Method for sealing and modifying surface defects of lithium manganate by using nano-metal phosphate clusters, lithium manganate sealed and modified by nano-metal phosphate clusters and application of lithium manganate sealed and modified by nano-metal phosphate clusters

Abstract

The invention discloses a method for sealing and modifying surface defects of lithium manganate by nano-metal phosphate clusters, the lithium manganate sealed and modified by the nano-metal phosphate clusters and application of the lithium manganate, and relates to the technical field of lithium ion batteries. According to the method for sealing and modifying the surface defects of the lithium manganate by the nano metal phosphate clusters, firstly, the lithium manganate powder is subjected to primary high-energy ball milling, potential hidden defects are exposed out, adsorption sites of metal phosphate are increased, heteroatoms can be promoted to enter the superficial surface of the lithium manganate in the dipping process, and the surface defects of the lithium manganate are effectively modified. And conditions are created for forming a heterogeneous interface. The subsequent sintering step can further repair cracks and defects on the surface of lithium manganate and is beneficial to construction of uniform nano-metal phosphate clusters, so that the high-temperature shelving capacity retention rate, the recovery rate and the normal-temperature and high-temperature cycling stability of a battery applying the material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular, to a method for sealing and modifying surface defects of lithium manganate with nano metal phosphate clusters, lithium manganate sealed and modified with nano metal phosphate clusters, and their applications. Background Art

[0002] As a cathode material, lithium manganate (LiMn₂O₄, LMO) has been favored for its affordability, high discharge voltage, and excellent safety performance, and has been widely used in many lithium ion battery applications. However, in practical applications, they also face some challenges. In LMO, Mn 3+ has a high-spin electron configuration (3d 4 4s 0 ), so the e g orbital has an asymmetric electron occupancy state. The resulting Jahn-Teller effect causes strong geometric distortion of the MnO₆ octahedron, leading to instability of the crystal structure and the risk of easy dissolution of Mn. In addition, during the synthesis process, the oxygen in LMO is lower than the standard stoichiometry. The presence of oxygen defects will accelerate the capacity decay. Moreover, the oxygen defects will also weaken the bond energy between metal atoms and oxygen atoms, and exacerbate the dissolution of manganese. The existence of defects results in poor battery cycle stability, fast high-temperature cycle decay, and low high-temperature shelf capacity retention rate.

[0003] To control the oxygen defect concentration in LMO, researchers usually perform bulk doping and surface coating on LMO to regulate the valence state of Mn and construct a passivation layer respectively. Doping heteroatoms to regulate the valence state often requires adding a large amount of heteroatom metal sources, and this process will lead to phase separation in the final product. On the other hand, methods such as solid-phase mixing sintering, atomic layer deposition, and liquid-phase coating can increase the cycle stability of LMO and slow down the high-temperature Mn dissolution phenomenon by constructing a coating layer on the surface of LMO, but this method has limitations such as high cost and long time consumption, and the thickness of the obtained coating layer is generally difficult to control, thus affecting the Li ion transport and the kinetics of Li ion deintercalation.

[0004] Therefore, it is of great significance to use a simple and low-cost preparation process to control the oxygen defect concentration in LMO and precisely modify and improve the defect sites on the surface of LMO to promote its wide application in energy storage and conversion.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for sealing and modifying surface defects of lithium manganate with nano metal phosphate clusters, lithium manganate sealed and modified with nano metal phosphate clusters, and their applications, so as to reduce the defects in lithium manganate and improve the cycle performance of the battery using it.

[0007] The present invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for surface defect encapsulation modification of lithium manganese oxide with nano metal phosphate clusters, including:

[0009] Step S1: Perform primary high-energy ball milling on lithium manganese oxide powder to obtain lithium manganese oxide with amplified defects, denoted as D-LMO;

[0010] Step S2: Immerse D-LMO in a precursor solution containing phosphate ions and metal ions, and then perform secondary high-energy ball milling to obtain lithium manganese oxide with nano phosphate clusters adsorbed on its surface, denoted as MPO NCs / D-LMO;

[0011] Step S3: Sinter a mixture including MPO NCs / D-LMO and a lithium source to obtain lithium manganese oxide encapsulated and modified with nano metal phosphate clusters, denoted as MPO NCs@LMO.

[0012] In an optional embodiment, the chemical formula of the lithium manganese oxide with amplified defects is Li x Mn2O y ; where the range of x is 0.5 - 1, the range of y is 3 - 4, and x and y should satisfy the condition: 6 < 2y - x < 8;

[0013] And / or, the defect concentration range in the lithium manganese oxide with amplified defects is 10 -15 ~10 -6 , and the defect concentration is characterized by electron paramagnetic resonance.

[0014] In an optional embodiment, the mass ratio of balls to materials in the primary high-energy ball milling is 0.9 - 1.1, the rotation speed of ball milling is 80 - 100 rpm, the time of ball milling is 0.5 - 4 hours, and the materials for ball milling are selected from at least one of zirconia, silicon carbide, and alumina;

[0015] And / or, the defect concentration range in the lithium manganese oxide with amplified defects is 10 -10 ~10 -8 ;

[0016] And / or, the defect concentration range in the lithium manganese oxide with nano phosphate clusters adsorbed on its surface is 10 -10 ~10 -9 ;

[0017] And / or, the defect concentration in the lithium manganese oxide with amplified defects is greater than the defect concentration in the lithium manganese oxide with nano phosphate clusters adsorbed on its surface.

[0018] In an optional embodiment, the molar ratio of metal ions to phosphate ions in the precursor solution is 1 - 3;

[0019] And / or, the phosphate radical is derived from at least one of phosphoric acid, lithium dihydrogen phosphate, lithium hydrogen phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, potassium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, magnesium hydrogen phosphate, calcium hydrogen phosphate and calcium phosphate;

[0020] And / or, the metal ions are derived from at least one of sulfates, carbonates, acetates, nitrates, chlorides and hydroxides of metals in Group IA, Group IIA, Group IIIB, Group IVB, Group VB, Group VIB, Group VIIB and Group VIIIB;

[0021] And / or, the solvent in the precursor solution is at least one of water and alcohol.

[0022] In an optional embodiment, in the step S2, the molar ratio of the D-LMO to the phosphate radical in the precursor solution is 1 to 1000, and the mass ratio of the D-LMO to the precursor solution is 0.1 to 2.

[0023] In an optional embodiment, the impregnation time is 0.5 to 10 h;

[0024] And / or, ultrasound is accompanied during the impregnation process, and the ultrasound frequency is 10 to 40 kHz; and / or, stirring is accompanied during the impregnation process, and the rotation speed of the stirring is 50 to 200 rpm.

[0025] In an optional embodiment, the mass ratio of the balls to the material in the secondary high-energy ball milling is 0.8 to 1.2, the rotation speed of the ball milling is 20 - 70 rpm, the time of the ball milling is 0.5 to 2 h, and the material of the balls is selected from at least one of zirconia, silicon carbide and alumina.

[0026] And / or, after the secondary high-energy ball milling, the powder is washed to obtain lithium manganate with nano-phosphate clusters adsorbed on the surface.

[0027] In an optional embodiment, the sintering temperature is 200 to 800 °C, and the sintering time is 0.5 to 4 hours;

[0028] And / or, the sintering atmosphere is one of air, 5% hydrogen, oxygen, argon and nitrogen.

[0029] In a second aspect, the present invention provides a lithium manganate encapsulated and modified with nano-metal phosphate clusters. In the lithium manganate encapsulated and modified with nano-metal phosphate clusters, the mass ratio of the nano-metal phosphate clusters to the lithium manganate is 0.0001 to 0.005;

[0030] And / or, the ratio of the average particle size of the nano-metal phosphate clusters to the average particle size of the lithium manganate is 10 -4 ~10-3 ;

[0031] And / or, the average particle size of the nano metal phosphate cluster is 0.5 - 5 nm.

[0032] In a third aspect, the present invention provides an application of lithium manganate modified by encapsulation with the nano metal phosphate cluster described in the foregoing embodiments in a lithium ion battery.

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

[0034] When the lithium manganate material modified by encapsulation with the nano metal phosphate cluster prepared by the method of the present application is applied to a battery, it is more stable during the charge and discharge cycle process, effectively alleviates the dissolution phenomenon of Mn, and improves the safety of the battery. In addition, after assembling the modified lithium manganate material with a graphite negative electrode into a full battery, the high-temperature storage capacity retention rate, recovery rate, and normal-temperature and high-temperature cycle stability of the battery core are all significantly improved. Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0036] Figure 1 XRD pattern of MPO NCs@LMO prepared in Example 1;

[0037] Figure 2 SEM image of MPO NCs@LMO prepared in Example 1. Detailed Embodiments

[0038] In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0039] The embodiment of the present invention provides a method for modifying the surface defects of lithium manganate by encapsulation with nano metal phosphate clusters, including:

[0040] Step S1: Perform high-energy ball milling on lithium manganate powder once to obtain lithium manganate with amplified defects, denoted as D-LMO;

[0041] Step S2: D-LMO is immersed in a precursor solution containing phosphate and metal ions, and then subjected to secondary high-energy ball milling to obtain lithium manganese oxide with nano-phosphate clusters adsorbed on the surface, which is recorded as MPO NCs / D-LMO;

[0042] Step S3: sintering the mixture including MPO NCs / D-LMO and the lithium source to obtain lithium manganese oxide modified by nano-metal phosphate clusters, which is recorded as MPO NCs@LMO.

[0043] In the method for sealing and modifying the surface defects of lithium manganese oxide with nano-metal phosphate clusters in the embodiment of the present application, the lithium manganese oxide powder is first subjected to high-energy ball milling to expose potential hidden defects, increase the adsorption sites for metal phosphate, and the impregnation process can promote the entry of heterogeneous atoms into the shallow surface of lithium manganese oxide, creating conditions for the formation of heterogeneous interfaces. The subsequent sintering step can further repair the cracks and defects on the surface of lithium manganese oxide, which is conducive to the construction of uniform nano-metal phosphate clusters.

[0044] The nano-metal phosphate clusters obtained in the embodiment of the present application are used in batteries to modify the lithium manganese oxide material, which is more stable during the charge and discharge cycle, effectively alleviates the dissolution of Mn, and improves the safety of the battery. In addition, after the modified lithium manganese oxide material is assembled with a graphite negative electrode into a full battery, the high-temperature storage capacity retention rate, recovery rate, and normal temperature and high temperature cycle stability of the battery cell are significantly improved.

[0045] In order to replenish the Li lost on the surface of lithium manganate during the ball milling process, a small amount of lithium salt needs to be added again during the sintering process. The lithium salt can be lithium carbonate, lithium chloride or lithium sulfate, and the mass ratio of the lithium salt to the mass ratio of the lithium manganate powder in step 1 can be 0.02 to 0.1.

[0046] In an optional embodiment, the chemical formula of the lithium manganese oxide of the amplified defect is Li x Mn2O y ; The range of x is 0.5~1, the range of y is 3~4, and x and y should meet the condition: 6<2y-x<8;

[0047] And / or, the defect concentration range of the amplified defect lithium manganese oxide is 10 -15 ~10 -6 The defect concentration is obtained by electron paramagnetic resonance characterization. The test method is: take 50 mg of sample and place it on the sample table. After the test is completed, the Q factor is calculated using the calculation module provided by the software to obtain the absolute defect concentration.

[0048] If the D-LMO has fewer defects, there are fewer adsorption sites for phosphates, which is not conducive to promoting the entry of heteroatoms into the superficial layer of lithium manganate during the impregnation process, and is not conducive to constructing uniform nano-metal phosphate clusters on the surface of lithium manganate subsequently; if there are too many defects, too many heteroatoms are adsorbed, resulting in a decrease in the content of lithium phosphate, and further reducing the capacity of MPO NCs@LMO. In some embodiments, the defect concentration range in the lithium manganate with amplified defects is 10 -10 ~10 -8 and the defect concentration range in the lithium manganate with surface-adsorbed nano-phosphate clusters is 10 -10 ~10 -9 , and the defect concentration in the lithium manganate with amplified defects is greater than the defect concentration in the lithium manganate with surface-adsorbed nano-phosphate clusters. The impregnation process can promote the entry of heteroatoms into the superficial layer of lithium manganate, thereby facilitating the reduction of the defect concentration.

[0049] In an alternative embodiment, the mass ratio of balls to materials in the first high-energy ball milling is 0.9 - 1.1, the rotation speed of the ball milling is 80 - 100 rpm, the time of the ball milling is 0.5 - 4 hours, and the materials for the ball milling are selected from at least one of zirconia, silicon carbide, and alumina.

[0050] By adjusting the conditions of the first high-energy ball milling, D-LMO with defects meeting the requirements is obtained.

[0051] In an alternative embodiment, the molar ratio of metal ions to phosphate ions in the precursor solution is 1 - 3;

[0052] and / or, the phosphate is derived from at least one of phosphoric acid, lithium dihydrogen phosphate, lithium hydrogen phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, potassium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, magnesium hydrogen phosphate, calcium hydrogen phosphate, and calcium phosphate;

[0053] and / or, the metal ions are derived from at least one of sulfates, carbonates, acetates, nitrates, chlorides, and hydroxides of metals in Group ⅠA, Group ⅡA, Group ⅢB, Group ⅣB, Group ⅤB, Group ⅥB, Group ⅦB, and Group ⅧB;

[0054] and / or, the solvent in the precursor solution is at least one of water and alcohol.

[0055] During impregnation, metal ions are adsorbed on the adsorption sites of lithium manganese oxide powder, and phosphate groups form metal phosphates adsorbed on the adsorption sites of lithium manganese oxide by binding with metal ions. Therefore, by adjusting the molar ratio of metal ions to phosphate ions in the precursor solution, the composition of metal phosphates in MPO NCs@LMO can be adjusted to more effectively improve the capacity retention rate, recovery rate, and cycle stability at room temperature and high temperature of the battery using MPO NCs@LMO, etc.

[0056] In an alternative embodiment, in step S2, the molar ratio of D-LMO to phosphate in the precursor solution is 1 to 1000, and the mass ratio of D-LMO to the precursor solution is 0.1 to 2.

[0057] By adjusting the concentration and quantity of phosphate and metal ions in the precursor solution, the quantity and rate of the precursor adsorbed by lithium manganese oxide powder can be adjusted, which is beneficial to adjusting the mass ratio of nano-metal phosphate clusters to lithium manganese oxide in MPO NCs@LMO.

[0058] In an alternative embodiment, the impregnation time is 0.5 to 10 h;

[0059] And / or, ultrasound is accompanied during impregnation, and the ultrasound frequency is 10 to 40 kHz; and / or, stirring is accompanied during impregnation, and the rotation speed of the stirring is 50 to 200 rpm.

[0060] The accompaniment of ultrasound or stirring during impregnation is beneficial to the uniform mixing of materials in the liquid and the full contact of metal ions and phosphate groups with lithium manganese oxide.

[0061] In an alternative embodiment, the mass ratio of balls to materials in the secondary high-energy ball milling is 0.8 to 1.2, the rotation speed of the ball milling is 20 - 70 rpm, the ball milling time is 0.5 to 2 h, and the material of the balls is selected from at least one of zirconia, silicon carbide, and alumina;

[0062] And / or, the powder is washed after the secondary high-energy ball milling to obtain lithium manganese oxide with nano-phosphate clusters adsorbed on its surface.

[0063] The secondary high-energy ball milling can promote the entry of heteroatoms into the surface layer of lithium manganese oxide, creating conditions for the subsequent formation of hetero-interfaces.

[0064] In an alternative embodiment, the sintering temperature is 200 to 800 °C, and the sintering time is 0.5 to 4 hours;

[0065] And / or, the sintering atmosphere is one of air, 5% hydrogen, oxygen, argon, and nitrogen, preferably inert gases such as argon and nitrogen.

[0066] The sintering step further enhances the interaction between the phosphate clusters and lithium manganese oxide, enabling the original nano-metal phosphate clusters adsorbed on the surface of lithium manganese oxide to be supported on the surface of lithium manganese oxide through chemical bond interactions and forming a heterogeneous interface, ultimately resulting in the encapsulation and modification of lithium manganese oxide by nano-metal phosphate clusters.

[0067] An embodiment of the present invention also provides a lithium manganese oxide encapsulated and modified by nano-metal phosphate clusters. In the lithium manganese oxide encapsulated and modified by nano-metal phosphate clusters, the mass ratio of the nano-metal phosphate clusters to lithium manganese oxide is 0.0001 - 0.005;

[0068] and / or, the ratio of the average particle size of the nano-metal phosphate clusters to the average particle size of lithium manganese oxide is 10 -4 ~10 -3 ;

[0069] and / or, the average particle size of the nano-metal phosphate clusters is 0.5 - 5 nm.

[0070] By regulating the average particle size and content of the nano-metal phosphate clusters, a uniform layer of nano-metal phosphate clusters can be constructed on the surface of lithium manganese oxide, enhancing the structural stability and electrochemical performance of the lithium manganese oxide material while reducing the capacity loss caused by the introduction of excessive nano-metal phosphate clusters.

[0071] An embodiment of the present invention also provides an application of the lithium manganese oxide encapsulated and modified by the aforementioned nano-metal phosphate clusters in a lithium-ion battery.

[0072] The features and properties of the present invention are further described in detail below in conjunction with examples.

[0073] Example 1

[0074] This example provides a method for encapsulating and modifying the surface defects of lithium manganese oxide with nano-metal phosphate clusters, including the following steps:

[0075] Step S1: Perform primary high-energy ball milling on lithium manganese oxide powder. The ball milling speed is 90 rpm, the ball-to-material mass ratio is 1, the ball milling time is 2 hours, and the ball milling material is zirconia, obtaining lithium manganese oxide with amplified defects, denoted as D-LMO. After XPS characterization to determine the element ratio, with the stoichiometric ratio of Mn being 2, the calculated chemical formula is Li 0.93 Mn2O 3.91 ; The defect concentration measured using an electron paramagnetic resonance spectrometer is 7.1*10 -9 .

[0076] In step S2, D-LMO is impregnated in a precursor solution containing phosphate and metal ions, followed by secondary high-energy ball milling. The ball milling speed is 50 rpm, the ball-to-material mass ratio is 1, the ball milling time is 1 h, and the ball milling material is zirconia. After secondary high-energy ball milling, the powder is washed to obtain lithium manganate with surface-adsorbed nano-phosphate clusters, denoted as MPO NCs / D-LMO. The defect concentration measured by an electron paramagnetic resonance spectrometer is 3.3×10 -10 ;

[0077] Among them, the precursor solution is a mixed aqueous solution of phosphoric acid and lithium phosphate. The molar ratio of metal ions to phosphate ions is 2. The molar ratio of D-LMO to phosphate in the precursor solution is 500. The mass ratio of D-LMO to the precursor solution is 1. The impregnation time is 5 h, and ultrasound is applied during the impregnation process. The ultrasonic frequency is 25 kHz;

[0078] In step S3, a mixture of MPO NCs / D-LMO and lithium carbonate mixed at a mass ratio of 1:0.05 is sintered at a sintering temperature of 500 °C for 2 h in an argon atmosphere to obtain lithium manganate closed-modified with nano-metal phosphate clusters, denoted as MPO NCs@LMO. The XRD and SEM diagrams are as shown in Figure 1 and Figure 2 shown. Among them, the mass ratio of the nano-metal phosphate clusters to lithium manganate is 0.002. The ratio of the average particle size of the nano-metal phosphate clusters to the average particle size of lithium manganate is 3.5×10 -3 , and the average particle size of the nano-metal phosphate clusters is 3.1 nm.

[0079] Example 2

[0080] This example provides a method for surface defect encapsulation modification of lithium manganate with nano-metal phosphate clusters, including the following steps:

[0081] In step S1, lithium manganate powder is subjected to primary high-energy ball milling. The ball milling speed is 80 rpm, the ball-to-material mass ratio is 0.9, the ball milling time is 4 h, and the ball milling material is zirconia to obtain lithium manganate with amplified defects, denoted as D-LMO. The elemental ratio is determined by XPS characterization. With the stoichiometric ratio of Mn being 2, the chemical formula is calculated as Li 0.94 Mn2O 3.87 ; The defect concentration measured by an electron paramagnetic resonance spectrometer is 1.0×10 -8 .

[0082] In step S2, D-LMO is immersed in a precursor solution containing phosphate and metal ions, followed by secondary high-energy ball milling at a ball milling speed of 30 rpm, a ball-to-material mass ratio of 1.2, a ball milling time of 0.5 h, and the ball milling material is zirconia. After the secondary high-energy ball milling, the powder is washed to obtain lithium manganate with nano-phosphate clusters adsorbed on its surface, denoted as MPO NCs / D-LMO. The defect concentration measured by an electron paramagnetic resonance spectrometer is 9.5*10 -10 ;

[0083] Among them, the precursor solution is an aqueous mixture of phosphoric acid, lithium dihydrogen phosphate, and iron chloride. The molar ratio of metal ions to phosphate ions is 1. The molar ratio of D-LMO to phosphate in the precursor solution is 1000. The mass ratio of D-LMO to the precursor solution is 0.1. The impregnation time is 0.5 h, and ultrasound is applied during the impregnation process. The ultrasound frequency is 10 kHz;

[0084] In step S3, a mixture of MPO NCs / D-LMO and lithium carbonate mixed at a mass ratio of 1:0.1 is sintered at a sintering temperature of 200 °C for 4 hours in a nitrogen atmosphere to obtain lithium manganate with nano-metal phosphate clusters used for closed modification, denoted as MPO NCs@LMO.

[0085] Example 3

[0086] This example provides a method for surface defect modification of lithium manganate by nano-metal phosphate clusters, including the following steps:

[0087] In step S1, lithium manganate powder is subjected to primary high-energy ball milling at a ball milling speed of 100 rpm, a ball-to-material mass ratio of 1.1, a ball milling time of 0.5 hours, and the ball milling material is zirconia to obtain lithium manganate with amplified defects, denoted as D-LMO. The elemental ratio is determined by XPS characterization. Taking the stoichiometric ratio of Mn as 2, the chemical formula is calculated as Li 0.96 Mn2O 3.79 , and the defect concentration measured by an electron paramagnetic resonance spectrometer is 4.7*10 -9 ;

[0088] In step S2, D-LMO is immersed in a precursor solution containing phosphate and metal ions, followed by secondary high-energy ball milling at a ball milling speed of 40 rpm, a ball-to-material mass ratio of 0.8, a ball milling time of 2 h, and the ball milling material is zirconia. After the secondary high-energy ball milling, the powder is washed to obtain lithium manganate with nano-phosphate clusters adsorbed on its surface, denoted as MPO NCs / D-LMO. The defect concentration measured by an electron paramagnetic resonance spectrometer is 8.3*10 -10 ;

[0089] Among them, the precursor solution is an aqueous mixture of ammonium dihydrogen phosphate, cobalt nitrate, and iron chloride, where the molar ratio of metal ions to phosphate ions is 3, the molar ratio of the D-LMO to the phosphate in the precursor solution is 1, the mass ratio of the D-LMO to the precursor solution is 2, the impregnation time is 10 h, and ultrasound is accompanied during the impregnation process, and the ultrasound frequency is 40 kHz;

[0090] In step S3, a mixture including MPO NCs / D-LMO and lithium carbonate mixed in a mass ratio of 1:0.05 is sintered at a sintering temperature of 800 °C for 0.5 h in an argon atmosphere to obtain lithium manganate modified by nano-metal phosphate clusters and denoted as MPO NCs@LMO.

[0091] Example 4

[0092] This example provides a method for surface defect encapsulation modification of lithium manganate with nano-metal phosphate clusters. The difference from Example 1 is only that stirring is accompanied during the impregnation process, ultrasound is not introduced, the rotation speed of the stirring is 200 rpm, and the second ball milling treatment is not performed in step S2.

[0093] Example 5

[0094] This example provides a method for surface defect encapsulation modification of lithium manganate with nano-metal phosphate clusters. The difference from Example 1 is only that the high-energy ball milling parameters in step S1 are adjusted. Specifically, the ball-to-material mass ratio is 0.9, the ball milling rotation speed is 60 rpm, the ball milling time is 0.5 h, and the ball milling material is zirconia to obtain lithium manganate with amplified defects denoted as D-LMO. After XPS characterization to determine the element ratio, with the stoichiometric ratio of Mn being 2, the chemical formula is calculated as Li 0.97 Mn2O 3.94 , and the defect concentration measured using an electron paramagnetic resonance spectrometer is 1.35*10 -10 .

[0095] Comparative Example 1

[0096] This comparative example provides a method for surface defect encapsulation modification of lithium manganate with nano-metal phosphate clusters. The difference from Example 1 is only that step S1 is omitted and no secondary high-energy ball milling is performed in step S2.

[0097] Comparative Example 2

[0098] This comparative example provides a method for surface defect encapsulation modification of lithium manganate with nano-metal phosphate clusters. The difference from Example 1 is only that step S1 is omitted.

[0099] Comparative Example 3

[0100] This comparative example provides a method for surface defect encapsulation modification of lithium manganese oxide with nano metal phosphate clusters. The difference from Example 1 is only that step S2 is omitted. In step S3, a mixture of D-LMO and lithium carbonate mixed at a mass ratio of 1:0.05 is sintered.

[0101] The lithium manganese oxide encapsulated and modified with nano metal phosphate clusters prepared in the above examples and comparative examples was assembled into a battery, and the cycle performance, high-temperature storage capacity retention rate, and recovery rate of the battery were tested. The results are shown in Tables 1 and 2.

[0102] The test methods for the cycle performance, high-temperature storage capacity retention rate, and recovery rate of the battery are as follows:

[0103] Cycle performance:

[0104] In an environment with a temperature of 25°C ± 2°C, the assembled battery is charged at a constant current rate of 0.5C until the voltage reaches 4.2V, and then charged at a constant voltage of 4.2V until the current reaches 0.05C. After being fully charged, it is left to stand for 0.5h, and then discharged at a constant current rate of 1C until the voltage reaches 2.7V. Record the discharge time and calculate the discharge capacity.

[0105] After one charge-discharge cycle test of the battery, it is left to stand for 0.5h, and then the next charge-discharge cycle is carried out.

[0106] High-temperature storage capacity retention rate:

[0107] In an environment with a temperature of 25°C ± 2°C, the assembled battery is charged at a constant current rate of 0.5C until the voltage reaches 4.2V, and then charged at a constant voltage of 4.2V until the current reaches 0.05C. After being fully charged, it is left to stand for 0.5h, and then discharged at a constant current rate of 1C until the voltage reaches 2.7V. Record the discharge time and calculate the discharge capacity.

[0108] After that, in an environment with a temperature of 25°C ± 2°C, the assembled battery is charged at a constant current rate of 0.5C until the voltage reaches 4.2V, and then charged at a constant voltage of 4.2V until the current reaches 0.05C. After charging is completed, the battery is placed open-circuited in an environment with a temperature of 45°C ± 2°C for 7 days, and then discharged at a constant current rate of 1C in an environment with a temperature of 25°C ± 2°C until the voltage reaches 2.7V. Record the discharge time and calculate the discharge capacity.

[0109] High-temperature storage capacity recovery rate:

[0110] In an environment with a temperature of 25°C ± 2°C, the battery that has completed the high-temperature shelf capacity retention is charged at a constant current rate of 0.5C until the voltage reaches 4.2V, then charged at a constant voltage of 4.2V until the current reaches 0.05C. After being fully charged, it is left on the shelf for 0.5h, and then discharged at a constant current rate of 1C until the voltage reaches 2.7V. Record the discharge time and calculate the discharge capacity.

[0111] The assembly of the battery includes the following steps:

[0112] 1. The main positive electrode material, conductive carbon black, CNT, and binder are fed in a mass ratio of 96.0:1.0:1.0:2.0 to prepare a positive electrode slurry with a solid content of 60%. After coating on aluminum foil, it is processed through processes such as rolling and die-cutting to obtain a positive electrode sheet.

[0113] 2. Graphite, conductive carbon black, thickening agent, and binder are fed in a ratio of 95.0:1.0:1.5:2.5 to prepare a negative electrode slurry with a solid content of 52%. After coating on copper foil, it is processed through processes such as rolling and die-cutting to obtain a negative electrode sheet.

[0114] 3. The positive and negative electrode sheets and the separator are stacked in a certain quantity, placed in the housing, and then processed through processes such as welding, casing, drying, liquid injection, formation, and grading to obtain a single cell.

[0115] Table 1

[0116]

[0117] Table 2

[0118]

[0119]

[0120] Through adsorption impregnation and subsequent ball milling and sintering, the phosphate can be firmly bonded to the surface of LMO. After the LMO defect sites are modified by metal phosphate, the surface oxygen defects of LMO are reduced, the valence state of surface Mn ions is increased, the distortion of the surface MnO6 octahedral structure is reduced, the surface structure stability of the material is improved, and the phosphate has the property of resisting protonic acid, which can improve the corrosion resistance of the positive electrode material to hydrofluoric acid. The synthesized MPO NCs@LMO has good corrosion resistance and structural stability, so it has good high-temperature stability and cycle stability in the battery cell.

[0121] Compared with Example 1, in Comparative Example 1, the oxygen defects of LMO were not amplified and ball milling was not carried out. Therefore, the binding amount of metal phosphate was small and the stability was reduced. In Comparative Example 2, the oxygen defects of LMO were not amplified. Although ball milling was carried out, due to the small number of phosphate adsorption sites on the surface, the phosphate content introduced on the surface of LMO in the subsequent impregnation and ball milling steps was still small. Although the high-temperature cycling performance was improved compared with Comparative Example 1, it was much lower than that of Example 1. In Comparative Example 3, the oxygen defects on the surface of LMO were amplified, but phosphate modification was not carried out. Therefore, the capacity decay was the fastest.

[0122] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for surface defect encapsulation modification of lithium manganate by nano metal phosphate clusters, characterized in that Including: Step S1: Conduct primary high-energy ball milling on lithium manganese oxide powder to obtain lithium manganese oxide with amplified defects, denoted as D-LMO; Step S2: Immerse D-LMO in a precursor solution containing phosphate groups and metal ions, and then conduct secondary high-energy ball milling to obtain lithium manganese oxide with nano-phosphate clusters adsorbed on its surface, denoted as MPO NCs / D-LMO; Step S3: Sinter a mixture including MPO NCs / D-LMO and a lithium source to obtain lithium manganese oxide modified by nano-metal phosphate clusters in a closed manner, denoted as MPO NCs@LMO.

2. The method for surface defect encapsulation modification of lithium manganate by nano metal phosphate clusters according to claim 1, wherein The chemical formula of the manganese lithium oxide with amplification defect is Li x Mn2O y ; wherein the range of x is 0.5 to 1, the range of y is 3 to 4, and x and y should satisfy the condition: 6 < 2y - x < 8; And / or, the defect concentration ranges of both the lithium manganese oxide with amplification defects and the lithium manganese oxide with surface-adsorbed nano-phosphate clusters are 10 -15 ~10 -6 , and the defect concentration is characterized by electron paramagnetic resonance.

3. The method for surface defect passivation of lithium manganate by nano metal phosphate clusters according to claim 1, characterized in that The mass ratio of balls to materials in the primary high-energy ball milling is 0.9 - 1.1, the rotation speed of ball milling is 80 - 100 rpm, the time of ball milling is 0.5 - 4 hours, and the material of the balls is selected from at least one of zirconia, silicon carbide, and alumina; and / or, the defect concentration range in the manganese lithium oxide with amplification defect is 10 -10 ~10 -8 ; and / or, the defect concentration range in the lithium manganate with surface-adsorbed nano-phosphate clusters is 10 -10 ~10 -9 ; And / or, the defect concentration in the lithium manganese oxide with amplified defects is greater than the defect concentration in the lithium manganese oxide with nano-phosphate clusters adsorbed on its surface.

4. The method for surface defect encapsulation modification of lithium manganate by nano metal phosphate clusters according to claim 1, characterized in that The molar ratio of metal ions to phosphate ions in the precursor solution is 1 - 3; And / or, the phosphate group is derived from at least one of phosphoric acid, lithium dihydrogen phosphate, lithium hydrogen phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, potassium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, magnesium hydrogen phosphate, calcium hydrogen phosphate, and calcium phosphate; And / or, the metal ions are derived from at least one of sulfates, carbonates, acetates, nitrates, chlorides, and hydroxides of metals in Group IA, Group IIA, Group IIIB, Group IVB, Group VB, Group VIB, Group VIIB, and Group VIIIB; And / or, the solvent in the precursor solution is at least one of water and alcohol.

5. The method for surface defect passivation modification of lithium manganate by nano-metal phosphate clusters according to claim 1, characterized in that In Step S2, the molar ratio of D-LMO to phosphate groups in the precursor solution is 1 - 1000, and the mass ratio of D-LMO to the precursor solution is 0.1 - 2.

6. The method for surface defect passivation modification of lithium manganate by nano metal phosphate clusters according to claim 1, characterized in that The immersion time is 0.5 - 10 h; And / or, ultrasonic waves are accompanied during the immersion process, and the ultrasonic frequency is 10 - 40 kHz; and / or, stirring is accompanied during the immersion process, and the rotation speed of the stirring is 50 - 200 rpm.

7. The method for surface defect encapsulation modification of lithium manganate by nano metal phosphate clusters according to claim 1, characterized in that The mass ratio of balls to materials in the secondary high-energy ball milling is 0.8 - 1.2, the rotation speed of ball milling is 20 - 70 rpm, the time of ball milling is 0.5 - 2 h, and the material of the balls is selected from at least one of zirconia, silicon carbide, and alumina; And / or, the powder is washed after the secondary high-energy ball milling to obtain lithium manganese oxide with nano-phosphate clusters adsorbed on its surface.

8. The method for surface defect passivation modification of lithium manganate by nano metal phosphate clusters according to claim 1, characterized in that The sintering temperature is 200 - 800 °C, and the sintering time is 0.5 - 4 hours; And / or, the sintering atmosphere is one of air, 5% hydrogen, oxygen, argon, and nitrogen.

9. Lithium manganate encapsulated and modified by nano metal phosphate clusters obtained by the method according to any one of claims 1-8, characterized in that, In the lithium manganese oxide modified by nano-metal phosphate clusters in a closed manner, the mass ratio of the nano-metal phosphate clusters to lithium manganese oxide is 0.0001 - 0.005; and / or, the ratio of the average particle size of the nano metal phosphate cluster to the average particle size of lithium manganate is 10 -4 ~10 -3 ; And / or, the average particle size of the nano-metal phosphate clusters is 0.5 - 5 nm.

10. Application of the lithium manganese oxide modified by nano-metal phosphate clusters in a closed manner as claimed in claim 9 in a lithium-ion battery.

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