Graphite negative electrode material and preparation method and application thereof

Abstract

The application provides a graphite negative electrode material and a preparation method and application thereof. The graphite negative electrode material comprises graphite and lithium phosphate coated on the surface of the graphite. The negative electrode material has better fast charging performance and can be stably cycled in PC-based electrolyte. As a fast ion conductor of lithium ions, the lithium phosphate can improve the rate performance of the graphite. Compared with the graphite material without coating, the negative electrode material coated with lithium phosphate can be stably cycled in PC-based electrolyte, and the reversible capacity is more than 90% of the theoretical capacity. The graphite negative electrode material coated with lithium phosphate can achieve better low-temperature performance in PC-based electrolyte than in EC-based electrolyte, and can maintain more than 70% of the reversible capacity at-20 DEG C. The graphite negative electrode material coated with lithium phosphate can achieve high capacity retention rate under a large current density in EC-based electrolyte, and can maintain more than 75% of the initial capacity under 4C charging and discharging, and more than 60% of the initial capacity under 6C charging and discharging.

Description

Technical Field

[0001] This invention belongs to the field of graphite anode material technology, and particularly relates to a graphite anode material, its preparation method and application. Background Technology

[0002] Since its commercial application began in the 1990s, lithium-ion batteries have been widely used in mobile electronic devices, electric vehicles, large-scale energy storage, and other fields. However, the fast charging performance and low-temperature performance of lithium-ion batteries cannot currently meet the needs of electric vehicles and other similar applications.

[0003] In liquid electrolyte systems, during rapid charge and discharge, commercially available graphite anodes are prone to lithium plating due to significant structural changes and polarization effects, leading to battery cycle performance degradation and safety issues such as thermal runaway. Currently, the main solvent in commercial lithium-ion battery electrolytes is EC (ethylene carbonate), which has a high melting point (35-38℃) and hinders lithium-ion transport at low temperatures. PC (propylene carbonate), with its low melting point of -48.8℃ and high dielectric constant of 64.9, is considered an excellent solvent below zero degrees Celsius. However, in commercial lithium-ion batteries, the graphite anode undergoes a solvent intercalation reaction in PC, resulting in the stripping of the graphite layer and preventing normal cycling. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a graphite anode material, its preparation method, and its application. In this graphite anode material, lithium phosphate is physically adsorbed on the graphite surface, preventing the PC solvent from intercalating into the graphite layer, thus enabling the graphite to cycle stably in a PC-based (EC-free) electrolyte. Furthermore, lithium phosphate, as a fast ion conductor of lithium ions, can improve the rate performance of graphite.

[0005] This invention provides a graphite anode material, comprising graphite;

[0006] And lithium phosphate coated on the surface of the graphite.

[0007] The graphite anode material provided by this invention has excellent rate performance and can be stably cycled in PC-based electrolyte.

[0008] In this invention, the lithium phosphate content in the negative electrode material is 0.1–15 wt%.

[0009] The lithium phosphate is coated on the surface of the graphite particles by physical adsorption.

[0010] The graphite is a commercially available product, preferably including natural or artificial graphite.

[0011] This invention provides a method for preparing the graphite anode material described in the above technical solution, comprising the following steps:

[0012] Graphite is dispersed in an alcohol solvent containing phosphate and lithium salt, mixed evenly, dried, and then sintered to obtain a graphite anode material.

[0013] In this invention, the phosphate is selected from one or more of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium dihydrogen phosphate;

[0014] The lithium salt is lithium hydroxide or lithium carbonate.

[0015] The phosphate is selected from one or more of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium dihydrogen phosphate; the lithium salt is lithium hydroxide or lithium carbonate.

[0016] In this invention, the sintering temperature is 400–1000°C, preferably 400–900°C. The sintering time is 0.1–48 h. Preferably, the temperature is increased from room temperature to 400–1000°C at a heating rate of 10°C / min.

[0017] This invention prepares a lithium phosphate-coated graphite composite anode material by a simple wet chemical method via sintering reaction. Lithium phosphate can provide a fast transport channel for lithium ions, allowing ions to diffuse rapidly into the electrode interior. At the same time, the coating on the graphite surface can also hinder the co-intercalation reaction of PC solvent, enabling the graphite to cycle stably in PC-based electrolyte.

[0018] This invention provides a lithium-ion battery, comprising a PC-based electrolyte and a graphite negative electrode;

[0019] The graphite anode is the graphite anode material described in the above technical solution or the graphite anode material prepared by the preparation method described in the above technical solution.

[0020] This invention provides a graphite anode material, comprising graphite and lithium phosphate coated on the surface of the graphite. This anode material exhibits better fast-charging performance and stable cycling in PC-based electrolytes. Lithium phosphate, as a fast ion conductor of lithium ions, enhances the rate performance of graphite. Compared to uncoated graphite, the lithium phosphate-coated anode material achieves stable cycling in PC-based electrolytes, with a reversible capacity exceeding 90% of the theoretical capacity. The lithium phosphate-coated graphite anode material achieves better low-temperature performance in PC-based electrolytes than in EC-based electrolytes, maintaining over 70% of the reversible capacity at -20°C. Furthermore, the lithium phosphate-coated graphite anode material achieves high capacity retention at high current densities in EC-based electrolytes, retaining over 75% of the initial capacity at 4C charge / discharge and over 60% of the initial capacity at 6C charge / discharge. Attached Figure Description

[0021] Figure 1 This is a SEM image of the lithium phosphate-coated graphite prepared in Example 1 of the present invention. Detailed Implementation

[0022] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a graphite anode material, its preparation method, and its applications, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0023] Example 1

[0024] 114 mg of ammonium hydrogen phosphate and 62 mg of lithium hydroxide precursor (molar mass ratio of 1:2) were dispersed with 1 g of graphite in 5 mL of ethanol solvent, mixed evenly, stirred until completely evaporated, and calcined at 900 °C for 6 hours under argon atmosphere to obtain graphite material coated with lithium phosphate.

[0025] Example 2

[0026] The materials obtained in Example 1 were assembled into a half-cell for testing. The reversible capacity in an EC-based electrolyte (1M LiPF6 + EC:DMC:EMC = 1:1:1 (volume ratio)) was 358.4 mAh g. -1 At 4C rate, it still has 280.9mAh g. -1 The specific capacity (capacity retention rate) is 78.4%, and the specific capacity at 6C is 221.8 mAh g. -1 (Capacity retention rate was 61.8%).

[0027] Example 3

[0028] The materials obtained in Example 1 were assembled into a half-cell for testing. The reversible capacity at room temperature in a PC-based electrolyte (1M LiPF6 + PC:DMC:EMC = 1:1:1 (volume ratio)) was 342.3 mAh g. -1 It still has 290.5 mAh g at -20℃ -1 Reversible capacity (capacity retention rate of 84.8%).

[0029] Comparative Example

[0030] Graphite samples were assembled into half-cells for testing. The reversible capacity in an EC-based electrolyte (1M LiPF6 + EC:DMC:EMC = 1:1:1 (volume ratio)) was 389.3 mAh g. -1 At 4C rate, it still has 133.5mAh g. -1 The specific capacity (capacity retention rate) is 34.3%, and the specific capacity at 6C is 67.5 mAh g. -1 (Capacity retention rate was 17.3%). It failed directly after the first discharge in PC-based electrolyte (1M LiPF6 + PC:DMC:EMC = 1:1:1 (volume ratio)).

[0031] Table 1. Electrochemical test results of the materials prepared in the examples and comparative examples.

[0032]

[0033]

[0034] As can be seen from the data in Table 1, the lithium phosphate-coated anode material in the examples exhibits good tolerance in PC-based electrolytes without EC addition, and can demonstrate high reversible capacity. In contrast, the graphite materials without lithium phosphate coating all failed in the PC-based electrolyte.

[0035] As can be seen from the above examples, the lithium phosphate-coated anode material, compared to uncoated graphite material, can achieve stable cycling in PC-based electrolytes, with a reversible capacity of over 90% of the theoretical capacity. The lithium phosphate-coated graphite anode material exhibits better low-temperature performance in PC-based electrolytes than in EC-based electrolytes, maintaining over 70% of the reversible capacity at -20℃. Furthermore, the lithium phosphate-coated graphite anode material achieves high capacity retention at high current densities in EC-based electrolytes, retaining over 75% of the initial capacity at 4C charge / discharge and over 60% of the initial capacity at 6C charge / discharge.

[0036] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A lithium ion battery suitable for use in a low temperature environment, comprising a PC-based electrolyte and a graphite anode; the material of the graphite anode comprises graphite and lithium phosphate coated on the surface of the graphite in a physical adsorption manner, and the content of the lithium phosphate in the graphite anode is 0.1-15wt%; wherein the lithium phosphate is formed by mixing graphite with an alcohol solvent containing a phosphate salt and a lithium salt, drying, and then sintering at 400-1000℃.

2. The lithium-ion battery of claim 1, wherein, the graphite comprises natural graphite or artificial graphite.

3. The lithium-ion battery of claim 1, wherein, the phosphate salt is selected from one or more of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium dihydrogen phosphate; the lithium salt is lithium hydroxide or lithium carbonate.

4. The lithium-ion battery of claim 1, wherein, the alcohol solvent is selected from methanol, ethanol, or propanol.

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