Name: primary, rechargeable batteries and fuel cells
Uploaded: 2020-09-24T15:06:52.000Z
Duration: 3 min 12 s
Channel: JoVE

K12 Standards

Pennsylvania State Academic Standards

9-12

Physical Science

Forces and Interactions

3.2.9-12.M

Batteries and Fuel Cells

Le batterie sono celle voltaiche usate come fonti elettriche portatili. Sono classificati in batterie primarie o non ricaricabili e secondarie o ricaricabili. La batteria primaria comune è la pila a secco.

Contiene una custodia di zinco come anodo, e un catodo di grafite immerso in una pasta elettrolitica umida e acida di ossido di manganese e cloruro di ammonio. Lo zinco si ossida a cloruro di zinco, e l'ossido di manganese si riduce a ossido di manganese solido generando un potenziale di 1, 5 volt. Quando vengono azionati, gli elettrodi si esauriscono, rendendo monouso le batterie a secco.

Le batterie alcaline sono simili, ma usano un elettrolita alcalino che ne prolunga la durata e la vita lavorativa. Le batterie al piombo sono batterie secondarie usate prevalentemente nelle automobili. Questi hanno tipicamente sei celle elettrochimiche collegate in serie, che generano un potenziale totale di 12 volt.

Ogni cella ha un anodo di piombo e un catodo di ossido di piombo immersi in acido solforico. Durante la scarica, le reazioni redox depositano solfato di piombo solido su entrambi gli elettrodi, che vengono riconvertiti durante la ricarica usando una fonte di alimentazione esterna. Le batterie ricaricabili al nichel-cadmio contengono un catodo di ossidrossido di nichel, un anodo di cadmio, e un elettrolita di idrossido di potassio.

Quando viene azionato, l'anodo si ossida in idrossido di cadmio solido e il catodo si riduce in idrossido di nichel solido, generando un potenziale cellulare di 1, 3 volt. Tuttavia, la tossicità del cadmio spinge la sostituzione delle batterie al nichel-cadmio con batterie ecologiche all'idruro di nichel-metallo. Qui, il catodo rimane lo stesso, ma l'anodo è una lega che assorbe l'idrogeno.

La reazione anodica prevede la formazione di acqua dall'idrogeno. Le batterie agli ioni di litio sono le batterie secondarie più recenti. Il leggero litio metallico rende queste batterie portatili con un'elevata densità di energia.

Una batteria agli ioni di litio contiene un anodo di grafite litiata e un catodo di ossido di metallo di transizione al litio. Una volta caricato, il metallo di transizione viene ossidato, mentre gli ioni di litio sono incorporati fra gli strati di grafite anodica. Dopo essersi scaricati, gli ioni di litio fluiscono dall'anodo al catodo, generando un potenziale di 3, 7 volt.

Infine, le celle a combustibile sono celle voltaiche che richiedono una fornitura esterna continua di reagenti redox per la produzione di energia. Una tipica cella a combustibile a idrogeno usa l'idrogeno e l'ossigeno dell'aria per generare una corrente, mentre emette acqua. Gli elettrodi di grafite contengono catalizzatori a base di platino, per accelerare la reazione redox.

batterie e celle a combustibile

Una batteria è una cella galvanica utilizzata come fonte di energia elettrica per applicazioni specifiche. Le batterie moderne esistono in una moltitudine di forme per adattarsi a varie applicazioni, dalle minuscole batterie a bottone come quelle che alimentano gli orologi da polso alle batterie molto grandi utilizzate per fornire energia di riserva alle reti elettriche comunali. Alcune batterie sono progettate per applicazioni monouso e non possono essere ricaricate (celle primarie), mentre altre si basano su reazioni cellulari opportunamente reversibili che consentono la ricarica tramite una fonte di alimentazione esterna (celle secondarie).

Batterie monouso (primarie).

Una cella a secco è una comune batteria primaria che utilizza lo zinco sia come contenitore che come anodo (terminale “-”) e un'asta di grafite come catodo (terminale “+”). Il contenitore per lo zinco è riempito con una pasta elettrolitica contenente ossido di manganese (IV), cloruro di zinco (II), cloruro di ammonio e acqua. Un'asta di grafite viene immersa nella pasta elettrolitica per completare la cella. La reazione cellulare spontanea prevede:

<img alt="Eq1" src="/files/ftp_upload/11439/11439_Equation_1.png" style="text-align: center; height: 168px;" />

La tensione (potenziale della cella) di una cella a secco è di circa 1,5 V (E_cell ~ 1,5 V). Le celle a secco sono disponibili in varie dimensioni (ad esempio D, C, AA, AAA). Tutte le dimensioni delle celle a secco comprendono gli stessi componenti e presentano la stessa tensione, ma le celle più grandi contengono quantità maggiori di reagenti redox e quindi sono in grado di trasferire quantità corrispondentemente maggiori di carica. Come altre celle galvaniche, le celle a secco possono essere collegate in serie per produrre batterie con tensioni di uscita maggiori, se necessario.

Le batterie alcaline sono state progettate attorno alle stesse coppie redox delle celle a secco. Come suggerisce il nome, questi tipi di batterie utilizzano elettroliti alcalini e spesso idrossido di potassio. Le reazioni sono

<img alt="Eq2" src="/files/ftp_upload/11439/11439_Equation_2.png" style="text-align: center; height: 130px;" />

Una batteria alcalina può fornire da tre a cinque volte l'energia di una batteria a secco di dimensioni simili (E_cell = +1,43 V). Le batterie alcaline tendono a perdere idrossido di potassio, quindi devono essere rimosse dai dispositivi per la conservazione a lungo termine. Sebbene alcune batterie alcaline siano ricaricabili, la maggior parte non lo è.

Batterie ricaricabili (secondarie).

Le batterie al nichel-cadmio, o NiCd, sono costituite da un catodo placcato in nichel, un anodo placcato in cadmio e un elettrodo di idrossido di potassio. Le piastre positive e negative, a cui viene impedito il cortocircuito grazie al separatore, vengono arrotolate insieme e inserite nella custodia. Questo design consente alla cella NiCd di fornire molta più corrente rispetto a una batteria alcalina di dimensioni simili. Le reazioni sono

<img alt="Eq3" src="/files/ftp_upload/11439/11439_Equation_3.png" style="text-align: center; height: 130px;" />

Se adeguatamente trattata, una batteria NiCd può essere ricaricata circa 1000 volte (E_cell ~ 1,3 V). Il cadmio è un metallo pesante tossico, quindi le batterie NiCd non dovrebbero mai essere rotte o incenerite e dovrebbero essere smaltite in conformità con le pertinenti linee guida sui rifiuti tossici.

Le batterie agli ioni di litio sono tra le batterie ricaricabili più popolari e vengono utilizzate in molti dispositivi elettronici portatili. Le reazioni sono

<img alt="Eq4" src="/files/ftp_upload/11439/11439_Equation_4.png" style="text-align: center; height: 130px;" />

La stechiometria variabile della reazione cellulare porta a variazioni nelle tensioni delle celle, ma per condizioni tipiche, x non è solitamente superiore a 0,5 e la tensione delle celle è di circa 3,7 V (E_cell ~ 3,7). Le batterie al litio sono popolari perché possono fornire una grande quantità di corrente, sono più leggere di batterie comparabili di altri tipi, producono una tensione quasi costante mentre si scaricano e perdono la carica solo lentamente quando vengono riposte.

La batteria al piombo è anche un tipo di batteria secondaria comunemente utilizzata nelle automobili. È poco costosa e in grado di produrre l'elevata corrente richiesta dai motorini di avviamento delle automobili. Le reazioni per una batteria al piombo sono

<img alt="Eq5" src="/files/ftp_upload/11439/11439_Equation_5.png" style="text-align: center; height: 160px;" />

Ciascuna cella produce 2 V (E_cell ~ 2 V), quindi sei celle sono collegate in serie per produrre una batteria per auto da 12 V. Le batterie al piombo sono pesanti e contengono un elettrolita liquido caustico, H_2SO_4 (aq), ma spesso sono ancora le batterie preferite a causa della loro elevata densità di corrente. Poiché queste batterie contengono una notevole quantità di piombo, devono essere sempre smaltite correttamente.

Celle a combustibile

Una cella a combustibile è una cella galvanica che utilizza combustibili tradizionali, molto spesso idrogeno o metano, che vengono continuamente immessi nella cella insieme a un ossidante. All'interno della cella, il combustibile e l'ossidante subiscono la stessa chimica redox di quando vengono bruciati, ma attraverso un processo elettrochimico catalizzato che è significativamente più efficiente. Ad esempio, una tipica cella a combustibile a idrogeno utilizza elettrodi di grafite incorporati con catalizzatori a base di platino per accelerare le due reazioni delle semicelle:

<img alt="Eq6" src="/files/ftp_upload/11439/11439_Equation_6.png" style="text-align: center; height: 130px;" />

Questi tipi di celle a combustibile producono generalmente tensioni di circa 1,23 V (E_cell ~ 1,23 V). Rispetto a un motore a combustione interna, l’efficienza energetica di una cella a combustibile che utilizza la stessa reazione redox è in genere più che doppia (~20%–25% per un motore contro ~50%–75% per una cella a combustibile). Le celle a combustibile a idrogeno sono comunemente utilizzate nelle missioni spaziali estese e sono stati sviluppati prototipi per veicoli personali.

Questo testo è adattato da <a href="https://openstax.org/books/chemistry-2e/pages/17-5-batteries-and-fuel-cells">Openstax, Chemistry 2e, Section 17.5: Batteries, and Fuel Cells.</a>

Batterie e celle a combustibile

Una batteria è una cella galvanica che viene utilizzata come fonte di energia elettrica per applicazioni specifiche. Le batterie moderne esistono in una moltitudine di forme per ...

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primary, rechargeable batteries and fuel cells

Batteries and fuel cells are galvanic cells that supply electrical power for many applications. They range from tiny button batteries in wristwatches to large systems that can provide backup energy to municipal power grids. Some are primary cells, which are single-use and cannot be recharged. Others are secondary cells, which use reversible reactions and can be charged again by an external power source.

A common primary battery is the dry cell. It uses zinc as both the container and the anode, or negative terminal, and a graphite rod as the cathode, or positive terminal. The zinc can holds an electrolyte paste with manganese(IV) oxide, zinc(II) chloride, ammonium chloride, and water. A dry cell has a voltage of about 1.5 V. It comes in sizes such as D, C, AA, and AAA. These sizes use the same parts and the same voltage, but larger cells contain more reactants and can transfer more charge. Dry cells can also be connected in series to increase voltage.

Alkaline batteries use the same redox couples as dry cells, but they use an alkaline electrolyte, often potassium hydroxide. They can deliver about three to five times the energy of a dry cell of similar size and have a cell potential of about 1.43 V. These batteries can leak potassium hydroxide, so they should be removed from devices during long-term storage. Some alkaline batteries are rechargeable, but most are not.

Rechargeable batteries include nickel-cadmium, or NiCd, batteries, lithium-ion batteries, and lead-acid batteries. A NiCd battery has a nickel-plated cathode, a cadmium-plated anode, and a potassium hydroxide electrode. The positive and negative plates are rolled together with a separator to keep them from shorting. This design lets a NiCd cell deliver much more current than a similar-sized alkaline battery. When treated properly, it can be recharged about 1000 times, and its cell potential is about 1.3 V. Cadmium is toxic, so NiCd batteries should not be ruptured or burned and must be disposed of as toxic waste.

Lithium-ion batteries are widely used in portable electronic devices. Their reaction has variable stoichiometry, so the voltage can vary, but under typical conditions the cell potential is about 3.7 V. These batteries are popular because they can provide a large amount of current, are lighter than comparable batteries of other types, and keep a nearly constant voltage as they discharge. They also lose charge slowly during storage. Lead-acid batteries are common in automobiles. They are inexpensive and can deliver the high current needed by starter motors. Each cell produces 2 V, so six cells are connected in series to make a 12-V car battery. These batteries are heavy and contain a caustic sulfuric acid electrolyte, and they also contain a significant amount of lead, so they must be disposed of properly.

A fuel cell is also a galvanic cell, but it uses a fuel that is continuously fed into the cell along with an oxidant. The fuel is often hydrogen or methane. Inside the cell, the same redox chemistry that occurs in combustion is carried out by a catalyzed electrochemical process that is much more efficient. A typical hydrogen fuel cell uses graphite electrodes with platinum-based catalysts to speed the half-cell reactions. These fuel cells usually produce about 1.23 V. Compared with an internal combustion engine, a fuel cell using the same redox reaction is typically more than twice as efficient. Hydrogen fuel cells are used on extended space missions, and prototypes for personal vehicles have been developed.

Primary, Rechargeable Batteries and Fuel Cells

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Redox reactions involve electron transfer and changes in oxidation number. In electrochemistry, these reactions connect chemical changes with electrical energy. They also power technologies such as industrial metal processing and rechargeable batteries used in electric vehicles. Oxidation number is a way to track how an atom's electronic environment changes compared with the pure element, where the oxidation number is zero. For a simple ionic compound, the oxidation number matches the ion...

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batteries and fuel cells

Batteries and fuel cells are galvanic cells that supply electrical power for many applications. They range from tiny button batteries in wristwatches to large systems that can provide backup energy to municipal power grids. Some are primary cells, which are single-use and cannot be recharged. Others are secondary cells, which use reversible reactions and can be charged again by an external power source. A common primary battery is the dry cell. It uses zinc as both the container and the anode,...

corrosion

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electrolysis

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Electrolysis uses electrical energy to drive a nonspontaneous redox reaction. In a galvanic cell, a spontaneous redox reaction does electrical work on the surroundings by sending electrons through an external circuit. In electrolysis, an external circuit does work on the redox system by applying a voltage large enough to force the reaction in the opposite direction. This process is used in several real-world settings. Recharging a battery is one example, because an outside power source drives...

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Explore dry cells, alkaline batteries, NiCd, lithium-ion, and lead-acid batteries, plus how hydrogen fuel cells turn fuel into electricity more efficiently.

Primary, Rechargeable Batteries and Fuel Cells | JoVE K12

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Motion And Stability: Forces And Interactions

HS-PS2-5

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HS.P1

HS.P1U3.4

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HS+Phy.P4U2.7

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PHYS.6

PHYS.6.D

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South Carolina College and Career Ready Science Standards

Energy

P-PS3-3

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Primary, Rechargeable Batteries and Fuel Cells

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