## Performance | Specific energy density | 100 to 250 W·h/kg (360 to 900 kJ/kg)[\[154\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-154) | |---|---| | Volumetric energy density | 250 to 680 W·h/ L (900 to 2230 J/cm3)[\[155\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-155)[\[156\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-156) | | Specific power density | 1 to 10,000 W/kg[\[1\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-mw-1) | Because lithium-ion batteries can have a variety of positive and negative electrode materials, the energy density and voltage vary accordingly. The open-circuit voltage is higher than in aqueous batteries (such as lead–acid, nickel–metal hydride and nickel–cadmium).[\[157\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-157)\ _[failed verification_\] Internal resistance increases with both cycling and age,[\[158\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-FOOTNOTEAndrea201012-158) although this depends strongly on the voltage and temperature the batteries are stored at.[\[159\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-159) Rising internal resistance causes the voltage at the terminals to drop under load, which reduces the maximum current draw. Eventually, increasing resistance will leave the battery in a state such that it can no longer support the normal discharge currents requested of it without unacceptable voltage drop or overheating. Batteries with a lithium iron phosphate positive and graphite negative electrodes have a nominal open-circuit voltage of 3.2 V and a typical charging voltage of 3.6 V. Lithium nickel manganese cobalt (NMC) oxide positives with graphite negatives have a 3.7 V nominal voltage with a 4.2 V maximum while charging. The charging procedure is performed at constant voltage with current-limiting circuitry (i.e., charging with constant current until a voltage of 4.2 V is reached in the cell and continuing with a constant voltage applied until the current drops close to zero). Typically, the charge is terminated at 3% of the initial charge current. In the past, lithium-ion batteries could not be fast-charged and needed at least two hours to fully charge. Current-generation cells can be fully charged in 45 minutes or less. In 2015 researchers demonstrated a small 600 mAh capacity battery charged to 68 percent capacity in two minutes and a 3,000 mAh battery charged to 48 percent capacity in five minutes. The latter battery has an energy density of 620 W·h/L. The device employed heteroatoms bonded to graphite molecules in the anode.[\[160\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-160) Performance of manufactured batteries has improved over time. For example, from 1991 to 2005 the energy capacity per price of lithium-ion batteries improved more than ten-fold, from 0.3 W·h per dollar to over 3 W·h per dollar.[\[161\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-161) In the period from 2011 to 2017, progress has averaged 7.5% annually.[\[162\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-162) Overall, between 1991 and 2018, prices for all types of lithium-ion cells (in dollars per kWh) fell approximately 97%.[\[163\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-Ziegler-2021-163) Over the same time period, energy density more than tripled.[\[163\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-Ziegler-2021-163) Efforts to increase energy density contributed significantly to cost reduction.[\[164\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-164) Energy density can also be increased by improvements in the chemistry if the cell, for instance, by full or partial replacement of graphite with silicon. Silicon anodes enhanced with graphene nanotubes to eliminate the premature degradation of silicon open the door to reaching record-breaking battery energy density of up to 350 Wh/kg and lowering EV prices to be competitive with ICEs.[\[165\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-165) Differently sized cells of the same format (shape) with the same chemistry may have different energy densities. Jelly roll cells "Jelly roll (battery)") usually have a higher energy density than coin or prismatic cells of the same Ah, because of a tighter/compresses packing of the cell layers. Among cylindrical cells, those with a larger size have a larger energy density, albeit the exact value strongly depends on the thickness of the electrode layers. The disadvantage of large cells is decrease of the heat transfer from the cell to its surroundings.[\[156\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-Quinn-2018-156) ### Round-trip efficiency The table below shows the result of an experimental evaluation of a "high-energy" type 3.0 Ah 18650 NMC cell in 2021, round-trip efficiency which compared the energy going into the cell and energy extracted from the cell from 100% (4.2v) SoC to 0% SoC (cut off 2.0v). A roundtrip efficiency is the percent of energy that can be used relative to the energy that went into charging the battery.[\[166\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-166) | C rate | efficiency | estimated charge efficiency | estimated discharged efficiency | |---|---|---|---| | 0.2 | 86% | 93% | 92% | | 0.4 | 82% | 92% | 90% | | 0.6 | 81% | 91% | 89% | | 0.8 | 77% | 90% | 86% | | 1.0 | 75% | 89% | 85% | | 1.2 | 73% | 89% | 83% | Characterization of a cell in a different experiment in 2017 reported round-trip efficiency of 85.5% at 2C and 97.6% at 0.1C[\[167\]](https://en.wikipedia.org/wiki/Lithium-ion_battery?utm_source=chatgpt.com#cite_note-167)