In the evolving landscape of energy infrastructure, the integration of renewable sources and the demand for reliable power backup have propelled the development of advanced battery energy storage systems. Among various technologies, lead-acid batteries remain a cornerstone for applications such as uninterruptible power supply (UPS) in critical facilities, including thermal power enterprise information centers. Their maturity, cost-effectiveness, and recyclability make them a preferred choice for automation control systems. However, challenges like capacity fade, limited cycle life, and performance degradation under extreme temperatures necessitate material innovations. This study focuses on enhancing lead-acid battery energy storage systems by incorporating lanthanum, a rare-earth element, into the grid alloy. We investigate the effects on electrochemical properties, mechanical characteristics, and long-term reliability, aiming to optimize the battery energy storage system for prolonged operational stability in grid-tied applications.
The grid, serving as the current conductor and support for active materials, is pivotal in determining battery performance. Traditional lead-calcium alloys are widely used, but their susceptibility to corrosion and active material detachment limits lifespan. Rare-earth elements, known for their unique physicochemical properties, offer a promising avenue for improvement. Prior research has highlighted benefits in chemical stability and microstructure, yet applications in thermal network UPS contexts are sparse. Our work bridges this gap by systematically evaluating lanthanum-doped lead-calcium-tin-aluminum alloys through controlled rolling processes, performance testing, and real-world embedding in a battery energy storage system. We employ a first-person perspective to detail experimental procedures, data analysis, and implications for future battery energy storage system designs.
Rolling Process and Alloy Properties
We conducted experiments on a continuous lead strip production line, where molten lead alloy was cast into a wheel and subjected to five-pass rolling to achieve a final thickness of 0.70 mm and width of 80 mm. The rolling parameters, such as temperature, speed, and reduction ratio, were varied across five distinct processes (labeled Process 1 to 5), yielding corresponding samples (Sample 1 to 5). These parameters directly influence the microstructure and properties of the alloy, which we assessed through corrosion rate, conductivity, metallographic organization, tensile strength, and hardness tests. The goal was to identify the optimal process for battery energy storage system grids, balancing mechanical integrity and electrochemical efficiency.
Corrosion resistance is critical for grid longevity in a battery energy storage system. We performed constant-current polarization at 1.72 V for 3,000 minutes using a potentiostatic corrosion platform. After cleaning and drying, mass loss was measured to compute corrosion rates. The formula for corrosion rate is expressed as:
$$ v = \frac{\Delta m}{A \cdot t} $$
where \( v \) is the corrosion rate in g·m\(^{-2}\)·h\(^{-1}\), \( \Delta m \) is the mass loss in mg, \( A \) is the surface area in m\(^2\), and \( t \) is the time in hours. Results, summarized in Table 1, show a decreasing trend with process optimization, indicating enhanced anti-corrosion properties. Tin (Sn) plays a key role by forming a protective layer; when Sn content exceeds 1 wt%, its impact plateaus, aligning with literature on lead-alloy behavior in aggressive environments.
| Sample No. | Mass Loss (mg) | Corrosion Rate (g·m\(^{-2}\)·h\(^{-1}\)) |
|---|---|---|
| 1 | 103.65 | 3.5842 |
| 2 | 98.82 | 3.4351 |
| 3 | 95.63 | 3.3524 |
| 4 | 93.12 | 3.2783 |
| 5 | 90.76 | 3.1951 |
Conductivity affects energy efficiency in a battery energy storage system. We machined strips into 8.5 mm × 3 mm × 20 mm specimens and measured resistivity using a volt-ampere method on a Wheatstone bridge. Conductivity was derived from resistivity (\( \rho \)) via:
$$ \sigma = \frac{1}{\rho} $$
where \( \sigma \) is conductivity in %IACS (International Annealed Copper Standard). As shown in Table 2, conductivity improved with process adjustments, attributed to reduced undercooling and slower cooling rates that enlarge grains and decrease grain boundary scattering. Higher conductivity minimizes ohmic losses, enhancing the overall efficacy of the battery energy storage system.
| Sample No. | Resistivity (Ω·mm\(^2\)·m\(^{-1}\)) | Conductivity (%IACS) |
|---|---|---|
| 1 | 21.78 × 10\(^{-4}\) | 7.9185 |
| 2 | 21.76 × 10\(^{-4}\) | 7.9283 |
| 3 | 21.72 × 10\(^{-4}\) | 7.9421 |
| 4 | 21.67 × 10\(^{-4}\) | 7.9526 |
| 5 | 21.64 × 10\(^{-4}\) | 7.9691 |
Metallographic analysis involved polishing and etching samples with a hydrogen peroxide-acetic acid mixture. Scanning electron microscopy revealed microstructures dominated by α-solid solution and minor Pb\(_3\)Ca compounds, given the calcium content near the eutectic point (ω(Ca) = 0.0953%). Grain size increased with reduced undercooling, impacting mechanical properties. Tensile tests demonstrated that finer grains (e.g., Sample 1) yielded higher strength but lower elongation, whereas coarser grains (Sample 5) improved ductility. For instance, Sample 1 had tensile strength of 52 MPa, yield strength of 26 MPa, and elongation of 7.6%; Sample 5 showed 41 MPa, 21 MPa, and 9.8%, respectively. This trade-off influences grid formability during expansion, crucial for manufacturing efficiency in battery energy storage system production.
Hardness measurements, conducted using a Vickers indenter, complemented these findings, with values ranging from 18 HV to 22 HV across samples. The optimal process (Sample 5) was selected for subsequent battery assembly due to its balanced corrosion resistance, conductivity, and ductility, which are vital for durable battery energy storage system performance.
Battery Fabrication
We fabricated two types of 12 V 150 Ah lead-acid batteries for UPS applications in thermal network information centers. Both used rolled grids from Sample 5, but one incorporated lanthanum-doped positive grids (ω(La) = 0.01%), while the other used conventional lead-calcium-tin-aluminum alloys. Grid design parameters and physical specifications are listed in Tables 3 and 4. The assembly followed standard lead-acid battery procedures, including paste application, curing, formation, and electrolyte filling, with meticulous tracking to ensure consistency. The battery energy storage system was designed to power automation controls, emphasizing reliability under cyclic loads.
| Grid Type | Thickness (mm) | Dimensions (mm) | Alloy Composition | Number per Cell |
|---|---|---|---|---|
| Positive | 2.9 | 179 × 161 | Pb-Ca-Sn-Al-La | 9 |
| Negative | 1.7 | 179 × 161 | Pb-Ca-Sn-Al | 10 |
| Parameter | La-doped Battery | Non-doped Battery |
|---|---|---|
| Casing Mass (kg) | 2.41 | 2.41 |
| Electrolyte Mass (kg) | 8.4 | 8.3 |
| Lead Alloy Usage (kg) | 38.1 | 38.4 |
| Total Battery Mass (kg) | 52 | 52 |
The batteries were conditioned and tested according to GB/T 31485-2015 standards, simulating real-world battery energy storage system conditions. We evaluated initial capacity, charge-discharge behavior, cycle life, and embedding performance in a thermal network UPS unit.
Performance Evaluation
Capacity tests at room temperature involved discharging to 11 V at various rates (1 h, 3 h, 5 h, 10 h, 1 C, 2 C). Average initial capacities over four cycles are presented in Table 5. The La-doped battery exhibited slightly lower capacities across all rates, suggesting that lanthanum inhibits the formation of loose PbO\(_2\) layers during charging, which initially boosts capacity but may impair longevity. This trade-off is acceptable for a battery energy storage system prioritizing cycle life over peak initial output.
| Discharge Rate | La-doped Battery (Ah) | Non-doped Battery (Ah) |
|---|---|---|
| 1 h | 125 | 129 |
| 3 h | 144 | 148 |
| 5 h | 152 | 160 |
| 10 h | 169 | 177 |
| 1 C | 120 | 126 |
| 2 C | 96 | 100 |
Charge-discharge performance was assessed at 40°C, 25°C, and -20°C using a 3 h rate discharge. The La-doped battery consistently outperformed the non-doped one, especially under extreme temperatures. Discharge curves, modeled by a modified Peukert equation, illustrate this:
$$ C = I^n \cdot t $$
where \( C \) is capacity, \( I \) is current, \( t \) is time, and \( n \) is the Peukert exponent. For the La-doped battery, \( n \) approached 1.05, indicating better rate capability versus 1.12 for the non-doped variant. This enhancement stems from lanthanum promoting dendritic oxide growth, strengthening the active material-grid interface and improving conductivity in the corrosion layer.
Charge acceptance, crucial for fast recharging in a battery energy storage system, was evaluated via a 60-minute quick charge at 30 A with a 14.8 V limit. As referenced in Figure 1 (conceptual representation), the La-doped battery achieved 100% of rated capacity, whereas the non-doped battery reached only 86%. Traction and starter batteries showed inferior performance, highlighting the superiority of La-modification for UPS applications. The charge acceptance ratio \( \eta \) can be expressed as:
$$ \eta = \frac{Q_{\text{charged}}}{Q_{\text{rated}}} \times 100\% $$
where \( Q_{\text{charged}} \) is the capacity replenished during quick charge.
Cycle life testing involved 80% depth-of-discharge (DoD) cycles until capacity fell to 80% of initial. The La-doped battery endured over 600 cycles, compared to 450 for the non-doped one. Voltage divergence during cycling, plotted in Figure 2, remained lower for the La-doped version (1.11 V after 500 cycles versus 2.1 V), indicating reduced sulfation and internal resistance growth. The cycle life \( N \) correlates with DoD via an empirical model:
$$ N = k \cdot \text{DoD}^{-\alpha} $$
where \( k \) and \( \alpha \) are constants. For La-doped grids, \( \alpha \) decreased, implying extended life at high DoD, a key advantage for battery energy storage systems undergoing frequent deep discharges.
Embedding tests in a thermal network UPS unit simulated real-world demands. Both batteries powered automation control actions without maintenance. Initially, the non-doped battery supported more actions, but after 200 cycles, the La-doped battery surpassed it, and after 600 cycles, it still enabled 35 control operations versus near-zero for the non-doped battery. This demonstrates the practical benefit of lanthanum in prolonging service life for critical battery energy storage systems. The number of supported actions \( A \) as a function of cycles \( n \) can be approximated by:
$$ A(n) = A_0 \cdot e^{-\beta n} + \gamma $$
where \( A_0 \) is initial actions, \( \beta \) is decay rate, and \( \gamma \) is a constant offset higher for La-doped batteries.
Discussion
The incorporation of lanthanum into lead-calcium grid alloys profoundly impacts battery energy storage system performance. Mechanistically, lanthanum alters the oxide film morphology on grid surfaces. During anodic polarization, it suppresses the growth of non-adherent PbO\(_2\) layers, reducing active material shedding. Instead, it fosters dendritic or branched oxide structures that enhance electrical contact and mechanical bonding. This explains the improved charge acceptance and cycle life, as corroborated by metallurgical analyses showing refined grain boundaries and increased interfacial strength.
Furthermore, lanthanum’s influence on electrochemical kinetics can be described using Butler-Volmer equations for corrosion and charge transfer. For a La-doped electrode, the exchange current density \( i_0 \) increases, lowering polarization losses:
$$ i = i_0 \left[ \exp\left(\frac{\alpha_a F \eta}{RT}\right) – \exp\left(-\frac{\alpha_c F \eta}{RT}\right) \right] $$
where \( i \) is current, \( \alpha_a \) and \( \alpha_c \) are transfer coefficients, \( F \) is Faraday’s constant, \( \eta \) is overpotential, \( R \) is gas constant, and \( T \) is temperature. Enhanced \( i_0 \) facilitates faster ion diffusion, beneficial for high-rate operations in a battery energy storage system.
The slight initial capacity reduction is offset by long-term gains, making La-doped batteries ideal for applications prioritizing durability over peak capacity. In the context of renewable integration, where battery energy storage systems face irregular charge-discharge patterns, such alloys offer resilience against capacity fade. Our rolling process optimization also underscores the importance of manufacturing parameters in tailoring alloy properties for specific battery energy storage system requirements.
Conclusion
Our investigation demonstrates that doping lead-calcium grid alloys with lanthanum significantly enhances the performance of lead-acid battery energy storage systems. While initial capacity experiences a minor decrease, improvements in charge acceptance, high- and low-temperature discharge capability, cycle life, and operational reliability are substantial. The La-doped batteries maintained superior functionality in embedding tests within a thermal network UPS, supporting automation controls well beyond conventional batteries. These benefits arise from microstructural modifications that strengthen grid-active material interfaces and inhibit degradation mechanisms.
Future work should explore synergistic effects with other rare-earth elements, scale-up production techniques, and integration into larger battery energy storage system architectures. Overall, lanthanum-doped alloys present a viable path toward more robust and efficient energy storage solutions, aligning with global efforts to modernize grid infrastructure and support sustainable energy systems.