Energy storage: top conclusions into batteries?

Conclusions into batteries

Thunder Said Energy is a research firm focused on economic opportunities that drive the energy transition. Our top ten conclusions into batteries and energy storage are summarized below, looking across all of our research.

(1) Transportation: a revolution. Gasoline and diesel vehicles are 15-25% efficient, on a wagon to wheel basis, due to immutable laws of thermodynamics. Electric vehicles using lithium ion batteries are 75-95% efficient. The technology is only getting better, including via power electronics and electric motors. So this is a game changer for light transportation, which becomes >70% electric in our oil models by 2050.

(2) Bottlenecks in battery materials will set the limit on the scale up. Numerically, the largest bottlenecks are in lithium; followed by fluorinated polymers and battery-grade nickel; then graphite and copper. We are less worried about cobalt. Our best data-file into materials used in a lithium ion battery, and their costs, is linked here.

(3) Power grids: efficiency drawbacks. Amidst materials bottlenecks, we think vehicle applications will generally outcompete grid applications. While an EV is 3-4x more efficient than what it replaces, grid scale storage usually has a 10%+ energy penalty. Thus the 65kWh battery in a typical EV saves 2-4x more energy and 25-150% more CO2 each year than a typical grid battery (note here).

(4) Power grids: the best battery is no battery. All batteries have a cost, usually $1,000-2,000/kW, which is re-couped through a storage spread, usually around 20c/kWh for daily charging-discharging (model here). Conversely, there are many loads in the power grid that can shift their demand (e.g., to the times when grids are over-saturated with renewables). This often has no cost. And no efficiency losses. Some of our favorite examples are catalogued here.

(5) Power grids: short-term first. The biggest challenges for ramping up wind and solar stem from short-term volatility (inertia, reactive power compensation, frequency regulation, <1-minute power drops). This requires short-term energy storage first, in the 2020s and 2030s. Many short term batteries can also earn their keep through recuperative energy savings. But note short term energy storage favors capacitor banks, STATCOMs, flywheels, synchronous condensers, supercapacitors. It is debatable whether lithium ion is well suited to short-term smoothing. Eaton has even recently started integrating supercapacitors into its industrial batteries, amidst increasing customer demand for short-term performance (case studies here).

(6) Long-term storage is for the 2040s, if at all. If you cycle your battery 10 times per day, you amortize its capex across 3,650 cycles per year, and the cost per cycle is <1c/kWh. Cycle 1 time per day, and it is 10-20c/kWh. Cycle 1 time per month and you are well above 200c/kWh. The maths are reviewed here. You can also stress test numbers in our pumped hydro model, other battery models. So we do not think long term storage (via batteries or hydrogen) will ever come into the money. We see more opportunity in long-distance power transmission, decarbonized gas, next-gen nuclear; fully decarbonizing future grids while keeping costs below 10-20c/kWh.

(7) Density will improve, but not enough for mass deployment of battery trucks, ships or planes. Today’s lithium ion batteries store 200Wh/kg. In a best case scenario, this could reach 1,250 Wh/kg. Oil products contain 12,000Wh/kg. Thus a battery-powered Class 8 truck will have 70-80% lower range than a diesel truck. And a battery-powered airliner has a range of c60-miles. We do not currently see battery powered trucks, ships or planes going mainstream.

(8) Next-gen batteries: can we de-risk them? There is constant progress and innovation in batteries, to improve density, duration, chemistry, longevity, cost, charging speeds. So we are constantly screening patent libraries. As a general rule we have found incremental innovations easier to de-risk. But we have been less able to de-risk big changes. Replacing lithium with sodium has issues with ionic radius. Solid state batteries often have issues with dendrites and longevity. Redox flow likely works but has 70-75% efficiency.

(9) End-of-life is most unresolved. If there is one TSE research note on batteries, which we think decision-makers should read it is this one, explaining battery degradation, the best antidotes and their implications (lithium upside?, manufacturer upside?). This matters, because despite some interesting inroads, we still do not think the industry has really cracked battery recycling, a potential $100bn pa market in the 2040s.

(10) Which battery companies? We have been most impressed by manufacturing technologies from 24M and CATL, followed by integrated battery offerings from Eaton, Stem and Powin. There are some interesting innovations from Amprius, Enovix, Quantumscape. But so far, we have found it more challenging to entirely de-risk concepts from Sila, Form Energy, Solid Power, Storedot. Please email us if there are any battery technologies you would like us to explore.

Around 60 reports and data-files into batteries and energy storage have led us to these conclusions above; listed in chronological order on our batteries category page. The best way to access our PDF reports and data-files is through a subscription to TSE research.

Lithium ion batteries: energy density?

Energy density of lithium ion batteries

Today’s lithium ion batteries have an energy density of 200-300 Wh/kg. I.e., they contain 4kg of material per kWh of energy storage. Technology gains can see lithium ion batteries’ energy densities doubling to 500Wh/kg in the 2030s, trebling to 750 Wh/kg by the 2040s, and the best possible energy densities are around 1,250 Wh/kg. This is still 90% below hydrocarbons, at 12,000 Wh/kg. Numbers and underlying assumptions are broken down in this data-file.

The energy stored in a battery can be calculated by thinking about the active ions. Active ions are intercalated at the anode when the battery is charged. They surrender electrons to an external circuit. Then these ions diffuse across the electrolyte. Finally, they intercalate at the cathode, where electrons are re-accepted. Thus the energy stored (in Joules) can be calculated by multiplying Faraday’s Constant (in Coulombs per mol) by the cell voltage (in Volts) and the number of mols of ions making this journey from anode to cathode (in mols).

Today’s lithium ion batteries have an energy density of 200-300 Wh/kg. In other words, there is 4kg of material per kWh of energy storage. Of this material build-up, 2 kg is in the cathode, 1 kg is in the anode, 0.6 kg in the current collectors, 0.3 kg in the electrolyte and 0.1 kg in the balance. Different chemistries are assessed in our data-file here.

The maximum energy density of a lithium ion battery can be calculated by increasing the voltage and decreasing the weights of all of the other components. So how much can the energy density of lithium ion batteries improve?

For example, today’s graphite anodes only intercalate 1 lithium ion for every 6 graphite atoms, which weigh 12 g/mol, yielding a charge density of 372 mAh/gram. Silicon anodes weigh more (28g/mol), but they can intercalate 15 lithium ions per 4 silicon atoms, yielding a charge density of 2,577 mAh/gram. (Satisfyingly, these numbers are calculated from first principles in the data-file). So this is an avenue being explored by Amprius, Sila, Enovix. Even denser, could be solid state batteries.

We think the best lithium ion batteries could ultimately reach 1,250 Wh/kg energy densities, although this includes some heroic assumptions and technology gains. It includes a 50% increase in cell voltage, eliminating the anode, eliminating all other excess materials, doubling the charge density of the cathode, thrifting out 90% of the electrolyte and 50% of the current collectors and separators. You can stress test all of these numbers in the data-file.

The biggest uncertainty, in our view, is over cell voltages. Today’s lithium ion batteries run at an average mid-point of 3.6V. Energy density is a direct linear function of voltage. But excess voltages will degrade the battery. For example, 5.9V is the standard potential for decomposition LiF into Li metal and fluorine gas (!).

Could sodium ion batteries have higher energy density? Basic chemistry of the periodic table makes it quite unlikely that any other metal ion could ferry ‘holes’ across an electrochemical cell with the same energy density as lithium. Lithium ions carry a charge of +1 and have a molar mass of 6.94 g/mol. Sodium ions carry a charge of +1 and have a molar mass of 22.9 g/mol.

The energy densities of lithium ion batteries are, in our view, unlikely to surpass 1,250 Wh/kg, on realistic technology pathways, simply based on electrochemistry and simple molar masses, which are broken down in this data-file. This can be compared with the energy density of hydrocarbons and as calculated from bond enthalpies.

Even 200-300Wh/kg energy density of lithium ion batteries justifies the electrification of light passenger vehicles, as electric motors are 2-6x more efficient than combustion engines. But we still see high-density hydrocarbons retaining a major role in aviation, long-distance trucking and shipping. These numbers underpin some of our key vehicle conclusions, hydrocarbon conclusions and battery conclusions amidst the energy transition.

Electric vehicles: breaking the ICE?

Electric vehicle outlook

Electric vehicles are a world-changing technology, 2-6x more efficient than ICEs, but how quickly will they ramp up to re-shape global oil demand? This 14-page note finds surprising ‘stickiness’. Even as EV sales explode to 200M units by 2050 (2x all-time peak ICE sales), the global ICE fleet may only fall by 40%. Will LT oil demand surprise to the upside or downside?

Amprius: silicon anode technology review?

Amprius silicon anode technology

Amprius is commercializing a lithium-ion battery with a near-100% silicon anode, which has 80% higher energy density than conventional lithium and can achieve 80% charge rates within around 6-minutes. The company is listed on NYSE. We have reviewed Amprius’ silicon anode technology. The patent library is excellent, goes back to 2009 and has locked upon a specific design. This allows us to guess at costs, degradation and longevity.

Silicon has an anode capacity of 3,400 mAh/gram, which is 10x higher than a graphite anode at 355 mAh/gram. Hence using a silicon anode in a lithium-ion battery confers higher energy density and faster charging (as the lithium ions have ‘less far to travel’). What has hindered silicon anode batteries in the past is swelling 3-4x when lithium ions intercalate. This can cause battery degradation, reviewed in detail in our note here.

Amprius states that its technology uses a 99.5-99.9% pure silicon nanowire, which can accommodate 300-400% volume expansion without degrading. The battery has been tested, validated by partners and is being deployed. By early-2023, 10,000+ batteries have been shipped, extending across 10 SKUs; and GWh-scale manufacturing started in 2021.

The majority of Amprius’ patents that we reviewed were focused on overcoming degradation challenges resulting from graphite anodes expanding by 4x when lithium ions intercalate, which typically causes stresses and crumbling of the anode.

The patent library goes back to 2009. Earlier patents are quite broad ranging. But later patents have quite clearly locked in upon a specific design (some of the images in these patents directly match up to the images in Amprius’ latest investor presentations).

Helpfully, these patents also explain how the silicon anode is to be manufactured (we think there are three separate vapor deposition stages: forming nano-wires above oxidized nucleation points on a substrate; coating the nano-wires with a first silicon layer; then coating the nano-wires with a second, differently shaped silicon layer).

Manufacturing costs of Amprius’ silicon anode batteries can be guessed, approximately in $/kWh terms, using some rules of thumb over the costs of these manufacturing processes compared to battery-grade graphite, and then flowing the higher anode costs through to our build-up of battery costs.

Longevity of Amprius’ silicon anode batteries can also be estimated from technical data that are presented in the patents. We think lifespan is good enough to de-risk large-scale deployment of the technology in specific applications. However, we think the longevity of well managed lithium-ion batteries can still be at least 10x higher.

Further details on Amprius’ silicon anode technology are covered in the data-file. We have also reviewed an interesting silicon anode battery technology from Enovix. Our top conclusions into batteries and energy storage are summarized here.

Hillcrest: ZVS inverter breakthrough?

Hillcrest Technology Review

Hillcrest Energy Technologies is developing an ultra-efficient inverter, which has 30-70% lower switching losses, up to 15% lower system cost, weight, size; low thermal management needs, high reliability, and confers up to 13% higher range than today’s inverters, especially for use in EV powertrains; but also in wind, solar, batteries and fast-chargers. It is based on SiC semiconductors. This Hillcrest technology review presents our conclusions from patents and technical papers.

Hillcrest was founded in 2006, is based in Vancouver, Canada with c15-20 employees. It is publicly listed, with market cap of $25M (Feb-23) and shares traded on the OTCQB Venture Market and Frankfurt Stock Exchange.

It is developing a Zero Voltage Switching (ZVS) inverter. What does this mean, and why does it matter?

Inverters convert DC power to AC power via pulse width modulation, which is covered in our primer into electricity. Specifically, electrical switches create bursts of current, of increasing frequency, then decreasing frequency, then increasing frequency, then decreasing frequency. When these power bursts are averaged out, they resemble an AC sine wave (chart below). This AC power signal can be used to feed power into the grid, or to drive the electric motors in an electric vehicle. The switches are MOSFETs or IGBTs.

The quality of the AC power signal depends on the switching frequency. Fewer pulses (each with longer length and longer gaps) creates a jagged AC sine wave. Whereas more pulses (with shorter length and shorter gaps) produces a smoother sine wave. A nice analogy is thinking about how video quality increases with a higher frame rate. So why don’t inverters dial up the switching frequency to the max?

Switches incur a small power loss every time they switch on and switch off. The reason is that when the switch is off, there is a potential difference (aka a voltage) across the junction (dark green, chart below). When the switch starts to turn on, current starts to flow from source to drain (light green, chart below). The current ramps up as the voltage ramps down. And thus, in the middle, power is dissipated, as power = voltage x current (yellow line, chart below). And so usually, the higher the switching frequency, the higher the switching losses.

Zero Voltage Switching, as the name implies, cuts the voltage from source->drain towards zero BEFORE the current from source->drain ramps up. Thus the power dissipated per switching event (VxI) is very close to zero (chart below). This is conventionally done using active snubber circuits or software on micro-controllers. In principle, ZVS enables faster switching frequencies without astronomical switching losses.

Hillcrest’s technology includes Zero Voltage Switching algorithms, which can be implemented in a micro-controller, and coupled with next-generation SiC semi-conductors, which are creating an exciting jolt forwards in the power electronics behind practically all of the core areas of the energy transition (TSE research note here).

Hillcrest’s white papers show that its algorithms achieve 30-70% lower switching losses than others using similar semi-conductors, especially at higher switching frequencies (chart below). They are also shown to operate over a wider operating range than existing solutions, and produce a particularly high quality output (low ripple, low harmonics, low EMI) .

Another benefit highlighted is that higher quality power signals should allow for downsizing of other components in the traction inverter; especially the DC link capacitor, which typically comprise 21% of the weight of the inverter, 14% of its cost, and 30% of the failures (chart below). This should be interesting for manufacturers of electric vehicles, and others in wind, solar, batteries, fast-charging, power grids.

The data-file linked below is our Hillcrest technology review. As usual, our goal is to review the company’s patents, and its White Papers, to assess (a) can we understand precisely how the company is achieving a technical breakthrough? (b) can we de-risk that breakthrough and (c) can we find a clear moat around the technology, conferring an edge for the company.

Eaton: breakdown of revenues by product category?

Eaton revenue breakdown

Eaton is a power-electronics super-giant, listed in the US, employing 86,000 people, generating $20bn per annum of revenues and with a market cap of $57bn at the time of writing. Large conglomerate companies can be opaque. The data-file is an Eaton revenue breakdown. We have aimed to guess how $20bn pa of net sales is distributed across 200 different product categories.

All roads lead to power electronics. A finding across our research is that energy transition, as a theme, is going to be a kingmaker for power electronics, in order to integrate volatile wind and solar resources into grids, protect sensitive equipment and electrify more industrial and consumer processes.

We have written excitedly about power grid capex quadrupling to $1trn pa in the 2040s, with constructive thematic outlooks on power lines, industrial UPS, capacitor banks, variable frequency drives, transformers, power quality, next-gen switchgear and smart energy systems.

Eaton is increasingly focused on Power Electronics. Eaton’s revenue has shifted from 40% power-electronics in 2011-12 to 75% power-electronics in 2022 (chart below), especially after the company sold its hydraulics business to Danfoss in August-2021 for $3.3bn.

Eaton revenue breakdown

This data-file aims to break down Eaton’s revenues across product categories, using simple educated guesswork. The complexity is overwhelming (chart below). Eaton has over 10,000 SKUs, across 200 different categories. Its product split covers everything from electric vehicle charging, through to missile guidance systems, illuminated emergency exit signs and golf grips. Nevertheless, our breakdown does yield some conclusions.

Eaton revenue breakdown

Exposure to the energy transition. We think 25% of Eaton’s business is less directly exposed to the energy transition, albeit it is still important for the world to invest in aerospace & defence, and efficient vehicles. Another 25% of our Eaton revenue breakdown is exposed to themes with positive tailwinds in the energy transition. And the largest, c50% of the business is exposed to themes with very supportive tailwinds in the energy transition.

Disclaimer. In many cases, there is not much public information to go on. So this data-file is very much a case of educated guesswork, based on our understanding of what different product categories are, how big their market sizes are, and then juggling some plausible combinations of price x volume, estimated across each category.

Battery degradation: causes, effects & implications?

What causes battery degradation?

This 14-page note offers five rules of thumb to maximize the longevity of lithium-ion batteries, in grid-scale storage and electric vehicles. The data suggest hidden upside in the demand for batteries, for lithium and high-quality power electronics, especially if batteries are to backstop renewables.

Battery degradation: what causes capacity fade?

Battery degradation rates

We have aggregated and cleaned publicly available data into lithium ion battery degradation rates, from an excellent online resource, integrating 7M data-points from Sandia National Laboratory. Our data-file quantifies how battery degradation is minimized by limited cycling, slower charging-discharging, stable temperatures and LFP chemistries.

In the underlying laboratory studies that we have assessed, researchers have charged and discharged different batteries, across several thousand cycles, while measuring their capacity fade and round trip efficiencies. The goal is to understand how charging rates, state of charge, cycling conditions, temperatures and cell chemistry interact to determine battery degradation.

Battery lifespans range from 500 cycles to 20,000 cycles, depending on conditions.

The best conditions for long life spans of lithium ion batteries are using LFP chemistry, charging within a limited range, at low charge-discharge rates (C-rates) at a stable temperature of around 25C. This might be associated with a decline rate for batteries of around 2% per 1,000 cycles.

The fastest degradation rates for lithium ion batteries were seen in NCA chemistries, cycled from 0% state of charge to 100% state of charge, at high temperatures, and high discharge rates around 3C.

These lab studies show quite high variability, which is frustrating, as we would all like to pull out good rules of thumb for what drives battery degradation. But there is a fair degree of randomness in when a cell ultimately ‘fails’, as shown in the chart below, which aggregates the data on four different NMC cells tested under exactly the same conditions.

Battery degradation rates

We have also tabulated other data into lithium ion battery degradation rates from technical papers that crossed our screen, as a useful reference, in case you are looking for aggregated data on the degradation rates of lithium ion batteries. Our notes on these technical papers are summarized in the final tab of the data-file.

Please note, this data-file does not contain any of the raw data from, which is free to download and to visualize from the underlying source. We draw out the implications of battery degradation data in our latest battery research, and in our broader battery research.

Supercapacitors: case studies for renewable-heavy grids?

Supercapacitor case studies

The purpose of this data-file is to review supercapacitor case studies, to see if they are being used to back up renewable-heavy grids? Our conclusion is that super-capacitors are well-suited to backstopping short-term wind and solar volatility, and their deployment will gradually surprise to the upside, in combination with other power-electronics.

The motivation for this work is that we recently evaluated the second-by-second volatility of solar and wind output, which incur 80-100 volatility events per day, of which c70-80% last less than 60-seconds. In turn, this volatility profile is well suited to be backed up by super-capacitors, directly, or in combination with other batteries such as lithium ion. So do case studies show increasing deployment of super-capacitors?

The build-up in our data-file has aggregated a dozen recent examples of super-capacitor deployments, based on the disclosures from leading companies, such as Skeleton, Eaton, Vinatech. Many companies endorsed the logic above (quoted in the data-file). Installations typically range from 10kW to 10MW, with 5 – 30 seconds of energy storage (chart below-left), and costs of $30/kW.

Supercapacitor case studies

Advantages of super-capacitors, cited in many of the case studies, are very rapid responses (20 milliseconds), up to 1M charge-discharge cycles over 15-years (i.e., very low degradation) and safe functionality across wide-temperature ranges (-40ºC to +65ºC). Again, details are in the data-file.

Uses of super-capacitors are broadening. Short-term volatility events may cause $100bn pa of damage to electrical equipment. Around 100,000 wind turbines now use super-capacitors to feather their blades. Many industrial machines also have jagged power demand profiles (example above right, a servo-press used to stamp metal plates in auto-manufacturing). Peak power draw can be reduced over 80% with ultracapacitors. This matters as ‘peak power use’ can explain 50% of industrial power bills.

At grid scale, progress is slowly accelerating. One excellent case study from Eaton highlighted how a data-center could earn €50k per year by providing 1MW of demand-smoothing, kicking in within <1-second to prevent frequency drops in an increasingly renewable-heavy grid. Vinatech also noted a MW-scale super-capacitor in Korea, deemed to be more cost-effective and safe than other grid-scale batteries.

Our conclusion from these supercapacitor case studies is that this market will likely surprise to the upside. Ultracapacitors are particularly well-suited to back up the short-term volatility of renewables. But the trend is opaque, as many of the super-capacitor installations overleaf are small, not subject to the fanfare of large press releases, and integrated alongside other power electronics.

Powin: grid-scale battery breakthrough?

Powin technology review

Powin commercializes energy storage solutions. Its hardware and software are branded as ‘Powin Stack’ and ‘Stack OS’. Hence we have used our usual patent framework to conduct a Powin technology review.

Powin — Company and Patent Review

Powin is privately owned. Its roots go back to 1989. It is based in Portland, Oregon. And it has c300 employees at the time of writing. By 2022, the company has delivered 2.5 GWH of storage projects.

Our Powin technology review finds a moat around specific process improvements for the installation and operation of grid-scale batteries. These are described in the data-file.

Overall, the patent library scores well on our patent framework. The patent library is robust enough to deter simple copy-catting. Although there may also be some controversy around the differentiation of some patent claims. (Differentiation is always a question mark for companies in these kinds of supply chains).

Advantages of Powin’s battery systems are their modularity, streamlined installation and software. A guideline is 200 MWH-AC of storage per acre. This is 30% more compact than other solutions. The total time to procure a Centipede system, of inter-connected Powin battery modules, is c50% less than stick-built solutions.

Our patent review found that half of Powin’s IP is software-side. This includes smart features allowing operators to control the way batteries are balanced. The technology also tracks whether batteries are still covered within warranty, on systems envisaged to have a 20-year life.

Context for grid-scale batteries

Grid-scale batteries are growing increasingly important, especially in regions with high renewables penetrations, to backstop the short-term volatility of solar and short-term volatility of wind.

The chart below captures 30 deployments of Powin battery systems. They range from 1 – 90 MW. These deployments have been growing more frequent, and larger.

Interestingly, some recent solar projects have elected to construct 0.2 – 1.0 MW of battery capacity per MW of solar capacity.

Powin technology review

Our full conclusions on Powin’s patents and technology, and the data behind charts, are spelled out in the data-file…

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