In the evolving landscape of automotive technology, particularly with the trend of younger truck drivers and diversified demands for in-vehicle electrical appliances, the performance and technical requirements for vehicle starting batteries are continuously increasing. The traditional lead-acid battery, while widely used, faces several pain points: poor cold-start performance in low-temperature environments, prolonged cold-start times, inability to support high-power parking electrical systems like long-duration parking air conditioning, short battery life leading to frequent vehicle maintenance, high whole-lifecycle battery costs, and significant volume and weight. These issues negatively impact vehicle layout, lightweight design, and overall operating costs. As a potential successor, the li-ion battery offers high energy density, low self-discharge rates, and a lifespan comparable to that of the vehicle, potentially eliminating replacements during service and reducing maintenance and usage costs significantly. In this article, I will explore the feasibility of li-ion batteries as starting power sources through preliminary testing and analysis of engine starting performance, providing data support for such applications. I find that li-ion batteries can be suitable for starting power in southern regions with moderate temperatures, but performance may be insufficient in extremely low temperatures (below -30°C), where battery insulation techniques could enhance capability. Overall, the li-ion battery shows promise in replacing lead-acid batteries for vehicle starting systems.
The power supply system in a vehicle typically consists of the battery, generator, regulator, and status indicators (such as an ammeter or charge indicator light), functioning to provide low-voltage direct current to all electrical devices. In commercial vehicles, the power source is a parallel arrangement of the generator (or DCDC in new energy vehicles) and the battery. The battery’s role is crucial: it supplies power to the starter motor, ignition system, and other key electrical devices during engine startup; it provides energy to various electrical loads when the engine is off or running at low speeds; it assists the generator when electrical demand exceeds the generator’s capacity; and it stabilizes system voltage, acting as a large capacitor to absorb transient overvoltages and protect electrical equipment.
Currently, the vast majority of commercial vehicles rely on lead-acid batteries for this purpose. Common parameters for lead-acid batteries are summarized in Table 1, where products 1-3 are primarily used in light-duty vehicles and passenger cars, while products 4-5 are geared towards medium and heavy-duty commercial vehicles. Their energy density generally ranges from 40 to 55 Wh/kg, making them relatively bulky. Warranty life is typically around one year, and for vehicles stored for extended periods, regular charging maintenance is required every two months at most.
| Item | Lead-Acid Battery (12V) – Product 1 | Lead-Acid Battery (12V) – Product 2 | Lead-Acid Battery (12V) – Product 3 | Lead-Acid Battery (12V) – Product 4 | Lead-Acid Battery (12V) – Product 5 | Li-ion Battery (System Level) |
|---|---|---|---|---|---|---|
| Capacity (Ah) | 55 | 65 | 90 | 180 | 240 | Varies (e.g., 1.5 kWh pack) |
| Volume (L) | 7.4 | 7.4 | 10.4 | 22.5 | 30.5 | Lower for equivalent energy |
| Energy Density (Wh/kg) | 45.2 | 50.6 | 51.4 | 52.7 | 40.6 | 80–200 (system) |
| Reference Price (USD approx.) | ~25 | ~28 | ~42 | ~70 | ~210 | ~100–140 per kWh (system) |
| Warranty Life | 8 months–1 year | 8 months–1 year | 8 months–1 year | 8 months–1 year | 8 months–1 year | 5–8 years or more |
| Annualized Cost per kWh (USD approx.) | 35–42 | 35–42 | 35–42 | 35–42 | 35–42 | 14–28 |
| Cycle Life (cycles) | ~300 | ~300 | ~300 | ~300 | ~300 | 2500–10000 |
| Self-Discharge Rate (% per month) | 25–30 | 25–30 | 25–30 | 25–30 | 25–30 | 3–5 |
| Environmental Impact | Lead pollution | Lead pollution | Lead pollution | Lead pollution | Lead pollution | More environmentally friendly |
| Temperature Adaptability | Strong (-40°C to 70°C) | Strong (-40°C to 70°C) | Strong (-40°C to 70°C) | Strong (-40°C to 70°C) | Strong (-40°C to 70°C) | Poor at extreme temperatures |
| Optimal Operating Temperature | -40°C to 70°C | -40°C to 70°C | -40°C to 70°C | -40°C to 70°C | -40°C to 70°C | -20°C to 55°C |
| Memory Effect | Present | Present | Present | Present | Present | Absent |
| Safety | Good | Good | Good | Good | Good | Slightly inferior (requires BMS) |
| Maintenance Cost | High | High | High | High | High | Essentially maintenance-free |
Lead-acid batteries and li-ion batteries represent two distinct electrochemical systems. The lead-acid battery uses lead oxide and metallic lead as electrode materials with a concentrated sulfuric acid electrolyte, making it an inorganic system. In contrast, a li-ion battery comprises four main components: cathode (lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, or ternary materials), anode (graphite), separator, and electrolyte (organic solvent with lithium salts). This structural divergence leads to significant performance differences. Compared to lead-acid batteries, the li-ion battery offers advantages such as higher energy density, longer cycle life, and lower self-discharge, but it faces challenges in safety, low-temperature performance, and rate capability at extremes.
Currently, lithium prices have fallen noticeably, with cell quotes potentially controlled below 400 CNY/kWh or even 300 CNY/kWh. System prices for power li-ion batteries can be kept within 600–800 CNY/kWh, diminishing the price advantage of lead-acid batteries at 250–300 CNY/kWh. The cycle life of a li-ion battery is markedly superior: it can achieve 2500 to over 7000 cycles, whereas a lead-acid battery typically manages only 300–500 cycles. This longevity allows for extended warranty periods, often 5–8 years or even over 10 years, compared to about one year for lead-acid batteries. The long lifespan of a li-ion battery substantially reduces maintenance and usage costs when deployed as a starting power source.
Energy density is another key metric: lead-acid batteries offer 45–50 Wh/kg, while li-ion battery cells can reach up to 300 Wh/kg, and pack-level energy density can exceed 160 Wh/kg. For the same energy capacity, a li-ion battery system is significantly smaller and lighter, contributing to vehicle lightweighting and flexible system layout.
Moreover, the li-ion battery boasts a low self-discharge rate, typically 3–5% per month, compared to 25–30% per month for lead-acid batteries. This characteristic alleviates issues of battery depletion and starting difficulties in vehicles left idle for extended periods. However, the li-ion battery has drawbacks: its organic electrolyte raises safety concerns, and low-temperature and high-rate performance are inferior to lead-acid. To ensure lifespan and safety, a sophisticated Battery Management System (BMS) is required to control operating temperature, voltage, and current within appropriate ranges. This must be carefully considered when designing a li-ion starting power system.
To evaluate the starting performance, I conducted tests by placing a vehicle (equipped with an MC13 engine) in a climate chamber set to -30°C, -10°C, and 0°C. After sufficient soak time, I connected a 180 Ah/24 V lead-acid battery and a lithium titanate battery (1.5 kWh/25.3 V; peak discharge rate: 50C at room temperature, 15C at -20°C, 8C at -40°C) for starting tests, monitoring output current and voltage during cranking. The results, summarized in Table 2, show that the lead-acid battery started successfully at temperatures down to -30°C, while the high-rate lithium titanate li-ion battery failed at -30°C due to a rapid voltage drop to single-digit levels under high-current discharge in cold conditions, failing to meet starting requirements. This data indicates technical requirements for commercial vehicle starting power sources: (1) operating voltage range of 18–36 V; (2) battery voltage must not fall below 18 V during cranking; and (3) peak starting current at -30°C should not be less than 1023 A.
| Battery Type | Ambient Temperature | Starting Outcome | Starting Duration (s) | Peak Characteristics | Voltage Drop Pre/Post Start (mV) |
|---|---|---|---|---|---|
| Lead-Acid Battery (180 Ah/24 V) | -40°C | Failure | – | 280 A, 1.2 kW, voltage drops rapidly to 2 V | – |
| -30°C | Success | 6.83 | 1023 A, 14.5 kW | 375 | |
| 0°C | Success | 1.5 | 280 A, 6.17 kW | 0 | |
| Lithium Titanate Li-ion Battery (1.5 kWh/25.3 V) | -40°C | Failure | – | 5 V, 400 A, voltage and current drop within 4 s | – |
| -30°C | Failure | – | 950 A, 14.5 kW, voltage drops sharply | – | |
| 0°C | Success | 3.5 | 410 A, 9.2 kW | 500 |
I collected current and voltage data from the lead-acid battery during engine starts at -30°C and 0°C to analyze the feasibility of using li-ion batteries for starting applications. For cold-start analysis, I transformed the operational data to test li-ion battery performance, focusing on whether li-ion batteries could serve as starting power for northern versions (minimum ambient temperature -30°C) and southern versions (minimum ambient temperature -10°C). Meeting low-temperature cold-cranking requirements is critical. Among various li-ion battery types, ternary lithium batteries (NCM) exhibit the best low-temperature performance. Thus, I selected a high-rate ternary li-ion battery for testing, with cell parameters listed in Table 3.
| Parameter | Value |
|---|---|
| Cathode Material | NCM111 |
| Anode Material | Graphite |
| Operating Voltage Range (V) | 2.7–4.1 (short-term 2.5–4.1 at low temperature) |
| Discharge Rate (C) at -30°C, 2s pulse | 34 (100% SOC), 12 (50% SOC), 8 (30% SOC) |
| Discharge Rate (C) at 0°C, 2s pulse | 47 (100% SOC), 25 (50% SOC), 20 (30% SOC) |
For northern versions, the starting power source must operate at -30°C or lower. Considering that battery insulation blankets could be installed in extremely cold environments to maintain temperature above -30°C after soaking at -35°C for 12 hours, I tested starting performance only at -30°C. The results are in Table 4. Using high-rate ternary li-ion batteries, when the State of Charge (SOC) drops below 30%, even a 7.15 kWh pack fails to meet starting requirements. However, with SOC maintained above 50%, a 4.468 kWh pack suffices. To ensure reliable starting, lead-acid batteries typically reserve about 60% capacity; from Table 4, a li-ion starting power source also needs to reserve 50% or more capacity. Overall, applying li-ion batteries as low-temperature starting power in northern regions presents significant challenges.
| Post-Start Cut-off Voltage @ -30°C | 100% SOC | 50% SOC | 30% SOC | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Pack Capacity (kWh) | 1.787 | 2.681 | 3.574 | 4.468 | 5.361 | 4.468 | 5.361 | 6.25 | 7.15 | |
| Cell Voltage (V) | 2.53 | 2.69 | 2.78 | 2.54 | 2.58 | 2.17 | 2.25 | 2.28 | 2.34 | |
| Pack Voltage (V) | 17.71 | 18.83 | 19.46 | 17.78 | 18.06 | 15.19 | 15.75 | 15.96 | 16.38 | |
For southern versions, the starting power source needs to function in environments as low as -10°C to 0°C. With possible insulation to elevate battery temperature, I tested performance at 0°C, with results in Table 5. The ternary li-ion battery excels as a southern starting power source: with capacity as low as 0.357 kWh and SOC ranging from 30% to 100%, it meets starting requirements. In practice, reserving only 30–40% capacity can ensure sufficient starting energy.
| Post-Start Cut-off Voltage @ 0°C | 100% SOC | 50% SOC | 30% SOC | |||
|---|---|---|---|---|---|---|
| Pack Capacity (kWh) | 0.179 | 0.357 | 0.179 | 0.357 | 0.179 | 0.357 |
| Cell Voltage (V) | 2.99 | 3.33 | 2.61 | 2.97 | 2.41 | 2.85 |
| Pack Voltage (V) | 20.93 | 23.31 | 18.27 | 20.79 | 16.87 | 19.95 |
To further quantify performance, I can use mathematical models. The discharge behavior of a li-ion battery can be approximated by the equivalent circuit model, where the terminal voltage \( V \) under load is given by:
$$ V = OCV(SOC, T) – I \cdot R_{int}(SOC, T) $$
Here, \( OCV \) is the open-circuit voltage dependent on SOC and temperature \( T \), \( I \) is the discharge current, and \( R_{int} \) is the internal resistance, also a function of SOC and \( T \). For cold cranking, the peak current \( I_{peak} \) must satisfy:
$$ I_{peak} \geq \frac{T_{crank} \cdot C_{req}}{\Delta t} $$
where \( T_{crank} \) is the cranking torque requirement, \( C_{req} \) is a constant related to engine displacement and compression, and \( \Delta t \) is the cranking duration. The li-ion battery’s ability to deliver high current at low temperatures is limited by increased internal resistance, which follows an Arrhenius-type relationship:
$$ R_{int}(T) = R_0 \cdot e^{\frac{E_a}{k} \left( \frac{1}{T} – \frac{1}{T_0} \right)} $$
where \( R_0 \) is resistance at reference temperature \( T_0 \), \( E_a \) is activation energy, and \( k \) is Boltzmann’s constant. This explains why li-ion battery performance degrades in extreme cold.
The energy density advantage of li-ion batteries can be expressed as:
$$ \text{Specific Energy} = \frac{E}{m} \approx \frac{n \cdot F \cdot V_{avg}}{M} $$
where \( E \) is energy, \( m \) is mass, \( n \) is number of electrons transferred per mole, \( F \) is Faraday’s constant, \( V_{avg} \) is average cell voltage, and \( M \) is molar mass of active materials. For a li-ion battery with NCM cathode and graphite anode, \( V_{avg} \approx 3.7 \, \text{V} \), yielding higher specific energy than lead-acid (\( V_{avg} \approx 2.0 \, \text{V} \)).
Cycle life of a li-ion battery is often modeled using empirical degradation laws, such as:
$$ Q_{loss} = A \cdot e^{-\frac{E_a}{kT}} \cdot t^z $$
where \( Q_{loss} \) is capacity loss, \( A \) is a pre-exponential factor, \( t \) is time or cycles, and \( z \) is an exponent. This underscores the longevity of li-ion batteries compared to lead-acid.
In designing a li-ion starting battery system, key considerations include thermal management to mitigate low-temperature issues. For instance, using a heating element integrated with the BMS can maintain optimal temperature. The power required for heating can be estimated:
$$ P_{heat} = \frac{m \cdot c_p \cdot \Delta T}{t_{heat}} $$
where \( m \) is battery mass, \( c_p \) is specific heat capacity, \( \Delta T \) is temperature rise, and \( t_{heat} \) is heating time. This adds complexity but enhances low-temperature performance of the li-ion battery.
Another aspect is the cost analysis over the vehicle’s lifecycle. The total cost of ownership (TCO) for a starting battery can be calculated as:
$$ TCO = C_{initial} + \sum_{i=1}^{N} C_{maintenance,i} + C_{replacement} $$
For lead-acid, \( N \) is number of replacements over vehicle life (e.g., every 2–3 years), while for li-ion, \( N \) may be zero if it lasts the vehicle’s lifetime. Given falling li-ion battery prices, TCO favors li-ion batteries in many scenarios.
Safety protocols for li-ion batteries necessitate a BMS with functions like overcharge protection, over-discharge protection, short-circuit protection, and thermal runaway prevention. The BMS ensures cell balancing, described by:
$$ \Delta V_{cell} = \frac{I_{bal} \cdot t}{C_{cell}} $$
where \( \Delta V_{cell} \) is voltage difference, \( I_{bal} \) is balancing current, \( t \) is time, and \( C_{cell} \) is cell capacity. Proper BMS design is crucial for reliable li-ion battery operation.
Self-discharge rates impact long-term storage. For a li-ion battery, the self-discharge current \( I_{sd} \) can be modeled as:
$$ I_{sd} = I_0 \cdot e^{-\frac{Q}{kT}} $$
where \( Q \) is activation energy for self-discharge reactions. The low self-discharge of li-ion batteries reduces maintenance needs.
In terms of application, for southern regions where temperatures rarely drop below -10°C, a li-ion starting battery with moderate capacity (e.g., 0.5–1 kWh) and SOC reservation of 30–40% appears feasible. For northern regions, larger capacities (above 4 kWh) and higher SOC reserves (50%+) are necessary, possibly coupled with insulation or heating. Advanced li-ion battery chemistries like lithium iron phosphate (LFP) or improved ternary systems may offer better low-temperature performance in the future.
To summarize, the li-ion battery presents a compelling alternative to lead-acid for vehicle starting applications due to its high energy density, long cycle life, and low self-discharge. However, challenges remain in extreme cold environments, where performance limitations necessitate careful system design. Through testing and analysis, I conclude that li-ion batteries are suitable for southern version starting power with minimal capacity reservation, while for northern versions, they require significant capacity boosts or supplemental thermal management. As technology advances and costs decline, the li-ion battery is poised to play a transformative role in automotive power systems, aligning with trends toward electrification and efficiency.