Battery Tech Report: Lithium-Ion vs Vanadium Redox Flow Batteries (VRFB)

Batteries will play a greater and greater role in the green energy revolution. From electric vehicles (EVs) to efficient electronics, there are a variety of batteries on the market applicable for various uses, the ubiquitous energy source being the Lithium-ion (Li-on) battery. Vanadium Redox Flow Batteries (VRFB) are a cutting-edge type of rechargeable flow battery, that employs vanadium ions as the active materials .

The unique properties of VRFBs gives manufacturers an edge in certain applications (e.g., utility/grid energy) over other batteries in the space. Below we will lay out the similarities and differences between a Vanadium battery and Lithium-ion. To illustrate this, let’s look at some of the main features and differences between VFRBs and Lithium-ion batteries.

What are VRFBs and Li-ion Batteries

A vanadium redox battery consists of an assembly of power cells in which two electrolytes are separated by a proton-exchange membrane. The electrodes in a VFRB cell are carbon based. Both electrolytes are vanadium-based. The electrolyte in the positive half-cells contains V⁴⁺ and V⁵⁺ ions, while the electrolyte in the negative half-cells consists of V³⁺ and V²⁺ ions. The electrolytes can be prepared by several processes, including dissolving vanadium pentoxide (V₂O₅) in sulfuric acid (H₂SO₄).

A lithium-ion battery is a rechargeable battery made up of cells in which lithium ions move from the negative electrode through an electrolyte to the positive electrode during discharge and back when charging. Lithium-ion cells use an intercalated-lithium compounds as the electrode materials, which are typically graphite as the positive electrodes and metal oxides as the negative electrodes. Lithium batteries have a high energy density, and low self-discharge.

Cells can be manufactured to prioritize either energy or power density. Vanadium batteries have a lower energy density – they are better at delivering a consistent amount of power over significantly longer periods. More importantly, a vanadium flow battery can handle far more charge-discharge cycles than a lithium-ion battery.

Cell Architecture

Lithium batteries store all of the components inside the cells, which makes them simple and well suited for small devices, such as in laptops and cellphones. They are relatively small and heat up very quickly, one of their strengths being they respond quickly to changes in power demands. Lithium-ion batteries are also currently the main use-type for electric vehicles, because of their unmatched energy density. One of the negatives of using Li-on for electric vehicles is that they take hours to charge, which can be an inconvenience if there is no charging station available for a traveling driver.

The main drawback to lithium batteries for large-scale projects, is that hundreds of thousands of cells are needed. This is an inefficient way of storing energy and uses far more materials than a VFRB battery, since each of these individual Li-on battery cells can only store a relatively small amount of energy. There is a limit to the amount of active materials that one can hold inside the electrodes, since thick electrodes result in poor performance and shorter lifetimes.

In contrast, VRFBs store their energy in two electrolyte tanks, which are connected to a stack of cells. The electrolyte is the fluid that stores the active materials dissolved in the liquid, and is pumped from the two tanks through the cell stack during charging and discharging process. The energy capacity of a VFRB battery can easily be expanded by adding more solution to the tank. This battery design makes it much easier to adapt VRFBs to industrial-scale operations without adding much costs since the tanks can be any size desired. In other words, as the energy capacity of a VRFB battery increases, the price per kilowatt hour decreases.

VRFBs outperform Li-on batteries and are a far superior energy storage option for stationary applications, where their feature of storing chemicals in external tanks enables large-scale energy storage from a renewable source during peak-production times and consistent supply when energy production drops below demand.

Energy Capacity

Capacity retention is where VRFBs really stand out. Lithium batteries decay over time and lose capacity;

A well-designed VRFB System can run at 100% capacity forever. 

To make up for their capacity loss, lithium batteries are built to be oversized at the time of installation, which increases costs to the end user. The average age of a substation transformer is 42 years.

According to Battery University, the capacity of lithium-ion cells can drop to a 50 percent level after 1,200 to 1,500 discharges while VRFBs retain 100% capacity up to 14,000 discharges.

Energy Density & Power Density

Energy is measured in kilowatt-hours (kWh) and is the amount of power (kilowatts, or kW) delivered over a period of time.

Battery energy density is the amount of energy a battery contains compared to its weight (i.e., specific energy density) and size (i.e., volumetric energy density).

Power density is similar but measures the power output per kilogram (kW/kg), vs total power per kilogram (kWh/kg) with battery density. Power density measures how fast energy can be delivered, and energy density measures how much energy a battery can hold.

If one thinks of electrical energy as a liquid, then power is the flow rate and energy is the total volume of the liquid.

Li-ion batteries are like coffee cups, which can be readily emptied (high flow rates) but have low storage capacity (low volume).

VRFBs are like water bottles, which can hold large amounts of energy (large volumes). VRFBs can also be designed to deliver whatever ratio of power (flow rate) to energy (volume) one desires for a given application, due to the decoupled and flexible architecture.

Lithium-ion batteries have higher energy densities than VRFBs. However, lower energy density is fine for stationary applications where size and weight are less important than in mobile devices or EVs. VRFBs are ideally suited for long-duration energy storage applications on the electric grid, where capacity, safety and lifespan are far more important than density.

The high energy density and output levels of lithium-ion batteries come at a cost – lithium batteries contain flammable electrolytes and have a relatively higher hazard than VRFBs. If damaged or charged incorrectly, they can cause damage or fires.

Safety

All energy-storage systems have safety concerns.

However, VRFBs are inherently safer than Li-on batteries, since the energy is stored separately from the conversion device (i.e., the cell stacks).

Li-ion batteries use flammable electrolytes, are prone to “thermal runaway” during charging, and are never truly “off” since all of the materials are connected at all times.

VRFBs use aqueous electrolytes, which are not flammable. VRFBs are also well equipped for emergency power delivery, which has to remain off for long periods of time to be kept in reserve for powering a grid. , The self-discharge rates of VFRBs are very low due to the energy being stored separately where it cannot react during idle periods.

Lifespan

VRFBs have inherently much longer lifetimes than Li-on batteries. This is because Li-ion electrodes undergo significant physical changes with each charge-discharge cycle in order to accommodate the insertion and removal of the Li ions in the intercalation electrodes.

These changes are greater for deeper discharge cycles. In contrast, VRFBs electrodes do not have to undergo changes during cycling, since they are simply sites for the electrochemical reactions of the V ions, which remain dissolved in the electrolytes. A VRFBs lifetime does not depend on the number of cycles or the depth of the charge each cycle.

VRFBs have an avg. lifespan of 25 years or longer, more than double the 7 to 10 years of a typical lithium battery. Li-on battery life span can vary significantly depending on the number and depth of the charge-discharge cycles.

The VFRB Sustainability Advantage is a Game Changer

When a VFRB needs to be replaced, the vanadium electrolyte can be easily reused and repurposed in other batteries since the electrolyte is already separated from the rest of the battery system. It is very challenging and currently uneconomic to extract Li from Li-ion batteries, meaning these batteries are not currently recycled.

Recapturing the vanadium is a game changer for VFRBs and make them one of the lowest carbon energy storage options on the market.

Vanadium recapture means less mining, less emissions burned in the manufacturing process and fewer overall lifecycle emissions. VFRB adoption would go a long way to helping government’s achieve emission reduction targets.

Price / Innovations

According to Bloomberg, the average cost of a lithium-ion battery is about $137 per kilowatt hour and is forecasted to drop as low as $100 kilowatt-hour by 2023.

However, these are the cost of the cells only; a complete Li-ion battery system for grid-scale stationary storage currently costs approximately $350 to $400 per kWh. It has been estimated that the overall cost for VFRB Systems are $500/kWh, but that will fall significantly over time as production volumes increase. Adoption of VFRB batteries is still in the early stages, leaving significant room for scale-driven cost declines.

The upfront dollar per kilowatt hour for VFRBs also does not take into account the lifespan and safety advantages.

Vanadium batteries are at the beginning of their development cycle and will go through many innovations and improvements in the foreseeable future as usage increases and economies of scale are realized. The management systems are software-based, so they are easily upgraded and improved.

Vanadium Batteries are Primed to Disrupt Utility Scale Storage

To review. Lithium batteries need to be replaced more often and lose capacity over time compared to VRFBs. VRFBs are also easily expandable and can be customized to a customer’s specifications for far less cost than Li-on.

VRFBs can handle many more cycles and are far safer than compared to Li-ion. VFRBs. They have a smaller carbon footprint than to Li-ion batteries which themselves are far cleaner than fossil fuels. The inherent safety of the battery chemistry means VRFBs can be installed anywhere (e.g., within city limits or even in existing utility stations). VRFBs are especially advantageous for applications that require long discharge durations at rated power. Energy can be stored and delivered over long periods of time (e.g., > 5 hours per discharge); for example, energy converted from solar panels can be collected during the day and used throughout the night.

In a world already struggling to reach emission reduction targets set only 7 years ago, VFRBs could be a key tool to cutting greenhouse gas emissions. The reusable nature of vanadium makes VRFBs a far greener alternative to Li-on with much easier end-of-life processing.

Li-ion batteries have been the long-time choice for mobile devices and EVs for good reasons, but as battery demand increases for utility applications, VFRBs are primed to become a preferred storage method. They have also been used for grid-scale storage for applications that only require short discharge durations (e.g., < 4-h per cycle).

However, with the explosion in renewable but intermittent electricity generation (think windmills and solar panels), VRFBs have a real opportunity to upend the energy-storage industry today, especially as the demand for longer discharge durations starts to grow. Although, there are drawbacks to VRFBs today, low energy density and higher upfront cost per kwh, improvements in technology and the ongoing ramp up in production volumes will only close the gap against Li-ion technologies.

VRFB’s potential as a renewable, sustainable, and highly safe energy-storage system make it an exciting technology with the potential to make a huge impact.

For investor’s interested in gaining exposure to lithium, there are a few promising companies in the space. Namely SQM (NYSE:SQM), Albemarle (NYSE:ALB) and Lithium Americas (NYSE:LAC). For exposure to Vanadium and VFRB batteries there is really only one game in town, industry leader Largo Inc. (TSX:LGO NASDAQ:LGO).

Largo Inc. is a market awareness client of Capital 10X.