from combustion to chemistry: Na ion batteries

what is combustion

oxidation → carbon driving towards most table oxidation state (+4)

what is combustion accompanied by

CO formation, NO formation in air and radical chemistry

air quality legislation targeted

NOx, VOCs, particulates

catalytic converters

used surface redox chemistry to reduce emissions

During COVID lockdowns

• Traffic dropped dramatically

• Urban NO2 concentrations fell sharply

• Primary particulate matter decreased

sustainable energy authority of Ireland (2020)

• Energy related CO2 emissions from combustion of fossil fuels accounted for 57% of Ireland's total greenhouse gas emissions

• Energy related CO2 emissions decreased by 6.3% - this is less than the amount that will need to be achieved on average every year from 2021 - 2030 to meet our long-term decarbonisation goals

UK 2008 climate change act

• Set 2050 target reduction of greenhouse gas emissions and a path to get there

• Set carbon budgets for 5-year periods

• Established committee on climate change, and trading schemes for limiting greenhouse gas emissions

• Financial incentives to produce less domestic waste and recycle more

• Provision about the collection of household waste and charging for single use carrier bags

• Amend provisions of the energy act 2004 about renewable transport fuel obligations

• To make provision about carbon emissions reduction targets

energy conversion

Fuel cells convert chemical energy to electricity -> green alternative to combustion

energy storage

Batteries widely applied electrical energy storage devices

→ Small scale portable electronics, increasingly electric vehicles

electrical generation via combustion

Multiple steps involving conversions through chemical -> heat -> mechanical -> electrical, where each conversion step brings with it some inefficiency

electrical generation via fuel cell

• Can run on variety of fuels, including hydrogen, natural gas, biogas, with higher efficiency

• Reduced fuel consumption, CO2 emission, and emissions of other pollutants

• Note: even for H2 fuel cells, CO2 is produced in making H2 from natural gas

fuel cell advantage → high efficiency

• Waste heat can be recovered and be used

• Low CO2 emission

• Potential to produce local or centralised power

fuel cell advantage → low emission of other pollutants

• Sulphur removed

• Low NOx

• Low CO

• No particulates

primary applications

include vehicles and stationary power plants

speciality applications

• Stable backup power for telecommunications

• Could use 'waste' fuels (typically methane) from landfills/wastewater treatment/breweries to generate electricity and meet heating/cooling needs of industry, campuses

• Forklifts without batteries or engine emissions

• Portable power in <1 kW range - where electric grid is not available, emergency backup, military (UAV), remote sensors

costs

fuel cell versus internal combustion engine, typically ~2 orders of magnitude higher

fuel cells usually require hydrogen fuel

• Major difficulties/inefficiencies in producing, storing, and transporting hydrogen

• Hydrogen infrastructure will be very costly

Storing electricity in chemical form usually involves electrochemical devices

• Batteries

• Fuel cells/electrolysers

mismatch between electrical grid supply and demand

both in time and geographically

why sodium

Lithium ion batteries dominate today, but global electrification requires massive materials qualities. Sodium is abundant, widely distributed and inexpensive.

during charge

• Na+ leaves cathode, moves through electrolyte towards anode

• Electrons move through external circuit to maintain charge neutrality

• Transition metal changes oxidation state

polyanions lower oxygen energy levels which

increases voltage

PO4 3- acts as an electron-withdrawing group

• Drawing electron density closer to P5+ means bridging oxygens have less electron density available to share with V

• V-O bonds become more ionic; ionic bonding lowers metal d-electron energy

• Lower electron energy more stabilised, so harder to remove and electron, meaning higher voltage

hard carbon anodes

Hard carbon structurally disordered non-graphitising carbon

• Turbostratic graphene layers, defects, micropores, irregular spacing

• Structurally flexible and heterogenous

• Provides Na+ with expanded interlayer spacing, nanopores that can hose ions, defects sides for adsorption

• Storage mechanisms still debated

Na+ storage mechanism can be categorised into 4 models

• 'Intercalation-filling’ model where Na+ ions intercalate into graphitic layers in sloping region, insert into nanopores between randomly stacked layers at plateau region

• Adsorption-intercalation model: Na+ ions adsorb at the surface or defect sites in sloping region; intercalate into the graphitic layers in plateau region

• Adsorption-filling model: in sloping region, Na+ ions adsorb at defect sites, while filling nanopores in plateau region

• 'Three-stage’ model: defect adsorption of Na+ in the sloping region, but in the plateau region, the Na+ ions first intercalate into the graphitic layers and eventually fill in the nanopores

hard carbon can be produced from biomass

Lignin, cellulose, nutshells, agricultural waste

these biomass-derived hard carbons often show

High reversible capacity, good Na+ diffusion pathways, stable cycling

Heteroatoms found in biomass polymers may also

Modify electronic conductivity, create active adsorption sites

electrifications reduces

• NO formation in engines

• VOC emissions

• Urban smog chemistry

if electricity is renewable…

CO2 emissions also decrease → battery chemistry can change atmospheric chemistry