A lithium titanate ultra-low voltage safety battery, its preparation method, and a suitable electrode thickness measuring instrument.

Abstract

This invention provides an ultra-low voltage safety lithium titanate battery, its preparation method, and a suitable electrode thickness measuring instrument. The battery includes a positive electrode, a negative electrode, an electrolyte, and a composite separator. The positive electrode active material is a composite material of lithium iron phosphate and spinel lithium manganese oxide. The negative electrode active material is spinel-type lithium titanate. The electrolyte is a mixed solution of lithium bis(fluorosulfonyl)imide, a mixed solvent, and additives. The lithium titanate negative electrode of this invention has the advantages of zero-strain characteristics, excellent fast-charging performance, and long cycle life. Furthermore, the electrolyte and insulating layer further improve the battery's safety. The positive electrode of this invention, through bandgap matching design of lithium iron phosphate and spinel lithium manganese oxide, and by modifying the electrolyte, increases the ionic conductivity to over 9.8 mS / cm, achieving constant voltage output for the lithium titanate system. The battery of this invention can achieve 8C high-rate charge / discharge and 6-10 minute ultra-fast charging, while ensuring long cycle life, high safety, and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to lithium titanate batteries of 2.5V and below, their preparation methods, and preparation fixtures. Background Technology

[0002] Currently, the power sources widely used in portable electronic devices are mainly alkaline zinc-manganese primary batteries and nickel-metal hydride rechargeable batteries. Both types of batteries have significant drawbacks: the annual amount of discarded primary batteries exceeds 10 billion units, and the heavy metals they contain, such as mercury, cadmium, and lead, will pollute the soil and groundwater through leachate after landfilling, causing serious environmental pollution; nickel-metal hydride batteries have low energy density (≤120Wh / kg), high self-discharge rate (3-5% per month), poor low-temperature performance (capacity decay of over 40% at -20℃), and the risk of overcharge thermal runaway, making it difficult to meet the requirements for long-term stable use.

[0003] Although lithium-ion batteries have a significant advantage in energy density, the traditional lithium cobalt oxide / graphite system has inherent safety hazards. The thermal runaway temperature is below 180°C, the electrolyte is flammable, and lithium deposition at the negative electrode can easily cause internal short circuits, which cannot meet the intrinsic safety requirements.

[0004] Moreover, the existing batteries have insufficient fast charging capabilities, and regular charging takes more than 30 minutes. Forcibly shortening the charging time to within 15 minutes can easily cause lithium plating on the negative electrode and decomposition of the electrolyte, resulting in a sharp drop in battery cycle life. Furthermore, the high-rate discharge performance is poor. When discharging at an 8C rate, the polarization voltage exceeds 0.8V, the temperature rise exceeds 40℃, and the capacity retention rate is less than 70%, which cannot meet the demand for short-term, high-frequency discharge.

[0005] On the other hand, automotive power batteries (such as lithium titanate batteries), with the cooperation of cooling and management systems, exhibit excellent performance in fast charging and long range. However, there is zero tolerance for issues with ultra-low voltage small batteries without any third-party protection or coordination. Specifically, these issues manifest as follows:

[0006] ① No gas is allowed (as it can cause equipment deformation and leakage).

[0007] ② High self-discharge is not allowed (long standby time required)

[0008] ③ Low-temperature failure is not allowed (outdoor temperature control is not supported)

[0009] ④ Requires over 8000 ultra-long cycles.

[0010] ⑤ Requires absolute safety without BMS or cooling.

[0011] ⑥ Requires wide temperature stability from -30℃ to 60℃

[0012] ⑦ Requirements: low current, long-term static storage, and reliable float charging.

[0013] If the materials, electrolytes, structures, and processes of automotive power batteries are directly applied to ultra-low voltage small batteries of 2.5V and below, the defects that automotive batteries can tolerate will directly lead to fatal failures in small batteries: gas swelling, bulging, leakage, water leakage during cycles, low-temperature failure, starvation due to static storage, and interface passivation. Summary of the Invention

[0014] To address the shortcomings of existing technologies, this invention provides a lithium titanate ultra-low voltage safe battery and its preparation method, thereby solving the technical problems existing in the background technology.

[0015] To achieve the above objectives, the present invention adopts the following technical solution:

[0016] In a first aspect, the present invention provides a lithium titanate ultra-low voltage safety battery, comprising a positive electrode, a negative electrode, an electrolyte, and a composite separator; wherein...

[0017] The positive electrode includes a positive current collector and a positive active material coated on the positive current collector, and the negative electrode includes a negative current collector and a negative active material coated on the negative current collector.

[0018] The positive electrode active material is lithium iron phosphate. Lithium spinel manganese oxide Composite materials;

[0019] The aforementioned negative electrode active material employs high-purity spinel-type lithium titanate with precise spinel structure control; the spinel-type lithium titanate, after control, satisfies the following conditions: it has a pure cubic Fd-3m space group single-phase spinel structure, without... , Impurity phase; cell constant a is 0.8355–0.8365 nm, lithium-titanium molar ratio is 0.80–0.82; particle size D50 is 0.5–1.5 μm, particle size distribution Span≤1.0; charge-discharge lattice volume change rate is <0.3%, exhibiting zero strain characteristics;

[0020] The electrolyte is lithium hexafluorophosphate. A mixed solution of lithium bis(fluorosulfonyl)imide (LiFSI), mixed solvent, and additives;

[0021] The composite diaphragm is a polyolefin composite membrane.

[0022] The spinel-type lithium titanate is coated with in-situ nano-carbon, satisfying the following conditions: carbon coating thickness 1–3 nm, carbon content 1.5–3.0 wt% of the total mass of the anode material; forming a continuous and uniform conductive network; and intrinsic electronic conductivity ≥ S / cm.

[0023] The lithium titanate battery has two or more independent electrode groups sharing the electrolyte and the same casing. Each electrode group has 3 to 5 positive and negative electrode stacks, independent aluminum foil current collectors, and each leads out a micro tab. The composite separator between adjacent electrode groups is replaced with an ultra-thin ceramic separator of 5–12 μm. The tabs of adjacent electrode groups have different widths and / or thicknesses, so that different areas on the same negative electrode or the same group of negative electrodes have different conductivity / rate characteristics, which in turn makes the discharge speed of different areas inside the same electrode different.

[0024] Lithium titanate ultra-low voltage safety batteries using composite separators can also have one or more of the following optimization schemes:

[0025] ① The lithium iron phosphate mentioned above Lithium spinel manganese oxide The mass ratio is 7:3.

[0026] ② The mixed solvent is ethylene carbonate EC, dimethyl carbonate DMC, and diethyl carbonate DEC in a volume ratio of 3:4:3.

[0027] ③ The concentrations of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) are 1.1-1.5 mol / L.

[0028] ④ The additives are 2-8 wt% ethyl acetate (EA) and 2-3 wt% ethylene carbonate (VEC).

[0029] ⑤ The thickness of the polyolefin composite film is 7~16μm, comprising a polyolefin base film and a coating applied to the polyolefin base film; the polyolefin base film is a polypropylene (PP) base layer or a polyethylene (PE) base layer; the coating is... coating or The coating has a thickness of 1-4 μm.

[0030] ⑥ The lithium titanate battery further includes a cylindrical metal casing, the inner and outer surfaces of which are anodized to form a thickness of 10-15 μm. Insulating layer.

[0031] ⑦ The positive and negative current collectors are made of aluminum foil.

[0032] Secondly, the present invention provides a method for preparing an ultra-low voltage safety battery of lithium titanate, comprising the following steps:

[0033] S1) High-purity spinel-type lithium titanate with precisely controlled spinel structure is used as the negative electrode active material; the spinel-type lithium titanate, after control, satisfies the following: it has a pure cubic Fd-3m space group single-phase spinel structure, without... , Impurity phase; cell constant a controlled between 0.8355 and 0.8365 nm, lithium-titanium molar ratio controlled between 0.80 and 0.83; particle size D50 between 0.5 and 1.5 μm, particle size distribution Span ≤ 1.0; charge-discharge lattice volume change rate < 0.2%, possessing zero strain characteristics;

[0034] S2) Mix the negative electrode active material, conductive carbon black, dispersant, and negative electrode binder PVDF according to a certain mass ratio, add NMP and stir to prepare a negative electrode slurry with a viscosity of 2000~4000mPa·s;

[0035] S3) Mix the positive electrode active material, conductive carbon black, and positive electrode binder PVDF according to a certain mass ratio, add NMP and stir to prepare a positive electrode slurry with a viscosity of 3000~5000mPa·s;

[0036] S4) The negative electrode slurry and the positive electrode slurry are coated on the negative electrode current collector and the positive electrode current collector respectively. Then, they are dried in an oven with a temperature gradient of 80℃-120℃-90℃ and then rolled. Finally, they are cut to obtain the negative electrode sheet and the positive electrode sheet.

[0037] S5), then the negative electrode, composite separator, and positive electrode are wound into a cylindrical or flat cell; installed in a metal casing, and the tabs and top cover are welded; then the electrolyte is injected, sealed and left to stand for 12~24 hours to obtain a lithium titanate battery.

[0038] Preferably, in step S1), the spinel-type lithium titanate is first modified by in-situ surface nano-carbon coating, with a carbon coating layer thickness of 1-3 nm and a carbon content accounting for 1.5-3.0 wt% of the total mass of the negative electrode material; and it satisfies the requirement of forming a continuous and uniform conductive network, and the intrinsic electronic conductivity of the material is ≥ S / cm.

[0039] Preferably, in step S2), the negative electrode active material is spinel-type titanate.

[0040] Preferably, in step S3), the positive electrode active material is lithium iron phosphate. Lithium spinel manganese oxide The composite material, namely lithium iron phosphate Lithium spinel manganese oxide The mass ratio is 7:3.

[0041] Preferably, in step S4), the negative electrode current collector and the positive electrode current collector aluminum foil; the negative electrode slurry coating thickness is 50-100μm and the areal density is 10-20mg / cm².

[0042] The thickness of the positive electrode slurry coating is 70-110 μm; the areal density is 15-30 mg / cm².

[0043] Preferably, in step S5), the thickness of the polyolefin composite film is 7-16 μm, comprising a polyolefin base film and a coating applied to the polyolefin base film; the polyolefin base film is a polypropylene (PP) base layer or a polyethylene (PE) base layer; the coating is... coating or The coating has a thickness of 1-4 μm.

[0044] Preferably, in step S5), the electrolyte is lithium hexafluorophosphate. A mixed solution of lithium bis(fluorosulfonyl)imide (LiFSI), mixed solvent, and additives.

[0045] Preferably, in step S5), the lithium hexafluorophosphate The concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 1.1~1.5 mol / L;

[0046] The mixed solvent is ethylene carbonate EC, dimethyl carbonate DMC, and diethyl carbonate DEC in a volume ratio of 3:4:3;

[0047] The additives are 2-8 wt% ethyl acetate (EA) and 2-3 wt% ethylene carbonate (VEC).

[0048] The beneficial effects of this invention are as follows:

[0049] 1. The lithium titanate anode of the present invention has the advantages of zero strain characteristics, excellent fast charging performance, and long cycle life, and lithium titanate... It has a zero-strain spinel structure, a lattice change rate of <0.2%, and a lithium insertion / extraction potential as high as [missing information]. It has a potential much higher than the reduction decomposition potential of the electrolyte, which can fundamentally avoid SEI film rupture, lithium dendrite growth, and electrolyte oxidation side reactions. It also possesses physical and chemical inertness such as high temperature resistance, corrosion resistance, and non-oxidation. Furthermore, it is compatible with electrolytes and... The insulating layer further enhances the safety of the battery;

[0050] 2. The positive electrode of this invention achieves constant voltage output of lithium titanate system by using a band-matching design between lithium iron phosphate and spinel lithium manganese oxide and modifying the electrolyte to increase the ionic conductivity to 9.8 mS / cm.

[0051] 3. This invention utilizes a mixed solvent, combined with a high concentration of 1.1-1.5 mol / L. LiFSI electrolyte enhances ion concentration and migration rate;

[0052] 4. The battery of the present invention can achieve 8C high-rate discharge and 6-10 minute fast charging, while ensuring long cycle life, high safety and environmental protection.

[0053] 5. The electrode thickness measuring instrument of this invention adopts a non-contact air-float support, which is compatible with LTO soft electrodes, eliminating scratches, material loss, and local compaction anomalies, thus overcoming the defects of support structures that easily damage the electrodes. Wide-spot laser thickness measurement effectively suppresses surface roughness interference, resulting in more stable thickness measurements with no data jumps or distortions, achieving an accuracy of ±0.1μm. Visual sub-pixel edge positioning is employed, with an edge positioning error ≤0.5mm, accurately locking the effective coating area and avoiding interference from abnormal edge data, improving overall detection accuracy. Full-width reciprocating scanning achieves full coverage detection in the electrode width direction, with no blind spots or missed measurements, ensuring electrode thickness consistency. Real-time hot thickness compensation eliminates measurement deviations caused by high temperatures during gradient drying, achieving high-precision detection under hot conditions. Through closed-loop thickness control, real-time judgment, automatic alarm, and feedback adjustment of coating parameters ensure stable electrode thickness from the source, solving the stringent requirements of low-voltage small batteries (zero gas expansion, high consistency, and long cycle life) that automotive equipment cannot meet. Attached Figure Description

[0054] Figure 1 The voltage-time curve of the battery prepared in Example 1 of this invention during the 8C fast charging process;

[0055] Figure 2 The discharge curve of the battery prepared in Example 1 of this invention at a 2C rate is shown.

[0056] Figure 3 The capacity retention rate trend of the battery prepared in Example 1 of the present invention during 8C fast charging and 2C discharge cycles is shown in the figure.

[0057] Figure 4 This is a schematic diagram of the structure of the 1450 cylindrical LFP-LTO system battery of the present invention;

[0058] Figure 5 This is a schematic diagram of the flat LFP-LTO battery system of the present invention;

[0059] Figure 6 This is a flowchart of the electrode thickness detection system. Detailed Implementation

[0060] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0061] Example 1

[0062] This embodiment provides a method for preparing an ultra-low voltage safety lithium titanate battery, including the following steps:

[0063] S1) Spinel-type lithium titanate is first modified by in-situ surface coating with nano-carbon, with a carbon coating thickness of 3 nm and a carbon content accounting for 2.5 wt% of the total mass of the anode material; and it satisfies the requirement of forming a continuous and uniform conductive network, and the intrinsic electronic conductivity of the material is ≥ S / cm.

[0064] S2) High-purity spinel-type lithium titanate with precisely controlled spinel structure is used as the negative electrode active material; the spinel-type lithium titanate, after control, satisfies the following: it has a pure cubic Fd-3m space group single-phase spinel structure, without... , Impurity phase; cell constant a controlled between 0.8355 and 0.8365 nm, lithium-titanium molar ratio controlled between 0.80 and 0.82; particle size D50 between 0.5 and 1.5 μm, particle size distribution Span ≤ 1.0; charge-discharge lattice volume change rate ∈ (0.2%, 0.3%), possessing zero strain characteristics.

[0065] S3) Mix spinel lithium titanate, conductive carbon black SP and polyvinylidene fluoride PVDF in a mass ratio of 92:4:4, add NMP, and stir under vacuum until the viscosity is 2500 mPa·s to obtain the negative electrode slurry.

[0066] S4), lithium iron phosphate is mixed in a mass ratio of 93:3:4. Lithium spinel manganese oxide The composite material, conductive carbon black SP, and polyvinylidene fluoride PVDF were mixed and vacuum stirred until the viscosity reached 2000 mPa·s to obtain the positive electrode slurry.

[0067] S5) The negative electrode slurry is coated on an aluminum foil with a thickness of 12μm, with a double-sided coating thickness of 180μm and an areal density of 18mg / cm².

[0068] The positive electrode slurry was coated onto an aluminum foil with a thickness of 12 μm, and the double-sided coating thickness was 190 μm with an areal density of 23 mg / cm².

[0069] Then, after drying in an oven using a temperature gradient of 80℃-120℃-90℃, the electrode undergoes roll pressing. The negative electrode has a roll pressing density of 2.0 g / cc and a porosity of 38%; the positive electrode has a roll pressing density of 2.55 g / cc and a porosity of approximately 28%.

[0070] Then, the negative electrode and the positive electrode are obtained by cutting; the size of the negative electrode is 48mm×38mm; the size of the positive electrode is 46mm×36mm.

[0071] S4) The negative electrode, composite separator, and positive electrode are wound into a cylindrical battery cell; the cell is installed in a metal casing, and the tabs and top cover are welded together; then the electrolyte is injected, and the cell is sealed and left to stand for 12-24 hours to obtain a lithium titanate battery.

[0072] The composite membrane has a thickness of 12 μm; the electrolyte is 1.2 mol / L lithium hexafluorophosphate. A mixed solution of lithium bis(fluorosulfonyl)imide (LiFSI), a mixed solvent, and additives; wherein the mixed solvent is ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a volume ratio of 3:4:3.

[0073] The additives are 2-8 wt% ethyl acetate (EA) and 2-3 wt% ethylene carbonate (VEC).

[0074] The capacity is 565mAh at 0.5C, and the capacity retention rate is 92.1% at 8C. It takes 6 minutes and 30 seconds to fast charge at 8C (from 10% to 95% SOC). The capacity does not decrease significantly after 1000 cycles, and all safety tests are met.

[0075] from Figure 1 It can be seen that the 8C fast charging voltage of the battery in this embodiment is stable, and it takes 6 to 10 minutes to go from 10% to 90% SOC.

[0076] from Figure 2 It can be seen that the 2C discharge voltage plateau of the battery in this embodiment is stable, and the polarization voltage is ≤0.2V;

[0077] from Figure 3 As can be seen, the battery in this embodiment retains ≥95% of its capacity after 1000 cycles, demonstrating excellent cycle stability.

[0078] In this embodiment, EA can also be replaced with 1,3-PS or PST.

[0079] Example 2

[0080] This embodiment provides a method for preparing an ultra-low voltage safety lithium titanate battery, including the following steps:

[0081] S1) Spinel-type lithium titanate is first modified by in-situ surface coating with nano-carbon, with a carbon coating thickness of 1 nm and a carbon content accounting for 1.5 wt% of the total mass of the anode material; and the formation of a continuous and uniform conductive network is satisfied, with the intrinsic electronic conductivity of the material ≥ S / cm.

[0082] S2) High-purity spinel-type lithium titanate with precisely controlled spinel structure is used as the negative electrode active material; the spinel-type lithium titanate, after control, satisfies the following: it has a pure cubic Fd-3m space group single-phase spinel structure, without... , Impurity phase; cell constant a is controlled between 0.8355 and 0.8365 nm, lithium-titanium molar ratio is controlled between 0.80 and 0.83; particle size D50 is 0.5 to 1.5 μm, particle size distribution Span≤1.0; charge-discharge lattice volume change rate is <0.2%, exhibiting zero strain characteristics.

[0083] S3) Mix spinel lithium titanate, conductive carbon black SP and polyvinylidene fluoride PVDF in a mass ratio of 92:4:4, add NMP, and stir under vacuum until the viscosity is 2500 mPa·s to obtain the negative electrode slurry.

[0084] S4), lithium iron phosphate is mixed in a mass ratio of 90:5:5. Lithium spinel manganese oxide The composite material, conductive carbon black SP, and polyvinylidene fluoride PVDF were mixed and vacuum stirred until the viscosity reached 2000 mPa·s to obtain the positive electrode slurry.

[0085] S5) The negative electrode slurry is coated on an aluminum foil with a thickness of 12μm, with a double-sided coating thickness of 180μm and an areal density of 18mg / cm².

[0086] The positive electrode slurry was coated onto an aluminum foil with a thickness of 12 μm, and the double-sided coating thickness was 190 μm with an areal density of 23 mg / cm².

[0087] Then, after drying in an oven using a temperature gradient of 80℃-120℃-90℃, the electrode undergoes roll pressing. The negative electrode has a roll pressing compaction density of 2.0 g / cc and a porosity of 38%; the positive electrode has a roll pressing compaction density of 2.55 g / cc and a porosity of 28%.

[0088] Then, the negative electrode and the positive electrode are obtained by cutting; the size of the negative electrode is 48mm×38mm; the size of the positive electrode is 46mm×36mm.

[0089] S4), then the negative electrode, composite separator, and positive electrode are wound into a flat cell; the metal casing is installed, and the tabs and top cover are welded; then the electrolyte is injected, and the cell is sealed and left to stand for 12~24 hours to obtain a lithium titanate battery.

[0090] The composite membrane has a thickness of 12 μm; the electrolyte is 1.1 mol / L lithium hexafluorophosphate. A mixed solution of lithium bis(fluorosulfonyl)imide (LiFSI), a mixed solvent, and additives; wherein the mixed solvent is ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a volume ratio of 3:4:3.

[0091] The additives are 2-8 wt% ethyl acetate (EA) and 2-3 wt% ethylene carbonate (VEC).

[0092] Performance test results: 0.5C capacity is 602mAh, 8C discharge capacity retention rate is 94.6%, 8C fast charging time is 6 minutes and 35 seconds; capacity basically does not decrease after 1000 cycles, and safety test meets the standards.

[0093] The embodiments and descriptions above are merely illustrative of the principles and preferred embodiments of the present invention. Various changes and modifications may be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

[0094] Example 3

[0095] like Figure 6 As shown, this embodiment provides an electrode thickness measuring instrument used in the preparation method described in Embodiment 1 or 2, including an equipment frame and a data acquisition unit, a thermal thickness compensation unit, a real-time thickness display screen, and a control system box disposed on the equipment frame; the equipment frame is provided with an air-bearing support frame at the electrode station, the air-bearing support frame having densely packed small holes to allow clean compressed air to be introduced to support the electrode; a C-shaped frame is slidably mounted on the upper and lower double sides of the equipment frame along the air-bearing support frame, and a wide-spot laser probe, a vision camera, and a temperature sensor for thermal compensation are respectively disposed on the outer end face of the C-shaped frame.

[0096] The equipment frame provides an overall installation reference and structural rigidity, ensuring the stability and reliability of the testing system.

[0097] The air-bearing support frame forms a uniform air film through dense small holes, providing non-contact, stress-free, and friction-free support for the electrode sheet, preventing LTO soft electrode sheet from falling off, indenting, or deforming, and ensuring the authenticity of thickness detection.

[0098] Sliding installation (e.g., linear guide rail) + C-frame: drives the detection component to reciprocate and scan the full width of the electrode sheet, achieving full coverage detection from the left edge to the right edge with no measurement blind spots.

[0099] The wide-spot laser probe, as the core thickness detection element, adopts reflective laser ranging; by averaging the micro-undulations of the surface with a wide spot, it improves the stability and accuracy of thickness measurement and is compatible with LTO porous rough electrode sheets.

[0100] The vision camera is used for precise positioning of the electrode edge. It achieves an edge positioning error of ≤0.5mm through backlight imaging and sub-pixel algorithm, and defines an effective measurement range for the laser probe.

[0101] The hot thickness compensation unit consists of a temperature sensor and a compensation algorithm, which corrects the thickness drift caused by the three-stage high-temperature drying process in real time, ensuring stable measurement accuracy.

[0102] The real-time thickness display screen displays the thickness value, uniformity, fluctuation, and pass / fail status in real time, facilitating on-site monitoring.

[0103] The control system box completes data acquisition, calculation, comparison, alarm, and output control signals to achieve closed-loop control of thickness detection, feedback, and adjustment.

[0104] Working principle:

[0105] After undergoing three-stage gradient drying, the electrode sheets enter the testing station, where they are supported by a stable air film formed by an air flotation support frame to prevent damage, deformation, or abnormal local compaction of the electrode coating; C The frame moves along a linear guide rail to synchronously scan a wide-spot laser probe, a vision camera, and a temperature sensor. The vision camera, in conjunction with a backlight and a sub-pixel edge detection algorithm, identifies the left and right edges of the electrode sheet in real time, with an edge positioning error ≤0.5mm. This accurately delineates the effective coating measurement range for the laser probe, eliminating invalid data such as edge burrs, bare foil, and blank areas. The wide-spot laser probe uses laser reflection ranging, suppressing measurement fluctuations caused by electrode surface roughness and particle undulations through the large spot area averaging effect, achieving stable electrode thickness acquisition. The temperature sensor collects the electrode temperature and ambient temperature in real time, and the thermal thickness compensation unit dynamically corrects the high-temperature electrode thickness, eliminating measurement errors caused by thermal expansion. All data is transmitted in real time to the control system box for calculation, analysis, and judgment, and displays information such as average thickness, uniformity, fluctuation, and pass / fail status on the real-time thickness display screen. The system compares the measured thickness with the preset process threshold. Qualified electrodes proceed to the subsequent rolling process, while unqualified electrodes trigger an automatic alarm and feedback to adjust coating parameters, achieving closed-loop thickness control.

Claims

1. A lithium titanate ultra-low voltage safety battery, comprising a positive electrode, a negative electrode, an electrolyte, and a composite separator; characterized in that: The positive electrode includes a positive current collector and a positive active material coated on the positive current collector, and the negative electrode includes a negative current collector and a negative active material coated on the negative current collector. The positive electrode active material is lithium iron phosphate. Lithium spinel manganese oxide Composite materials; The negative electrode active material is spinel-type lithium titanate; The electrolyte is lithium hexafluorophosphate. Lithium difluorosulfonylimide A mixed solution of solvents and additives; The composite diaphragm is a polyolefin composite membrane.

2. The lithium titanate ultra-low voltage safety battery according to claim 1, characterized in that: The spinel-type lithium titanate has a pure cubic crystal system, Fd-3m space group, single-phase spinel structure, and satisfies: [missing information - likely related to crystal structure or properties]. , Impurity phase; cell constant a is 0.8355–0.8365 nm, lithium-titanium molar ratio is 0.80–0.82; particle size D50 is 0.5–1.5 μm, particle size distribution Span≤1.0; charge-discharge lattice volume change rate is <0.3%, exhibiting zero strain characteristics.

3. A lithium titanate ultra-low voltage safety battery according to claim 1 or 2, characterized in that: The spinel-type lithium titanate is coated with in-situ nano-carbon, satisfying the following conditions: carbon coating thickness 1–3 nm, carbon content 1.5–3.0 wt% of the total mass of the anode material; forming a continuous and uniform conductive network; and intrinsic electronic conductivity ≥ S / cm.

4. The lithium titanate ultra-low voltage safety battery according to claim 3, characterized in that: The lithium titanate battery has two or more independent electrode groups sharing the electrolyte and the same casing. Each electrode group has 3 to 5 positive and negative electrode stacks, independent aluminum foil current collectors, and each has a micro tab. The polyolefin composite membrane between adjacent electrode groups is replaced with an ultra-thin ceramic membrane of 5–12 μm. The width and / or thickness of the tabs of adjacent electrode groups are different.

5. A lithium titanate ultra-low voltage safety battery according to claim 4, characterized in that: Different regions on the same negative electrode or the same group of negative electrodes have different conductivity / rate characteristics, resulting in different discharge rates in different regions within the same electrode.

6. The lithium titanate ultra-low voltage safety battery according to claim 1, characterized in that: the safety battery further has one or more of the following features: The lithium iron phosphate described in 6.1 Lithium spinel manganese oxide The mass ratio is 7:

3. 6.2 The mixed solvent is ethylene carbonate EC, dimethyl carbonate DMC, and diethyl carbonate DEC in a volume ratio of 3:4:

3. Lithium hexafluorophosphate as described in 6.3 Lithium difluorosulfonylimide The concentration is 1.1-1.5 mol / L. 6.4 The additives mentioned are 2-8 wt% ethyl acetate (EA) and 2-3 wt% ethylene carbonate (VEC). 6.5 The thickness of the polyolefin composite film is 7~16μm, comprising a polyolefin base film and a coating applied to the polyolefin base film; the polyolefin base film is a polypropylene (PP) base layer or a polyethylene (PE) base layer; the coating is... Coating or The coating has a thickness of 1-4 μm. 6.6 The lithium titanate battery further includes a cylindrical metal casing, the inner and outer surfaces of which are anodized to form a thickness of 10-15 μm. Insulating layer.

7. A method for preparing an ultra-low voltage safety lithium titanate battery, characterized in that, Includes the following steps: S1) High-purity spinel-type lithium titanate with precisely controlled spinel structure is used as the negative electrode active material; the spinel-type lithium titanate, after control, satisfies the following: it has a pure cubic Fd-3m space group single-phase spinel structure, without... , Impurity phase; cell constant a controlled between 0.8355 and 0.8365 nm, lithium-titanium molar ratio controlled between 0.80 and 0.83; particle size D50 between 0.5 and 1.5 μm, particle size distribution Span ≤ 1.0; charge-discharge lattice volume change rate < 0.2%, possessing zero strain characteristics; S2) Mix the negative electrode active material, conductive carbon black, dispersant, and negative electrode binder PVDF according to a certain mass ratio, add NMP and stir to prepare a negative electrode slurry with a viscosity of 2000~4000mPa·s; The negative electrode active material is spinel-type lithium titanate; S3) Mix the positive electrode active material, conductive carbon black, and positive electrode binder PVDF according to a certain mass ratio, add NMP and stir to prepare a positive electrode slurry with a viscosity of 3000~5000mPa·s; The positive electrode active material is lithium iron phosphate. Lithium spinel manganese oxide Composite materials; S4) The negative electrode slurry and positive electrode slurry are coated onto the negative electrode current collector and positive electrode current collector, respectively, and then dried in an oven using a temperature gradient of 80℃-120℃-90℃. After drying, the electrode thickness is continuously measured using a non-contact laser full-width online thickness measuring instrument, realizing simultaneous double-sided detection, real-time data acquisition, automatic alarm for out-of-tolerance, and thickness uniformity analysis. The detection accuracy is ±0.1μm, the resolution is 0.01μm, and it has hot thickness compensation and low-stress anti-damage functions. After passing the inspection, it is gently rolled to control the electrode thickness and porosity to stabilize, and then sliced ​​to obtain positive and negative electrode sheets. S5) The negative electrode, composite separator, and positive electrode are wound into a cylindrical or flat cell; the cell is installed in a metal casing, and the tabs and top cover are welded together; then the electrolyte is injected, and the cell is sealed and left to stand for 12-24 hours to obtain a lithium titanate battery. The electrolyte is lithium hexafluorophosphate. Lithium difluorosulfonylimide A mixed solution of solvents and additives; The lithium hexafluorophosphate The concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 1.1~1.5 mol / L; The mixed solvent is ethylene carbonate EC, dimethyl carbonate DMC, and diethyl carbonate DEC in a volume ratio of 3:4:3; The additives are 2-8 wt% ethyl acetate (EA) and 2-3 wt% ethylene carbonate (VEC).

8. The method for preparing a lithium titanate ultra-low voltage safety battery according to claim 7, characterized in that: Step S1) The spinel-type lithium titanate is first modified by in-situ surface nano-carbon coating, with a carbon coating layer thickness of 1-3 nm and a carbon content accounting for 1.5-3.0 wt% of the total mass of the negative electrode material; and it satisfies the requirement of forming a continuous and uniform conductive network, and the intrinsic electronic conductivity of the material is ≥ S / cm.

9. The method for preparing a lithium titanate ultra-low voltage safety battery according to claim 7, characterized in that: Step S2) also has one or more of the following characteristics: 9.1 The mass ratio of the negative electrode active material, conductive carbon black, and negative electrode binder PVDF is 90~95:3~5:3~5. 9.2 The mass ratio of the positive electrode active material, conductive carbon black, and positive electrode binder PVDF is 90~95:3~5:2~5.

10. An electrode thickness measuring instrument applicable to the preparation method of lithium titanate ultra-low voltage safety battery as described in claim 6, characterized in that: The equipment includes a frame and a data acquisition unit, a thermal thickness compensation unit, a real-time thickness display screen, and a control system box mounted on the frame. The frame has an air-bearing support frame at the electrode station, which has densely packed small holes to allow clean compressed air to support the electrode. A C-shaped frame is slidably mounted on the upper and lower sides of the frame along the air-bearing support frame at the electrode station. A wide-spot laser probe, a vision camera, and a temperature sensor for thermal compensation are respectively mounted on the outer end face of the C-shaped frame.

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