A wide-temperature-range lithium iron phosphate power battery and a preparation method thereof

Abstract

The application provides a wide-temperature-range lithium iron phosphate power battery and a preparation method thereof, and belongs to the technical field of lithium batteries. The battery comprises: a positive active material: a composite structure composed of a lithium iron phosphate matrix and a conductive layer and a metal oxide layer coated in sequence, wherein the metal oxide layer is a bismuth-based oxide; a negative active material: graphitized petroleum coke particles; an electrolyte: containing a lithium salt, an organic solvent and an additive, wherein the additive comprises a sulfur-containing cyclic ester compound, an organic phosphate ester and a fluorine-containing lithium salt; and a separator: a ceramic-coated polyolefin separator. By coating the conductive layer and the metal oxide layer on the surface of the lithium iron phosphate matrix in sequence, the conductivity and the cycle stability of the positive active material are significantly improved; the electrolyte improves the high-temperature storage performance and the low-temperature charge-discharge performance of the battery, and the stability of the battery at a wide-temperature-range interface is comprehensively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a wide-temperature-range lithium iron phosphate power battery and a preparation method thereof. BACKGROUND

[0002] For the positive electrode material of lithium batteries, the conductivity of lithium iron phosphate material is 1-2 exponential levels lower than that of other systems (lithium manganate, ternary, etc.). Especially in an environment close to 0℃ or lower than 0℃, the capacity performance, discharge rate performance, and cycle life of lithium ion secondary batteries of the lithium iron phosphate positive electrode system are significantly reduced compared with those in a normal temperature environment. This limits the use of lithium ion secondary batteries of the lithium iron phosphate positive electrode system in high-cold regions and during winter low-temperature periods.

[0003] In existing lithium iron phosphate batteries, the following two cases exist: (1) the high-temperature performance of the battery is good but the low-temperature performance is poor (0℃ and below cannot be charged or the cycle life of the battery is poor); (2) the low-temperature performance of the battery is excellent but the high-temperature performance is poor and the energy density is low. Therefore, the technology for improving the comprehensive electrochemical performance of wide-temperature-range lithium iron phosphate power batteries in high-temperature and low-temperature environments is of great importance in the production of lithium iron phosphate batteries. SUMMARY

[0004] The present application is made in view of the above problems, and aims to provide a wide-temperature-range lithium iron phosphate power battery and a preparation method thereof, to improve the use effect of the wide-temperature-range lithium iron phosphate power battery in high-temperature and low-temperature environments (-20℃-60℃).

[0005] Specifically, the first aspect of the present application provides a wide-temperature-range lithium iron phosphate power battery, comprising:

[0006] The positive electrode active material is composed of a lithium iron phosphate matrix and a conductive layer and a metal oxide layer coated in sequence, and the metal oxide layer is a bismuth-based oxide.

[0007] The negative electrode active material is graphitized petroleum coke particles.

[0008] Further, the conductive layer is a carbon layer with a thickness of 3-6 nm, and / or the carbon content accounts for 1.5-2.5wt% of the mass of the lithium iron phosphate matrix; and / or

[0009] The metal oxide layer is Bi2O3 with a thickness of 2-5 nm, and / or the bismuth element accounts for 0.5-1.5wt% of the total mass of the positive electrode active material.

[0010] Further, it further comprises an electrolyte, and the electrolyte comprises a lithium salt, an organic solvent, and an additive, and the additive comprises a sulfur-containing cyclic ester compound, an organic phosphate ester, and a fluorine-containing lithium salt.

[0011] The organic solvent is composed of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, and the mass ratio is (15-25):(35-45):(30-40); and / or

[0012] The lithium salt is LiPF6, and the concentration is 1.2-1.5 mol / L.

[0013] Further, the additive includes vinyl sulfate 0.5-1.5 wt%, butyl phenyl phosphate 1.0-3.0 wt%, and lithium difluorophosphate 0.3-0.8 wt%.

[0014] Further, a separator is further included, and the separator is a ceramic-coated polyolefin separator.

[0015] Further, the positive electrode sheet in the wide-temperature-range lithium iron phosphate power battery has a gradient pore structure, and the porosity of the current collector side is 20-28%, and the porosity of the surface layer is 30-38%.

[0016] The second aspect of the present application provides a preparation method of the wide-temperature-range lithium iron phosphate power battery, comprising:

[0017] S1: positive electrode material preparation: forming a conductive layer and a metal oxide layer on the surface of lithium iron phosphate in sequence;

[0018] S2: negative electrode material preparation: crushing and pre-carbonizing the graphitized petroleum coke particles;

[0019] S3: electrolyte preparation: mixing organic solvents, lithium salts and additives under inert atmosphere;

[0020] S4: battery assembly: injecting electrolyte after coating, rolling and winding the positive and negative electrodes;

[0021] S5: step aging: sequentially performing 25-40°C standing, 40-50°C charge-discharge cycling, 50-70°C high-temperature storage and -15~-5°C low-temperature storage.

[0022] Further, in step S1, the metal oxide layer is deposited by spray pyrolysis, the pyrolysis temperature is 280-320°C, and the precursor is bismuth nitrate alcohol solution.

[0023] Further, in step S4, the rolling adopts two-stage pressure control: the first-stage pressure is 7-10T to form a dense layer on the current collector side, and the second-stage pressure is 4-7T to maintain a porous layer on the surface; and / or

[0024] The winding tension is 1.0-2.0N, and the thickness of the separator is 14-18μm.

[0025] Further, step S5 of the step aging includes:

[0026] The first stage: standing for 18-30h at 25-40℃;

[0027] The second stage: charging and discharging for 2-5 times at 0.1-0.3C at 40-50℃;

[0028] The third stage: storing for 40-56h at 50-70℃;

[0029] The fourth stage: storing for 10-15h at-15~-5℃.

[0030] Further, the step S3 electrolyte preparation is carried out in an environment with dew point ≤-40℃, and the moisture content is ≤10ppm; and / or

[0031] The liquid injection amount is 3.0-5.0g / Ah; and / or

[0032] The vacuum injection pressure is ≤-90kPa.

[0033] The present application has the following beneficial effects:

[0034] The present application significantly improves the conductivity and cycle stability of the positive electrode material by coating a conductive layer and a metal oxide layer on the surface of the lithium iron phosphate substrate in sequence, especially in a low temperature environment, which can effectively improve the discharge rate performance and cycle life of the battery; the graphitized petroleum coke particles are used as the negative electrode active material, which improves the lithium intercalation performance and structural stability of the negative electrode material, and helps to improve the energy density and cycle performance of the battery; specific additives are added in the electrolyte, including sulfur-containing cyclic ester compounds, organic phosphate esters and fluorine-containing lithium salts, which can synergistically optimize the physical and chemical properties of the electrolyte, improve the high-temperature storage performance and low-temperature charging and discharging performance of the battery; the ceramic coated polyolefin separator is used, which improves the thermal stability and mechanical strength of the separator, and helps to prevent thermal runaway and short circuit of the battery under abuse conditions. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the drawings, and other drawings can be obtained by those skilled in the art without creative labor.

[0036] Figure 1 The process flow chart of the present application is shown in the figure.

[0037] Figure 2 The structure of the positive electrode sheet of the present application is shown in the figure.

[0038] The realization of the purpose of the present application, the functional characteristics and advantages will be further described with reference to the embodiments and the drawings. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0040] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0041] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0042] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0043] An embodiment of the first aspect of this application provides a wide-temperature-range lithium iron phosphate power battery, comprising:

[0044] Positive electrode active material: It consists of a lithium iron phosphate matrix and a conductive layer and a metal oxide layer sequentially coated thereon, wherein the metal oxide layer is a bismuth-based oxide;

[0045] Negative electrode active material: graphitized petroleum coke particles;

[0046] Electrolyte: contains lithium salt, organic solvent and additives, wherein the additives include sulfur-containing cyclic esters, organophosphates and fluorinated lithium salts;

[0047] Separator: Ceramic-coated polyolefin separator.

[0048] In a preferred embodiment, the metal oxide layer can also be a titanium-based oxide or a vanadium-based oxide.

[0049] The graphitized petroleum coke particles in the negative active material are petroleum coke single particles, and the single particle size is D50: 8-11 um. The graphitized petroleum coke particles are treated by pre-carbonization to modify the regularity of the surface.

[0050] The present application significantly improves the conductivity and cycle stability of the positive electrode material by sequentially coating a conductive layer and a metal oxide layer on the surface of the lithium iron phosphate substrate. Especially in a low temperature environment, it can effectively improve the discharge rate performance and cycle life of the battery. The use of graphitized petroleum coke particles as the negative active material improves the lithium intercalation performance and structural stability of the negative electrode material, which helps to improve the energy density and cycle performance of the battery. The electrolyte is added with specific additives, including sulfur-containing cyclic ester compounds, organic phosphate esters and fluorine-containing lithium salts. These additives can synergistically optimize the physical and chemical properties of the electrolyte, improve the high-temperature storage performance and low-temperature charge-discharge performance of the battery. The ceramic-coated polyolefin separator improves the thermal stability and mechanical strength of the separator, which helps to prevent thermal runaway and short circuit of the battery under abuse conditions.

[0051] The particle size D50 of the lithium iron phosphate substrate is 80-120 nm, preferably 95-110 nm, and the specific surface area is 15-25 m 2 / g, wherein the molar ratio of Li:Fe:P is 1:0.99:1.

[0052] In the present embodiment, the conductive layer is a carbon layer with a thickness of 3-6 nm, and the carbon content accounts for 1.5-2.5 wt% of the mass of the lithium iron phosphate substrate. The carbon source of the carbon layer is a 20 wt% glucose aqueous solution. The carbon coating process is as follows: the lithium iron phosphate substrate is mixed with the carbon source by ball milling at a speed of 300-350 rpm for 2-2.5 h, and then sintered at 650℃ for 4 h under nitrogen protection to obtain the carbon-coated lithium iron phosphate material.

[0053] The metal oxide layer is Bi2O3 with a thickness of 2-5 nm, and the bismuth element accounts for 0.5-1.5 wt% of the total mass of the positive active material.

[0054] The precursor of the metal oxide layer is a Bi(NO3)3·5H2O ethanol solution with a concentration of 0.1 mol / L. The coating process of the metal oxide layer is as follows: using a spray pyrolysis equipment, the temperature is 300-320℃, the atomization pressure is 0.30-0.35 MPa, the carrier gas is nitrogen, the nitrogen flow is 10 L / min, and the oxygen content is <10 ppm. The carbon-coated lithium iron phosphate material is coated with a metal oxide layer with a thickness of 2-3 nm.

[0055] In the embodiment, the raw material of the negative active material is graphitized petroleum coke particles, purchased from Henan Antong Environmental Protection Technology Co., Ltd., with sulfur content <0.5%, which is crushed by an air flow crusher into D50 = 8-11 μm.

[0056] In the embodiment, the organic solvent is composed of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, with a mass ratio of (15-25):(35-45):(30-40); the lithium salt is LiPF6, with a concentration of 1.2-1.5 mol / L.

[0057] Preferably, the mass ratio of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate is 20:40:38, which can better balance the solubility, viscosity and ion conductivity of the electrolyte. The concentration of the lithium salt LiPF6 is preferably 1.35 mol / L, at which the solubility of the lithium salt in the electrolyte is higher, and the ion conductivity of the electrolyte can be effectively improved.

[0058] In the embodiment, the sulfur-containing cyclic ester compound in the electrolyte is selected from one or more of vinyl sulfate and vinyl sulfite, with an addition amount of 0.5-1.5 wt% of the total mass of the electrolyte, which helps to improve the low-temperature charge-discharge performance of the battery; the organic phosphate ester is selected from one or more of butyl benzyl phthalate, butyl phenyl phosphate ester and ethyl diphenyl phosphate ester, with an addition amount of 1.0-3.0 wt% of the total mass of the electrolyte, which helps to improve the high-temperature storage performance of the battery; the fluorine-containing lithium salt is selected from one or more of lithium difluorophosphate and lithium tetrafluoroborate, with an addition amount of 0.3-0.8 wt% of the total mass of the electrolyte, which can further optimize the physical and chemical properties of the electrolyte and improve the comprehensive performance of the battery.

[0059] Further, the additives include vinyl sulfate 0.5-1.5 wt%, butyl phenyl phosphate ester 1.0-3.0 wt%, and lithium difluorophosphate 0.3-0.8 wt%.

[0060] Further, the positive electrode sheet of the wide-temperature-range lithium iron phosphate power battery has a gradient pore structure, with a porosity of 20-28% on the side of the current collector and a porosity of 30-38% on the surface layer. The design of the gradient pore structure enables the electrolyte to better infiltrate the positive electrode material, improves the migration rate of lithium ions, and also helps to alleviate the volume change of the battery during charging and discharging, further prolonging the cycle life of the battery.

[0061] Figure 2 The figure is a structural diagram of the positive electrode sheet in the present application, in which the tab is an aluminum strip with a thickness of 0.1 mm and a width of 5 mm as a current lead conductor; the coating area is the area where the positive active material is coated on the aluminum foil; and the blank welding area is the welding area reserved for the tab.

[0062] Referring to Figure 1 Embodiments of the second aspect of the application provide a preparation method of the wide-temperature-range lithium iron phosphate power battery described above, comprising:

[0063] S1: positive electrode material preparation: forming a conductive layer and a metal oxide layer on the surface of lithium iron phosphate in sequence;

[0064] S2: negative electrode material preparation: crushing and pre-carbonizing the graphitized petroleum coke particles;

[0065] S3: electrolyte preparation: mixing organic solvents, lithium salts and additives under inert atmosphere;

[0066] S4: battery assembly: injecting electrolyte after coating, rolling and winding the positive and negative electrodes;

[0067] S5: step aging: sequentially performing 25-40°C standing, 40-50°C charge-discharge cycling, 50-70°C high-temperature storage and -15~-5°C low-temperature storage.

[0068] In this embodiment, when step S1 is performed to prepare the positive electrode material, the following specific operations are performed: first, the lithium iron phosphate substrate and the 20wt% glucose aqueous solution are placed together for ball milling mixing. The ball-mixed lithium iron phosphate substrate and the glucose aqueous solution are subjected to high-temperature sintering treatment under a nitrogen protective atmosphere. The sintering temperature is controlled at about 650°C, and the duration is 4h, so as to ensure that the carbon layer can be uniformly and tightly coated on the surface of the lithium iron phosphate substrate. The carbon-coated lithium iron phosphate material obtained in this way not only improves the electrical conductivity of the material, but also enhances the structural stability thereof. Subsequently, a spray pyrolysis technology is used to further coat a metal oxide layer on the surface of the carbon-coated lithium iron phosphate material. An ethanol solution of Bi(NO3)3·5H2O is used as a precursor, and by precisely controlling the temperature of the spray pyrolysis equipment to be 280-320°C, the atomization pressure, the carrier gas flow rate and the oxygen content and other parameters, the metal oxide layer can be uniformly and densely deposited on the carbon layer. This metal oxide layer, especially Bi2O3, can further improve the cycle stability and low-temperature performance of the positive electrode material.

[0069] Positive electrode coating: after the lithium iron phosphate is coated, it is mixed with PVDF:SP at 96:2:2, the viscosity is 4000cP, the current collector is aluminum foil, the coating surface density is 180-200g / m 2 , and the electrode thickness is 160-1705μm.

[0070] Step S2 preparation of negative electrode material, i.e. crushing and pre-carbonization treatment of graphitized petroleum coke particles. The graphitized petroleum coke particles are crushed to a specific particle size range by an air flow crusher, and the pre-carbonization treatment is carried out at a temperature of 400-600°C for 2-4h to modify the regularity of the surface and improve the lithium intercalation performance and structural stability of the negative electrode material. When coating the negative electrode, the treated graphitized petroleum coke particles are mixed with a binder and a conductive agent in a certain proportion, wherein the binder can be selected from styrene-butadiene rubber (SBR) and the conductive agent can be selected from acetylene black (AB), and the mixing ratio is graphitized petroleum coke particles: binder: conductive agent = 95:2:3. The viscosity of the uniformly mixed slurry is controlled at 3000-5000cP, the current collector is copper foil, the coating area density is 100-120g / m 2 , and the thickness of the electrode sheet is 120-130μm.

[0071] Step S3 in terms of electrolyte preparation, the embodiment uses a specific combination of organic solvents, lithium salts and additives. The electrolyte preparation is carried out in an environment with a dew point ≤-40°C, the moisture content is ≤10ppm, the organic solvent is a mixture of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate in a certain proportion to balance the solubility, viscosity and ion conductivity of the electrolyte. LiPF6 is selected as the lithium salt and controlled within a certain concentration range to ensure its solubility and ion conductivity in the electrolyte. The additives include vinyl sulfate, butyl phenyl phosphate and lithium difluorophosphate, which can synergistically optimize the physical and chemical properties of the electrolyte and improve the high-temperature storage performance and low-temperature charge-discharge performance of the battery.

[0072] Step S4: The prepared positive and negative electrode materials are coated, rolled, and wound, and then electrolyte is injected, wherein the rolling adopts two-stage pressure control: the first-stage pressure is 7-10T to form a dense layer on the side of the current collector, and the porosity of the current collector side is 23-27%; the second-stage pressure is 4-7T to maintain a porous surface layer, and the porosity of the surface layer is 33-37%; a full-automatic winding machine is used, the winding tension is 1.0-2.0N, and the thickness of the separator is 14-18μm. The amount of electrolyte injection is 3.0-5.0g / Ah; the vacuum injection pressure is ≤-90kPa, and the maintaining time is 30min. Subsequently, formation is carried out: at room temperature, 0.05C constant current to 3.0V, standing for 2h; 0.1C constant current to 3.6V, constant voltage to current ≤0.01C. Specifically, the rolling adopts two-stage pressure control, the first-stage pressure 7-10T can effectively compact the material on the side of the current collector, form a dense layer, and improve the structural stability of the battery; and the second-stage pressure 4-7T can maintain a porous surface layer, which is beneficial to the infiltration of electrolyte and the migration of lithium ions. Through the rolling operation with different pressures, the positive electrode sheet forms a gradient change in porosity from the side of the current collector to the surface layer. The first-stage larger pressure makes the material particles on the side of the current collector arrange more closely, and the porosity is relatively low, generally controlled at 23-27%, which can enhance the bonding force between the sheet and the current collector, improve the electron conduction efficiency, and at the same time ensure the mechanical strength of the sheet. The second-stage smaller pressure acts on the surface layer, so that more gaps are reserved between the material particles, and the porosity of the surface layer reaches 33-37%, which is beneficial to the better penetration of electrolyte into the positive electrode material, provides more channels for the migration of lithium ions, and thus improves the charge-discharge performance of the battery.

[0073] The winding tension is controlled between 1.0-2.0N, which can ensure the close fit of the sheet and avoid the increase of internal stress caused by over-tightening. The thickness of the separator is selected as 14-18μm, which can provide sufficient mechanical strength and ensure the smooth transmission of lithium ions. The preparation and injection process of the electrolyte are carried out under strictly controlled environmental conditions to ensure the performance and quality of the battery. The electrolyte is prepared under the operation of extremely low dew point environment, which effectively avoids the adverse effects of moisture on the performance of the electrolyte. At the same time, the strict control of the injection amount and the application of vacuum injection technology further improve the sealing performance of the battery and the uniformity of the electrolyte distribution, laying a solid foundation for the high performance of the battery. In addition, the gradient porosity structure of the positive electrode sheet optimizes the infiltration effect of the electrolyte, accelerates the migration of lithium ions, effectively alleviates the volume change of the battery during the charge-discharge process, and thus significantly prolongs the cycle life of the battery.

[0074] The step S5 step-by-step aging includes: a first stage: standing at 25-40℃ for 18-30h; a second stage: 0.1-0.3C charging and discharging 2-5 times at 40-50℃; a third stage: storing at 50-70℃ for 40-56h; a fourth stage: storing at -15~-5℃ for 10-15h.

[0075] The step-by-step aging is an effective battery activation and performance optimization process, which helps the internal components of the battery to be fully infiltrated, activated and stabilized by simulating the working conditions of the battery at different temperatures. In the first stage, the standing process at 25-40℃ makes the internal components of the battery gradually reach thermal equilibrium, and the electrolyte fully infiltrates the positive and negative electrode materials, preparing for the subsequent charging and discharging cycles. In the second stage, 0.1-0.3C small current charging and discharging cycles are carried out at 40-50℃, which helps to further activate the internal materials of the battery, promotes the embedding and extraction of lithium ions, and detects the performance of the battery, discovers and eliminates potential performance defects in time. In the third stage, the battery is stored in a high temperature environment of 50-70℃, simulating the working conditions of the battery at high temperature, investigating the thermal stability and safety of the battery, and ensuring that the battery can still maintain good performance in a high temperature environment. Finally, the low temperature storage of -15~-5℃ in the fourth stage simulates the working conditions of the battery in cold environment, which helps to optimize the charging and discharging performance of the battery in low temperature conditions and improve the low temperature adaptability of the battery. Through this series of step-by-step aging process, the comprehensive performance of the wide temperature range lithium iron phosphate power battery can be comprehensively improved, and the battery can perform well in actual application.

[0076] In summary, the thickness of the bismuth oxide coating layer in the present application is controlled in the range of 2-3nm, which not only helps to improve the cycle stability of the positive electrode material, but also effectively solves the low temperature phase change problem, thereby improving the discharge rate performance and cycle life of the battery in low temperature environment. By fine-tuning the thickness of the bismuth oxide coating layer, the present application realizes the optimization of the performance of the positive electrode material, so that the battery can maintain excellent performance in a wide temperature range.

[0077] The ratio of DTD / BBP / LiPO2F2 ternary additive is carefully designed to have a synergistic effect, taking into account the high temperature and low temperature performance of the battery. The addition of DTD (vinyl sulfate) helps to improve the low temperature charging and discharging performance of the battery, so that it can still maintain high activity in cold environment; BBP (butyl phenyl phosphate) helps to improve the high temperature storage performance of the battery, ensuring that the battery can still operate stably under high temperature conditions; and the addition of LiPO2F2 (lithium difluorophosphate) further optimizes the physical and chemical properties of the electrolyte, improving the comprehensive performance of the battery. This combination of ternary additives not only reflects the innovation of the present application, but also highlights its unique advantages in the field of wide temperature range lithium iron phosphate power battery.

[0078] The four-stage temperature aging sequence as another key process combination in the present application is not obvious in that by simulating the working state of the battery under different temperature conditions, sufficient infiltration, activation and stabilization of the internal components of the battery are achieved. This sequence includes four stages of standing, charge-discharge cycling, high-temperature storage and low-temperature storage, each of which plays an indispensable role. Through the aging treatment of this sequence, the comprehensive performance of the battery is comprehensively improved, laying a solid foundation for excellent performance in actual application.

[0079] Embodiments

[0080] The present disclosure is described in more detail by the following examples, which are merely illustrative and not limiting of the present disclosure, as various modifications and changes can be suggested by those skilled in the art. All parts, percentages, and ratios reported in the following examples are based on weight unless otherwise stated. All reagents used in the examples were obtained from common commercial sources and used without further purification unless otherwise stated. The instruments used in the examples were obtained from common commercial sources unless otherwise stated.

[0081] Example 1

[0082] A preparation method of the wide-temperature-range lithium iron phosphate power battery comprises the following steps:

[0083] S1: positive electrode material preparation: forming a conductive layer and a metal oxide layer on the surface of lithium iron phosphate in sequence: first, put the lithium iron phosphate matrix and the 20wt% glucose aqueous solution together for ball milling mixing, wherein the use amount ratio of the lithium iron phosphate matrix and the glucose aqueous solution is 5:1, the ball milling time is controlled to be 3h, and the ball milling rotation speed is 400r / min; the lithium iron phosphate matrix and the glucose aqueous solution after ball milling mixing are concentrated to dryness, and the solid phase is collected; the solid phase is subjected to high-temperature sintering treatment under a nitrogen protective atmosphere, the sintering temperature is controlled to be about 650℃, and the duration is 4h, so as to ensure that the carbon layer can be uniformly and closely coated on the surface of the lithium iron phosphate matrix; a metal oxide layer is further coated on the surface of the carbon-coated lithium iron phosphate material by using a spray pyrolysis technology, Bi(NO3)3·5H2O ethanol solution is used as a precursor (the molar ratio of Bi to Fe is controlled to be 2:100), the concentration of the Bi(NO3)3·5H2O ethanol solution is 0.1mol / L, the temperature of the spray pyrolysis equipment is accurately controlled to be 300℃, the atomization pressure is 0.4MPa, the carrier gas flow is 20L / min, and the oxygen content is 2%, so that the metal oxide layer can be uniformly and densely deposited on the carbon layer; after the lithium iron phosphate is coated, PVDF:SP is mixed at 96:2:2, the viscosity is 4000cP, the current collector is aluminum foil, and the coating surface density is 200g / m 2, pole piece thickness 160-1705 μm;

[0084] S2: negative electrode material preparation: crush the graphitized petroleum coke particles, and perform 3 h pre-carbonization treatment at a temperature of 500°C;

[0085] When coating the negative electrode, the treated graphitized petroleum coke particles are mixed with a binder and a conductive agent in a proportion, wherein the binder is selected from styrene-butadiene rubber (SBR), the conductive agent is selected from acetylene black (AB), and the mixing proportion is graphitized petroleum coke particles: binder: conductive agent = 95:2:3; the viscosity of the uniformly mixed slurry is controlled at 4000 cP, the current collector is copper foil, and the coating area density is 100 g / m 2 , pole piece thickness 125 μm;

[0086] S3: electrolyte preparation: mix organic solvents, lithium salt and additives under inert atmosphere; EC: DMC: EMC = 20:45:35 + LiPF61.3 mol / L + DTD 1.0% + BBP 2.0% + LiPO2F20.5%;

[0087] S4: battery assembly: after coating, rolling and winding the positive and negative electrodes, inject the electrolyte; use two-stage pressure control for middle rolling: the first stage pressure is 8T to form a dense layer on the current collector side, the current collector side porosity is 25%, the second stage pressure is 6T to maintain a surface porous layer, the surface layer porosity is 35%, so that the positive electrode piece has a gradient porosity structure; use a full-automatic winding machine, the winding tension is 1.5N, the separator thickness is 16 μm; the electrolyte injection amount is 4.0 g / Ah; the vacuum injection pressure is -90 kPa, and the maintaining time is 30 min; then, perform formation: at room temperature, 0.05C constant current to 3.0V, stand for 2h; 0.1C constant current to 3.6V, constant voltage to current ≤0.01C;

[0088] S5: step aging: sequentially perform 25°C × 24h → 45°C 0.2C cycle for 3 times → 60°C × 48h → -10°C × 12h.

[0089] Example 2

[0090] This example is basically the same as Example 1, except that the positive electrode piece has a gradient porosity structure, the current collector side porosity is 23%, the surface layer porosity is 37%, and the electrolyte contains DTD 1.2%.

[0091] Example 3

[0092] This example is basically the same as Example 1, except that the positive electrode piece has a gradient porosity structure, the current collector side porosity is 27%, the surface layer porosity is 33%, the electrolyte contains BBP 1.8%, and the separator thickness is 18 μm.

[0093] Example 4

[0094] This example is substantially the same as Example 1, except that the electrolyte contains LiPO2F2 0.6%.

[0095] Example 5

[0096] This example is substantially the same as Example 1, except that the electrolyte contains PS 0.5% instead of BBP.

[0097] Comparative Example 1

[0098] This comparative example is substantially the same as Example 1, except that the lithium iron phosphate matrix in the positive electrode material is only coated with carbon.

[0099] Comparative Example 2

[0100] This comparative example is substantially the same as Example 1, except that the electrolyte additive contains only FEC 5%.

[0101] Comparative Example 3

[0102] This comparative example is substantially the same as Example 1, except that the positive electrode sheet is uniform in porosity and is not gradient-rolled.

[0103] Comparative Example 4

[0104] This comparative example is substantially the same as Example 1, except that the aging process is only 25°C standing for 48h.

[0105] Experimental Case:

[0106] 1. General process for battery preparation

[0107] Preparation of the positive electrode: LiFePO4@C@Bi2O3, PVDF, SP were mixed at 96:2:2 and coated on a 12 μm aluminum foil;

[0108] Gradient rolling: 8T (current collector side) in the first zone → 5T (surface) in the second zone;

[0109] Preparation of the negative electrode: modified petroleum coke: CMC: SBR = 96:2:2 was coated on an 8 μm copper foil;

[0110] Assembly: winding (32700 cylindrical), liquid injection amount 5.5 g / Ah;

[0111] Formation: 0.05C to 3.0V → 0.1C to 3.6V.

[0112] 2. Test method

[0113] Cycle life: GB / T 31486-2024, charge-discharge cut-off voltage 2.5-3.65V;

[0114] Low temperature discharge: -20℃ for 4h, discharge to 2.5V at 0.2C;

[0115] High temperature storage: 60℃ full charge storage for 7 days, 25℃ capacity recovery rate test.

[0116] The above tests were carried out on Examples 1-5 and Comparative Examples 1-4, and the test results are shown in Table 1.

[0117]

[0118] As can be seen from the above table, Examples 1-4 significantly improve the comprehensive performance of wide-temperature-range lithium iron phosphate power batteries through a finely designed step-by-step aging process. Specifically, compared with the batteries in Comparative Example 4 which only use normal temperature aging, the batteries in Examples 1-4 have their internal components fully infiltrated, activated and stabilized after undergoing a four-step temperature aging sequence. This process not only promotes the formation of a stable solid electrolyte interface (SEI) film of DTD / FEC additives on the electrode surface, but also solidifies the mechanical strength of the SEI layer through high-temperature storage, so that it can maintain good structural stability in a wide temperature range. At the same time, the low-temperature storage stage at -10℃ makes the battery pre-adapt to the low-temperature lattice stress, thereby optimizing the charge-discharge performance of the battery under low-temperature conditions. These mechanisms work together to enable the batteries in Examples 1-4 to still exhibit high cycle capacity retention at -20℃ low temperature, and to exhibit excellent performance in high-temperature cycling at 55℃ and high-temperature storage at 60℃.

[0119] Although Example 5 uses a ternary additive combination of DTD, BBP and LiPO2F2, the synergistic effect between the additives is weakened due to the replacement of BBP with PS. In particular, in the high-temperature storage test, the capacity recovery rate of the battery in Example 5 is significantly lower than that in Example 1, indicating that the addition of PS may affect the stability of the electrolyte or the formation of the SEI layer. Therefore, the selection and ratio of additives are crucial for optimizing the performance of wide-temperature-range lithium iron phosphate power batteries. In summary, the present application significantly improves the comprehensive performance of wide-temperature-range lithium iron phosphate power batteries through the key technologies of finely designed positive electrode Bi2O3 coating layer, DTD / BBP / LiPO2F2 ternary additive, and four-step temperature aging sequence.

[0120] In Comparative Example 1, the positive electrode material was only carbon-coated without introducing a Bi2O3 coating layer. This design difference led to a significant decrease in the performance of the battery in Comparative Example 1 in a low-temperature environment. Specifically, after 0.2C cycling for 800 cycles at -20°C, the capacity retention rate of the battery in Comparative Example 1 was only 42.5%, which was much lower than the 82.1% of Example 1. This result directly reflects the important role of the Bi2O3 coating layer in improving the low-temperature performance of the battery. In addition, the performance of Comparative Example 1 in high-temperature cycling and storage tests was also relatively poor, further demonstrating the effectiveness of the positive electrode material design in the present application. Therefore, by comparing the performance differences between Example 1 and Comparative Example 1, the key role of the Bi2O3 coating layer in improving the comprehensive performance of lithium iron phosphate power batteries in a wide temperature range can be clearly seen.

[0121] In Comparative Example 2, the electrolyte additive only used FEC, without using the combination of DTD and BBP. This change led to an improvement in the performance of the battery in Comparative Example 2 at low temperatures, but it was still much lower than the level of Example 1, and the performance in the high-temperature storage test was significantly deteriorated. Specifically, the capacity retention rate of the battery in Comparative Example 2 after 0.2C cycling for 800 cycles at -20°C was 51.8%, which was higher than that of Comparative Example 1 without Bi2O3 coating, but still much lower than the 82.1% of Example 1. In terms of capacity recovery rate after full-charge storage at 60°C for 7 days, Comparative Example 2 was only 85.3%, which was significantly lower than the 98.5% of Example 1. This result not only highlights the synergistic effect of DTD and BBP additives in improving the high and low temperature performance of the battery, but also further verifies the rationality of the electrolyte additive combination design in the present application.

[0122] In Comparative Example 3, the positive electrode sheet used a uniform pore structure, rather than the gradient pore structure in Example 1. This design difference led to poor performance of the battery in Comparative Example 3 in terms of low-temperature electrolyte wetting, which in turn affected the overall performance of the battery. In particular, in the electrolyte wetting experiment at -20°C, the complete wetting time of the electrode sheet in Comparative Example 3 was as long as 45 minutes, which was much longer than the 15 minutes of Example 1. This result directly reflects the advantages of the gradient pore structure in accelerating the capillary penetration of the low-temperature electrolyte and improving the low-temperature performance of the battery. Therefore, by comparing the performance of Comparative Example 3 with Example 1, the important role of the gradient pore structure in optimizing the performance of lithium iron phosphate power batteries in a wide temperature range can be clearly seen.

[0123] In Comparative Example 4, the aging process only used normal temperature standing, and the four-stage temperature aging sequence was not implemented. This simplification resulted in the battery of Comparative Example 4 having significantly insufficient performance in a wide temperature range. Specifically, compared with Example 1 which experienced the complete four-stage temperature aging sequence, the capacity retention rate and recovery rate of the battery of Comparative Example 4 were significantly reduced in low-temperature cycling at -20°C, high-temperature cycling at 55°C, and high-temperature storage tests at 60°C. After 0.2C cycling at -20°C for 800 cycles, the capacity retention rate of the battery of Comparative Example 4 was only 43.8%, which was much lower than 82.1% of Example 1. This result directly reflects the important role of the four-stage temperature aging sequence in activating the interface stability in a wide temperature range and improving the comprehensive performance of the battery.

[0124] In summary, through the performance comparison of Examples 1-5 and Comparative Examples 1-4, it can be clearly seen that the present application has innovative points in the design of the positive electrode material, the combination of the electrolyte additives, and the aging process, and plays a key role in improving the comprehensive performance of the lithium iron phosphate power battery in a wide temperature range. These innovations enable the battery to maintain excellent cycle stability, high and low temperature adaptability, and safety in a wide temperature range.

[0125] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, and other ways constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A wide temperature range lithium iron phosphate power battery, characterized in that, Comprise: Positive active material: composed of lithium iron phosphate matrix and sequentially coated conductive layer, metal oxide layer, the metal oxide layer is bismuth-based oxide; Negative active material: graphitized petroleum coke particles. 2.The wide-temperature-range lithium iron phosphate power battery according to claim 1, characterized in that, The conductive layer is a carbon layer, the thickness is 3-6 nm, and / or the carbon content accounts for 1.5-2.5wt% of the mass of the lithium iron phosphate matrix; and / or The metal oxide layer is Bi2O3, the thickness is 2-5 nm, and / or the bismuth element accounts for 0.5-1.5wt% of the total mass of the positive active material. 3.The wide-temperature-range lithium iron phosphate power battery according to claim 1, characterized in that, Also include electrolyte, the electrolyte contains lithium salt, organic solvent and additive, the additive includes sulfur-containing cyclic ester compound, organic phosphate and fluorine-containing lithium salt; and / or The organic solvent is composed of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and the mass ratio is (15-25):(35-45):(30-40); and / or The lithium salt is LiPF6, and the concentration is 1.2-1.5mol / L. 4.The wide-temperature-range lithium iron phosphate power battery according to claim 3, characterized in that, The additive includes 0.5-1.5wt% of vinyl sulfate, 1.0-3.0wt% of butyl phenyl phosphate, and 0.3-0.8wt% of lithium difluorophosphate. 5.The wide-temperature-range lithium iron phosphate power battery according to claim 1, characterized in that, The positive electrode sheet in the wide temperature range lithium iron phosphate power battery has a gradient pore structure, the porosity of the current collector side is 20-28%, and the porosity of the surface layer is 30-38%.

6. A method for preparing the wide-temperature-range lithium iron phosphate power battery according to any one of claims 1-5, characterized in that, Comprise: S1: positive material preparation: sequentially forming a conductive layer and a metal oxide layer on the surface of lithium iron phosphate; S2: negative material preparation: crushing and pre-carbonizing the graphitized petroleum coke particles; S3: electrolyte preparation: mixing organic solvent, lithium salt and additive under inert atmosphere; S4: battery assembly: after coating, rolling and winding the positive and negative electrodes, injecting electrolyte; S5: step aging: sequentially performing 25-40℃ standing, 40-50℃ charge-discharge cycle, 50-70℃ high temperature storage and-15~-5℃ low temperature storage.

7. The preparation method of the wide-temperature-range lithium iron phosphate power battery according to claim 6, characterized in that, In step S1, the metal oxide layer is deposited by spray pyrolysis, the pyrolysis temperature is 280-320℃, and the precursor is bismuth nitrate alcohol solution.

8. The preparation method of the wide-temperature-range lithium iron phosphate power battery according to claim 6, characterized in that, The rolling in step S4 adopts two-stage pressure control: the first stage pressure is 7-10T to form a dense layer on the current collector side, and the second stage pressure is 4-7T to maintain a porous layer on the surface; and / or The winding tension is 1.0-2.0N, and the thickness of the separator is 14-18μm.

9. The method for preparing a wide-temperature-range lithium iron phosphate power battery according to claim 6, characterized in that, Step S5 step aging includes: First stage: 25-40℃ standing for 18-30h; Second stage: 0.1-0.3C charge-discharge 2-5 times at 40-50℃; Third stage: 50-70℃ storage for 40-56h; Fourth stage: -15~-5℃ storage for 10-15h.

10. The method of claim 6, wherein the lithium iron phosphate power battery with wide temperature range is prepared by the following steps. Step S3 electrolyte preparation is carried out in an environment with dew point ≤-40℃, and the moisture content is ≤10ppm; and / or The injection amount is 3.0-5.0g / Ah; and / or The vacuum injection pressure is ≤-90kPa.

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