Positive electrode material, positive electrode sheet, secondary battery and electronic device

Abstract

Provided in the present application are a positive electrode material, a positive electrode sheet, a secondary battery and an electronic device. The positive electrode material comprises lithium manganese iron phosphate. The positive electrode material comprises a first element and a second element, wherein the first element comprises at least one of magnesium, nickel, cobalt or zinc; the second element comprises at least one of titanium or zirconium; and the mass ratio of the first element to the second element is 1 to 20. The positive electrode material satisfying the above-mentioned characteristics can improve the dynamic performance and cycle performance of the positive electrode material, and the positive electrode material also has a relatively high capacity.

Description

Positive electrode materials, positive electrode sheets, secondary batteries and electronic devices

[0001] This application claims priority to Chinese Patent Application No. 202411511535.5, filed on October 28, 2024, entitled "Positive Electrode Material, Positive Electrode Sheet, Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a positive electrode material, a positive electrode sheet, a secondary battery, and an electronic device. Background Technology

[0003] To address the severe global energy crisis, environmental pollution, climate change, and the development of a low-carbon economy, the research and application of electric vehicles, large-scale power supplies, and energy storage technologies have become inevitable. Lithium iron phosphate (LFP) batteries, as a crucial component, offer advantages such as long lifespan, safety, and affordability; however, LFP batteries suffer from relatively low energy density.

[0004] Lithium iron manganese phosphate (LiFeMnPO4) incorporates a certain proportion of Mn into lithium iron phosphate, which increases its average voltage and energy density. However, lithium iron manganese phosphate exhibits the Jan Taylor effect, resulting in poor kinetic and cycle performance. Summary of the Invention

[0005] The purpose of this application is to provide a positive electrode material, a positive electrode sheet, a secondary battery, and an electronic device to improve the kinetic performance and cycle performance of the positive electrode material, while also enabling the positive electrode material to have a higher capacity. The specific technical solution is as follows:

[0006] The first aspect of this application provides a cathode material comprising lithium manganese iron phosphate. The cathode material includes a first element and a second element. The first element includes at least one selected from magnesium, nickel, cobalt, or zinc, and the second element includes at least one selected from titanium or zirconium. The mass ratio of the first element to the second element is 1 to 20. When the cathode material includes lithium manganese iron phosphate and comprises the first and second elements, and the types and mass ratio of the first and second elements are within the scope of this application, the kinetic performance and cycle performance of the cathode material can be improved, while also giving the cathode material a higher capacity.

[0007] In one or more embodiments of this application, at least a portion of the surface of lithium manganese iron phosphate is provided with carbon material. Providing at least a portion of the surface of lithium manganese iron phosphate with carbon material can improve the electronic conductivity of lithium manganese iron phosphate, thereby improving the kinetic performance and cycle performance of the cathode material.

[0008] In one or more embodiments of this application, the first element includes magnesium, and the second element includes titanium, with a mass ratio of magnesium to titanium of 1 to 8. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, magnesium is included as the first element. Doping with magnesium can improve the lattice volume change between delithiated MnFeMgPO4 and lithium-intercalated LiMnFeMgPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, titanium, being a high-valence metal element, can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, which in turn leads to improved cycle performance. Furthermore, with a suitable mass ratio of magnesium to titanium, the cathode material exhibits higher capacity and compaction density.

[0009] In one or more embodiments of this application, the first element includes nickel, and the second element includes titanium, with a mass ratio of nickel to titanium of 1 to 15. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes nickel. Doping with nickel can improve the lattice volume change between delithiated MnFeNiPO4 and lithium-intercalated LiMnFeNiPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, titanium, being a high-valence metal element, can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, which in turn leads to improved cycle performance. Furthermore, with a suitable mass ratio of nickel to titanium, the cathode material exhibits high capacity and compaction density.

[0010] In one or more embodiments of this application, the first element includes cobalt, and the second element includes titanium, with a mass ratio of cobalt to titanium of 1 to 15. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, cobalt is included as the first element. Doping with cobalt can improve the lattice volume change between delithiated MnFeCoPO4 and lithiated LiMnFeCoPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, titanium, being a high-valence metal element, can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, which in turn leads to improved cycle performance. Furthermore, with a suitable mass ratio of cobalt to titanium, the cathode material exhibits higher capacity and compaction density.

[0011] In one or more embodiments of this application, the first element includes zinc, and the second element includes titanium, with a zinc to titanium mass ratio of 1 to 20. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, zinc is included as the first element. Doping with zinc can improve the lattice volume change between delithiated MnFeZnPO4 and lithium-intercalated LiMnFeZnPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, titanium, being a high-valence metal element, can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, which in turn leads to improved cycle performance. Furthermore, with a suitable zinc to titanium mass ratio, the cathode material exhibits high capacity and compaction density.

[0012] In one or more embodiments of this application, the first element includes magnesium, and the second element includes zirconium, with a mass ratio of magnesium to zirconium of 1 to 4. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes magnesium. Doping with magnesium can improve the lattice volume change between delithiated MnFeMgPO4 and lithium-intercalated LiMnFeMgPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, the second element includes zirconium, a high-valence metal element that can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, with a suitable mass ratio of magnesium to zirconium, the cathode material exhibits high capacity and compaction density.

[0013] In one or more embodiments of this application, the first element includes nickel, and the second element includes zirconium, with a mass ratio of nickel to zirconium of 1 to 6. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes nickel. Doping with nickel can improve the lattice volume change between delithiated MnFeNiPO4 and lithium-intercalated LiMnFeNiPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, the second element includes zirconium, a high-valence metal element that can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, a suitable mass ratio of nickel to zirconium results in a cathode material with high capacity and compaction density.

[0014] In one or more embodiments of this application, the first element includes cobalt, and the second element includes zirconium, with a mass ratio of cobalt to zirconium of 1 to 6. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes cobalt. Doping with cobalt can improve the lattice volume change between delithiated MnFeCoPO4 and lithiated LiMnFeCoPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, the second element includes zirconium, a high-valence metal element that can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, a suitable mass ratio of cobalt to zirconium results in a cathode material with high capacity and compaction density.

[0015] In one or more embodiments of this application, the first element includes zinc, and the second element includes zirconium, with a mass ratio of zinc to zirconium of 1 to 10. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes zinc. Doping with zinc can improve the lattice volume change between delithiated MnFeZnPO4 and lithium-intercalated LiMnFeZnPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, the second element includes zirconium, a high-valence metal element that can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, with a suitable mass ratio of zinc to zirconium, the cathode material exhibits high capacity and compaction density.

[0016] In one or more embodiments of this application, the cathode material further includes a third element, which includes at least one of niobium, vanadium, or tungsten. The third element is within the scope of this application; it is a high-valence metal element that can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, the third element can improve electronic conductivity and ionic conductivity, thereby increasing the specific capacity and kinetic performance of the cathode material.

[0017] In one or more embodiments of this application, the third element includes niobium, and the mass ratio of magnesium to niobium is 5 to 9. Within the scope of this application, by controlling the type of the third element and the mass ratio of magnesium to the third element, the third element includes niobium. Niobium is a high-valence metal element, which can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, niobium can improve electronic conductivity and ionic conductivity, increasing the specific capacity and kinetic performance of the cathode material. Doping with magnesium can reduce volume expansion, further improving the kinetic and cycle performance of the cathode material. Moreover, when magnesium and niobium have a suitable mass ratio, the cathode material exhibits higher capacity and compaction density.

[0018] In one or more embodiments of this application, the third element includes vanadium, and the mass ratio of magnesium to vanadium is 2 to 5. Within the scope of this application, by controlling the type of the third element and the mass ratio of magnesium to the third element, the third element includes vanadium. Vanadium is a high-valence metal element, which can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, and improved kinetic performance leads to improved cycle performance. Furthermore, vanadium can improve electronic conductivity and ionic conductivity, increasing the specific capacity and kinetic performance of the cathode material. Doping with magnesium can reduce volume expansion, further improving the kinetic and cycle performance of the cathode material. Moreover, when magnesium and vanadium have a suitable mass ratio, the cathode material has higher capacity and compaction density.

[0019] In one or more embodiments of this application, the third element includes tungsten, and the mass ratio of magnesium to tungsten is 10 to 20. Within the scope of this application, by controlling the type of the third element and the mass ratio of magnesium to the third element, the third element includes tungsten. Tungsten is a high-valence metal element, which can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, and improved kinetic performance leads to improved cycle performance. Furthermore, tungsten can improve electronic conductivity and ionic conductivity, increasing the specific capacity and kinetic performance of the cathode material. Doping with magnesium can reduce volume expansion, further improving the kinetic and cycle performance of the cathode material. Moreover, when magnesium and tungsten have a suitable mass ratio, the cathode material has higher capacity and compaction density.

[0020] In one or more embodiments of this application, the cathode material further includes a fourth element, which includes at least one of sodium or potassium. The cathode material further includes a fourth element, and the type of the fourth element is within the scope of this application. Doping the lithium site with the fourth element can further improve the conductivity of the cathode material and further improve its kinetic performance.

[0021] In one or more embodiments of this application, the fourth element includes sodium, and the mass ratio of magnesium to sodium is 10 to 14. Within the scope of this application, by controlling the type of the fourth element and the mass ratio of magnesium to the fourth element, sodium is included as the fourth element. Doping sodium at the lithium site can further improve the conductivity of the cathode material and its kinetic performance; doping magnesium can reduce volume expansion, further improving the kinetic and cycle performance of the cathode material; and, with a suitable mass ratio of magnesium to sodium, the cathode material exhibits high capacity and compaction density.

[0022] In one or more embodiments of this application, the fourth element includes potassium, and the mass ratio of magnesium to potassium is 10 to 20. Within the scope of this application, by controlling the type of the fourth element and the mass ratio of magnesium to the fourth element, potassium is included as the fourth element. Doping potassium at the lithium site can further improve the conductivity of the cathode material and further improve its kinetic performance. Doping magnesium can reduce volume expansion, further improving the kinetic and cycle performance of the cathode material. Furthermore, with a suitable mass ratio of magnesium to potassium, the cathode material exhibits high capacity and compaction density.

[0023] In one or more embodiments of this application, the mass ratio of magnesium to manganese is 0.01 to 0.02. Doping with magnesium can improve the lattice volume change between the delithiated MnFeMgPO4 and the lithiated LiMnFeMgPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Manganese in the cathode material can increase its energy density. By controlling the mass ratio of magnesium to manganese within the scope of this application, the cathode material exhibits both high kinetic and cycle performance as well as high energy density.

[0024] A second aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, wherein the positive electrode material layer includes the positive electrode material in any of the foregoing embodiments. Therefore, when this positive electrode sheet is applied to a secondary battery, the secondary battery exhibits better kinetic performance, better cycle performance, and higher capacity.

[0025] A third aspect of this application provides a secondary battery, which includes the positive electrode sheet in any of the foregoing embodiments. Therefore, the secondary battery provided by this application has good kinetic performance, cycle performance, and also has high capacity.

[0026] A fourth aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good kinetic performance, good cycle performance, and high capacity.

[0027] The beneficial effects of this application are:

[0028] This application provides a positive electrode material, a positive electrode sheet, a secondary battery, and an electronic device. The positive electrode material includes lithium manganese iron phosphate and comprises a first element and a second element. The first element includes at least one selected from magnesium, nickel, cobalt, or zinc, and the second element includes at least one selected from titanium or zirconium. The mass ratio of the first element to the second element is 1 to 20. The positive electrode material satisfies the above characteristics, which can improve the kinetic performance and cycle performance of the positive electrode material, while also giving it a higher capacity.

[0029] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0031] Figure 1 is a scanning electron microscope image of the positive electrode material of Embodiment 1-1 of this application. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0033] It should be noted that the following explanation uses lithium-ion batteries as an example of secondary batteries to illustrate this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0034] The first aspect of this application provides a cathode material comprising lithium manganese iron phosphate. The cathode material includes a first element and a second element. The first element includes at least one selected from magnesium (Mg), nickel (Ni), cobalt (Co), or zinc (Zn). The second element includes at least one selected from titanium (Ti) or zirconium (Zr). The mass ratio of the first element to the second element is from 1 to 20. Exemplarily, the mass ratio of the first element to the second element can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range consisting of any two of the above values. It is understood that the first element and the second element can be used as doping elements.

[0035] The inventors discovered that the cathode material includes lithium manganese iron phosphate, and the cathode material includes a first element and a second element. The first element is an inactive element with a radius between Mn and n. 2+ / Fe 2+ and Mn 3+ / Fe 3+ In this process, doping with the first element can improve the lattice volume change between the delithiated and lithium-ionized states of lithium manganese iron phosphate (LFP), reducing volume expansion and improving the kinetic and cycle performance of the cathode material. Simultaneously, the second element, being a high-valence metal, can reduce particle size; smaller particle size improves the kinetic performance of the cathode material, which in turn improves cycle performance. Excessive doping of the first and / or second elements leads to capacity loss in the cathode material; conversely, insufficient doping of the first and / or second elements has a minimal impact on improving the kinetic and cycle performance. Therefore, when the cathode material includes LFP, and the cathode material includes both the first and second elements, and the types and mass ratio of the first and second elements are within the scope of this application, the kinetic and cycle performance of the cathode material can be improved, while also giving the cathode material a higher capacity.

[0036] In this application, based on the mass of the cathode material, the mass percentage content W1 of the first element is 0.1% to 1.5%, and the mass percentage content W2 of the second element is 0.02% to 0.1%. When the first element includes two or more elements, this application does not impose any particular limitation on the mass percentage content of each element, as long as the mass percentage content of the first element meets the scope of this application. When the second element includes two or more elements, this application does not impose any particular limitation on the mass percentage content of each element, as long as the mass percentage content of the second element meets the scope of this application.

[0037] In one or more embodiments of this application, at least a portion of the surface of lithium manganese iron phosphate is provided with carbon material. The lithium manganese iron phosphate may have carbon material on a partial or complete surface. The carbon material can be obtained by carbonizing an organic compound, which may include, but is not limited to, glucose. Providing carbon material on at least a portion of the surface of lithium manganese iron phosphate can improve its electronic conductivity and enhance the kinetic and cycle performance of the cathode material.

[0038] In one or more embodiments of this application, the first element includes magnesium, and the second element includes titanium, with a magnesium to titanium mass ratio of 1 to 8. Exemplarily, the magnesium to titanium mass ratio can be 1, 2, 3, 4, 5, 6, 7, 8, or a range of any two of the above values. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes magnesium. Doping with magnesium can improve the lattice volume change between the delithiated MnFeMgPO4 and the lithium-intercalated LiMnFeMgPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, titanium, being a high-valence metal element, can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, with a suitable magnesium to titanium mass ratio, the cathode material exhibits high capacity and compaction density.

[0039] In one or more embodiments of this application, the first element includes nickel, and the second element includes titanium, with a mass ratio of nickel to titanium of 1 to 15. Exemplarily, the mass ratio of nickel to titanium can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range of any two of the above values. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes nickel. Doping with nickel can improve the lattice volume change between delithiated MnFeNiPO4 and lithium-intercalated LiMnFeNiPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, titanium, being a high-valence metal element, can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, with a suitable mass ratio of nickel to titanium, the cathode material exhibits high capacity and compaction density.

[0040] In one or more embodiments of this application, the first element includes cobalt, and the second element includes titanium, with a mass ratio of cobalt to titanium of 1 to 15. Exemplarily, the mass ratio of cobalt to titanium can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range of any two of the above values. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes cobalt. Doping with cobalt can improve the lattice volume change between delithiated MnFeCoPO4 and lithiated LiMnFeCoPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, titanium, being a high-valence metal element, can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, with a suitable mass ratio of cobalt to titanium, the cathode material exhibits high capacity and compaction density.

[0041] In one or more embodiments of this application, the first element includes zinc, and the second element includes titanium, with a zinc to titanium mass ratio of 1 to 20. Exemplarily, the zinc to titanium mass ratio can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range of any two of the above values. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes zinc. Doping with zinc can improve the lattice volume change between delithiated MnFeZnPO4 and lithium-intercalated LiMnFeZnPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, titanium, being a high-valence metal element, can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, with a suitable zinc to titanium mass ratio, the cathode material exhibits high capacity and compaction density.

[0042] In one or more embodiments of this application, the first element includes magnesium, and the second element includes zirconium, with a mass ratio of magnesium to zirconium of 1 to 4. Exemplarily, the mass ratio of magnesium to zirconium can be 1, 2, 3, 4, or a range consisting of any two of the above values. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes magnesium. Doping with magnesium can improve the lattice volume change between delithiated MnFeMgPO4 and lithium-intercalated LiMnFeMgPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, the second element includes zirconium, a high-valence metal element that can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, with a suitable mass ratio of magnesium to zirconium, the cathode material exhibits high capacity and compaction density.

[0043] In one or more embodiments of this application, the first element includes nickel, and the second element includes zirconium, with a mass ratio of nickel to zirconium of 1 to 6. Exemplarily, the mass ratio of nickel to zirconium can be 1, 2, 3, 4, 5, 6, or a range of any two of the above values. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes nickel. Doping with nickel can improve the lattice volume change between delithiated MnFeNiPO4 and lithium-intercalated LiMnFeNiPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, the second element includes zirconium, a high-valence metal element that can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, with a suitable mass ratio of nickel to zirconium, the cathode material exhibits high capacity and compaction density.

[0044] In one or more embodiments of this application, the first element includes cobalt, and the second element includes zirconium, with a mass ratio of cobalt to zirconium of 1 to 6. Exemplarily, the mass ratio of cobalt to zirconium can be 1, 2, 3, 4, 5, 6, or a range consisting of any two of the above values. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes cobalt. Doping with cobalt can improve the lattice volume change between delithiated MnFeCoPO4 and lithiated LiMnFeCoPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, the second element includes zirconium, a high-valence metal element that can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, with a suitable mass ratio of cobalt to zirconium, the cathode material exhibits high capacity and compaction density.

[0045] In one or more embodiments of this application, the first element includes zinc, and the second element includes zirconium, with a mass ratio of zinc to zirconium of 1 to 10. Exemplarily, the mass ratio of zinc to zirconium can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range of any two of the above values. Within the scope of this application, by controlling the types and mass ratio of the first and second elements, the first element includes zinc. Doping with zinc can improve the lattice volume change between delithiated MnFeZnPO4 and lithium-intercalated LiMnFeZnPO4, reducing volume expansion and further improving the kinetic and cycle performance of the cathode material. Simultaneously, the second element includes zirconium, a high-valence metal element that can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, leading to improved cycle performance. Furthermore, with a suitable mass ratio of zinc to zirconium, the cathode material exhibits high capacity and compaction density.

[0046] In one or more embodiments of this application, the cathode material further includes a third element, which includes at least one selected from niobium (Nb), vanadium (V), or tungsten (W). The cathode material further includes a third element, and the type of the third element is within the scope of this application. The third element is a high-valence metal element, which can reduce the particle size. Smaller particle size can further improve the kinetic performance of the cathode material, and improved kinetic performance leads to improved cycle performance. Furthermore, the third element can improve electronic conductivity and ionic conductivity, thereby increasing the specific capacity and kinetic performance of the cathode material.

[0047] In this application, the mass percentage of the third element W3 is 0.03% to 0.75% based on the mass of the cathode material.

[0048] In one or more embodiments of this application, the third element includes niobium, and the mass ratio of magnesium to niobium is 5 to 9. Exemplarily, the mass ratio of magnesium to niobium can be 5, 6, 7, 8, 9, or a range consisting of any two of the above values. Within the scope of this application, by controlling the type of the third element and the mass ratio of magnesium to the third element, the third element includes niobium. Niobium is a high-valence metal element, which can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, and improved kinetic performance leads to improved cycle performance. Furthermore, niobium can improve electronic conductivity and ionic conductivity, increasing the specific capacity and kinetic performance of the cathode material. Doping with magnesium can reduce volume expansion, further improving the kinetic and cycle performance of the cathode material. Moreover, with a suitable mass ratio of magnesium to niobium, the cathode material has higher capacity and compaction density.

[0049] In one or more embodiments of this application, the third element includes vanadium, and the mass ratio of magnesium to vanadium is 2 to 5. Exemplarily, the mass ratio of magnesium to vanadium can be 2, 3, 4, 5, or a range consisting of any two of the above values. Within the scope of this application, by controlling the type of the third element and the mass ratio of magnesium to the third element, the third element includes vanadium. Vanadium is a high-valence metal element, which can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, and improved kinetic performance leads to improved cycle performance. Furthermore, vanadium can improve electronic conductivity and ionic conductivity, increasing the specific capacity and kinetic performance of the cathode material. Doping with magnesium can reduce volume expansion, further improving the kinetic and cycle performance of the cathode material. Moreover, with a suitable mass ratio of magnesium to vanadium, the cathode material has higher capacity and compaction density.

[0050] In one or more embodiments of this application, the third element includes tungsten, and the mass ratio of magnesium to tungsten is 10 to 20. Exemplarily, the mass ratio of magnesium to tungsten can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range of any two of the above values. Within the scope of this application, by controlling the type of the third element and the mass ratio of magnesium to the third element, the third element includes tungsten. Tungsten is a high-valence metal element, which can reduce particle size. Smaller particle size can further improve the kinetic performance of the cathode material, and improved kinetic performance leads to improved cycle performance. Furthermore, tungsten can improve electronic conductivity and ionic conductivity, increasing the specific capacity and kinetic performance of the cathode material. Doping with magnesium can reduce volume expansion, further improving the kinetic and cycle performance of the cathode material. Moreover, with a suitable mass ratio of magnesium to tungsten, the cathode material has a higher capacity and compaction density.

[0051] In one or more embodiments of this application, the cathode material further includes a fourth element, which includes at least one of sodium (Na) or potassium (K). The cathode material further includes a fourth element, and the type of the fourth element is within the scope of this application. Doping the fourth element at the lithium site can further improve the conductivity of the cathode material and further improve its kinetic performance.

[0052] In this application, the mass percentage content of the fourth element W4 is 0.005% to 0.05% based on the mass of the cathode material.

[0053] In one or more embodiments of this application, the fourth element includes sodium, and the mass ratio of magnesium to sodium is 10 to 14. Exemplarily, the mass ratio of magnesium to sodium can be 10, 11, 12, 13, 14, or a range consisting of any two of the above values. Within the scope of this application, by controlling the type of the fourth element and the mass ratio of magnesium to the fourth element (including sodium), doping sodium at the lithium site can further improve the conductivity of the cathode material and its kinetic performance; doping magnesium can reduce volume expansion, further improving the kinetic and cycle performance of the cathode material; and, with a suitable mass ratio of magnesium to sodium, the cathode material has high capacity and compaction density.

[0054] In one or more embodiments of this application, the fourth element includes potassium, and the mass ratio of magnesium to potassium is 10 to 20. Exemplarily, the mass ratio of magnesium to potassium can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range of any two of the above values. Within the scope of this application, by controlling the type of the fourth element and the mass ratio of magnesium to the fourth element, the fourth element includes potassium. Doping potassium at the lithium site can further improve the conductivity of the cathode material and further improve its kinetic performance; doping magnesium can reduce volume expansion and further improve the kinetic and cycle performance of the cathode material; and, with a suitable mass ratio of magnesium to potassium, the cathode material has high capacity and compaction density.

[0055] In one or more embodiments of this application, the mass ratio of magnesium to manganese (Mn) is from 0.01 to 0.02. Exemplarily, the mass ratio of magnesium to manganese can be 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, or a range consisting of any two of the above values. Doping with magnesium can improve the lattice volume change between the delithiated MnFeMgPO4 and the lithiated LiMnFeMgPO4, reduce volume expansion, and further improve the kinetic and cycle performance of the cathode material. Manganese in the cathode material can increase the energy density of the cathode material. By controlling the mass ratio of magnesium to manganese within the scope of this application, the cathode material exhibits both high kinetic and cycle performance as well as high energy density.

[0056] This application does not impose any particular limitation on the preparation method of the cathode material. For example, the preparation method of the cathode material may include, but is not limited to, the following steps: adding manganese source, iron source, lithium source, phosphorus source and dopant element precursor to water in a certain molar ratio, adding glucose to obtain an intermediate solution, mixing and grinding the intermediate solution, then spray granulation, sintering, cooling, and air jet pulverization to obtain the cathode material.

[0057] When glucose is added, it reacts with the precursor during heating, causing Mn to... 3+ / Fe 3+ Restored to Mn 2+ / Fe 2+The process involves the formation of LiFeMnPO4, and the addition of glucose further enhances the electronic conductivity of the cathode material by forming a carbon coating layer. The cathode material includes lithium manganese iron phosphate. The aforementioned precursors refer to manganese, iron, lithium, and phosphorus sources. This application does not impose any particular limitation on the manganese source, as long as it achieves the purpose of this application. For example, the manganese source may include, but is not limited to, Mn3O4. This application does not impose any particular limitation on the iron source, as long as it achieves the purpose of this application. For example, the iron source may include, but is not limited to, FePO4. This application does not impose any particular limitation on the lithium source, as long as it achieves the purpose of this application. For example, the lithium source may include, but is not limited to, Li2CO3. This application does not impose any particular limitation on the phosphorus source, as long as it achieves the purpose of this application. For example, the phosphorus source may include, but is not limited to, LiH2PO4. This application does not impose any particular limitation on the doping element precursor, as long as it achieves the purpose of this application. For example, the doping element precursor may include, but is not limited to, oxides, carbonates, hydroxides, sulfates, or phosphates of the doping element. Exemplary examples show that the oxides of the doping elements may include, but are not limited to, MgO, TiO2, NiO, CoO, ZnO, ZrO2, Nb2O5, V2O5, or WO3; the carbonates of the doping elements may include, but are not limited to, Na2CO3 or K2CO3; the hydroxides of the doping elements may include, but are not limited to, Mg(OH)2 or NaOH; the sulfates of the doping elements may include, but are not limited to, MgSO4 or CoSO4; and the phosphates of the doping elements may include, but are not limited to, Na2HPO4 or NaH2PO4. This application does not impose any particular limitation on the mass ratio of glucose to lithium manganese iron phosphate, as long as the purpose of this application is achieved. For example, the mass ratio of glucose to lithium manganese iron phosphate may be (0.04:1) to (0.2:1). This application does not impose any particular limitation on the solid content of the intermediate solution, as long as the purpose of this application is achieved. For example, the solid content of the intermediate solution may be 20wt% to 35wt%. This application does not impose any particular restrictions on sintering temperature or sintering time, as long as the purpose of this application can be achieved. For example, the sintering temperature can be 600℃ to 800℃, and the sintering time can be 6h to 20h.

[0058] This application does not impose any particular restrictions on the method for adjusting the mass ratio of the first element to the second element, as long as the purpose of this application can be achieved. For example, the cathode material can be made to have the corresponding element by adding the corresponding dopant precursor, and then the mass ratio of the first element to the second element can be adjusted by adjusting the mass of the added corresponding dopant precursor.

[0059] This application does not impose any particular restrictions on the method for controlling the mass ratio of magnesium to the third element, as long as the purpose of this application can be achieved. For example, the cathode material can be made to have the corresponding element by adding the corresponding dopant precursor, and then the mass ratio of magnesium to the third element can be controlled by controlling the mass of the added corresponding dopant precursor.

[0060] This application does not impose any particular restrictions on the method for controlling the mass ratio of magnesium to the fourth element, as long as the purpose of this application can be achieved. For example, the cathode material can be made to have the corresponding element by adding the corresponding dopant precursor, and then the mass ratio of magnesium to the fourth element can be controlled by controlling the mass of the added corresponding dopant precursor.

[0061] This application does not impose any particular restrictions on the method for controlling the mass ratio of magnesium to manganese, as long as the purpose of this application can be achieved. For example, the cathode material can be made to have the corresponding elements by adding the corresponding dopant precursor, and then the mass ratio of magnesium to manganese can be controlled by adjusting the mass of the added dopant precursor and the mass of the manganese source.

[0062] The second aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode active material, which includes the positive electrode material in any of the aforementioned embodiments. Therefore, when the positive electrode sheet is applied to a secondary battery, the secondary battery exhibits better kinetic performance, cycle performance, and higher capacity. The aforementioned "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or only a portion thereof; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0063] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0064] The positive electrode material layer of this application also includes a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitations on the positive electrode conductive agent and positive electrode binder in the positive electrode material layer, as long as they can achieve the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The aforementioned conductive carbon black may include, but is not limited to, at least one of Super P, acetylene black, or Ketjen black. The aforementioned carbon nanotubes may include, but is not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but is not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The positive electrode binder may include at least one of the following: polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber, SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, lithium carboxymethyl cellulose, lithium polyacrylate, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0065] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be from 6 μm to 25 μm. This application also does not impose any particular limitation on the thickness of the positive electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of a single-sided positive electrode material layer can be from 25 μm to 250 μm.

[0066] Optionally, the positive electrode may further include a conductive layer, which is located between the positive current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and they can be at least one of the aforementioned positive electrode conductive agents and positive electrode binders. This application does not impose any particular limitation on the mass ratio of the conductive agent to the binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0067] A third aspect of this application provides a secondary battery, which includes the positive electrode sheet in any of the foregoing embodiments. Therefore, the secondary battery provided by this application has good kinetic performance, cycle performance, and also has high capacity.

[0068] In this application, the secondary battery further includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The aforementioned "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or only a portion thereof; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0069] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collectors.

[0070] The negative electrode material layer of this application includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO₂, etc. x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 The negative electrode material layer of this application includes at least one of the following: Li-Al alloy or metallic lithium. The negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. This application does not impose any particular limitation on the negative electrode binder and negative electrode conductive agent in the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the negative electrode binder can be at least one of the aforementioned positive electrode binders, and the negative electrode conductive agent can be at least one of the aforementioned positive electrode conductive agents. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode binder, and negative electrode conductive agent in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the Dv50 of the negative electrode active material, as long as the purpose of this application can be achieved. In this application, Dv50 refers to the particle size that reaches 50% of the volumetric particle size in the particle size distribution based on the volume of the material.

[0071] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be from 4 μm to 20 μm. This application also does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the single-sided negative electrode material layer can be from 30 μm to 250 μm.

[0072] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and they can be at least one of the aforementioned negative electrode conductive agents and negative electrode binders. This application does not impose any particular limitation on the mass ratio of the conductive agent and binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0073] In this application, the secondary battery also includes an electrolyte. The electrolyte includes a lithium salt. This application does not particularly limit the type of lithium salt; lithium salts known in the art can be used. Exemplarily, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), or lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB). This application does not particularly limit the mass percentage of lithium salt in the electrolyte, as long as the purpose of this application is achieved. The electrolyte also includes a non-aqueous organic solvent. This application does not particularly limit the non-aqueous organic solvent, as long as the purpose of this application is achieved. For example, the non-aqueous organic solvent may contain at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), vinylene carbonate, propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, at least one of 1,3-propanesulfonyl lactone, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters.This application does not impose any particular limitation on the mass percentage of non-aqueous organic solvents in the electrolyte, as long as the purpose of this application can be achieved.

[0074] In this application, the secondary battery also includes a separator. The separator is used to separate the positive electrode and the negative electrode, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0075] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a diaphragm binder. This application does not particularly limit the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the aforementioned diaphragm binder, and may include at least one of the aforementioned negative electrode binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or polyvinylidene fluoride-hexafluoropropylene copolymer.

[0076] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0077] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. In this application, the secondary battery may include, but is not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries (lithium-ion polymer batteries), etc.

[0078] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and pre-lithiated negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator, and pre-lithiated negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0079] A fourth aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good kinetic performance, good cycle performance, and high capacity.

[0080] This application does not specifically limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0081] Example

[0082] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0083] Test methods and equipment:

[0084] Mass ratio test of elements:

[0085] The lithium-ion battery was disassembled, the positive electrode was removed, and cleaned with DMC before being dried. Then, the positive electrode material layer powder was scraped off with a ceramic knife, and inductively coupled plasma atomic emission spectrometry (ICP) was used to detect the types of elements and the mass ratios of different elements in the powder. 0.2g of the positive electrode material layer powder was weighed and dissolved in a 42% nitric acid solution. The nitric acid solution containing the dissolved powder was then analyzed to obtain the types of elements and the mass ratios of different elements in the powder.

[0086] DC Impedance (DCR) Test:

[0087] At 25℃, the lithium-ion battery is charged to 4.3V at a constant current of 0.1C, then charged to 0.025C at a constant voltage of 4.3V, and left to stand for 10 minutes. Then it is discharged at a constant current of 0.1C for 5 hours (at which point the lithium-ion battery is at 50% state of charge). Then it is discharged at a constant current of 1C for 1 second. The voltage before the 1C constant current discharge is V0, the voltage after the 1C constant current discharge is V1, and the current of the 1C constant current discharge is A. Calculate the DC impedance R corresponding to the 50% state of charge (SOC) of the lithium-ion battery as (V0-V1) / A.

[0088] The lower the DC impedance at 50% state of charge (SOC) of a lithium-ion battery, the better its dynamic performance.

[0089] Cyclic performance test:

[0090] The lithium-ion battery was charged and discharged for the first time at 45℃. The specific steps were as follows: the lithium-ion battery was charged at a constant current of 0.5C to 4.3V, then charged at a constant voltage of 4.3V to 0.025C, allowed to stand for 10 minutes, and then discharged at a constant current of 0.5C to 2.5V. The ratio of discharge energy to discharge capacity during the above discharge process was the initial equal voltage. This constituted one charge-discharge cycle. This process was repeated for 100 charge-discharge cycles. The ratio of discharge energy to discharge capacity during the 100th discharge cycle was the equal voltage of the 100th cycle. The difference between the equal voltage of the 100th cycle (cls) and the initial equal voltage was the voltage drop. The unit of discharge energy was mWh, and the unit of discharge capacity was Ah.

[0091] The smaller the average voltage drop, the better the stability of the cathode material and the better the cycle performance of the lithium-ion battery.

[0092] Capacity test:

[0093] Take the positive electrode sheet from Example 1-1, punch it into small discs required for a 2025 coin cell, and obtain positive electrode discs. Stack the lithium sheet, separator, and positive electrode discs in sequence to assemble a coin cell, and inject 50 microliters of electrolyte. The electrolyte includes a base solvent and lithium salt LiPF6. The base solvent is obtained by mixing EC:EMC:DEC in a mass ratio of 30:50:20, and the mass percentage of LiPF6 in the electrolyte is 12.5%.

[0094] At 25°C, the assembled coin cell was charged to 4.3V at a constant current of 0.5C, then charged to 0.025C at a constant voltage of 4.3V, left to stand for 10 minutes, and then discharged to 2.5V at a constant current of 0.5C. The discharge capacity during the discharge process was recorded. Specific capacity = discharge capacity / mass of positive electrode material.

[0095] Example 1-1

[0096] <Preparation of cathode materials>

[0097] The LiMn alloy was designed using manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, MgO, and TiO2 in the molar ratio corresponding to that in this embodiment. 0.6 Fe 0.3763 Mg 0.0203 Ti 0.0034 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with LiMn. 0.6 Fe 0.3763 Mg 0.0203 Ti 0.0034 The mass ratio of PO4 was 0.15:1 to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was mixed and ground, then spray-granulated, and sintered under a nitrogen atmosphere at a temperature of 700℃ for 8 hours. After cooling, the cathode material was obtained by air jet milling.

[0098] <Preparation of the positive electrode>

[0099] The above-mentioned positive electrode material, positive electrode conductive agent Super P, and positive electrode binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96.7:0.8:2.5. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred until homogeneous to obtain a positive electrode slurry with a solid content of 60 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil current collector and dried at 90°C to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. The sheet was dried under vacuum at 90°C for 1 hour, and then cold-pressed, cut, and slit to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm. The coating weight of the positive electrode material layer was 180 g / m², and the compaction density during the cold pressing process was 2.3 g / cm³. 3 .

[0100] <Preparation of Negative Electrode Sheets>

[0101] Artificial graphite (negative electrode active material), Super P (negative electrode conductive agent), and lithium polyacrylate (PAA-Li) (negative electrode binder) were mixed in a weight ratio of 97.3:1.5:1.2. Deionized water was added as a solvent, and the mixture was stirred until homogeneous to obtain a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector and dried at 110 °C to obtain a negative electrode sheet with a single-sided coating of the negative electrode material layer. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode material layer. The negative electrode sheet was dried under vacuum at 110 °C for 1 hour, and then cold-pressed, cut, and slit to obtain a negative electrode sheet with a size of 78 mm × 875 mm. The particle size Dv50 of the artificial graphite (negative electrode active material) was 14 μm, and the coating weight of the negative electrode material layer was 84 g / m². 2 The compaction density during the cold pressing process is 1.6 g / cm³. 3 .

[0102] <Preparation of Electrolyte>

[0103] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a mass ratio of EC:EMC:DEC = 30:50:20 to obtain a base solvent. Then, lithium hexafluorophosphate (LiPF6) was added and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium salt LiPF6 was 12.5%, with the remainder being the base solvent.

[0104] <Preparation of the diaphragm>

[0105] A diaphragm binder PVDF and inorganic granular alumina were mixed at a mass ratio of 1:2, and NMP was added as a solvent to prepare an inorganic layer slurry with a solid content of 12 wt%. The mixture was stirred until homogeneous and then uniformly coated onto one surface of a 15 μm thick polyethylene substrate. The substrate was then dried at 85°C for 4 hours to obtain a diaphragm with a single-sided inorganic layer coating thickness of 3 μm. Next, PVDF was added to NMP solvent and stirred until homogeneous, preparing a polymer layer slurry with a solid content of 25 wt%. This polymer layer slurry was then uniformly coated onto the surface of the inorganic layer, with a coating weight of 1.5 mg / 1540.25 mm². 2 Then, it is dried at 85℃ for 4 hours. Finally, a polymer layer slurry is uniformly coated on the other surface of the polyethylene substrate. The coating weight of the polymer layer slurry is 1.5 mg / 1540.25 mm. 2 Then, it is dried at 85°C for 4 hours to obtain a diaphragm with an inorganic layer and a polymer layer on one side and only a polymer layer on the other side.

[0106] <Preparation of Lithium-ion Batteries>

[0107] The positive electrode, separator, negative electrode, and separator prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode to act as a separator. The electrode assembly is then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 85°C vacuum oven for 12 hours to remove moisture. Electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation (charged at a constant current of 0.02C to 3.3V, then charged at a constant current of 0.3C to 4.3V), degassing, edge trimming, and capacity processing to obtain the lithium-ion battery.

[0108] Examples 1-2 to Examples 1-30

[0109] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0110] Example 2-1

[0111] Except for the preparation of the cathode material according to the following method, the rest is the same as in Example 1-1.

[0112] <Preparation of cathode materials>

[0113] LiMn was designed using manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, MgO, TiO2, and Nb2O5 in the molar ratio corresponding to this example. 0.6 Fe 0.3752 Mg 0.0203 Ti 0.0034 Nb 0.0011The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with LiMn. 0.6 Fe 0.3752 Mg 0.0203 Ti 0.0034 Nb 0.0011 The mass ratio of PO4 was 0.15:1 to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was mixed and ground, then spray-granulated, and sintered under a nitrogen atmosphere at a temperature of 700℃ for 8 hours. After cooling, the cathode material was obtained by air jet milling.

[0114] Examples 2-2 to 2-12

[0115] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Example 2-1.

[0116] Example 2-13

[0117] Except for the preparation of the cathode material according to the following method, the rest is the same as in Example 1-1.

[0118] <Preparation of cathode materials>

[0119] The Li source was designed using manganese Mn3O4, iron FePO4, lithium Li2CO3, phosphorus LiH2PO4, MgO, TiO2, and Na2CO3 in the molar ratio corresponding to this example. 0.9979 Na 0.0021 Mn 0.6 Fe 0.3763 Mg 0.0203 Ti 0.0034 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 0.9979 Na 0.0021 Mn 0.6 Fe 0.3763 Mg 0.0203 Ti 0.0034 The mass ratio of PO4 was 0.15:1 to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was mixed and ground, then spray-granulated, and sintered under a nitrogen atmosphere at a temperature of 700℃ for 8 hours. After cooling, the cathode material was obtained by air jet milling.

[0120] Examples 2-14 to 2-19

[0121] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 2-13.

[0122] Examples 2-20 to 2-24

[0123] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Example 2-1.

[0124] Comparative Example 1

[0125] Except for the preparation of the cathode material according to the following method, the rest is the same as in Example 1-1.

[0126] <Preparation of cathode materials>

[0127] LiMn was designed using manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, and phosphorus source LiH2PO4 in the corresponding molar ratio of the comparative proportion. 0.6 Fe 0.4 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with LiMn. 0.6 Fe 0.4 The mass ratio of PO4 was 0.15:1 to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was mixed and ground, then spray-granulated, and sintered under a nitrogen atmosphere at a temperature of 700℃ for 8 hours. After cooling, the cathode material was obtained by air jet milling.

[0128] Comparative Examples 2 to 5

[0129] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0130] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0131] Table 1

[0132] Note: (1) In Table 1, “ / ” indicates that there are no relevant preparation parameters; (2) Taking Example 1-1 as an example, “doped element precursor” is “MgO+TiO2”, “first element” is “Mg”, and “second element” is “Ti”, indicating that “MgO” is the doped element precursor corresponding to the first element Mg, and “TiO2” is the doped element precursor corresponding to the second element Ti. Other examples follow the same pattern; (3) Taking Example 1-25 as an example, “doped element precursor” is “MgO+NiO+TiO2”, “first element” is “Mg+Ni (mass ratio is 1:1)”, and “second element” is “Ti”, indicating that the first element includes Mg and Ni, “MgO” is the doped element precursor corresponding to Mg, “NiO” is the doped element precursor corresponding to Ni, the mass ratio of Mg and Ni is 1:1, and “TiO2” is the doped element precursor corresponding to the second element Ti. Other examples follow the same pattern.

[0133] As can be seen from Examples 1-1 to 1-30 and Comparative Examples 1 to 5, when the cathode material includes lithium manganese iron phosphate, and the cathode material includes a first element and a second element, and the types and mass ratio of the first element and the second element are within the scope of this application, the prepared lithium-ion battery has lower DC resistance, lower average voltage drop, and higher specific capacity, indicating that the kinetic performance and cycle performance of the cathode material can be improved, while also giving the cathode material a higher capacity. In Comparative Example 1, the cathode material does not include the first element and the second element, and the prepared lithium-ion battery has higher DC resistance, higher average voltage drop, and lower specific capacity, indicating that the kinetic performance and cycle performance of the cathode material are relatively poor, and the capacity is also low. In Comparative Example 2, the cathode material does not include the second element, and the prepared lithium-ion battery has higher DC resistance, higher average voltage drop, and lower specific capacity, indicating that the kinetic performance and cycle performance of the cathode material are relatively poor, and the capacity is also low. In Comparative Example 3, the cathode material does not include the first element, and the prepared lithium-ion battery has higher DC resistance, higher average voltage drop, and lower specific capacity, indicating that the kinetic performance and cycle performance of the cathode material are relatively poor, and the capacity is also low. In Comparative Examples 4 and 5, the mass ratio of the first element to the second element is outside the scope of this application. The prepared lithium-ion batteries have high DC resistance, high average voltage drop and low specific capacity, indicating that the kinetic performance and cycle performance of the cathode material are relatively poor, and the capacity is low.

[0134] As can be seen from Figure 1, the morphology of the cathode material in Example 1-1 is granular.

[0135] Table 2

[0136] Note: (1) In Table 2, “ / ” indicates that there are no relevant preparation parameters; (2) Taking Example 2-1 as an example, “doped element precursor” is “MgO+TiO2+Nb2O5”, and “third element” is “Nb”, indicating that the doped element precursor includes MgO and TiO2, and also includes Nb2O5. “Nb2O5” is the doped element precursor corresponding to the third element Nb. Other examples follow the same pattern; (3) In Example 2-1, the number of moles of Mn element is the same as in Example 1-1, and the mass ratio of Mg element to Ti element is the same as in Example 1-1. Other examples follow the same pattern.

[0137] Doping elements in cathode materials typically affect their kinetic performance, cycle performance, and capacity. As seen in Examples 1-1, 2-1 to 2-12, the cathode material also includes a third element. The type of the third element and the mass ratio of magnesium to the third element are within the scope of this application. The prepared lithium-ion battery exhibits lower DC resistance, lower voltage drop, and higher specific capacity, indicating that it can improve the kinetic performance and cycle performance of the cathode material, while also giving the cathode material a higher capacity.

[0138] As can be seen from Examples 1-1, 2-13 to 2-19, the cathode material also includes a fourth element, and the type of the fourth element and the mass ratio of magnesium to the fourth element are within the scope of this application. The prepared lithium-ion battery has a lower DC impedance, a lower average voltage drop, and a higher specific capacity, indicating that it can improve the kinetic performance and cycle performance of the cathode material, while also enabling the cathode material to have a higher capacity.

[0139] As can be seen from Examples 1-1, 2-20 to 2-24, the cathode material also includes a third element and a fourth element. The types of the third and fourth elements, the mass ratio of magnesium to the third element, and the mass ratio of magnesium to the fourth element are within the scope of this application. The prepared lithium-ion battery has lower DC resistance, lower average voltage drop, and higher specific capacity, indicating that the kinetic performance and cycle performance of the cathode material can be improved, while also enabling the cathode material to have a higher capacity.

[0140] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0141] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0142] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A cathode material comprising lithium manganese iron phosphate, the cathode material comprising a first element and a second element, the first element comprising at least one of magnesium, nickel, cobalt or zinc, the second element comprising at least one of titanium or zirconium, the mass ratio of the first element to the second element being 1 to 20.

2. The cathode material according to claim 1, wherein, At least a portion of the surface of the lithium manganese iron phosphate is provided with carbon material.

3. The cathode material according to claim 1 or 2, wherein, The first element includes magnesium, and the second element includes titanium, wherein the mass ratio of magnesium to titanium is 1 to 8.

4. The cathode material according to claim 1 or 2, wherein, The cathode material satisfies at least one of the following characteristics: (1) The first element includes nickel, and the second element includes titanium, wherein the mass ratio of nickel to titanium is 1 to 15. (2) The first element includes cobalt, and the second element includes titanium, wherein the mass ratio of cobalt to titanium is 1 to 15. (3) The first element includes zinc, the second element includes titanium, and the mass ratio of zinc to titanium is 1 to 20. (4) The first element includes magnesium, the second element includes zirconium, and the mass ratio of magnesium to zirconium is 1 to 4. (5) The first element includes nickel, the second element includes zirconium, and the mass ratio of nickel to zirconium is 1 to 6. (6) The first element includes cobalt, the second element includes zirconium, and the mass ratio of cobalt to zirconium is 1 to 6; (7) The first element includes zinc, the second element includes zirconium, and the mass ratio of zinc to zirconium is 1 to 10.

5. The cathode material according to claim 3, wherein, The cathode material also includes a third element, which includes at least one of niobium, vanadium, or tungsten.

6. The cathode material according to claim 5, wherein, The third element includes niobium, and the mass ratio of magnesium to niobium is 5 to 9.

7. The cathode material according to claim 5, wherein, The cathode material satisfies at least one of the following characteristics: (1) The third element includes vanadium, and the mass ratio of magnesium to vanadium is 2 to 5; (2) The third element includes tungsten, and the mass ratio of magnesium to tungsten is 10 to 20.

8. The cathode material according to claim 3, wherein, The cathode material also includes a fourth element, which includes at least one of sodium or potassium.

9. The cathode material according to claim 8, wherein, The fourth element includes sodium, and the mass ratio of magnesium to sodium is 10 to 14.

10. The cathode material according to claim 8, wherein, The fourth element includes potassium, and the mass ratio of magnesium to potassium is 10 to 20.

11. The cathode material according to claim 3, wherein, The mass ratio of magnesium to manganese is 0.01 to 0.

02.

12. A positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, the positive electrode material layer comprising the positive electrode material according to any one of claims 1 to 11.

13. A secondary battery, the secondary battery comprising the positive electrode sheet as described in claim 12.

14. An electronic device comprising the secondary battery of claim 13.

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