Technical analysis of unified cell by Powerco (VOLKSWAGEN)

Standardardisation attempts for Lithium-ion cell dimensions

There have been various standardisation attempts in the Lithium-ion cell industry in terms of cell dimensions. Still, it is difficult to find two chemistries, such as LFP and NMC cells, with similar dimensions (capacities may be different). For example, LFP is popular in , and cylindrical cell formats, whereas NMC is popular in , , and formats.

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cylindrical was the first attempt to make LFP and NCA cells with the exact same form factor. LFP from BYD (FinDreams battery) cell exhibits 15Ah, and NCA from Panasonic (for Tesla) exhibits close to 26Ah capacity. Another such attempt was made by Volkswagen in the prismatic cell form factor, which we will discuss soon in this article.

Many companies manufacture cells up to 100Ah capacity in prismatic form factor with 148mm width in LFP and NMC, but their thickness and height tend to vary. Cells from 150Ah to 280Ah in prismatic form factor have 173mm width and 204mm height (without terminal) and varying thickness. Both 148 mm and 173mm widths come under the VDA cell standard. VDA stands for Verband derAutomobilindustrie (German Association of the Automotive Industry). It is a German interest group of the German automobile industry that proposed standards for the size of the battery cell technology used for the automotive industry.

Volkswagen PowerCo’s UC (unified cell) is a concept one step ahead, where the three dimensions of the cell will be the same and different chemistries will be used for different scenarios. Similarities in the cell dimensions allow for the following advantages:

• Reuse the cell manufacturing equipment for various chemistries; this is recommended to maximise the capacity utilisation factor (CUF) of the plant setup.

• Improved CUF allows costs to be reduced and efficiency improved.

• Similar cell dimensions allow for a lower cost of battery pack assembly for building various packs in terms of sourcing the balance of systems for battery packs (except BMS).

• Similar cell dimensions allow for the creation of low-range and high-range versions of the same electric vehicle. LFP is preferred in short-range vehicles, and NMC is preferred in vehicles where the expected range is higher.

• It saves costs during cell manufacturing and battery pack assembly.

Volkswagen says it will use the Unified cell for 80% of its requirements across many vehicles, leading to a 50% reduction in cost.

80% of the cells would include LFP for lower-range EVs, High Manganese no Cobalt chemistry for mid-range EVs and NMC for high-range EVs. The remaining 20% of the cells would be for specific solutions, which could mean different form factors and chemistry.

Below is the discussion about these chemistries (that would comprise 80% of the cells).

Lithium Iron Phosphate (LFP)

The LFP chemistry cells are expected to be charged at a higher voltage, up to 3.8V, to achieve higher capacity and a volumetric energy density above 430Wh/L in prismatic format. This will allow it to come closer to NMC prismatic cells (which are 500-600Wh/L). Traditionally, LFP prismatic cells have much lower than 400Wh/L volumetric energy density.

Contrary to popular belief that gravimetric energy density is important in EVs, it is actually the volumetric energy density that allows to pack more energy in a given space and enables a higher range. The weight difference is minimal when the gravimetric energy density is improved. For example, if a cylindrical LFP cell is improved to 190Wh/Kg from the existing 175Wh/Kg in a30kWh electric car, the overall weight of the battery pack would be only 20Kg less, and this weight reduction is not significant compared to the weight of the car which is close to 1.5 ton. On the other hand, volumetric energy density allows for more cells to fit and, therefore, allows for a higher range.

Charging a particular type of cell at a higher voltage is not a new concept, but there is a trade-off in cell cycle life. For example, charging an LFP cell up to 3.8V could deliver between and cycles, which is almost half of the cycle life when an LFP prismatic cell is charged up to 3.6Vvoltage. But lower cycle life is typically enough for decently long-range EVs, allowing for either a lower depth of discharge (DoD) per cycle or a smaller number of cycles at a higher DoD. Either way, the battery will deliver a high number of kilometres on the odometer over a 10-to-15-year period of EV ownership.

High Manganese Chemistry

Volkswagen did not mention the exact chemistry for this category, though high Manganese refers to LMO, LNMO or LMFP chemistries.

LMO (Lithium Manganese Oxide) faded from the market due to poor cycle life at high temperatures and manganese dissolution problems. Later, it was relaunched as a composite with NMC. Many companies in the LMO+NMC market are now migrating to other chemistries; it is unlikely that Volkswagen will produce this, given the presence of Cobalt.

LNMO (Lithium Nickel Manganese Oxide) is a modified version of LMO with Nickel. LNMO has been gaining popularity in the European region due to its lack of cobalt and high voltage nature. This cell has the highest possible voltage, but its overall energy density is lower than nickel-rich NMC and NCA cells. This has a price advantage, but it has certain commercialisation challenges, such as finding a suitable electrolyte to work with. Existing electrolyte technologies max out at close to 4.6V potential operation, and LNMO operates over 4.6V. Due to Volkswagen’s European nature and no Cobalt in LNMO, this is a highly likely contender for a high Manganese cell. Also, recently, Toshiba launched a cell with LNMO cathode material, although it uses a different anode (NTO).

LMFP (Lithium Manganese Iron Phosphate) is an upcoming cell type in Asia and is gaining popularity to compete with NMC, providing advantages such as similar voltage, better cycle life and and lower costs. LMFP is a modified LMP (Lithium Manganese Phosphate) with the incorporation of Iron. Contrary to popular belief that LMFP is a competitor to LFP, it is actually a competitor to NMC cells. Certain applications have no competition for LFP, such as heavy-duty vehicles and energy storage applications. LFP is priced lower than LMFP and has a higher cycle life and value for money. LMFP could also be a contender for this category, considering that Volkswagen has a partnership with Gotion (China) and that Gotion has already launched LMFP cells at a commercial scale. By the way, most LMFP cells use LMFP+NMC material to provide stable performance, but this mix is an unlikely choice for Volkswagen because of its Cobalt content. Only LMFP might be a likely contender.

This is Volkswagen’s long-term strategy, we will find out more about high Manganese and no Cobalt type cell in times to come.

Lithium Nickel Manganese Cobalt Oxide (NMC)

NMC has been in the news frequently due to its pros and cons.

Pros – High gravimetric energy density, high volumetric energy density (>50% higher than LFP in Nickel rich NMC) for higher EV range, high-power rating of charge for fast charging and high-power rating of discharge for achieving higher driving speeds and its ability to provide a predictable voltage profile.

Cons – Comparatively unsafe, expensive and uses Cobalt (concerns of sustainability and availability).

Because of their high volumetric energy density, NMC/NCA (high Nickel) cells are the absolute choice for long-range cars. Volkswagen would use these cells for their long-range cars.

The remaining 20% of the cells would be for specific solutions, which could mean different form factors and chemistry. Volkswagen is also eyeing solid-state batteries in collaboration with Quantum Scape, where it aims for less than half charging time and 30% more range.

The image are from Volkswagen’s ‘Power Day’, where the unified cell was first unveiled in .

This article was first published in EVreporter March magazine.

About the author:

Rahul Bollini is an R&D expert in Lithium-ion cells with 9 years of experience. He founded Bollini Energy to assist in deep understanding of the characteristics of Lithium-ion cells to EV, BESS, BMS and battery data analytics companies across the globe. Rahul can be reached at +91- and .

• Electric Vehicles (EVs),

  Lmfp lithium-manganese phosphate cells have great utility in the electric vehicle industry. These cells have a large amount of energy density combined with enhanced thermal stability and high safety. Because of this, they make suitable candidates for the EV battery system. They offer longer driving distances and faster charging times compared to traditional lithium-ion batteries. In addition, their safety level reduces thermal runaway risks, thus enabling battery packs to operate reliably and stably in auto use.

• Renewable Energy Storage Systems,

  Renewable energy sources such as solar and wind are very inconsistent and depend on the weather conditions. LMFP cells afford a very reliable energy storage solution that bridges this gap. These cells sheer the energy generated by renewable sources and stock this energy for later usage. They keep the stored energy in the form of chemical potential energy and release it as electrical energy when needed. Thus, these cells help balance energy supply and demand, which increases the utilization of renewable energy.

• Grid Energy Storage,

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  LMFP cells are used for large-scale grid energy storage systems capacitors. These cells help store excess energy during low-demand periods and release it when the energy needs are high. They stabilize the energy grid, improve reliability, prevent blackouts, and handle frequency. Additionally, these cells facilitate the integration of more renewable energy sources into the grid, simplifying the operation of the energy system.

• Industrial and Commercial Backup Power Systems,

  LMFP cells are used in industrial and commercial applications requiring uninterrupted power systems. These cells provide energy backup for critical applications such as data centers, telecommunications, and manufacturing plants when power interruptions occur. They boost the reliability of these operations and minimize downtime. THese cells also integrate with other power sources, including generators and solar power, to provide seamless energy.

• Portable Power Tools and Devices,

  Traditionally, LMFP cells were used in portable battery-operated power tools such as drills, saws, and grinders. The properties of these cells: lightweight, high-energy density, and long cycle-life. They make the ideal choice for power tools requiring long usage times and quick charging. They permit power tools to operate efficiently and wirelessly, which is convenient for work on construction sites and in other jobs.

• Energy Density,

  The feature of LMFP lithium manganese phosphate cells that makes them very suitable for many applications is their energy density. Usually, these cells have an energy density that approaches 150-200 Wh/kg. It allows them to store much energy per given cell mass. Therefore, this allows electric vehicles and portable power tools to achieve longer operating times.

• Long Cycle Life,

  Cycle life is another feature that makes these cells prominent. Usually, they have a cycle life of about – cycles. This length permits many charges and discharges without losing much of the cell capacity. Therefore, this property is very important for applications such as grid storage and renewable energy, where frequent cycling occurs.

• Safety and Stability,

  The safety level and stability of the LMFP cells are significant features. Lithium iron and manganese phosphate are highly thermally stable and stored at high temperatures. It reduces the risk of thermal runaway associated with other lithium-ion chemistries. Thus, it improves battery pack and cell safety for electric vehicles and stationary storage systems. Additionally, these cells feature a stable voltage during discharge, leading to reliable performance.

How to Install

Installation of LMFP lithium manganese phosphate cells involves several key steps; they include preparation, connection configuration, security, testing, and monitoring. In preparation, the tools required for the installation are gathered, and the cells are inspected for any signs of damage. During the configuration stage, each cell is connected to the battery management system to ensure proper functionality. In the security stage, all connections are made sure to tight and secured to prevent malfunctioning. The next step is testing, where the entire system is powered up, and several tests are performed to ensure the system is operating as required. Finally, monitoring involves the establishment of a regular performance check to keep track of cell conditions and overall battery health. This is a simple overview of how to install an LMFP lithium manganese phosphate cell.

Usage and Scenarios

The LMFP lithium manganese phosphate cell has a wide range of usage in various sectors. The implementation of these cells in electric vehicles for energy storage has improved the performances of these vehicles by allowing them to operate on a longer range with faster charging times. In the renewable energy sector, these cells store excess solar or wind energy, enabling a constant power supply even when the sun is not shining or the wind is not blowing. These cells are also found in power tools, providing reliable cordless operation. In industrial applications, they back up power systems to ensure uninterrupted power to critical operations. Lastly, portable electronic devices are powered by LMFP cells due to their lightweight and compactness.

Maintenance and Repair

Maintenance and repair are the key factors that ensure LMFP lithium manganese phosphate cells last longer. Regular monitoring of cell voltage, temperature, and state of charge is necessary to maintain optimal performance. One needs to keep the battery area free of dust and debris to avoid overheating, besides ensuring proper ventilation. Usage of a battery management system (BMS) is necessary, as it helps prevent overcharging and deep discharging. Repairs should be done with original spare parts. In case of damage, consulting a specialist is required.

Quality and Safety Considerations of lmfp lithium manganese phosphate cell

Quality Considerations

• Source Materials,

  Material sourcing causes the quality of LMFP lithium manganese phosphate cells. The materials used to make these cells should be of high purity. The presence of impurities in the materials leads to performance degradation and affects battery life. Therefore, reputable manufacturers ensure that their lithium, manganese, and iron phosphate precursors come from reliable suppliers.

• Manufacturing Process,

  Cell design, formation, and aging are some of the important steps in the manufacturing process that determine the quality of the final product. Adequate control during these processes guarantees consistent performance and increased cell safety. Manufacturers must adhere to strict guidelines in temperature and humidity during production to achieve the desired characteristics.

• Testing and Certification,

  Testing is important to ensure the quality of LMFP cells. Standard tests include capacity, internal resistance, and cycle life and must be performed before these cells are sold to the users. Certification, like CE and RoHS, provides additional assurance that the products meet the required performance and safety standards.

Safety Considerations

• Thermal Stability,

  The great safety feature of LMFP cells is their thermal stability. Unlike other lithium-ion chemistries, these cells have minimal risks of thermal runaway. Electric vehicle users and battery system operators understand how important a safe system is and those who work with these products.

• Battery Management Systems (BMS),

  The role of BMS is to maintain battery operation within the safe limits of voltage and current. These systems help in preventing overcharging, deep discharging, and excessive heating. It is important that customers use products with integrated BMS or are advised on how to manage the battery cell properly.

• Protective Equipment,

  Protective equipment such as circuit breakers and fuses are play significant roles in battery pack safety. These devices are used to isolate fault conditions and thereby prevent accidents. Customers should be advised on the importance of these devices and ensure these systems function well.

• Proper Handling,

  Slight care during handling and transportation is important for safety. Customers should be advised to avoid mechanical damage to cells and maintain an appropriate state of charge during transportation. Further, avoid exposure to extreme temperatures and keep cells away from wet or high-humidity areas.

Q&A

Q1. What are the benefits of LMFP lithium manganese phosphate cells over traditional lithium-ion batteries?

A1. LMFP cells have better thermal stability, higher safety, longer cycle life, and faster charging rates. These characteristics make them suitable for electric vehicles and energy storage.

Q2. Which materials are used to make LMFP cells?

A2. LMFP cells involve the utilization of lithium, manganese, and phosphate as key materials. The cells offer high energy density and stability because of this combination.

Q3. How do LMFP cells contribute to renewable energy storage?

A3. LMFP cells store excess energy from solar and wind power, later releasing it when energy demand is high. This balance between supply and demand improves renewable energy efficiency.

Q4. How long can LMFP cells last in portable power tools?

A4. Due to their long cycle life, LMFP cells can last several years in portable power tools. Normally, they perform the optimal function of efficient power provisioning for many hours and require minimal maintenance.

Q5. Are LMFP cells eco-friendly?

A5. Yes, LMFP cells are eco-friendly. They are stable, reliable, and safe for the environment. Also, the materials used are more abundant and less harmful compared to other lithium-ion battery chemistries.

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