Semi-Solid-State Battery Breaks Through the 100,000-Yuan Market, SAIC MG4 Launches New Era at 99,800 Yuan

SMM September 16 News:

Key points: [NCM sulfide electrolyte/Ag@C] NCM, sulfide electrolyte, and Ag@C respectively represent the positive electrode material, electrolyte, and negative electrode structure in solid-state batteries. Their combination is one of the core directions in the current research and development of high-energy-density batteries.

In all-solid-state battery technology, the combination of using NCM (nickel-cobalt-manganese) as the cathode material, sulfide as the electrolyte, and Ag@C (silver-coated carbon) as the anode material is a common configuration. This combination leverages the high ionic conductivity of sulfide electrolytes and the high capacity and stability of silver-coated carbon anodes. According to search results, the combination of sulfide electrolytes and NCM cathode materials reacts at high temperatures, generating a large amount of SO₂ accompanied by a massive release of heat. This reaction is referred to as the gas-solid reaction failure pathway. Additionally, both sulfide electrolytes and NCM811 exhibit significant exothermic reactions. Among them, Li₃PS₄ and Li₇P₃S₁₁ start to react at 200°C, and under rapid heating conditions, NCM811 + sulfide solid electrolytes can undergo deflagration. These characteristics indicate that this combination has potential application prospects in all-solid-state batteries, but at the same time, in-depth research and optimization of safety are required.

I. NCM (Lithium Nickel Cobalt Manganese Oxide)
NCM is a high-nickel ternary cathode material with the general formula LiNiₓCoᵧMn₁₋ₓ₋ᵧO₂, where x is typically ≥0.6 (e.g., NCM622, NCM811), and it has core advantages.
1. High Energy Density: When the nickel content exceeds 80%, the theoretical capacity can reach 200-210 mAh/g, which is more than 50% higher than traditional LFP.
2. High Working Voltage: The average discharge voltage is about 3.7-3.8 V. When matched with a sulfide electrolyte, the battery energy density can reach 300-450 Wh/kg.
3. Cost Efficiency: The cobalt content is reduced (e.g., only 10% in NCM811), resulting in a cost reduction of about 30% compared to NCM111.
However, NCM faces interfacial issues when in direct contact with sulfide electrolytes:
1. Chemical Side Reactions: High-nickel NCM can oxidize sulfide electrolytes (e.g., Li₆PS₅Cl) at high voltages (>4.2 V), producing high-impedance products such as Li₂SO₄ and P₂S₅, leading to a sharp increase in interfacial resistance (up to thousands of Ω·cm²).
2. Volume Expansion: NCM undergoes a volume change of about 10-15% during charge and discharge. Contact with rigid sulfide electrolytes can generate mechanical stress, causing interfacial delamination.

II. Sulfide Electrolytes
Sulfide electrolytes are a class of solid-state electrolytes with sulfur as the primary anion. Typical examples include:
1. Argyrodite-Type (e.g., Li₆PS₅Cl): Room-temperature ionic conductivity as high as 10⁻³-10⁻² S/cm, close to that of liquid electrolytes, and soft texture (Young's modulus 20-30 GPa), ensuring good contact with electrode interfaces.
2. LGPS-Type (e.g., Li₁₀GeP₂S₁₂): Through element doping (e.g., Sb⁵⁺, O²⁻), ionic conductivity can be further increased to 25 mS/cm, and air stability is enhanced (20-fold improvement at -10°C dew point).
Their core advantages are:
1. Ultra-High Ionic Conductivity: Three-dimensional lithium-ion transport channels (e.g., the "48h-16e-48h" path in Li₅.₅PS₄.₅Cl₀.₇₅Br₀.₇₅) ensure fast charging and discharging, supporting 20C rates (full charge in 10 minutes).
2. High Safety: No liquid electrolytes, thermal decomposition temperature >200°C, passing nail penetration tests (no open flame) and hot box tests (no explosion at 130°C). However, sulfide electrolytes face the following challenges:
1. Air sensitivity: They readily react with water to generate H₂S gas (e.g., Li₆PS₅Cl + H₂O → LiOH + Li₂SO₄ + H₂S↑), requiring production in an inert gas environment with a dew point ≤ -40°C.
2. Interfacial stability: When in contact with NCM cathodes, transition metal ions (e.g., Ni²⁺) catalyze sulfide decomposition, forming an insulating space charge layer (SCL) that impedes ion transport.

III. Ag@C (Silver-Carbon Core-Shell Structure)
Ag@C is a composite functional material formed by encapsulating silver nanoparticles (AgNPs) in a carbon matrix to create a core-shell structure. Its functions include: anode host + volume buffering
1. Anode host:
1.1 Lithium deposition guidance: Ag’s high electrical conductivity (6.3×10⁷ S/m) and low nucleation barrier (0.12 eV) promote uniform lithium deposition and suppress dendrite growth. Samsung SDI’s Ag@C composite anode demonstrated >90% capacity retention after 1,000 cycles and a critical current density of 10 mA/cm².
1.2 Volume buffering: The carbon matrix (e.g., graphene, carbon nanotubes) accommodates lithium metal volume expansion (200%), reducing interfacial stress.
2. Interfacial modification:
2.1 Cathode-side application: Ag@C can serve as a surface coating on NCM, reducing interfacial impedance through Ag’s catalytic effect. For example, the interfacial resistance of Ag@C-modified NCM811 with Li₆PS₅Cl decreased from 800 Ω·cm² to 150 Ω·cm².
2.2 Electrolyte modification: Adding Ag@C to sulfide electrolytes (e.g., Li₆PS₅Cl/Ag@C composite) enhances electronic insulation (preventing internal short circuits) and improves mechanical strength (puncture resistance >50 N/cm).

IV. Synergistic Mechanism
1. Interface optimization between NCM and sulfide electrolyte
Surface coating: Coating NCM with a LiNbO₃-Li₃BO₃ composite layer (thickness ≤10 nm) leverages LiNbO₃’s high ionic conductivity (10⁻⁶ S/cm) and Li₃BO₃’s chemical stability to suppress sulfide decomposition. For instance, the SC-Ni92@LiNbO₃-Li₃BO₃/Li₆PS₅Cl battery exhibited 88.4% capacity retention after 100 cycles at 1C and a discharge capacity of 150.1 mAh/g at a 5C rate. Sulfide Coating: A sulfide layer (e.g., Li₂S-P₂S₅) is formed on the NCM surface via low-temperature solid-state method, blocking direct contact and mitigating the space charge layer effect. The SC-Ni90-0.2%S/Li₆PS₅Cl battery exhibited a capacity retention of 87% after 500 cycles at 1C, with an areal capacity of 11.44 mAh/cm².

2. Role of Ag@C in the Anode
Lithium Metal Deposition Regulation: Ag@C serves as a current collector coating, where AgNPs preferentially form Ag-Li alloy (Li₃Ag) with lithium, guiding uniform lithium growth along carbon matrix pores and preventing dendrite penetration. Samsung SDI's Ag@C composite anode demonstrated a Coulombic efficiency >99.8% after 1,000 cycles at a volumetric energy density of 900 Wh/L.

Side Reaction Suppression: The carbon matrix adsorbs sulfur species (e.g., S²⁻) generated from sulfide decomposition, reducing Li₂S deposition and extending battery life. The Ag@C/Li₆PS₅Cl/Li symmetric cell stably cycled for over 1,000 hours at a current density of 1 mA/cm².

V. Typical Battery Structure and Performance
1. Cathode: NCM811@LiNbO₃-Li₃BO₃
Design: Monocrystalline NCM811 coated with a 10 nm thick LiNbO₃-Li₃BO₃ composite layer to enhance interfacial stability.
Performance: When paired with Li₆PS₅Cl electrolyte, the battery showed >85% capacity retention after 500 cycles at 4.3 V high voltage, with an energy density of 350 Wh/kg.

2. Electrolyte: Li₆PS₅Cl/Ag@C Composite Material
Preparation: Ag@C (5 wt%) dry-mixed with Li₆PS₅Cl and hot-pressed into form, thickness 20 μm.
Performance: Room-temperature ionic conductivity of 1.2×10⁻² S/cm, bending modulus increased from 25 GPa to 38 GPa, and puncture resistance improved by 40%.

3. Anode: Ag@C/Li Metal Composite Structure
Process: Ag@C layer (thickness 5-10 μm) deposited on copper foil, followed by electrochemical deposition to form a lithium metal layer (thickness 20 μm).
Performance: Critical current density of 12 mA/cm², lithium dendrite penetration time >1,000 hours after 1,000 cycles, and volumetric energy density of 942 Wh/L.

VI. Industrialisation Progress and Challenges
Top-Tier Enterprise Layout: Samsung SDI + CATLSamsung SDI: The sulfide battery with Ag@C composite anode has entered the pilot stage, with mass production planned for 2027, offering an energy density of 900 Wh/L and supporting an EV driving range of 800 km.
CATL: Developing an NCM@LiNbO₃/Li₆PS₅Cl battery, with samples to be launched in 2025 and a cycle life exceeding 2,000 cycles.
Technical Bottlenecks: Cost + Low-Temperature Performance
Cost Control: Lithium sulfide (Li₂S) prices are as high as $150/kg, and Ag@C material costs are approximately $80/kWh. Scaling up production (e.g., dry coating) is required to reduce costs below $100/kWh.
Low-Temperature Performance: The ionic conductivity of sulfide electrolytes drops to 10⁻⁴ S/cm at -20°C, necessitating optimization via nanocomposites (e.g., Li₆PS₅Cl/Al₂O₃) or plasticizers (e.g., ionic liquids).
Future Directions:
Material Innovation: Developing cobalt-free NCM (e.g., LiNiO₂) and all-sulfide cathodes (e.g., Li₂S/FeS₂) to further increase energy density beyond 500 Wh/kg.
Process Breakthrough: Adopting roll-to-roll dry stacking technology to enhance sulfide battery production speed from 0.5 m/min to 5 m/min and yield from 65% to 95%.
Summary: The combination of NCM sulfide electrolyte/Ag@C is the mainstream direction in current solid-state battery R&D. Leveraging NCM's high energy density, sulfide's high ionic conductivity, and Ag@C's interface regulation, overall battery performance can be comprehensively improved. Despite challenges in interface stability and cost, breakthroughs in material design and process innovation are expected to enable large-scale commercialization by 2030, driving revolutionary changes in the EV and ESS sectors. According to SMM forecasts, all-solid-state battery shipments are projected to reach 13.5 GWh by 2030, with semi-solid-state battery shipments at 160 GWh.

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Contact: Chaoxing Yang. Thank you!