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In recent years, emerging fields such as new energy vehicles, energy storage, communications, and data centers have experienced rapid growth, significantly driving the development of large-capacity lithium-ion batteries. As these industries evolve, there is an increasing demand for higher energy density in lithium-ion batteries. [1].
The active materials in a lithium-ion battery—specifically the positive and negative electrodes—play a crucial role in determining its energy density. To enhance this, the discharge voltage and capacity of the positive electrode are typically increased, while the negative electrode should offer high capacity and a low average delithiation voltage. In third-generation lithium-ion batteries, where energy density is a primary focus, both positive and negative materials are undergoing continuous improvements [2-3]. Future advancements may even lead to the use of metal lithium anodes, which could further boost energy density.
Calculating the energy density of a lithium battery is therefore essential. This involves considering both active and inactive materials, excluding packaging and tabs, to estimate the energy density of different cell types. The cylindrical 18650 monomer is often used as a reference, and based on these calculations, the expected energy density and battery cost can be determined.
**Figure 1: Development chart of energy density of lithium-ion battery in 1990–2030**
**I. Energy Density Calculation of Lithium Ion Battery Cells with Different Anode Materials**
The energy density of a battery is primarily determined by its positive and negative electrode materials. However, many studies only consider the mass of the cathode material, neglecting the contribution of the anode and other inactive components. This leads to overestimations of actual performance.
According to literature [4], the energy density of various lithium battery materials was calculated, with results shown in Table 1 and Table 2. Although cathode capacities are improving, they still fall short of theoretical limits. The selected values in the tables take into account technical feasibility, including challenges like volume expansion, rate capability, and cycle life. Table 3 provides typical parameters for cells without packaging or tabs [4].
However, battery shapes vary, and the calculation method may not fully align with real-world production due to differences in electrode coating thickness, shape, and inactive material characteristics. These factors can cause discrepancies between calculated and actual energy densities.
Figures 2(a)–(j) illustrate the energy density of cells formed by combining 10 different anode materials with 16 cathode materials. Notably, the Li-rich-300 vs. Si-C-2000 system achieved the highest mass energy density of 584 Wh/kg and a volumetric energy density of 1645 Wh/L (excluding packaging and tabs).
**Table 1: Calculate the positive active material used and its specific capacity and voltage**
**Table 2: Calculate the mass of the negative active material used and its specific capacity and voltage**
**Figure 2: Calculation of cell energy density for different anode materials and different cathode materials (a) graphite; (b) soft carbon SC-400; (d) hard carbon-250; (e) SiOx-420; (f) SiOx-1000; (g) Si-C-450; (h) Si-C-1000; (j) lithium titanate**
**II. Energy Density Calculation of Metal Lithium Ion Battery Cells**
While traditional anode materials like graphite have a theoretical specific capacity of 372 mAh/g, current reversible capacities are around 365 mAh/g. High-capacity anodes can reach 1000–1500 mAh/g, but issues like volume expansion limit their practical performance. In contrast, metallic lithium has a much higher theoretical capacity of 3860 mAh/g, making it an attractive option despite its safety concerns, such as dendrite formation and electrolyte reactivity.
This study evaluated the energy density of lithium metal batteries at different utilization rates (100%, 80%, 50%, and 33%). Comparing with previous results, metal lithium-based systems showed significantly higher energy densities. For example, using Li-rich-300 as the cathode, the energy density reached 649 Wh/kg when full lithium capacity was utilized, and even at 33% utilization, it remained at 521 Wh/kg.
**III. Estimation of 18650 Single Cell Energy Density**
When accounting for tabs and packaging, the energy density of individual cells can be more accurately estimated. Tables 4 and 5 provide performance parameters for the NCR18650 and prismatic batteries. For example, the NCR18650 typically has 15–20% of its mass attributed to tabs and packaging. Table 6 summarizes the highest energy densities for various anode materials, and Table 7 shows the energy density of cells with Si-C-1000 anodes and different cathode materials. The LCO-220 cell had a mass energy density of 492 Wh/kg, and the monomer energy density was 416 Wh/kg. Packaging materials reduce the overall energy density further.
**IV. Relationship Between Battery Energy Density and Driving Range**
Energy density directly impacts the driving range of electric vehicles. Increasing battery capacity or module size boosts range but raises costs. Alternatively, improving energy density within the same battery pack size enhances efficiency.
For example, the Beiqi EV200, with a total weight of 1.29 tons, consumes 14 kWh per 100 km and requires a 200,000 km lifespan. At a mass energy density of 180 Wh/kg, the EV200 achieves a 200 km range. If the energy density reaches 400 Wh/kg, the range increases to 521 km, with a cycle life of 600 times. This meets consumer expectations for electric vehicle range and addresses concerns about battery longevity.
**V. Cost of High Energy Density Lithium Batteries**
Estimating battery costs involves analyzing raw material prices. Table 9 outlines the cost of materials for a 100 Ah battery. The cathode and electrolyte account for 37–56% of the total cost, while silicon-carbon anodes make up 38–48%. Using metallic lithium as an anode can reduce costs significantly, with Li-rich NCM cells costing 0.2–0.29 yuan per watt-hour.
It's important to note that material costs represent 60–70% of the total manufacturing cost. After adjusting for this, the actual cost per battery is lower. With continued improvements, metal lithium-ion batteries could even become cheaper than lead-acid batteries.
**VI. Comprehensive Technical Indicators**
Battery performance depends on more than just energy density—it also includes power density, charge rate, cycle life, safety, and cost. Meeting all these requirements is essential for real-world applications. Figure 5 shows a spider diagram of technical indicators across different applications, highlighting the gap between current levels and future expectations. New battery technologies are needed to close this gap.
From 1990 to today, energy density has been improved through better active material ratios and reduced inactive material content. While further reductions in separator and foil thickness are possible, they pose significant technical challenges. Choosing new electrode materials remains a more feasible path for increasing energy density.
With advanced silicon-carbon anodes and lithium-rich manganese-based cathodes, the 18650 battery can achieve 442 Wh/kg, with a cost of 0.4 yuan per watt-hour. The lithium-rich manganese-based metal ion battery can reach 521 Wh/kg, with a cost of 0.2 yuan per watt-hour. Solid-state batteries are expected to address current limitations in liquid electrolyte systems.
In conclusion, while increasing energy density is a key goal, it must be balanced with other performance metrics. This requires ongoing research and innovation, offering both challenges and opportunities for the future of energy storage.