate and lith­i­um nick­el man­ganese cobalt oxide. This would help to make great strides towards the new cir­cu­lar eco­nomy of e‑waste, and power our lives in a green­er and more sus­tain­able man­ner.” The research, which comes under NTU SCARCE, is sup­por­ted by the Nation­al Research Found­a­tion, the Min­istry of Nation­al Devel­op­ment, and the Nation­al Envir­on­ment Agency under the Clos­ing the Waste Loop R&D Ini­ti­at­ive as part of the Urb­an Solu­tions & Sustainability−Integration Fund. Source: NTU, Media Release, 26.08.2020